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Information Circular 8925

Explosives and Blasting Procedures

Manual

By Richard A. Dick, Larry R. Fletcher,

and Dennis V. D'Andrea

UNITED STATES DEPARTMENT OF THE INTERIOR

James G. Watt, Secretary

BUREAU OF MINES

Robert C. Horton, Director



As the Nation's principal conservation agency, the Department of the Interior

has responsibility for most of our nationally owned public lands and natural

resources. This includes fostering the wisest use of our land and water re-

sources, protecting our fish and wildlife, preserving the environmental and

cultural values of our national parks and historical places, and providing for

the enjoyment of life through outdoor recreation. The Department assesses

our energy and mineral resources and works to assure that their development is

in the best interests of all our people. The Department also has a major re-

sponsibility for American Indian reservation communities and for people who

live in Island Territories under U.S. administration.

T his p ub lic atio n h as b ee n c ata lo ge d a s fo llo w s:

Dick, Richard AExplosives and blasting procedures manual.

(Bureau of Mines Information circular; 8925)

Supt. of Docs. no.: I 28.27:8925.

1. Blasting-Handbooks, manuals, etc. 2. Explosives-Handbooks,

manuals, etc. I. Fletcher, Larry R. II. D'Andrea, Dennis V. III.

Title. IV. Series: Information circular (United States. Bureau of

Mines) ; 8925.

TN295.U4 [TN279] 622s [622' .23] 82·600353

For sale by the Superintendent of Documents, U.S. Government Printing Office

Washington, D.C. 20402



iii

CONTENTS

Abstract .

Introduction .

C ha pte r 1 .-E xp lo siv es P ro du cts

Chem istry and physics o f explos ives .Types of e xp los ives and blasting agents .

N itrog lycerin -based high explosives .Dry b las ti ng agents , .Slurries .Two-component exp losives .Perm iss ib le explos ives .Prim ers and boosters .L iqu id oxygen explosive and black powder .

P ropert ies o f explosives "Strength "Detonation veloc ity "

Density .W ater resistance .Fume class .Detonation pressure .Borehole pressure "Sensitivity and s ensitiveness .

Explosive select ion criteria .Explosive cost .Charge diameter .C os t o f drilling .Fragmentation difficulties .W ater conditions .Adequacy of ventila tion .A tmospheric temperature .Propagating ground .

Storage considerations ,Sensitiv ity considerations .Explosive atmospheres .

References .

C ha pte r 2 .-ln itia tio n a nd P rim in g

In itiation systems .Delay series .E lectric initia tion .

Types of c ircu its .C ircu it ca lcu lations .Power sou rces .Circuit testing .Extraneous electricity .

Additional considerations .Detonating cord initia tion .Detonating cord products .F ield application .Delay systems .Genera l considerations .Deta line system .

Cap-and-fuse initia tion .Components .Field applications .Delays .Genera l considerations .

O ther nonelectric in itiation systems .Hercudet .Nonel .

Page

12

212122

23252528

30

3030

31313334343535353636

3637

39

Page

3

4

5

7

9

1011

"3141414

141515161616

1717i l ; l

1 e18

18

18

1919

191920

20

Ch ap te r 2 .- ln itia tio n a nd P rim in g- Co n.

Pr iming.. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. 43Types of explos ive used 43Primer makeup.............. 45Primer location 46Multip le prim ing 47

References.................................................................. 47

C ha pte r 3 .-B la sth ole L oa din g

Check ing t he blast hole 49General loading procedures. .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . 49Smal l -diameter blastholes........................................... 50

Car tr ic lged p roduc ts .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. . 50Bulk dry blasting agents 50Bulk slurries............................................................. 52Perm iss ib le blasting ...... 52

L a rg e -d iame te r b la s tho le s .. .... ..... .... .... ..... .... ..... .... ..... . 5 2Packaged products.................................................. 52Bulk dry blasting agents 53Bulk s lu r ri es .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. . 54

References........ 56

C ha pter 4.-B la st D es ign

P ro pe rtie s a nd g eo lo gy o f th e ro ckmass,,;................. 57Characterizing the rock mass ;;..................Rock density and hardness 57Voids and incompetent zones 57Jointing... . . 58Bedding . .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. 58

Surface blasting.. 59B lastho le d iameter 59Types of b last patterns 61Burden..................................................................... 61Subdrilling................................................................ 62Co ll ar d is tance (stemming)...................................... 62Spacing 63Ho le d ep th 64Delays 64Powde r f ac to r.... ..... .... ..... .... .... ..... .... ..... .... ..... .... .... . 6Secondary blasting :..... 65

Underground b la s ti ng .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. 66Openi ng cu ts . 66

Blasting r ounds. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. . 68Delays 69

Powde r f ac to r. .... ..... .... ..... .... .... ..... .... ..... .... ..... .... .... 7Underground c oal mine blasting 70Contro lled blasting techniques 70

Line drilling . 70Presplitting .. 71Smooth blasting ........... 73Cushion blasting...................................................... 74

Re fe re n ce s : ... .. .. .. .. .. ... .. .. .. .. .. .. .. ... .. .. .. .. .. ... .. .. .. . 74

C ha pte r 5 .-E nv iro nm en ta l E ffe cts o f B la stin g

Flyrock 77Causes and a lle v ia tio n n

Protective measures............................................... 77



Iv

Page

Chapter 5.-Environmental Effects of Blasting-Con.

Ground vibrations .

Causes ................................................•...................

Prescribed vibration levels and measurementtechniQues .

Scaled distance equation .

Reducing ground vibrations ; .

Airblast .

Causes ..................................•.................................

Prescribed airblast levels and measurement

techniques i•••••••••••••••••••••••••••••••••Reducing airblast .

Dust and gases .

References .

Chapter 6.-Blasting Safety

Explosives storage .

Chapter 6.-Blasting Safety--Con.

77

78

79

80

80

80

81

82

8283 '

M

Transportation from magazine to jobsite .

Precautions be fo re loading .

Primer preparation .Borehole loading .

Hooking up the shot .

Shot firing .

Postshot safety .

Disposing of misfires .

Disposal of explosive materials .

Principal causes of blasting accidents .

Underground coal mine blasting .

References .

85

Bibliography .

Appendix A.-Federal blasting regulations .

Appendix B.-Glossary of terms used in explosives

and blasting .

ILLUSTRATIONS

Page

85

86

8888

9090

92

92

92

92

93

93

94

96

99

1. Energy released by common products of detonation 3

2. Pressure profiles created by detonation in a borehole ;............................................................................ 4

3. Relative ingredients and properties of nitroglycerin-based high explosives............... 5

4. Typical cartridges of dynamite ....•.. 6

5. Types of dry blasting agents and their ingredients 7

6. Porous ammonium nitrate prills ;..,,;................................... 8

7. Water-resistant packages of AN-FO for use in wet boreholes ;i................................... 9

8. Formulations of water-based products r o

9. Slurry bulk loading trucks 11

10. Loading slurry-filled polyethylene bags....................... 12

11. Cast primers for blasting caps and detonating cord 13

12. Delay cast primer 13

13. Effect of charge diameter on detonation velocity 14

14. Nomograph for finding loading density 15

15. Nomograph for finding detonation pressure 16

16. Field mixing of AN-FO 17

17. Instantaneous detonator................................................................................................................................................ 21

18. Delay detonator 22

19. Electric blasting caps..................................................................................................................................................... 23

20. Delay electric blasting cap............................................................................................................................................. 23

21. Types of electric blasting circuits... ....•................................................... 24

22. Recommended wire splices........................................... 24

23. Calculation of cap circuit resistance 25

24. Capacitor discharge blasting machine........................................................................................................................... 26

25. Sequential blasting machine.......................................................................................................................................... 27

26. Blasting galvanometer 28

27. Blasting multimeter 2928. Detonating cord 31

29. Clip-on surface detonating cord delay connector 32

30. Nonel surface detonating cord delay connector 32

31. Recommended knots for detonating cord...................................................................................................................... 33

32. Potential cutoffs from slack and tight detonating cord lines... 33

33. Typical blast pattern with surface delay connectors 33

34. Misfire caused by cutoff from burden movement........................................................................................................... 34

35. Blasting cap for use with safety fuse 35

36. Cap, fuse, and Ignitacord assembly........... 3637. Hercudet blasting cap with 4-in tubes............................................................................................................................ 37

38. Extending Hercudet leads with duplex tubing................................................................................................................ 38

39. Hercudet connections for surface blasting..................................................................................................................... 38

40. Hercudet pressure test module 39



v

Page

ILLUSTRATIONS-Continued

41. Hercudet tester for small hookups.......................... 40

42. Hercules bottle box and blasting machine 41

43. Nonel blasting cap......................................................................................................................................................... 4144. Nonel Primadet cap for surface blasting........................................................................................................................ 42

45. Nonel noiseless trunkline delay unit 42

46. Noiseless trunkline using Nonel delay assemblies 42

47. Nonel noiseless lead-in line........................................................................................................................................... 43

48. Highly aluminized AN-FO booster....................... 44

49. Cartridge primed with electric blasting cap.................................................................................................................... 45

50. Priming cast primer with electric blasting cap............ 46

51. Priming blasting agents in large-diameter blastholes 47

52. Corrective measures for voids................................ 49

53. Pneumatic loading of AN-FO underground.................................................................................................................... 51

54. Ejector-type pneumatic AN-FO loader...... 51

55. AN-FO detonation velocity as a function of charge diameter and density 52

56. Pouring slurry into small-diameter borehole 53

57. Pumping slurry into small-diameter borehole 54

58. Slurry leaving end of loading hose ,............................................................................................ 5559. Loss of explosive energy through zones of weakness................................................................................................... 5860. Effect of jointing on the stability of an excavation 58

61. Tight and open corners caused by jointing 58

62. Stemming through weak material and open beds 59

63. Two methods of breaking a hard collar zone 59

64. Effect of dipping beds on slope stability and potential toe problems 59

65. Effect of large and small blastholes on unit costs...... 60

66. Effect of jointing on selection of blasthole size 60

67. Three basic types of drill pattern 61

68. Corner cut staggered blast pattern-simultaneous initiation within rows....................................................................... 6169. V-echelon blast round.................................................................................................................................................... 61

70. Isometric view of a bench blast 61

71. Comparison of a 12%-in-diameter blasthole (stiff burden) with a 6-in-diameter blasthole (flexible burden) in a 40-ft

bench.......................................................................................................................................................................... 62

72. Effects of insufficient and excessive spacing.......................... 6373. Staggered blast pattern with alternate delays................................................................................................................ 63

74. Staggered blast pattern with progressive delays 63

75. The effect of inadequate delays between rows.. 64

76. Types of opening cuts................................................................................................................................................... 66

77. Six designs for parallel hole cuts - 67

78. Drill template for parallel hole cut.. 6779. Blast round for soft material using a sawed kerf 68

80. Nomenclature for blastholes in a heading round.. 68

81. Angled cut blast rounds 68

82. Parallel hole cut blast rounds 6883. Fragmentat ion and shape of muckpile as a function of type of cut.. ... ... .. ... .. ... .. ... ... .. ... .. ... .. ... ... .. ... .. ... .. ... ... .. ... .. ... .. ... ... 69

84. Fragmentation and shape of muckpile as a function of delay 69

85. Typical burn cut blast round delay pattern..... 69

86. Typical V-cut blast round delay pattern 69

87. Shape of muckpile as a function of order of fir ing.......................................................................................................... 6988. Stable slope produced by controlled blasting 71

89. Crack generated by a presplit blast 72

90. Three typical blasthole loads for presplitting............................................................................................ 7391. Typical smooth blasting pattern..................................................................................................................................... 73

92. Mining near a residential structure................................................................................................................................ 75

93. Example of a blasting record.................. 76

94. Seismograph for measuring ground vibrations from blasting......................................................................... 78

95. Effects of confinement on vibration levels..................... 79

96. Effect of delay sequence on particle velocity 79

97. Blasting seismograph with microphone for measuring airblast...................................................................................... 81

98. Causes of airblast.......................................................................................................................................................... 81

99. Proper stacking of explosives........................................................................................................................................ 86

100. AN-FO bulk storage facility.. 87



vi

Page

ILLUSTRATIONS-Continued

101. Checking the rise of the AN-FO column with a weighted tape ,...... 89102. Blasting shelter.............................................................................................................................................................. 91

TABLES

1. Properties of nitroglycerin-based explosives................................................................................................................ 5

2. Fume classes designated by the Institute of Makers of Explosives.............................................................................. 153. Characteristics of pneumatically loaded AN-FO in small·diameter blastholes.............................................................. 524. Approximate BID ratios for bench blasting. 625. Approximate JIB ratios for bench blasting.. 626. Typical powder factors for surface blasting 657. Average specifications for line drilling........................................................................................................................... 718. Average specifications for presplitting .. 739. Average specifications for smooth blasting 73

10. Average specifications for cushion blasting.................................................................................................................. 7411. Maximum recommended airblast levels 82

A-1. Federal regulatory agency responsibility....................................................................................................................... 96

UNIT OF MEASURE ABBREVIATIONS USED IN THIS REPORT

amp

cm

cucm

cu ft

cu yd

dB

ampere

centimeter

cubic centimeter

cubic foot

cubic yard

decibel

degree

degree Fahrenheit

foot per second

ft

ggr

Hzin

kb

kcal

Ib

mi

foot

gram

grainhertz

inch

kilobar

kilocalorie

pound

mile

min

ms

pet

ppm

psi

secsq ft

sqin

yd

minute

millisecond

percent

parts per mil lion

pound per square inch

second

square foot

square inch

yard



EXPLOSIVES AND BLASTING PROCEDURES MANUAL

By Richard A. Dick,1 Larry R. Fletcher,2 and Dennis V. D'Andrea3

.ABSTRACT

This Bureau of Mines report covers the latest technology in explosives and blasting

procedures. It includes information and procedures developed by Bureau research, explo-

sives manufacturers, and the mining industry. It is intended for use as a guide in developing

training programs and also to provide experienced blasters an update on the latest state of

technology in the broad field of explosives and blasting.Types of explosives and blasting agents and their key explosive and physical properties

are discussed. Explosives selection criteria are described. The features of the traditional

initiation systems-electrical, detonating cord, and cap and fuse-are pointed out, and thenewer nonelectric initiation systems are discussed. Various blasthole priming techniquesare described. Blasthole loading of various explosive types is covered. Blast design, includ-

ing geologic considerations, for both surface and underground blasting isdetailed. Environmental

effects of blasting such as flyrock and air and ground vibrations are discussed along with

techniques of measuring and alleviating these undesirable side effects. Blasting safety

procedures are detailed in the chronological order of the blasting process.

.The various Federal blasting regulations are enumerated along with their Code of Federal

RegUlations citations. An extensive glossary of blasting related terms is included along with

references to articles providing more detailed information on the aforementioned items.

Emphasis in the report has been placed on practical considerations.

'M in in g e ng in ee r, T win C itie s R es ea rc h C en te r, B ure au o f M in es , M in ne ap olis , M N.

2 Mln in g e ng in ee rin g te ch nic ia n, T win C itie s R es ea rc h C en te r, B ure au o f M in es , M in ne ap olis , M N.

3 SU p er vi8 0ry p hy si ca l s ci en ti st, T w in C itie s R es ea rc h C e nte r, B ure au o f M in es , M in ne ap olis , M N .



2

INTRODUC1"ION

The need for better and more widely available blasters' training has long been recognized in the

blasting community. The Mine Safety and Health Administration (MSHA) of the Department of Labor

requires health and safety training for blasters. In 1980, the Office of Surface Mining Reclamation and

Enforcement (OSM), Department of the Interior, promulgated regulations for the certification of

blasters in the area of environmental protection. These regulations are certain to have a positive

influence on the level of training and competence of blasters. They will, however, present a problem to

the mining industry. That problem is a scarcity of appropriate training material. Although numerous

handbooks and textbooks are available (9, 24, 27, 29-30, 32, 46)4 none are geared for use in training

the broad spectrum of people involved in pract ical blasting. This manual isdesigned to fulfi ll that need.

It is appropriate that the Bureau of Mines prepare such a manual. Since its inception, the Bureau has

been involved in all aspects of explosives and blasting research including productivity, health and

safety, and environment, and has provided extensive technical assistance to industry and regulatory

a~Elncies in the promotion of good blast ing practices.

This manual serves two basic functions. The first is to provide a source of individual study for the

practlcal blaster. There are literally tens of thousands of people involved in blasting at mines in the

country and there are not enough formal training courses available to reach the majority of them. The

second function is to provide guidance to industry, consultants, and academic institutions in the

preparation of pract icai training courses on blast ing.

The manual has been broken down into a series of discrete topics to facilitate self-study and the

preparation of training modules. Each section stands on its own. Each student or instructor can uti lizeonly those sections that suit his or her needs. An attempt has been made to provide concise, yet

comprehensive coverage of the broad field of blasting technology. Although liberal use has been made

of both Bureau and non-Bureau literature inpreparation of this manual, none ofthe topics are dealt with

in the depth that would be provided by a textbook or by a publication dealing with a specific topic. Each

section is supplemented by references that can be used to pursue a more in-depth study. These

references are limited to practical items that are of direct value to the blaster in the field. Theory is

included only where it is essential to the understanding of a concept.

Where methods of accomplishing specific tasks are recommended, these should not be considered

the only satisfactory methods. In many instances there is more than one safe, effective way to

accomplish a specific blasting task.

None of the material in this manual is intended to replace manufacturers' recommendations on the

use of the products involved. It is strongly recommended that the individual manufacturer be consulted

on the proper use of specific products.

'Ita lic iz ed n um be rs in p are nth es es r efe r to ite ms in th e b ib lio gr ap hy p re ce din g th e a pp en dix es .



3

Chapter 1.-EXPLOSIVES PRODUCTS

CHEMISTRY AND PHYSICS OF EXPLOSIVES

It is not essentia l that a blaster have a strong know ledge ofchem istry and physics. H ow ever, a brief discussion of there actio ns o f e xp lo siv es w ill b e he lp fu l in u nd ersta nd in g h owth e e ne rg y re qu ire d to b re ak ro ck is d eve lo pe d.An e xp lo siv e is a chem ic al c ompound o r m ix tu re o f c ompounds

th at u nd erg oe s a v ery ra pid d ecomp ositio n w he n in itia te d bye nerg y in th e fo rm of h ea t, im pa ct, frictio n, o r sh oc k (4)1. Thisdecomposi tion p roduces more s tab le subs tances , mos tly gases ,and a large amount of heat. The very hot gases producee xtre me ly h ig h p re ssu re s w ithin th e b ore ho le , a nd it is th esep re ssu re s th at ca us e th e roc k to b e f ra gm en te d. If th e s pee d o f

reaction of the explosive is faster than the speed of sound inthe expl os ive (de tonat ion ), the p roduc t i s ca ll ed a h igh explos ive . I fth e re actio n o f the ex plo siv e is s lo we r th an the sp ee d o f s o un din the explosive (deflagration), the product is called a lowexplosive.T he p rin cip al re ac tin g in gre die nts in a n e xp lo siv e a re fu els

a nd o xid iz ers . C ommon fu els in c ommerc ia l p ro du cts in clu defuel oil, carbon, alum inum , TNT, smokeless powder,m on om ethy lam in e n itra te, an d m on oe th an ol a min e n itra te .F ue ls o ft en per fo rm a sensit iz in g f un ct io n. Common exp lo siv es en sitiz ers a re n itro glyc erin , n itro sta rc h, a lu min um , T NT ,smokele ss powder , monomethy lam in e n it ra te , a nd monoetha l-am ine n it ra te . M i croba lloons and ae ra ti ng agen ts a re some timesadded to enhance sensitiv ity. T he m ost common oxidizer isammon ium n it ra te , a lt ho ugh sod ium n it ra te and calc ium n it ra tem ay also be used. O ther ingredients of explosives includewa te r , gums, thi ckene rs and c ross- lin k ing agen ts used in s lu rr ies(11 ), ge la tin ize rs , dens if ie rs , an tac ids , s tab il ize rs , abso rbents,and flame retardants. In molecular explosives such asn it rog lycer in ,TNT , and PETN, the fue l and ox id ize r a re combinedin th e same comp ou nd .

Most in gr ed ie nt s o f e xp lo siv es a re composed o ft he e lemen tso xy ge n, n itro ge n, h yd ro ge n, a nd c ar bo n. In a dd itio n, me ta llice lemen ts s uch a s a lum inum a re some times u sed. For e xp lo siv em ix tu re s, e ne rg y re le as e is o ptim iz ed a t z ero o xy ge n b ala nc e(5 ). Zero oxygen balance is defined as the point at w hich am ixture has sufficient oxygen to com pletely oxidize all thefue ls it c on ta in s b ut th ere is n o e xc es s o xy ge n to re ac t w ith th en itro ge n in th e m ixtu re to fo rm n itro ge n ox ide s.T heoret ic ally , a t z er o o xygen bala nce t he gaseous p rodu ct s

of detonation are H20, CO2, and N2, a lth ou gh in re ality sma ll

am ounts of N O, CO, N H2, CH4, and o th er g ases a re generat ed .Figure 1 show s the energy released by som e of the commonp ro du cts o f d eto na tio n. P artia l o xid atio n o f c arb on to c arb onmo no xid e, whic h re su lts from a n o xy ge n d efic ie nc y, r ele as esless heat than com plete oxidation to carbon dioxide. Theo xid es o f n itro ge n, w hic h a re p ro du ced w he n th ere is e xc essoxygen, are "heat robbers;" that is, they absorb heat w heng en era te d. F re e n itro ge n, b ein g a n e leme nt, n eith er a bs or bsn or re le as es h ea t u po n lib er atio n.

It should be noted that the gases resulting from im propero xy ge n b ala nc e a re n ot o nly in effic ie nt in te rm s o f h ea t e ne rg yreleased but are also poisonous. Although the oxidation ofalum inum yields a solid, rather than a gaseous, product the

'It al ic iz ed n umber s in p ar en th es es r ef er t o it ems in t he li st o f r ef er en ce s a t t h e

e nd o f th is c ha pte r.

0100 -

e

~80-

s

~60-

~40-

.:r: 20"-

-20 I-

"o---~----------------..,

040

S TA NO AR O H EA TS O F F ORM AT IO N.

II.COI/II\OIt

120 - .,0AI203 -399

H20 - ~8

CO2 - 94

co - Z6

N, 0

H02 + 8

NzO + 19

NO +22

~N , I ~ I-

_40--- ~ _J

Figure 1.-Energy released by common products ofdetonation.

l a rge amount o f heat re leased adds s ign if ican tl y to the exp los ive 'se nerg y. M ag ne siu m is e ve n b etter fro m th e s ta nd po in t o f h ea tr ele as e, b ut is to o s en sitiv e to u se in c ommerc ia l e xp lo siv es .The principle of oxygen balance is best illustrated by the

react ion of ammonium ni tra te - fue l o i l [ (NH4N03)-(CH2 ) J mixtures.C ommon ly c alle d A N-FO, th ese m ix tu re s a re th e m os t w id ely

u se d b la stin g a ge nts . F rom th e re ac tio n e qu atio ns fo r AN- FO ,o ne c an re ad ily s ee th e re la tio ns hip b etwee n o xy ge n b ala nc e,d et onat io n p ro du ct s, a nd hea t r ele ase. T he equat io ns a ssumea n id ea l d eto na tio n re ac tio n, whip h in tu rn a ss ume s th or ou ghm ixing of ingredients, proper partic le siz ing, adequateco nfin em en t, ch arg e d ia me te r a nd p rim in g, a nd p ro te ctionf rom wa te r . Fuel o il is ac tua ll y a va ri ab le m i xture o f hydroca rbonsand is not precisely C H2, b ut th is id en tific atio n s imp lifie s th eequations-and is accurate enough for the purposes of thism anual. In review ing these equations, keep in m ind that theamo un t o f h ea t p ro du ce d is a me as ure o f t h e e ne rg y re le as ed .

(94.5 pct AN )-(5.5 pct FO ):3N H4N03 + CHz->7H~ +~ + 3N 2 + O.93kcal/g.

(1 )

(92.0 pct AN )-(8.0 pct fO ):2N H4N03 + CHz->5H20 +CO + 2N 2 + 0 .81 kcal /g .

( 2 )

(96.6 pct AN )-(3.4 pct FO ):5N H4N03 + C Hz-> 11 H20 + CO2 +

4N 2 + 2N O + 0 .60 kcal /g .(3)

Equ atio n 1 re pre se nts th e re ac tio n o f a n o xy ge n-b ala nc edm ixture containing 94.5 pct AN and 5.5 pct FO . N one of thedetonation gases are poisonous and 0.93 kcal of heat isreleased for each gram of AN ·FO detonated. In equation 2,representing a m ixture of 92.0 pct AN and 8.0 pet FO , theexcess fuel creates an oxygen deficiency. As a result, the



4

carbon in the fuel oil is oxidized only to CO, a poisonous gas,

rather than relatively harmless CO2, Because of the lower heat

of formation of CO, only 0.81 kcal of heat is released for each

gram of AN-FO detonated. In equation 3, the mixture of 96.6

pet AN and 3.4 pet FO has a fuel shortage that creates anexcess oxygen condition. Some of the nitrogen from the

ammonium nitrate combines with this excess oxygen to form

NO, which will react with oxygen in the atmosphere to form

extremely toxic N02. The heat absorbed by the formation of

NO reduces the heat of reaction to only 0.60 kcal, which is

considerably lower than that of an overfueled mixture. Also the

CO produced by an overfueled mixture is less toxic than NO

and N02. For these reasons a slight oxygen deficiency is

preferable and the common AN-FO mixture for field use is 94

pet AN and 6 pet FO.AlthoUgh the simple AN-FO mixture is optimum for highest

energy release per unit cost of ingredients, products with

higher energies and densities are often desired. The common

high-energy producing additives, which may be used in both

dry blasting agents and slurries, fall into two basic categories:

explosives, such as TNT, and metals, such as aluminum.

Equations 4 and 5 illustrate the reaction of TNT and aluminum

as fuel-sensitizers with ammonium nitrate. The reaction products,

again, assume ideal detonation, which is never actually attained

in the field. In practice, aluminum is never the only fuel in the

mixture, some carbonaceous fuel is always used.

(78.7 pct AN)-(21.3 pet TNT):

21NH4N03 +2CeH2CH3(N02h-,47H20 +

14C02 + 24N2 + 1.01 kcal/g.

(81.6 pct AN)-(18.4 pet AI):

3NH4N03 + 2A1-,6H20 +

AI203 + 3N2 + 1.62kcal/g.

Both of these mixtures release more energy, based onweight, than ammonium nitrate-carbonaceous fuel mixtures

and have the added benefit of higher densities. These

advantages must be weighed against the higher cost of such

high-energy additives. The energy of aluminized products

continues to increase with larger percentages of metal, even

though this "overfuetlnq" causes an oxygen deficiency.

Increasing energy by overfueling with metals, however, is

uneconomical except for such specialty products as high-

energy boosters.The chemical reaction of an explosive creates extremely

high pressures. It is these pressures which cause rock to be

broken and displaced. To illustrate the pressures created in

the borehole, a brief look will be taken at the detonation

process as pictured by Dr. Richard Ash of the University of

Missouri-Rolla. Figure 2, adapted from Ash's work shows (top)a column of explosive or blasting agent that has been initiated.

Detonation has proceeded to the center of the column. The

Direction at eetcnctrcn movement -

Shock I ront

Point of initiation

EJlploSlon products \

H,O,CO"N, ~

'" ----------~C-J plone

Pr im ar y r ea ct io n z on e

Unfeocled product

NH.NO~,CH2

Pd-s1urry ellplostve

Pd slurry bloslinQ oqenl

I Pe-slurry • • p losive

I

L----------------~-----------KE~Y----~Pd Oefonorion pressure

Pe E.plosion pressure

Figure 2.-Pressure profi les created by detonationin a borehole.

( 4 )

primary react ion occurs between a shock front at the leading

edge and a rear boundary known as the Chapman-Jouguet

(C-J) plane. Part of the reaction may occur behind the C·J

plane, particularly if some of the explosive's ingredients are

coarse. The length of the reaction zone, which depends on the

explosive's ingredients, particle size, density, and confinement,

determines the minimum diameter at which the explosive will

function dependably (critical diameter). High explosives, which

have short reaction zones, have smaller critical diametersthan blasting agents. ..The pressure profi les infigure 2 (bottom) show the explosive

forces applied to the rock being blasted. A general comparison

is given between an explosive and a blast ing agent, although it

should be understood that each explosive or blasting agent

has its own particular pressure profile depending on itsingredients, particle size, density, and confinement

The initial pressure, called the detonation pressure (P), is

created by the supersonic shock front moving out from the

detonation zone. The detonation pressure gives the explosive

its shattering action inthe vicinity of the borehole. Ifthe explosive

reacts slower than the speed of sound, which is normally the

case with black powder, there is no detonation pressure.

The detonation pressure isfollowed by a sustained pressure

called explosion pressure (Pe)' or borehole pressure. Borehole

pressure is created by the rapid expansion of the hot gases

within the borehole. The detonation pressure of high explosives

is often several t imes that of blasting agents, but the borehole

pressures of the two types of products are of the same general

magnitude. The relative importance of detonation pressure

and borehole pressure in breaking rock will be discussed inthe "Properties of Explosives" sect ion of this chapter.

(5)

TYPES OF EXPLOSIVES AND BLASTING AGENTS

This sect ion will cover all explosive products that are used

for industrial rock blasting. with the exception of initiators.

Products used as the main borehole charge can be divided

into three categories: ni troglycerin- (or nitrostarch-) based

high explosives, dry blasting agents, and slurr ies, which may

also be referred to as water gels or emulsions. These products

can also be broadly categorized as explosives and blasting

agents. For ease of expression, the term explosives will often

be used in this manual to collectively cover both explosives

and blasting agents. The difference between an explosive and

a blasting agent is as follows.

A high explosive is any product used in blasting that is

sensitive to a No.8 cap and that reacts at a speed faster than

the speed of sound in the explosive medium. A low explosive



is a product in which the reaction is slower than the speed of

sound. Low explosives are seldom used in blasting today. A

blasting agent is any material or mixture consisting of a fuel

and an oxidizer, intended for blasting, not otherwise classified

as an explosive, provided that the finished product, as mixed

and packaged for shipment, cannot be detonated by a No.8

blasting cap in a specific test prescribed by the Bureau of

Mines. Slurries containing TNT, smokeless powder, or other

explosive ingredients, are classed as blast ing agents if they

are insensitive to a No.8 blasting cap.AN-Fa, which in normal form is a blasting agent, can be

made cap sensitive by pulverizing it to a fine part icle size, and

a slurry can be made cap sensitive by including a sufficient

amount of finely flaked paint-grade aluminum. Although neither

of these products contains an explosive ingredient, their cap

sensitivity requires their being classif ied as explosives. The

term nitrocarbonitrate, or NCN, was once used synonymously

with blasting agent under U.S. Department of Transportation

(DOT) regulations for packaging and shipping blasting agents.

DOT no longer uses this term.

NITROGL YCERIN·BASED

HIGH EXPLOSIVES

Nitroglycerin-based explosives can be categorized as to

their nitroglycerin content (4). Figure 3 shows this breakdown

5

Ingredients Nonqelu ti noua ~ Properties

, ritroglycerin Btasting qero t i n f ~0

n~o

~~§~~ < ~.=.; nn Struiqtn dyno rnite Slroiqht qel o t in ~ ~,

-0~, , ;;~

o ~ . :.~ ~~"' = e, ~0

~.

-, ,~ High-density 0. : : ; ' " rD ;j"~.

~"'n;" Ammonia gelatinn ammonia dynamite ~ '< g -,, o Q ~-a , ~~

"', 3 ~ Low-density ~

n ;;3 , Serntqel otin ~0

~ ~g ommoni c dynamite ,

3 I Dry blosling agents Slurries IIncreas inC} waler res is ton!e

Figure 3.-Relatlve ingredients and properties of

nitroglycerhi~sed hlgn explosives.

along with some relat ive propert ies and ingredients of these

products. Table 1 shows some properties of nitroglycerin-

based explosives. Property values are averages of manufac-

turers' published figures. As a group, nitroglycerin-basedexplosives are the most sensit ive commercial products used

today (excluding detonators). Because of this sensitivity they

offer an extra margin of dependability in the blasthole but are

somewhat more susceptible to accidental detonation. This isa

tradeoff that many operators using small-diameter boreholes

Table 1.• Properties of nitroglycerin-based explosives

Weight Bulk Specific Detonat ion Water Fume

st rength, s trength, gravity velocity , resistance classpe t pe t fp s

STRA IGHT DYNAM ITE

50 50 1.4 17,000 G oo d .............................. P oo r.

H IG H· DEN SIT Y AMMON IA D YNAM IT E

60 50 1.3 12,500 F air ................................ G oo d.

40 35 1.3 10,500 ...do ............................... Do .

20 15 1.3 6,000 ...do ............................... Do.

L OW ·D EN SIT Y AMMON IA D YN AM IT E, H IG H V EL OC IT Y

65 50 1.2 11,000 Fair ................................ Fair.

65 40 1.0 10,000 ...do ............................... Do.

65 30 .9 9,500 Poor ............................... Do .

65 - 20 .6 6,500 ...do ............................... Do .

L OW -D EN SIT Y AMMON IA D YN AM IT E, L OW V EL OC IT Y

65 50 1.2 6,000 F air ................................ F air

65 40 1.0 7,500 P oor . .............................. Do.

65 30 .9 7,000 ...d o .................................. D o .

65 20 .6 6,500 ...do ............................... Do .

B LAST ING GELAT IN

100 90 1.3 25,000 Excellent ........................ Poor.

STRA IGHT GELAT IN

90 e o 1.3 23,000 Excellent ........................ Poor.

60 60 1.4 20,000 ....do .............................. Good.

40 45 1.5 16,500 ....do .............................. Do .20 30 1.7 11,000 ....do .............................. Do.

AMMON IA G E LA TIN

60 70 1.3 20,000 Very good .. .. . .. . .. . .. . . .. . .. . . Good.

60 60 1.4 17,500 ...do ............................... V ery g oo d .

40 45 1.5 16,000 ...do ............................... Do .

SEMIGELATIN

65 60 1.3 12,000 V ery good ...................... Very good.

65 50 1.2 12,000 ...do ............................... Do .

65 40 1.1 11,500 Good .............................. Do .

65 30 .9 10,500 Fair ................................ Do .



6

m ust m ake. N itrog lycerin dynam ites account for less than 5p et, b y w eig ht, o f t he ex plo sives m arket (12 ), a nd a lm ost a ll ofth a t is in sma ll -d iame te r wo rk . D y nam it e is a va il ab le in c a rt rid gesof various sizes and shapes, as show n in figure 4.

Nitroglycerin (NG), th e fir st h ig h e xp lo siv e, is th e s en sitiz erin dynam ites and is se ldom used alone, although it has beenus ed in a s om ew ha t d ese ns itize d fo rm for sh oo tin g o il w ells . Itha s a sp ec ific gra vity o f 1.6 an d a de ton ation v eloc ity s lig htly

Figure 4.- Typical cartridges of dynamite. ( Co ur tMY A tl• • P ow d er Co.)



o ve r 2 5,0 00 fp s. Its e xtre me se nsitivity to sh oc k, fric tio n, a ndheat m ake it hazardous to use.

S tr ai gh t ( ni tr og ly ce rin ) d ynam it e cons is ts o f n it rog lycer in ,s od ium n it ra te , a n antac id , a car bonaceous f ue l, a nd some timessu lfu r. T he te rm "stra ig ht" m ea ns th at a d yn am ite co nta in s n o

ammon ium n it ra te . The we igh t s treng th , usua ll y 50 pe t, i nd ica test he app ro xima te per cent age o f n it ro gly ce rin o r o th er e xp lo siv eo il. T he u se o f s tra igh t d yn am ite is lim ite d b ec au se o f its h ig hc os t a nd s en sitiv ity to s ho ck a nd fric tio n. F ifty p er ce nt s tra ig htd ynam it e, b y f ar t he most c ommon s tr aig ht d ynam it e, is r ef er re dto a s d itc hin g .d yn am ite a nd is u se d in p ro pa ga tio n b la stin g.

High -dens It y ammon ia dynamI te , a lso ca lled extra dynamite ,is th e m ost w id ely us ed d yn am ite . It is like stra ig ht d yn am ite .e xcep t t ha t ammon ium n it ra te r ep la ce s par t o f t he n it ro gly ce rinand sodium nitrate. Ammonia dynam ite is m anufactured ing ra de s o f 2 0 to 6 0 p et w eig ht stre ngth , a lth ou gh th es e g ra de sare not truly equivalent to straight dynam ites of the sameweig ht s te ng th (s ee p ro pe rtie s in ta ble 1 ). Ammon ia d yn am iteis le ss s en sitiv e to s ho ck a nd fr ic tio n th an s tra ig ht d yn am ite . Itis m ost commonly used in sm all quarries, in undergroundm in es , in c on stru ctio n, a nd a s a n a gric ultu ra l e xp lo siv e.

Low -dens it y ammon ia d ynam i te is manu fa ct ur ed in a we ig htstre ng th o f a bo ut 6 5 p et. T he ca rtrid ge (b ulk) stre ng th ra ng esf rom 20 to 50 pe t,c l epending on the bu lk dens it y o f the ing red ien ts .A h igh-ve loc ity ser ies and a low-ve loc ity ser ies are manufactured.

Low -density ammonia dynam ite is useful in very soft orprefractured rock or where coarse rock such as riprap isrequired... B la stin g g ela tin is a to ug h, ru bb er- te xtu re d e xp lo siv e mad eby adding n it rocell ulose, a lso ca ll ed gunco tton , to n it rog lycer in .

. A n a nta cid is a dd ed to p ro vid e s to ra ge s ta bility a nd woo d mealis a dd ed to im pro ve se nsitiv ity . B la stin g g ela tin emits la rg ev olume s o f n ox io us fume s u po n d eto na tio n a nd is e xp en sive .It is s eld om u se d to da y. S ome times c alle d o il w ell e xp lo siv e, ithas been used in deep wells w here high heads of water areencountered . B las ti ng ge la tin is the mos t power fu l n it rog lycer in -

based explos ive .S t ra igh t ge la tin is b asic ally a b la stin g g ela tin w ith s od ium

n itra te , c arb on ace ou s fu el, a nd some tim es s ulfu r a dd ed . It ismanufactured in grades ranging from 20 to 90 pct weights tr engt h and is t he gela tin ou s equ iv ale nt o f s tr aig ht d ynam it e.S tra ig ht g ela tin h as b ee n u se d main ly in s pec ialty are as s ucha s se is mic or d eep w ell w ork , w he re a la ck o f c o nfin em en t o r ah ig h h ead o f w ate r m ay a ffe ct its ve lo city. T o o ve rcome th es econditions a high-velocity gelatin is available w hich is likes tr aig ht g ela tin e xc ep t th at it d eto na te s n ea r its ra te d v elo cityd esp ite h ig h h ea ds o f w ate r.

Ammon ia ge la tin, a lso ca ll ed spec ia l ge la ti n o r ex tra ge la tin ,is a stra ig ht g ela tin in w hic h ammon ium n itra te h as re pla ce dp art o f th e nitro glyc erin a nd so dium n itra te . M an ufa ctu re d inw eig ht stre ng th s ra ng in g fro m 4 0 to 80 p et, it is th e g ela tin ou s

equ iv ale nt o f ammon ia d ynam it e. Ammon ia 'g ela tin is s uit ab lefor underground w ork, in w et conditions, and as a toe load,p rima rily in sma ll-d iamete r b ore ho le s. T he h ig he r g ra de s (7 0p et or h ig he r) a re u se fu l as p rim ers fo r b la stin g a ge nts .

Semige/atin has a we ig ht s tr engt h nea r 65 pet . T he car tr id ge(b ulk) s tre ng th ra ng es fro m 30 to 6 0 p et w ith va ria tio ns in th eb ulk d en sity o f th e in gr ed ie nts . S em ig ela tin is v er sa tile a nd isu se d in sm all-d ia me te r w ork w he re some wate r re sista nce isrequired. It is useful underground, w here its soft, p lasticc on sis te nc y makes it id ea l f or lo ad in g in to hole s d rille d upwa rd .

N it ro st ar ch e xp lo si ve s are sensitized w ith nitrostarch, as olid m ole cu la r e xp lo siv e, ra th er th an an ex plo siv e oil. T he ya re ma nu fa ctu re d in v ario us g ra de s. s tre ng th s, d en sitie s. a nddegrees of w ater resistance to com pete w ith m ost grades ofn it ro gly ce rin -b ased dynam it es . T he y a re s im ila r t o d ynam it es

7

in m any w ays w ith their m ost significant differences beingsomewha t h ig he r impac t r es is ta nce and the ir " headache -f re e"nature.

DRY BlAS"rlNG

AGENTSIn this m anual, the term dry blasting agent describes any

m aterial used for blasting w hich is not cap sensitive and iw hich w ater is n ot u se d in th e form ula tion . F ig ure 5 d esc rib esth e d ry b la stin g a ge nts in u se to da y.

Early dry blasting agents em ployed solid carbon fuelsc om bin ed w ith ammon ium n itra te in v ario us fo rm s. T hro ug hexperim entation it w as found that diesel fuel oil m ixed w ithp oro us ammonium n itr ate p riU s (fig . 6 ) g av e th e b es t b la stin gre su lts. H en ce , th e te rm AN·FO (ammon ium n itra te -fu el o il)has been synonym ous w ith dry blasting agent. An oxygen-b ala nc ed AN-FO is th e ch ea pe st s ou rc e o f e xp lo siv e e ne rg ya va ila ble to da y. A dd in g fin ely d iv id ed o r fla ked a lumin um todry blasting agents increases the energy output but at anincrease in cost. Alum inum ized dry m ixes are som etim es

us ed in comb in atio n w ith c ast prim ers a s p rim ers fo r A N-FO.A lumin ize d m ix es m ay a ls o b e u se d a s a h ig h-e ne rg y to e lo ada nd a s th e m ain c olu mn ch arg e w he re b la stin g is d ifficu lt.

Ammonium nitrate

1-------,

I Fuel, 1

I usually fuel oil IL..- _

1--- 1

1 Aluminum I1 ..J

Dryblasting

agent(AN-FO)

Aluminized

dryblasting

agent

Densified

dryblasting

agent

Figure 5.-Types of dry blasting agents and thIngredients.



8

Figure 6.-Porous ammonium nitrate prllls. (Cour teay He rcu lea lnc .)

Itis difficult to give precise numerical values for the properties

of dry blasting agents because the properties vary with ingredient

part icle size, density, confinement, charge diameter, water

conditions, and coupling ratio (5). Yancik has prepared an

excellent manual on explosive properties of AN·FO (9).

Coupling rat io is the percentage of the borehole diameter

filled with explosive. Poured bulk products are completely

coupled, which increases their efficiency. Cartridged products

are partial ly decoupled, and thus lose some efficiency.

AN·FO's theoretical energy is optimized at oxygen balance

(approximately 94.5 pctAN and 5.5 pctFO), where the detonationvelocity approaches 15,000 fps in large charge diameters.

Excess fuel oil (8 pct or more) can seriously reduce sensitivity

to ini tiation. Inadequate fuel oil causes an excess of harmful

nitrogen oxide fumes in the detonation gases. Specific gravities

of AN·FO range from 0.5 to 1.15; 0.80 to 0.85 is the most

common range. The lighter products are useful in easily

fragmented rock or to eliminate the need for alternate decks of

explosive and stemming where a low powder factor isdesirable.

The densified dry mixes are packaged inwaterproof containers

for use in wet blast holes (fig. 7).

Densification isnecessary to enable the cartridges to sink in

water. To obtain a higher specific gravity, part of the pril ls are

pulverized and thsn the mixture of whole and pulverized prills

is vibrated or otherwise compressed into rigid cartridges or

polyburlap bags. Densifying ingredients, such as ferrosilicon,

are seldom used today because they add litt le or nothing tothe

explosive's energy. The sensit ivity of AN-FO decreases with

increased density. The "dead press" limit, above which

detonation is undependable, is about 1.25 g/cu cm.

The detonation velocity of AN-FO is strongly affected by

charge diameter. The critical diameter is near 1 in with a

normal prill and oil mixture. The velocity increases with diameter

and levels off near a 15·in diameter at a velocity of nearly

15,000 fps. The minimum primer required for AN~FO increases

as charge diameter increases. There is a tendency to underprimein large-diameter boreholes. A good rule of thumb is, when in

doubt, overprime. Many operators claim improved results when

they use primers that fil l, or nearly fil l, the blasthole diameter.

,he undesirable enect of water on dry blasting agents has

often been seen in poor blasts where AN-FO was used in wet

boreholes with insufficient external protection. Excess water

adversely affects the velocity, sensitivity, fume class, and

energy output of a dry blasting agent. The extreme result is a

misfire. Itis essential when using AN-FO in wet conditions that

positive protection in the form of a waterproof package or aborehole liner be used (3).

Dry blasting agents can be purchased in four forms. In

increasing order of cost they are as follows:



9

Figure 7.-Water-reslstant packages of AN-FOfor use in wet boreholes. (Courtesy Gulf 011Chemicals Co.)

1 . A s sep arate in gre dien ts in bu lk fo rm fo r on site m ixing2 . P rem ix ed in b ulk fo rm fo r o ns ite s to ra ge o r d ire ct b ore ho le

delivery (a prem ixed product m ay cost about the sam e assepara te ing red ien ts ).

3 . In paper or po lyethy lene packages for pouring in to theborehole.

4 . In w ate rp ro of c artrid ge s o r p oly bu rla p c on ta in ers .

W aterproof conta iners are the m ost expensive form s andelim inate the advantage of d irect boreho le coupling. They

shou ld be used on ly wher e bo rehole cond iti on s d ic ta te . B e causeimprope r i ng red ien t p ropo rt ions o r an insu ff ic ien tl y m ixed p roductc au se in effic ie nt d eto na tio n a nd p oo r fume q ua litie s, th oro ug hm ixing and close quality control should be exerc ised in anon s ite m iX ing operation. The use of a colored dye in the fuelg ives a visual check on m ixing and a lso m akes the b lastinga ge nt m ore e as ily visib le in ca se o f m isfire .

R ece nt tria ls in ta co nite m in es ha ve em ploye d a d en se dryb la stin g a ge nt c om po se d o f 8 7 p ct c ru sh ed ammon ium n itra tep riU sand 13 pe t o f a 50 -50 m ix tu re o f n it ro p ropane and me thano l.Th is product has sligh tly m ore energy per un it weight thanAN-FO and can be loaded at a density o f approxim ate ly 1 .2g/cu cm , g iving it a high energy density. Because of thee xp erim e nta l n atu re o f t h is p ro du ct, MSHA s ho uld b e c on su lte dbe fore p uttin g it to use .

SLURRIES

A slurry (fig .8) is a m ixture of nitra tes such as am moniumn itra te a nd s od ium n itra te , a fu el s en sitiz er, e ith er e xp lo siv e o rn on ex plo siv e, a nd v ary in g amo u n ts o f w ate r (1 ). A w ate r g el ise ss en tia lly th e s ame a s a s lu rry a nd th e tw o te rm s a re fre qu en tlyu se d in te rc ha ng ea bly . A n emuls io n is s omewh at d iffe re nt froma w ater ge l o r slu rry in p hysic al ch ara cter bu t sim ila r in m anyf un c tio nal r espec ts . T he p rin c ip a l d if fe re n ce s a re an emu ls io n 'sg en erally high er d eton ation ve loc ity a nd a te nd en cy to w et or

adhere to the blasthole, wh ich in som e cases m ay affect itsb ulk lo ad in g c ha ra cte ris tic s. In th is d is cu ss io n, s lu rrie s, w ate rg els, a nd e mu lsion s w ill be tre ated a s a fa mily of p rod ucts .

A lth ou gh th ey c on ta in la rg e amo un ts o f amm on ium n itra te ,slu rries are m ade w ater res istant through the use of gum s,w ax es , a nd c ro ss -lin kin g a ge nts . T he v arie ty o f p os sib le s lu rryfo rm u la tio ns is a lm o st in fin ite . F re qu en tly a s lu rry is s pe cia llyfo rm u la te d fo r a s pe cific jo b. T he lis t o f p os sib le fu el s en sitiz ersi s e spec ia lly lo ng ( 11 ), a lt hough ca rbonaceous f ue ls , a lum inum ,a nd a mine nitrates are th e m os t comm on .

S lu rries m ay be class ifie d a s e ithe r e xp lo sive s o r b la stingag en ts. T ho se th at are s en sitiv e to a N O.8 cap a re cla ssifiedas explosives, even though they are less sensitive thand yn am ite s. It is im po rta nt th at s lu rrie s b e s to re d in m ag az in esappr op ria te t o t he ir c la s si fi ca ti on .



10

Ammonium nitrate

---,..---

---, ...---

T , I I Aluless I I amine

der, I I microtorch I I other__I L. . .__

r--

sive- I Staized '---e-tergel

Smdiawat

expl

Air- sensitized

water gelblasting agent

Aluminizedwater gelblastingagent

Explosensitlarg

diamewater

all-

meterer gel

osive

F ig ure 8 .-F ormulatlo ns o f w ater-b as ed p ro du cts .

Ex cep t f or t he ir e xc e ll en t wa te r r es is tance and h igher dens it y

and bulk strength, s lurries are sim ilar in many ways to dryb la stin g a ge nts. G oo d oxyg en b ala nce , d ecre ase d p articles ize a nd in cre ase d d en sity , in cre ase d ch arg e d iame te r, g oo dc on fin em en t a nd co up lin g, a nd a de qu ate p rim in g a ll in cre aseth eir e fficie ncy. A lth ou gh slu rry b la stin g a ge nts te nd to lo ses en sitiv ity a s th eir d en sity in cr ea se s, s ome e xp lo siv e- ba se dslurries function well a t densities up to 1.6. The effect ofc ha rg e d iame te r o n th e d eto na tio n ve lo city o f slu rrie s is n ot a sp ro no un ce d a s it is o n A N-F O.

M o st n on -c ap -s en sitiv e s lu rr ie s d ep end on entr ap pe d a ir fo rtheir sensitiv ity and m ost cap-sensitive varieties are alsod ep en de nt, to a le ss er d eg re e, o n th is e ntra pp ed a ir. If th is a iris re mo ve d fro m a slu rry th rou gh pre ssu re fro m an a dja ce ntb la st, p ro lo ng ed p erio ds o f tim e in th e b ore ho le , o r p ro lo ng eds to ra ge , th e s lu rr y m a y b ec ome des en sitiz ed .

S lu rrie s ca n b e d eliv ere d a s se pa ra te in gre die nts fo r o nsitem ix in g, p rem ix ed fo r b ulk lo ad in g (fig .9), in p oly eth yle ne b ag sfor bulk loading or loading in the bag (fig. 10), or they m ay beca rtrid ge d. T he ir co nsiste ncy m ay b e a nyw he re fro m a liq uidto a cohesive gel.

C a rtrid ge d s lu rrie s fo r u se in sma ll-d iam ete r b la sth ole s (2 -ind iame te r o r le ss) a re n orm ally m ad e c ap se nsitive s o th ey ca nb e s ub stitu te d fo r d yn am ite s. H owe ve r, th eir low er s en sitiv ityas compared w ith dynam ite should be kept in m ind. Thesensitiv ity and perform ance of som e grades of s lurries area dv ers ely a ffe cte d b y low tempe ra tu re s. S lu rrie s d es ig ne d fo ru se in m ed ium-d iame te r b la sth ole s (2 - to 5 -in d iame te rs) m ayb e ca p se nsitive b uU he y o fte n a re n ot. T ho se th at a re n ot ca ps ens iti ve must be p rimed w it h a c ap -s ens it iv e exp lo si ve . S lu rr ie sfor use in large diameters (greater than 5 in) are the leastsensi ti ve s lu r ri es .

S lur ri es con ta in ing ne ither a lum inum nor exp los ive sensi ti ze r sa re th e c he apes t, b ut th ey a re a ls o th e le as t d en se a nd powe rfu l.In w et conditions w here dew atering is not practica l, and ther oc k i s no t ext reme ly d if fi cu lt t o f ragmen t, t hese low -c os t s lu rr ie so ffe r c om pe titio n to AN-FO.

A lum In iz ed s lu rrie s o r th os e c on ta in in g s ig nific an t amountso f o th er h ig h-e ne rg y s en sitiz ers , d ev elo p s uffic ie nt e ne rg y fo rb la stin g in h ard , d en se ro ck . H ow ev er, th e e co nomics o f u sin gto ta l co lumn c ha rg es o f h ig hly a lumin iz ed slu rry a re d ou btfu lbecause of the significantly h igher cost of these products .H ig h-e ne rg y slu rrie s h av e im pro ve d b la stin g e fficie nc y w he nused in com bination w ith the prim er at the toe or in anotherz on e o f d iffic ult b re ak ag e.

D eto na tin g co rd d ow nlfn es ca n h ave a h arm fu l e ffe ct o n th ee fficien cy o f b la stin g a ge nt slu rrie s, d ep en din g o n th e size o fth e b la sth ole a nd th e stre ng th o f th e c ord . W h en u sin g d eto na t-ing cord dow nlines, the slurry m anufacturer should be con-su ite d co nce rnin g th e e ffe ct o f th e co rd o n th e slu rry.

T he te ch no lo gy o f s lu rries is very dyn am ic. N ew p ro ductsa re c on tin ua lly b ein g d ev elo pe d. T he b la ste r sh ou ld ch ec k th ete ch nica l lite ra tu re to b e awa re o f d eve lo pm en ts th at a ffe ct h iso r h er b la $tin g p ro gram.

TWO-COMPONENT

EXPl.OSIVES

In div id ua lly , th e c omponen ts o f tw o -c omponen t e xp lo siv es ,a ls o c alle d b in ary e xp lo siv es , a re n ot c la ss ifie d a s e xp lo siv es .W hen shipped and stored separately they are not norm allyregulated as explosives, but they should be protected fromth eft. H ow ever, so me o rg anizatio ns su ch as th e U .S . F ore stS ervice , a nd s om e S ta te a nd lo ca l g ov ernme nt a ge nc ie s, m aytre at th es e c om po ne nts a s e xp lo sive s fo r s to ra ge p urp os es.

T he m ost co mm on tw o-co mp on en t e xp lo sive is a m ixtu re o f

pu lv er iz ed ammonium n it ra te and n it rome thane , a lt hough o the rfuel sensitizers such as rocket fuel have been used. Thec om po ne nts a re c arrie d in s ep ara te c on ta in ers to th e jo bs ite ,w he re th e co nta in er o f liq uid fu el is p ou re d in to th e amm on iumn itra te c on ta in er . A fte r th e p re sc rib ed wa itin g tim e th e m ix tu rebecom es cap sensitive and is ready for use.

T wo -comp on en t e xp lo sive s a re some tim es u se d w he re o nlys ma ll amo un ts o f e xp lo siv es a re re qu ire d s uch a s in p ow erlin einsta lla tion and light construction. W here large am ounts ofexplosives are needed, the higher cost per pound and thein co nv en ie nc e o f o ns ite m ix in g n eg ate th e s av in gs a nd c on ve n-ie nc e re aliz ed th ro ug h le ss s trin ge nt s to ra ge a nd d is tr ib utio nre qu ireme nts . In s om e S ta te s, fo r e xamp le P en ns ylva nia , th eu se r o f tw o-co mp on en t e xp lo sive s is co nsid ere d a m an ufa c-tu re r a nd m us t o bta in a m an ufa ctu re r's lic en se .



11

Figure g.-Slurry bulk loading trucks. ( Co u rt es y Gu lf 0 1 1Ch em l cs ls Co.)

PERMISSIBLEEXPLOSIVES

Permissible explosives are designed for use in underground

coal mines, where the presence of explosive gases or dust

presents an abnormal blasting hazard. Both nitroglycerin-based

permissibles and slurry, water gel, and emulsion permissibles

are available. Briefly stated, the specifications of a permissible

explosive are as follows:

1. The chemical composition furnished by the applicant

must agree, within tolerance, with that determined by MSHA.

2. The explosive must pass a series of propagation tests.

3. The airgap sensitivity of 1%-in cartridges must be at

least 3 in.

4. The explosive must pass nonignition tests when fired

unstemmed into a mixture of natural gas, air, and bituminouscoal dust.

5. The explosive must pass tests for non ignit ion when fi red

stemmed in a gallery of air and natural gas.

6. The volume of poisonous gases produced by a pound of

explosive must not exceed 2.5 cu ft.

7. The explosive must exhibit insensitivity in the pendulumfriction test.

Permissible explosives must be used in a permissible manner,

as described briefly in the "Underground Coal Mine Blasting"

section of chapter 4. MSHA must also approve explosives

used ingassy noncoal mines. For gassy noncoal mines, MSHA

sometimes approves products such as AN-FO, and specifies

the manner in which they are to be used.

Sodium chloride or other flame depressants are used in

permissible explosives to minimize the chance of igniting the

mine atmosphere. As a result, permissible explosives are less

energetic than other explosives and have a lower rock-breakingcapability. They should be used only where required by a

gassy atmosphere. Permissible explosives are allowed to gener-

ate more fumes than other explosives, but most do not. MSHA

periodically publishes an up-dated list of brand names and

properties of permissjble explosives (14).

PRIMERS ANDBOOSTERS

The terms "primer" and "booster" are often confused. Accord-

ing to MSHA a primer, sometimes called a capped primer. is a

unit of cap-sensitive explosive used to initiate other explosives

or hlasting agents. A primer contains a detonator. A booster is



12

. ' - - ' -,-~-

Figure 1a.-Loading slurry-fi lled polyethylene bags. ( Co urt es y A tl.s P owde r Co.)

often, but not always, cap sensitive, but does not contain a

detonator. A booster is used to perpetuate or intensify an

explosive reaction.

Although various products have been used as primers and

boosters, an explosive with a high detonation pressure such

as a high-strength ammonia gelatin or a cast mil itary explosive

(composit ion B or pentolite) (fig. 11) is recommended. Cast

primers have a sensitive inner core that wil l accept detonation

from a detonator or detonating cord, but are quite insensit ive

to external shock or friction. Cast primers are available which

have built-in mil lisecond delay units (fig. 12). These primers,

when strung on a single detonating cord downline, enable the

blaster to place as many delayed decks in the blasthole as the

blast design requires.



CAST PRIMER FOR

DETONATING CORD

II

II

IIIj

IIJ

I

II

II

III

III

_---t-!---_- II

I II It: . ::t

Tunnel

CAST PRIMER FOR

BLASTING CAP

Cop well

Tunnel

13

Although small 1-lb cast primers are popular, even in large

boreholes, a primer functions best when its diameter is near

that of the borehole. A two-stage primer, with a charge of

high-energy dry blasting agent or slurry poured around a cast

primer or ammonia gelatin, isfrequently used in larqe-diameter

blastholes. InSweden, in small-diameter work, excellent results

have been reported with a high-strength blasting cap used toinitiate AN-Fa, thus eliminating the need for a primer. In the

United States, a more common practice in small-diameter

work is to use a small primer designed to fit directly over a

blasting cap, or a small cartridge of ammonia gelatin. More

d~tailed priming recommendations are given in chapter 2.

I

I

II

I

I

III

II It:-".

I

III

I

II

I

II

I

I

I

II

II

II

II

I :- - - i - i - - - - ~ -I II ,

I::'~:.'j

LIQUID OXYGEN EXPLOSIVE

AND BLACK POWDER

Liquid oxygen explosive (LOX) and black powder merit a

brief mention because of their past importance. LOX consists

of a cartr idge of lampblack, carbon black, or charcoal, dipped

into liquid oxygen just before loading. Itderives its energy from

the reaction of the carbon and oxygen to form carbon dioxide.LOX isfired with an ordinary detonator and attains velocities of

12,000 to 19,000 fps. LOX, primarily used in U.S. strip coal

mining, has been replaced by blasting agents, although it is

sti ll used in foreign countries.Figure 11.--east primers for blastingcaps and det-

onating cord.

Figure 12.-Delay cast primer. ( Cou rt es y A tl ss Powder ce.)



14

Black powder, a mixture of potassium or sodium nitrate,

charcoal, and sulfur, dates from ancient times. Once the principal

commercial explosive, black powder is extremely prone to

accidental initiation byflame or spark. When initiated, itundergoes

buming at avery rapid rate. This rapid burning, called deflagration,

is much slower than typical detonation velocities. Black powder

has a specific gravity of 1.6 or less, depending on granulation,

has poor water resistance, and emits large volumes of noxious

gases upon deflagration. Black powder finds limited use in

blasting dimension stone where a minimum of shattering effect

is desired. It is not an efficient explosive for fragmenting rock.

PROPERTIES OF EXPLOSIVES

Explosives and blasting agents are characterized by various

propert ies that determine how they. will function under f ield

condit ions. Propert ies of explosives which are particularly

important to the blaster include "strength," detonation velocity,

density, water resistance, fume class, detonation pressure,

borehole pressure, and sensitivity and sensitiveness. Numerous

other properties can be specified for explosives but have not

been included here because of their lack of importance to the

field blaster.

STRENGTH

The strength of explosives has been expressed in various

terms since the invention of dynamite. The terms "weight

strength" and "cartridge strength," which originally indicated

the percentage of nitroglycerin in an explosive, were useful

when nitroglycerin was the principal energy-producing ingredient

in explosives. However, with the development of products with

decreasing proportions of nitroglycerin, these strength ratings

have become misleading and inaccurate (4) and do not

realistically compare the effectiveness of various explosives.

More recently, calculated energy values have been used to

compare the strengths of explosives with AN·FO being used

as a base of 1.0. Although this system has not been universallyadopted, it is an improvement over weight strength and cartridge

strength in estimating the work an explosive will do. Other

strength rating systems such as seismic execution value,

strain pulse measurement, cratering, and the ballistic mortar

have been used, but do not give a satisfactory prediction ofthe

field performance of an explosive.

Underwater tests have been used to determine the shock

energy and expanding gas energy of an explosive. These two

energy values have been used quite successfully by explosive

manufacturers in predicting the capability of an explosive to

break rock.

DETONATION

VELOCITY

Detonation velocity is the speed at which the detonation

front moves through a column of explosives. It ranges from

about 5,500 to 25,000 fps for products used commercially

today. A high detonation velocity gives the shattering action

that many experts feel isnecessary for difficult blasting conditions,

whereas low-velocity products are normally adequate for the

less demanding requirements typical of most blast ing jobs.

Detonation velocity, particUlarly in modern dry blasting agents

andslurries, may vary considerably depending on field conditions.

Detonation velocity can often be increased by the following

(5):

1. Using a larger charge diameter (see fig. 13, after Ash).

2. Increasing density (although excessively high densities

in blasting agents may seriously reduce sensitivity).

3. Decreasing particle size (pneumatic injection of AN-Fa

in small diameter boreholes accomplishes this).

4. Providing good confinement in the borehole.

5. Providing a high coupling ratio (coupling ratio is the

percentage of the borehole diameter fil led with explosive).

6. Using a larger initiator or primer (this will increase the

velocity near the primer but will not alter the steady state

velocity).

There is a difference of opinion among experts as to how

important detonation velocity is in the fragmentation process.

It probably isof some benefit in propagating the initial cracks in

hard, massive rock. In the softer, prefractured rocks typical of

most operations, it is of l ittle importance.

DENSITY

Density is normally expressed in terms of specific graVity,

which is the ratio of the density of the explosive tothat of water.

~ 25,-:I==;X=:;;:;l::::;::;::I=::r=::::r==:r:=:::::l:=:::::I====l- Cast 50-50 pentolite high explosive

""Q

~! : : : 20u

sl J . J

>Zo 15~z

~l J . J

o

l J . J 10>V io. . . . J

0-

Xl J . J 5 ~ . L L J - - ' - - - - - - ' ' - - - - ' ' - - - - ' - - - - ' - - - - ' _ - - - - L _ - - ' - _ - - - ' _ _

o

Straight gelatin, 60 pet high explosive

turry (water gel) blasting agent

Premixed AN-FOblasting agent

2 3456789

CHARGE DIAMETER, in

F igure 13 .-E ff ect o f charge d iam et er o n d eto n atio n v elo cit y.



15

Cha'9"diGm,'",

in

18

Load inq 1 6dlRlily,

Ibill

200.014

rao.o160.0

140,0 12120.0

100.0

80.0 10

Specific 600

itavity

1.8 40.0

1.630.0

1.420.0

15.0

1.210.0

8.01.0

6.0

.9

4.0

.83.0

.72.0

.6 1.5

/.0

.5 .80

.60

.40

.20

.10

Figure 14.--Nomograph for finding loading density.

A useful expression of density is loading density, which is theweight of explosive per unit length of charge at a specified

diameter, commonly expressed in pounds per foot. Figure 14

shows a nomograph for finding loading density. Cartridge

count (number of 1V4- by a-in cartridges per 50-lb box) is

useful when dealing with cartridged high explosives and is

approximately equal to 141 divided bythe specific gravity. The

specific gravity of commercial products ranges from 0.5 to 1.7The density of an explosive determines the weight that can

be loaded into a given column of borehole. Where drilling is

expensive, a higher cost, dense product is frequently justified.

The energy per unit volume of explosive is actually a more

important consideration, although it is not a commonly reported

explosive property.

WATER RESISTANCE

Water resistance is the ability of an explosive product to

withstand exposure to water without losing sensitivity or

efficiency. Gelled products such as gelatin dynamites and

water gels have good water resistance. Nongelatinized high

explosives have poor-to-good water resistance. Ammonium

nitrate pril ls have no water resistance and should not be used

in the water-filled portions of a borehole. The emission of

brown nitrogen oxide fumes from a blast often indicates inefficient

detonation frequently caused by water deterioration, and signifies

the need for a more water-resistant explosive or external

protection from water in the form of a plastic sleeve or a

waterproof cartridge.

FUME CLASS

Fume class is a measure of the amount of toxic gases,

primarily carbon monoxide and oxides of nitrogen, produced

by the detonation of an explosive. Most commercial blasting

products are oxygen balanced both to minimize fumes and to

optimize energy release per unit cost of ingredients. Fumes

are an important considerat ion in tunnels, shafts, and other

confined spaces. Certain blasting conditions may produce

toxic fumes even with oxygen-balanced explosives. Insufficient

charge diameter, inadequate priming or initiation, water

deterioration, removal of wrappers, or the use of plastic borehole

liners all increase the likelihood of generating toxic gases.

Table 2 shows fume classes adopted bythe Institute of Makers

of Explosives (7). MSHA standards limit the volume of poisonous

gases produced by a permissible explosive to 2.5 cu ft/lb of

explosive.

Table 2•• Fume classes designated by theInstitute of Makers of Explosives

( Si ch el g ag e me th o d)

F ume c la ss

1 .

2 .

3 .

Cu bic lo o t 0 1 po is on o us g as es

pe r 200 g 01exp lo s iv e

0.16

0.16- .33

.33- .67



16

DETONATION PRESSURE

The det onat io n p re ssur e o f a n e xp lo siv e is p rima rily a f un ct io no f th e d eton atio n ve lo city s qu are d tim es the d en sity . It is th ehead-on p re ssur e o f t he det onat io n wave p ropaga tin g t hr oughthe explosive column, measured at the C-J plane (fig.2).

A lth ou gh th e re la tio ns hip o f d eto na tio n v elo city a nd d en sity todetonation pressure is som ew hat com plex, and depends onth e in gr ed ie nts o f a n e xp lo siv e, th e fo llo win g a pp ro xima tio n isone of several that can be m ade (4):

P = 4.18x 1Q-70C 2/(1 + 0.80),

where P = d eto natio n p re ss ure , in k ilo ba rs , (1 kb = 14,504psi),

D = spec if ic gravi ty ,and C = d eto na tio n v elo city , in fe et p er s ec on d.

The nom ograph in figure 15, based on this form ula, can beu se d to a pp ro ximate th e d eto na tio n p re ss ur e o f a n e xp lo siv e

Detonation

velocity,:3

10 fp s

25Detonation

pressure,

k b

20 300---ir---

200---ir----

I 5 0 ------ol'--

100---ir--15

Specific

gravity

1.6~.3

1.0

.8

.6

10

50---ir--

40---ir--

30---ir--

20---1r--

15-+--

10---1'--

5-+--

5

Figure 15.-N()mograph for finding detonation pressure.

whe n th e d eto na tion v elo city a nd s pe cific g ra vity a re k no wn .Some autho ritie s f ee l t ha t a h ig h det onat io n p re ssur e r esult in gin a stro ng sh ock w av e is o f m ajo r im po rta nce in b re akin g ve ryd en se , c omp ete nt ro ck . O th ers , in clu din g Swed is h e xp erts (8 )feel that it is of little or no importance. As a generalre commend atio n, in h ard , mas siv e ro ck , if th e e xp lo siv e b ein g

used i s no tg i v ing adequate b reakage, a h igher ve loc it y explos ive( hence, a h ig he r d et onat io n p re ssur e e xp lo siv e) may a lle via teth e p ro ble m. D eto na tio n p re ssu re s fo r commercia l pro du ctsrange from about 5 to over 150 kb.

BOREHOLE PRESSURE

Bore ho le p re ss ure , s ome times c alle d e xp lo sio n p re ss ur e,is th e p re ss ure e xe rte d o n th e b or eh ole walls b y t he e xp an din ggases of detonation after the chem ical reaction has beencom pleted. B orehole pressure is a function of confinem enta nd th e q ua ntity an d temp era tu re o f th e g as es o f d eto natio n.B or ehole p re ssur e is g enerally c on sid er ed t o p la y t he dom inan tro le in b re ak ing m ost ro ck s a nd in d isp la cin g a ll ty pe s o f ro ck s

encountered in blasting. This accounts for the success ofA N-Fa and alum inized products w hich yield low detonationpressures but relatively high borehole pressures. The 100p ct co up lin g ob ta in ed w ith th ese p ro du cts als o co ntrib ute s toth eir su cce ss. B ore ho le pre ss ure s fo r commercia l pro du ctsrange from less than 10 to 60 kb or m ore. Borehole pressuresare calculated from hydrodynam ic computer codes ora ppro xim ate d fro m u nd erw ate r te st re su lts , s in ce b ore ho lep re ss ure c an no t be m eas ure d d ire ctly . M an y A N-F a m ix tu re shave bo rehol e p ressu res la rge r than the ir de tonat ion p ressu res .In mo st h ig h e xp lo siv es th e d eto na tio n p re ss ure is th e g re ate r.A Swed ish fOnl 1u la (8 ) for compa ri ng the rel at ive rock -b reaki ng

c ap ab ility o f e xp lo siv es is

S = 1/ 6 (VxN) + 5/ 6 (a/a),

where S is the strength of the explosive, V is the reactionp rod uc t g as v olu me , a is the heat energy, the subscript xd en ote s th e e xp lo siv e b ein g ra te d, a nd th e s ub sc rip t0denotesa s ta ndar d e xp lo siv e. T his c or re sponds c lo se ly t o t he bor eholepressure of an explosive. Although the com plexity of thefra gm en ta tio n p ro ce ss p re clu de s th e u se o f a s in gle p ro pe rtyfo r r atin g e xp lo siv es , mo re a nd mor e e xp lo siv es e ng in ee rs a rerely ing on borehole pressure as the single m ost im portantdesc rip to r i n evalua ti ng an explos ive 's rock -b reaki ng capab il it y .

SENSITIVITY ANDSENSITIVENESS

T he se a re tw o clo se ly re la te d p ro pe rtie s th at h av e b ecome

in cre as in gly im po rta nt w ith th e a dve nt o f d ry b la stin g a ge ntsand s lu rr ies , wh ich a re less sens it ive than dynamites . Sens it iv it yis de fined as an expl os ive 's suscept ib ili ty to i nit ia tion . Sensi tiv it yto a No. 8 test blasting cap, under certain test conditions,m ea ns th at a p rod uc t is cla ss ifie d a s a n e xp lo siv e. L ac k o f c apsens it iv ity resul ts in a c lass if ica tion as a b las ting agent. Sens it iv i tyamon g d iffe re nt ty pe s o f b la stin g a ge nts v arie s c on sid era blyand is dependent upon ingredients, partic le size, density,charge diam eter, confinem ent, the presence of w ater, ando ften , pa rt icu la rl y w i th s lu rr ies , tempe ra tu re (2) . Manu fac tu re rso ft en spe cif y a m in imum recommended p rime r f or t he ir p ro du ct s,based on fie ld data. In general, products that require largerprim ers are less susceptib le to accidental in itiation and ares afe r to h an dle .

S en sitiv en es s is th e c ap ab ility o f a n e xp lo siv e to p ro pa ga te



a detonation once it has been init iated. Extremely sensit ive

explosives, under some conditions, may propagate from hole

to hole. An insensitive explosive may fail to propagate throughout

its charge length if its diameter is too small. Sensitiveness is

17

closely related to critical diameter, which is the smallest diameter

at which an explosive will propagate a stable detonation.

Manufacturers' technical data sheets give recommended

minimum diameters for individual explosives.

EXPLOSIVE SELECTION CRITERIA

Proper selection of the explosive isan important part of blast

design needed to assure a successful blasting program (6).

Explosive selection is dictated by economic considerations

and field conditions. The blaster should select a product that

wil l give the lowest cost per unit of rock broken, while assuring

that fragmentation and displacement of the rock are adequate

for the job at hand. Factors which should be taken into

consideration in the selection of an explosive include explosive

cost, charge diameter, cost of drilling, fragmentation difficulties,

water conditions, adequacy of ventilation, atmospherictemperature, propagating ground, storage considerations,

sensitivity considerations, and explosive atmospheres.

EXPLOSIVE COST

No other explosive product can compete with AN-FO on the

basis of cost per unit of energy. Both of the ingredients,

ammonium nitrate and fuel oil, are relatively inexpensive, both

participate fully in the detonation reaction, and the manufacturing

process consists of simply mixing a solid and a liquid ingredient

(fig. 16). The safety and ease of storage, handling, and bulk

loading add to the attractive economics of AN-FO. Itis because

ofthese economics that AN-FO now accounts for approximately

80 pet, by weight, of all the explosives used in the United

States. By the pound, slurry costs range from slightly more

than AN·FO to about four times the cost ofAN-FO. The cheaper

slurries are designed for use in large-diameter blastholes and

contain no high-eost, high-energy ingredients. They are relativelylow in energy per pound. The more expensive slurries are (1)

those designed to be used in small diameters and (2) high-

energy products containing large amounts of aluminum or

other high-energy ingredients. Dynamite cost ranges trom

four to six times that of AN-FO, depending largely on the

proportion of nitroglycerin or other explosive oil.

Despite its excellent economics, AN-FO is not always the

best product for the job, because it has several shortcomings.

AN·FO has no water resistance, it has a low specific gravity,

Figure 16.-Field mixing of AN-FO. (Courtesy Hercules Inc.)



16

and under adverse fie ld conditions it tends to detonatein efficie ntly . F ollo win g a re a dd itio na l fa cto rs th at sh ou ld b eta ke r. in to a cc ou nt whe n s ele ctin g a n e xp lo siv e.

CHARGE DIAMETER

T he de pe nd ab ility a nd e ffic ie nc y o f A N-FO a re s om etim esreduced at sm aller charge diam eters, especially in dam pcondit io ns o r w it h in adequa te con fin ement . I n d iameter s under2 in , A N-FO fu nctio ns b es t w he n p ne umatica lly lo ad ed in to ad ry b la sth ole . Wh en u sin g c ha rg e d iamete rs sma lle r th an 2 in ,man y b la ste rs p re fe r th e g re ate r d ep en da bility o f a c artrid ge ds lu rry o r d yn am ite d es pite th e h ig he r c os t. T he c os t s av in g th atAN -FO offers can be lost through one bad blast.

At interm ediate charge diam eters, betw een 2 and 4 in, theu se o f d ynam it e is s eld om ju st if ie d because AN-FO and s lu rr ie sfu nctio n q uite w ell at th ese d iame te rs . S lurrie s d es ign ed fo ru se in in te rme dia te c ha rg e d iame te rs a re s omewh at c he ap erth an sma ll-d ia me te r s lu rrie s a nd a re m ore e co nomic al th an

dynamite. The pe rformance o fAN-FO in a 4 - in -d iame te r b las tho leis s ub st an tia lly b et te r t han a t 2 in . Where p ra ct ic al, b ulk lo ad in gin in te rmedia te cha rge d iameter s o ff er s a tt ra ct iv e e conom ic s.

In b la sth oie d iamete rs la rg er th an 4 in , a b ulk -lo ad ed AN -FOor slurry should be used unless there is som e com pellingreason to use a cartridged product. A N-FO 's efficiency anddependability increase as the charge diam eter increases.Wh er e th e u se o f a s lu rry is in dic ate d, lo w-c os t v arie tie s fu nc -tio n well in la rg e c ha rg e d iamete rs .

COST OF DRILLING

Und er n orma l d rillin g c on ditio ns , th e b la ste r s ho uld s ele ctth e lowe st c os t e xp lo siv e th at w ill g iv e a de qu ate , d ep en da ble

f ragmen ta ti on . Howeve r, when d ril li ng costs inc rease , typ ica ll yin hard, dense rock, the cost of explosive and the cost ofd rillin g s ho uld b e o ptim iz ed th ro ug h c on tro lle d, in -th e-m in ee xp erim en ta tio n w ith c are fu l co st an alys is . W he re drillin g ise xp en siv e, th e b la ste r w ill w an t to in cre as e th e e ne rg y d en sityof the explosive, even though explosives w ith high-energydensities tend to be m ore expensive. W here dynam ites areu se d, g ela tin d yn am ite s w ill g iv e h ig he r e ne rg y d en sitie s th ang ra nu la r d yn am ite s. T he e ne rg y de ns ity o f a slurry d ep en dso n its d en sity a nd th e p ro po rtio n o f h ig h-e ne rg y in gre die nts ,such as alum inum , used in its form ulation. Because of thediverse varieties of slurries on the m arket, the individualman ufa ctu re r s ho uld b e c on su lte d fo r a r ec ommen da tio n o n ah igh -energy s lu rry.

In sm all-d ia me ter b la sth ole s, th e d en sity of A N-FO may be

in cre as ed b y u p to 2 0 p et b y h ig h- ve lo city p ne umatic lo ad in g.T he lo ad in g d en sity (weig ht p er fo ot o f b ore ho le ) o f d en sifie dAN-FO cartridges is about the sam e as that of bulk AN-FObecause of the void space between the cartridge and theb ore ho le wall. T he e ne rg y d en sity o f AN -FO c an b e in cre as edb y th e a dd itio n o f fin ely d ivid ed a lumin um . T he e co nomics o fa lu min iz ed A N-FO im pro ve w he re th e ro ck is m ore d ifficu lt tod rill a nd b la st .

FRAGMENTATION

DIFFICULTIES

Expensiv e d rillin g and f ra gmentat io n d if fic ult ie s f re quen tlygo hand in hand because hard, dense rock m ay cause both.D espite the controversy as to the im portance of detonation

velocity in rock fragm entation, there is evidence tnat a highvelocity does help in fragm enting hard, m assive rock (10).

With c ar trid ge d d yn am ite s, th e d eto na tio n v elo city in cre as esa s th e n itro gly ce rin c on te nt in cre as es , w ith g ela tin d yn am ite shaving h igher ve loc it ie s than the ir g ranu la r coun te rpa rts. Seve ra lvar ie t ies of s lu r ry , and par ti cularl y emulslons, have h igh ve loc it ies .The individual manufacturer should be consulted for arecommendation on a high-velocity product, In general,emuls io ns e xh ib it h ig he r v elo citie s th an wate r g els .

T he d eto na tio n v elo city o f A N-FO is h ig hly d ep en de nt o n itscharge diameter and particle size. In diameters of 9 in org rea te r, AN-FO's de tonat ion ve loc it y w i ll no rma ll y exceed 13 ,000f ps , p ea kin g nea r 15, 000 f ps in a 15- in d iameter . T he se velo cit ie scom pare favorably w ith velocities of m ost other explosivep rodu ct s. I n smalle r d iameter s t he detonat io n velo cit y f alls o ff ,until at diam eters below 2 in the velocity is less than half the1 5,OOO -fp sma ximum . In th es e sma ll d iamete rs , th e v elo citymay be in cr ea sed to nea rly 1 0, 000 f ps b y h ig h velo cit y p neuma ticloading, w hich pulverizes the AN-FO and gives it a higherlo ad in g d en sity. A s a c au tio na ry n ote , p re ssu res h ig her th an

3 0 p si sh ou ld n eve r b e u sed w ith a pre ss ure v ess el p ne um aticlo ad er. F ull lin e p re ssu re s o f 90 to 1 10 p si are sa tisfa cto ry fo re je ct or s. I n many ope ra tio ns w it h e xpensiv e d rillin g and d if fic ultfragm entation, it may be advantageous for the blaster tocom prom ise and use a dense, high-velocity explosive in thelow er position of the borehole and AN -FO as a top load.

WATER CONDITIONS'

AN-FO h as n o w ate r re sista nce . It m ay, h ow eve r, b e u se d inb la st ho le s con ta in in g wa te r if o ne o f two techn iq ue s is f ollowed .First, the AN-FO m ay be packaged in a water-resistant,p oly bu rla p c on ta in er. T o e na ble th e AN -FO c artrid ge to s in k inwater, part of the prills are pulverized and the m ixture is

vibrated to a density of about 1.1 g/cu em . Of course. if ac artrid ge is ru ptu red d urin g th e lo ad in g p ro ces s, th e A N·FOw ill q uic kly b ec ome d es en sitiz ed . In th e s ec on d te ch niq ue , th eb la sth ole is d ewate re d b y u sin g a d own-th e-h ole s ubme rs ib lepump (3). A wate rp roo f lin er is th en p la ce d in to th e b la sth olea nd AN- FO is lo ad ed in sid e th e lin er b efo re th e wate r re en te rsth e h ole . A ga in , th e AN- FO w ill q uic kly b ec ome d es en sitiz ed ifthe borehole liner is ruptured. The appearance of orange-b ro wn n itro ge n ox id e fume s u po n d eto na tio n is a sig n o f w a te rd ete riora tio n, a nd a n in dic atio n th at a m ore w ate r-re sis tan tp ro du ct o r b ette r e xte rn al p rote ctio n s ho uld be u se d.

Slurries are gelled and cross-linked to provide a barriera ga in st wate r in tru sio n, a nd a s a r es ult, e xh ib it e xc elle nt wate rr es is ta nc e. T he manu fa ctu re r w ill u su ally s pe cify th e d eg re eo f w ate r res ista nce o f a s pe cific p ro duc t. W he n d yn am ite s a re

u sed in we t hole s, g ela tin ou s var ie tie s a re p re fe rr ed . A lt houghsome g ranu la r d ynam it es have f air wa te r r es is ta nce, t he s lig ht lyh ig he r c os t o f g ela tin s is mo re th an ju stifie d b y th eir in cre as edrelia bility in w et b la st' ,le s.

ADEQUACY

OF VENTILATION

A lt hough most e xp lo siv es a re o xygen-ba la nced to maxim iz eenergy and minim i ze tox ic de tonat ion gases , some are inheren tl y" dir ty " f rom the s ta ndpo in t o f f umes. E ven w it h o xygen-ba la ncedproducts, unfavorable fie ld conditions may increase thegenerat io n o f t ox ic f umes, p ar tic ula rly when exp lo siv es w it houtw ater resistance get w et. The use of plastic borehole liners,i nadequate charge d iame te rs , remova l o f a ca rt ri dged explos ive



f rom it s w rappe r, in adequa te p rim in g, o r a n imp rope r e xp lo siv ein gre die nt m ix m ay c au se e xce ssive fu me s.

In areas w here efficient evacuation of detonation gasesc an no t b e a ss ure d (n orma lly u nd er gro un d), AN -FO s ho uld b eu se d o nly in a bs olu te ly d ry c on ditio ns . M os t sm all-d ia me te rs lu rr ie s have ver y good f ume qua lit ie s. L ar ge -d iameter s lu rr ie s

have variable fum e qualitities. The m anufacturer should beconsu lted for a recommenda ti on whe re fume cont ro l is impo rtan t.O f the ca rt ri dged dynamites , ammon ia ge la ti ns and semige la tinshave t he bes t f ume qua lit ie s. H ig h- dens it y ammon ia d ynam it esa re ra te d g oo d, lo w-d en sity ammon ia dy namite s a re fair, an ds tra ig ht d yn am ite s a re p oo r, a s s hown in ta ble 1. In permissibleb la stin g, whe re fumes a re a c on ce rn , c ar e s ho uld b e e xe rc is edin se le ctin g the e xp lo siv es b eca us e m an y p erm iss ib le s h avepoor fum e ratings. P erm issibles w ith good fum e ratings areavailable.

ATMOSPHERIC TEMPERATURE

Un til t he develo pment o f s lu rr ie s, a tmosphe ric t emperat ur esw ere not an im portant factor in selecting an explosive. Formany yea rs , d ynam it es have emplo yed low -f re ez in g e xp lo siv eoils which perm its their usa in the lowest tem peraturese nc ou nte red in th e U nite d S ta te s. A N-FO a nd s lu rries a re n ots er io us ly a ffe cte d b y low tempe ra tu re s if p rim in g is a de qu ate .A p ote ntia l p ro blem e xis ts w ith s lu rrie s th at a re d es ig ne d to b ecap sensitive. At low tem peratures, m any of these productsmay lo se tl1 eir c ap s en sitiv ity , a lth ou gh th ey w ill s till fu nc tio nwell if adequately primed. If a slurry is to be used in coldwea the r the manu fac tu re r shou ld be asked abou t the tempe ra tu relim it at io n on t he p ro du ct ,

The effect of tem perature is allevlated if explosives ares to re d in a h ea ted m ag azin e o r if th ey a re in th e b ore ho le lo nge no ug h to a ch ie ve th e ambie nt b ore ho le temp er atu re . E xc ep tin permafrost or in extremely cold weather, boreholetem peratures are seldom low enough to render slurries

insensitive.

PROPAGATING

GROUND

Propagation is the transfer or m ovem ent of a detonationfrom one point to another. A lthough propagation norm allyoccurs w ithin an explosive colum n, it m ay occur betweenadjacent blastholes through the ground. In ditch blasting, aver y s en sit iv e s tr aig ht n itr og ly ce rin d ynam it e is s ome time usedt o pur po se ly a ccomp lis h p ro paga tio n t hr ough t he g ro und. Thissaves the cost of putting a detonator into each blasthole.P ro paga tio n d it ch b la st in g wo rk s bes t in s of t, wa te r- sa tu ra te dground.

In a ll oth er typ es of b la stin g, pro pa ga tio n b etw ee n h ole s isundes irab l~ because i t nega tes the e ffec t o f de lays. P ropaga ti onbetw een holes w ill result in poor fragm entation, fa ilure of around to pu ll p roper ly , and excessive g round v ib ra ti ons , a irbl as t,a nd fly ro ck . In u nd erg ro un d b la stin g, th e e ntir e ro un d ma y fa ilt o p ull. T he p roblem is most s er io us when usin g small b la st ho le slo ad ed w ith d yn am ite . Small b la sth ole s re qu ire sma ll b ur de nsand spac ings, inc reasing the chance o f ho le - to -ho le p ropaga tion ,pa rt icu la rl y when sens it ive explos ives a re used . Wa ter sa tu ra tedma te ria l a nd b la st ho le dev ia tio n compound t he p ro blem . Whenp ropaga tio n is s uspe ct ed , ow in g t o poo r f ra gmentatio n, v io le ntshots, or high levels of ground Vibrations, the use of a lesssensitive product usually solves the problem . Straightn i trog lycerin dynamite is the most sens it ive commerc ia l exp los ive

19

available, fo llow ed by other granular dynam ites, gelatindynam ites, cap-sensitive slurries, and blasting agents, id ec re as in g o rd er o f s en sit iv it y.A d iffe re nt p romern c an o cc ur whe n AN- FO o r s lu rry b la stin g

agents are used at close spacings in soft ground. The shocfrom an adjacent charge m ay dead press a blasting agen

co lu mn a nd ca us e it to m is fire .

STORAGE

CONSIDERA"nONS

F ed era l re qu ire me nts fo r m ag azin e c on struc tio n a re lesstringent for blasting agents than for high explosives (13).

M agazines for the storage of high explosives m ust be w eve ntila te d a nd m us t b e re sis tan t to b ulle ts , fire, w ea th er, a ntheft; w hereas a blasting agent rnaqazine need only be ther es is ta nt . A lt hough t his is n ot a n o ve rr id in g r ea son f or s ele ct in ga blasting agent rather than an explosive, it is an additionap oin t in fa vo r o f b la stin g a ge nts .

Som e activities such as pow erline installation and lighc on stru ctio n r eq uire th e p erio dic u se o f v ery small amo un ts oexplos ives. In th is type o f wo rk the operator can advan tageousl yu se two-c ompo ne nt e xp lo siv es . Two -c omp on en t e xp lo siv esa re sold a s separat e in gr ed ie nts , n eit he r o f wh ic h is e xp lo siv eThe tw o com ponents are m ixed at the jobsite as needed, anth e m ix tu re is co ns id ere d a h ig h e xp lo siv e. P erso ns w ho m itwo-component explosives are often required to havemanufac tu re r' s li cense .

Federal regulations do not require ingredients of twoc omp on en t e xp lo siv es to b e s to re d in ma ga zin es n or is th er eminimum d is tance requ iremen t for sepa ra tion o tthe ing red ien tsfrom each other or from explosive products. Even thougthere is no Federal regulati~ n requiring m agazine storagetw o-com ponent explosives should be protected from thefTwo- component e xp lo siv es s to re d under t he ju ris dic tio n o f t hU .S . F ore st S erv ic e m ust be sto re d in m ag az ine s.

T he u se o f tw o-c om po ne nt e xp lo sive s e lim in ate s th e n eefo r fre qu en t tr ip s to a ma ga zin e. Howev er, w he n la rg e amou nto f e xp lo siv es a re u sed, t he h ig he r c os t a nd t he t ime -c on sum ingpro ce ss o f ex plo siv e m ixin g b eg in to o utw eig h th e sa vin gstraveltime.

SENSITIVITY

CONSIDERATIONS

Sen sitiv ity c on sid era tio ns a dd re ss q ue stio ns o f th e s afe tand the dependab il it y o f an expl os ive . Mo re sens it ive expl os ivesuch a s d ynam it es a re somewha t mo re vuln er ab le t o a cc id en tain itia tio n b y imp ac t o r s pa rk th an b la stin g a ge nts . S lu rrie s a nn itr os ta rc h-b as ed e xp lo siv es a re g en era lly le ss s en sitiv e tim pa ct th an n itro gly ce rin -b as ed d yn am ites . H ow eve r, m or

s en sit iv e e xp lo siv es , a ll c ondit io ns bein g equal, a re le ss lik elt o m is fir e in t he b la st ho le . F or in st an ce , u pon a cc id en ta l impacfro m a d rill b it, a b la stin g a ge nt is le ss lik ely to d eto na te th and yn am ite . T his do es n ot m ea n th at th e b la stin g a ge nt w ill ndetonate when acc identa ll y impacted. Converse ly , under adversesituations such as charge separation in the blasthole, versm all c ha rg e d ia me te rs, o r lo w temp eratu re s, d ynamite s a rle ss lik ely t o m is fir e t han b la st in g agent s. T h is tr adeo ff must bco ns id ere d p rim arily w he n se le ctin g an e xp lo siv e fo r sm ald iame te r work . O th er s ele ctio n c rite ria u su ally d ic ta te th e u so f b la stin g a ge nts w he n the b la sth ole d ia me te r is la rg e.

I t ca n be con clu ded f rom 1981 exp los ive consumpt ion f igures(12) a nd fie ld o bs erv atio ns th at mo st o f th e d yn am ite s till u sein this country is used in construction, sm all quarries, an



20

underground mines, where many operators consider a more

sensitive explosive beneficial in their small-diameter blasting.

When safely handled and properly loaded, dynamites, dry

blasting agents, and slurries all have a place in small-diameter

blasting.

EXPLOSIVE ATMOSPHERES

Blasting in a gass~. tatmosphere can be catastrophic if the

atmosphere is ignited by the flame from the explosive. All

underground coal mines are classified as gassy; some metal-

nonmetal mines may contain methane or other explosive gases;

and many construct ion projects encounter methane. Where

gassy conditions are suspected, MSHA or OSHA should be

consulted for guidance.

Permissible explosives (14) offer protection against gas

explosions. Most permissible explosives are relatively weak

explosives, and will not do an adequate job in most rock,

although some relatively powerful permissible gelatins,

emulsions, and slurries are available.

All underground coal mines are classified as gassy by MSHA,

and permissible explosives are the only type ofaxpiosives that

can be used in these mines without a variance from MSHA.Salt, l imestone, uranium, potash, copper, trona, and oil shale

mines may contain methane or other explosive gases andmay be classified gassy on an individual basis by MSHA. In

these gassy metal-nonmetal mines, MSHA may permit the

use of nonpermissible products such as AN-Fa, detonating

cord, and certain other high explosives and blast ing agents.

These mines are required to operate under modified permissible

rules developed by MSHA on a mine-by-mine basis.

REFERENCES

1. Cook, M. A. Explosives-A Survey of Technical Advances. Ind.

and Eng. Chem., v. 60, No.7, July 1968, pp. 44-55.

2. Damon, G. H., C. M. Mason, N. E. Hanna, and D. R. Forshey.Safety Recommendations for Ammonium Nitrate-Based Blasting Agents.

BuMines IC 8746,1977,31 pp.

3. Dannenberg, J. Blasthole Dewatering Cuts Costs. Rock Products,

v. 76, No. 12, December 1973, pp. 66-68.

4. Dick, R. A. Factors in Selecting and Applying Commercial

Explosives and Blast ing Agents. BuMines IC 8405, 1968, 30 pp.

5. . The Impact of Blasting Agents and Slurries on

Explosives Technology. BuMines ~C8560, 1972, 44 pp.

6. Drury, F., and D. G. Westmaas. Considerations Affecting the

Selection and Use of Modern Chemical Explosives. Proc. 4th Cont.on

Explosives and Blasting Technique, New Orleans, LA, Feb. 1-3, 1978.

Society of Explosives Engineers, Montvi lle, OH, pp. 128-153.

7. E. I. du Pont de Nemours & Co., Inc. (Wilmington, DE). Blaster's

Handbook. 16th ed., 1978, 494 pp.

8. Johansson, C. H., and U. Langefors. Methods of Physical

Character ization of Explosives. Proc. 36th Internat. Congo of Ind.

Chem., Brussels, v. 3, 1966, p. 610.; available for consultation at

Bureau of Mines Twin Cit ies Research Center, Minneapolis, MN.

9. Monsanto Co. (St. Louis, MO). Monsanto Blasting ProductsAN-FO Manual. Its Explosive Properties and Field Performance

Oharacterlstics. September 1972, 37 pp.

1O . ~orter, D. D. Use of Fragmentation To Evaluate Explosives for

Blasting. Min. Congo J. , v. 50, No.1, January 1974, pp. 41-43.

11. Robinson, R. V. Water Gel Explosives-Three Generations.

Canadian Min. and Met. Bull., v. 62, No. 692, December 1969, pp.

1317-1325.

12. U.S. Bureau of Mines. Apparent Consumption of Industrial

Explosives and Blasting Agents in the United States, 1981. Mineral

Industry Survey, June 23, 1982, 12 pp.

13. U.S. Department of the Treasury; Bureau of Alcohol, Tobacco,

and Firearms. Explosive Materia ls Regulations. Federal Register, v.

42, Nov. 149, Aug. S,1977, pp. 39316-39327; Federal Register, v. 45,

No. 224,Nov. 18, 1980,pp. 76191-76209.

14. U.S. Mine Enforcement and Safety Administ ration. Active List

of Permissible Explosives and Blasting Devices Approved Before

Dec. 31, 1975. MESA Inf. Rep. 1046, 1976, 10 pp.



Chapter 2.-INITIATION AND PRIMING

INITIATION SYSTEMS

A considerable amount of energy is required to initiate a

high explosive such as a dynamite or cap-sensit ive slurry. In

blasting, high explosives are initiated by a detonator, which is

a capsule containing a series of relatively sensitive explosives

that can be readily initiated by an outside energy source.

Blasting agents, which are the most common products used

as the main column charge in the blasthole, are even less

sensitive to initiation than high explosives. To assure dependable

initiation of these products, the initiator is usually placed into a

container of high explosives, which in turn is placed into the

column of blasting agent.

An initiat ion system consists of three basic parts.

1. An init ial energy source.2. An energy distribut ion network that conveys energy into

the individual blast holes. .3. An in-the-hole component that uses energy from the

distribution network to initiate a cap-sensitive explosive.

The initial energy source may be electrical, such as a generator

or condenser-discharge blasting machine or a powerline used

to energize an electric blast ing cap, or a heat source such as a

spark generator or a match. The energy conveyed to and into

the individual blastholes may be electricity, a burning fuse, a

high-energy explosive detonation, or a low-energy dust or gas

detonation. Figure 17 shows a typical detonator or "business

end" of the initiation system. This detonator, when inserted

into a cap-sensitive explosive and activated, will initiate the

detonation of the explosive column. Commercial detonatorsvary in strength from No.6 to No. 12. Although No.6 and NO.8

detonators are the most common, there is a trend toward

higher strength detonators, part icularly when blasting with

cap-sensitive products which are less sensitive than dynamites.

The primer is the unit of cap-sensitive explosive containing

the detonator. Where the main blasthole charge is high explosive,

the detonator may be inserted into the column at any point.

However, most of the products used for blasting today (blasting

agents) are insensitive to a NO.8 detonator. To detonate these

products, the detonator must be inserted into a unit of cap-

sensitive explosive, which in turn is inserted into the blast ing

agent column at the desired point of initiat ion.The discussions of the various initiation and priming systems

will concentrate primarily on common practice. With each

system there are optional techniques and "tricks of the trade"

that increase system versatil ity. It is a good idea to confer withthe manufacturer before finalizing your initiation and priming

program, so you fully understand how to best use a specific

system.

Energy.....--_input

21

Crimp

Ignitioncompound

Priming

charge

Basecharge

Figure 17.-lnstantaneous detonator.

DELAY SERIES

Figure 17 shows an instantaneous detonator. Inthis type of

detonator, the base charge detonates within a millisecond or

two after the external energy enters the detonator. However,

in most types of blasting, time intervals are required between

the detonation of various blastholes or even between decks

within a blasthole. To accomplish this, a delay element containing



22

,...-__ Energy

input

Figure 18.-Delay detonator.

Crimp

Delay

powder

Priming

charge

Base

charge

a burning powder is placed immediately before the priming

charge in the detonator. Figure 18 shows a delay detonator.

There are three basic delay senes: slow or tunnel delays,

fast or millisecond delays, and coal mine delays for use in

underground coal mines. For all commercial delay detonators,

the delay time is determined by the length and burning rate of

the delay powder column. As a result, slow delay caps may be

quite long in dimension whereas lower period millisecond

delays are shorter. Although the timing of delay detonators is

sufficiently accurate for most blasting needs, these delays are

not precise, as indicated by recent research. Recently, however,

manufacturers' tolerances for some delay caps have been

tightened. Itis important to use the manufacturer's recommended

current level to initiate electric blasting caps. Current levels

above or below the recommended firing level can further

increase the scatter in delay cap firing times. Extremely high

currents can speed up delay firing times. Near the minimum

firing current, delays can become extremely erratic.

Slow delays are useful underground under tight shooting

conditions where it is essential that the burden on one hole

moves before a subsequent hole fires. This situation may

occur in tunnels, shafts, underground metal-nonmetal mines,

and in trenching. Slow delays are available with all initiationsystems except surface detonating cord and delay cast primers.

Delay intervals are typically 0.5 to 1 sec.

Mil lisecond delays are the most commonly used delays and

are useful wherever the tight conditions previously mentioned

are not present. Millisecond delays provide improved

fragmentation, controlled throw, and reduced ground vibration

and airblast, as compared with simultaneous firing. They are

available with all initiation systems. In millisecond detonators,

delay intervals are 25 to 50 ms in the lower periods and are

longer in the higher periods. In detonating cord delay connec-

tors, the delay may be as short as 5 ms.

Coal mine delays are a special series of mil lisecond delays.

Since only electric initiation systems are permissible in

underground coal mines, coal mine delays are available only

with electric initiators. Delay intervals are from 50 to 100 ms,with instantaneous caps being prohibited. Coal mine delay

caps always utilize copper alloy shells and iron leg wires. Iron

leg wires are also available optionally with ordinary electric

detonators and are used primarily to facilitate magnetic removal

of the wires from the muck pile, such as in trona and saltmines.

ELECTRIC INITIATION

Electric initiation has been used for many years in both

surface and underground blasting. An electric blasting cap

(fig. 19) consists of two insulated leg wires that pass through a

waterproof seal and into a metal capsule containing a series of

explosive powders (fig. 20). Leg wires of various lengths are

available to accommodate various borehole depths. Inside the



23

Figure 19.-Electric blasting caps. (Courtesy Du Pont Co.)

Leg wires---..- .....

Rubber plug

wire

Crimps

Ignition charge

Delay element

Primer charge

Base charge

Figure 20.-Delay electric blasting cap.

capsule the two leg wires are connected by a fine filament

bridge wire embedded in a highly heat-sensit ive explosive.

Upon application of electric current the bridge wire heats

sufficiently to initiate the ignition mixture, which in turn initiates

a series of less sensitive, more powerful explosives. Detonators

are available in strengths ranging from about No.6 to No. 12,

with NO.6 and No.8 being most common. Trends recently are

toward higher strength detonators.

Most electric blasting caps have copper leg wires. Iron leg

wires are available for use where magnetic separation is used

to remove the leg wires atthe preparation plant. Atlas Powder 1Co. has prepared an excellent handbook that describes electricblasting procedures in detail(2).2

The Saf-T-Det and Magnadet electric blast ing caps are tworecent developments. The Saf-T-Det resembles a standard

electric blasting cap but has no base charge. A length of

1OO-gror less detonating cord is inserted into a well to act as a

base charge just before the primer is made up. The device is

similar to an electric blasting cap in regard to required firing

currents and extraneous electricity hazards. The Saf-T-Det is

manufactured in India and isnot available inthe United States

at this time.The Magnadet is also similar to a standard electric blast ing

cap, except that the end of each cap lead contains a plastic-

covered ferrite toroidal ring. The system is hooked up by

passing a single wire through each ring. A special blasting

machine is used to f ire these detonators. The manufacturer,

ICI of Scotland, claims ease of hookup and protection against

extraneous electricity as advantages of this system.

TYPES OF CIRCUITS

In order to fire electric blasting caps, the caps must be

connected into circuits and energized by a power source.

There are three types of electric blasting circuits (fig. 21). In

order of preference they are series, parallel series, and parallel.

, Re f er en ce t o sp e c if ic t ra d e n ames o r manuf ac tu r er s d o es n o t imp ly e n do rsement

b y the B ure au of M in es .

'Ita lic iz ed n um b ers in p ar en th es es re fe r to ite ms in th e lis t o f re fe re nc es a t t he

e nd o f th is c ha pte r.



24

SERIES

Connecting

wire

Leg wires

Electric blasting

cops

Powersource

P AR AL LE L S ER IES

Bus wi re

Electric blasting

cops

Powersource

Connectingwire

L eg wires

Bus wire

PARALLEL Bus wires

Electric blasting

cops

~::1--Leg wires

Connecting

wire

Figure 21.- Types of electric blas,lng circuits.

In series circuits all the caps are connected consecutively so

that the current from the power source has only one path to

follow. The series circuit is recommended because of its

simplicity. Also, all the caps receive the same amount ofcurrent.

Figure 22 shows recommended wire splices for blasting

circuits. To splice two small wires, the wires are looped and

twisted together. To connect a small wire to a large wire, the

small wire is wrapped around the large wire.

The electrical resistance of a series of caps is equal to the

sum of the resistances of the individual caps. For most blasting

machines, it is recommended that the number of caps in a

single series be limited to 40 to 50, depending on the leg wire

LIGHT GAGE TO UGHf GAGE

(TWISTED LOOP)

LIGHT GAGE TO HEAVY GAGE

Figure 22.-Recommended wire splices.

length. Longer leg wires require smaller series. The limit for

most small twist-type blasting machines is 10 caps with 30-ft

leg wires.

Many blasters minimize excess wire between holes to keep

the blast site from being cluttered. The ends of the cap series

are extended to a point of satety by connecting wire, which is

usually 20 gage, but should be heavier where circuit resistanceis a problem or when using parallel circuits. This connecting

wire is considered expendable and should be used only once.

The connecting wire is in turn connected to the firing line,

which in turn is connected to the power source.

The firing line contains two single conducting wires of 12

gage or heavier, and is reused from shot to shot. It may be on a

reel mechanism for portability, or may be installed along the

wall of a tunnel in an underground operation. Installed firing

lines should not be grounded, should be made of copper

rather than aluminum, and should have a 150ft lightning gap

near the power source to guard against premature blasts. The

firing line should be inspected frequently and replaced when

necessary.

When the number of caps in a round exceeds 40 to 50, the

parallel series circuit is recommended. In a parallel seriescircuit, the caps are divided into a number of individual series.

Each series should contain the same number of caps or the

same resistance to assure even current distribut ion. The leg

wires of the caps in each series are connected consecutively.

Next, two bus wires, as shown in figure 21, are placed in such

a position that each end of each series can be connected as

shown in the figure. The bus wire is usually about 14 gage or

heavier and may be either bare or insulated. Where bare wires

are used, care must be exercised to prevent excessive current

leakage to the ground. It is recommended that insulated bus

wires be used and that the insulation be cut away at point of

connection with the blasting cap series. To assure equal current

distribution to each series, one bus wire should be reversed as

shown in figure 21. With parallel series circuits, 14 gage or

heavier gage connecting wire is used to reduce the total circuit

resistance.

The third type of blasting circuit isthe straight parallel circuit.

The straight parallel circuit is less desirable to use than the

series or series parallel circuits for two reasons. First, its

nature is such that it cannot be checked. Broken leg wires or

faulty connections cannot be detected once the circuit has

been hooked up. Second, because the available current is

divided by the number of caps in the circuit, powerline firing

must often be used to provide adequate current for large

parallel circuits. The problems associated with powerline firing

wil l be discussed later.

Parallel circuits are not appropriate for surface blasting but

they are used to some extent for tunnel blasting. Parallel

circuits are similar to parallel series except that instead of each

end of a series circuit being connected to alternate bus wires,

each leg wire of each cap is connected directly to the busWires, as shown in figure 21. In underground blasts using

parallel circuits, bare bus wire is usually strung on wooden

pegs driven into the face to avoid grounding. As with parallel

series circuits, the bus wires are reversed as shown in figure

21.

In a parallel ci rcui t the lead wire (f iring l ine) represents the

largest resistance inthe circuit. Keeping the lead wire as short

as possible, consistent with safety, is the key to firing large

numbers of caps with paraliel circuits. Doubl ing the length of

the lead wire reduces the number of caps that can be fired by

almost half. Heavy (12 to 14 gage) bus wires are used to

reduce the resistance. A 14-gage connecting wire, rather than

a lighter gage, is recommended to reduce the circuit resistance.



CIRCUITCALCULATIONS

O n ly th e v ery b as ic s o f c irc uit c alc ula tio ns a re c ov er ed h er e.For m ore detail on circuit calculations or other of the m anyintricacies of electrical blasting the reader should refer to ad et aile d e le ct ric b la stin g h an db oo k s uc h a s r ef er en ce 2 . F ig ur e2 3 s ho w s t he r es is ta nc e c alc ula tio ns f or c ap c ir cu it s f or s er ie s,p ar alle l s er ie s, a nd s tr aig ht p ar alle l c ir cu it s.

T he r es is ta nc e o f a s erie s c irc uit is th e e as ie st to c alc ula te .F irst, the resistance of a single cap, as specified by them an ufa ctu re r, is m u ltip lie d b y th e n um be r o f c ap s to d ete rm in eth e re sis ta nc e o f th e c ap c irc uit. T o th is is a dd ed th e re sis ta nc eof the connecting w ire and that of the firing line to determ ineth e r es is ta nc e o f th e to ta l c ir cu it. S in ce th e fir in g lin e c on ta in stw o w ires, there w ill be 2 ft of w ire for every foot of firing line.W h ere b us w ir e is u se d (p ara lle l o r p ara lle l s er ie s c irc uits ) th ere sis ta nce o f o ne -h alf o f th e le ng th o fth e b us w ire is a dd ed tofin d th e to ta l c irc uit re sis ta nc e. W h en firin g fro m a p ow erlin e,the voltage of the line divided by the resistance of the circuitw ill g ive the current flow . In a single series circuit, a ll of th isc urre nt flo ws th ro ug h e ach ca p. T he m in im um re co mm en ded

firing current per cap is 1.5 am p de or 2.0 am p ac. T he currento utp ut o f c on de ns er (c ap ac ito r) d is ch ar ge b la stin g m a ch in esm ay vary w ith the circuit resistance, but not linearly.M a nu fa ct ur er 's s pe cif ic at io ns m u st b e c on su lte d t o d et er m in eth e a m pe ra ge o f a s pe cific m a ch in e a cr os s a g iv en re sis ta nc e.F or a g en er ato r b la stin g m ac hin e, th e m an ufa ctu re r ra te s th em achine in term s of the num ber of caps it can fire.

SIMPLE SERIES

RC

RC RT= NRc

RC

PARALLEL SERIES

RC Rc Rc_1- =_I_+_I_+_1_ +____RT NIRc NzRc N3RC

Rc Rc Rc If N1=Nz=N3.

N1

Rc Rc Rc then RT=Rc NS'

PARALLEL

RT = ! ! £ . .N

KEY

RT Total resistance

RC Resistance of I ca p

N Number of capsNs Number of series

N'.Z,3 Number of caps in a series

Figure23.-ealculatlon of cap circuit resistance.

25

T he re sista nce c alc ula tio n fo r a p ara lle l s erie s circ uit is asfo llo ws . F irs t th e re sis ta nc e o f e ac h c ap s erie s is c alc ula te d a spreviously described. R em em ber, in a good paralle l seriescircuit the resistance of each series should be equal. Theresistance of a single series is then divided by the num ber ofseries to find the resistance of the cap circuit. To this areadded the resistance of half the length of bus w ire used, theresistance of the connecting w ire, and the resistance of thef ir in g lin e, t o o bt ain t he t ot al c ir cu it r es is ta nc e. T h e lo ca tio ns o fthe bus w ire, connecting w ire, and firing line are shown infig ur e 2 1. T he c urre nt flo w is d ete rm in ed e ith er b y d iv id in g th epow erline voltage by the circuit resistance or in the case of acondense r d ischa rge mach ine , by check ing the manu fac tu re r 'sspecifications. T he current flow is divided by the num ber ofse rie s to d ete rm in e th e cu rre nt flo w th ro ug h ea ch s erie s.

F or s tr aig ht p ar alle l c ir cu it S, th e r es is ta nc e o f t he c ap c ir cu itis e qu al to th e re sis ta nc e o f a s in gle c ap d iv id ed b y t h e n um b erof caps. As can readily be seen, this is usually a very sm allvalue. F or 20 short leg w ire caps, the resistance is less than0 .1 o hm . T he r es is ta nc e o f th e c on ne ctin g w ir e, th e fir in g lin e,a nd o ne -h alf th e b us w ire a re a dd ed to fin d th e to ta l r es is ta nc e.The current flow is determ ined in the sam e m anner as w ith

s er ie s a nd p ara lle l s erie s c irc uits . T he c urre nt flo w is d iv id edby the num ber of caps to determ ine the current flow throughe ac h c ap .

POWER SOURCES

E lec tr ic b las ting c ir cu it s can be energi zed by gene ra to r -t ypeb la st in g m a ch in es , c on de ns er -d is ch ar ge b la st in g m a ch in es ,a nd p ow erlin es. S to ra ge a nd d ry ce ll b atte rie s a re d efin ite lyno t recommended for b las ti ng because they canno t be dependedo n for a co ns is te nt o utp ut.

G en erato r b la stin g m ac hin es m ay b e o f th e ra ck -b ar (p us hd ow n) o r th e k ey -tw is t ty pe . T he c ap ac ity o f ra ck -b ar m a ch in esranges from 30 to 50 caps in a single series, w hile key-tw ist

m a ch in es w ill n orm a lly in itia te 1 0 o r 2 0 c ap s in a s in gle s erie s.T he a ctu al c urre nt p ut o ut b y th es e m ach in es d ep en ds o n thecondition of the m achine and the effort exerted by the shot-fir er. W h en u sin g a r ac k-b ar m ac hin e, th e te rm in als s ho uld b eon the opposite side of the m achine from the operator. B othth e r ac k- ba r a nd t wis t m a ch in es s ho uld b e o pe ra te d v ig or ou slyto the end of the stroke because the current flow s only at thee nd o f t he s tr ok e. B ec au se t he c on dit io n o f a g en er at or b la st in gm a ch in e d et er io ra te s w it h t im e , it is im p or ta nt t ha t t he m a ch in ebe pe ri od ica lly checked with a rheostat designed for tha t pu rpose .T he d ire ctio ns fo r te stin g w ith a rh eo sta t a re co nta ine d o n th er he os ta t c as e o r o n th e r he os ta t its elf. A lth ou gh th e g en era to rmachi ne has been a dependab le b las ti ng too l, i ts li m ited capac it yand variable output have caused it to be replaced, for m osta pp lic at io ns , b y t he c on de ns er ( ca pa cit or ) d is ch ar ge m a ch in e.

A s th e n am e im plie s, th e c ap ac ito r d is ch ar ge (C D ) m a ch in e( fig .24 ) emp loys d ry ce ll ba tter ies to charge a se ri es o f capac itors.T he e ne rg y s to re d in th e ca pa cito r is th en d is ch arg ed in to th eblasting circuit. C D m achines are available in a variety ofd es ig ns a nd c ap ac itie s, w ith s om e c ap ab le o f firin g o ve r 1 ,0 00c ap s in a p ara lle l s er ie s c ir cu it.

All C D m achines operate in basically the sam e m anner.O ne b utto n o r sw itch is a ctiva te d to ch arg e th e c ap acitors a nda second .button or sw itch is activated to fire the blast. Anin dic at or lig ht o r d ia l in dic at es w h en t he c ap ac it or is c ha rg ed t oit s r at ed c ap ac ity . I de ally , t he o ve ra ll c on dit io n o f a C D b la st in gm ach in e s ho uld b e ch ec ke d w ith a n o sc illo sco pe . H ow eve r,t he c ur re nt o ut pu t c an b e c he ck ed b y u sin g a s pe cia lly d es ig ne dsetup com bining a rheostat and a resistor (2) or by using a



26

Figure 24.-capacitor discharge blasting machine. (Courtesy Du Pont Co.)



27

capacitor discharge checking machine (7). The powder supplier

should be consulted as to the availability of machines for

checking capacitor discharge machines.A sequential blasting machine (fig. 25) is a unit containing

10 capacitor discharge machines that will fire up to 10 separate

circuits with a preselected time interval between the individual

circuits. When used in conjunction with millisecond delay electric

blasting caps, the sequential machine provides a very large

number of separate delay intervals (3). This can be useful in

improving fragmentation and in controlling ground vibrations

and airblast. Because blast pattern design and hookup can be

quite complex, the sequential blasting machine should be

Figure 25.-Sequentlal blasting machine.



28

used only by w ell-tra ined persons or under the guidance of aconsultant or a pow der com pany representative. A poorlyp lanned sequent ia l t iming pat te rn wi ll resul t i n poor f ragmentat ionand excessi ve overbreak , f ly rock, g round v ib ra ti ons , and no ise .

T he t hir d a lt er na tiv e f or e ne rg iz in g e le ct ric b la st in g c ir cu it sis th e p owerlin e. P ower lin e b la stin g is o fte n d on e w ith p ara lle l

circ uits w he re th e ca pa city o f a va ila ble b la stin g m ac hin es isinadequate. W hen firing off a pow erline, the line should bededicated to blasting alone, should contain at least a 15-ftlig htn in g g ap , a nd s ho uld b e v is ua lly c he ck ed fo r d ama ge a ndfo r res ista nce o n a re gu la r b as is . P ow erlin e sh oo tin g s ho uldnot be done unless precautions are taken to prevent arcing.A rcin g ca n re su lt in e rra tic tim in g, a h an gfire , o r a m isfire .

A rc in g in a c ap re su lts fr om e xc es siv e h ea t b uild up , whic h iscaused by too m uch current applied for too long a period oftim e. A current of 10 am p or m ore continuously applied for ase con d o r m ore ca n ca us e a rcin g. T o g ua rd ag ain st a rcin g th eb la ste r may e ith er u se a b la stin g switc h in c on ju nc tio n w ith th ep ow erlin e o r a dd a N o.1 p erio d m illis eco nd d ela y c ap , p la ce din a quarter stick of explosive, to the circuit and tape theexplosive to one of the connecting w ires leading to the cap

circuit. A n even better solution, if possible, is to use a high-output capacitor discharge m achine to fire the shot, using aparalle l s er ie s c ir cu it if n eces sa ry .

CIRCUIT TESTING

It is im p orta nt to c he ck th e re sis ta nc e o f th e b la stin g c irc uitto m ake sure that there are no broken w ires or short c ircuitsand that the resistance of the circuit is com patib le w ith thec ap acity o f th e p ow er so urce . T here a re tw o ty pes o f b la stin gc ;: ir cu ites te rs ; a b las ting ga lvanome te r (actua ll y an ohmmete r)s how n in fig ure 2 6 a nd a b la stin g m ultim ete r, s ho wn in fig ure2 7. T he b la stin g g alv an omete r is u se d o nly to c he ck th e c ir cu itresistance, w hereas a blasting m ultim eter can be used to

c hec k re sis ta nc e, ac a nd d e vo lta ge , s tra y cu rre nts, a nd cu r-ren t l eakage (2). Only a me te r s pe cific ally d es ig ne d fo r b la st-ing should be used to check blasting circuits. The output ofs uch m ete rs is lim ite d to 0 .0 5 amp , w hic h w ill n ot d eto nate a nelectric blasting cap, by the use of a silver chloride batteryand/or i nternal cu rrent -lim it ing c ir cu it ry .

O th er e qu ip me nt su ch a s a "th row -a wa y" go-no go dev ic efo r te stin g c irc uits a nd a c on tin uo us g ro un d c urre nt mo nito r isa va ila ble . T he e xp lo siv e supplie r s hould be con su lt ed t o det er -m in e wha t s pe cific e le ctric al b la stin g a cc es so ry e qu ipme nt isavailable and w hat equipm ent is needed for a given job ..

It is generally recommended that each com ponent of thecircu it b e ch eck ed a s h oo ku p p ro gre ss es. A fte r e ach c om po -nent is tested, it should be shunted. Each cap should bec he ck ed a fte r th e h ole h as b ee n lo ad ed a nd b efo re s temmin g.In th is w ay , a n ew p rim er ca n b e in se rte d if a b ro ke n le g w ire isdetected. A total deflection of the circuit tester needle (noresistance) indicates a short circuit. Zero deflection of theneedle (infin ite resistance) indicates a broken w ire. E itherco nd itio n w ill pre ve nt a b la stin g ca p, a nd p oss ib ly the w ho lec ir cu it , f rom f ir ing .

B efo re te stin g th e b la stin g c irc uit, its r es is ta nc e s ho uld b ec alc ula te d. A fte r th e ca ps h ave b ee n c on ne cte d in to a c ircu itth e res ista nce o f th e circ uit is c he ck ed a nd comp are d w ith th ecalculated value. A zero deflection at this tim e indicates ab ro ke n w ire o r a m iss ed co nn ectio n a nd a n e xce ssive d efle c-tio n in dic ate s a sh ort circ uit b etw ee n tw o w ire s.

A ft er t he c ir cu it r es is ta nce has been che cked and compared ,the connecting w ire is then added and the circuit is checkeda ga in . If a p ara lle l se rie s circ uit is u se d, th e ch an ge in re sis-

tance should be checked as each series is added to the busw ire. In a straight paralle l c ircuit, a break in the bus w ire cansom etim es be detected. H ow ever, a broken or a shorted capw ire c an no t b e d ete cte d in a s tra ig ht p ar alle l c irc uit b ec au se itw ill n ot a ff ec t t he r es is ta nce s ig nif ic an tly .

A fin al ch eck o f th e circ uit is m ad e a t th e s ho ttlre r's lo ca tio n

a fte r th e firin g lin e h as b ee n c on ne cte d. If a p ro blem is fo un d ina comp le te d c ircu it, th e circu it s ho uld b e b ro ke n u p in to s ep a-rate parts and checked to isolate the problem . The firing lineshould be checked for a break or a short after each blast, or atthe end of each shift, as a m inim um .

To check for a break in the firing line, the tw o w ires at oneend of the line are shunted and the other end is checked w ith ab la stin g me te r. A la rg e d efle ctio n in dic ate s th at th e firin g lin e isn ot b ro ke n; a z ero d efle ctio n in dic ate s a b ro ke n w ire . T o te stfor a short, the w ires at one end of the lead line are separateda nd th e o th er e nd is ch ec ke d w ith th e m ete r. A z ero d efle ctio ns ho uld re su lt. If th ere is a d efle ctio n, th e le ad lin e h as a s hortc ircu it. E mb ara ssin g, h az ard ou s, a nd c os tly m is fire s ca n b eavoided through proper use of the blasting galvanom eter orb las t ing mul timeter .

Ce rtai n cond it ions such as damaged i nsu la tion , damp g round ,a c on du ctive o re b od y, w ate r in a b ore ho le , b are w ire s to uc h-ing the ground, or bulk slurry in the borehole may causecurrent to leak from a charged circuit. A lthough this is not acom mon occurrence, you m ay want to check for it if you aree xp erie nc in g u ne xp la in ed m is fire s. T o p ro pe rly c he ck fo r c ur-re nt le ak ag e y ou s ho uld ch eck w ith a co ns ulta nt o r a n e le ctricb las ti ng handbook (2). Meas ur es fo r c omb atin g c urre nt le ak "age include using few er caps per circuit, using heavier gagelead lines and connecting w ires, keeping bare w ire connec-tio ns fr om to uc hin g th e g ro un d, o r u sin g a n on ele ctric in itia tio nsystem.

Figure 26.-Blastlng galvanometer. (Courte.y Du Pont CG.)



29

Figure 27.-Blasting multimeter. (Court.sy Du Pont Co.)



30

EXTRANEOUS ELECTRICITY

The principal hazard associated with electric blast ing sys-

tems is lightning. Extraneous electricity in the form of stray

currents, static electricity, and radiofrequency energy, and

from high-voltage powerlines can also be a hazard. Electric

blasting caps should not be used in the presence of stray

currents of 0.05 amp or more. Stray currents usually come

from heavy equipment or power systems in the area, and are

often carried by metal conductors or high-voltage powerlines.

Atlas (2) outlines techniques for checking for stray currents.

Instruments have recently been developed which continu-

ously monitor ground currents and sound an alarm when an

excess current is detected. The supplier should be consulted

as to the availabil ity of these units.

Static electricity may be generated by pneumatic loading,

particles carried by high winds, particularly in a dry atmosphere,

and by rubbing of a person's clothes. Most electric blasting

caps are static resistant. When pneumatically loading blasting

agents with pressure pots or venturi loaders, a semiconductive

loading hose must be used, a plastic borehole liner should not

be used, and the loading vessel should be grounded.Electrical storms are a hazard regardless of the type of

initiation system being used. Even underground mines are

susceptible to lightning hazards. Upon the approach of an

electrical storm, loading operations must cease and all person-

nel must retreat to a safe location. The powder manufacturer

should be consulted on the availabi lity of commercial storm

warning devices. Some operators use static on an AM radio as

a crude detector of approaching storms. Weather reports arealso helpful.

Broadcasting stations, mobile radio transmitters, and radar

installations present the hazard of radiofrequency energy. The

IME (11) has prepared charts giving transmission specifica-

tions and potentially hazardous distances.

High-voltage powerlines present the hazards of capacitive

and inductive coupling, stray current, and conduction of lightning.

Atlas (2) details precautions to be taken when blasting near

high-voltage powerlines. A specific hazard with powerlines is

the danger of throwing partof the blasting wire onto the powerline.

This shorts the powerline to the ground and has been responsi-

ble for several deaths. Care should be exercised in laying out

the circuit so that the wires cannot be thrown on a powerline.

Other alternatives are to weigh down the wires so they cannot

be thrown or attach a charge that cuts the blasting wire.

ADDITIONAL

CONSIDERATIONS

Electric blasting is a safe, dependable system when used

properly under the proper conditions. Advantages of the sys-

tem are its reasonably accurate delays, ease of circuit testing,

control of blast initiation time, and lack of airblast or disruptive

effect on the explosive charge. In addition to extraneous

electricity, one should guard against kinks in the cap leg wires,

which can cause broken wires, especially in deep holes. Differ-ent brands of caps may vary in electric propert ies, so only one

brand per blast should be used. It is recommended that the

blaster carry the key or handle to the power source on his or

her person so the shot cannot be inadvertently fired while he orshe is checking out the shot.

A device called an exploding bridge wire is available for use

where a single cap is used to init iate a nonelectric circuit. This

device has the safety advantages of a lack of primary explo-

sive in the cap and a high voltage required for firing. A special

firing box is required for the system. The high power required

and high cost of the exploding bridge wire device make it

unsuitable for use in rnultlcap circuits.

DETONATING CORD INITIATION

Detonating cord initiation has been used for many years as

an alternative to electric blasting where the operator prefers

not to have an electric initiator in the blasthole. Detonating

cord (fig. 28) consists of a core of high explosive, usually

PETN, contained in a waterproof plastic sheath enclosed in a

reinforcing covering of various combinations of textile, plastic,

and waterproofing. Detonating cord is available with PETN

core loadings ranging from 1 to 400 grift.All cords can be detonated with a blasting cap and have a

detonation velocity of approximately 21,000 fps. Detonating

cord is adaptable to most surface blast ing situat ions. When

used in a wet environment the ends of the cord should be

protected from water. PETN will slowly absorb water and as a

result will become insensitive to initiat ion by a blast ing cap.

Even when wet, however, detonating cord will propagate if

initiated on a dry end. Understanding the function of a detonat-

ing cord initiation system requires a knowledge of the products

available. The Ensign Bickford Co. has published a manual (8)

that describes detonating cord products in detail. Technical

data sheets are available from Austin Powder Co. and Apache

Powder Co.

DETONATING

CORD PRODUCTS

The most common strengths of detonating cord are from 25

to 60 grift. These strengths are used for trunklines, which

connect the individual blastholes into pattern, and fordownlines,

which transmit the energy from the trunkline to the primer

cartridge. The lower strength cords are cheaper, but somehave less tensile strength and may be somewhat less depend-

able under harsh field conditions. Some cast primers are not

dependably init iated by 25-gr cord or lighter cord. However,

under normal conditions, the lighter core loads offer economy

and their greater flexibility makes field procedures such as

primer preparation and knot tying easier.Detonating cord strengths of 100 to 200 grift are occasion-

ally used where continuous column initiation of a blasting

agent is desired. Cords with 200 to 400 grof PETN per foot are

occasionally used as a substitute for explosive cartridges in

very sensi tive or small, controlled blast ing jobs. Controlled

blast ing is described in the "Blast Design" chapter.



31

E X P L O S I V E S • D A N G E R O U S

. •C O R D U U D E T O H A H T F U S E

00 OOT C LASS C ""0, , " ' \ < : . < , ;

Figure 28.-Detonatlng cord. (Courtesy Austin Powder Co.)

De tona tin g cor d s tr engt hs lower t han 25 g rif t a re s ome timesu se d. F ifte en - to tw en ty -g ra in p ro du cts ma y b e u se d fo r sma ll-d iam ete r h ole s, fo r s eco nd ary b la stin g, a nd in th e N on el sy s-tem described later. A 7.5-gr cord is also used in the N onels ys tem . A 4 -g rlft p rod uc t is u se d as p art o f a n a ss em bly c alle da Prim aline Primadet. A Prim aline Primadet consists of alength of 4-gr cord crim ped to a standard instantaneous ord ela y b la stin g ca p. T he ca p is in se rte d in to th e p rim er a nd th e

4-gr cord serves as a downline. Various cord lengths area va ila ble to s uit sp ecific b ore ho le d ep th s. T h ese P rim ad etsa re p rim arily u se d in u nd erg ro un d m in es , su ch a s sa lt, w he reN onel tubes w ould be a product C ontam inant. D u Pont's newDeta lin e S y stem u tiliz es a 2 .4 -g r c or d.

M illis ec on d d ela y s ur fa ce c on ne cto rs a re u se d fo r d ela yin gdetonating cord blasts. T o place a delay betw een tw o holes,th e tru nk lin e b etw ee n th e h ole s is cu t a nd th e e nd s are jo in edwith a delay connector. O ne type of delay connector is ap la stic a ss emb ly c on ta in in g a d ela y e leme nt ( fig . 2 9). A t e ac hend of the element is an opening into which a loop of thes ev ere d tr un klin e c an b e in se rte d. A ta pe re d p in is u se d to lo ckth e tr un klin e c ord in to p la ce . A Non el d ela y c on ne cto r h as a ls obeen developed for detonating cord blasting (fig. 30). This

connector consists of tw o plastic blocks, each containing adelay initiator, connected by a short length of N onel tubing.E ac h e nd o f t he s ev ere d tru nk lin e is w ra pp ed a ro un d th e n otc hin o ne o f th e p la stic b lo cks . B oth typ es o f d ela y c on ne cto r a rebidirectional.

FIELD APPLICATION

A fter the prim er has been low ered to its proper location inth e b la sth ole , th e d eto na tin g c ord is cu t fro m th e s po ol. A b ou t2 o r 3 ft o f c o rd sh ou ld e xte nd fro m th e h ole to a llo w fo r c harg ese ttle me nt a nd ty in g in to th e tru nkline . W he n th e e ntire sh oth as b ee n lo ad ed an d s temmed , th e tru nklin e is la id ou t a lo ngthe path of des ired ini ti at ion progression . Trunk line- to - trunkl ineco nn ec tio ns are u sua lly m ad e w ith a sq ua re k no t. A tig ht kn ot,u su ally a c lo ve h itc h, a h alf h itc h, o r a d ou ble -w ra p h alf h itc h, isused to connect the dow nline to the trunkline (fig. 31). A nye xc es s c ord fr om th e d ownlin e s ho uld b e c ut o ff a nd d is po se d.If Prim adets or other in-hole delay assem blies are used, ap las ti c connector o ften se rves as the connect ion to the t runkl ine .T he cord lines should be slack, but not excessively so. If too



32

Figure 29.-elip-on surface detonating cord delay connector. (Courtesy Hercules Inc.)

Figure 30.-Nonelsurface detonating cord delay connector. (Courtesy Ensign Bickford Co.)



Dawnline 10Trunkhne cceeecncee

Holf hlfch Double-wrap halt hilch

= + =J r

I'''"''''~"Ii",

ShU cord downtinll

Holt hitch :?;:..e

~DO_""" 'Cord-to-cord connection

Square knot

~~

~"'"'"Downline

Figure 31.-Recommended knots for detonating cord.

much slack is present, the cord may cross itself and possibly

cause a cutoff (fig. 32). Also, if the lines are too tight and form

an acute angle; the downline may be cut off without detonating.

Downlines of detonating cord can adversely affect the col-

umn charge of explosive in the blasthole. With cap-sensitive

explosives, continuous, axial initiation wil l occur with any cord

containing 18 or more grains of PETN per foot of cord. Lower

strength cords may also cause axial initiation. Four-grain cord

wi ll not initiate most cap-sensit ive explosives. With blasting

agents, the effect of detonating cord is less predictable. The

blasting agent may be desensitized or it may be marginally

initiated. Hagan (10) has studied this problem. The effect

depends on the cord strength, blasting agent sensitivity, blasthole

diameter, and position of the cord within the blasthole. As a

general rule, 50-gr cords are compatible with blasthole diame-ters of 8 in or more. In charge diameters of 5 to 8 in, 25-gr or

SLACK LINE

Blasthale

Blasthole

Potentialcutoff

Knot

TIGHT LINE

Blasthole

Knot

Direction of propagation-

Figure 32.-Potential cutoffs from slack and tight del-onatlngcordllnes:

33

lighter down lines should be used. In diameters below 5 in

low-energy (4- to 10-gr) downlines or alternative, nondisrup-

tive initiation systems are recommended. The manufacturer

should be consulted for recommendations on the use of deto-

nating cord with various explosive products. A low-energy

initiation system called Detacord, developed by du Pont, isdescribed later in this chapter.

DELAY SYSTEMS

Surface delay connectors offer an unlimited number of delays

For instance, a row of 100 holes could be delayed individually

by placing a delay between each hole and initiating the row

from one end. Typical delay intervals for surface connectors

are 5, 9, 17, 25, 35, 45, and 65 ms. Since these connectors are

normally used for surface blasting, half-second delay periods

are not available.Cutoffs may be a problem with surface delay connectors.

When the powder column in one hole detonates, the connec

tions between holes to be fired later may be broken by crater

ing or other movement of the rock mass. This may causesubsequent hole to misfire. To correct this situation, MSHA

requires that the pattern of trunklines and delay connectors b

designed so that each blasthole can be reached by two path

from the point of init iation of the blast round. The patterns ca

become somewhat complex and should be laid out and care

fUl ly checked on paper before attempting to lay them out in th

f ield. Where possible the pattern should be designed so tha

the delay sequence in which the holes fire is the same n

matter which path istaken from the point of blast initiation. Th

"Blast Desigrl"chapter gives suggestions for selecting th

actual delay intervals between blastholes.

Figure 33 shows a typical blast laid out with delay connectors

Note that each hole can be reached by two paths from th

point of initiation. A time of 1 ms is required for 21 ft o

detonating cord to detonate. This time is not sufficient tsignificantly alter the delay interval between holes.

When detonating cord downlines are used, detonation o

the cord in the blasthole proceeds from the top down. Thi

presents two disadvantages. First, the detonation of the cor

may have an undesirable effect on the column charge as

proceeds downward and the stemming may be loosened

Second, if the hole is cut off by burden movement caused b

detonation of an earlier hole (fig. 34) the powder in the lowe

portion of the hole will not detonate. The use of a Primaline

9 6 7 9

X Delay connector

.6 Delay period of blostho

Figure 33.- Typical blast pattern with surface

delay connectors.



34

Explosivedetonates

Burdenmovement

~Explosivedoes notdetonate

Figure 34.-Mlsflre caused by cutoff from burdenmovement.

Primadet delay unit in the hole w ill correct both of theseproblems.

T he P rim aline Prim adet is a delay cap attached to a lengtho f 4 -g rlft d et onat in g cor d. I t i s a va ila ble in bot h m illis ec ond andlong delay periods. T he P rim aline P rim adet is connected tothe trunkline w ith a plastic connector or a double-w rap halfh itc h. If t he d ela y p atte rn o f t he b la st is su ch th at th e n um ber o fa va ila ble P rima de t d ela y p erio ds is a de qu ate , a n u nd ela ye dtru nklin e m ay b e u se d. T he d elay p erio d o f t he c ap w ou ld the nbe the delay period of the hole. As an exam ple, to attain thedela y pat te rn in f ig ur e 33, c ap d ela y p erio ds o ne th rou gh n in ewou ld b e p la ce d in th e a pp ro pria te h ole s a nd tru nk lin es wou ldcontain no delays. In this situation. the delay in every capw ou ld b e a ctu ate d b efo re th e firs t h ole d eto na te s. T his w ou ld

re du ce th e c ha nc e o f a c uto ff. T he 4 -g r P rim alin e P rim ad et iss teadi ly be ing rep laced by o the r none lec tr ic systems , desc ri bed

later in this chapter. . .A no th er a lte rn ativ e to o bta in th e d ela y p atte rn in fig ur e33,

and avoid the cutoff problem , would be to use the array ofsurface delays show n in the figure and an in-hole delay of anidentical period in each blasthole. For instance, if a 75-m sd elay is us ed in e ac h h ole , a nd th e tru nklin e d ela ys are e ac h 9rns, the delays in all of the holes except the tw o rear cornerh ole s w ill b e a ctu ate d b efo re th e firs t h ole in th e p atte rn fire s,thus alleviating the cutoff problem . M ore com plex patternsinvolving both surface and in-hole delays can be designedw he re d esira ble . A n a lte rna tive m eth od o f o bta in in g in -h oledelays w ith detonating cord is to use delay cast prim ers (fig.1 2). T he se a re c as t p rime rs w ith b un t- in n on ele ctric m illis ec -

o nd d ela ys . T he y ca n b e stru ng o n d eto na tin g co rd d ow n lin eso f 2 5 g r o r m ore a nd a re p artic ula rly u se fu l in o bta inin g m ulti-p le delayed deck charges w ith a single downline. It bearsr epea tin g t ha t d ela y pat te rn s in vo lV in g bot h sur fa ce and in -h oled ela ys c an b e somewh at comp le x a nd s ho uld b e ca re fu lly la id

out on paper before attem pting to install them in the fie ld.

GENERAL CONSIDERATIONS

Two o f th e p rima ry a dv an ta ge s o f d eto na tin g c ord in itia tio nsystem s are their ruggedness and their insensitiv ity. T heyfunction w ell under severe conditions such as in hard, abra-sive rock, in w et holes, and in deep, large-diam eter holes.T he y a re n ot s us ce ptib le to e le ctric al h az ar ds , a lth ou gh lig ht-ning is alw ays a haz~ rd w hile loading any blast. D etonatingc ord is q uite sa fe fro m a cc id en ta l in itia tio n u ntil th e in itia tin gcap or delay connectors are attached. Available delay sys-tems a re e xtremely fle xib le a nd re as on ab ly a cc ura te .

T here a re s eve ra l d isa dv an ta ge s {h at m ay b e sign ific an t in

ce rta in s itu atio ns . S ys te ms emp lo yin g o nly s urfa ce c on ne c-to rs fo r d ela ys p re se nt th e po te ntia l fo r c uto ffs. S urfa ce co n-nectors also present the hazard of accidental in itlatton byimpac t. De tonat ing co rd t runkl ines c rea te a cons ide rab le amounto f ir rit at in g, h ig h- fr equenc y a ir bla st ( no is e) . I n p opula te d a re asthe cord should be covered w ith 15 to 20 in of fine m aterial ora lte rn ative , n oise le ss sy ste ms sh ou ld b e u se d. D eto na tin gcord dow n lines present the problem of charge or stemmingd is ru ptio n. A s d is cu ss ed p re vio us ly , th is d ep en ds o n th e b or e-hole diam eter, the type of explosive, and core load of explo-sivlll iJ :lth e co rd . T he m ean s o f ch ec kin g th e s ys te m is visu alexamination.

V eh ic le s s ho uld n ev er p as s o ve r a lo ad ed ho le b ec au se th ed eto na tin g co rd lin es m ay b e d am ag ed , res ultin g in a m is fireo r prematu re ig nitio n. A p rema tu re ign itio n c ou ld re su lt fro md riV in g o ve r a s urfa ce d ela y c on ne cto r.

DETALINE SYSTEM

Du P on t's Deta lin e S ys tem is a re ce ntly d ev elo pe d in itia tio nsystem that is based on low -energy detonating cord. It func-t io ns s im ila rly to c on vent io na l d et onat in g cor d s ys tems excep tth at th e tru nk lin e is lo w in no ise , d ow nlin es w ill n ot dis ru pt th ecolum n of explosive, it w ill not in itiate blasthole products,excep t dynamites , and a ll connec tions a re made with connectors,rather than knots. The four com ponents of the system areDe ta lin e Co rd , De ta lin e S ta rt er s, De ta lin e MS Sur fa ce De la ys ,a nd D eta lin e MS In-H ole D ela ys .

T he D eta lin e C ord (D eta co rd ) is a 2 .4 -g r/ft de to na tin g c ordwho se a pp ea ra nc e is s im ila r to s ta nd ard d eto na tin g c ord . T he

cord is cut to lengths required for the blast pattern. This low -ene rg y cor d, wh ile low in nois e, h as suf fic ie nt e ne rg y t o d is in te -g ra te th e c or d u po n d eto na tio n, whic h is a dv an ta ge ou s whe recon tam inat io n o f t he b la st ed p ro du ct must b e a vo id ed . De ta co rdw ill n ot p ro pa ga te thro ug h a kn ot, w hic h is w hy co nn ecto rs a rere qu ire d. T o s plic e a lin e o r to ma ke a n on de la ye d c on ne ctio n,a D '3 ta lin e S ta rte r is re qu ir ed . T he b od y o f th e s ta rte r is s ha pe dml .ch li ke a c li p-on de tonat ing co rd mi lli second de lay connector ,except that the starter is shaped like an arrow to show thedirection of detonation. To m ake a splice, the starter is con-nected to the two ends of the Detacord using the attacheds aw to oth p in , ma kin g s ur e th at th e a rrow p oin ts in th e d ire ctio nof detonation. To m ake a connection, the donor trunkline ish oo ke d in to th e ta il o f th e s ta rte r a nd th e a cc ep to r tru nk lin e, o rd ow nlin e, is h oo ke d in to th e p oin te d e nd of th e co nn ecto r.



The Detaline System has provisions for both surface and

in-hole delays. The surface delays, which come in periods of

9,17,30,42,60, and 100 ms, are shaped like the starter but

are colored according to the delay. The surface delays are

also unidirectional, with the arrow showing the direction of

detonation. The surface delays can be hooked into a trunkline

in which case their function is similar to that of a standard

millisecond delay connector. They can also be used as starters,

connected between the trunkline and down line at the collar of

the blasthole. Inthis situation the delay affects only the downline,

and not the trunkline.

A Detaline MS In-Hole Delay resembles a standard blastTng

cap except for a special top closure for insertion ofthe Detacord.

Itfunctions similarly to a surface delay. Nineteen delay periods,

ranging from 25 to 1,000 ms, are available. The delay is

connected to the downline and is inserted into the primer.

Hookup of the Detaline System is similar to conventional

detonating cord except that connectors are used rather than

knots and right-angle connections are not necessary. When it

is time to hook up, the Detaline trunkline is reeled out over the

length of each row. Each downline is connected to the arrow

end of a starter or a surface delay. The tail of each starter or

surface delay is then connected into the trunkline. The open

sides of the pattern are then connected in a manner similar to

conventional detonating cord systems using Detacord and

appropriate starters and surface delays. It is essential that all

35

Detacord-to-Detacord connections be made with starters or

surface delays rather than knots.

The Detaline System bears many similarities to conven-

tional detonating cord systems. The system is checked out

visually before firing. Combining surface and in-hole delays

gives a pract ically unlimited number of delay combinations. I t

is convenient to build redundancy into the system. At firing

time, the end of the trunkline tail extending from the shot is

placed into the arrow end of a starter, and an electric or fuse

blasting cap is inserted into the tail end of the starter and

initiated.

The detonation energy of the 2.4-gr Detacord is adequate to

disintegrate the trunkl ine. However, the resulting trunkline

noise is quite low; typically about 13 dB lower than 25-gr

detonating cord in field trials. A downline of Detacord will

detonate most dynamites but will not detonate most water

gels. A major advantage of a Detacord downline is that it will

not disrupt a column of blast ing agent. Detacord can be used

as a total system or in conjunction with some standard detonat-

ing cord components. As with most newer systems, evolution-

ary changes may occur inthe coming years. Itis important that

the manufacturer be consulted for recommended procedures

for using Detacord. The manufacturer will also be able to

recommend which variation of the system best suits a particu-

lar field situation.

CAP-AND-FUSE INITIATION

Cap and fuse isthe oldest explosive initiation system; however,

its use has dwindled steadily. Its primary remaining use is in

small underground mines, although a few large mines sti ll use

it. Surface applicat ions are limited to secondary blasting and

the initiat ion of detonating cord rounds with a single cap.

COMPONENTS

The detonator used in a cap-and-fuse system is a small

capsule that is open at one end (fig. 35). The capsule contains

a base charge and a heat-sensitive primer charge of explosive.

The powder charge in the cap is ini tiated by a core of flamma-

ble powder in the safety fuse. Safety fuse has an appearance

somewhat similar to detonating cord except that the surface of

safety fuse is smoother and more waxy and the core load is

black. The core load of detonating cord is white.

To assemble a cap and fuse, the fuse iscarefully cut squarely

and inserted into the cap until it abuts against the explosive

charge in the cap. The fuse should never be twisted against

the explosive charge in the cap. The cap is then crimped nearthe open end with an approved hand or bench crimper. The

ShellRecommended

crimp location

Figure 35.-Blasting cap for use with safety fuse.

crimp should be no more than three-eiqhths of an inch from the

open end of the cap.

FIELD APPLICATIONS

Currently, all safety fuse burns at the nominal rate of 40

sec/ft . Both dampness and high altitude will cause the fuse to

burn more slowly. Fuse should be test burned periodically so

that the blaster can keep a record of its actual burning rate.

"Fast fuse" has been blamed for blasting accidents but the

fact is that this rarely if ever occurs. However, pressure on the

fuse may increase its burning rate.

One of the most important considerations in the use of

cap-and-fuse systems is the use of a positive, approved light-

ing mechanism. Matches, cigarette lighters, carbide lamps, or

other open flames are not approved for lighting fuse. MSHA

regulations specify hotwire lighters, lead spitters, and Ignitacord

as approved ignition systems. The safest, most controllable

lighting method is Ignitacord. In South Africa, where safety

fuse is most often sold as an assembly with an Ignitacordconnector attached, the safety record with cap and fuse is

much better than it is in the United States.

The Ignitacord connector f its over the end of the fuse and is

crimped in a manner similar to the cap. Figure 36 shows a

typical cap, fuse, and Ignitacord assembly. The cap is attached

to the fuse with a bench or hand crimper, and never with the

teeth or pliers. When crimping the cap, care should be taken

not to crimp the zone containing the powder. The Ignitacord

connector is crimped to the other end of the fuse with a hand

crimper. The Ignitacord is inserted into the notch near the end

of the connector and the notch is closed using the thumb.

To guard against water deterioration, it is a good idea to cut

off a short length of fuse immediately before making cap-and-



36

COMPONENTS

Safety fuse Ignitacord

~Ignitocord

Primer~charge

Basecharge

Burningpowder

ASSEMBLY

Powder- fuseinterface Fuse

caP--......c:::t:::::;t====~=======::::

Ignitocordconnector

Crimp

Figure 36.-cap, fuse, and Ignitacord assembly.

fu se as semb lie s. In d ecid in g th e le ng th o f fu se to c ut fo r e ac hp rime r, th e lig htin g p ro ce du re mu st b e c on sid ere d. Ig nita co rdis stro ng ly re commen de d b eca us e o f its sa fe ty re cord .

W hen Ignitacord is used, each fuse m ust have a burningtim e of at least 2 m in. To m ake sure of this tim e, the fuse m ustbe calibrated periodically by test burning. The Ignitacord isa tta ch ed to th e Ig nita co rd c on ne cto rs in th e d esire d o rd er o ffirin g. If a ll th e fu se s a re c ut a cc ura te ly to th e s am e le ng th , th ed es ir ed o rd er o f firin g w ill b e a ch ie ve d.

W ith Ignitacord, only one lighting is required before thes hotfire r re tu rn s to a s afe lo ca tio n. H otw ire lig hters a nd le ads pitte rs re qu ire th at e ac h fu se b e lit in div id ua lly . T he p rima ryh az ar d o f u sin g s afe ty fu se is th e te nd en cy o f b la ste rs to lin ge rtoo long at the face, m aking sure that all the fuses are lit. Tog ua rd a ga in st th is , MSHA r eg ula tio ns s pe cify m in imum burn -in g tim es fo r fu se s, d ep en din g o n h ow many fu se s o ne p ers onlig hts. K ee p in m in d th at tw o p ers on s a re re qu ire d to b e a t t hefa ce while lig htin g fu se r ou nd s.

If a p ers on lig hts o nly on e fu se , th e m in im um b urn in g tim e is

2 m in ; fo r 2 to 5 fuses the m inimum is 2-213 m in; for 6 to 10fuses the m inim um is 3-1/3 m in; and for 11 to 15 fu se s th e

m inim um is 5 m in. O ne person m ay not light m ore than 15fuses in a round. A lthough individual fuse lengths m ay bevaried for delay purposes it is m ore dependable to cut all thefuses to the sam e length and use the sequence of lighting todet erm in e t he f ir in g sequence.

To avoid m isfires due to cutoff fuses, M SH A requires thatth e fu se in th e la st h ole to fire is b urn ing w ith in th e h ole b efo reth e first h ole fire s. K in ks a nd s harp b en ds in th e fu se s ho uld b ea vo id ed b ec au se th ey m ay c ut o ff th e p ow de r tra in a nd c au sea m isfire. M any people w ho use cap and fuse do so becauseth ey fe el th at it is sim ple r to u se th an o th er in itia tio n sy ste ms .However, proper use of cap and fuse requires as much orm ore skill and care as the other system s.

DELAYS

Cap a nd fu se is th e o nly in itia tio n sy ste m th at o ffe rs n eith erflexibility nor accuracy in delays. Because of variations inle ng th s o f fu se , b urn in g ra te s, a nd tim e o f lig htin g th e in div id -

u al h ole s w ill f ir e a t e rr at ic in te rv als a t b es t, a nd out o f s equencea t w orst. It is im po ss ib le to ta ke a dv an ta ge of th e fra gm en ta -tion benefits of m illisecond delays w hen using the cap-and-f us e s ys tem .

GENERAL CONSIDERATIONS

There is no situation in w hich cap and fuse can be recom -mended as the best system to use. The system has twoove rpowe rin g f 1aws- in ac cu ra te t im in g and a poo r s af ety r ecor d.T he form er re sults in g en era lly p oo r fra gm en tatio n, a h ig he rin cid en ce o f c uto ffs, a nd le ss e fficie nt p ull o f th e ro un d. A ll o fth es e fa cto rs nUllify th e sma ll c os t a dv an ta ge d eriv ed from th es lig htly lo we r c os t o f th e s ys tem c ompon en ts . T he p oo r s afe tyrecord attained by cap and fuse is an even more seriousdrawback. It is the only system that requires the blaster toa ctiv ate th e b la st from a h az ard ou s lo ca tio n a nd th en re tre at tosa fe ty. T he u se of Ig nita co rd ra th er th an in divid ua l fu se lig ht-ing alleviates this problem . A B ureau study (14) determinedthat the accident rate w ith cap and fuse is 17 tim es that ofelectric blasting, based on the num ber of units used. Toooften, the person lighting the fuse is still at the face w hen theround detonates. T he tim e lag betw een lighting the fuse andth e d eto na tion o f th e ro un d m ak es se cu rity m ore d ifficu lt th anw ith other systems. .

C ap and fuse does have the advantages of lack of airblast,n o ch arg e d is ru ptio n, somewh at lo we r comp on en t c osts , a ndp ro te ctio n fro m e le ctric al h aza rd s. If a n o pe ra to r d ec id es tou se th e ca p-a nd -fu se sy ste m. in co rpo ra tio n o f Ig nita co rd fo rlig htin g mump le h ole s is s tro ng ly re commend ed b ec au se o f its

sa fe ty reco rd .

OTHER NONELECTRIC INITIATION SYSTEMS

Begi nn ing abou t i n 1970, e ffor ts we re devo ted towa rd deve lop -ing new initiation system s that com bined the advantages ofe le ctric a nd de to na tin g c ord s ys tem s. B as ic ally, th ese sy s-tem s consist of a cap sim ilar to an electric blasting cap, w ithone or two sm all tubes extending from the cap In a m anners im ila r to le g w ire s. In sid e th es e tu be s Is a n e xp lo siv e mate ria lthat propagates a m ild detonation w hIch activates the cap.

D elay periods sim ilar to those of electric blasting caps areavailable except that there are no coal m ine delays, sincethese devices are not approved for use in underground coalm in es . T he se in it ia tio n s ys tems a re not s us cept ib le t o e xt ra ne -ous electricity, create little or no airblast, do not disrupt thec ha rg e In th e b la sth ole , a nd h av e d ela y a ccu ra cie s s im ila r totho se of e le ctric o r d eto natin g co rd sy ste ms (5 ).



At'the time this manual was written, two relatively new

nonelectric init iation systems-Hercudet and Nonel-were

on the market. Other nonelectric systems are either under

development or in the conception stage. Both Hercudet and

Nonel were introduced to the U.S. market in the mid-1970's.

Because of their relative recency, minor changes are stillbeing made in these systems. The following discussions are

intended to give only general information on the systems.

Persons planning to use the systems should contact the

manufacturers, Hercules Inc. and Ensign Bickford Co.,

respectively, for specific recommendations on their use. A

third system, du Pont's Detaline System, is discussed in the

"Detonating Cord Initiation" section of this chapter.

HERCUDET

The hookup of the Hercudet (also called gas detonation)

blasting system resembles a plumbing system. The cap is

higher strength than most electric blasting caps. Both millisec-

ond and long delays are available. Instead of leg wires, twohollow tubes protrude from the cap. The cap may be used in a

primer in the hole or at the collar of the hole for initiating

detonating cord downlines. In addition to the Hercudet cap,

system accessories include duplex trunkline tubing, single

trunkl ine tubing; various types of tees, connectors, ells, and

manifolds for hooking up the system; circuit testers; a gas

supply unit containing nitrogen, oxygen, and fuel cylinders;

and a blasting machine. The system functions by means of the

low-energy detonation of an explosive gas mixture introduced

into the hollow tubes. This low-energy detonation does not

burst or otherwise affect the tubing.

37

For surface blast ing, a cap with 4-in leads is used (fig. 37).

For surface ini tiation of detonating cord downlines this cap is

connected directly to the trunkline tubing by means of the

reducing connector that is factory-attached to the cap. The

reducing connector is needed because the trunkline tubing is

larger than the capline tubing. A special plastic connector isused to attach the cap to the detonating cord downl ine.

When in-hole initiation is desired, the 4·in cap leads are

extended by connecting them to an appropriate length of

larger diameter duplex trunkline tUbing (fig. 38). This trunkline

tubing is cut squarely, leaving 2 to 3 ft of tubing extending from

the borehole collar, and a plastic double ell f itting is inserted.

Trunkline tubing is later connected hole to hole. Figure 39

shows typical Hercudet connections for surface blasting with

in-hole delays.

Not all cast primers have tunnels large enough to accept the

Hercudet duplex tubing. This should be checked before pur-

chasing cast primers. When using cartridge primers with

Hercudet, the tubing is taped to the primer, not half-hitched tojt,

For undergrouna Dlasting, millisecond and long period delaycaps are available with 16· to 24-ft lengths oftubing. The tubes

are cut to the appropriate length by the blaster. The tubes are

then connected in series or series-in-parallel, similar to elec-

triccap circuits, using capline connectors and manifolds instead

of the wire splices used in electric blasting. In all Hercudet

blast ing circuits, the tubing at the end of each series is vented

to the atmosphere. The tubing network should be kept free of

kinks.

When the circuit has been hooked up, a length of trunkline

tubing isstrung out to the fir ing position, similar to the fir ing line

in an electric system. Atthis t ime nitrogen from the gas supply

Figure 37.-Hercudet blasting cap with 4-ln tubes. (Courtesy Hercules lne.)



38

Fiyure 38.-Extendlng Hercudet leads with duplex tUDing. (Courtesy Hercules Inc.)

Double' e ll Trl.lnklll'le I •• Trl.lnklinl ecneeeter

unit is turned on and the pressure test module is used to check

the integrity of the tube circuit (fig. 40). The tester uses flow

and/or pressure checks to locate blockages or leaks in the

circuit. As with a galvanometer in electric blasting, each series

should be checked individually, followed by a check of the

entire system. The Hercudet tester is a smaller unit than the

pressure test module and uses a hand air pump to test singleboreholes or small hookups (fig. 41). If a plug or a leak is

detected when checking the completed circuit, the circuit is

broken into segments and checked with the Hercudet tester or

pressure test module.

Once the system has been checked and the blast is ready to

fite, the blasting machine, connected to the bottle box (gas

supply unit), is used to meter a fuel and oxidizer mixture into

the fir ing circuit (fig. 42). Until this detonable gas mixture is put

into the tubes, the connections between the caps are totally

inert. The explosive gas must be fed into the system for an

adequate period of time to assure that the system is entirely

fil led. Gas feeding continues until the blaster isready to fire the

shot. The time required to charge the circuit with gas depends

on the size of the circuit.

Tru nk li ne l ee

Trl.lnkline

eIO$tin~

_m hinBlasthole

Duplex

'runkline

4- in c ap le ad s

Cop

B la sI h ol e

Figure 39.-Hercudet connections for surface blasting.



39

Figure 40.-Hercudet pressure test module. (Courte.y Hercule. lne.)

W he n th e sy stem h as be en ch arge d, the b la stin g m achinec on tro l le ve r is m ov ed to "a rm " a nd th e "fire " b utto n is p us he d,causing a spark to ignite the gas m ixture. A low-energy gasde ton atio n tra vels thro ug h the tub in g circu it a nd th rou gh th eair space inside the top of each ind iv idua l cap at a speed of8,000 fps and ign ites the de lay elem ent in the cap.

The relatively slow (8,000 fps) detonation ra te of the gasintroduces an additional delay e lem ent in to the system . Forin stan ce , a ssu min g a g as de ton ation rate o f 8ftlms, w ith c ap sa t a d ep th of 3 0 ft in bla sth ole s spa ce d 1 2 f t a pa rt (a tota l tra velpath of 72 ft from cap to cap), a s-m s delay betw een caps w illbe in troduced by the tub ing. It is essentia l tha t these tubed ela ys b e ta ke n in to a cc ou nt w he n c alc ula tin g th e a ctu al firin gtim es o f th e in div id ua l c ap s. A lth ou gh th e c alc ula tio ns a re n otcom plex, it is im portant that they are done carefu lly , be fore

h oo kin g u p th e b la st, to a vo id p os sib le e rro rs in th e la st m in uterush to get the shot o ff. The de lay tim e of the tU b ing can beused to advantage by co iling tub ing in the trunkline at anylo ca tio n w he re a n a dd itio na l s urfa ce d ela y is d es ire d.

Th e H erc ud et sys te m ha s th e ad va nta ge s of n o a irb la st, n ocharge d isrupt ion , no e lectr ica l hazards, versat ile de lay capab il it y ,a nd s ys te m c he ck ou t c ap ab ility . T he in ert n atu re o f t h e s ys te muntil the gas is in troduced is a safe ty benefit. Specific crewtra in in g b y a re pre se nta tiv e o f th e m an ufa ctu re r is n ec es sa ryb ec au se th e s ys te m is s om ew ha t d iffe re nt in p rin cip le th an th eo ld er syste ms s uch as de to natin g co rd a nd elec tric blasting .C are m ust be taken not to get fo re ign m aterial such as d irt orw ate r in sid e th e tU bin g o r c on ne cto r w hile h oo kin g u p th e s ho t,and to avoid knots or kinks in the tubing.

NONEL

The hookup of the N one l (a lso ca lled the shock tube) sys-te m is s im ila r in s om e re sp ec ts to th e d eto na tin g c ord s ys te m.The cap used in the system is h igher strength than m oste le ctric b la stin g c ap s. In ste ad o f le g w ire s, a s in gle h ollo w tu bepro trudes from the cap (fig . 43). The N onel tube has a th inc oa tin g o f re ac tiv e m ate ria l o n its in sid e s urfa ce , w hic h d eto -n ate s a t a s pe ed o f 6 ,0 00 fp s. T his is a v ery m ild d us t e xp lo sio nth at h as in su ffic ie nt e ne rg y to d am a ge th e tu be . S ev era l v aria -tions of the N onel system can be used, depend ing on theb la stin g s itu atio n. In a dd itio n to th e N o ne l tu be -c ap a ss em b ly ,s ys te m a cc es so rie s in clu de n ois ele ss tru nk lin es w ith b uilt-ind ela ys , n ois ele ss le ad -in lin es , a nd m illis ec on d d ela y c on ne c-to rs fo r d eto na tin g c ord tru nk lin es .

O n e N o ne l s ys te m fo r s urfa ce b la stin g u se s a N o ne l P rim a de tin each b lastho le w ith 25- to 60-gr/ft detonating cord as atru nk lin e. T he N on el c ap u se d in th is s ys te m is fa cto ry c rim pe dto a 24-in length of shock tube w ith a loop in the end (fig . 44).T he c ap s a re a va ila ble in a v arie ty o f m illis ec on d d ela y p erio ds .A 7 .5 -g r d eto na tin g c ord d ow nlin e is a tta ch ed to th e lo op w ith adouble- wrapped squar e kno t. T he 7 .5 - gr de tona ti ng co rd ex tendsout of the borehole. Th is dow nline w ill no t disrupt a colum nc ha rg e o f b la stin g a ge nt b ut it m ay in itia te d yn am ite a nd o th erc ap -s en sitiv e p ro du cts . A s a p re ca utio n, 7 .5 -g r to 7 .5 -g r c on -nections shou ld never be m ade, because propagation fromo ne co rd to the o th er is no t d ep en dab le . S in ce the fo rce of th es ho ck tu be d eto na tio n is n ot s tro ng e no ug h to d is ru pt th e tu be ,it w ill no t in itia te high exp losives. A 25- to 60-gr trunkline is



40

Figure 41.-Hercudet tester for small hookups. (Courtesy Hercules lne.)

u se d in th is s ys tem w ith a d ou ble c lo ve h itc h u se d fo r d ownlin e-to-trunkline connections. T he delay system s used w ith thism ethod of in itiation are the sam e as those discussed in the"De to na tin g Cord In itia tio n" s ec tio n. T he y in clu de in -h ole c apd ela ys a nd s ur fa ce d ela y c on ne cto rs .

In s om e ca se s th is s ys te m crea te s a n e xce ssive am ou nt o fa irbl as t and no ise . To p reven t thi s, the de tonat ing co rd t runkli necan be replaced by an electric blasting cap circuit w ith a capc on ne cte d to e ach d ow nlin e, o r a n oise le ss N on el tru nk lin ecan be used.

T he n ois ele ss Non el tru nk lin e is emplo ye d a s fo llo ws . F ir st,each hole is prim ed and loaded. The dow n l ine should be an1 8-g r o r la rg er d eto na tin g c ord . A 7 .S -g r d ownlin e c an b e u se dif a 2 S-gr p ig ta il is u se d a t th e to p e nd , tie d in to th e co nn ecto rb lo ck . T he n ois ele ss tr un klin e d ela y u nit c on sis ts o f a le ng th o fs ho ck tu be , 2 0 to 6 0 ft in le ng th , w ith a q uic k c on ne ctin g s le ev eo n o ne e nd a nd a p la stic b lo ck c on ta in in g a m illise co nd de la yblasting cap (delay assem bly) on the other end, and a tagd en otin g th e d ela y p erio d (fig . 4 5). T he d ela y m ay b e fro m S t o200ms.T he sleeve is attached to the initia l hole to be fired and the

shock tube is extended to the next hole in sequence. Thed ow nlin e fro m th is n ext ho le is co nn ecte d to th e p la stic b lo ckc on ta in in g th e d ela y c ap , u sin g a bQut- 61 n- at co rd a t th e e nd o fth e d ow n lin e. A no th er d ela y u nit is se le cte d a nd th e s le ev e isattached to the dow n line below the plastic block. The shocktu be is ex te nd ed to th e n ext h ole , w he re th e d ela y a ss em bly is

connected to the dow nline. The process is repeated until a llthe holes are connected. Figure 46 show s a portion of a shothooked up in this w ay.

T he d ow nlin es a nd th e p la stic b loc ks c on ta in in g th e d ela ycap should be covered to reduce noise and flying shrapnel.W he n th e b la ste r is re ady to fire th e s ho t, a n in itia tin g d ev ic e isattached to the dow nline of the first hole. This device m ay bean electric blasting cap, a cap and fuse, or a N onel noiselessle ad -in (fig . 4 7). A n ois ele ss le ad -in is a le ng th of sh oc k tu be ,u p to 1 ,0 00 ft lo ng , c rim pe d to a n in sta nta ne ous b la stin g c ap .The shock tube is in itiated by using an electric blasting cap,cap and fuse, or other in itiating device recommended by themanufacturer.

F o r u ndergr ound b la st in g, m illis ec ond and lo ng per io d dela ycaps are available w ith 10- to 20-ft lengths of shock tubea tta che d. C ommon p ra ctic e is to u se a tru nk lin e o f 1 8- o r 2 5-g rd eto na tin g cor d. T he None l t ube f rom each b la st ho le is a tt ac hedto th e tru nk lin e w ith a J-co nn ecto r. A sim ple r m eth od is to us ethe bunching system , w here up to 30 tubes are tied togetherparalle l, in a bunch, and detonating cord is clove-hitchedaround the bunch. The m anufacturer should be consulted todem onstrate the bunching technique and to determ ine thenum ber of w raps of detonating cord required for a given sizebunch.

W hen pneum atic loading is used, a plastic cap holder canbe utilized to center the cap in the hole and to reduce m ove-ment of the cap. It is important that the Nonel tube is in a



41

Figure 42.-Herc~les bottle box and blasting machine. (Courtesy Hercules Inc.)

Figure 43.-Nonel blasting cap. (Courtesy Ensign Bickford Co.)



42

Figure 44.-Nonel Prlmadet cap for surface blasting. (Court.sy Ensign BlcIdord Co.)

...NONELPrimadet

N O I S E l E S S T R U N K L IN E D E l A Y

20 FT

Figure 45.-Nonel noiseless trunkline delay unit.

(Courtesy Ensign Bickford co.)

LhO•• '.... ~

E=====:!:.========l-~

conn.ctar TYPICAL DELAY PATTERN Mumbly

Figure 46.-Nolseless trunkllne using Nonel delay

assemblies.

straight l ine, fairly taut, and that crossovers or contact with the

trunkline are avoided. This is true in all Nonel blasting but

particularly in heading rounds, where the blast face is more

crowded. Just before blast ing, an electric cap or cap and fuseis connected to the trunkline.The Nonel system has the advantages of no 'alrblast (when

a noiseless trunkline is used), no charge disruption (when

Nonel tube or a 7.S-gr cord inconjunction with a Nonel Primadet

is used as a downline), no electrical hazards, and a versatile

delay capability. Keep in mind that electrical storms are a

hazard with any initiation system. System checkout is done

through visual inspection. Nonel shock tube assemblies should

never be cut or trimmed, as that may cause the system to

malfunction. The shock tube will initiate nothing but the cap

crimped onto it. Because of the variations available and new

concepts involved, specific crew training by a manufacturer's

representative is highly recommended before using the Nonel

system.



43

Figure 47.-Nonel noiseless lead-In line. (Courtesy Ensign Bickford Co.)

PRIMING

Essentially, the term primer is used to describe a unit of

cap-sensit ive explosive that contains a detonator, while the

term booster describes a unit of explosive that mayor may not

be cap sensitive, and is used to intensify an explosive reaction

but which does not contain a detonator. Although a primer is

general ly thought of as containing a blast ing cap, the primer

cartridge may also be detonated by a down line of detonating

cord.

The possible undesirable effect of the cord on blasting

agents, described in the "Detonating Cord Initiation" section,

must be considered. If the column charge is cap sensitive,

detonating cord will cause initiation to proceed from the top

down. The manufacturer should be consulted to determine the

minimum strength detonating cord that will reliably initiate a

specific type of primer. Most cast primers require a detonating

cord strength greater than 25 grift for reliable initiation.

TYPES OFEXPLOSIVE USED

The primer should have a higher detonation velocity than

that of the column charge being primed. Some experts feel

that priming efficiency continues to increase as the primer's



44

detonation velocity increases. In blastholes of 3-in diameter

and less, cartridged dynamites and cap-sensitive cartridged

slurries are commonly used as primers. For maximum efficiency,

the diameter of the cartridge of explosive should be as near to

the blasthole diameter as can be conveniently loaded. Gelatin

dynamites are preferred over granular types because of their

higher density, velocity, and water resistance. Some granular

dynamites may be desensitized when subjected to prolonged

exposure to water or to the fuel oil in AN-FO. Cast primers (f ig.

11) may be used if the borehole is large enough to accommo-

date them. Small units of explosive that fit directly over the

shell of a blasting cap can be used for priming bulk blasting

agents in small-diameter holes. In some situations, where

boreholes are dependably dry, a high-strength cap alone has

been used to prime a bulk-loaded AN-FO in a small-diameter

hole. However, it isstrongly recommended that a small booster

fitting directly over the shell of the cap be used rather than a

high-strength blasting cap alone. The cap manufacturer should

be consulted for a recommendation if you are in doubt.

In larger diameter blastholes, cast primers are predomi-

nately used, although some operators prefer to use cartridged

high explosives. Ideally, the primer should fill the diameter of

the blasthole as nearly as possible. However, primers are

relatively expensive in comparison to the blasting agents used

in larger boreholes, so economics are a factor in primer choice.

AII61asting agents are subject to transient detonation veloci-

Figure 48.-Highly aluminized AN-FO booster. ( Cou rt es y Gu lf 0 11Ch em ic als ce.)



t ies (4,6). That is. they may begin detonating at a relatively low

velocity at the point of initiation with the velocity rapidly build-

ing up until the blasting agent reaches its stable velocity,

called the steady state veiocity. This buildup occurs within

about three charge diameters. A low init ial velocity probably

causes some loss of energy at the primer locat ion. Low initial

velocities can result when the primer is too small or of inade-

quate strength, or when the blasting agent is poorly mixed orpartially desensitized by water.

In large-diameter slurry columns, a 1-lb cast primer or a

cartridge of gelatin dynamite is often an adequate primer. In

AN-FO columns where conditions are dependably dry, a 1-lb

primer is sometimes adequate. However, where dampness

exists, orwhere low transient velocities are a particular concem,

it is recommended that a 25- or 50-lb charge of high-energy

slurry or aluminized AN-FO be poured around the primer. This

is called combination priming. High detonation pressure slur-

ries (12-13) and highly aluminized products (9) have been

recommended as combination primers (fig. 48). Bureau of

Mines research (4) indicates that each type of product does a

good job of raising the velocity in the transient zone. An added

benefi t of combination priming is the margin of safety in damp

boreholes that may partial ly desensitize AN-FO.Cast primers have been developed which incorporate an

internal millisecond delay. The cast primers and the delay

devices are supplied separately, with directions for assembly

(f ig. 12). These delay primers are slipped onto a detonating

cord downline and are especially useful in providing multiple

delays in the blasthole on a single downl ine.

PRIMERM A K E U P

Proper care and technique in making primers is very impor-

tant because this is the time in the blasting process at which

the sensitive initiator and the powerful explosive cartridge are

first combined. Because of the additional hazard involved,primers should be made up as close to the blast site as

practical and immediately before loading.

Inlarge tunnel projects, it is generally agreed that an outside

primer makeup facility is best, assuming that transportation

from the facility to the working face is safeguarded. Primers

should be dismantled before removal from the blasting site. An

adequate hole must be punched into the cartridge to insure the

detonator can be fUlly imbedded. Care must be taken to assure

that the detonator does not come out of the primer cartridge

during loading. The primer cartridge should never be tamped

or dropped down the borehole. One or more cartridges or a

few feet of AN-FO should be placed above the primer cartridge

before dropping or tamping begins.

In smal l-diameter notes, it is especially important that the

end of the cap points in the direction of the main charge. It is

also strongly recommended in small-diameter holes that the

primer cartridge be the first cartridge placed into the blasthole.

When priming small-diameter cartr idges, the hole for the deto-

nator is usually punched in the end of the cartridge. With

electric caps, the wires are usually half hitched around the

cartridge (fig. 49). Two half hi tches are commonly used. The

tubes or fuse from nonelectric detonators are not half hitched.

It is recommended that the tubes or fuse be taped to the

cartridge to assure that the cap is not pulled out during loading.

Some safety fuse will not stand the sharp bend required for

end priming. In this case, a diagonal hole is punched all the

way through the cartridge and a second diagonal hole is

punched partial ly through. The cap and fuse isstrung through

45

Electric

blastingcap

c;l

Half hitch

- -,,,-

I

Leg wires

Figure 49.-eartrldge primed with electric blasting cap.

the f irst hole, placed into the second hole, and pulled secure.

Here again, taping of the fuse to the cartridge will assure that

the cap is not pUl led out during loading.

When attaching detonating cord directly to the small-diameter

primer cartridge, the detonating cord is usually inserted into a

deep axial hole in the end of the cartridge. The cord is then

either taped to the cartridge, passed through a diagonal hole in

the cartridge, or secured with a half hitch to assure that the

cord wi ll not pull out.

When priming large-diameter cartridges with electric blast-

ing caps, a diagonal hole is punched from the top center of the

cartridge and out the side about 8 in from the top. The capwires are doubled over, threaded through the hole, and wrapped

around the cartridge. The cap is placed into a hole punched

into the top of the cartridge and the assembly is pulled tight.

Tape may be used for extra securi ty.

Detonating cord is secured to large-diameter cartridges by

punching a diametrical hole through the cartr idge, passing the

cord through the cartridge, and tying the cord at the top of the

cartridge with a secure knot. This should not be done when

using non-water-resistant explosive products inwet boreholes



46

because m e cartridge m ay becom e desensitized by w aterehtering the punched hole. C ap and fuse is not com monlyu sed w it h la rg e car tr id ge s. W it h o th er n onele ct ric in it ia to rs , it isre commen de d th at c ast p rim ers ra th er th an la rg e-d ia me te re xp lo siv e c ar trid ge s b e u se d.

Cast prim ers (fig. 11) are m ost com monly used to prim e

large-diam eter blastholes. For use w ith detonating cord, aca st p rim er w ith a s in gle a xia l h ole is u se d. T he co rd is p ass edthorugh the cord "tunnel" and tightly knotted at the bottom ofth e p rimer . S in ce th is k no t w ill n ot p ull b ac k th ro ug h th e tu nn elit is not necessary to tie the cord around the prim er. S ubse-q ue nt p rim ers ca n b e a dd ed w here ve r d es ired b y p as sin g thed ownlin e a t th e b la sth ole c olla r th ro ug h th e p rimer tu nn el a nds lid in g th e p rimer d own th e d ownlin e. P la cemen t o f d ela y c as tp rime rs o n th e d ownlin e is d on e in a s im ila r fa sh io n e xc ep t th atthe tunnel for the cord is connected to the perim eter of theprim er rather than passing through the center of the prim eritself.

Cast primers for use w ith detonators have a cap well ina dd itio n to a tu nn el. T he c ap is in se rte d th ro ug h th e tu nn el a ndb ac k u p in to th e w ell, m akin g su re th at th e c ap is se ate d in th eb otto m o f th e w ell (fig . 5 0). A lth oug h th e c ap w ill u su ally sta ysecurely in the prim er using this type of configuration, it is agood idea to use a w rap of tape around the end containing the

c ap w ell fo r s ecu rity. R em embe r th at n ot a ll c ast p rim ers h avetu nn els la rg e e nou gh to a cc ept th e H ercu de t d up le x tU bin g.

PRIMERLOCATION

Proper location of the prim er is im portant from the stand-p oin t o f b oth s afe ty a nd e ffic ie nc y ( 1,6). When usin g car t r id gedp ro du cts in sm all-d ia me ter b la sth ole s, th e p rim er sh ou ld b ethe first cartridge placed into the hole, w ith the cap pointingtowa rd th e c olla r. T his a ss ure s ma ximum c on fin emen t a nd th emos t e ffic ie nt u se o f t h e e xp lo siv e's e ne rg y. P la cin g th e p rime rin the bottom m inim izes bootlegs and also protects againstle avin g u nd eton ate d ex plo siv es in th e b otto m o f th e h ole if th eca rtrid ge s be come se pa ra te d. T he p rim er ca rtrid ge m ust n otb e c ut, d efo rme d, o r tampe d. If b ulk p ro du cts a re b ein g lo ad ed ,the prim er m ay be raised slightly from the bottom of the hole.

In ben ch b la st in g w it h a bulk lo aded p rodu ct , where subdr illin gis u se d, th e p rim er s ho uld b e p la ced a t to e le ve l, ra th er th an inthe b otto m o f th e h ole , to re du ce g ro un d vib ra tio ns . If th ere iss om e comp ellin g re aso n to pla ce th e p rim er at th e c olla r o f t heh ole th e d eto nato r s ho uld be p oin te d to wa rd th e b otto m o f th e

hole.

Figure 5O.-Prlmlng cast primer with electric blasting cap. (Courtesy Austin Powder Co.)



In large-diameter blastholes, the location of the primer is

more a matter of choice, althouqh bottom init iation is recom-

mended to maximize confinement of the charge. To help

reduce vibrations, the primer should be at toe level rather than

in the bottom of the hole, where subdrilling is used. Bottom-

initiated holes tend to produce less flyrock and airblast than

top-init iated holes, assuming that all other blast dimensionsare equal. If pul ling the toe is not a signi ficant problem, some

operators prefer to place the primer near the center of the

charge. This gives the quickest total reaction of the explosive

column and may yield improved fragmentat ion. Top priming is

seldom recommended except where the only fragmentation

difficulty is a hard band of rock in the upper portion of the

bench. A rule of thumb, when using a single primer in a large-

diameter blasthole, is to place the primer in the zone of most

difficult breakage. This will normally be the toe area. Figure 51

summarizes some desirable and undesirable locations for

primers in large-diameter blastholes.

KEY

.1.lb cast prim.,

• H91 alM'QY II con do r, p rim. ,

E J eta,tint atlnl

To.

priminoBollom J Top I Aiiol=~r~,.. : ~ j W . ~

""OCIl)

I.H)£$IRABLEESIRABLE

Figure 51.-Prlmlng blasting agents in large-diameterblastholes.

47

MULTIPLE PRIMING

In many blasting situations, single-point priming may be

adequate. However, there are some situations in which multi-

ple primers in a single borehole may be needed. The first is

where deck charges are used. Deck charges are used (1) to

reduce the powder factor in a blast while still maintainingsatisfactory powder distribution, (2) to break up boulder-prone

caprock in the stemming area of the blast, or (3) to reduce the

charge weight per delay to reduce vibrations. In situation 3,

each deck in the hole is on a different delay period. In 1 and 2,

the decks within a single hole may be on the same or on

different delays. In any case, each deck charge requires a

separate primer. Some States, such as Pennsylvania, require

at least two primers per blasthole.

The second reason for mult iple priming is as a safety factor

to assure total column detonation. With modern explosives

and blast ing agents, once detonation has been established it

will proceed efficiently through the entire powder column.

However, an offset in the powder column (fig. 34) may occur

before detonation and cause part of the column not to propagate.

This is most likely to occur with very long, thin charges orwhere slip planes are present in the burden area. In these

cases, two or more primers should be spaced throughout the

powder column. Frequently, these primers wil l be on the same

delay. Where single point priming is preferred, but one or more

additional primers are needed to assure total column propagation,

the addit ional primers are put on a later delay period.

With multiple delayed decks ina blasthole, detonation should

proceed from the bottom up where a good free face exists.

Where the shot is tight, such as in area coal mining, detonation

from the top down will give some relief to the lower decks.

Axial priming, which employsacentral core ofprimer through-

out an AN-FO column, has been used successfully but appears

to have no particular advantage over single point or multiple

point priming. Axial priming is more expensive than conven-

tional priming.

REFERENCES

1. Ash, R. L. The Mechanics of Rock Breakage, Parts I, II, III, and

IV. Pit and Quarry, v. 56, No.2, August 1963, pp. 98-112; No.3,

September 1963, pp. 118-123; No.4, October 1963, pp. 126-131; No.

5, November 1963, pp. 109-111, 114-118.

2. Atlas Powder Co. (Dallas, TX). Handbook of Electr ic Blasting.

Rev. 1976, 93 pp.

3. Chironis, N. P. New Blasting Machine Permits Custom-

Programmed Blast Patterns. Coal Age, v. 79, No.3, March 1974, pp.

78-82.

4. Condon, J. L., and J. J. Snodgrass. Effects of Primer Type and

Borehole Diameter on AN-Fa Detonation Veloci ties. Min. Congo J., v.

60, No.6, June 1974, pp. 46-47, 50-52.

5. Dick, R. A. New Nonelectric Explosive Init iation Systems. Pit &

Quarry, v. 68, No.9, March 1976, pp. 104-106.

6. __ . Puzzled About Primers for Large Diameter AN-Fa

Charges? Here's Some Help to End the Mystery. Coal Age, v. 81, No.

8, August 1976, pp. 102-107.

7. E. I .duPont de Nemours & Co., Inc. (Wilmington, DE). Blaster's

Handbook. 16th ed., 1978, 494 pp.

8. Ensign Bickford Co. (Simsbury, CN). Primacord Detonating Cord.

9th printing, copyr ight 1963, 68 pp.

9. Grant, C. H. Metallized Slurry Boosting: What It Is and How It

Works. Coal Age, v, 71, No.4, April 1966, pp. 90-91 .

10. Hagan, T. N. Optimum Priming for Ammonium Nit rate Fuel-Oil

Type Explosives. Proc. Southern and Central Queensland Conf. of

the Australasian Insl. of Min. and Mel., Parkvi lle, Austral ia, July 1974,

pp. 283-297; avai lable for consul tation at Bureau of Mines Twin Cit ies

Research Center, Minneapol is, MN.

11. Insti tute of Makers of Explosives Safety Library (Washington,

DC). Safety Guide for the Prevention of Radio Frequency Radiation

Hazards in the Use of Electric Blasting Caps. Pub. No. 20, October

1978,20 pp.

12. Junk, N. M. Overburden Blast ing Takes on New Dimensions.

Coal Age, V. 77, No.1, January 1972, pp. 92-96.

13. __ . Research on Primers for Blasting Agents. Min. Congo

J., v. 50, No.4, April 1964, pp. 98-101.

14. Sengupta, D., G. French, M. Heydari, and K. Hanna. The

Impact of El iminating Safety Fuse From Metal/Nonmetal Mines (Con-

tract J029501 0, Sci. Applications, Inc.). BuMines OFR 61-81, August

1980,21 pp.; NTIS PB 81-214386.



49

Chapter 3.-BLASTHOLE LOADING

Blasthole loading involves placing all of the necessary ingredi-

ents into the blasthole, including the main explosive charge,deck charges, initiation systems, primers, and stemming.

Blasthole loading techniques vary depending on borehole

diameter, type of explosive, and size of the blast. For the

purpose of this discussion, boreholes have been arbitrarily

classified as small diameter « 4 in) and large diameter

(>4 in). Small-diameter boreholes may be drilled at practi-

cally any inclination from vertically down to vertically up. Large-

diameter blastholes are usually drilled vertically down, but insome cases are angled or horizontal.

As a specific precaution.blastholes should never be loaded

during the approach or progress of an electrical storm. Gen-

eral descriptions of blasthole loading procedures are in theliterature (2-5).1

CHECKING THE BLAS·rHOLE

Before loading begins, the blastho/es should be checked.

Depending on the designed depth, either a weighted tape

measure or a tamping pole should be used to check that the

boreholes are at the proper depth. If a hole is deeper than theplan calls for, drill cuttings or other stemming material should

be used to bring the bottom of the hole up to the proper level.

Loading an excessively deep blasthole is a waste of explosive

and usually increases ground vibrations. Boreholes that are

less than the planned depth should either be cleaned out with

the drill or compressed air, or redri lled. Sometimes economics

or equipment limitat ions may dictate that a shot be fired with a

few short holes. The blasting foreman should make this decision.

Occasionally a borehole may become obstructed. On a

sunny day, a mirror may be used to check for obstructions.

Obstructions in small holes may sometimes be dislodged with

a tamping pole. In large, vertical holes, a heavy weight sus-

pended on a rope and dropped repeatedly on the obstruction

may clear the hole. It may be necessary to use the drill 'string to

clear a diffi-::ult obstruction or, if the obstruction cannot be

cleared, redrilling may be necessary.

I f it is necessary to redrill a hole adjacent to a blocked hole,

the blocked hole should be filled with stemming. If this is not

done, the new hole may shoot into the blocked hole and vent,

causing excessive flyrock, airblast, and poor fragmentation. A

hole must not be redril led where there isa danger of intersect-

ing a loaded hole.

WtiTIecnecking the hole for proper depth, it is convenient to

check for water in the borehole. With just a litt le experience,

the blaster can closely estimate the level of water ina borehole

by visually checking the tamping pole or weighted tape for

wetness after the borehole depth check has been made. To

get a more accurate check, the weighted end of the tape can

be jiggled up and down at the water level. A splashing sound

will indicate when the weight is at the water level.

A blasthole may pass through or bottom into an opening.

Where this opening is not unduly large, it may be filled with

'"r -" .' X : : .\ :, :; 1Sltmm,,,q

_EsgoSve

Figure 52.-Corrective measures for voids.

'stemrntnq material (fig. 52). Where the opening istoo large for

this to be practical, the hole must either be left unloaded,

redri lled in a nearby location, or plugged.

A simple method for plugging a blasthole is as follows. A

stick is tied to the end of a rope, lowered into the void, and

pulled back up so it lodges crosswise across the hole. The

rope is staked securely at the borehole collar. Bulky materials

such as empty powder bags or rags are then dropped down

the hole, dirt is then shoveled down the hole to form a solid

bottom, after which explosive loading can proceed. Where

voids are commonplace, you may want to develop a tailormade

borehole plugging device.In some districts hot holes may be encountered, although

this is not very common. Hot holes may occur in anthracite

mining or other areas of in situ coal seam fires. If there is

reason to suspect a hot hole, the hole can be checked by

suspending a thermometer in i t for a few minutes. Explosive

materials should not be loaded into holes hotter than 1500 F.

GENERAL LOADING PROCEDURES

Blastholes may be loaded with bulk or packaged products.

Bulk products are either poured into the hole, augered, pumped,

or blown through a loading hose. Packaged products are

either dropped into the hole, pushed in with a tamping pole or

other loading device, or loaded through a pneumatic tube. It is

a good idea to check the rise of the powder column frequently

as loading progresses, using a tamping pole, weighted tape,

1I ta licized numbers in parentheses refer to items in the l ist of refer-

ences at the end of this chapter.



50

o r lo ad in g h os e. T his w ill g iv e warn in g o f a c av ity o r o ve rs iz edhole that is causing a serious overcharge of explosive to beloaded, and w ill a lso assure that sufficient room is left at thetop of the hole for the proper am ount of stemming. W hen thep ow de r co lu mn h as re ach ed the pro pe r lo ca tion , th e p rim er islo ad ed in to th e b ore ho le . It is im po rta nt th at th e w ire s, tu be s,o r d eto na tin g cor d le ad in g f rom the p rime r a re p ro pe rly s ecur ed

a t t he b ore ho le c olla r in v ertic al o r n ea rly v er tic al h ole s, u sin g ar oc k o r s ta ke .

In a lmo st a ll s itu atio ns it is re commend ed th at th e e xp lo siv e.c ha rg e be t ot ally c ouple d. T ot al c ouplin g means t ha t t he cha rgec omp le te ly fills th e b ore ho le d iamete r. B ulk lo ad in g o f e xp lo -sive s a ssu re s go od c ou plin g. W he n c artrid ge d p ro du cts a reu se d, c ou plin g is imp ro ve d b y s littin g th e c artrid ge s a nd tamp -ing them firm ly into place. There are four situations w hereca rtrid ge s o r p ack ag es o f e xp lo siv es s ho uld n ot b e tamp ed .

1 . In p erm iss ib le co al m in e b la stin g, w he re d eform in g th eca rt ridge is agai ns t requ la tl ons .

2. In controlled blasting, w here string loads or even gapsb etw ee n c artrid ge s a re u sed to re du ce th e c ha rg e lo ad in th e

per ime te r h ole s t o p re vent s ha tt er in g,

3. In w ater, w here the package serves as protection for anon-wa te r- res is tan t expl os ive p roduc t.

4. A prim ed cartridge is never tam ped.

I t i s r ec ommended t ha t a ll b la st ho le s be s temmed to imp ro vethe effic iency of the explosive and to reduce airblast andflyrock. A s a rule of thum b, the length of stemming should befrom 14 to 28 tim es the borehole diam eter. S ized crushed

stone m akes the m ost efficient stemming. H ow ever, for rea-sons of econom y and convenience, drill cuttings are m ostcommonly used. Large rocks should never be used as stem -m in g a s th ey c ou ld b ecome a d an ge ro us so urc e o f fly ro ck a ndm ay also dam age the w ires, cord, or tubes of the initiations ys te m. B ec au se it is in co nve nie nt to s te m h oriz onta l h ole s,h oriz on ta l ro un ds a re some tim es le ft u ns te mmed , a lth ou gh it

is recommended that all b lastholes be stemmed to im proveb las ting e ff ic iency . By regu la ti on , unde rg round coal m ine roundsm ust be sfem med with noncom bustible stem ming such aswa te rf ille d car tr id ge s o r c la y " dumm ie s. "

Car e mus t b e e xe rc is ed in u sin g d eto na tin g c ord d ownlin esin re la tive ly sm all b la sth ole s. S ee "F ie ld A pp lic atio n" in th e"D etonating C ord Initiation" section of chapter 2 for recom -mended g ra in lo ad s o f d et onat in g cor d a s a f un ct io n o f b la st ho lediameter.

O ne solution to blasting in w et boreholes is to use a w ater-r es is ta nt e xp lo siv e. However , e conom ic s o ft en f avor d ewa te r-in g th e b la sth ole a nd lo ad in g it w ith AN -FO in sid e a p ro te ctiv eplastic borehole liner. A lthough dew atering has been usedm ostly in large-diam eter holes, it can be used in diam etersbelow 4 in. To dew ater, a pum p is low ered to the bottom of the

h ole . W he n th e w ate r h as b ee n remo ve d, th e h ole is lin ed w itha plastic sleeve as follow s. A roll of hollow plastic tubing isb ro ug ht to th e c olla ro f th e h ole . A ro ck is p la ced in sid e th e e ndof the tubing and a knot is tied in the end of the tubing to holdthe rock in place. The tubing is reeled into the borehole, andcare is taken not to tear it. The tubing is cut off at the collar,a llow ing 4 to 6 ft extra for charge settlem ent. The A N-F O andprim er are loaded inside the tubing and the hole is stemmed.W here w ater is seeping into the borehole, it is im portant thatthe tubing and AN -FO be loaded quickly to prevent the holefr om re fillin g w ith wate r.

SMALL-DIAMETER BLASTHOLES

When sma ll- diamete r b la sth ole s a re lo ad ed , th e p rime r c ar-trid ge is n orm ally loa de d a t th e b otto m o f th e h ole . T his g iv esma ximum c on fin eme nt a t t h e p oin t o f in itia tio n a nd a ls o g ua rd sagainst leaving undetonated explosive in the bottom of theb ore ho le if it s ho uld b ec om e p lu gg ed d uring lo ad in g o r c ut o ffd Uring th e b la stin g p ro ce ss . S om e e xp erts c on do ne , o r e ve nr ec ommen d a c us hio n s tic k o r t w o, b ut th e g en era l re commen-dation is not to use a cushion stick. To avoid having thed eto na to r fa ll o ut o f th e p rime r c artrid ge , th e c artrid ge s ho uldn ev er b e s lit, ro lle d, or o th erw is e d efo rm ed . T he p rim er c ar-trid ge s ho uld n ev er b e tampe d.

CARTRIDGED

PRODUCTS

C artridged dynam ites and slurries (w ater gels) are com -m on ly u se d in sm all-dia me te r b la sth ole s. T he se c artrid ge sa re u su ally slit,lo ad ed by h an d, a nd tamp ed to p ro vid e m ax i-m um coupling and loading density. O ne or tw o cartridgesshould ' be loaded after the prim er before tam ping begins.T amp in g s ho uld h e d on e firm ly , b ut n ot e xc es siv ely . U sin g th ela rg es t d iameter c ar tr id ge compat ib le w it h t he bor ehole d iame-te r w ill in cre as e c ou plin g a nd lo ad in g d en sity .

Pneum atic system s for loading w ater gel cartridges area va ila ble . T he car tr id ge s a re p ro pe lle d t hr ough a lo ad in g hosea t h ig h v elo city a t a ra te o f u p to o ne c artrid ge p er se con d. T hecar tr id ge s a re aut oma tic ally s lit a s t he y ent er t he b la st ho le and

e ac h c artrid ge sp lits u po n im pa ct. B eca us e o f th e h igh im pa ctimp arte d to th e c artrid ge s, lo ad in g d yn am ite s w ith th is ty pe o flo ad in g s ys tem is n ot p ermitte d. P ne umatic c artr id ge lo ad er sare especially useful in loading holes that have been drilledupward.

BULK DRY

BLASTiNG AGENTS

Bulk d ry b la stin g a ge nts , u su ally AN -FO , ma y b e lo ad ed in tosm all-d iam eter blastholes by pouring from a bag or by pneu-matic lo ad in g th ro ug h a lo ad in g h os e (fig . 5 3) . P ou re d c ha rg esin diam eters less than 4 in lose som e effic iency because ofAN -FO 's low density and its reduced detonation velocity atsm all d iam eters. As w ith all bulk loading, good coupling isa ch ie ve d. Cau tio n s ho uld b e e xe rc is ed in u sin g p ou re d AN -FOcharges in diam eters less than 2 in. This should be done onlyunder bone-dr y c ondit io ns becau se AN-FO 's e ff ic ie nc y beg in sto d ro p s ig nific an tly a t t his p oin t, a nd w ate r w ill c om po un d th eproblem.

P ne uma tic lo ad in g o f AN -FO in sma ll h ole s is re commend edbecause of ease of handling, faster loading rates, and theimpr ov ed p erfo rma nc e o f th e AN- FO c au se d b y p artia l p ulv er-iz ing of the prills , w hich gives a higher loading density andg rea te r sens it iv it y (1 . 4). The tw o basic types of pneum aticloading system s are the pressure vessel and the ejector orventur i- type l oader .



51

Figure 53.-Pneumatic loading of AN-FO underground. (Courtesy Hercules Inc.)

A pressure vessel type AN-FO loader should have a pres-

sure regulator so that the tank pressure does not exceed the

manufacturer's recommendation, usually 30 psi. This low-

pressure type loader propels the prills into the borehole at a

low velocity and high volume rate, loading the AN-FO at a

density slightly above its poured density with a minimum amount

of prill breakage. In a pressure vessel, the compartment con-

taining the AN·FO is under pressure during loading. Loading

rates of over 100 Ib/min can be achieved with some equipment

and pressure vessels with AN-FO capacities of 1,000 Ib are

available. The smaller and more portable pressure vesselloaders have loading rates of 15 to 50 Ib/min and AN-FO

capacit ies of 75 to 200 lb. Pressure vessels larger than 1 au ft

in volume should meet ASME specifications for construction.

The ejector-type system (fig. 54) uses the venturi principle

to draw AN-FO from the bottom of an open vessel and propel it

at a high velocity but low volume rate into the borehole, pulveriz-

ing the prills and giving bulk loading densities near 1.00.

Ejector systems operate from line pressures of 40 to 80 psi

and ioad at rates of 7 to 10 Ib/min. Combination loaders are

available that force feed a venturi from a pressurized pot. This

system gives the same high loading density and prill breakage

as the straight venturi loader with an increase in loading rate.

Specifications of pneumatic loading systems are given intable

3. The detonation velocity of AN-FO as a function of charge

AN-FO

hopper!

Borehole ----L . . - _ - - - - J - - , , - - - - - "

Figure 54.-Ejector-type pneumatic AN-FO loader.



52

Table 3 - Characteristics of pneumatically loaded AN-FOin small-diameter blastholes

Loadingdevice

Tank Jetpresure, pressure,psi psi

Loadingdensity,g/cu cm

Loadingrate,'Ib/min

Pressure vessel .Ejector loader (jet ) .Combination loader .

10-30 NApNAp 40-8020 20-80

15-707-1015-25

0.80-0.85.90-1.00.90-1.00

NAp Not appl icable. 'Varies withhosediameter.

diameter for poured and pneumatically loaded charges is

shown in figure 55, The benefits of high-velocity pneumatic

loading are significant at small borehole diameters.

A problem may arise where a high-pressure ejector loader

is used to load AN-FO in small holes in soft formations such as

uranium ore. The pulverized prills may be dead pressed by the

compression from adjacent charges f ired on earlier delays.

This can cause the AN-FO not to fire.Static electricity can be a hazard when' loading AN-FO

pneumatically into small-diameter boreholes. Static electricity

hazards can be reduced bl using antistatic caps or nonelectricinitiators such as Hercudet, Nonel, or DetaUne.A semiconductive

hose with a minimum resistance of 1,000 ohms/ft and 10,000

ohms total resistance, and a maximum total resistance of

2,000,000 ohms for the entire system, should be used. The

pneumatic loader should be properly grounded.

.Homemade loading equipment should not be used. All equip-

ment should be operated at the proper pressure. Gaps in the

powder column can be avoided by keeping the hopper full and

maintaining a constant standoff 'distance between the end of

the loading hose and the column of AN-FO. Loading profi-

ciency improves through operator experience.

' " /s , - - - - ,- - - , - -- - , - - -- - , , -- - - , - -- , - - - -- . - - - -,Q

Pneumatically

p'I.I~:.::_ loaded charges

-: r9S9/CUCm

/I.,/-oso g/cu cm (poured charge)

"'21 2

,:I-U

:: 9U .J

>Zo

~ 6

zoI-

'"o 3L-_-'---_---' __ -'---_---'__ -'---_---'L-_-'---_---'o

/

/I

234 S 6

CHARGE DIAMETER, in

Figure 55.-AN-FO detonation velocity as a function

of charge diameter and density.

7

The pneumatic loading tube is useful for blowing standing

drill water from a horizontal borehole. However, ifthe borehole

is "making water," external protection for the AN-FO by means

of a plastic sleeve is required. Loading inside a plastic bore-

hole sleeve isnot recommended for underground work because

of the static electricity hazard during loading and toxic fumesgenerated during blast ing. I f plastic-sleeve protection with

pneumatic loading in well-ventilated locat ions is required, a

nonelectric detonating system should be used because the

insulating effect of the sleeve is likely to cause a buildup of

static electricity.

BULK SLURRIES

Slurries may be bulk loaded into blasthole diameters as

small as 2 in. These products are frequently poured from bags

(fig. 56), but occasionally bulk pumping units are used (fig. 57).

The sensitivity of slurries, and hence the diameter at which

they may be effectively used, depends largely on their

formulation. The use of bulk slurries in diameters below those

intended for the product can result in substandard blasts ormisfires. The manufacturer should be consulted when loading

bulk slurries into small-diameter blastholes.

PERMISSIBLE

alASTING

Loading blastholes in underground coal mines is strictly

regulated by MSHA in order to prevent ignition of explosive

atmospheres. Only permissible explosives may be used in

underground coal mines. Certain nitroglycerin-based explosives,

emulsions, slurries, and water gels have been certified as

permissible by MSHA (6).

The primer plus the remaining cartridges are string loaded

and pushed back into the hole as a single unit to avoid gett ingcoal dust between the cartridges. Charge weights may not

exceed 31b per borehole. Black powder, detonating cord, and

AN-FO are not permissible. Blastholes are initiated with cop-

per alloy shell electric blasting caps. All holes must be stemmed

with noncombustible material such as water bags or clay

dummies. The stemming length must be at least 24 in or

one-half the depth of the borehole, whichever is less. Addi-

tional rules for permissible blasting are given in the "Blast

Design" chapter. Permissible blasting procedures are also

required for gassy noncoal mines, but are frequently less

stringent than for coal mines.a

LARGE-DIAMETER BLASTHOLES

With few exceptions, economics and efficiency favor the

use of bulk loading in blasthole diameters larger than 4 in. The

products are cheaper, loading is faster, and the well-coupled

bulk charge gives better blasting efficiency. As described in

the "Priming" section of chapter 2, large-diameter blastholes

may be top, center, or toe primed, or multiple primers may be

used.

2Re fe re nc e to s p ec ific t'a de n am e s d oe s n ot im ply e nd ors em e nt b yth e B ure au o f M in es .

PACKAGED PRODUCTS

Large-diameter dynamite cartridges are seldom used today

except for occasional use as primers. AN-FO and slurries give

better economy in large-diameter blastholes. When wet bore-

holes are encountered, and the operator wants to use AN-FO,

water-resistant polyburlap packages of partial ly pulverized,

densified AN-FO are used (fig. 7). Densification is necessary

so that the packages will sink in water. AN-FO packages

should be carefully lowered into water-fi lled holes rather than

dropped, because a broken bag will result in desensitizedAN-FO, an interruption in the powder column and, most likely,



53

Figure 56.-Pourlng alurry Into amallodlameter borehole. (Courtesy Atlss Powder Co.)

som e unfired AN -FO . A disadvantage of w aterproof AN -FOp ack ag es is th at s om e b ore ho le c ou pling is lo st. A ls o th e h ea tlost to the w ater w ill reduce the energy released. W here it isd esire d to u se A N-F O in w et b ore ho le s, th e o ptio n o f b oreh oled ew a te rin g s ho uld b e in ve st ig at ed .

. Slu rr ie s a re a va ila ble in p oly eth yle ne p ac ka gin g in d ia m e-ters up to 8 in (fig. 10). S om e o f th ese p ro du cts a re s em irig ida nd o the rs a re in d im en sio nle ss b ag s th at w ill s lu mp to fit th eb ore ho le d ia me te r. W ith th e s em irig id c artr id ge s, th e a dv an -

ta ge o f b ore ho le c ou plin g is lo st.

BULK DRYBLASTING AGENTS

B ulk lo adin g o ffers s ig nific an t a dv an ta ge s o ve r lo ad in g o fp ack ag ed p ro du cts in la rg e-d iam ete r b la sth ole s, in clu din gch ea pe r p rod uc ts, fa ste r lo ad in g, a nd b ette r u se o f th e a va il-a ble sp ace in the b oreh ole .

The bulk A N -F O or priU s are stored in overhead storagebins, from w hich they are loaded into the bulk trucks. TheA N-F O m ay b e tru ck ed to th e b la st site in pre mix ed fo rm or theoil m ay be m etered into the priU s a s they are placed into the

b la st ho le . B u lk lo ad in g s ys te m s f or d ry b la st in g a ge nt s ( AN - FO )m ay be of the auger or pneum atic type.

A ug er lo ad in g g iv es th e fa ste st lo ad in g ra te s. A s id e-b oo mauger is satisfactory for loading one row of holes at a tim e.W here it is desired to reach m ore holes from one setup, anoverhead-boom auger w ith a 3500 radius of S W ing can beu s ed . W i th t his t yp e o f e q ui pm e n t, f le x ib le t ub in g u s ua ll y e x te n dsfro m th e e nd o f th e a ug er b oo m to g ro un d le ve l. T he a mo un t o fb la stin g a ge nt d eliv ere d in to th e b la sth ole is s om e tim e s in di-

ca te d o n a m ete r in the tru ck . In o th er situ atio ns a h op pe r w itha given volum e of capacity is hung at the end of the augerboom to m easure the A N -FO as it is loaded. Bulk loadingtrucks have capacities of from 2,000 to 10,000 Ib of A N-F O,and w ith auger system s can deliver up to 600 Ib of A N-F O perm in ute in to a b la sth ole .

P n eu m at ic lo ad in g is a ls o u se d in la rg e- dia m et er b or eh ole s.P ne um atic u nits a re e sp ec ia lly u se fu l in ro ug h te rra in , w he re alo ng lo ad in g h ose is u se d to lo ad nu me ro us bla sth ole s fro m as in g le s e tu p .

H and pouring AN -FO from 50-lb bags is still practiced ato pe ra tio ns w he re th e c ap ita l e xp en se o f a b ulk s ys te m c an no tb e ju stifie d. T his , o f c ou rs e g iv es th e s am e c om p le te c ou plin ga s b ulk lo ad in g.



54

Figure 57.-Pumplng slurry Into small-dlameter borehole. (Court • • y D u P on t Co.)

BULK SLURRIES different energy densities to be loaded from hole to hole or in

different locations within a single hole.

The slurry is pumped as a liquid (fig. 58) and a cross-linking

ingredient is added just as the slurry enters the loading hose.

Cross linking to a gelatinous consistency begins in the hose

and is completed in the borehole. A meter on the bulk truck

indicates the amount of slurry that has been loaded.

Hand pouring of slurry from polyethelene packages (fig. 56)

is stil l practiced at operat ions where the volume of slurry used

does not justify a bulk-loading truck, Pouring, rather than

loading the entire package. gives complete borehole coupling.

Bulk slurry pumping iscommonplace in large-diameter vertical-

hole blasting. Some slurry trucks have capacities of up to

30,000 Ib of slurry and have typical pumping rates of 200 to

400 Ib/min. A bulk slurry truck may bring a plant-mixed

slurry to the borehole or it may carry separate ingredients for

onsite mixing.

Onsite slurry mixing is more complex than AN-FO mixing

and is usually done by a competent explosive distr ibutor rather

than the consumer. Plant mixing permits closer quality control

In the blending of Ingredients, whereas onsite mixing permits



55

Figure 58.-Slurry leaving end of loading hose. (Courtesy Du Pont Co.)



56

REFERENCES

1. Atlas Powder Co. (Dallas, TX). Pneumatic Loading of Nitro-

Carbo-Nitrates; Static Electricity, Fumes, and Safe Handling. Undated,

17 pp.

2. Dannenberg, J. How To Solve Blasting Materlals HandlingProblems. Rock Products, v. 74, No.9, September 1971, pp. 63-65.

3: Dick, H. A. Explosives and BorehOle Loading. SUDsectfon 11.7,

SME Mining Engineering Handbook, ed. by A. B. Cummins and I. A.

Given. Society of Mining Engineers of the American Institute of Mining,

Metallurgical, and Petroleum Engineers, Inc., New York, v. 1, 1973,pp.11-78--11-99.


Handbook. 16th ed. , 1978, 494 pp.

5. Langefors, U., and B. A. Kihlstrom. The Modern Technique of

Rock Blasting. John Wiley&Sons, Inc., New York, 1963, 405 pp.

6. U.S. Mine Enforcement and Safety Administration. Active List of

Permissible Explosives and Blasting Devices Approved Before Dec.

31, 1975. MESA Inf. Rep. 1046, 1976, 10 pp.



57

Chapter 4.-BLAST DESIGN

Blast design is not a precise science. Because of the widelyvarying nature of rock, geologic structure, and explosives, it is

impossible to set down a series of equations which will enable

the blaster to design the ideal blast without some field testing.

Tradeoffs must frequently be made indesigning the best blast

for a given situation. This chapter will describe the fundamen-

tal concepts of blast design. These concepts are useful as a

first approximation for blast design and also in troubleshooting

the cause of a bad blast. Field test ing isnecessary to refine the

individual blast dimensions.

Throughout the blast design process, two overriding princi-

pies must be kept in mind. (1) Explosives function best whenthere is a free face approximately parallel to the explosive

column at the time of detonation and (2) there must be ade-

quate space into which the broken rock can move and expand.

Excessive confinement of explosives is the leading cause of

poor blasting results such as backbreak, ground vibrations,

airblast, unbroken toe, flyrock, and poor fragmentation.

Many of the principles discussed in this section were first

presented by Ash (2) 1 and later reported by Pugleise (7)

during a study of quarrying practices in this country.

PROPERTIES AND GEOLOGY OF THE ROCK MASS

The character of the rock mass is a critical variable affect ing

the deslgn and results of a blast. The nature of rock is very

qualitative and cannot be quantified numerically. Rock charac-

ter often varies greatly from one part of a mine to another or

from one end of a construction job to another. Decisions on

explosive selection, blast design, and delay pattern must take

firsthand knowledge of the rock mass into account. For this

reason, the onsite blaster usually has a significant advantage

over an outside consultant in designing a blast. Although the

number of variations in the character of rock is practically

infinite, a general discussion of the subject wil l be helpful. The

Bureau has published a report (7) that discusses the effects of

geology on blast design.

CHARACTERIZING"rHE ROCK MASS

The keys to characterizing the rock mass are a good geolo-

gist and a good driller. The geologist concentrates on obtain-

ing data from the rock surface. Jointing is probably the most

significant geologic feature of the rock. The geologist should

document the direction, severity, and spacing between the

joint sets. In most sedimentary rocks there are at least three

joint sets, one dominant and two less severe. The strike and

dip of bedding planes are also documented by the geologist.The presence of major zones of weakness such as faults,

open beds, solution cavities, or zones of incompetent rock or

unconsolidated material are also determined. Samples of freshly

broken rock can be used to determine the hardness and

density of the rock.An coservant driller can be of great help in assessing rock

variations that are not apparent from the surface. Slow pene-

tration and excessive drill noise and vibration indicate a hard

rock that will be difficult to break. Fast penetration and a quiet

drill indicate a softer, more easily broken zone of rock. Total

lack of resistance to penetration, accompanied by a lack of

cutt ings or return water or air, means that the drill has hit a void

zone. Lack of cuttings or return water may also indicate the

presence of an open bedding plane or other crack. A detailed

dril l log indicating the depth at which these various conditions

exist can be very helpful to the person designing the blast. The

driller should also document changes in the color or nature of

the drill cuttings, which will tell the blaster the location of

various beds in the formation.

ROCK DENSITYAND HARDNESS

Some amount of displacement is required to prepare a

muckpile for efficient excavation. The density of the rock is a

major factor in determining how much explosive is needed to

displace a given volume of rock (powder factor). The burden-to-

charge diameter ratio, which will be discussed in the next

sect ion, "Surface Blasting," varies with rock density, causing

the change in powder factor. The average burden-to-charge-

diameter ratio of 25 to 30 is for average density rocks such as

limestone (2.5 to 2.8 g/cu ern), schist (2.6 to 2.8 g/cu ern), or

porphyry (2.5 to 2.6 g/cu ern), Denser rocks such as basalt (2.9

g/cu cm) and magnetite (4.9 to 5.2 g/cu ern) require smaller

ratios (higher powder factors). Lighter materials such as some

sandstones (2.0 to 2.6 g/cu cm) or bituminous coal (1.2 to 1.5

g/cu cm) can be blasted with higher ratios (lower powder

factors).

The hardness or brittleness of rock can have a strong effect

on blasting results. Soft rock is much more "forgiving" than

hard rock. If soft rock is slightly underblasted, it will probably

st il l be diggable. I f soft rock is slightly overblasted, excessive

violence will not usually occur. On the other hand, slight

underblasting of hard rock will often result in a tight muckpile

that is difficult to dig. Overblasting of hard rock is likely to

cause excessive f/yrock and airblast. Blast designs for hard

rock, then, require closer control and tighter tolerances than

those for soft rock.

VOIDS ANDINCOMPETENT ZONES

Unforeseen voids and zones of weakness such as solut ion

cavities, underground workings, mud seams, and faults are

serious problems in blast ing. Explosive energy always seeks

the path of least resistance (fig. 59). Where the rock burden is

composed of alternate zones of hard material and incompe-

tent material or voids, the explosive energy will be vented

through the incompetent zones, resulting inpoor fragmentation.

Depending on the orientation of the zones of weakness with

respect to free faces, excessive violence inthe form of airblast

' Ital ic ized numbers inparenthese~ refer to i tems in the l ist of references at the

end of this chapter.



58

Solution cavity

Figure 59.-Loss of explosive energy through zones

of weakness.

a nd fly ro ck m ay occ ur. A p articular p ro ble m occ urs w hen th eb la sth ole in te rs ec ts a v oid z on e. In th is s itu atio n, u nle ss p ar tic -

u la r c are is ta ke n in lo ad in g th e c ha rg e, th e v oid w ill b e lo ad edw ith a h ea vy c on ce ntr atio n o f e xp lo siv e, re su ltin g in e xc es siv ea ir bla s t a nd f ly ro c k.

If these vo ids and zones of weakness can be identified ,s te p s can be t aken du rin g bo rehole lo adin g to imp ro ve f ra gmen ta -tio n a nd a vo id v io le nc e. T he b es t to ol fo r th is is a g oo d d rill lo g.The depths of vo ids and incom petent zones encountered bythe drill should be docum ented. The geolog ist can he lp byplottin g the tre nd s o f m ud se am s an d fau lts. W he n ch arg in g.th e b la sth ole , in ert s temm in g ma te ria l, ra th er th an e xp lo siv es ,sho uld b e lo ad ed th rou gh th es e w ea k zo ne s. V oid s sh ou ld befille d w ith s temm in g (fig . 5 2). W h ere th is is im p ra ctic al b ec au seof the s ize of the vo id , it m ay be necessary to block the holeju st a bo ve th e v oid b efo re c on tin uin g th e e xp lo siv e c olu mn , a sd es crib ed in th e "C he ck in g th e B la sth ole " s ec tio n o f c ha pte r 3 .

W here the cond ition of the boreho le is in doubt, the rise ofthe p ow de r co lu mn sho uld b e che cke d freq uen tly as lo ad .in gproceeds. If the colum n fails to rise as expected, there isp ro ba bly a v oid . A t th is p oin t a d ec k o f in ert s te mm in g m ate ria lshou ld be loaded before pow der load ing continues. If thec olu mn ris es m ore ra pid ly th an e xp ec te d, fre qu en t c he ck in gw ill a ssu re th at a de qu ate sp ace is left for ste mm ing .

A lte rn ate z on es o f c om pe te nt a nd in comp ete nt ro ck u su allyre su lt in u na cc ep ta bly b lo ck y fra gm en ta tio n. A h ig he r p ow de rfa cto r w ill s eld om c orre ct th is p ro ble m; it w ill m ere ly c au se th eb lo ck sto b e d is pla ce d fa rth er. U s ua lly th e b es t w a y to a lle via teth is situa tion is to use sm alle r blastholes w ith sm alle r blastpatte rn dim ensions to get a better pow der d istribu tion. Theexp lo siv e ch arge s sh ou ld b e con ce ntra ted in th e com pe te ntrock, w ith the incom petent zones being stem med throughwher eve r po ss ib le .

Unstableperimeter'

Figure 60.-Effect of jointing on the stability of anexcavation.

Figure 61.- Tight and open corners caused by jointing. '

JOINTING

Jointing ca n ha ve a p ro no un ced e ffe ct on b oth frag me nta -tio n an d the sta bility of th e pe rim eter of th e ex cav atio n. C losejo in tin g u su ally re su lts in g oo d fra gme nta tio n. H owe ve r, w id elys pa ce d jo in tin g, e sp ec ia lly w he re th e jo in tin g is p ro no un ce d,o fte n re su lts in a v ery b lo ck y m uc kp ile b ec au se th e jo in t p la ne ste nd to is ola te la rg e b lo ck s in p la ce . W h ere th e fra gm en ta tio nis u na cc ep ta ble , th e b es t s olu tio n is to u se sma lle r b la sth ole s

w ith sm aller b la st pa tte rn dim ension s. T his e xtra drilling an dblas ting e xp en se w ill b e m ore tha n ju stifie d by th e sa Vin gs inload ing, hau ling, and crushing costs and the savings in sec-o nda ry b la st in g .

W here possib le , the perim eter ho les of a b last shou ld bealign ed w ith th e p rin cipa l jo in t sets. T his w ill te nd to p rod uce am ore s ta ble e xc av atio n, w he re as ro ws o f h ole s p erp en dic ula rto a primary jo in t se t w ill tend to produce a more ragged,u ns ta ble p erim ete r (fig . 6 0). J oin tin g w ill o fte n d ete rm in e h owth e co rne rs a t the b ack o f the blas t w ill bre ak o ut. T o m in im izebackbreak and violence, tight corners, show n in figure 61,should be avo ided. The open corner a t the le ft of the figure isp re fe ra ble . G iv en th e p re domin an t jo in tin g in fig ure 6 1, m ores ta ble c on ditio ns w ill re su lt if th e firs t b la st is o pe ne d a t th e fa rrigh t an d is de sig ne d so th at th e h ole in the re ar inside corne rc on ta in s th e h ig he st n um be re d d ela y.

BEDDING

B edd in g ca n a lso ha ve an e ffe ct o n bo th th e fra gm en tatio nan d the stab ility o f th e exca va tion p erim ete r. O pe n b edd in gplan es or b ed s o f w ea k m ate ria l s ho uld b e trea ted a s zo nes o fw ea kn es s. S temm in g, ra th er th an e xp lo siv e, s ho uld b e lo ad edin to the borehole at the location of these zones as show n infig ure 6 2. In a be d of ha rd m aterial, it is often b en eficia l to loa dan e xp lo sive o f h ig he r d en sity tha n is use d in the re ma in de r ofthe borehole. To break an iso la ted bed of hard m aterial nearthe c ollar of th e blasth ole, a de ck ch arg e is reco mm en de d, a ss ho wn in fig ure .6 3, w ith th e d ec k b ein g fire d o n th e s am e d ela yas the m ain ch arg e o r on e de la y la te r. O cca sio nally, s ate llite



kE Y

& i ll ] Stemming

_ E~plo5ive

Open bed

Weak

mater ia I

Figure 62.-Stemmlng through weak material and

open beds.

D EC K C HA RG E SATELLITE HOLE

Hardlone

--i~::~: ~~~_ ',"f\I----'--

KE Y_ Stlmmin9

_ E.pIO,hrt

Figure 63.-Two methods of breaking a hard collar zone.

BLASTHOLE

DIAMETER

l

59

trn • ••• " •• ,,~iable wall

~ /pat.ntlal to._/ problem

Figure 64.-Effect of dipping beds on slope stability

and potential toe problems.

holes are used to help break a hard zone in the upper part of

the burden. Satellite holes are short holes, usual ly smaller in

diameter than the main blastholes, which are drilled betweenthe main blastholes. .

A pronounced bedding plane is frequently a convenient

location for the floor of the bench. It not only gives a smoother

f loor but also may reduce subdril ling requirements.

Dipping beds frequently cause stabili ty problems and diffi-

culty in breaking the toe of the burden. When the beds dip into

the excavation wall, the stabili ty of the slope is enhanced (fig.64). However, when beds dip outward from the wall they form

slip planes that increase the likelihood of slope deterioration.

Blasthole cutoffs caused by differential bed movement are

also more likely. Beds dipping outward from the final slope

should be avoided wherever possible.Altnough beds dipping into the face improve stope stabili ty,

they do create toe problems (fig. 64), as the toe material tends

to break out along the bedding planes. Dipping beds such as

these require a tradeoff. Which is the more serious problem in

the job at hand. a somewhat unstable slope or an uneven toe?

In some cases advancing the opening perpendicular to the

dipping beds may be a good compromise.

Many blasting jobs encounter site-specific geologic condi-

tions not covered in this general discussion. A good explo-

sives engineer is constantly studying the geology of the rock

mass and making every effort to use the geology to his or her

advantage, or at least to minimize its unfavorable effects.

SURFACE BLASTING

The size of blasthole is the first consideration of any blast

design. The blasthole diameter, along with the type of explo-

sive being used and the type of rock being blasted, will deter-

mine the burden. All other blast dimensions are a function of

the burden. This discussion assumes that the blaster has the

freedom to select the borehole size. In many operations one is

limited to a specific size borehole based on available drillingequipment.

Practical blasthole diameters for surface mining range from



60

1------I

I•,: Drilling and blasting costsIII

t300' !II,III1I• Loading ,hauling ,and crushing costs

IIIl. _

~50,~

Blast area = 15,000 sq ft

Borehole diameter = 20 in

Number of holes = 4Total borehole area = 1,256 sq in

Burden = 50 ft

Spacing = 75 It

Blast area = 15,000 sq ft

Barehale diameter = 2 in

Numb!lr 01 holes = 400

Total borehole area = 1,256 sq in

Burden = 51t

Spacing = 7.5 ft

Figure65.-Effect of large and small blastholeson

unit costs.

2 to 17 in. As a general rule, large blasthole diameters yield

low drilling and blasting costs because large holes are cheaper

to drill per unit volume and less sensitive, cheaper blasting

agents can be used in larger diameters. However, larger diam-

eter blastholes also result in large burdens and spacings and

collar distances and hence, they tend to give coarser

fragmentation. Figure 65 (3) illustrates this comparison using

2· and 20-in-diameter blastholes as an example. Pattern Acontains four 20-in blastholes and pattern B contains 400 2-in

blastholes. In all bench blasting operations some compromise

between these two extremes is chosen. Each pattern repre-

sents the same area of excavation, 15,000 sq ft, each involves

approximately the same volume of blastholes, and each can

be loaded with about the same weight of explosive.

Ina given rock formation, the four-hole pattern will give

relatively low dril ling and blasting costs. Drilling costs for the

large blastholes will be low, a low-cost blasting agent will be

used, and the cost of detonators will be minimal. However, in a

difficult blasting situation, the broken material wi ll be blocky

and nonuniform in size, resulting in higher loading, hauling,

and crushing costs as well as requiring more secondary

breakage. Insuff icient breakage at the toe may also result.

On the other hand, the 400-hole pattern will yield highdrilling and blasting costs. Small holes cost more to drill per

unit volume, powder for small-diameter blastholes is usually

more expensive, and the cost of detonators will be higher.

However, the fragmentation will be finer and more uniform,

resulting in lower loading, hauling, and crushing costs. Sec-

ondary blasting and toe problems will be minimized. Size of

equipment, subsequent processing required for the blasted

material, and economics will dictate the type of fragmentation

needed, and hence the size of blasthole to be used.

Geologic structure is a major factor in determining blasthole

diameter. Planes of weakness such as joints and beds, or

zones of soft, incompetent rock tend to isolate large blocks of

rock in the burden. The larger the blast pattern, the more likely

these blocks are to be thrown unbroken into the muckpile.

o

o o

L ar Qer h oles

o o o o

o

Sma Iler holes

Figure 66.-Effect of jointing on selection of blast-hole size. .

Note that in the top pattern in figure 66 some of the blocks are

not penetrated by a blasthole, whereas in the smaller bottom

pattern all of the blocks contain at least one blasthole. Owing

to the better explosives distribution, the bottom pattern will

give better fragmentation. .As more blasting operations are carried out near populated

areas, environmental problems such as airblast and flyrock

often occur because of an insufficient collar distance above

the explosive charge. As the blasthole diameter increases, the

collar distance required to prevent violence increases. The

ratio of collar distance to blasthole diameter required to pre-

vent violence varies from 14:1 to 28:1, depending on the

relative densities and velocities of the explosive and rock, the

physical condition of the rock, the type of stemming used, and

the point of initiat ion. A larger collar distance is required where

the sonic velocity of the rock exceeds the detonation veloci ty

of the explosive or where the rock is heavily fractured or low in

density. A top-initiated charge requires a larger collar distance

than a bottom-initiated charge. As the collar distance increases,

the powder distribution becomes poorer resulting in poorerfragmentation of the rock in the upper part of the bench.

Ground vibrations are controlled by reducing the weight ofexplosive fired per delay interval. This is more easily done with

small blastholes than with large blastholes. Inmany situations

where an operator uses large-diameter blastholes near popu-

lated areas, several delayed decks must be used within each

hole to control vibrations.

Large holes with large blast patterns are ideally suited to an

operat ion with the following characterist ics: A large volume of

material to be moved; large loading, hauling, and crushing

equipment; no requirement for f ine, uniform fragmentation; an

easi ly broken toe; tew ground vibration or airblast problems

(few nearby neighbors); and a relatively homogeneous, easily

fragmented rock without excessive, widely spaced planes of



weakness or voids. Many blasting jobs, however, present

constraints that require smaller blastholes.

In the final analysis, the selection of blasthole size is based

on economics. It is important to consider the economics of the

overall excavation or mining system. Savings realized through

indiscriminate cost cutting in the dril ling and blasting program

may well be lost through increased loading, hauling, and crush-ing costs and increased li tigation costs owing to disgruntledneighbors.

TYPES OFB1.AST-PATTERNS

There are three commonly used drill patterns; square,

rectangular, and staggered. The square drill pattern (fig. 67)

has equal burdens and spacings, while the rectangular pattern

has a larger spacing than burden. In both the square and

rectangular patterns, the holes of each row are lined up directly

behind the holes inthe preceding row. Inthe staggered pattern

(fig. 67), the holes in each row are positioned in the middle of

the spacings of the holes in the preceding row. In the stag-gered pattern, the spacing should be larger than the burden.

the staggered drTIi ing pattern is used for row-on-row fir ing;

that is, where the holes of one row are fired before the holes in

the row immediately behind them as shown in figure 68. The

square or rectangular dri ll ing patterns are used for firing V-cut

(fig. 69) or echelon rounds. Either side of the blast round in

figure 69 by itself would be called an echelon blast round. In

V-cut or echelon blast rounds the burdens and subsequent

rock displacement are at an angle to the original free face.

Looking at figure 69, with the burdens developed at a 450

angle with the original free face, you can see that the originally

square drilling pattern has been transformed to a staggered

blasting pattern with a spacing twice the burden. The simple

patterns discussed here acount for the vast majority of the

surface blasts fired.

Square Rectangular Staggered

I I0 0 0 0

I0 0 0

010 0 0 0

0 I0 0 0 0 I 0 0 0

0 0 0

I0 0 0

I0 0 0 0

0 0 0 0

I 0 0 0 I 0

Figure 67.- Three basic types of drill pattern •

= = I EIJI;/1

Figure 68.-Corner cut staggered blast pattern-

Simultaneous initiation within rows (blasthole spacing,

S, is twice the burden, B).

61

S=28

Figure 69.-V-echelon blast round (true spacing,

S, Is twice the true burden, B).

BURDEN

Figure 70 is an isometric view showing the relationship of

the various dimensions of a bench blast. The burden isdefined

as the distance from a blasthole to the nearest free face at the

instant of detonation. In multiple row blasts, the burden for a

blasthole is not necessarily measured in the direction of the

original free face. One must take into account the free faces

developed by blastholes fired on lower delay periods. As an

example, in figure 68, where one entire row is blasted before

the next row begins, the burden is measured in a perpendicu-

lar direction between rows. However, in figure 69 the blast

progresses in a v-shape. In this situat ion, the true burden on

most of the holes is measured at an angle of 450

from the

original free face, as shown in the f igure.

lfis very important that the proper burden be calculated,

taking into account the blasthole diameter, the relative density

•I

B BurdenJ Subdrilling

T Collar distanceS Spacing

H Hole depth

Figure 70.-lsometric view of a bench blast.



62

of the rock and the explosive, and to som e degree, the lengtho f th e b la sth ole . A n in su ffic ie nt b urd en w ill c au se e xce ssivea irb la st an d flyro ck. T oo la rg e a b urd en w ill g iv e in ad eq ua tef ra gmentat io n, t oe p ro blems, a nd e xces siv e g ro und v ib ra tio ns .W he re it w ill b e n ec ess ary to d rill a ro un d b efo re th e p re vio us

ro un d h as b ee n e xc av ate d, it is im po rta nt to sta ke ou t th e firs tro w o f th e se co nd ro un d b efo re th e firs t ro un d is fire d. T his w illassure a proper burden on the first row of blastholes in thes ec on d b la st ro un d.

T he b urde n d im ens ion is a fu nc tio n o f th e c ha rg e d ia me te r.F or b ulk-lo ad ed c ha rg es, th e c ha rg e d ia me te r is e qu al to th eb la sth ole d iamete r. F or tamp ed c ar trid ge s, th e c ha rg e d iame -ter w ill be betw een the cartridge diam eter and the blastholed iamete r, d ep en din g o n th e d eg re e o f tampin g. F or u ntampe dca rt ridges .the charge d iame te r i s equa l to the ca rt ridge d iame te r.Wh en b la stin g w ith AN -FO o r o th er lo w d en sity b la stin g a ge ntsw ith d en sitie s n ea r 0 .8 5 glcu cm, in ty pic al r oc k w ith a d en sityn ea r 2 .7 glcu cm, th e n orma l b urd en is a pp ro xima te ly 2 5 time sthe charge diam eter. W hen using denser products such asslurries or dynam ites, w ith densities near 1.2 glcu cm , then orma l b urd en is a pp ro ximate ly 3 0 time s th e c ha rg e d iamete r.I t s h ou ld be s tr es sed aga in t ha t t he se a re f ir st a pp ro xima tio ns ,and fie ld testing often results in m inor adjustm ents to theseva lu es. T he b urd en-to -ch arg e-d ia me te r ra tio is se ld om le ssthan 20 or seldom m ore than 40, even in extrem e cases. Forin st an ce , when b la st in g w it h a low densit y b la st in g agent , s uchas A N-F O, In a dense form ation such as iron ore, the desiredburden m ay be about 20 tim es the charge diam eter. W henb la st in g w it h den se r s lu rr ie s o r d ynam it es in low densit y f orma-tions such as som e sandstones or m arbles, the burden m aya pp ro ac h 40 tim es th e c ha rg e d ia me te r. T ab le 4 s ummariz esthese approx imat ions .

Table 4 •• Approxim ate BID ratios for bench blasting

AN·FO (density-O.85 gleu em):Ughl rock (density-2.2 glcu em).... .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. . 28

Average roek (density-2.7 glcu em).... .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. . 25Dense rock (density-3.2 gleu em).... .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. 23

Slurry, dynamile (denslty-1.2 glcu em):

Ughl rock (density-2.2 g/cu em)................................................. 33

Average rock (denslty-2.7 g/cu em)........................................... 30

Dense rock (density-3.2 gleu em).... .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. 27

B Burden D Charge diameler

H ig h-s pe ed p ho to gr ap hs o f b la sts h av e s hown th at fle xin go f th e b urd en pla ys a n im po rta nt role in ro ck fra gm enta tio n. Are la tiv ely lo ng , s le nd er b urd en fle xe s, an d th us bre aks m oree asily th an a sh ort. s tiffe r bu rd en. F ig ure 7 1 s ho ws th e d iffe r-e nc e b etwee n u sin g a 6 -/n b la sth ole a nd a 1 21 /4 -inb la sth ole ina 40-ft bench. w ith a burden-to-charge-diam eter ratio of 30

a nd a pp ro pr ia te sUb dr illin g a nd s temmin g d imen sio ns . Noteth e inh ere nt stiffne ss o f th e b urd en w ith th e 1 21/4-inblastholeas compa red with the B - in b las tho le . Based on this cons ide ra ti on ,lo we r b urde n-to-ch arg e-d ia me te r ra tio s s ho uld b e u sed a s afirst approxim ation w hen the blasthole diam eter is large incom parison to the bench height. C are m ust be taken that theburden ratio is not so sm all as to create violence. O nce thebur den has been det erm in ed , it b ecomes t he bas is f or c alc ula t-in g subdr illin g, c olla r d is ta nce ( st emm ing) , a nd spa cin g.

SUBDRILLING

S ubdrilling is the distance drilled below the floor level toassure that the full face of rock Is rem oved, W here there Is a

A

1+ -1---30---8

r

I , .

1L'L

40'

3'

r

Figure 71.-C om parison of a 121/4-in-diam eter (A)

b la sth ole (stiff b urd en ) w ith a 6 -in-d ia me te r (B) blasthole

(flexible burden) In a 40-ft bench.

p ro noun ced par tin g a t f lo or le ve l, t o wh ic h t he e xp lo siv e cha rgecan conveniently break, subdrilling m ay not be required. Incoal stripping, it is common practice to drill dow n to the coaland then backfill a foot or two before loading explosives,re su ltin g in a n eg ativ e su bd rill. In m ost su rfa ce b la stin g jo bs,how ever. it is necessary to do som e subdrilling to m ake suret~e sho t p ulls t o g ra de . A good f ir st a pp ro xima tio n f or s ubdr illin gunder average conditions is 30 pct of the burden. W here theto e b re ak s v ery e as ily , th e s ub dr ill c an s ome time s b e re du ce dto 10 to 20 pct of the burden. Even under the m ost difficultc on ditio ns , th e s ub drill s ho uld n ot e xc ee d 5 0 p et o f th e b ur de n.If t h e to e c an no t b e p ulle d w ith a s ub drill-to -b urd en ra tio o f 0 . 5,the fault probably lies in too large a burden.

P rim ing the explosive colum n at the toe level gives m axi-

mum c on fin eme nt a nd n orma lly g iv es th e b es t b re ak ag e. O th erfac to rs be ing equa l, toe p rim ing usua lly reqU ires l ess subd ri ll ingt h~n colla r p rim in g.

Too m uch subdrilling is a waste of drilling and blastingexpense and m ay also cause excessive ground vibrationso win g to th e h ig h d eg re e o f c o nfin em en t o f the e xp los ive in th eb otto m o f b la sth ole , p artic ula rly w he n th e p rim er is p la ce d inth e b otto m o f th e h ole . In m ultip le -b en ch o pera tio ns , e xc es-s iv e su bd rillin g m ay ca use u nd ue frac tu rin g in th e u pp er p or-tio n o f th e b en ch b elow, c re atin g d iffic ultie s in c olla rin g h ole sin the low er bench. Insufficient subdrilling w ill cause highbottom , resulting in increased w ear and tear on equipm entand expensive secondary blasting. Table 5 summarizes therecommended subd ri ll ing approximat ions.

T ab le 5 • • A pp ro xima te JIB ratios for bench blastingRalio

Open bedding plane alloe.... .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. . 0

Easy loe 0.1-0.2

Normal loe........................................................................................ .3Dlffleulltoe .4-.5

B Burden J Subdrilling

COLLAR DISTANCE

(STEMMING)

Colla r d ista nc e Is th e d ista nce fro m th e top of th e e xp lo sivech arg e to th e co lla r o f th e b la sth ole . T his z on e is u su ally filled



with an inert material called stemming to give some confine-

ment to the explosive gases and to reduce airblast, Research

has shown that crushed, sized rock works best as stemming

but it is common practice to use drill cuttings because of

economics. Too smal l a collar distance results in excessive

violence in the form of airblast and fly rock and may causebackbreak. Too large a collar distance creates boulders inthe

upper part of the bench. The selection of a collar distance is

often a tradeoff between fragmentation and the amount of

airblast and flyrock that can be tolerated. This is especially

true where the upper part of the bench contains rock that is

difficult to break. In this situation the difference between a

violent shot and one that fails to fragment the upper zone

properly may be a matter of only a few feet of stemming. Collar

priming of blastholes normally causes more violence than

center or toe priming, and requires the use of a longer collar

distance.

Field experience has shown that a collar distance equal to

70 pet of the burden is a good first approximation except where

collar priming is used. Careful observation of airblast, flyrock,

and fragmentat ion will enable the blaster to further ref ine this

dimension. Where adequate fragmentat ion in the collar zone

cannot be attained while stil l controlling airblast and flyrock,

deck charges or satellite holes may be required (fig. 63).

A deck charge is an explosive charge near the top of theblasthole, separated from the main charge by inert stemming.

Ifboulders are being created in the collar zone but the operator

fears that less stemming would cause violence, the main

charge should be reduced slight ly and a deck charge added.

The deck charge is usually shot on the same delay as the main

charge or one delay later. Care must be exercised not to place

the deck charge too near the top of the blasthole, or excessive

f1yrockmay result. As an altemative, short satellite holes between

the main blastholes can be used. These satellite holes are

usually smaller in diameter than the main blastholes and are

loaded with a light charge of explosives.

From the standpoint of publ ic relat ions, collar distance is avery important blast design variable. One violent blast can

permanently alienate neighbors. In a delicate situation, it may

be best to start with a collar distance equal to the burden andgradually reduce this if conditions permit. Collar distances

greater than the burden are seldom necessary.

SPACING

Spacing is defined as the distance between adjacent

blastholes, measured perpendicular to the burden. Where the

rows are blasted one after the other as infigure 68, the spacing

is measured between holes in a row. However, in figure 69,

where the blast progresses on an angle to the original free

face, the spacing is measured at an angle from the originalfree face.

Spacing is calculated as a function of the burden and also

depends on the timing between holes. Too close a spacing

causes crushing and cratering between holes, boulders in the

burden, and toe problems. Too wide a spacing causes inade-

quate fracturing between holes, accompanied by humps on

the face and toe problems between holes (fig. 72).

When the holes in a row are initiated on the same delay

period, a spacing equal to twice the burden will usually pull the

round satisfactori ly. Actually, the V-cut round in figure 69 also

i llustrates simultaneous init iation within a row, with the rows

being the angled lines of holes fired on the same delay. The

true spacing is twice the true burden even though the holes

were originally dri lled on a square pattern.

63

INSUFFICIENT SPACING

Plan View Section View

~r"p"OI,m~ l n ' " , " ,•. .•. ' I'

liGlg,~e\E5)I3(Q) 5kt~e: ,: I,:Boulder lone ,./f# i : : :

Crushed--' • I ' , ~ B O U ' d e r L- - - - - - - - - - - - , 1 -

, • • • • • "- -~--+--t- - -t-- /' \, ;- ; ( r ' , ' , ' , -Overbrealo. Heavi 1 '1crushed and crcterec

EXCESSIVE SPACINGSec lion View

(Between holes)

Hump in face

Plan View

l'

~

i 80.,Ulders~,

iz.L~--

ro o

Toe problem_ Toe problez

I~"lC"""""L••"" ea("'''E''''''=€S''''E''--'''~'"'''El''''''''"Boulder zone Boulder lone

;7-/ - - / . . . • . • .

.-_ '-.-_ <-.------

~Hum.s In fac •

Figure 72.-Effects of insufficient and excessive

ipacing.

Field experience has shown that the use of millisecond

delays between holes in a row results in better fragmentation

and also reduces the ground vibrations produced by the blast.

When millisecond delays are used between holes in a row, the

spacing-to-burden ratiomust be reduced to somewhere between

1.2 and 1.8,with 1.5 being a good first approximation. Various

delay patterns may be used within the rows, including alter-

nate delays (fig. 73) and progressive delays (fig. 74). Generally,

large-diameter blastholes require lower spacing-to-burden ratios

(usually 1.2 to 1.5with millisecond delays) than small-diameter

blastholes (usually 1.5 to 1.8). Because of the complexities of

geology, the interaction of delays, differences in explosive and

• • • • •7 8 7 8 7

'" • • •, • •i\" 5 6 5 6 5

~"

14'"", •,

'O/~• r~ •, % 4 4 3

"

•I

III. - - t2 III

•I

•2

•I

5·148

Figure 73.-5taggered blast pattern with alternate

delays (spacing, S, is 1.4 times the burden, B).

• • •10 II 12

" " - - -,"" 7 8 9",

'l\\~-z -

•,,'0/-4

" "5

",

- -3 14

- -0 II

r-s~f- -7al

-8" ,~,~~"~I? a: J

~\.".,II=III=/'1=01 =11I;/11 ~IIIEIII=/1I:/11 =11I~I/I~1I1 :=/1/':1/ .::,

- I -3 -4 •5

Figure 74.-5taggered blast pattern with progressive

delays (spacing, S, is 1.4 times the burden, B).



64

ro ck s tre ng th s, a nd o th er v ariab le s, th e p ro pe r s pa cin g-to -bu rden ra tio mus t be de te rm ined through onsi te expe rimen ta tion ,u sin g th e p re ce din g v alu es a s fir st a pp ro xim atio ns .

E xc ep t w he n u sin g co ntro lle d b la stin g te ch niq ue s s uch a ssmo oth b la stin g a nd c us hio n b la stin g, w hic h w ill b e d es crib edlate r in th is c hap te r, th e sp ac in g s hou ld n ev er b e le ss th an th eburden.

HOLE DEPTH

In any blast design it is im portant that the burden and theb la sth ole d ep th (o r b en ch h eig ht) b e re as on ab ly c omp atib le .As a r ul e o ft humb for b en ch b la st in g, t he hol e d ep th -t o- bu rd enra tio s ho uld b e b etw ee n 1 .5 a nd 4 .0 . H ole d ep th s le ss th an 1 .5tim es the burden cause excessive airb last and flyrock and,b eca use o f th e s ho rt, th ick sh ap e o f th e b urd en , g iv e c oa rse ,u ne ve n fr agme nta tio n. Wh er e o pe ra tio na l c on ditio ns re qu ir ea ratio of less than 1.5, the prim er should be placed at the toeof the bench to assure m axim um confinem ent. K eep in m indthat placing the prim er in the subdrill can cause increased

g ro un d v ib ra tio ns . If a n o pe ra to r c on tin ua lly fin ds u se o f a h oled ep th -to -b urde n ra tio o f le ss th an 1 .5 n ec ess ary , co ns id er-a tio n sh ou ld b e g ive n to in cre as in g th e b en ch h eig ht o r u sin g asma ller d ri ll .

. l-Io ied-eplhs greater than four tim es the burden are alsou nd esira ble. T he lo nge r a h ole is in re sp ec t to its d ia me te r th em ore e rro r th ere w ill b e in its lo catio n a t t oe lev el, w hich is th em ost critic al po rtio n o f th e b la st. A p oo rly c on tro lle d b la st w illre su lt. E xtre me ly lo ng , s le nd er h ole s h ave e ve n b ee n kn ow nto in te rsec t .

H ig h b en ch es w ith s ho rt b urd en s a ls o c re ate h az ard s, s uc has a sm all drill having to put in the front row of holes near thee dg e o f a h ig h le dg e o r a sm all sh ov el h avin g to d ig a t t he to e o fa p re ca rio us ly h ig h fa ce . T he o bv io us s olu tio n to th is p ro blemis to use a low er bench height. There is no real advantage to a

h ig h b en ch h eig ht. L ower b en ch es g iv e mo re e ffic ie nt b la stin gresults, low er drilling cost and chances for cutoffs, and ares afe r from a n e qu ipmen t o pe ra tio n s ta nd po in t. If it is im pr ac ti-ca l to re du ce th e b en ch h eig ht, la rg er d rillin g a nd roc k h an d-lin g e qu ip me nt sh ou ld b e u se d, w hic h w ill e ffe ctiv ely re du cet he b la st ho le d ep th -t o- bu rd en r at io .

A m ajor problem w ith long slender charges is the greaterp ote ntia l fo r c uto ffs in th e e xp lo siv e c olumn. Wh ere it is n ec es -sary to use blast designs w ith large hole depth-to-burdenra tio s, m ultip le p rim in g s ho uld b e u se d a s in su ra nc e a gain stcutoffs.

DELAYS

M illisecond delays are used betw een charges in a blastro un d fo r th re e r ea so ns :

1. To assure that a proper free face is developed to enableth e e xp lo siv e c ha rg e to e fficie ntly fra gm en t a nd d isp la ce itsburden.

2 . T o e nh an ce fragme nta tio n b etw ee n ad ja ce nt h ole s.

3. To reduce the ground vibrations created by the blast.

There are num erous possib le delay patterns, several ofw hich w ere covered in figures 68,69,73, and 74.

Andrews (1), o f d u Pont , c on du ct ed nume ro us f ie ld i nv es tig a-tio ns to d ete rm in e o ptim um d ela y in te rv als fo r b en ch b la stin gand r ea ched t he f ol low in g con cl us io ns .

IN AO EO UA TE D ELA YS A DEO UA TE D ELA YS

- - - - - - P l I · - ± " " - " • •- - ---- ---Pi floor

Figure 75.- The effect of Inadequate delays betweenrows.

1 . T he d ela y tim e b etw ee n h ole s in a ro w sh ou ld b e b etw ee n1 and 5 m s per foot of burden. D elay tim es less than 1 m s perf oo t o f b ur de n cau se p rematur e s hear in g between hole s, r es ul t-in g in c oa rs e fra gme nta tio n. If a n e xc es siv e d ela y tim e is u se d

b etw ee n h ole s, ro ck mo veme nt from th e fir st h ole p re ve nts th ea dja cen t h ole fro m c re atin g a dd itio nal fra ctu re s b etw ee n th etwo holes. A delay of 3 ms per foot of burden gives goodresults in m any K inds of rock .

2. The delay time between rows should be two to threetim es the delay tim e between holes in a row. This is longerthan m ost previous recommendations. H ow ever, in order toobtain good fragm entation and control flyrock, a sufficientd ela y is n ee de d so th at th e b urd en fro m p re vio us ly fire d h ole shas enough tim e to m ove forw ard to accom modate brokenrock from subsequent row s. If the delay betw een row s is tooshort, m ovem ent in the back row s w ill be upw ard rather thano utw ard (fig . 7 5) .

3. W here airb last is a problem . the delay betw een holes in arow should be at least 2 ms per foot of spacing. This w illp re ve nt a irb la st fro m o ne ch arg e fro m a dd in g to th at o f su bse -quent charges as the blast proceeds dow n the row .

4. For the purpose of contro lling ground vibrations, m ostregulatory authorities consider tw o charges to be separateevents if they are separated by a delay of 9 m s or m ore.

F ollo win g th es e r ec ommen da tio ns s ho uld y ie ld g oo d b la st-in g re su lts. H ow ev er, w he n u sin g su rfac e d ela y s ys tem s su cha s d eto na tin g c ord c on ne cto rs a nd s eq ue ntia l tim in g b la stin gm ach in es, th e ch an ce s fo r c uto ffs w ill b e inc re as ed . T o s olv eth is p ro ble m, in -h ole de la ys sh ou ld b e u se d in a dd itio n to th es urfa ce d ela ys . F or in sta nc e, w he n u sin g s urfa ce d eto na tin g

cord connectors, one m ight use a 1 oo-m s delay in each hole.This causes ignition of the in-hole delays w ell in advance ofrock m ovem ent, thus m inim izing cutoffs. W ith a sequentia ltim er, the sam e effect can be accom plished by avoid ing theuse of electric caps w ith delays shorter than 75 to 100 m s.

F rom th e s ta nd po in t o f s im p lic ity in b la st d es ig n it is b es t if a llth e e xp lo siv e in a b las th ole is fire d as a s in gle c olu mn c ha rg e.Howeve r , i t i s somet imes necessa ry, whe re f ir ing large b las tho lesin populated areas, to use tw o or m ore delayed decks w ith in ab la sth ole to re du ce g ro un d v ib ra tio ns . B la st ro un ds o f th is ty pec an b ec om e q uite c om ple x, a nd sh ou ld b e d es ig ne d u nd er th eg uid an ce o f a comp ete nt p erso n.

A ll c ur re nt ly u se d del ay d et on at or s emplo y p yr ot ec hn ic d el ayelem ents. That is, they depend on a burning pow der train forthe ir d ela y. A lth ou gh th es e d ela ys a re re aso na bly ac cu ra te ,



overlaps have been know n to occur (9). T he re fo re , w he n it isessential that one charge fires before an adjacent charge,such as in a tight corner of a blast, it is a good idea to skip adelay period. D evelopm ent of blasting caps w ith electronicd ela ys is a g oo d fu tu re p os sib ility .

POWDER FACTOR

P ow der factor, in the opinion of the authors, is not the bestto ol fo r d es ig nin g b la sts .B la st d es ig ns s ho uld b e b as ed o n th e d ime ns io ns d is cu ss ed

e ar lie r in th is c ha pte r. H owev er , p owde r fa cto r is a n ec es sa ryca lcu latio n fo r c ost a cc ou ntin g p urp os es. In b la stin g o pe ra -tions such as coal stripping or construction w ork w here theexcavated m aterial has little or no inherent value, pow derfa cto r is u su ally e xp re ss ed in te rm s o f p ou nd s o f e xp lo siv e p ercubic yard of m aterial broken. Pow der factors for surfaceb la sting c an va ry fro m 0 .2 5 to 2 .5 Ib /c u y d, w ith 0 .5 to 1 .0 Ib /cuy d b ein g mo st ty pic al.

Pow der factor for a single blasthole is calculated by thefol low ing formu la :

L(0.3405d)(D 2)

P.F. = (B)(S)(H)/(27)

whe re P .F . = pow der factor, pounds of explosive per cubicy ard o f ro ck ,

L = le ng th o f th e e xp lo siv e c ha rg e, fe et,d = density 01 th e e xp lo siv e, g rams p er c ub ic c en ti-

meter,D = cha rge d iameter , in ches ,B = burden d imens io n, f ee t,S = spacin g d imens io n, f ee t,

and H = b en ch h eig ht, fe et.

Many exp lo siv es compan ie s pub lis h t ab le s t ha t g iv e lo ad in gd en sitie s in p ou nd s p er fo ot o f b la sth ole fo r d iffe re nt c omb in a-tions of d and D . The nom ograph in figure 14 also calculatesthe density in pounds per foot of borehole. P ow der factor is afu nc tio n o f ty pe o f e xp lo siv e, ro ck d en sity , a nd g eo lo gy . T ab le6 g iv es ty pic al p owde r fa cto rs fo r s ur fa ce b la stin g.H ig he r e ne rg y e xp los ive s, s uch a s th os e c on tain in g la rg e

am ounts of alum inum , can break m ore rock per pound thanlow er energy explosives. H ow ever, m ost of the commonlyu se d e xp lo siv e p ro du cts h av e fa ir ly s im ila r e ne rg y v alu es a ndth us h av e s im ila r ro ck b re ak in g ca pa bilitie s. S oft, lig ht ro ckre qu ir es le ss e xp lo siv e p er y ard th an h ard , d en se ro ck . L arg e-ho le p atte rn s re qu ire le ss e xp lo sive p er ya rd o f roc k b la ste db ec au se a la rg er p ro po rtio n o f ste mm in g is us ed . O f c ou rse ,

la rg er b la sth ole s fre qu en tly re su lt in c oa rs er fr agme nta tio nb ec au se o f p oo re r p owde r d is tr ib utio n. Mas siv e ro ck w ith fewex isting c ra ck s o r pla ne s o f w ea kn es s re qu ire s a h ig he r p ow -d er fa cto r th an a fo rmatio n th at h as n ume ro us , c lo se ly s pa ce dg eo lo gic fla ws . F in ally , th e mo re fre e fa ce s a b la st h as to b re ak

Table 6. - Typical powder factors for surtaea blasting

Degree of difficulty

in rock breakage

Powder factor,

Ib/cu yd

Low .................................•..............................................

Medium .. .

High .

Very high .

0.25-0.40

.40- .75

.75-1.25

1.25-2.50

65

to, the low er w ill be the pow der factor. For instance a cornerc ut, w ith two v ertic al fre e fa ce s, w ill re qu ir e le ss p owde r th an abox cut w ith only one vertical free face; and a box cut w illrequire less powder than a sinking cut, which has only theground surface as a free face. In a sinking cut it is desirable,

w here possible, to open a second free face by using a V-cuts omewh ere n ea r th e c en te r o f th e r ou nd . V -c uts a re d is cu ss edin m ore detail in the "U nderground Blasting" section of thischapter.

Wh en b la stin g ma te ria ls th at h av e a n in he re nt v alu e p er to n,su ch a s lim es ton e o r m eta llic o re s, p ow de r fac to rs a re some -tim es e xp re sse d a s p ou nd s o f e x plo siv e p er to n o f ro ck o r t on so f ro ck p er p ou nd o f e xp lo sive .

SECONDARYBLAS'!ING

Som e prim ary blasts, no m atter how well designed, w illleave boulders that are too large to be handled efficiently by

the loading equipm ent or large enough to cause plugups inc ru sher s o r p re pa ra tio n p la nts . Seconda ry f ra gmentat io n t ech-n iq ue s m us t b e u se d to b re ak the se b ould ers .In the case of boulders too large to be handled, the loader

o pe ra to r w ill s et th e b ou ld er s a sid e fo r tre atme nt. Id en tify in gm ate ria l la rg e e no ugh to c au se p lu gu ps is n ot a lw ay s q uite soa pp are nt. T he op era tor m ust b e in stru cte d to w atc h fo r m ate -ria l that is sm all enough for convenient loading but w hich islarge enough to cause a bottleneck later in the processingcycle.Seconda ry f ra gmentat io n can be accomp lis hed in f ou r ways :

1. A heavy ball suspended from a crane m ay be droppedrepeatedly on the boulder until the boulder breaks. This is arelatively ineffic ient m ethod, and breaking a large or tough(n on b rittle ) ro ck m ay ta ke a co ns id erab le p erio d o f tim e. T hism etho d is a de qu ate w he re th e n um be r o f b ould ers p ro duc edis not e xces siv e.

2. A hole may be drilled into the boulder and a wedgingd ev ic e in se rte d to s plit th e b ou ld er. T his is a ls o a s low me th odb ut ma y b e s atis fa cto ry whe re o nly a lim ite d amoun t o f s e co nd -a ry fra gm en ta tio n is n ece ss ary . A n a dv an ta ge o f th is m eth odis th at it d oe s n ot c re ate th e fly ro ck a ss oc ia te d w ith e xp lo siv ete ch niq ue s o r, to some d eg re e w ith d ro p b alls .

3. Loose explosive m ay be packed into a crack or depres-sio n in th e bo uld er, c ove re d w ith d am p e arth en m ate ria l, a ndfir ed . T his ty pe o f c ha rg e is c alle d a mudc ap , p la ste r, o r a do bech arg e. T his m eth od is in effic ie nt b eca us e o f a la ck o f e xp lo -s iv e co nfin em en t, a nd re la tiv ely la rg e am ou nts o f e xp lo siv e

a re re qu ire d. T he r es ult is c on sid era ble n ois e a nd fly ro ck , a ndo fte n, a n in ad eq ua te ly b ro ke n b ou ld er. T he s ys tem is h az ard -o us be ca use th e p rim ed c ha rg e, lyin g o n th e s urfa ce , is p ro net o a cc id en ta l in it ia tio n b y e xt er na l impac ts f rom fallin g r oc ks o requipm ent. External charges should be used to break boul-d ers o nly w he re d rillin g a h ole is im pra ctica l, a nd w he n u se d,e xtre me c au tio n c on ce rn in g n ois e, fly ro ck , a nd a ccid en ta lin it ia tio n t hr ough impac t must b e e xe rc is ed . I f i t is f ound neces -sary to shoot a m ultip le m udcap blast, long delays or cap andfu se a re n ot re commend ed .

4 . T he m ost e ffic ie nt m eth od o f s ec on da ry fra gm en ta tio n isthrough the use of small (1- to a-tn) b or eh ole s lo ad ed w ithexplosives. The borehole is norm ally collared at the m ostconvenient location such as a crack or a depression in the



• 0 0

• • 0 •0 0 •• 0 • 0 0

• 0 0

• •

•0 0

• •0 • • 000 • 00

0 0

• 0 0 ••EY• Loaded ncres o Unloaded holes

Figure n.-Six designs for parallel hole cuts.

tria l a nd e rro r is u su ally in vo lv ed in d ete rm in in g th e b es t p ara l-le l hole cut for a specific m ine.

F or a ll ty pe s o f op en in g cu ts it is im po rta nt th at th e c ut p ulls

to its planned depth, because the rem ainder of the round w ill

67

not pull m ore deeply than the cut. In blasting w ith burn cuts,ca re m ust b e e xe rcise d n ot to o ve rlo ad th e b urn h ole s, a s th ismay cause the cut to "freeze" or not pull properly. Properloading of the cut depends on the design of the cut and thetype of rock being blasted, and often m ust be determ ined byt ria l a nd e rr or .

S om e re se arch h as b ee n d on e in vo lv in g b urn c uts w ith on e

o r m ore la rg e ce ntra l h ole s (8 ), a nd a fe w m in es h av e a do pte dth is p ra ctic e. T he a dv an ta ge of th e la rge ce ntra l h ole is th at itg iv es a d ep en da ble v oid to whic h s uc ce ed in g h ole s c an b re ak ,w hich is not alw ays obtained w ith standard burn cuts. Thisassures a more dependable and deeper pull of the blastround. The disadvantages of the large central hole are thereq uire me nt fo r a n e xtra p ie ce o f e qu ipme nt to d rill th e la rg eh ole a nd th e e xtra tim e in vo lv ed . S om etim es a c om promis e isused whe re in te rmed ia te -s ized ho les ,such as 4 - o r 50 ind iame te r,a re d rille d u sin g th e s ame e qu ipmen t u se d to d rill th e s ta nd ar dblast holes.

In some s oft m ateria ls, p artic ula rly co al, th e b la ste d c ut isreplaced by a saw ed kerf, iJsually at floor level (fig. 79). Inaddition to giving the m aterial a dependable void to w hich tobre ak, th e s aw ed cu t a ss ure s tha t th e flo or of th e o pe nin g w ill

b e smoo th .

Figure 78.-Drill template for parallel hole cut. (Courtesy Du Pont Co.)



68

UNDERCUT

Front v iew Side view

=lfI~fI;;II/~I/=II/EIIF-/!/~111,.,11=1/1-'''- -I=1/1-, -'''-''',..",

III •

iii 5 ~ ~~

~

. . .~

- ::: 2 I 3 == -1111If-- ~

" I ~ III:~JIr"'I/I:: 111-;;1//;'1/1_111 :::1/l2IiT _ III

•

.I/I-III<]I/~III ~ // I >;/11 "ill -1/1=

OVERCUT

Side view

l1l=lllf§-Wsljt::;;.,1/ ~/!;::-I -

1 /1 ",1 1/" I= :I ~I/~ .;;JiI~/iI

KEY

~ Blosthole delay period

Figure 79.-8Iast round for soft material using asawed kerf.

BLASTINGROUNDS

Once the opening cut has established the necessary free

face, the remainder of the blastholes must be positioned so

that they successively break their burdens into the void space.

Itis important to visualize the progression of the blast round so

that each hole, at its time of initiation, has a proper free face

parallel or nearly parallel to it. Figure 80 gives the typicalnomenclature for blastholes in a heading round.

The holes fired immediately after the cut holes are called therelievers. The burdens on these holes must be carefully planned.

If the burdens are too small the charges will not pull their

share of the round. If the burdens are too large the round may

freeze owing to insufficient space into which the rock can

expand. After several relievers have been fired, the opening is

usually large enough to permit the design of the remainder of

.3 • • •2 2• • • 3•

• 1 0 I•

.3 • • 0 0 • • 3.

.,•3 • • •2 2• . . • 3 •

.5 • 5 • 5 • 5 5 • 5. 5• 5 •

KEY

o Empty holes 3 Ri~ holesI Loaded burn holes 4 Bock holes2 Helper~or relieyers 5 Lit te rs

Figure 8O.-Nomenclaturefor blastholes in a heading round.

V-CUT ROUND SL ABBING ROUND

Top view Top view

Front view Front view

~'. . . . . - .

> ! • • • •r~••••1····~:. .

. .· .· .· .· .FIgure 81.-Angled cut blast rounds.

the blast in accordance with the principles discussed underthe "Surface Blasting" section. In large heading rounds, the

burden and spacing rat ios are usually slightly less than those

for surface blasts. In small headings, where space is limited,

the burden and spacing ratios will be still smaller. This is

another area where trial and error plays a part in blast design.The last holes to be fired in an underground round are the

back holes at the top, the rib holes at the sides, and the lifters

at the bottom of the heading. Unless a controlled blasting

technique is used (discussed later in this chapter) the spacing

between these perimeter holes is about 20 to 25 blasthole

diameters. Figure 81 shows two typical angled cut blast rounds.

Afterthe initial wedge of rock isextracted by the cut, the angles

of the subsequent blastholes are progressively reduced until

the perimeter holes are parallel to the heading or looking

slightly outward. Indesigning burden and spacing dimensionsfor angled cut blast rounds, the location of the bottom of the

hole is considered rather than the collar.

t"igure 82 shows two typical parallel hole cut blast rounds. I t

can be seen that these rounds are much simpler to drill than

angled cut rounds. Once the central opening has been

established, the round resembles a bench round turned on its

REGULAR LARGE-HOLE

Top view Top view

U/IE = I 2/1 1$ ,: t

'M ( II

I III II II II II I

/=/ I " " , " , , 1 ,~/f III III~ III -

~ III'"II

Front view

~",=IJI:=/Ir=III=1/1 =11/""1II=1f(=/ I I • • • • • • If~ F -%. .~- =~ • : 0 : • • ~~ W- . • . • . • .• . :: :

III~IIII::; II / ::'111: 1/11_III:: IIII~ III

Front view

~ J/;;III~I"=J/I=-, :"1ff':I/1==///-'lf

III. • • • • _

~ fi,III =

~. . 0·· .;;j~ -~. . .~~ ' - • • • • • • • • / 1 1

~/I/"?=/II_11i -llIelll;<./I/:=t1l = . 0 11 = 0 / 11 _

Figure 82.-Parallel hole cut blast rounds.



69

• 10 .g .e .7 7. e. g• 10.

.9 .e •6 .4 4• 6. e. 9.

• 2 0 2 •.e .7 .5 0 0 5. 7. e•

• 1

.9 .e .6 • 3 3• 6. e. 9.

- =• 10 • 9 .e .7 7• e• 9. 10.

KE Y

0 Unloadedhole .9 Loadedhole withdelay period

Figure 85.- Typical burn cut blast round delay pattern.

BURN CUT

V-CUT

1\

Figure 83.-Fragmentation and shape of muckpileas a function of type of cut.

side. Figure 83 shows a comparison of typical muckpiles

obtained from V-cut and burn-cut blast rounds. Burn cuts give

more uniform fragmentation and a more compact muckpile

than V-cuts, where the muckpile is more spread out and

variable in fragmentation. Powder factors and the amount of

drilling required are higher for burn cuts.

DELAYS

Two series of delays are available for underground blasting;

millisecond delays, which are the same as those used in

surface blasting, and slow, or tunnel delays. The choice of

delay depends on the size of the heading being blasted and on

the fragmentat ion and type of muckpile desired. Slow delaysgive coarser fragmentat ion and usually give a more compact

muckpile whereas millisecond delays give finer fragmentation

and a more spread out muckpile (fig. 84). In small headings

where space is limited, part icularly when using paral lel hole

SLOW DELAY

'.

MILLISECONP DELAY

Figure 84.-Fragmentation and shape of muckpileas a function of delay.

TOP VIEW

KEY

. 4 Loaded hole with delay periodFigure 86.-Typical V-cut blast round delay pattern.

BACK HOLES FIRED LAST

LIFTERS FIRED LAST

Figure 87.-Shape of muckpile as a function of orderof firing.



70

c ut ro un ds, slo w d ela ys a re n ec ess ary to a ssu re th at the ro ckfr om e ac h b la sth ole h as tim e to b e e je cte d b efo re th e n ex t h olefire s. Wh er e a c ompr om is e b etwee n th e re su lts o f m illis ec on dd ela ys a nd s lo w d ela ys is d esire d, some o pe ra to rs u se m illi-s eco nd d ela ys an d s kip d ela y p erio ds.

In a n u nd erg ro un d b la st ro und it is e ss en tia l th at th e d ela y

p atte rn b e d es ig ne d s o th at e ac h h ole , a t its tim e o f f irin g, h as agood free face to w hich it can displace its burden. Figure 85show s a typical delay pattern for a burn cut blast round in aheading in hard rock. Figure 86 show s a delay pattern for aV -c ut b la st r ound .

The shape of the m uckpile is affected by the order in w hichthe d ela ys a re fire d (fig . 8 7). If th e b las t is d esig ne d so th at th eback holes at the roof are fired last, a cascading effect is

o bt ain ed , r es ult in g in a compac t muckpile . I f t he lif te rs a re f ir edla st, th e mu ck pile w ill b e d is pla ce d away from th e fa ce .

POWDER

FACTOR

A s w ith s urfa ce b la stin g, p ow de r fa cto rs fo r u nd erg ro un db la stin g v ary d ep en din g o n s ev er al fa cto rs . P owde r fa cto rs fo runderground blasting m ay vary from 1.5 to 12 Ib/cu yd. S oft,lig ht r oc k, h eadin gs w it h la rg e c ro ss sec tio ns , la rg e b la st ho le s,a nd a ng le c ut ro un ds a ll te nd to g ive lo we r p ow der fa cto rs th anh ard , d en se ro ck , small h ea din gs , sma ll b la sth ole s, a nd p ara l-le l h ole c uts .

UNDERGROUND COAL MINE BLASTING

Und er gro un d c oa l m in e b la stin g is d iffe re nt from mo st r oc k

b la stin g in tw o im po rta nt re sp ects . O pera tio ns ta ke p la ce in apot en tia lly e xp lo siv e a tmosphe re con ta in in g me thane and coa ldust, and the coal is much easier to break than rock. Thelo ad in g a nd firin g me th od s, a s well a s th e e xp lo siv e ty pe , mu stbe perm issible, as specified by the M ine Safety and H ealthA dm in istra tio n (MSHA). In a dd itio n, u nd erg ro un d co al m in eb la stin g is clo se ly reg ula te d b y S tate re gula to ry a gen cie s.This discussion is intended to point out som e of the m aind if fe re nces between coa l b la st in g and roc k b la st in g and shouldnot be considered as a guide to regulatory com pliance. Per-sons involved in underground coal m ine bla~ting need tob ecome th oro ug hly fa milia r w ith th e MSHA re gu la tio ns d ea l-in g w it h perm is sib le b la st in g, wh ic h a re id en tif ie d in AppendixA , a nd th os e o f th e S ta te in w hic h th ey b la st. H ercu le s (6 ) h aspubl ished a shot fi re r' s gu ide for unde rg round coal m ine b las ti ng .

B la ck powder o r o th er n onpe rm is sib le e xp lo siv es , in clu din g.detonating cord, m ay not be stored or used in undergroundco al m ine s. U nc on fin ed s ho ts, tha t is, th os e n ot c on ta in ed b yb ore hole s, m ay n ot b e fire d a ltho ug h a p erm iss ible , e xte rna lcharge is currently under developm ent. In m ost S tates thec oa l mu st b e u nd erc ut (fig . 7 9) b efo re b la stin g. T he b ore ho le ssh ou ld n ot b e d ee pe r th an th e cu t to a ss ure tha t th e c oa l is n otfired off the solid. The m inim um depth of cut should be 3% ft.

C ha rg e w eig hts sh ou ld n ot e xce ed 3 Ib p er b ore ho le . B ore -h ole s s ho uld h av e a m in im um 1 8-in b urd en in a ll d irec tio ns . Ifth is s pe cific atio n ca nn ot b e m et, th e ch arg e w eig ht sh ou ld b e

re du ce d to p re ve nt u nd erb urd en ed s ho ts . B la st ro un ds s ho uld

b e lim ite d to 2 0 h ole s. A ll h ole s s ho uld b e b otto m prim ed w iththe cap at the back of the hole, although this is not alwaysre qu ire d b y re gula tio n. A lu min um -c ase d d eto na to rs s ho uldnot be used and leg w ires should not be m ore than 16 ft long,o r o f e qu iv ale nt r es is ta nce. Perm is sib le b la st in g mach in es a redesigned to provide sufficient energy to a circuit using ther ate d n umb er o f e le ctric b la stin g c ap s w ith 1 6·ft iro n le g w ire s.S ho uld th ese m ach in es b e u se d w ith co pp er w ire d eto na to rs ,th eir a pp are nt c ap ac ity is in cre ase d. Z ero -d ela y d eto na to rsshou ld no t be used i n a c ir cu it w i th m i ll isecond-de lay de tonators.

P e rm is sib le e xp lo siv es must r ema in in t he o rig in al c ar tr id gew ra pp er th ro ug ho ut sto ra ge a nd u se , w ith ou t a dm ixtu re w itho th er su bs ta nce s. C artrid ge s m us t b e lo ad ed in a co ntin uo ustr ain , in c on ta ct w ith e ac h o th er, a nd s ho uld n ot b e d elib er ate lycrushed, deform ed, or rolled. P erm issible explosives m ust

c on fo rm w it h t he ir o rig in al s pe cif ic at io ns , w it hin lim it s o f t ole r-ance prescribed by M SHA. T he cartridge m ust be of a diam e-te r whic h h as b ee n a pp ro ve d. A ll b la sth ole s mu st b e s temmedw ith incom bustib le m ateria l. H oles deeper than 4 ft shouldco nta in a t l ea st 2 4 in o f ste mm in g a nd h oles le ss th an 4 ft de epshould be stemmed for at least half their length. W ater stem -m ing bags, when used, should be at least 15 in long andsh ou ld h ave a d ia me te r w ith in % in o f th e b ore ho le d iamete r.Shots m ust be fired w ith a perm issible blasting unit of ade-quate capac it y.

CONTROLLED BLASTING TECHNIQUES

The term controlled blasting is used to describe severaltechniques for im proving the com petence of the rock at thep er ime te r o f a n e xc av atio n. Du P on t, amon g o th er c ompa nie s,has published an excellent pam phlet describ ing and givinggeneral specifications for the four prim ary m ethods of con-trolled blasting (5). M uch of this discussion is adapted fromthat publication. The recommended dim ensions have beendet erm in ed t hr ough yea rs o f o n- th e- jo b t es tin g and e va lu at io n.T he se r ecommended d imens io ns a re g iv en a s r ange s o f v alu es .The best value for a given blasting job is a function of thegeology, specifically the num ber and severity of planes ofw eakness in the rock, and the quality of rock surface that is

re qu ire d. Norma l b la stin g a ctiv itie s p ro pa ga te c ra ck s in to th eexcavation w alls. These cracks reduce the stability of theo pe nin g. '[h e p urp os e o f c on tro lle d bla stin g is to re du ce th ispe rimeter c racki ng and thus i nc rease the s tab il it y o f the open ing .F ig ur e 88 shows a s ta ble s lo pe p rodu ced b y con tr olle d b la st in g.

LINE

DRILLING

L in e d rillin g in vo lve s th e d rillin g o f a ro w o f c lo se ly s pac edh ole s a lo ng th e fin al e xc av atio n lin e. It is n ot re ally a b la stin g



71

Figure 88.-Stable slope produced by controlled blasting. (Courtesy Austin Powder Co.)

technique since the line-drilled holes are not loaded with

explosive. The line-dri lled holes provide a plane of weakness

to which the final row of blastholes can break and also reflect a

portion of the blast's stress wave. Line drill ing isused mostly in

smal l blasting jobs and involves small holes in the range of 2-

to 3-;n diameter. Line drilling holes are spaced (center to

center) two to four diameters apart. The maximum practical

depth to which line drilling can be done is governed by how

accurately the alignment of the holes can be held at depth, and

is seldom more than 30 ft.- To further protect the final perimeter, the blastholes adja-

cent to the line drill are often more closely spaced and are

loaded more lightly than the rest of the blast, using deck

charges and detonating cord downlines if necessary. Best

results are obtained in a homogeneous rock with little jointing

or bedding, or when the holes are aligned with a major joint

plane.

. The use of line drilling is limited to jobs where even aUght

load of explosives inthe perimeter holes would cause unaccept-

able damage. The results of l ine dri ll ing are unpredictable, the

cost of dri ll ing is high, and the results are heavily dependent on

the accuracy of dril ling. Table 7 gives average specificationsfor line drilling.

Table 7.• Average specifications for line drilling

H ole d iame te r. in

2.00 .

3.00 .

Spac in g . I t

0.33-0.67

.50-1.00

PRESPLln·ING

Presplitting, sometimes calledpreshearing, issimilar to linedril ling except that the holes are dril led farther apart and a very

light load of explosive is used in the holes. Presplit holes are

fired before any of the main blastholes adjacent to the presplit

are fired. Although the specific theory of presplitting is in

dispute, the light explosive charges propagate a sheared zone,

preferably a single crack, between the holes, as shown in

figure 89. In badly fractured rock, unloaded guide holes may

be drilled between the loaded holes. The light powder load

may be obtained by using specially designed slender cartridges,

partial or whole cartridges taped to a detonating cord downline,

explosive cut from a continuous reel, or even heavy grain

detonating cord. A heavier charge of tamped cartridges is

used in the bottom few feet of hole. Figure 90 shows three



72

.. ".~< " • • • ~ { ,. , . • •

Figure 89-crack generated by a presplit blast. (Courtesy Austin Powder ce.)



Detonotingcord

Continuousreelexplosive

CouplerStandard

cartridgeSlender

cartridge

Heovier toe loads

Figure 90.- Three typical blasthole loads for presplitting.

ty pe s o f b la sth ole lo ad s u se d fo r p re sp littin g. M an y o pe ra to rs

n ow u se%-

o r % · in b y 2 -f t c ar tr id ge s c on ne ct ed w it h c ou ple rs .It is desirable to com pletely stem around and betw een thecartridges in the borehole. It is also desirable, although note ss en tia l, to fire a ll th e p re sp lit h ole s o n th e s am e d ela y p erio d.The m axim um depth for a single presplit is lim ited by thea cc ura cy o f th e drillh ole s, a nd is u su ally ab ou t 5 0 ft. A d evia -tion of greater than 6 in from the desired plane of shear w illg iv e in fe rio r re su lts . O ne s ho uld a vo id p re sp littin g fa r a he ad o fth e p ro du ctio n b la st. It is p re fe ra ble to p re sp lit a s ho rte r se c-tion and dig that section out so that the quality of the presplitc an b e c he ck ed . If th e p re sp lit is u ns atis fa cto ry , a dju stm e ntscan be m ade in subsequent blasts.

S om e o pe ra to rs p re fe r to fir e th e p re sp lit w ith th e m a in b la stb y firin g th e p re split h ole s o n th e first d ela y p erio d. A lth oug hp r es p li tt in g i s u s ua lly t ho u gh t o f a s a s u rf ac e b la s tin g t ec h ni qu e ,it is o cc as io na lly u se d u nd erg ro un d. T he in cr ea se d h ole s pa c-in g r ed uc es d rillin g c os ts a s c om pa re d w ith lin e d rillin g. T ab le8 g iv es a ve ra ge s pe cif ic at io ns fo r p re sp lit tin g.

Table 8.• Average specifications for presplltting

Hole Spacing, Explosive

diameter, II charge,

in Ibll l

1.50-1.75 1.00-1.50 0.08-0.25

2.00-2.50 1.50-2.00 .08- .25

3.00-3.50 1.50-3.00 .13- .50

4.00 2.00-4.00 .25- .75

73

SMOOTH BLASTING

S mo oth b la stin g, a lso ca lle d c on to ur b la stin g, p erim ete rb la stin g, o r s cu lp tu re b la stin g, is th e m o st w id ely u se d m e th odof controlling overbreak in underground openings such asd rifts a nd s to pe s. It is s im ila r to p re sp littin g in th at it in vo lv es a

row of holes at the perim eter of the excavation that is m orelig htly lo ad ed a nd m ore clo se ly s pa ce d th an th e o th er h ole s int he b la st r ou nd . T he lig ht p ow d er lo ad is u su ally a cc om p lis he db y " strin g lo ad in g" s le nd er c artr id ge s. U nlik e p re sp littin g, th es mo oth b la st h ole s a re fire d a fte r th e m a in b la st. T his is u su allyd on e b y lo ad in g a nd c on ne ctin g th e e ntire r ou nd a nd fir in g th eperim eter holes one delay later than the last hole in the m ainro un d. A s a first a pp ro xim atio n, th e b urd en o n th e p erim ete rh ole s s ho uld b e a pp ro xim a te ly 1 .5 t im e s t he s pa cin g, a s s ho w ni n f ig u re 91. Table 9 g iv es a ve ra ge s pe cific atio ns fo r s m oo thblasting.

-- A s- a com prom ise betw een standard blasting and sm oothb la stin g so me o pe ra to rs slig htly re du ce th e s pa cin g o f th eirp er im e te r h ole s, a s c om p ar ed w it h s ta nd ar d d es ig n, a nd s tr in glo ad re gu la r c artr id ge s o f e xp lo siv e. It is re co mm e nd ed p ro ce -

dure to seal the explosive colum n w ith a tam ping plug, clayd um m y, o r o th er o bje ct to p re ve nt th e s trin g-lo ad ed c ha rg esfrom being extracted from the hole by charges on earlierdelays.

B >S

S f S . . •S -

-8

~6

8-

.7 .7

-8

-8 .5 • 4 4• 5.

•6

.2 0 2•

o 0

.1

.5 5. 7.7

•7 7• 8.8

K E Y

o U nloaded hole . 7 Loaded hole w ithd ela y p erio d

Figure 91.- Typical smooth blasting pattern (burden,B, is larger than spacing, S).

Table 9. - Average specif ications for smooth blasting

Hole Spacing, Burden, Explosive

diameter, II II charge,

in Ibll l

1.50-1.75 2.00 3.00 0.12-0.25

2.00 2.50 3.50 .12- .25



74

Smooth blasting reduces overbreak and reduces the need

for ground support. This usually outweighs the cost of the

additional perimeter holes.

CUSHION BLASTING

Cushion blasting is surface blasting's equivalent to smooth

blasting. Like other controlled blasting techniques, it involves

a row of closely spaced,l ightly loaded holes atthe perimeter of

the excavation. Holes up to 6 1 / 2 in in diameter have been used

in cushion blast ing. Drilling accuracy with this size borehole

permits depths of up to 90 ft for cushion blasting. After the

explosive has been loaded, stemming is usually placed in the

void space around the charges. The holes are fired after the

m~in excavation is removed. A minimum delay between the

holes is desirable. The same loading techniques that apply to

presplitting are used with cushion blasting, except that the

latter often involves larger holes. The burden on the cushion

holes should always be larger than the spacing between holes.

The larger holes associated with cushion blast ing result in

larger spacings as compared with presplitt ing, thus reducing

drilling costs. Better results can be obtained in unconsolidated

formations than with prespli tting, and the larger holes permit

better alignment at depth. Table 10 gives average specifica-

tions for cushion blasting.

Table 10 •• Average specifications for cushion blasting

Hole Spacing, Burden. Explosivediameter, II II charge.

in Ib/ll

2.00-2.50 3.00 4.00 0.08-0.25

3.00-3.50 4.00 5.00 .13- .50

4.00-4.50 5.00 6.00 .25- .75

5.00-5.50 6.00 7.00 .75-1.00

6.00-6.50 7.00 9.00 1.00-1.50

REFERENCES

1. Andrews, A. B. Design of Blasts. Emphasis on Blasting. Ensign

Bickford Co. (Simsbury, CN), Spring 1980, pp. 1,4.

2. Ash, R. L. The Mechanics of Rock Breakage, Parts I, II, III, and

IV. Pit and Quarry, v. 56, No.2, August 1963, pp. 98-112; No.3,

September 1963, pp. 118-123; No.4, October 1963, pp. 126-131; No.

5, November 1963, pp.109-111, 114-118.

3. Dick, R. A. , and J. J. Olson, Choosing the Proper Borehole Size

for Bench Blast ing. Min. Eng., v. 24, No.3, March 1972, pp. 41-45.

4. E. I. du Pont de Nemours & Co., Inc. (Wilmington, DE). Blaster'sHandbook. 16th ed. , 1978,494 pp.

5. __ .FourMajorMethodsofControlledBlastlng.1964,16pp.

6. Hercules, Inc. (Wilmington, DE). Shot firer's Guide. 1978, 12 pp.

7. Pugleise, J. M. Designing Blast Pattems Using Empirical Formulas.

BuMines IC 8550, 1972, 33 pp.

8. Schmidt, R. L., R. J. Morrell, D. H. Irby, and R. A. Dick. Applica-

tion of Large-Hole Bum Cut in Room-and-Pillar Mining. BuMines RI

7994,1975,25 pp.

9. Winzer, S. R: The Firing Times of MS Delay Blasting Caps and

Their Effect on Blasting Performance. Prepared for National Science

Foundation (NSF APR 77-05171). Martin Marietta Laboratories

(Baltimore, MD), June 1978, 36 pp.; available for consultation at

Bureau of Mines Twin Cities Research Center, Minneapolis, MN.



75

Chapter 5.-ENVIRONMENTAL EFFECTS OF BLASTING

T he re a re fo ur e nv iro nm e nta l e ffe cts o f b la stin g.

1 . F ly ro ck

2 . G ro un d v ib ra tio ns

3 . A irb la st

4. Dust and gases

Flyrock is a potential cause of death, serious injury, andp ro pe rt y d am a ge . G r ou nd v ib ra tio ns a nd a ir bla st a re p ot en tia lcauses of property dam age and hum an annoyance, but areve ry un li ke ly to cause pe rsona l i nju ry. F ly rock,ground v ib ra ti ons ,a nd a ir bla st a ll r ep re se nt w a st ed e xp lo siv e e ne rg y. E xc es siv eam ounts of these undesirable side effects are caused byim proper blast design or lack of attention to geology. W hene xc es siv e s id e e ffe cts o cc ur , p ar t o f th e e xp lo siv e e ne rg y th atw as in te nd ed to g iv e th e p ro pe r a m ou nt o f r oc k fr ag m en ta tio nand d isp lacemen t is l os t to the su rroundi ng rock and a tmosphe re .S erio us d ust o r g as p ro ble ms a re se ld om ca us ed b y b la stin g.A larger than norm al am ount of dust m ay be caused by aviolent shot. N oxious gases, norm ally oxides of nitrogen orcarbon m onoxide, are the result of an ineffic ient explosivereaction. Because of its sporadic nature, blasting is not as ig nif ic an t s ou rc e o f a ir p ollu tio n.

W hen blasting in the vicinity of structures (fig. 92) such ash om es , h osp ita ls , sc hoo ls, a nd ch urch es , a p re bla st s urve y,d oc um e nt in g t he c on dit io n o f t he s tr uc tu re s, is o ft en b en ef ic ia l.

A preblast survey has a tw ofold purpose. First, it increasesc om m u nic at io ns b et we en t he c om m u nit y a nd t he m in e o pe ra to r.

It h as lo ng b ee n re co gn iz ed th at g oo d p ub lic re la tio ns a re th eoperator 's best means o f reducing b las ti ng compla in ts . A p reb las tsu rvey he lps the opera to r to ma in ta in good community rel at ions.M an y co mp an ie s h ave b ee n c on du ctin g p re bla stin g su rve ysfo r ye ars a nd ha ve fo un d th em to b e a n e xce lle nt in ve stm en t.

fhesecond purpose of a prebfast survey is to provide ab ase lin e re co rd o f th e c on dition o f a s tru ctu re a ga in st w hichth e e ffe cts o f b la stin g ca n be a ss ess ed . W he n c om bin ed w itha p os tb la st s urv ey , th is w ill h elp a ss ure e qu ita ble re so lu tio n o fb la st d am ag e c la im s. O ffic e o f S urfa ce M in in g (O S M) re gu la -tio ns re qu ire th at a p re bla st s urv ey b e c on du cte d, a t t he h om e -owners request, on all hom es within 0.5 m i of blasting ats urfa ce c oa l m in es .

U ood blast recordkeeping is essential to any successfulb la st in g o pe ra tio n. A b la st in g r ec or d is u se fu l in t ro ub le sh oo t-ing th e c aus e o f u nd es ira ble b la stin g re su lts s uch a s fly ro ck ,a ir bla st , g ro un d v ib ra tio ns , a nd p oo r f ra gm e nt at io n. T he b la st -in g r ec ord m ay a ls o p ro vid e e xc elle nt e vid en ce in litig atio n o nblast dam age or nuisance. Figure 93 gives an exam ple of ab la stin g re co rd . D ep en din g o n th e b la stin g s itu atio n, s om e o fth e in fo rm a tio n c on ta in ed in fig ure 9 3 m a y n ot b e re qu ir ed . O nthe reverse side of the blasting record a sketch of the blastp atte rn , in clu din g d ela ys , a nd a s ke tc h o f a ty pic al lo ad ed h oles ho uld b e d ra wn .

Figure 92.-Mining near a residential structure.



76

BLASTINGRECORD

Date:-------Company-

Location of blast: ----------------TiMeof hlast: ------------------Date of blast:

------------------Nameof blaster: License No:---------------- ------Direction: Distance: feet from blast to nearest dwelling,

school, church, cC!l:lInercial,or institutional building.

Weather data:------------"~-----------------

emperature: Nind direction

and speed: Cloud cover:

Type of material blasted:--------------------

No. of holes :__ ---.;Burden Spacing : Depth: Diarn.: _

Type of explosive used: ---------Maximumweight of explosive detonated within any 9-rns period: lb.

Maximumnumber of holes detonated within any 9-rns period: -------TOtal weight of explosives, including primers, this blast: lb.-----Methodof firing and type of circuit:

----------------Type and length of sternrning: _

Weremats or other protection used?-----------------

Type of delay detonator used: Delay periods used : _

Seismic data: T , V , L , dB'--- ---- -;...--- ---Location of seismograph: ~Distance from blast: ft.

Nameof person taking seismograph reading:-------------

Nameof person and firm analyzing the seismograph record: ------Signed: Blaster-----------

Figure 93.-Example of a blasting record.



78

Figure 94.-seismograph for measuring ground vibrations from blasting.

CAUSES

Excessive ground vibrations are caused either by putting

too much explosive energy into the ground or by not properly

designing the shot. Part of the energy that is not used in

fragmenting and displacing the rockwill go into ground vibrations.

The vibration level at a specific location is primarily deter-

mined bythe maximum weight of explosives that is used in any

single delay period inthe blast and the distance of that location

from the blast (9).

The delays in a blast break it up into a series of smaller, very

closely spaced individual blasts. The longer the intervals are

between delays, the better the separation will be between the

individual blasts. Most predictive schemes and regulatory agen-

cies use a guide of 8 or 9 ms as the minimum delay that can be

used between charges if they are to be considered as sepa-

rate charges for vibrations purposes. However, there is noth-

ing magical about the 8· or 9-ms interval. For small, close-in

blasts a smaller delay may give adequate separation.

With large blasts at large distances from structures, longer

delays are required to obtain true separation of vibrations

because the vibration from each individual charge lasts for a

longer period of time. In general, vibration amplitudes at struc-

tures sitting on the formation of rock being blasted will be



g reat er th an a t s tr uc tu re s s it tin g on o th er f ormat io ns . However ,th ey m ay b e h ig he r in fre qu en cy, w hich re du ce s th e re sp on seo f s tru ctu res a nd th e lik elih oo d o f d am ag e.

In a dd itio n to c ha rg e weig ht p er c ra la y, d is ta nc e, a nd d ela y"in te rv al, tw o fa cto rs ma y a ffe ct th e le ve l o f g ro un d v ib ra tio ns a ta g iv en lo ca tio n. T he firs t is o ve rco nfineme nt. A c ha rg e w ith a

p rope rly d es ig ned burden w ill p ro du ce le ss v ib ra tio n per poundof explosive than a charge w ith too m uch burden (fig. 95). Ane xc es siv e amou nt o f s ub drillin g, whic h re su lts in a n e xtremelyheavy confinem ent of the explosive charge, w ill a lso causeh ig he r le vels o f g ro un d v ib ratio n, p articu la rly if th e p rim er isplaced in the subdrilling. In m ultiple row blasts, there is aten de nc y for th e la te r ro ws to b ec om e o ve rco nfin ed (fig . 7 5).T o a vo id th is , it is o ften a dvisa ble to u se lo ng er d ela y p erio dsb etw ee n th ese la te r ro ws to g ive b ette r re lie f. In s om e typ es o fg ro und the se lo nger dela ys may in cr ea se t he chance o f c ut of fs ,s o s om e tra de offs m ust b e m ad e. S ec on d, if d ela ys p ro ce ed insequence dow n a row , the vibrations in the direction that thesequence is proceeding w ill be highest (fig. 96) because of asnowba ll ing e ffec t.

R ece nt stu die s (1 jJ ha ve sfio writh at m illis ec on aa ela ys lri

c ommerc ia l d eto na to rs a re le ss a cc ur ate th an was p re vio us ly

NORMAL VIBRATIONS

Normal

b u r d e n

----~f'EST1:

"Normal

s ub dr i I li ng

EXCESSIVE VIBRATIONS

----~_ . . .

Excessivesubdril lin9

Excessiveb u r d e n

------41J"1"!1!"!Ifl!

Figure 95.-Effects of confinement on vibration levels.

79

KE Y• Bla.thale and

3 delay per iod

Intermediate

vibrations

Lower+--- vibrations

Higher _

vibrations

Figure 96.-Effect of delay sequence on particle velocity.

b elie ve d. T his m ay re su lt in e xtre me ly clo se tim in g b etw ee na dja ce nt d elay p erio ds o r, ve ry ra re ly, a n o ve rlap . W he re it iscritical that one hole detonates before an adjacent hole toprovide relief, it m ay be a good idea to skip a delay periodb etw ee n th e tw o h ole s.

M ost u nd ergro un d m in es s ho ot re la tiv ely small b la sts a nddo not have vibration problem s. H ow ever, w here vlbratlonsa re a p ro ble m, th e dis cu ss ion s in th is ch ap te r a pp ly to u nd er-g ro un d b la stin g a s well a s s ur fa ce b la stin g.

PRESCRIBED VIBRATION LEVELS ANDMEASUREMENT TECHNIQUES

Tw o vibration lim its are im portant; the level above w hichd amage is lik ely to o cc ur a nd th e le ve l a bo ve whic h n eig hb orsare likely to complain. There is no precise level at whichdam age begins to occur. The dam age level depends on thetyp e, c on dition , a nd a ge o f the stru ctu re , th e typ e o f gro un d o nwhic h th e s tru ctu re is b uilt, a nd th e fre qu en cy o f th e v ib ra tio n,

in hertz. R esearch com pleted by the Bureau of M ines in thela te 1970's ( 9) r ecommends t ha t f or v er y c lo se -in c on st ru ct io nb la stin g, whe re th e fre qu en cy is a bo ve 4 0 Hz, v ib ra tio n le ve lsb e k ep t b elo w 2 in /s ec to m in im ize d am age . H ow ev er, a ll m in eand qua rr y b la st v ib ra tio ns , a nd t ho se f rom la rg e const ru ct io njobs, have frequencies below 40 Hz. For these blasts it isrecom mended that the vibration level be kept below 0.75in /s ec fo r h om es o f m od ern , d ryw all co ns tru ctio n a nd b elo w0 .5 0 in /s ec fo r o ld er h ome s w ith p la ste r- on -Ia th walls . T he sevalues could change as m ore research is done.

People tend to com plain about vibrations far below thedam age level. The threshold of com plaint for an individualdepends on health, fear of dam age (often greater w hen theowner occup ies the home), a tt it ude towa rd the mini ng opera tion ,diplom acy of the m ine operator, how often and w hen blastsa re fire d, a nd th e d ura tio n o f th e v ib ra tio ns . T he to le ra nc e le ve lcould be below 0.1 in/sec w here the local attitude is hostiletowa rd m in in g, whe re th e o pe ra to r's p ub lic r ela tio ns s ta nc e ispoor, or w here num erous older persons ow n their hom es. O nthe other hand w here the m ajority of people depend on them ine for their livelihood, and w here the m ine does a good jobo f p ub lic r ela tio ns , le ve ls abo ve 0 .5 0 in /s ec m ight b e t ole ra te d.By using careful blast design and good public relations it isu su ally p os sib le fo r a n o pe ra to r to live in h arm on y w ith n eig h-bor s w it hout r esor tin g t o e xpensiv e t echnolo gy .

S eve ra l o ption s a re a va ila ble fo r m ea su rin g g ro un d vi b ra -tlons (12). M any operators prefer to hire consultants to runt he ir monit or in g p rogr ams . E it he r pea k r eadin g seismog raphsor seism ographs that record the entire vibration event on apaper record m ay be used. Peak reading instrum ents are



80

c he ap er , e as ie r to u se , a nd a re a de qu ate fo r a ss urin g re gu la -to ry c om plia nc e in m os t ca se s. H ow ev er, se ism og ra ph s th atre co rd th e e ntir e time h is to ry a re mo re u se fu l fo r u nd ers ta nd -in g a nd tro ub les ho otin g g ro un d vib ra tio n p ro ble ms. In stru -ment s t ha t measure t hr ee mu tually p er pend ic ula r c omponen ts

( rad ia l, t ransve rse , ve rt ica l) a re mos t common, and mos t regu la -tions specify this type of m easurem ent. V ector sum instru-m ents w ill a lw ays give a higher reading (usually 10 to 25 pcth igher ) than the h ighes t s ing le component o f a three-componen tinstrum ent. Because vector sum instrum ents alw ays give ah ig he r r eadin g, t he y should be sat is fa ct or y f or r egula to ry com-p lia nce e ven where t he r egula tio n spe cif ie s t hr ee componen ts .S ome s eismo gr ap hs re qu ir e a n o pe ra to r to b e p re se nt while

o th er s ope ra te r emo te ly , u sually f or a per io d o f a month betweenbat te ry c hanges . Operat or -a tt ended in st rumen ts a re cheaperbut require the expense of the operator. They can be m ovedfrom p la ce to p la ce to ga th er s pe cific d ata o n sp ecific b la sts .R emote ly in sta lle d in stru me nts a re u sefu l in th at th ey re co rde ach b la st w ith ou t s en din g a n o pe ra to r o ut ea ch tim e. T he sein stru men ts s ho uld b e in sta lle d in p la ce s th at a re p ro te cte d

from w eather and tam pering. W hen recording rem otely, it ise asie r to d ete ct ta mp ering w ith s eis mo gra ph s th at rec ord th e~ ntire time h is to ry th an w ith p ea k re ad in g in str umen ts .

W hen accelerations larger than 0:3 g are expected, thes eis mo gra ph sh ou ld b e se cu re d to th e g ro und s urfa ce . M an yin strumen ts a re e qu ip pe d w ith s ta ke s fo r th is p urp os e. E po xyor bolting m ay be used on hard surfaces. W here possible,whe n th e e xp ec te d a cc ele ra tio n le ve l is h ig h, th e g ag e s ho uldb e b urie d in th e g ro und .

Se is r: nograph records p ro vid ee -x ce lle nt e vid en ce in case o flater com plaints or law suits on· dam age or nuisance fromblasting. A complete blast re-cord, as shown in figure 93,d es crib in g th e la yo ut, lo ad in g, in itia tio n, a nd o th er p er tin en ta sp ec ts o f th e b la st is a ls o e ss en tia l.

SCALED DISTANCE

EQUATION

Where v ib ra tio ns a re n ot a s erio us p ro blem , re gu la tio ns w illoften perm it the blaster to use the scaled distance equationrather than m easuring vibrations w ith a seism ograph. Thes ca le d d is ta nc e e qu atio n is a s fo llo ws :

S.D. = DIW'//.

w here S.D . is the scaled distance, 0 is the distance from theb la st to th e s tru ctu re o f c on ce rn , in fe et, a nd W is th e ma ximumcharge w eight of explosives, in pounds, per delay of 9 m s orm ore. The scaled distance perm itted depends on the allow -a ble v ib ra tio n le ve l. F or in sta nc e, B ulle tin 6 56 (7) says that a

s ca le d d is ta nc e o f 5 0 o r g re ate r w ill p ro te ct a ga in st v ib ra tio nsgre ater th an 2 in /se c. T he re fo re , at a d is ta nce o f 5 00 ft, 1 00 Ibof explosive could be fired; at 1,000 ft, 400 Ib; at 1,500 ft, 900Ib , e tc . T he o rig in al OSM r eg ula tio ns (2-3) specif ie d a s ca le ddistance of 60 or greater to protect against 1 in/sec, giv ingd is ta nc e-weig ht c omb in atio ns o f 6 0 0 ft a nd 1 00 Ib ; 1 , 20 0 ft a nd400 Ib, 1, B O O ft and 900 Ib, etc. This regulation is currentlybe ing revi sed .

The scaled distance approach w orks w ell w hen the m ine isan adequate distance from structures, vibrations are not aproblem , and the operator wants to save the expense ofmeasur in g v ib ra tio ns . A t c lo se d is ta nces , h oweve r, t he s ca le dd is ta nce becomes quit e r es tr ic tiv e in t erms o f a llowab le cha rge

w eig hts p er de la y a nd mon ito ring is o fte n a m ore e co nomic aloption.

REDUCING GROUND

VIBRAt iONS

A p rop erly d esig ne d b la st us in g th e p rin cip le s d esc ribe d inc ha pte r 4 w ill g iv e lowe r v ib ra tio ns p er p ou nd o f e xp lo siv e th ana p oo rly d esig ne d b la st. P ro pe r b la st d esig n in clu de s u sin g aspacing-to-burden ratio equal to or greater than 1.0, 'usingproper delay patterns, and using a proper powder factor.B lasthole locations should be carefully laid out and drillingshould be controlled as closely as possible. Bench m arkss ho uld b e es ta blish ed fo r u se in se ttin g o ut h ole lo ca tio ns fo r

th e n ex t b la st b efo re th e cu rre nt b la st is m ad e to a vo id p oss i-b le erro rs d ue to b ack bre ak (4).

--tlie follow ing techniques can be used to reduce groundvibrations:

1. R educe the charge w eight of explosives per delay. Thisis m ost e asily d on e b y re du cin g th e n um ber o f b las th ole s fire do n e ac h d ela y. If t h ere a re n ot e no ug h d ela y p er io ds a va ila ble ,this can be alleviated by using a sequential tim er blastingm ac hin e o r a c om bin atio n o f s urfa ce a nd in -h ole n on ele ctricd ela ys . T he manu fa ctu re r s ho uld b e c on su lte d fo r a dv ic e whe nusil')g the sequential tim er or com plex delay system s. If thebla st a lre ad y emp loy s o nly o ne b la sth ole p er d ela y, sm alle rd iamete r b la sth ole s, a lowe r b en ch h eig ht, o r s ev era l d ela ye dd ec ks in e ac h b la sth ole c an b e u se d. Dela ys a re o fte n re qU ire dwhen presp l it ti ng.

2. O verly confined charges such as those having too m uchb urd en or to o m uc h su bd rillin g s hou ld b e a vo id ed . T he p rim ers ho uld n ot b e p la ce d in th e su bd rilling . W he re it a pp ea rs tha t alater row of blastholes w ill have inadequate relief, a delaype rio d sh ou ld b e sk ipp ed b etw een ro ws .

3. T he length of delay betw een charges can be increased.T his is e sp ec ia lly h elp fu l w he n firin g la rg e c ha rg e weig hts p erd ela y a t la rg e b la st- to -s tr uc tu re d is ta nc es . Howev er , th is w illin cre as e th e d ura tio n o f th e b la st a nd may c au se mo re a dv ers er ea ct io ns f rom neig hbor s.

4. If delays in a row are arranged in sequence, the low estdelay should be placed in the hole nearest the structure of

concern. In other w ords, the shot should be propagated in ad ire ctio n awa y from th e s tru ctu re .

5 . T he pub lic 's p er cept io n o f g r o und v ib ra tio ns can be reducedby blasting during periods of high local activ ity such as then oo n h ou r o r s ho rtly a fte r s ch oo l h as b ee n d ismis se d. B la stin gd urin g ty pic ally q uie t p erio ds s ho uld b e a vo id ed , if p os sib le :

AIRBLAST

Airblast is a transient im pulse that travels through thea tm os ph ere . M uc h o f th e a irb la st p ro du ce d b y b la stin g h as a

fre qu en cy b elow 2 0 H z an d c an no t b e h ea rd e ffe ctiv ely by th eh uman e ar. Howev er , a ll a irb la st, b oth a ud ib le a nd in au dib le ,



81

Figure 97.-8Iasting seismograph with microphone for measuring airblast.

can cause a structure to vibrate in much the same way as

ground vibrations (8, 10). Airblast is measured with special

gages, pressure transducers, or wide-response microphones

(11). These instruments are often an integral part of blasting

seismographs (f ig. 97). As with ground vibrat ions, both ampli-

tude and frequency are measured. Ampl itude is usually mea-

sured in decibels, sometimes in pounds per square inch, and

frequency is measured in hertz. Research has shown that

airblast from a typical blast has less potential than groundvibrations to cause damage to structures. It is, however, fre-

quently the cause of complaints. When a person senses vibra-

tions from a blast, or experiences house rattling, it is usual ly

impossible to tell whether ground vibrat ions or airblast isbeing

sensed. A discussion of airblast should be part of any mine

public relations program.

Surface

detonati ng

cord

CAUSES

\\\l

\ \ .

i \.r: Movement ofI I vl l 1 the burden! i I

I i

,l/

Airblast iscaused byone ofthree mechanisms (6) as shown

in figure 98. The first cause is energy released from uncon-

fined explosives such as uncovered detonating cord trunklines Figure 9a.-Causes of airblast.



82

o r m ud ca ps u se d fo r s ec on da ry bla stin g. T he se co nd ca us e isth e re le as e o f e xp lo sive e nerg y fro m in ad eq ua te ly co nfin edborehole cha rg es . Some example s a re in adequa te s temm ing,inadequate burden, or m ud seam s. The third cause is m ove-m ent of the burden and the ground surface. M ost blasts ared esig ne d to d is pla ce th e b urd en . W he n th e fa ce m ove s o ut, it

a cts a s a p is to n to fo rm a n a ir c omp re ss io n wav e (a irb la st). F orthis reason, locations in front of the free face receive highera irb la st le ve ls th an th os e b eh in d th e fre e fa ce .

PRESCRIBED AIRBLAST LEVELS AND

MEASUREMENT TECHNIQUES

S is kin d (8 ) h as s tu die d th e p ro blem o f d ama ge fr om a irb la st.T ab le 1 1 s ho ws th e a irbla st le ve ls p re sc ribe d fo r p re ve ntin gdamage to s tr uc tu re s.

A s in dic at ed in t he t ab le , d if fe re nt in st rumen ts have d if fe re ntlow er frequency lim its. Because m uch of the airblast is con-tained in these low er frequency levels, som e of the instru-m ents m easure m ore of the airblast than others. That is the

reason for the different m axim um levels in the table. It isn ece ssa ry to m ee t o nly o ne o f the se v alu es, d ep en ding o n th es pe cific atio ns o f th e in str ume nt u se d.

B ec aus e a irb la st is a m ajo r c au se of bla stin g c om pla in ts,m ere ly m ee tin g th e lev els give n in th e ta ble is some tim es n ots uffic ie nt. A irb la st le ve ls s ho uld b e k ep t a s lo w a s p os sib le b yu sin g th e te ch niqu es d es crib ed la te r in th is s ec tio n. T his w illgo a long w ay tow ard reducing com plaints and conflicts w ithneighbors.

A ny in str umen t w ith a fr eq ue nc y ra ng e lis te d in ta ble 1 1 c anbe used to m easure airblast. M any operators prefer to hirec on su lta nts to m on ito r a irb la st. M os t o f th e d is cu ssio n u nde rground v ibra tion measurement techn iques a lso app lies to a irb las tm ea su reme nt. B oth p ea k re ad in g in stru me nts a nd th ose th atre co rd th e e ntire a irb la st tim e h is to ry a re a va ila ble . T he p ea k

r eadin g dev ic es a re satis fa ct or y f or r egula to ry c omp lia nce butthose that record the entire airblast tim e history are m uchb ette r fo r tro ub le sh oo tin g p urp os es . A s in gle a ir bla st r ea din gis ta ke n a t a g ive n lo ca tio n. T he g ag e s ho uld b e 3 to 5 ft a bo vethe ground and should be at least 5 ft to one side of anystructure to prevent distortion to the record due to airblastreflections.

A fr bT as t c an b e mea su re d b y a n o pe ra to r-a tte nd ed in stru -ment o r b y a r emo te ly in st alle d in str ument . Operat or -a tt endedins trumen ts a re cheaper bu t requ ire the expense o f the opera to r.T he y a re mo re fle xib le in th at d ata c an b e re co rd ed a t d iffe re ntlo ca tio ns f or d if fe re nt b la st s. Remotely in st alle d in st rumen tsa re u se fu l in th at th ey re co rd e ac h b la st fire d w ith ou t r eq uirin ga n o pe ra to r e ach tim e. O ne d is ad va nta ge o f re mo te m on ito r-ing is that a high reading can be induced by a loud noise nearth e in stru me nt. F or th is re as on , in stru me nts th at re co rd the

ent ir e a ir bla st e vent a re r ecommended f or r emo te monit or in g,s o th at a n on bla stin g e ve nt c an b e id en tifie d b y its n on ch ara c-t er is tic wave t ra ce .

It is recommended that all a irb last m onitors be equippedw ith w in d s cre en s to cu t d ow n th e b ack gro un d n ois e le vel a ndp ro tec t the mi crophone . Remo te ly i ns ta lled ins trumen ts shou ldb e p ro te cte d from th e wea th er.

Table 11•• Maximum recommended airblast levels

F requency range o f i ns tr umen ta t ion

0.1 to 200 Hz, fla t response .2 to 200 Hz, fla t response .6 to 200 Hz, fla t response .C -weighted. slow response .

M a xim um le ve l, d B

134 peak .

1 33 p ea k .1 2 9 p e ak .

105C.

A irb la st re co rd in gs p ro vid e g oo d ev ide nc e in ca se o f c om -p la in ts o r la ws uits . A irb la st re ad in gs ta ke n in c on ju nc tio n w ithg ro und v ib ra tio n r eadin gs a re e spec ia lly h elp fu l in d et erm in in gw hich of the tw o are the prim ary cause of com plaints.

REDUCINGAIRBlA-ST

P roperly executed blasts, w here surface explosives areadequately covered and borehole charges are adequatelyc on fin ed , a re n ot like ly to p ro du ce h arm fu l le ve ls o f a irb la st.C lose attention m ust be paid to geology to prevent the occa-sional "one that gets aw ay from you."

T he fo llo wing te ch niq ue s ca n b e u se d to re du ce a irb la st.

1. U nconfined explosives should not be used. W here sur-face detonating cord is used it should be buried. C ords w ithlig hte r c ore lo ad s re qu ire le ss d ep th o f b uria l.

2. Suffic ient burden and stem ming on the blastholes are

e sse ntia l. W he re th e le ng th o f s te mm in g is m arg in al, co ars es te mm in g m ate ria l w ill g iv e b etter ch arg e co nfineme nt th anfin es , p articu la rly w he re th ere is w ate r in the s te mm in g z on e.On e-fo urth -in ch ma te ria l ma ke s e xc elle nt s temm in g. A lo ng ers te mm in g d im ens ion s ho uld b e us ed w he re p art o f t he b urd enat the crest has been robbed from the front row of holes. Thefront row of holes usually creates m ore airblast than subse-q ue nt rows .

3 . G eo lo gic c on ditio ns th at c au se b lo wo uts s hou ld b e com-pensatedfor. T hese include m ud seam s, voids, or open bed·ding (should be stem med through) and solution cavities oro th er o penin gs ( a che ck o f c olumn r is e w ill a vo id o ve rlo ad in g) .

4 . H ole s mus t b e d rille d a cc ura te ly to ma in ta in th e d es ig ne d

b urd en . T his is e sp ec ia lly im p orta nt w ith in clin ed h ole s.

5. If there is a high free face in the direction of nearbyb uilt-u p a re as , th e fa ce s ho uld b e re orie nta te d, if p os sib le , o rr ed uc ed in h eig ht.

6. Collar prim ing should be avoided where airblast is ap ro blem . (Ac tu ally , c olla r p rim in g is s eld om des ir ab le .)

7 . E arly m orn in g, la te a fte rn oon , o r n ig ht firin g, w he n tem-p era tu re in ve rs io ns a re mo st lik ely , s ho uld b e a vo id ed . B la st-in g w he n a sig nifica nt w in d is b lo win g to wa rd n ea rb y b uilt-u pa re as w ill in cr ea se a ir bla st .

8. U se of longer delays betw een row s than betw een holesin a ro w w ill p ro mo te fo rw ard ra the r th an u pw ard m ov em en t o f

th e b urd en . F iv e m illis ec on ds p er fo ot o f b ur de n b etwee n rowsis a good rule of thum b, but this should be increased in laterrow s for shots w ith m any row s.

9 . E xce ssive ly lo ng d ela ys th at m ay c au se a h ole to b ecomeu nb urd en ed b efo re it fire s sh ou ld b e a vo ide d.

P ub lic re ac tio n to a irb la st c an b e re du ce d b y b la stin g d urin gperiods of high activity such as the noon hour or shortly afterschool has been dism issed. Blasting during quiet periodss ho uld b e a vo id ed .



83

DUST AND GASES

E ve ry b la st g en era te s s om e amo un t o f d us t a nd g ase s. T heam ounts of dust generated by blasting do not present a seri-

. ous problem . O ther phases of the m ining operation such as

lo ad in g, h au lin g, c ru sh in g, a nd p ro ce ss in g p rodu ce consid er a-bly m ore dust than blasting. E ven though a violent blast m ayproduce m ore than the norm al am ount of dust, blasting is ar ela tiv ely in fr equent o pe ra tio n and , a s a r esult , t he t ot al amountof dust produced in a day is insignificant w hen com pared too th er so urce s. W ell co ntrolled b la sts cre ate little o r n o d us t.Because dust in the muckpile can be a problem to m ineper sonnel, it is c ommon p ra ct ic e t o th or ough ly we t t he muckpileb efo re a nd d urin g mu ck in g o pe ra tio ns . In u nd er gro un d o pe ra -tions an appropriate am ount of tim e is allow ed for the dust tos ettle o r to b e e xp elle d fr om th e a re a b y th e v en tila tio n s ys temb efo re m in ers e nte r th e b la st are a.

The m ost com mon toxic gases produced by blasting arecarbon m onoxide and oxides of nitrogen. W hile these gases

a re con sid er ed t ox ic a t le ve ls o f 5 0 ppm and 5 ppm respect iv ely ,blast fum es are quickly diluted to below these levels by theve ntila tio n sy stems in u nd erg ro un d m in es a nd b y n atu ra l a ir

m oveme nt in su rfac e m in es . In u nd erg rou nd o pe ra tion s, it isim portant to allow tim e for toxic gases to be expelled by theventilation system before m iners enter the area. In surfacem in in g, it is a g oo d id ea to w ait fo r a sh ort p eriod of tim e b efo reen te ri ng the immed ia te b las t a rea , pa rt icu la rly if o range-b rownfumes (o xid es o f n itro ge n) a re p re se nt. It is e xtre me ly ra re fo rsignificant concentrations of toxic gases to leave the m inep ro pe rty . If la rg e amou nts o f o ra ng e-b rown fume s a re c on sis -te ntly p re se nt a fte r b la sts , th e s ou rc e o f th e p ro blem s ho uld b ed ete rm in ed a nd c orre cted . T he prim ary c au se s o f e xc ess iv en it ro gen oxid es a re poo r b la st in g agent m ix tu re s, d eg rada tio no f b la stin g a ge nts d ur in g s to ra ge , u se o f n on - wate r- re sis ta ntp ro du cts in w et b la sth ole s, a nd in effic ie nt d eton atio n o f theb la stin g a ge nt d ue to lo ss o f c on fin eme nt.

REFERENCES

1. Bauer, A., and J. W. Sanders. Good Blasting Techniques and

PUblic Relations. Min. Congo J., V. 54, No. 11, November 1968, pp.

81-85.

2. Dick, R. A. A Review of the Federal Surface Coal Mine Blast ing

Regulations. Proc. 5th Cont. on Explosives and Blasting Technique,

St. Louis, MO, Feb. 7-9, 1979. Society of Explosives Engineers,

Montvil le, OH, pp. 1-7.

3. Dick, R. A., and D. E. Siskind. Ground Vibration Technology

Pertaining to OSM Regulations. Proc. Symp. on SUrface Coal Mining

and Reclamation Coal Conf. & Expo., Louisville, KY, Oct. 23-25,

1979. McGraw-Hi li, New York, pp. 13-18.


Handbook. 16th ed., 1978, 494 pp.5. Lundborg, N., P. A. Persson, A. Ladegaard-Pederson, and R.

Holmberg. Keeping the Ud on Flyrock From Open Pit Blasting. Eng.

and Min. J, V. 176, No.5, May 1975, pp. 95-100.

6. Mil ler, P.Blasting Vibration and Airblast. Atlas Powder Co. (Dallas,

TX), 16 pp.

7. Nicholls, H. R., C. F. Johnson, and W. I . Duvall. Blast ing Vibra-

t ions and Their Effects on Structures. BuMines B 656, 1971, 105 pp.

8. Siskind, D. E., V. J. Stachura, M. S. Stagg, and J. W. Kopp.

Structure Response and Damage Produced by Airblast From Surface

Mining. BuMines RI 8485, 1980, 111 pp.

9. Siskind, D. E. , M. S. Stagg, J. W. Kopp, and C. H. Dowding.

Structure Response and Damage Produced by Ground Vibration

From Surface Mine Blast ing. BuMines RI 8507, 1980, 74 pp.

10. Siskind, D. E. , and C. R. Summers. Blast Noise Standards and

Instrumentation. BuMines TPR 78, May 1974,18 pp.

11. Stachura, V. J., D. E. Siskind, and A. J. Engler. Airblast Instru-

mentation and Measurement Techniques for Surface Mine Blasting.

BuMines RI 8508, 1981, 53 pp.

12. Stagg, M. S., and A. J. Engler. Measurement of Blast- Induced

Ground Vibrations and Seismograph Calibration. BuMines RI 8506,1980,62 pp.13. Winzer, S. R. The Fir ing Times of MS Delay Blasting Caps and



(Baltimore, MD), June 1978, 36 pp.; available for consultation at

Bureau of Mines Twin Cit ies Research Center, Minneapolis, MN.



85

Chapter 6.-BLASTING SAFETY

The foll ow i ng i sa d iscuss ion o f good , sa fe b las ti ng p rocedu res ,movin g chronolo gic ally f rom in it ia l e xp lo siv e s to ra ge t hr ough

p osts h ot sa fe ty m ea su re s. In a dd itio n to th es e p ro ce du re s,t he b la st er must f am ilia riz e h imself o r h er se lf w it h a ll t he saf et yre gu la tio ns w hic h go ve rn h is o r h er o pe ra tio n. T he se sa fe tyr egula tio ns con ta in add it io na l a dv ic e on saf e ope ra tin g p ro ce -dures for all phases of the blasting operation. The safetyp ro ce dure s d isc uss ed h ere a re n ot m ean t to b e, n or sh ou ld b e

.cons ideredto be, a substi tu te for adherance to safety regula tions.O f course, all general w orkplace safety recommendations

a ls o app ly t o b la st in g a ct iv it ie s.T he In stitu te o f M ake rs o f E xp lo siv es (IME) h as p ublish ed

an excelle nt s er ie s o f s af et y pub lic at io ns ( 5- 13 ). 1 The Na tio na lF ir e P ro te ct io n Assoc ia tio n (NFPA ) has pub lis hed recommen-d atio ns o n th e s to ra ge a nd h and ling o f ammon ium nitra te a ndb la st in g agent s ( 14 -16) .

EXPLOSIVES STORAGE

T he B ur ea u o f A l co ho l, T ob ac co a nd F ir ea rms (BATF) re gu -la te s e xp lo sive im po rta tio n, m an ufa ctu re, d is trib utio n an ds to ra ge , in clu din g p ro pe r r ec ord ke ep in g to p ro te ct th e p ub lic

from m is us e. S afe s to ra ge o f e xp lo siv es in th e m in in g in du stry ,including B ATF regulations, is enforced by the M ine Safetyand Healt h Adm in is tr at io n (MSHA ). I n a l l o th er in du st rie s, s af ee xp lo siv e s to ra ge is re gu la te d b y BATF a nd th e Occ up atio na lS afe ty a nd H ea lth A dm in istra tio n (OSHA). In a dd itio n, m ostStates, and m any county and local governm ent agencies,e nfo rc e th eir own e xp lo siv e s afe ty re gu la tio ns .

Magazin es f or e xp lo siv e s to ra ge must c on fo rm to specif ic a-tions laid dow n by BATF and M SH A or O SH A. IM E Pam phletNo.1 (13) gives recommended standards for magazinec on stru ctio n. Ma ga zin es mu st b e s ep ara te d fr om e ac h o th er,su rround ing bu ild ings, and r igh ts -o f-way acco rd ing to the Ameri-ca n T ab le of D is ta nce s [I ME P amph le t NO.2 (5 )]. S ep ara tio nd is ta nc e r eq uiremen ts b etwee n ammonium n itra te a nd b la st-in g ag en t s tora ge fa cilitie s are le ss th an for h ig h e xp lo sive s.However , t he d is ta nce requir ement s f or s eparat io n o f b la st in ga ge nts a nd ammon ium n itra te fro m o cc upie d s tru ctu re s a ndr ig hts -o f-way a re th e s ame a s th os e fo r h ig h e xp lo siv es . Deto -n ato rs m ay no t b e sto re d w ith o th er e xp lo siv e m ate ria ls. H ig he xp lo siv es must be s to re d in a t ype 1 (BATF) o r t ype 2 magazin e.B lasting agents m ay be stored in a type 1 m agazine w ith highe xp lo siv es. W hen e xp los iv es a nd b la stin g a gen ts a re s to re dto ge th er , a ll o f th e mate ria l in th e ma ga zin e is c on sid ere d to b eh ig h e xp lo siv es fo r se pa ratio n d ista nc e pu rp ose s. B la stin gagents m ay be stored in any approved m agazine.

E xc ep t whe n e xp lo siv es a re b ein g d ep os ite d o r w ith dr awn,m aga zin es m us t b e k ep t lo cke d. O nly a uth orize d p ers on nes ho uld d ep os it o r w ith draw e xp lo siv es . T he n umbe r o f a uth or-

ized persons should be kept to a m inim um for both safety ands ec urity p ur po se s. In th is way a cc ou nta bility p ro blems c an b em in im iz ed . E xp lo siv e s to ck s s ho uld b e p ile d n ea tly ( fig . 9 9) tofa cilitate s afe h an dlin g, a nd th e o ld es t e xp lo sive s sh ou ld beu se d firs t to a ss ure fre sh ne ss . T his is im po rta nt fo r a ll e xp los iv e ma te ria ls b ut e sp ec ia lly fo r AN -FO, to p re ve nt fu el s eg re -gation or evaporation. S egregation and evaporation of fuefro m AN-FO is a p articu la r pro ble m in b ulk s to ra ge (fig . 10 0)P ro lo ng ed s to ra ge s ho uld b e a vo id ed . Goo d h ou se ke ep in g

sta nd ard s sh ou ld b e m ain ta ine d b oth in sid e a nd o utsid e th emag az in e. T o m in im iz e th e fire h az ar d, v eg eta tio n o uts id e th emag az in e, e xc ep t liv e tr ee s o ve r 1 0ft h ig h, s ho Llld b e c le are dfo r a d is ta nce o f a t le as t 2 5 ft a nd ru bb ish sh ou ld b e cle are d foa t le ast 5 0 ft. S mo kin g o r fla me s a re n ot p erm itte d in o r w ithin50 ft of an outdoor storage m agazine. M agazines should beclearly marked. The IME recommends a sign stating"E xp lo sive s- K eep O ff" in 3 -in -h ig h le tte rs w ith a Y 2-in bru shs tr ok e. It is a dv is ab le th at th e e xp lo siv es s ig n b e p la ce d s o th ata b ulle t p as sin g th ro ug h th e s ig n w ill n ot s tr ik e th e ma ga zin e.

Prim ed explosives m ust never be stored in m agazines.M isfired explosives should be disposed of im mediately ostored in a separate magazine while awaiting disposalassi stance. Assi stance i nd ispos ing o f de te rio rated o r unwan tede xp lo siv es w ill b e p ro vid ed b y th e e xp lo siv es d is trib uto r u po nrequest.

TRANSPORTATION FROM MAGAZINE TO JOBSITE

If th e ro ute from th e mag az in e to th e jo bs ite le av es c ompa nyp ro pe rty , th e tr an sp orte r is s ub je ct to a ll S ta te a nd lo ca l tra ns -por ta t ion regulat ions regard ing veh ic le speci fi ca t ions, p lacard ing ,a nd o th er ope ra tio na l p ro cedu re s.E xp lo siv e t ra nspo rt at io n should be done only in an app ro ved

ve hic le in g oo d re pa ir a nd e sp ec ia lly o utfitte d fo r th e jo b. T hep rac tice o f u sin g th e m ost c on ve nien tly a va ila ble v eh ic le fo re xp lo siv e tra ns po rta tio n s ho uld b e a vo id ed . T he in te rio r o f th ee xp lo siv es c ompar tmen t mus t b e c on str uc te d o f n on sp ark in gm ate ria l. If d eto na to rs a re to b e h au le d o n th e s am e ve hicle a se xp lo siv es, th ey m us t be pro pe rly s ep ara ted . MSHA re gu la -tions require a m inim um separation by 4-in hardw ood or thee qu iv ale nt. D eto na to rs sh ou ld b e pro te cte d fro m e le ctric alc on ta ct. A de qu ate fire fig htin g e qu ipme nt sh ou ld b e k ep t o n

t he veh ic le a t a ll t imes. Small f ir es t ha t a re c le ar ly is ola te d f romth e e xp lo siv e c ar go s ho uld b e fo ug ht. H owev er, if fire re ac he sthe explosive cargo, the vehicle should be abandoned ang ua rd ed a t a s afe d is ta nce b ec au se it m ay d eto na te .T he ope ra to r o f th e e xp lo siv es veh ic le s hould be we ll t ra in ed

in both driving and explosives handling. B efore m oving ouw ith the e xp lo siv es lo ad , th e d rive r sh ou ld m ake s ure tha t the xp lo siv es c an no t fa ll from th e v eh ic le a s fr ic tio na l impa ct w ilre adily initiate e xp lo sive s. E xp lo sive s tra nsp ort b y ra il a ndtra ck e qU ipme nt is p artic ula rly su sce ptible to th e fric tio naimpact haza rd .

' Ital ic ized numbers in parentheses refer to items inthe l ist of references atthe

end of this chapter.



86

l\£01)!AJt¥ro)i

~. . . . . . . . • . . . . . . . . . . ..~'-'

Figure 99.-Proper Btacklng of explosives. (Courteey Auetln Powder Co.)

At the jobsite, the explosives should be stored in a safelo ca tio n, awa y from tra ffic if p os sib le . T he b la st a re a s ho uld b ed elin ea te d w ith c on es o r c ord on ed o ff, a nd u na uth oriz ed p er-sons shou ld no tbe pe rm i tted w ithi n this a rea . Where approp r ia te ,

th e e xp lo siv es s ho uld b e s to re d in a n a pp ro ve d d ay maga zin e.Explosives should not be stored where they can be hit byfa llin g ro ck o r work in g e qu ipmen t. E xp lo siv es s ho uld b e u nd erc on sta nt s urve illa nce w he ne ve r th ey a re n ot in a m ag az in e.

PRECAUTIONS BEFORE LOADING

Befo re a ny lo ad in g a ctiv itie s a re s ta rte d, th e b la st a re a mu stbe cle arly m arke d w ith fla gs, co ne s, o r oth er re ad ily id en tifi-ab le m ark ers. A ll u nn ec es sa ry e qu ipme nt m us t b e remo vedfrom th is a re a. A ll p er so ns n ot e ss en tia l to th e p owde r lo ad in go pe ra tio n sh ou ld le av e. O bs erv ers s ho uld b e u nd er th e c on -trol of a responsible person w ho w ill assure that they do notcre ate a h az ard b y w an de ring a bo ut th e are a. A ny e lec trica lpow er that m ight create a hazard should be disconnected.W here electric blasting is being used and the presence of

e xt ra neous e le ct ric it y is s uspect ed , a pp ropr ia te che ck s shouldb e mad e w ith a b la ste rs ' mu lti m e te r ( 1)o r a c on tin uo us g ro un dcur re nt monit or s hould be u tiliz ed . Whe re e xt ra neous e le ct ric -ity p ro blems p ers is t. a n on ele ctric in itia tio n s ys tem s ho uld b eu se d. T wo -w ay ra dio s in th e ne ar V icin ity s ho uld b e tu rn ed o ffw hen electric blasting is being used. IM E Pam phlet N o. 20(10) g iv es sa fe tra nsm itter d is ta nce s a s a fu nctio n o f th e typ ea nd p ower o f th e tra nsmitte r.



87

FIgure 100.-AN·FO bulk storage facil ity. (Courte.y AtI•• Powder Co.)



88

PRIMER PREPARATION

It is a cardinal rule that primers be made up at the working

face or as close to it as possible. The detonators and primer

cartridges or cast primers should be brought in as separate

components. The preparat ion of primers at a remote locat ionand their transportation to the jobsite presents an undue haz-

ard on the transportation route and should be permitted only

where required by extenuating circumstances. In large tunnel

projects, use of an outside primer makeup facility is often

considered safer than making the primers at the face. All

unused primers should be dismantled before removing them

from the jobsite. Assembled primers containing detonators

should never be stored.

A-rionsparking tool should be used to punch the hole in the

cartridge for cap placement. To assure control, the number of

persons making up primers should be as few as practical.

Electric;: hazards should be checked for if electric caps are

being used. It is extremely important that the cap be fully

imbedded into the cartridge and attached in such a way that it

will not be dislodged when tension is put on the wires or tubes.

A hard cartridge should not be rolled for softening. This will

destroy the integrity of the cartridge and the cap may not stay

fully imbedded. A good nonsparking powder punch should

make an adequate hole in any cartridge without rolling it . The

dangers of the cap falling out of the cartridge are twofold: (1)

The cap may be struck during loading or tamping operations

and cause a premature detonation, or (2) the cap may fail to

initiate the primer when it is activated. When using electric

caps with small-diameter explosive cartridges, the cartridge

should be punched at the end for cap insertion and the leg

wires should be fastened to the cartridge by a half hitch to

remove the possibility of tension on the cap (fig. 49).

The structure of larger cartr idges may require punching thecap hole in the side. With cast primers, the cap is passed

through the channel and into the cap well (fig.50). The leg

wires may be taped to the cast primer for extra secu rity. Primer

preparat ion for other types of blast ing caps, such as Nonel,"

Primadet, and Hercudet, is similar to that for electric blasting

caps. However, because propagation through the tubing of

some of these products may be hampered by sharp bends,

taping the tubing to the cartridge is recommended rather than

half hitching. The manufacturer should be consulted for

recommendations.

Where detonating cord is connected directly to the primer

cartridge, it should be secured with a tight knot, supplemented

by half hi tches. With a cast primer,detonating cord is passed

through the channel and a knot is tied at the end of the cord to

keep the primer from sl ipping off. Subsequent primers can beslid down the detonating cord. When using cap and fuse, a

diagonal hole is made through the cartridge. The cap and fuse

are passed through this hole and into a second hole made for

cap emplacement. Sometimes the cap is placed into a single,

diagonally placed side hole and the fuse is tied to the cartridge

with string. With fuse that will withstand a 1800 bend, end

priming, similar to that used with electr ic blasting caps, may be

used. Cast primers are not normally used with cap and fuse.

BOREHOLE LOADING

Before loading begins, the area should be doublecheckedfor unnecessary personnel and equipment. Ifelectric caps are

being used, possible electrical hazards should be double-

checked. If an electrical storm approaches at any time when

explosives are present, the area must be vacated, regardless

of whether electric detonators are being used. Weather reports,

l ightning detectors, or even static from AM radio receivers may

serve as warning of approaching electrical storms. Before any

detonators or explosives are brought into the blast area, all

circuits in the immediate vicinity should be deenergized.

Before loading begins, each borehole should be checked

for proper depth. This will help prevent excessive column

buildup, resulting in inadequate stemming and excessive flyrock.

In most situat ions, holes that are too deep should be partially

backfil led. Short holes may require cleaning or redri ll ing.

Using a weIghted tape, me Column buildup should be Checkedfrequently during loading. With relatively short, small-diameter

holes, atamping pole can be used to check the depth and also

to check for blockages. If the buildup is less than anticipated,

this may result in a cavity packed full of explosive which may

blowout violently when detonated. If the column builds up

more quickly than expected, frequent checking will prevent

overloading. Proper stemming length is described in the "Blast

Design" chapter. As a general rule of thumb, the stemming

should be 14 to 28 borehole diameters.

When loading small-diameter cartridges, a nonsparking tamp-

ing pole should be used. Although there are differences of

opinion, there is a consensus that a cushion stick should not

be used in small-diameter holes; therefore, the primer shouldbe the first cartridge placed into the hole. The base of the cap

should point toward the collar. The primer cartridge should

never be sli t and should be pushed into place firmly. I t should

never be tamped vigorously. Two or three cartridges may then

be sl it, placed as a column, and tamped firmly. The remaining

cartridges may be slit and tamped fi rmly. Excessive tamping

should never be done. Care should be taken not to damage

the detonator's leg wires or tubes.

Cartridges are often loaded in large-diameter blastholes by

dropping them down the hole. However, the primer cartridge

and a cartridge or two above the primer should be lowered to

prevent damage to the primer. Leg wires or tubes from detona-

tors may also be prone to damage from dropped cartridges.

"Wet bags" of AN-FO should not be dropped. They depend on

the cartr idge material for water resistance, and dropping themmay break the package and cause water leakage and subse-

quent desensitization of the AN-FO. A potential problem in

bulk loading of large diameter blastholes is overloading. Here

it is especially important to check the column rise frequently as

loading progresses (fig. 101).

When pneumatically loading blastholes with pressure pots

or venturi loaders, over electric blasting cap leg wires, it is

essential that the loader be properly grounded to prevent

buildup of static electricity. This grounding should not be to

2 Re fe re nc e to s pe cific tra de n am es d oe s n ot im ply e nd ors em en t b yth e B urea u of M in es.



89

"",~:."

Figure 101.-Checking the rise of the AN-FO column with a weighted tape.



90

p ip es , a ir lin es , r ails , o r o th er f ix tu re s t ha t a re good conduct or so f s tr ay c urre nt. E xtra ne ou s e le ctric ity is a ls o a p ote ntia l h az -a rd w ith n on ele ctric d eto na to rs . P la stic lin ers s ho uld n ot b eused w hen pneum atically loading sm all b last h oles, as thisin cre ase s th e c ha nce fo r s ta tic b uild up. T his is p articu la rly

h azar dous w it h e le ct ric d et onat or s. A sem ic ondu ct iv e lo ad in gh os e w ith a m in im um re sista nc e o f 1.000 o hms/ft a nd 10,000

ohm s total resistance, and a m axim um total resistance of

2,000,000 ohms should be used. Such a hose will perm it astatic charge to bleed off but w ill not allow stray currents toe nte r th e b ore ho le . Wh ere e xtra ne ou s e le ctr ic ity is a p ro blem,or w here it is illegal to load pneum atically over leg w ires, anonelectric in itiation system should be used. T his does not

e ntire ly e lim in ate th e h az ard , so th e sa fe gu ard s m en tio ne dp re vio us ly s hould s till b e f ollowed .

HOOKING UP THE SHOT

The size of crew used to hook up the shot should be kept toan absolute m inim um . A single person should be in charge offin al ch ec ko ut to a ss ure th at th e h ook Up p la n h as b ee n p ro p-erly follow ed and that the blast is ready to fire.

Wh en b la stin g e le ctr ic ailY , th e s erie s c ir cu it is th e e as ie st,s afe st, a nd s ur es t. If s ev era l s ho ts a re to b e fire d to ge th er , o r if

there is an excessive num ber of caps in one shot, a paralle lse rie s c irc uit sh ou ld b e u se d. M ak e su re th at e ach s erie s h asth e same re sis ta nce . A tw is te d lo op is th e b es t co nn ectio n fo rtw o relatively light gage w ires. S plices for connecting lightgage w ire to heavy gage w ires are show n in figure 22. Exces-sive w ire betw een holes m ay be coiled or rem oved for neat-n es s and t o f ac ilit at e v is ua l in spec tio n o f t he c ir cu it . Make sur etha t b are c on ne ctio ns d o n ot tou ch e ach o th er o r the g ro un d ino rd er to a void sh ort circ uits , c urre nt le ak ag e, o r p ick in g u p o fex traneous cu rren ts .

A fte r e ach p ortio n o f th e c irc uit h as b ee n h oo ke d u p, c he ckfo r c on tin uity a nd p ro pe r re sis ta nc e w ith a b la stin g mu lti m e te ror galvanom eter. The circuit should then be shunted untilready for the final hookup prior to blasting. It is especiallyim po rta nt th at th e le ad w ire be ke pt s hu nte d a t th e sh otfire r'slo ca tio n u ntil th e b la st is re ad y to b e fire d.

A bla stin g m ac hin e is re commen de d fo r firin g a ll s ho ts. If ap owe rlin e is u sed it s hould be one t ha t is s pe cif ic ally d ed ic at edto blasting and is equipped with a safeguard againsto ve re ne rg iz in g th e c ap s a nd a ga in st th e r es ultin g a rc in g. B at-t er ie s s hould never b e u sed f or f ir in g e le ct ric al b la st in g c ir cu it sbecause their output is unpredictable and m ay cause only ap ortio n o f th e ro un d to b e fir ed . P ara lle l c irc uits a re le ss d es ir-a ble b ec au se th ey re qu ir e h ig h c ur re nt a nd c an no t b e c he ck edf or s ho rt s o r b ro ken w ir es . I f p owe rlin e f ir in g o r s tr aig ht p ar alle lc ircu its a re n ece ssa ry, th e c ap m an ufa ctu rer s ho uld b e c on -s ulte d fo r p ro ce du re s fo r m in im iz in g p ro blems.

W hen firing w ith detonating cord system s, m ake sure the

knots are tight and secure. T ight lines and severe anglesb etw ee n lin es sh ou ld b e a void ed (fig . 32 ). T he c ord sh ou ld n otb e p erm itte d to c ro ss its elf. T he c ord circ uit sh ou ld b e la id o utso th at e ac h h ole ca n b e in itia te d b y a t le as t tw o p ath s from th ed eto na to r u se d to in itia te th e c irc uit. A fte r th e h oo ku p h as b ee nc omp le te d, th e c irc uit s ho uld b e c are fu lly c he ck ed v is ua lly b y

th e p erso n in ch arge o f th e b la st. T he in itia tin g ca p sh ou ld n otbe connected to the detonating cord until it is tim e to blast.

W hen blasting w ith fuse, the use of Ignitacord is recom -m ended for m ultip le hole blasts. A principal cause of fusea cc id en ts is try in g to lig ht to o ma ny fu se s a t o ne time . S ec on d-ary causes are w et or deteriorated fuse and insufficient orimp ro pe r lig htin g e qu ipmen t. Wh en u sin g Ig nita co rd , a ll fu se sshould be the sam e length. The path of the Ignitacord w illdeterm ine the delay sequence. The Ignitacord should notc ro ss its elf, b ec au se c ro ss lig htin g is a p os sib ility . A t le as t tw opersons m ust be present when lighting fuses. If fuses areb ein g in div id ua lly lit, n o p ers on s ha ll lig ht mor e th an 1 5 fu se s.MSHA re gu la tio ns s pe cify b ur nin g tim e s fo r fu se s, d ep en din gon the num ber of fuses a person lights. The burning speed offuse should be tested frequently. A ll fuse burns nom inally atabout 40 sec/ft. A ll fuses m ust be burning inside the holeb efo re th e firs t h ole d eto na te s.

A cc id en t ra te sS h o w that fuse blasting is inherently m oreh aza rdo us th an o th er in itia tio n m eth od s. M an y o f th ese in ci-d en ts o ccur w it h h ig hly e xper ie nced m iner s. I t i s r ec ommendedth at, w he re ve r p ra ctic al, fu se b la stin g b e re pla ce d b y a n a lte r-n ativ e in itia tio n s ys tem . When u sin g th e mor e re ce ntly d ev el-o ped in it ia tio n s ys tems such a s He rc udet , De ta lin e, a nd None l,the blaster should seek advice on the proper hookup proce-d ur es from th e ma nu fa ctu re r o r d is trib uto r. C erta in a sp ec ts o fthese system s are still evolving and recommended proce-dures change from tim e to tim e.

SHOT FIRING

M ore people are injured and killed during the shot firingo pe ra tio n th an a ny o th er p ha se o f b la stin g. T his is u su ally d ueto inadequate guarding, im proper signaling, or som e otherunsafe practice that perm its a person to be too close to theb la st w he n it is d eto na te d. It is e ss entia l th at th e b la ste r tak ep os itive s tep s to a ssu re th at n o o ne , in clu din g th e b la ste r a ndthe crew, is in the area of potentia l flyrock at the time ofdetonation.

T he b la ste r s ho uld a llo w a de qu ate tim e immed ia te ly b efo reb la stin g to in sp ec t th e b la st a re a fo r a ny la st m in ute p ro blems.H e or she should have a fail-safe system to assure that theb la st is n ot in ad ve rte ntly fire d. T his c an b e d on e b y s afe gu ard -

in g th e ke y o r h an dle to th e b la stin g m ach in e or s witch . W hilep ro ceed in g f rom the lo aded sho t toward t he sho tf ir in g lo ca tio n,th e b la ste r s ho uld mak e s ur e th at a ll c on ne ctio ns b etwee n th eb la stin g circ uit a nd th e firin g m ech an is m a re in ta ct.

T he bla ste r m us t m ake s ure th at th ere a re e no ug h g ua rd s tose al o ff th e a re a a nd p ro te ct p erso ns fro m in ad ve rte ntly p ro -ceeding into the blast area. It is common procedure to blockaccess to the blast zone 5 to 10 m in before the blast. Theg ua rd s sh ou ld p ro cee d o utw ard fro m th e b la st a re a, c le arin ga ll p ers on ne l fro m th e a re a a s th ey p ro cee d. T he y sh ou ld ta keu p g uard p os itio ns b ey on d th e ra ng e o f flyro ck , c on cu ssio n,and toxic gases. Once the area has been sealed off, the



91

guards must permit no one to pass unless they first inform the

shotfirer and receive assurance from the shotfirer that he or

she wi ll postpone the blast.

A warning siren with an audible range of about 0.5 mi should

be sounded before the blast. However, signs or audible warn-

ings alone are not dependable for keeping people out of the

blast area. These types of warning may not be understood byall persons in the area and they do not clearly delineate the

hazardous area. Many underground mines have check-in and

checkout procedures that are used to assure that no one will

stray into the blast area. These systems reduce the number of

guards required. The guards must be told if more than one

blast is to be fired. Even after all blasts have been fired, it is

important that the guards receive an audible or visual all-clear

signal before allowing persons to pass. Ifthe guard is indoubt,

he or she should keep the area secure until the doubt is

removed.

The shotf irer should choose a safe firing location with ade-

quate distance and/or cover (fig. 102) for protection from

flyrock, concussion, and toxic gases. Ideally he or she should

have two-way visual or audible contact with the guards. On a

surface blast the shotfiring locat ion should command a good

view of the area surrounding the blast. Just before the shotfiring

mechanism is prepared for activat ion the blaster should alert

the guards to seal off the area and should receive a positive

response from each guard. Immediately before fir ing the shot

guards are again alerted and if their response is posi tive, the

shot isfired. Ifthe shot fails to fire, security must be maintained

while the blaster attempts to correct the problem. Once secu-

rity is removed, the entire guarding procedure should be repeatedbefore the shot is f ired.

In some situations, particularly underground, contact between

the shotf irer and the guards may be impract ical. In this case,

the guards must clear and secure the area and maintain

security until al l shots are fired or until they are relieved of the

responsibili ty by the blaster. This may mean guarding the area

for an extended period of t ime.Obviously some situations will exist which will not fit the

preceding discussion. The principles, however, will remain the

same-(1) the blast area must be cleared and guarded and (2)

security must be maintained until i t is certain that the blast ing

act ivi ties in the area have ceased for the time in question.

Blast ing at night at surface mines is especially hazardous

because of the lack of visibility and should be done only in an

emergency.

Figure 102.-Blasting shelter. (Courtesy Hercules lne.)



92

POSTSHOT SAFETY

A t l eas t 15 s ec s ho uld b e a llo we d fo r a ll fly ro ck to d ro p. E ve na fte r a ll f1 yro ck h as s ub sid ed , th e h az ard s of to xic g as es an dloose rock in the blast area exist. The area should not be

re en te re d u ntil th e to xic g as es h av e b ee n d is pe rs ed . T he timere qu ire d fo r th 'd m ay ra ng e fro m a m in ute fo r s urfa ce b la stin gt o an hou r o r mo re fo r a poo rly v en tila te d undergr ound openin g.In ca se o f a k no wn o r s us pe cte d m is fire, a w aitin g p erio d o f a tle as t 3 0 m in w ith c ap -a nd -fu se b la stin g o r a t le as t15 min w it he le ctric in itia tio n s ys tems mus t b e o bs erv ed . If e xp lo siv es a res us pe cte d to b e b urn in g in a b la sth ole , a t-h r m in imum waitin gperiod m ust be observed. The practice of blasting betw eens hifts is re commend ed b ec au se it a vo id s o r m in im iz es g ua rd -in g p ro ble ms a nd a llo ws g ase s to cle ar b efo re re en try .

T he fir st p ers on r ee nte rin g th e b la st a re a s ho uld in sp ec t th ea rea fo r loo se ro ck th at p os es a h aza rd to p ers onn el. T he are ashould be dangered off until any loose rock has been barred

down or otherw ise taken care of. The blast area should bec hec ke d fo r m is fire s. Lo os e e xp lo siv es o r d eto na tin g co rd inth e m uck pile o fte n in dica te a m is fire . L eg w ire s, d eto na tin gcord, or tubes extending from a borehole may indicate am isfire. Another indicator is an area of the blast that has notb ro ke n o r p ulle d p ro pe rly o r a n u nu su al s ha pe o f th e mu ck pile .In man y c as es th is ta ke s th e fo rm o f a n u nu su ally lo ng b oo tle g.B eca us e a m isfire is n ot a lw ays o bv io us , a tra in ed e ye is o fte nrequired to detect one. O ther persons m ust not be perm ittedinto the blast area until it is certain that no hazards exist.

DISPOSING OF MISFIRES

A good method of m isfire disposal is to remove theundet onat ed cha rge b y wa te r f lu sh in g o r a ir p re ssur e. Ho riz on -ta l o r s ha llo w h ole s a re m os t ame na ble to th is te ch niq ue . It isim portant to visually inspect the hole using a light source toassure that all of the charge has been rem oved.

W here rem oval of the m isfired charge is too difficult, analternative is to detonate the charge. If leg w ires, tubes, ordetonating cord are protruding from the holes, and they areintact, they m ay be reconnected and fired. If th is cannot bed on e, th e s te mm in g m ay b e remo ve d, a n ew p rim er in se rte d a tthe top of the pow der colum n, and the hole refired. C autionm ust b e e xe rc is ed in re firin g m isfire d h oles fro m whic h m ucho f th e b urd en h as b ee n remo ve d. E xc es siv e fly r oc k is like ly tore su lt a nd th e a re a m us t b e g ua rd ed a cco rd in gly . If n eith er o f

th ese a lte rn ative s a re fe asib le , th e c ha rg e w ill h av e to b e d ugo ut. F irs t. th e h ole s ho uld b e flo od ed w ith wate r to d es en sitiz ea ny n on -wate r-re sis ta nt e xp lo siv e p re se nt. N ex t. th e ro ck s ur -rounding the m isfire is dug out carefully, w ith an observerpresent to guide the excavator. E xtrem e discretion m ust bee xe rc is ed in t his o pe ra tio n.

The practice of drilling and shooting a hole adjacent to them isfire h as b een u se d, b ut c an b e e xtre me ly h az ard ou s. P eo -ple have been killed using this technique w hen the new holeintersected the m isfired hole and detonated it. All of the pre-v io us ly d es cr ib ed t echn iq ue s a re p re fe ra ble to d rillin g an adja -c en t h ole . MSHA me ta l- nonme ta l r egula tio ns p ro hib it d rillin g ahole where there is a danger of intersecting a charged orm is fir ed hole .

DISPOSAL OF EXPLOSIVE MATERIALS

F or ye ars th e m eth od re commen ded by th e IME fo r d es tro y-in g e xp lo siv es was burnin g. However , t he r ecen t p ro lif er at io nof nonflammable explosive products has caused the IM E tow it hd raw this r ecommendat io n and it s p amphle t t ha t d es cr ib ed

p ro per b urn in g tec hn iq ue s. T he re commen da tio n n ow mad eby the IM E is to contact the nearest explosive distributor,w hether or not it handles the brand of explosive in question.T he d is trib uto r s ho uld d is po se o f th e u nwan te d e xp lo siv e.

PRINCIPAL CAUSES OF BLASTING ACCIDENTS

A lth ou gh th ere is a p ote ntia l fo r s erio us a ccid ents a t e ve rys ta ge o f e xp lo siv e u se , c erta in a sp ec ts o f bla stin g h av e m oreacci den t po ten ti al than o the rs . Case h is to ry a rt ic les desc rib ingtyp ica l b la stin g a ccide nts h av e b een w ritte n (2 -3 ). A vo id in gthe follow ing four types of accidents, listed in approxim ateorder of frequency, w ould significantly im prove the safetyr ecor d o f t he b la st in g in du st ry .

Improper Guarding. T his in clu de s imp ro pe r g ua rd in g o f th eb la st a re a o r b la stin g c rew members ta kin g in ad eq ua te c ov er .Ma ny p eo ple u nd ere stim a te th e p ote ntia l r an ge o f fly ro ck .Impacting Explosives. Most o fte n th is in vo lv es d rillin g in to

h ole s c on ta in in g e xp lo siv es , fre qu en tly b oo tle gs . Howev er, itmay i nvo lve s tr ik ing explos ives w ith excavator bucke ts , t racked

e qu ip me nt, or ra il e qu ip me nt. o r e xc ess iv e b ea tin g on e xp lo -sives w ith a tam ping pole.

Unsafe Cap and Fuse Practices. F or v ario us re as ons , a llin vo lv in g u ns afe a cts o r c are le ss ne ss , th e b la ste r is s till in th eV ic in ity o f th e b la st whe n it d eto na te s.

Extraneous Electricity. E xp os ure o f e le ctr ic b la stin g c ap s tos tra y g ro un d c ur re nt, s ta tic b uild up , ra dio fr eq ue nc y e ne rg y,inductive coupling, or im proper test instrum ents can causeu ns ch ed ule d d eto na tio n. L ig htn in g is a h az ard w ith a ll ty pe s o fexplos ive ma ter ia ls .

O th er c au se s o f a cc id en ts in clu de e xp lo siv e fire s th at d eto -nate (hangfires), poor w arning system s, loading hot holes,a nd e xp os ure to b la st fu me s.



93

UNDERGROUND COAL MINE BLASTING

A ll u nd erg ro un d c oa l m in e b la stin g is d on e e le ctric ally . T hef or ego ing d is c us si on appli es to unde rg round c oa l m ine b la s ti ng .T he re a re a dd itio na l h az ard s c au se d b y th e p ote ntia lly e xp lo -

s ive atm osphere present in underground coal m ines . Bothmethane and coal dus t present an explos ion hazard. As are su lt, u nd erg ro un d c oa l m in e b la ste rs mu st u nd erg o rig oro us ,

s pec ia li zed tr ain ing be fo re t hey c an become quali fie d s hotf ir er s.B eca us e o f its sp ecific ity , a discu ssio n o f un derg rou nd coa lm ine blasting safety is beyond the scope of th is m anual. An

e xc elle nt p oc ke t-s iz e p amphle t (4 ) is a va ila ble fr om Herc ule s,In c., w hic h g iv es re commen de d p ro ce du re s fo r u nd erg ro un dc oa l m i ne s hot fir er s.

REFERENCES

1. At las Powder Co. (Dallas, TX). Handbook of Electric Blasting.

Rev. 1976, 93 pp.

2. Dick, R. A.. and J. G. Gill. Metal and Nonmetal Mine Blasting

Accidents Dl,Jring 1975-1976. Min. Eng. , v. 29, No. 11, November

1977, pp. 36-39.3. __ . Recent Blasting Fatalities in Metal-Nonmetal Mining.

Pit and Quarry, v. 67, No. 12, June 1975, pp. 85-87.

4. Hercules, Inc. (Wilmington. DE). Shotflrer 's Guide. 1978, 12 pp.5. Inst itute of Makers of Explosives Safety Library (Washington,

DC). The American Table of Distances. Pub. No.2, April 1977, 17 pp.

6. __ . Do's and Don'ts Instructions and Warnings. Pub. No.4,

Rev. July 11, 1978, 12 pp.

7. __ . Glossary of Industry Terms. Pub. No. 12, September

1981,28 pp.

8. __ . IME Standard for the Safe Transportation of Electric

Blasting Caps in the Same Vehicle With Other Explosives. Pub. No.

22, Mar. 21, 1979, 8 pp.

9. _._. Recommended Industry Safety Standards. PUb. No.6,

Feb. 1977,46 pp.

10. __ .Safety Guide for the Prevention of Radio-Frequency

Radiation Hazards in the Use of Electric Blasting Caps. Pub. No. 20,October 1978, 20 pp. .

11. __ . Safety in the Transportation, Storage, Handling, and

Use of Explosives. Pub. No. 17, April 1974, 57 pp.

12. __ . Suggested Code of Regulations for the Manufacture,

Transpor tation, Storage, Sale, Possession and Use of Explosive

Materials. Pub. No.3, May 1980, 59 pp.13. __ . Typical Storage Magazines. Pub. No.1, October

1977,22 pp.

14. National Fire Protection Association (Boston, MA). Manufacture,

Storage, Transportation and Use of Explosives and Blasting

Agents-1973. Pamphlet 495, 1973, 69 pp.

15. __ . Separation of Ammonium Nitrate Blasting Agents

From Explosives-1976. Pamphlet 492,1976,10 pp.

16. __ . Storage of Ammonium Nitrate-1975. Pamphlet 490,

1975,22 pp.



94

BIBLIOGRAPHY

1. Andrews, A. B. Design of Blasts. Emphasis on Blast ing. Ensign

Bickford Co. (Simsbury, CN), Spring 1980, pp. 1, 4.

2. Ash, R. L. The Mechanics of Rock Breakage, Parts I, II, III, andIV. Pit and Quarry, v. 56, No.2, August 1963, pp. 98-112; No.3,

September 1963, pp. 118-123; No.4, October 1963, pp. 126-131 ;No.

5, November 1963, pp. 109-111,114-118.

3. At las Powder Co. (Dallax TX). Handbook of Electric Blasting.

Rev. 1976,93 pp.

4. __ . Pneumatic Loading of Nitro-Carbo-Nitrates; Static Elec-

tr icity, Fumes, and Safe Handling. Undated, 17 pp.

5. Bauer, A., and J. W. Sanders. Good Blasting Techniques and

Publ ic Relations. Min. Congo J., V. 54, No. 11, November 1968, pp.

81-85.

6. Chironis, N. P. New Blasting Machine Permits Custom-

Programmed Blast Patterns. Coal Age, v, 79, No.3, March 1974, pp.

78-82.

7. Condon, J. L., and J. J. Snodgrass. Effects of Primer Type and

Borehole Diameter on AN-FO Detonation Velocit ies. Min. CongoJ., V.

60, No.6, June 1974, pp, 46-47, 50-52.

8. Cook, M. A. Explosives-A Survey of Technical Advances. Ind.and Eng. Chem., V. 60, No.7, July 1968, pp.44-55.

9 .The Science of Industrial Explosives. Ireco Chemicals,

Salt Lake City, UT, 1974,449 pp.

10. Damon, G. H., C. M. Mason, N. E. Hanna, and D. R. Forshey.

Safety Recommendations for Ammonium Nitrate-Based Blasting Agents.

BuMines IC 8746,1977,31 pp.11. Dannenberg, J. Blasthole Dewatering Cuts Costs. Rock P!Uducts,

V. 76, No. 12, December 1973, pp. 66-68.

12. __ . How To Solve Blasting Materials Handling Problems.

Rock Products, v, 74, No.9, September 1971, pp. 63-65.

13. Dick, R. A. Explosives and Borehole Loading. Subsection 11.7,

SME Mining Engineering Handbook, ed. by A. B. Cummins and I.A.Given, Society of Mining Engineers of the American Institute of Mining,

Metal lurgical, and Petroleum Engineers, Inc., New York, v, 1, 1973,

pp.11-78-11-99.

14. __ . Factors in Selecting and Applying Commercial Explo-

sives and Blasting Agents. BuMines IC 8405, 1968, 30 pp.15. __ . The Impact of Blasting Agents and Slurries on Explo-

sives Technology. BuMines IC 8560,1972,44 pp.

16. __ . New Nonelectric Explosive Initiation Systems. Pit and

Quarry, V. 68, No.9, March 1976, pp. 104-106.

17. __ . Puzzled About Primers for Large Diameter AN-FO

Charges? Here's Some Help To End the Mystery. Coal Age, v,81, No.

8, August 1976, pp. 102-107.

18. __ . A Review of the Federal Surface Coal Mine Blasting

Regulations. Proc. 5th Conf. on Explosives and Blasting Technique,

St. Louis, MO, Feb. 7-9, 1979. Society of Explosives Engineers,

Montvil le, OH, pp. 1-7.

19. Dick, R. A., and J. G. Gill. Metal and Nonmetal Mine Blasting

Accidents During 1975-1976. Min. Eng., V. 29, No. 11, November

1977, pp. 36-39.

20. __ . Recent Blasting Fatalities in Metal-Nonmetal Mining.

Pit and Quarry, V. 67, No. 12, June 1975, pp. 85·87.

21. Dick, A.A. , and J. J. Olson. Choosing the Proper Borehole Sizefor Bench Blasting. Min. Eng., V. 24, No.3, March 1972, pp. 41-45.

22. Dick, R. A. , and D. E. Siskind. Ground Vibration Technology

Pertaining to OSM RegUlations. Proc. Symp. on Surface Coal Mining

and Reclamation, Coal Conf. & Expo, Louisvi lle, KY, Oct. 23-25, 1979.

McGraw-Hi li , New York, pp. 13-18.

23. Drury, F., and D. J. Westmaas. Considerations Affecting the

Selection and Use of Modern Chemical Explosives. Proc. 4th Conf. on

Explosives and Blasting Technique, New Orleans, LA, Feb. 1-3,

1978. Society of Explosives Engineers, Montville, OH, pp. 128-153.

24. E.I. duPontde Nemours & co., Inc. (Wilmington, DE). Blaster'sHandbook. 16th ed., 1978,494 pp.

25. __ . Four Major Methods of Controlled Blasting. 1964, 16

pp.

26. Ensign Bickford Co. (Simsbury, CN). Prlmacord Detonating

Cord. 9th printing, copyright 1963, 68 pp.

27. Friend, R. C. Explosives Training Manual. ABA Publishing Co.,

Wilmington, DE, 1975, 212 pp.

28. Grant, C. H. Metallized Slurry Boosting: What It Is and How.l!Works. Coal Age, V. 71, No.4, Apr il 1966, pp. 90-91.

29. Gregory, C. E. Explosives for North American Engineers. Trans

Tech Publications, Rockpor t, MA, 1979, 303 pp.

30. Gustattson, R . Swedish Blasting Technique. SPI, Gothenburg,

Sweden, 1973, 323 pp.; avai lable for consultat ion at Bureau of Mines

Twin Ci ties Research Center, Minneapol is, MN.

31. Hagan, T. N. Optimum Priming for Ammonium Nitrate Fuel-Oil

Type Explosives. Proc. Southern and Central Queensland Conf . of

the Australasian Inst. of Min. and Met., Parkville, Austral ia, July 1974,

pp. 283-297; avai lable for consultat ion at Bureau of Mines Twin Cit ies

Research Center, Minneapolis, MN.

32. Hemphill, G. B. Blasting Operations. McGraw-Hili, New York,

1981, 258 pp.

33. Hercules, Inc. (Wilmington, DE). Shotfirer's Guide. 1978, 12

pp.

34. Insti tute of Makers of Explosives Safety Library (Washington,

DC). The American Table of Distances. Pub. No.2, April 1977, 17pp.35. __ . Do's and Don'ts Instructions and Warnings. Pub. No.

4, Rev. July 11, 1978, 12 pp.

36. __ . Glossary of Industry Terms. Pub. No. 12, September

1981,28 pp.

37. __ . IME Standard for the Safe Transportation of Electric

Blasting Caps in the Same Vehicle With Other Explosives. Pub.

No. 22, Mar. 21, 1979,8 pp.

38. __ . Recommended Industry Safety Standards. Pub. No.6,

February 1977, 46 pp.

39. __ . Safety Guide for the Prevention of Radio-Frequency

Radiation Hazards in the Use of Electric Blasting Caps. Pub. No. 20,

October 1978, 20 pp.

40. __ . Safety in the Transportation, Storage, Handling, and

Use of Explosives,'Pub. No. 17, Apr il 1974, 57 pp.

41. __ . Suggested Code of RegUlations for the Manufac-

ture, Transportation, Storage, Sale, Possession and Use of Explosive

Materials. Pub. No.3, May 1980,59 pp.42. __ . Typical Storage Magazines. Pub. No.1, October

1977,22 pp.

43. Johansson, C. H., and U. Langefors. Methods of Physical

Characterization of Explosives. Proc. 36th Internat. Congo of Ind.

Chem., Brussels, V. 3, 1966, p. 610; available for consultation at

Bureau of Mines Twin Cities Research Center, Minneapolis, MN.

44. Junk, N. M. Overburden Blasting Takes on New Dimensions.

Coal Age, V. 77, No.1, January 1972, pp. 92-96.

45. __ . Research on Primers for Blasting Agents. Min. Congo

J., V. 50, No.4, April 1964, pp. 98·101.

46. Langefors, U., and B. A. Kihlstrom. The Modern Technique of

Rock Blasting. John Wiley & Sons, Inc., New York, 1963, 405 pp.

47. Lundborg, N., P. A. Persson, A. Ladegaard-Pederson, and R.

Holmberg. Keeping the Lid on Flyrock From Open Pit Blasting. Eng.

and Min. J., v, 176, No.5, May 1975, pp. 95·100.

48. Miller, P. Blasting Vibration and Airblast. Atlas Powder Co.

(Dallas, TX), 16 pp.49. Monsanto Co. (St. Louis, MO). Monsanto Blasting Products

AN-FO Manual. Its Explosive Properties and Field Performance

Characteristics. September 1972, 37 pp.

50. National Fire Protection Association (Boston, MA). Manufacture,

Storage, Transportation and Use of Explosives and Blasting

Agents-1973. Pamphlet 495,1973,69 pp.

51. __ . Separation of Ammonium Nitrate Blasting Agents

From Explosives-1976. Pamphlet 492,1976,10 pp.

52. __ . Storage of Ammonium Nitrate--1975. Pamphlet 490,

1975,22 pp.

53. Nicholls, H. R. , C. F. Johnson, and W.1. Duvall. Blasting Vibra-

tions and Their Effects on Structures. BuMines B 656, 1971, 105 pp.

54. Porter, D. D. Use of Fragmentation To Evaluate Explosives for

Blasting. Min. Congo J., V. 60, No.1, January 1974, pp. 41-43.



55. Pugliese, J. M. Designing Blast Patterns Using Empirical

Formulas. BuMines IC 8550, 1972, 33 pp.

56. Robinson, R. V. Water Gel Explosives-Three Generations.

Canadian Min. and Met. Bull., v. 62, No. 692, December 1969, pp.

1317-1325.

57. Schmidt, R. L., R .• 1 . Morrell, D. H. Irby, and R. A. Dick. Applica-

t ion of Large-Hole Burn Cut in Room-and-Pillar Mining. BuMines RI

7994, 1975, 25 pp.58. Sengupta, D., G. French, M. Heydari, and K.Hanna. The Impact

of Eliminat ing Safety Fuse From Metal/Nonmetal Mines (Contract

J029501 0, Sci. Applications, Inc.). BuMines OFR 61-81, August 1980,

11 pp.; NTIS PB 81-214386.

59. Siskind, D. E., V. J. Stachura, M. S. Stagg, and J. W. Kopp.

Structure Response and Damage Produced by Airblast From Surface

Mining. BuMines RI 8485, 1980, 111 pp.

6 0 . Siskind, D. E ~ , -M . S. Stagg, J. W. Kopp, and C. H. Dowding.

Structure Response and Damage Produced by Ground Vibration

From Surface Mine Blast ing. BuMines RI8507, 1980,74 pp.

61. Siskind, D. E. , and C. R. Summers. Blast Noise Standards and

Instrumentation. BuMines TPR 78, May 1974, 18 pp.

62. Stachura V. J., D. E. Siskind, and A J. Engler. Airblast Instru-

mentation and Measurement Techniques for Surface Mine Blasting.

BuMines RI8508, 1981,53 pp. .

95

63. Stagg, M.S., and A. J. Engler. Measurement of Blast-Induced

Ground Vibrations and Seismograph Calibration. BuMines RI 8506,

1980,62 pp.

64. U. S. Bureau of Mines. Apparent Consumption of Industrial

Explosives and Blast ing Agents in the United States, 1981. Mineral

Industry Survey, June 23, 1982, 12 pp.

65. U. S. Department of the Treasury; Bureau of Alcohol, Tobacco

and Firearms. Explosive Materia ls Regulations. Federal Register, v.42, No. 149, Aug. 3,1977, pp. 39316-39327; Federal Register , v. 45,

No. 224, Nov. 18, 1980,pp. 76191-76209.

66. U. S. Mine Enforcement and Safety Administ rat ion. Active List

of Permissible Explosives and Blasting Devices Approved Before

Dec. 31, 1975. MESA Inf. Rep. 1046, 1976, 10 pp.

67. U. S. Off ice of Sur face Mining. Surface Coal Mining and Recla-

mation Operations-Permanent Regulatory Program. Federal Register,

V. 44, No. 50, Mar. 13, 1979, Book 2, pp. 15404-15406 (requlanons),

Book 3, pp. 15179-15202 (preamble.)

68. Winzer, S. R. The Firing Times of MS Delay Blasting Caps and



(Baltimore, MD), June 1978, 36 pp.; available for consultation at Bureau

of Mines Twin Cit ies Research Center, Minneapolis, MN.



96

APPENDIX A.-FEDERAL BLASTING REGULATIONS

Numerous aspects of the manufacture, transportation, storage,

sale, possession, and use of explosives are regulated. These

regulations may be enforced at the Federal, State, county,

city, and township level of government. Some Federal regula-tions are enforced by State agencies. State and local agencies

often adopt regulations that duplicate or expand upon Federal

regulations. It ls important that every person or company

involved in handling explosives maintains a file of all the

regulations that appy to the operation. This appendix dis-

cusses the regulation picture at the Federal level. The powder

supplier will be able to direct the blaster to the other levels of

government that enforce regulations in a particular geographic

area. Where there is a conflict between two regulations in a

geographic area, the most restrictive, or the one that provides

the greatest degree of safety, should be complied with.

Unfortunately, this interpretation is not always clear cut.

Federal agencies that are specifically chartered by the Code

of Federal Regulations (CFR) to regulate blast ing are-

1. Department of Labor

A. Mine Safety and Health Administration-CFR 30, Parts

1-199

B. Occupational Safety and Health Administration-CFR

29, Parts 1900-1999

2. Department of Interior, Office of Surface Mining Reclama-

tion and Enforcement-eFR 30, Parts 700-999

3. Department of the Treasury, Bureau of Alcohol, Tobaccoand Firearms-GFR 27, Parts 1-299

4. Department of Transportation

A. Research and Special Programs Administration-CFR

49, Parts 100-177

B. Federal Highway Administration-CFR 49, Parts

301·399

Table A-1 summarizes the responsibilities of these agencies.

It is a good idea for the blaster to maintain copies of these

regulations and to read them. There is a good possibility that

some of the regulations a blaster may have on hand are out of

date, because regulations change frequently. The Federal

Register updates all the regulat ion changes on a daily basis.

Codified regulations are updated and published on an annualbasis. Also, some companies provide the service of keeping

operators informed of changes in regulations.

Departmentand agency

Table A·1 •• Federal regulatory agency responsibility

Primary responsibility Source of regulations

Departmentof Labor:MineSafetyand HealthAdministration. Onsltesafetyinthestorage, transportation, and use CFR30, Chapter I:

of explosives in m ining operations. Subchapter C, Parts 15, 16, 1 7.SUbchapterD, Parts 24, 25.Subchapter H, Part 48.Subchapter N, Parts55, 56, 57.

Subchapter 0, Parts75, 77

Occupational Safety and HealthAdministration.

Onsite safety inthe storage, transportation, and use CFR 29, Subtitle B, Chapter XVII:ofexplosives inconstruction and other nonmine Part 1910, Subpart H.blasting operations Part 1926, Subpart U.

Departmentof Interior: OffiCtlof Surface MiningReclamationand Enforcement.

Environmentalprotection for surface blasting CFR30, Chapter VII:associated with coal mines. Subchapter K, Parts 816, 817

Department of Treasury: Bureauof Alcohol,Tobacco and Firearms.

Security in t he importation, manufacture, CFR 27, Part 181:distribution, a nd storage of explosives. Subparts A, B,C ,D, E , F, G, H, I, J.

Departmentof Transportation:Researchand Special ProjectsAdministration.

Safeshipmento fexplosives in interstate CFR 49, Chapter I,Subchapter C:commerce. Parts 171,172,173,174,175,176,177.

Federal HighwayAdministration. ...do CFR 49, Chapter III. Subchapter B:Part 397.

MINE SAFETY AND HEALTH ADMINISTRATION (MSHA)

MSHA regulates safety in the handling of explosives in all

types of mining. Topics included are onsite storage, transporta-

tion from the magazine to the jobsite, and use. These regula-

tions can be found in CFR 30, in the following parts:

Chapter I-Mine Safety and Health Administration

Subchapter e-Explosives and Related Articles; Tests

for Permissibility and Suitability

Part 15-Explosives and Related Articles (including

permissible blasting practices)Part 16-Stemming Devices

Part 17-Blasting Devices

Subchapter D-Electrical Equipment, Lamps, Methane

Detectors; Tests for Permissibility; Fees

Part 24-Single-Shot Blasting Units



Part 25-Mult iple-Shot Blasting Units

SUbchapter H-Education and Training

Part 4&-- Training and Retraining of Miners

SUbchapter N-Metal and Nonmetallic Mine Safety and

Health

Part 55-Safety and Health Standards-Metal and Non-metallic Open Pit Mines

55.2 Definitions

55.6 ExplosivesPart 56-Safety and Health Standards-Sand, Gravel,

and Crushed Stone Operations

56.2 Definitions

56.6 ExplosivesPart 57-Safety and Health Standards-Metal and Non-

metallic Underground Mines

97

57.2 Definitions

57.6 Explosives

57.21 Gassy Mines; 57:21-95-57.21-101, Explosives

Subchapter O-Coal Mine Safety and Health

Part 75-Mandatory Safety Standards-

Underground Coal MinesSubpart N-Blasting and Explosives

Part 77-Mandatory Safety Standards, Surface Coal

Mines and Surface Work Areas of Under-

ground Coal Mines

Subpart N-Explosives and Blast ing

Subpart T-Slope and Shaft Sinking

In many cases MSHA regulations are enforced by State

agencies. Some States may have more stringent mine health

and safety regulations than those of MSHA.

OCCUPATIONAL SAFETY AND HEALTH ADMINISTRATION (OSHA)

OSHA is a companion agency of MSHA, both being in the

Department of Labor. OSHA regulates safety in the handling

of explosives in nonmining industries, most notably construction.

The OSHA blasting regulations are found in CFR 29, in the

following parts:

Subtitle B-Regulations Relat ing to Labor

Chapter XVII-oSHA, Department of Labor

SUbpart H-Hazardous Materials

1910.109--Explosives and Blasting Agents

Part 1926-Safety and Health Regulations for

Construction

Subpart U-Blasting and Use of Explosives (Sections

1926.900-1926.914)

In many cases, OSHA regulations are enforced by State

agencies. Some States may have more stringent heal th andsafety regulations for construction than OSHA.

OFFICE OF SURFACE MINING RECLAMATION AND ENFORCEMENT (OSM)

OSM regulations are the most recent Federal blasting

regulations, having been promulgated in 1979 (67).1 These

regulations, which deal only with surface coal mines and sur-

face operations associated with underground coal mines, are

environmental in nature. There are no Federal environmental

regulations for metal-nonmetal mines. The OSM blasting regula-

tions are designed to protect persons and property outside the

mine area from potentially harmful effects of blasting. They

deal with blaster qualifications, preblasting surveys, blasting

schedules, control of ground vibrations and airblast, seismo-

graphic measurements, and blast records. The OSM regula-

tions are found in CFR 30, in the following parts:

Chapter VII-OSM, Department of the Interior

Subchapter K-Permanent Program Performance

Standards

Part 816-Surface Mining Activities

Sections 816.61-816.68, Use of Explosives

Part 817-Underground Mining Activities

Sections 817.61-817.68, Use of Explosives

Inmost cases, OSM regulations are enforced by the individ-

ual States. Some of these States may have more stringent

environmental regulations than those of OSM.

BUREAU OF ALCOHOL~TOBACCO AND FIREARMS (BATF)

BATF regulates security in the importat ion, manufacture,

distribution, and storage of explosives. The primary goal of

BATF is to prevent explosives from being used by unautho-

rized persons. Recordkeeping and secure storage are key

requirements of the regulations. BATF has published updatesof these regulations (65).

1 Italicized numbers inparentheses refer to items in the bibliography

preceding the appendixes.

The BATF regulations are found inCFR 27, Part 181, Subparts

A through J, as follows:

Subpart A-IntroductionSubpart B-Definitions

Subpart G-Administrative and Miscellaneous Proceedings

Subpart D-Licenses and Permits

Subpart E-License and Permit Proceedings

Subpart F-Conduct of Business or Operat ionsSubpart G-Records and Reports



99

APPENDIX B.-GLOSSARY OF TERMS USED IN EXPLOSIVES AND BLASTING1

Acoustical impedance.- The ma thema tic al e xp re ss io n cha r-a cte rizin g a m ate ria l a s to its e ne rg y tra ns fe r p ro pertie s. T hep ro duc t o f its u nit de ns ity a nd its s on ic v elo city .Adobe charge.-See mud c ap .Airblast.-An a ir bo rn e sho ck wave result in g f rom the det ona-

tio n o f e xp lo siv es. M ay b e c au se d b y b urd en m ov em en t o r t here le ase o f e xp an din g g as in to the a ir. A irb la st m ay or m ay n otbe audib le .Airdox.-A system that uses 10,000 psi com pressed air to

break undercut coal. A irdox w ill not ignite a gassy or dustyatmosphere.Aluminum.-A me ta l c ommon ly u se d a s a fu el o r s en sitiz in g

agent in explosives and blasting agents. N orm ally used infin ely d iv id ed p ar tic le o r fla ke fo rm .American Table of Distances.-A quan tit y-dis tance tab le

published by IM E as pam phlet No.2, which specifies safee xp lo siv e s to ra ge d is ta nc es from in ha bite d b uild in gs , p ub lichighw ays, passenger railw ays and other stored explosive

materials.Ammoniumnitrate (AN).- The most c ommonly u sed o xid iz er

in e xp lo sive s a nd b las tin g a ge nts. Its fo rm ula is NH4N03•AN-FO.-An e xp lo sive m ate ria l co ns is tin g o f ammon ium

n itra te a nd fu el o il. T he m os t common ly us ed b la stin g a ge nt.Axial priming.-A system for prim ing blasting agents in

w hic h a c ore o f p rim in g m ateria l e xte nd s th ro ug h m os t o r a ll o fth e b la stin g a ge nt c ha rg e le ng th .

Back break.-Rock b rok en be yo nd th e lim its o f t he la st ro wo f h ole s.Back ho/es.- The top holes in a tunnel or drift round.Base charge.-The main e xp lo siv e c ha rg e in a d eto na to r.BATF.-Bureau of A lcohol, Tobacco and Firearm s, U .S .

D ep artm en t o f th e T re as ury , w hich en fo rce s e xp lo siv es c on -t ro l a nd secur it y r egula tio ns .Beds or bedding.-Layers o f s ed im en ta ry ro ck , u su ally

se pa ra te d b y a s urfa ce o f d isc on tin uity . A s a ru le , th e ro ck ca nb e re ad ily s ep ara te d a lo ng th es e p la ne s.Bench.- T he ho riz on tal le dg e in a q ua rry fa ce a lo ng w hich

hole s a re d rille d ver tic ally . B en ch in g is t he p ro ce ss o f e xcavat -ing whereby terraces or ledges are worked in a steppedsequence.

Binary explosive.-An e xp lo sive b ase d o n tw o n on exp lo -s iv e in gr ed ie nt s, s uch a s n it romethane and ammon ium n it ra te ,which are shipped and stored separately and mixed at thejo bsite to fo rm a h ig h e xp lo siv e.Black powder.-A low explosive consisting of sodium or

p ota ss ium n itr ate , c arb on , a nd s ulfu r. B la ck p owde r is s eld om

used today because of its low energy, poor fum e quality, ande xt reme sensit iv it y t o s pa rk s.Blast.- T he d eto natio n o f e xp lo sive s to b rea k ro ck.Blast area.- The area near a blast w ith in the influence of

f ly in g r oc k m is sile s, o r c on cu ss io n.Blaster.-A qualified person in charge of a blast. A lso, a

p erso n (b la ste r-in -c ha rg e) w ho h as p as se d a te st, a pp ro ve db y OSM , w hic h ce rtifie s h is o r h er q ua lifica tio ns to su pe rv is eb las t ing acti vi ti es .

'A dd itio na l d efin itio ns c an b e fo un d in In stitu te o f M ake rs o f E xp lo -s iv es P am ph le t N o. 1 2, G lo ssa ry o f In du stry T erm s, S ep temb er 1 98 1 ,28 pp.

Blasters' galvanometer; blasters' multimeter.-See galva-nome te r; mu lt ime ter .Blasthole.-A hole drilled in rock or other m ateria l for the

p la cemen t o f e xp lo siv es .Blasting agent.-An e xp lo sive th at m ee ts p re scrib ed cri-

te ria fo r in se ns itiv ity to in itia tio n. F or s to ra ge , a ny ma te ria l o rm ix tu re con sis tin g o f a f ue l a nd o xid iz er , in te nded f or b la st in g,n ot o th erw ise d efin ed a s an e xp los iv e, p ro vid ed th at th e fin -ished product, as m ixed and packaged for use or shipm ent,cannot be detonated by means of a N o. 8 test blasting capwhen uncon fi ned (BATF). Fo rt ranspo rtat ion , a ma ter ia l desi gnedfo r b la stin g w hic h h as b ee n te ste d in a cc ord an ce w ith C FR 4 9,S ection 173.14a, and found to be so insensitive that there isv ery little p ro ba bility o f a cc ide nta l in itia tio n to ex plo sio n o rtra ns itio n from d efla gra tio n to d eto na tio n (DOT).Blasting cap.-A d eto na to r th at is in itia ted b y s afe ty fus e

(MSHA ). S ee a ls o d eto na to r.Blasting circuit.- T he electrical circuit used to fire one or

mo re e le ct ric b la st in g cap s.Blasting crew.-A group of persons w hose purpose is to

lo ad e xp lo siv e cha rges .Blasting machine.-Any machine built expressly for the

p urp ose o f e ne rg iz in g e le ctric b la stin g c ap s o r o th er typ es o finitiator.Blasting mat.-See mat.Blasting switch.-A s witc h u se d to c on ne ct a po we r so urc e

to a b la stin g c irc uit.Blistering.-See mud c ap .Blockho/e.-A h ole d rille d in to a b ou ld er to a llo w th e p la ce -

m ent of a sm all charge to break the boulder.Booster.-A unit of explosive or blasting agent used for

p er pe tu atin g o r in te ns ify in g a n e xp lo siv e re ac tio n. A b oo ste rd oe s n ot c on ta in a n in itia tin g d ev ic e b ut is o fte n c ap s en sitiv e.

Bootleg.- T ha t p ortio n o f a b or eh ole th at remain s re la tiv elyintact after having been charged w ith explosive and fired. Abo otle g m ay co nta in u nfire d ex plo siv e an d s ho uld b e co nsid -e red haza rdous .

Borehole (blasthole).-A d rilled h ole , u su ally in ro ck, in towhic h e xp lo siv es a re lo ad ed fo r b la stin g.Borehole pressure.- The pressure w hich the hot gases of

detonation exert on the borehole w all. Borehole pressure isp rima rily a fu nc tio n o f th e d en sity o f th e e xp lo siv e a nd th e h ea to f exp los ion .Bridge wire.-A very fine filam ent w ire im bedded in the

ig nitio n e lemen t o f a n e le ctric b la stin g c ap . A n e le ctric c urre ntp as sin g th ro ug h th e w ire c au se s a s ud den h ea t rise , ca us in gth e ig nitio n e leme nt to b e ig nite d.Brisance.-A p ro pe rty o f a n e xp lo siv e ro ug hly e qu iv ale nt to

det onat io n velo cit y. A n e xp lo siv e w it h a h ig h det onat io n velo c-ity h as h ig h b ris an ce .Bubbleenergy.- The expandin g gas ene rg y o f a n e xp lo siv e,

a s m ea su red in a n u nde rw ate r te st.Bulk mix.-A mass of explosive m ateria l prepared for use

w ithou t packaging .Bulkstrength.-T he s tre ng th o f a n e x plo siv e p er u nit v olume .Bulldoze.-See mud c ap.Burden.- The distance from an explosive charge to the

n ea re st fre e o r o pe n fa ce . T ec hn ic ally , th ere ma y b e a n a pp ar-e nt bu rd en a nd a tru e b urde n, th e latte r b ein g m ea su re d in th ed ir ec tio n in wh ic h d is pla cemen t o f b ro ken r oc k w ill o cc ur f ollow -in g fir in g o f th e e xp lo siv e c ha rg e. A ls o, th e amou nt o f ma te ria lto be blasted by a given hole, given in tons or cubic yards.



100

Burn cut.-A parallel hole cut employing several closely

spaced blastholes. Not all of the holes are loaded with explosive.

The cut creates a cylindrical opening by shattering the rock,

Bus wires.- The two wires, joined to the connecting wire, to

which the leg wires of the electric caps are connected in a

parallel circuit. Each leg wire of each cap is connected to adifferent bus wire. In a series-in-parallel ci rcuit , each end of

each series is connected to a dif ferent bus wire.Butt.-See bootleg.

Cap.-See detonator.

Capped fuse.-A length of safety fuse to which a blasting

cap has been attached.

Capped primer.-A package or cartridge of cap-sensitive

explosive which is specifically designed to transmit detonation

to other explosives and which contains a detonator (MSHA).

Capsensitivity.- The sensitivity of an explosive to initiation,

expressed in terms of an IME No. a test detonator or a fraction

thereof.Carbon m~noxide.-A poisonous gas created by detonat-

ing explosive materials. Excessive carbon monoxide is causedby an inadequate amount of oxygen in the explosive mixture

(excessive fuel). .

Cardox.-A system that uses a cartridge filled with liquid

carbon dioxide, which, when initiated by a mixture of potas-

sium perchlorate and charcoal, creates a pressure adequate

to break undercut coal.

Cartridge.-A rigid or semirigid container of explosive or

blasting agent of a specified length or diameter.

Cartridge count.- The number of 1V o ; - by a-in cartridges of

explosives per 50-lb case.

Cartridge strength.-A rating that compares a given vol-

ume of explosive with an equivalent volume of straight nitro-

glycerin dynamite, expressed as a percentage.

Castprimer.-A cast unit of explosive, usually pentolite or

composition B, commonly used to initiate detonation in ablasting agent.

Chambering.- The process of enlarging a portion of blasthole

(usually the bottom) by firing a series of smail explosive charges.

Chambering can also be done by mechanical or thermal

methods.

Chapman-Jouguet (C-J) plane.-In a detonating explosive

column, the plane that defines the rear boundary of the pri-

mary reaction zone.

Circuit tester.-See galvanometer; multimeter.

Class A explosive.-Defined by the U.S. Department of

Transportation (DOT) as an explosive that possesses detonat-

ing or otherwise maximum hazard; such as, but not limited to,

dynamite, nitroglycerin, lead azide, black powder, blast ing

caps, and detonating primers.

Class B explosive.-Defined by DOT as an explosive thatpossesses flammable hazard; such as, but not limited to,

propellant explosives, photographic flash powders, and some

special fireworks.

Class C explosive.-Defined by DOT as an explosive that

contains Class A or Class B explosives, or both, as compo-

nents but in restricted quantities. For example, blasting caps

or electric blast ing caps in lots of less than 1,000.

Collar.- The mouth or opening of a borehole or shaft. To

collar in drilling means the act of start ing a borehole.

Collar distance.-The distance from the top of the powder

column to the collar of the blasthole, usually filled with stemming.

Columncharge.-A long, continuous charge of explosive or

blasting agent in a borehole.

Commercial explosives.-Expiosives designed and used

for commercial or industrial, rather than military applications.

Composition B.-A mixture of RDX and TNT which, when

cast, has a density of 1.65 g/cu cm and a velocity of 25,000 fps.

It is useful as a primer for blasting agents.

Condenser-dischargeblastingmachine.-A blasting machinethat uses batteries or magnets to energize one or more con-

densers (capacitors) whose stored energy is released into ablasting circuit.

Confined detonation ve/ocity.- The detonation velocity of

an explosive or blasting agent under confinement, such as in a

borehole.

Connecting wire.-A wire, smaller in gage than the lead

wire, used in a blasting circuit to connect the cap circuit with

the lead wire or to extend leg wires from one borehole to

another. Usually considered expendable.

Connector.-See MS connector.

Controlledblasting.- Techniques used to control overbreak

and produce a competent final excavation wall. See line drilling,

presplitt ing, smooth blasting, and cushion blasting.

Cordeau detonant fuse.-A term used to define detonating

cord.

Cornish cut.-See parallel hole cut.

Coromant cut.-See parallel hole cut.

Coupling.- The degree to which an explosive fillsthe borehole.

Bulk loaded explosives are completely coupled. Untamped

cartridges are decoupled. Also, capacitive and inductive cou-

pling from powerlines, which may be introduced into an elec-tric blasting circuit.

Coyote blasting.- The practice of driving tunnels horizon-

tally into a rock face at the foot of the shot. Explosives are

loaded into these tunnels. Coyote blasting is used where it is

impractical to drill vertically.

Critical diameter.-For any explosive, the minimum diame-

ter for propagation of a stable detonation. Critical diameter is

affected by confinement, temperature, and pressure on the

explosive.Crosslinking agent.-The f inal ingredient added to a water

gel or slurry, causing it to change from a liquid to a gel.

Current limiting device.-A device used to prevent arcing in

electric blasting caps by limiting the amount or duration of

current flow. Also used ina blasters' galvanometer or multime-

ter to assure a safe current output.

Cushion blasting.-A surface blasting technique used to

produce competent slopes. The cushion holes, f ired after the

main charge, have a reduced spacing and employ decoupledcharges.

Cushionstick.-A cartridge of explosive loaded into a small·

diameter borehole before the primer. The use of a cushion

stick is not generally recommended because of possible result-

ing bootlegs.

Cut.-An arrangement of holes used in underground miningand tunnel blasting to provide a free face to which the remain-

der ofthe round can break. Also the opening created by the cut

holes.

Cutoffs.-A portion of a column of explosives.that has failed

to detonate owing to bridging or a shifting of the rock formation,

often due to an improper delay system. Also a cessation of

detonation in detonating cord.

Dead pressing.-Desensitization of an explosive, caused

by pressurization. Tiny air bubbles, required for sensitivity, areliterally squeezed from the mixture.

Decibe/.- The unit of sound pressure commonly used to



measure airblast from explosives. The decibel scale islogarithmic.

Deck.-A small charge or portion of a blasthole loaded with

explosives which is separated from other charges by stem-ming or an air cushion.

Decoupling.- The use of cartr idged products significantly

smaller in diameter than the borehole. Decoupled charges arenormally not used except in cushion blasting, smooth blasting,

presplitting, and other situations where crushing is undesirable.

Deflagration.-A subsonic bLlfexfremely rapid explosive

reaction accompanied bygas formation and borehole pressure,

but without shock.

Delayblasting.- The use of delay detonators or connectorsthat cause separate charges to detonate at different times,

rather than simultaneously.

Delayconnector.-A nonelectric, short-interval delay device

for use in delaying blasts that are initiated by detonating cord.

Delaydetonator.-A detonator, either electric or nonelectric,

with a built-in element that creates a delay between the input

of energy and the explosion of the detonator.

Delay electric blasting cap.-An electric blasting cap with a

built-in delay that delays cap detonation in predetermined timeintervals, from milliseconds up to a second or more, between

successive delays.

Delayelement.- That portion of a blasting cap which causesa delay between the instant of application of energy to the cap

and the time of detonation of the base charge of the cap.Density.-The weight per unit volume of explosive, expressed

as cartr idge count or grams per cubic centimeter. See loadingdensity.

Department of Transportation (DOT).-A Federal agency

that regulates safety in interstate shipping of explosives and

other hazardous materials.

Detaline System.-A nonelectric system for initiating blast-

ing caps in which the energy is transmitted through the circuit

by means of a low-energy detonating cord.

Detonating cord.-A plastic-covered core of high-velocity

explosive, usually PETN, used to detonate charges of explosives.The plastic covering, in turn, is covered with various combina-

tions of textiles and waterproofing.

Detonation.-A supersonic explosive reaction that propa-

gates a shock wave through the explosive accompanied bya

chemical reaction that furnishes energy to sustain the shock

wave propagation in a stable manner. Detonation creates both

a detonation pressure and a borehole pressure.

Detonation pressure.- The head-on pressure created by

the detonation proceeding down the explosive column. Detona-

tion pressure is a function of the explosive's density and the

square of its velocity.Detonation ve/ocity.-See velocity.

Detanator.-Any device containing a detonating charge that

is used to initiate an explosive. Includes, but is not limited to,

blasting caps, electric blasting caps, and nonelectric instanta-neous or delay blasting caps.

Ditch blasting.-See propagation blasting.

DOT.-See Department of Transportation.

Downline.- The line of detonating cord in the borehole

which transmits energy from the trunkline down the hole to the

primer.Drilling pattern.-See pattern.

Drop ball.-Known also as a headache ball. An iron or steel

weight held on a wire rope which is dropped from a height onto

large boulders for the purpose of breaking them into smaller

fragments.bynamite.-The high explosive invented by-Alfred Nobel.

101

Any high explosive in which the sensitizer is ni troglycerin or a

similar explosive oil.

Echelonpattern.-A delay pattem that causes the true burden,

at the time of detonation, to be at an oblique angle from the

original free face.Electric blasting cap.-A blasting cap designed to be initi-

ated by an electr ic current.

Bectric stann.-An atmospheric disturbance of intense electri-

cal act ivity presenting a hazard in all blast ing activities.

Emulsion.-An explosive material containing substantial

amounts of oxidizers dissolved in water droplets surrounded

by an immiscible fuel. Similar to a slurry in some respects.

Exploding bridge wire (EBW).-A wire that explodes upon

application of current. It takes the place of the primary explo-

sive in an electric detonator. An exploding bridge wire detona-

tor is an electric detonator that employs an exploding bridge

wire rather than a primary explosive. An exploding bridge wire

detonator functions instantaneously.

Explosion.-A thermochemical process in which mixtures

of gases, solids, or liquids react with the almost instantaneousformation of gaseous pressures and sudden heat release.

Explosionpressure.-See borehole pressure.

Explosive.-Any chemical mixture that reacts at high veloc-

ity to liberate gas and heat, causing very high pressures.

BATF classifications include high explosives and low explosives.

Also, any substance classified as an explosive by DOT.

Explosive materials.-A term which includes, but is not

necessarily limited to, dynamite and other high explosives,

slurries, water gels, emulsions, blasting agents, black powder,

pellet powder, initiating explosives, detonators, safety fuses,

squibs, detonating cord, igniter cord, and igniters.

Extra dynamite.-Also called ammonia dynamite, a dyna-

mite that derives the major portion of its energy from ammo-

nium nitrate.

Extraneouselectricity.-Electrical energy, other than actual

firing current, which may be a hazard with electric blastingcaps. Includes stray current, static electricity, lightning, radio-

frequency energy, and capacitive or inductive coupling.

Face.-A rock surface exposed to air. Also called a free

face, a face provides the rock with room to expand upon

fragmentation.

Firing current.-Electric current purposely introduced into a

blasting circuit forthe purpose of initiat ion. Also, the amount of

current required to activate an electric blast ing cap.

Firing line.-A line, often permanent, extending from the

firing location to the electric blasting cap circuit. Also called

lead wire.Flash over.-Sympathetic detonation between explosive

charges or between charged blastholes.Flyrock.-Rock that is propelled through the air from a blast.

Excessive flyrock may be caused by poor blast design or

unexpected zones of weakness in thA rock.

Fractur1ng.- The breaking O f rock with or without move-

ment of the broken pieces.Fragmentation.- The extent to which a rock is broken into

pieces by blasting. Also the act of breaking rock.Fuel.-An ingredient in an explosive which reacts with an

oxidizer to form gaseous products of detonation.

Fuel 011.-The fuel, usually No.2 diesel fuel, in AN-FO.

Fume c/assification.-An IME quantification of the amount

of fumes generated by an explosive or blasting agent.



102

FumequaJity.-A measure of the toxic fumes to be expected

when a specific explosive is properly detonated. See fumes.

Fumes.-Noxious or poisonous gases liberated from a blast.

May be due to a low fume quality explosive or inefficient

detonation.

Fuse.-See safety fuse.

Fuse lighter.-A pyrotechnic device for rapid and depend-able lighting of safety fuse.

Galvanometer.-(More properly called blasters' galva-

nometer.) A measuring instrument containing a silver chloride

cell and/or a current limiting device which is used to measure

resistance in an electric blasting circuit. Only a device specific-

ally identified as a blasting galvanometer or blast ing multime-

ter should be used for this purpose.

Gap sensitivity.-A measure of the distance across which

an explosive can propagate a detonation. The gap may be air

or a defined sol id material. Gap sensitivity is a measure of the

likelihood of sympathetic propagation.

Gas detonation system.-A system for initiating caps in

which the energy istransmitted through the circuit by means of

a gas detonation inside a hollow plastic tube.

Ge/atin.-An explosive or blasting agent that has a gelati-

nous consistency. The term is usually applied to a gelatin

dynamite but may also be a water gel.

Gelatin dynamite.-A highly water-resistant dynamite with

a gelatinous consistency.

Generator blasting machine.-A blasting machine oper-

ated by vigorously pushing down a rack bar or twisting a

handle. Now largely replaced by condenser discharge blast-

ing machines.

Grains.-A system of weight measurement in which 7,000

grains equal 1 lb.

Ground vibration.-A shaking of the ground caused by the

elastic wave emanating from a blast. Excessive vibrations

may cause damage to structures.

Hangtire.- The detonation of an explosive charge at a time

after its designed fir ing t ime. A source of serious accidents.

Heading.-A horizontal excavation driven in an underground

mine.

Hercudet.-See gas detonation system.

Hertz.-A term used to express the frequency of ground

vibrations and airblast. One hertz is one cycle per second.

High explosive.-Any product used in blasting whichTs

sensitive to a No. 8 test blasting cap and reacts at a speed

faster than that of sound inthe explosive medium. A classifica-

tion used by BATF for explosive storage.

Highwall.- The bench, bluff. or ledge on the edge of a

surface excavation. This term is most commonly used in coal

strip mining.

Ignitacord.-A cordlike fuse that burns progressively along

its length with an external flame at the zone of burning and is

used for lighting a series of safety fuses in sequence. Burns

with a spitt ing f lame similar to a Fourth-of-July sparkler.1M£.-The Institute of Makers of Explosives. A trade organiza-

t ion dealing with the use of explosives, concerned with safety

in manufacture. transportation, storage, handling, and use.

The IME publishes a series of blasting safety pamphlets.

Initiatioo.- The act of detonating a high explosive by means

of a cap, a mechanical device, or other means. Also the act of

detonating the initiator.

Instantaneous detonator.-A detonator that contains nodelay element.

Jet loader.-A system for loading AN-FO into small blastholes

in which the AN-FO is drawn from a container by the venturi

principle and blown into the hole at high velocity through asemiconductive loading hose.

Joints.-Planes within a rock mass along which there is no

resistance to separation and along which there has been no

relative movement of the material on either side. Joints occur

in sets, the planes of which may be mutually perpendicular.

Joints are often called partings.

Jumbo.-A machine designed to contain two or more mounted

drill ing units that mayor may not be operated independently.

Kerf.-A slot cut in a coal or soft rock face by a mechanical

cutter to provide a ffee face for blasting.

Lead wire.-The wire connecting the electrical power source

with the leg wires or connecting wires of a blasting circuit. Also

called firing line.

LEDC.-Low energy detonating cord, which may be used to

initiate nonelectric blasting caps.

Leg wires.-Wires connected to the bridge wire of an elec-

tric blasting cap and extending from the waterproof plug. The

opposite ends are used to connect the cap into a circuit.

Ufters.- The bottom holes in a tunnel or drift round.

Une drilling.-A method of overbreak control in which a

series of very closely spaced holes are dri lled at the perimeter

of the excavation. These holes are not loaded with explosive.

Uquid oxygen explosive.-A high explosive made by soak-

ing cartridges of carbonaceous materials in liquid oxygen.

This explosive is rarely used today.

Loading density.-An expression of explosive density in

terms of pounds of explosive per foot of charge of a specificdiameter.

Loading factor.-See powder factor.

Loading poie.-A pole made of nonsparking material, used

to push explosive cartridges into a borehole and to break and

tightly pack the explosive cartridges into the hole.

Low explosive.-An explosive in which the speed of reac-

tion is slower than the speed of sound, such as black powder.

A classification used by BATF for explosive storage.

LOX.-5ee liqUid oxygen explosive.

Magazine.-A building, structure, or container specially con-

structed for storing explosives, blasting agents, detonators, or

other explosive materials.

Mat.-A covering placed over a shot to hold down flyingmaterial; usually made of woven wire cable, rope, or scrap

tires.

Maximum firing current.- The highest current (amperage)

recommended for the safe and effective performance, of an

electric blasting cap.MetaJlized.-Sensitized or energized with finely divided metal

f lakes, powders. or granules, usually aluminum.Michigan cut.-See parallel hole cut.

MicrobaJloons.-Tiny hollow spheres of glass or plasticwhich are added to explosive materials to enhance sensitivity

by assuring an adequate content of entrapped air.

Millisecond.- The unit of measurement of short delay

intervals, equal to 1/1000 of a second.



Millisecond delay c ap s.-D ela y d eto na to rs th at h av e b uilt-intim e d ela ys o f v ario us le ng th s. T he in te rv al b etwee n th e d ela ysat the low er end of the series is usually 25 m s. The intervalbetw een delays at the upper end of the series m ay be100 to300 ms.

Minimum firing current.- T he lo we st c urre nt (a mpe ra ge)

th at w ill in itia te a n e le ctr ic b la stin g c ap w ith in a s pe cifie d s ho rtin te rv al o f t ime .

Misfire.-A ch arg e, o r p art o f a ch arg e, w hic h fo r a ny re aso nh as fa ile d to fire a s p la nn ed . A ll m isfire s a re d ang ero us.

Monomethylaminenitrate.-A c omp ou nd u se d to s en sitiz esome w ate r g els .

MS connector.-A device used as a delay in a detonatingc ord circ uit c on nec tin g o ne h ole in the c ircu it w ith a no th er o rone row of holes to other row s of holes.

MSHA.-The M ine S a.1 ety a nd H ea lth A dm in istra tio n. A na ge ncy u nd er th e D ep anme nt o f L ab or w hic h e nfo rc es h ea ltha nd s afe ty re gu la tio ns in th e m in in g in du stry .

Muckpile.-A pile of broken rock or dirt that is to be loadedfor removal .

Mud c ap .-R efe rred to a ls o a s ad ob e, b ulld oze , b lis te rin g,

o r p la ste r s ho t. A ch arg e o f e xplo sive fire d in c on ta ct w ith th esurface of a rock, usually covered w ith a quantity of m ud, w etearth, or sim ilar substance. No borehole is used. .

Multimeter.-(More p rope rly c alle d b la st er s' mu ltime te r. ) Amu lt ip ur po se t es t in st rumen t u sed t o che ck lin e volt ages , f ir in gc irc uits , c urre nt le ak ag e, s tra y c ur re nts , a nd o th er me as ure -me nts p ertin en t to e le ctric b la stin g. On ly a me te r s pe cific allyd es ig na te d a s a b la ste rs ' multi m e te r o r b la ste rs ' g alv an ome -te r s ho uld b e u se d to te st e le ctric b la stin g c irc uits .

National Fire Protection Association (NFPA).-An industry-g ove rnme nt a sso cia tio n th at p ub lis he s sta nd ard s fo r e xp lo -s iv e ma te ria l a nd ammonium n itra te .

Nitrocarbonitrate.-A c la ss if ic at io n once g iv en t o a b la st in g

a ge nt b y DOT fo r s hip pin g p urp os es . T his te rm is n ow o bs ole te .Nitrogen o xid es.-P oiso no us g ase s c re ate d b y d eto natin ge xp lo siv e ma te ria ls . E xces siv e n it ro gen o xid es may be cau sedby an excessive am ount of oxygen in the explosive m ixture( ex ce ss iv e o xid iz er ), o r b y in ef fic ie nt d et onatio n.

Nitroglycerin (NG).- The explosive oil orig inally used asthe sensitizer in dynam ites, represented by the form ula

C3Hs(ON02h·Nitromethane.-A liquid com pound used as a fuel in tw o-

comp on ent (b in ary ) e xp lo siv es a nd a s ro ck et fu el.Nitropropane.-A liquid fuel that can be com bined with

p ulve riz ed ammon ium nitra te p riU s t o m ake a d en se bla stin gmixture.

Nitrostarch.-A so lid e xp lo sive , sim ila r to n itrog lyc erin infu nc tio n, us ed a s th e b ase o f "no n h ea da ch e" p ow de rs ,

None/.-See s ho ck tu be s ys tem.

Nonelectric delay blasting cap.-A d eto na to r w ith a d elay. e lemen t, c ap ab le o f b ein g in itia te d n on ele ctr ic ally . S ee s ho cktu be sy ste m; g as d eto na tio n s ys te m; D eta lin e S ys tem.

No.8 test blasting cap.-5ee te st b la stin g c ap No.8 .

OSHA.- The OCCupa tionalSa fe ty and Hea lth Admin is trat ion .An agency under the D epartm ent of Labor w hich enforceshealth and safety regulations in the construction industry,including b las t ing .

OSM.- The Office of Surface M ining Reclamation andEnforcem ent. An agency under the D epartm ent of Interiorwhic h e nfo rc es s urfa ce e nv iro nme nta l r eg ula tio ns in th e c oa lm ining i ndust ry .

103

Overbreak.-Excessive b reakage o f r oc k beyond t he des ir edexcavat ion l im i t.

Overburden.-Worthless mate ria l lyin g o n to p o f a d ep os itof u se fu l m ate ria ls. O ve rb urd en o fte n refe rs to d irt o r g ra ve l,but can be rock, such as shale over lim estone or shale andlimest one o ve r c oa l.

Overdrive.-The act of inducing a velocity higher than thesteady state velocity in a powder column by the use of ap ow erfu l p rim er. O ve rd rive is a te mp ora ry p he nome no n a ndth e p ow de r qu ick ly a ss um es its s te ad y sta te ve loc ity .

Oxides of nitrogen.-See n it rogen ox ides.Oxidizer.-An in gre die nt in a n e xp lo siv e o r b la stin g a ge nt

w hich supplies oxygen to com bine w ith the fuel to form gas-e ou s o r so lid p ro du cts o f d eto na tio n. Ammon ium n itra te is th emo st c ommon o xid iz er u se d in c ommer cia l e xp lo siv es .

Oxygen balance.-A state of equilibrium in a m ixture offu els a nd ox idiz ers a t w hic h th e g ase ou s p ro du cts o f d eto na -tion are p re domin ate ly ca rb on d io xid e, w ate r va po r (s te am ),a nd free n itro ge n. A m ixtu re co nta inin g e xce ss o xyg en h as ap os itiv e o xy ge n b ala nc e. On e w ith e xc es s fu el h as a n eg ativ eo xygen bala nce.

Parallel circuit.-A circuit in w hich tw o w ires, called busw ire s, e xte nd fro m th e le ad w ire . O ne le g w ire fro m e ach ca p inthe circuit is hooked to each of the bus w ires.

Parallel hole cut.-A g ro up of p ara lle l h ole s, s om e o f w hichare loaded w ith explosives, used to establish a free face intu nn el o r h ea din g b la stin g. O ne o r m ore o f t he u nlo ad ed h ole sm ay be larger than the blastholes. A lso called C orom ant,Cornish, burn, shatter, or M ichigan cut. __

Parallelseries circuit.-5imilar t o a pa ra ll el c ir cu it , bu t i nvo lv -ing tw o or m ore series of electric blasting caps. O ne end ofeach series of caps is connected to each of the bus w ires.Some times ca lled se ri es -in -pa rall el c ir cu it .

Particle ve/ocity.-A measure o f g ro und v ib ra tio n. Desc rib es

th e v elo city a t whic h a p artic le o f g ro un d v ib ra te s whe n e xc ite dby a seism ic w ave.Pattern.-A plan of holes laid out on a face or bench w hich

a re to b e d rille d fo r b la stin g. B urd en a nd s pa cin g d ime ns io nsa re u su ally e xp re ss ed in fe et.

Pellet powder.-Black p ow de r p res sed in to 2-in -lo ng , 1%-in to 2 ·in d iame te r c ylin dr ic al p elle ts .

Pentaerythritoltetranitrate (PETN).-A milit ar y e xp lo siv ecom pound used as the core load of detonating cord and theb ase ch arg e o f b la stin g ca ps .

Pentolite.-A m ix tu re o f P ETN a nd T NT which , w he n c ast, isused as a cast prim er.

Permissible.-A mac hin e, m ate ria l, a pp ara tu s, o r d ev icet ha t h as been in ve st ig at ed , t es te d, a nd app ro ved b y t he Bu reauo f M in es o r MSHA , a nd is ma in ta in ed in p ermis sib le c on ditio n(MSHA).

Permissible blasting.-Blasting a cc ord in g to MSHA re gu la -tio ns fo r u nd er gr ou nd c oa l m in es o r o th er g as sy u nd er gro un dmines.

Permissibleexplosives.-Explosives t ha t have been approvedby M SH A for use in underground coal m ines or other gassymines. '

PETN.-See pentaerythritoltetranitrate.Placards.-Signs p la ce d o n v eh ic le s tra ns po rtin g h az ard -

o us m ate rials, in clu din g e xplo sive s, in dic atin g th e n atu re o fth e car go .

Plaster shot.-See m ud cap.Pneumatic loader.-Qne o f a v arie ty o f ma ch in es , p owere d

by compressed a ir , used to l oad bu lk b las ting agen ts o r ca rt ridgedwa te r g els .



104

Powder.-Any so lid exp los ive .Powder chest.-A subs tan tia l, nonconduct ive po rtab le con-

ta in er e qu ip pe d w ith a lid a nd u se d a t b la stin g s ite s fo r tempo -r ar y s to ra ge o f e xp lo siv es .Powder factor.-A ratio between the amount of powder

loaded and the am ount of rock broken, usually expressed aspounds per ton or pounds per cubic yard. In som e cases, there cip ro cals o f th es e te rm s a re u se d.

Preblast survey.-A d oc um en ta tion o f th e e xistin g c on di-tion of a structure. The survey is used to determ ine w hetherSUbs eq ue nt b la stin g c au se s d ama ge to th e s tr uc tu re .

Premature.-A c ha rg e th at d eto na te s b efo re it is in te nd ed .P rematu re s c an b e h az ard ou s.Preshearing.-See prespli tting.Presplitting.-A fo rm o f c on tro lle d b la stin g in whic h d ec ou -

p le d c ha rg es a re fire d in c lo se ly s pa ce d h ole s a t t he p erime te ro f t h e e xc av atio n. A p re sp lit b la st is fire d b efo re th e ma in b la st.A lso ca ll ed p reshea ri ng .

Pressure vesse/.-A s ys te m fo r lo ad in g A N-FO in to sma ll-d iam eter blastholes: The AN-FO is contained in a sealedvessel, to w hich air pressure is applied, forcing the AN -FO

through a sem iconductive hose and into the blasthole. Alsokn ow n a s pre ss ure p ot.

Prill.-In blasting, a sm all porous sphere of am moniumn itra te ca pa ble of a bso rb in g m ore th an 6 p et b y w eig ht o f fu elo il. B la stin g p rills h av e a b ulk d en sity o f0.80 to 0.85 g /cu em.Primaryblast.- The ma in b las t execu ted to sustai n p roduc tion .Primaryexplosive.-An explos ive o r expl os ive mi xture, sens i-

tive to spark, flam e, im pact or friction, used in a detonator toi nit ia te the expl os ion .

Primer.-A un it , package , o r ca rt ridge o f cap-sensit ive expl o-sive used to initiate other explosives or blasting agents andwhic h c on ta in s a d eto na to r (MSHA ).

Propagation.- T he detonation of explosive charges by anim pu ls e fro m a n ea rb y e xp lo sive c harg e.Propagation blasting.- The use of closely spaced, sensi-

tive charges. The shock from the first charge propagatesth ro ug h th e g ro un d, s ettin g o ff th e a dja ce nt c ha rg e, a nd s o o n.O nly o ne d eto na to r is re qu ire d. P rim arily u se d fo r d itch in g indamp g round.Propellant explosive.-An ex plo siv e th at n orm ally d efla -

g ra te s a nd is u se d fo r p ro pu ls io n.Pull.- T he q uan tity o f ro ck o r le ng th o f ad va nce e xc ava te d

by a blast round.

Radiofrequencyenergy.-Electrical energy t raveli ng throughthe a ir as rad io o r e lec tromagnet ic waves . Under ideal cond it ions,th is e ne rg y c an fir e a n e le ctric b la stin g c ap . IME P amphle t No.20 re commen ds s afe d is ta nce s fro m tra nsm itte rs to e lec tricb las ti ng caps .

Radiofrequency transmitter.-An e le ctric d ev ic e, s uc h a s as ta tio na ry o r mobile r ad io t ra nsm it tin g s ta tio n, wh ic h t ra nsm it sa ra dio fr eq ue nc y wav e.

ROX.- -eyc lo t rimethy lenetr in i tramine, an exp los ive substanceused in the m anufacture of com positions 8, C-3, and C-4.C om position 8 is useful as a cast prim er.Relievers.-In a heading round, holes adjacent to the cut

holes, used to expand the opening m ade by the cut holes.Ribho/es.- T he h ole s a t t he s id es of a tu nn el o r d rift ro un d,

w hich d ete rm in e th e w idth o f th e o pe nin g.Rip rap.-Coarse ro ck s u se d fo r r iv er b an k o r d am s ta biliz a-

tio n to re duc e ero sio n b y w ater flo w.Rotational firing.-A delay blasting system in w hich each

ch arge s uc ce ssive ly d isp la ce s its b urd en in to a v oid c re ate db y a n e xp lo siv e d eto na te d o n a n e arlier d ela y p erio d.

Round.-A g ro up o r se t o f b la sth ole s re qu ire d to pro du ce au nit o f a dv anc e in u nd erg ro un d h ea din gs o r tu nn els.

Safety fuse.-A core of potassium nitrate black pow der,

enclosed in a covering of textile and w aterproofing, w hich isu se d to in itia te a b la stin g c ap o r a b la ck p owde r c ha rg e. S afe tyfu se b urn s a t a co ntin uo us , u nifo rm ra te .

Scaled distance.-A r at io u sed t o p re dic t g ro und v ib ra tio ns .A s c ommon ly used in blasting, scaled distance equals thed ista nc e fro m th e b la st to th e p oint o f c on ce rn , in fe et, div id edb y th e sq ua re ro ot o f th e ch arg e w eig ht o f e x plo siv e pe r d ela y,in p ou nd s. Norma lly , w he n u sin g th e e qu atio n, th e d ela y p er io dm ust be at least 9 m s.Secondary blasting.-Using e xp lo siv es to b re ak b ou ld er s

o r h igh b ottom re su ltin g fro m th e p rim ary b la st.Seismograph.-An in str umen t th at me as ur es a nd ma y s up -

ply a perm anent record of earth borne vibrations induced byearthquakes o r blasting. .Semiconductive h os e.- A h os e, u se d fo r p ne umatic lo ad in g

o f A N-FO, w hic h h as a m in im um e le ctrica l re sis ta nc e o f1,000

o hm s/ft a nd 10,000 ohm s total resistance and a m axim umto ta l r es is ta nc e o f 2,000,000 ohms.

Sensitiveness.-A measure o f a n e xp lo siv e's a bilit y t o p ro pa -g at e a det onat io n.

Sensitivity.-A mea su re o f a n e xplo siv e's s usc ep tib ility tod eto na tio n u po n re ce iv in g a n e xte rn al im pu ls e s uc h a s imp ac t,s ho ck , f lame, o r f ric tio n.

Sensitizer.-An in gre die nt u se d in e xp lo siv e c ompo un ds top romote g re at er e ase in in it ia tio n o r p ro paga tio n o f t h e det ona-t ion reac tion .

Sequential blasting machine.-A s erie s o f co nd en se r d is -charge blasting m achines in a single unit w hich can be acti-vated at various accurately tim ed intervals follow ing theapp lic at io n o f e le ct ric al c ur re nt .Series circuit.-A c irc uit of e le ctric bla stin g c ap s in w hic h

each leg w ire of a cap is connected to a leg w ire from theadjacent caps so that the electrical current follow s a singlep ath th ro ug h th e e ntir e c irc uit.

Series-in-parallel circuit.-See pa ra lle l se ries c ir cu it .Shatter cut.-See paralle l h ole c ut .Sheillile.- T he length of tim e for w hich an explosive can be

s to re d w it hout lo sin g it s e ff ic ie nt p er fo rmance cha ra ct er is tic s.Shockenergy.- The sha tt er in g f or ce o f a n e xp lo siv e cau sed

by th e d eto natio n w ave .Shock tube system.-A sy ste m fo r in itia tin g c ap s in w hich

the energy is transm itted to the cap by m eans of a shock w avein sid e a h ollo w p la stic tu be .

Shock wave.-A p re ssu re p ulse th at p ro pa ga te s a t su pe r-son ic ve loc ity .

Shot.-See blast.

Shot firer.-Also re fe rre d to a s th e s ho ote r. T he p ers on w hoactually fires a blast. A pow derm an, on the other hand, m aych arg e o r lo ad b la sth oles w ith e xp lo siv es b ut m ay n ot fire th eblast.

Shunt.-A piece of m etal or m etal fo il w hich short c ircuitsthe ends of cap leg w ires to prevent stray currents from caus-in g ac cid en ta l d eton atio n of th e ca p.

Silver chloride cell.-A lo w-c urren t c ell u se d in a b las tin gg alv an ome te r a nd o th er d ev ic es u se d to mea su re c on tin uity ine le ct ric b la st in g cap s and c ir cu it s.

Siurry.-An a qu eo us so lu tio n o f ammon ium n itra te , s en si-tized w ith a fuel, th ickened, and crosslinked to provide ag ela tin ou s co ns is te ncy . S om etim es ca lle d a w ate r g el. DOTmay c la ss if y a s lu rr y a s a C la ss A exp lo siv e, a C la ss B exp lo siv e,o r a b la stin g a ge nt. A n e xp lo siv e o r b la stin g a ge nt c on ta in in g



substantial portions of water (MSHA). See emulsion; waterg~1.

Smooth blasting.-A method of controlled blasting, used

underground, in which a series of closely spaced holes is

dril led at the perimeter, loaded with decoupled charges, and

fired on the highest delay period of the blast round.

Snake ho/e.-A borehole dril led slightly downward fromhorizontal into the floor of a quarry face. Also, a hole drilled

under a boulder.

Sodiumnitrate.-An oxidizer used in dynamites and some-

times in blasting agents.

Spacing.- The distance between boreholes or charges in a

row, measured perpendicular to the burden and parallel to the

free face of expected rock movement.

Specific gravity.- The ratio of the weight of a given volume

of any substance to the weight of an equal volume of water.

Spitter cord.-See Ignitacord.

Springing.-See chambering.

Squarepattern.-A pattern of blastholes in which the holes

in succeeding rows are dri lled directly behind the holes in the

front row. In a truly square pattern the burden and spacing areequal.

Squib.-A firing device that burns with a flash. Used to

ignite black powder or pellet powder.

Stability.- The ability of an explosive material to maintain

its physical and chemical properties over a period of time in

storage.

Staggered pattern.-A pattern of blastholes in which holes

ineach row are drilled between the holes inthe preceding row.

Static electricity.-Electrical energy stored on a person or

object in a manner similar to that of a capacitor. Static electric-

ity may be discharged into electrical initiators, thereby detonat-ing them.'

Steady state velocity.- The characteristic velocity at which

a specific explosive, under specific conditions, in a given

charge diameter, wil l detonate ..

Stemming.- The inert material, such as drill cuttings, used

inthe collar portion (or elsewhere) of a blasthole to confine thegaseous products of detonation. Also, the length of blasthole

left uncharged.

Stick count.-See cartridge count.

Straycurrent.-Current flowing outside its normal conductor.

A result of defective insulation, it may come from electrical

equipment, electrified fences, electric railways, or similar items.

105

Sympathetic propagation (sympathetic detonation).-Detonation of an explosive material by means of an impulse

from another detonation through air, earth, or water.

Tamping.The process ofcompressing the stemming orexplo-

sive in a blasthole. Sometimes used synonymously withstemming.

Tamping bag.-A cylindrical bag containing stemming

material, used to confine explosive charges in boreholes.

Tamping po/e.-See loading pole.

Test blasting cap No. 8.-A detonator containing 0.40 to

0.45 g of PETN base charge at a specific gravity of 1.4 g/cu

cm, and primed with standard weights of primer, depending on

the manufacturer.

Toe.- The burden or distance between the bottom of a

borehole and the vertical free face of a bench inan excavation.

Also the rock left unbroken at the foot of a quarry blast.

Transient ve/ocity.-A veloci ty, di fferent from the steady

state velocity, which a primer imparts to a column of powder.

The powder column quickly attains steady state velocity.

Trinitrotoluene(TNT).-A military explosive compound used

industrially as a sensitizer for slurries and as an ingredient in

pentolite and composition B. Once used as, a free-running

pelletized powder.

Trunkline.-A detonating cord line used to' connect the

down lines or other detonating cord lines in a blast pattern.

Usually runs along each row of blastholes.

Tunnel.-A horizontal underground passage.

Two-component explosive.-See binary explosive.

Unconfineddetonation velocity.- The detonation velocity of

an explosive material not confined by a borehole or other

confining medium.

V-cut.-A cut employing several pairs of angled holes, meet-ing at the bottoms, used to create free faces for the rest of the

blast round.

Velocity.- The rate at which the detonation wave travels

through an explosive. May be measured confined or unconfined.

Manufacturer's data are sometimes measured with explo-

sives confined in a steel pipe.