the report of tile technical committee on electrical equipment€¦ · technical committee on...

Report of the Committee on

Electrical Equipment in Chemical Atmospheres

IL F. Schwab, Chair Allied-Signal Inc., NJ im

Mark C. Ode, Nonvoting Secretary Nat'l. Fire Protection Assn., MA

Alonza W. Ballard, Crouse-Hinds, NY t~ Rep. Nat'l Electrical Mfgs., Assoc.

Michael IC Baucom, BEBCO Industries, Inc., TX ~ Francis X. Bender, Hm,~ards Research Corp., NJ t~ Edward M. Briesch, Underwriters Laboratories Inc., IL t~

J oseph A. Cannatelli, Arco Chemical Co., PA t~ ames DeLuca, Bechtel Corp., CA t~

William T. Fiske, Inehcape Testing Services, NY t~ William G. LawrenceJr . , Factory Mutual Research Corp., MAm Richard C. Masek, Bailey Controls, OH t~ Robert E. McKenney, City of Tacoma WA t~ John M. Mesina, U'.S. Dept. of Labor, WV t~ George W. Moore, Industrial Risk Insurers, CT t,~ Richard E. Munson, The DuPont Co., DE t~ Milton H. Ramsey, Chevron U.S.A. Inc., TX t~

Rep. InsL of Electrical & Electronics Engr, Inc. Jsoseph V. Saverino, Aic Products and Chemicals, Inc., PA t~

ukanta Sengupta, FMC Corp., NJ t~ George H. St Onge, Bernardsville, ~ t JRames G. Stallcup, GRAYBOY & Assoc., TX t~l

onaldJ. Strancar, BP Oil Co., OH i~ Rep. American Petroleum Inst.

Dann M. Strube, Lanesville, IN t~ David Wechsler, Union Carbide Corp., WV t~

Rep. Chemical Mfrs. ,~ssoc. Charles J. Wolf, Teledyne Brown Engr - Energy Systems, MD t~ Jack H. Zewe, Electrical Consultantslnc. , LA r~J

Alternates

Jane I. Lataille, Industrial Risk Insurers, CT t, (Alt. to G. W. Moore)

Kerry L. McManama, Underwriters Laboratories Inc., IL t,~ (Air. to E. M. Briesch)

Robert S. Pellizze, Inchcape Testing Services NA Inc., NY t,~ (Att. to W. T. Fiske)'

James A. Robertson, Dow Chemic~al Co., TX t~ (AIt. to M. H. Ramsey)

James W. Stallcup, GRAYBOY & Assoc., TX ~,~L (AIt. toJ . G Stallcup)

Novoting

Richard Y. LeVine, Smnfford, CT (Member Emeritus)

John E. Rogerson, Cedar Lane Farm, OH (Member Emeritus)

Staff Liaison: Mark C. Ode

This list represents the membership at the time the Committee was balloted on the text of this edition. Since that time, changes in the membership may have occurred. A key to classifications is found at the front of the book.

Committee Scope: "Hfis Cormnittee shall have primary responsibility for documents on (1) developing data on the properties of chemicals enabling proper selection of electrical equipment for use in atmospheres containing flammable gases, vapors or dusts; (2) n~tking recommendat ions for the prevention of fires and explosions through the use of continuously purged, pressurized, explosion-proof, or dust-ignition-proof electrical equipment where installed in such chemical atmospheres.

The Report of tile Technical Committee on Electrical Equipment in Chemncai Atmospheres is presented for adoption in 3 parts.

Part I of dds Report was prepared by the Technical Committee on Electrical Equipment in Chemical Atmospheres, and proposes for adoption a complete revision of NF'PA 497A-1992, Recommended Practice for Classification of Class I Hazardous (Classified) Locations for Electrical Installations in Chemical Process Areas, and incorporates tile flammable liquids, gases and vapor information from NFPA 497M-1991, Manual for Classification of Gases, Vapors, and Dusts for Electrical Equipment in Hazardous (Classified) Locations. The document will be renumbered and retitled NFPA 497, Recommended Practice for the Classification of Flammable Liquids, Gases, or Vapors and of Hazardous (Classified) Locations for Electrical Installations in Chemical Process Areas. NFPA 497A- 1992 is published in Volume 11 of the 1996 National Fire Codes and in separate pamphlet form.

Part I of this Rel?ort has been submitted to letter ballot of the Technical Comma.tee on Electrical Equipment in Chemical Atmospheres, which consists of 24 voting members. The results of the balloting, after circulation of any negative votes, can be found in the report.

Part II of this Report was prepared by tile Technical Committee on Electrical Equipment in Chemical Atmospheres, and proposes for adoption a complete revision of NFPA 49713-1991, Recommended Practice for Classification of Class II Hazardous (Classified) Locations for Electrical Installations in Chemical Process Areas, and incorporates the combustible dust information from NFPA 497M- 1991, Manual for Classification of Gases, Vapors, and Dusts for Electrical Equipment in Hazardous (Classified) Locations. The document will be renumbered and retitled NFPA 499, Recommended Practice for dae Classification of Combustible Dusts and of Hazardous (Classified) Locations for Electrical Installations in Chemical Process Areas. NFPA 497B-1991 is published in Volume 11 of the 1996 National Fire Codes and in separate panlphlet form.

Part II of dais Report has been submitted to letter ballot of the Technical Committee on Electrical Equipment in Chemical Atmospheres, which consists of 24 voting members. The results of the balloting, after circulation of any negative votes, can be found in the report.

Part III of dais Report was prepared by d~e Technical Committee on Electrical Equipment in Chemical Atmospheres, mad proposes for adoption tile withdr:iwal of NFPA 497M-1991, Manual for Classification of Gases, Vapors, and Dusts for Electrical Equipment in Hazardous (Classified) Locations. NFPA 497M-1991 is published in Volume 11 of the 1996 National Fire Codes and in separate pamphlet form.

Part III of dais Report has been submitted to letter ballot of the Technical Committee on Electrical Equipment in Chemical Atmospheres, which consists of 24 voting members. The results of the balloting, after circulation of any negative votes, can be found in the report.

289

N F P A 4 9 7 A - - A 9 7 R O P

PART I

(Log #4) 497A- 1 - (2-1.7 (New)): Accept in Principle SUBMITTER: Jo lm Propst, Shell Oil Company RECOMMENDATION: Add new text as follows:

2-1.7 Article 505 has been ' added to the 1996 NEC to provide a founda t ion for the es tabl i shment of area classification us ing the zone concept. This concept, which is the widely used outside of the Uni ted States, is no t inc luded in dais s tandard. SUBSTANTIATION: T he 1996 NEC includes fine f ramework for an ,alternate m e t h o d of area classification. This s tandard either needs to include a section on the applicat ion o f the zone concept, include a s ta tement as draf ted above to exclude the zone concept f rom dais st,-mcLard, or develop an addit ional s tandard to address the concept. As a m e m b e r of the API task g roup responsible for revisin~ RP-500, we are pursu ing the last alternative o f developing an addit ional s tand a lone s tandard. T he purpose for dais c o m m e n t is to highl ight the need to address the zone concept and no t to necessarily suggest the approach. COMMITTEE ACTION: Accept in Principle. COMMrITEE STATEMENT: T he snbmi t te r ' s in ten t llas been satisfied in Proposal 497A - 15 (Log #CP1) by the addit ion o f a note to the Scope. NUMBER OF COMMITTEE MEMBERS ELIGIBLE TO VOTE: 24 VOTE ON COMMITTEE ACTION:

AFFIRMATIVE: 24

(Log #5) 497A- 2 - (2-7.1 (g) and (h) (New)): Reject SUBMITTER: J o h n Propst, Shell Oil Company RECOMMENDATION: Add new text as follows:

The volatility of the material I ~ The velocity o f t h e materiai being released

SUIK~.;TANTIATION: The volatility of the material has a significant impact on the size of the vapor cloud. Appendix B of Institute of Pe t ro leum Area Classification Code for Pe t ro leum Installations provides significant detail on the relat ionship between a materials vapor pressure at the tempera ture of the release and the volatility o f the material. As a m e m b e r of the API RP-500 task group, we are pursu ing the inclusion of this approach as part of an al ternate m e t h o d for area classification, wifich will be inc luded as an Appendix.

The velocity of the material being released may well be one of the single most significant criteria in de te rmin ing the ex ten t of a vapor clo/ad in a pe t ro leum facility. This factor is very evident when reviewing dispersion mode l ing results. This relates to 2-7.7 which I will cover unde r a different proposal. There would be a significant difference whether the :95 liter per minu te (of say gasoline) were released f rom a fuel injection nozzle versus being pou red f rom a beaker. The issue is one of mist ing and one associated with the velocity of the rrkaterial at the poin t of release.

NOTE: Suppor t ing material is available for review at NFPA Headquarters . C O M M I T r E E ACTION: Reject. COMMITTEE STATEMENT: T he velocity of the material released is d e p e n d e n t upon the scenario o f the release. T he leak velocity is variable, as is o ther critical information, suda as various sizes of holes or openings in the process piping or equipment . T he size of the release is m u c h more easily def ined ,and quant i f ied than the velocity of the material in a leak. The submi t te r has not provided the addit ional informat ion necessary to include tiffs in the documen t . NUMBER OF COMMITTEE MEMBERS ELIGIBLE TO VOTE: 24 VOTE ON COMMITTEE ACTION:

AFFIRMATIVE: 24

(Log #6) 497A- 3 - (2-7.7): Reject SUBMrITER: Jo im Propst, Shell Oil Company RECOMMENDATION: Revise the four th sen tence to read:

'Net, i f a quar t bottle were empt ied each minu te outdoors at a low the zone made hazardous would be difficult to locate with a

combust ible gas detector." SUBSTANTIATION: Tile velocity o f the material being released may well be one of the single most significant criteria in de te rmin ing the extent o f a v a p o r cloud in a pe t ro leum facility. This factor is very evident wilen reviewing dispersion mode l ing results. The re would be a significant difference whether the .95 liter per minu te (of say gasoline) were released f rom a filel injection nozzle versus being poured f rom a beaker. T he issue is one of mist ing and one associated with the velocity o f the material at the poin t of release.

NOTE: Suppor t ing material is available for review at NFPA Headquarters .

COMMITTEE ACTION: Reject. COMMITTEE STATEMENT: The Commi t tee assumes that the submit ter is referencing 2-7.6 in NFPA 497/L A leak of one quar t per minu te is already considered to be a "low flow" leak. This addit ional in format ion is no t necessary for the user to unders tand the issue. This Section can now be found in Proposal 497A- 15 (Log #CP1) Section 3-4.5. NUMBER OF COMMrVrEE MEMBERS ELIGIBLE TO VOTE: 24 VOTE ON COMMITTEE ACTION:

AFFIRMATIVE: 24

( Log #7 ) 497A- 4 - (2-7.8 (New)): Reject SUBMITTER= J o t m Propst, Shell Oil Company RECOMMENDATION: Add new text as follows:

2-7.8 Mist may form or be present at the same time as f lammable vapors. This may affect the way f lammable material disperses and the extent of any classified area- The strict application of area classification for gases a n d vapors may no t be appropria te because the flammabili ty characteristics of mists are no t always predictable. While it can be difficult to decide upon the extent of classified areas, the criteria applicable to gases and vapors will, in mos t cases give safe results. However, special considerat ions shou ld always be given to the danger of ignition of f lammable mists. SUBSTANTIATION: Mists present a special case that needs to be addressed in the text. These words were pa r aph ra sed f rom a Draft Working Copy of proposed changes for IEC 79-10. COMMITrEE ACTION: Reject. COMMITTEE STATEMENT: The presen t text a l readyprovides e n o u g h informat ion about the format ion of mist in a release scenario, as well as the f lammable vapors tha t are present. The addit ional text reques ted does no t have specific technical substantia- t ion to justify the additional warning above the f lammable vapor p rob lem and possible ignition of the vapor. NUMBER OF COMMITTEE MI~BF.RS ELIGIBLE TO VOTE: 24 VOTE ON COMMITTEE ACTION:

AFFIRMATIVE: 24

(Log #8) 497A- 5 - (2-7.9 (New)): Reject SUBMITTER: J o h n Propst, Shell Oil Company RECOMMENDATION: Add new text as follows:

2-7.9 For a given source of release, the release rate increases with tile release velocity. In the case of a p roduc t conta ined within process equ ipment , the release velocity is related to the process pressure and the geometry of the source of release. The size of a cloud of f lammable gas or vapor is de t e rmined by the rate of f lammable vapor release and the rate of dispersion. Gas and vapor flowing f rom a leak at h igh velocity will develop a c o n e s h a p e d j e t which will entrain air a n d be self-diluting. Ti~e extent of the explosive a tmosphere will be almost i n d e p e n d e n t of wind velocity, ff the release is at low velocity or ff its velocity is destroyed by impinge- m e n t on a solid object, it will be carried by the wind and its dilution a n d ex ten t will d e p e n d on wind velocity. SUBSTANTIATION: The velocity of release is an impor tan t criteria tha t needs to be addressed in the text. These words were para- phrased f rom a Draft Working Copy of p roposed changes for IEC 79- 10. COMMITrEE ACTION: Reject. COMMITTEE STATEMENT: The velocity o f the material released is d e p e n d e n t u p o n the scenario of the release. The leak velocity is variable, as is o ther critical information, such as various sizes of holes or openings in the process piping or equ ipment . The size of the release is m u c h more easily def ined a n d quant i f ied than the velocity of the material in a leak. The submit ter has not provided the addit ional informat ion necessary to include this m the document . NUMBER OF COMMITTEE MEMBERS ELIGIBLE TO VOTE: 24 VOTE ON COMMITTEE ACTION:

AFFIRMATIVE: 24

(Log #3) 497A- 6 - (Table 3-2 (New)): Reject SUBMITrER: Richard E. Munson, Wilmington, DE RECOMMENDATION: Replace Table 3-2 with the following table:

Process e q u i p m e n t Units Low Moderate High Pressure psi <100 >100 >100

AND OR AND Flow rate gpm <500 >500 >500

Revise figures to match as follows: Figures 1 to 8 are dele ted in a separate proposal and so they are not

revised. For Figures 3-4.9 to 3-4.12, delete table and show as high

290

N F P A 497A - - A97 R O P

hazard. For Figure 3-4.13, delete table and showas low hazard. For Figure 3-4.14, delete table and show as high hazard. For Figure 3- 4.15, delete table and show as low hazard. For Figure 3-4.16, delete table and show as low ,and moderate hazards. For Figure 3-4.19, delete tahle. SUBSTANTIATION: There are no figures to support the "low" classification separately from "moderate" and therefore no reason for differentiating benveen low and moderate using the existing tables. Similarly, "high" is not separated from "moderate" in most sketches. The existing Table 3-2 does no t indicate if all or any of the conditions must apply for a particular hazard level. If you have a large size system is that sufficient for fl~e hazard to be large or must pressure also be high? The same confusion exism when you look at the sketches.

T h e p r o p o s e d classification clearly differentiates between the three hazardlevels and allows easy application of diagrams for the three hazard levels. The proposed table has been used successfully by the DuPont Company for many years. COMMITTEE ACTION: Reject. COMMITTEE STATEMENT: Table 3-2 is to be applied with sound engineering judgment . The submitter has provided no technical substantiation to support the changes suggested. NUMBER OF COMI~TrEE MEMBFARgELIGIBLE TO VOTE: 24 VOTE ON COMMITTEE ACTION:

AFFIRMATIVE: 24

(Log #9) 497A- 7 - (3-2.4): Accept in Principle SUBMITrER: John Propst, Shell Oil Company RECOMMENDATION: Delete paragraph 3-2.4 and Table 3-2 or modify it to make it technically correct. SUBSTANTIATION: Paragraph 3-2.4 and Table 3-2 has caused more confusion in file industry than it has eliminated. The root cause for the conclusion is twofold. First it is unclear to the user if the size, pressure, and flow rate relate to the release from the equipment or if it relates to the nameplate rating of the equipment. Second, if the proposal is to draw some correlation between the nameplate rating, of the equip ment and the actual conditions experienced d u n n g fl~e release of hydrocarbons at a source, the NFPA needs to explain what the correlation is so that the user can determine if theyapply. If one follows the methodology outl ined in the Institute of Petroleum Area Classification Code for Petroleum Installations, one will f ind exception after exception to the guidelines presented in Table 3-2. If NFPA has a desire to retain Table 3- 2, then it should be updated to reflect the release rate and volatility of the source and not tbe nameplate of the equipment. COMMITrEE ACTION: Accept in Principle.

See the Committee Action on Proposal 497A- 15 (Log #CP1). COMMITTEE STATEMENT: The submitter 's intent has been addressed by the Committee action on the Proposal 497A - 15 (Log #CP1 ) rewrite in new Section 3-7.3. NUMBER OF COMMITTEE MEMBERS ELIGIBLE TO VOTE: 24 VOTE ON COMMITTEE ACTION:

AFFIRMATIVE: 24

(Log #1) 497A- 8 - (3-4 (New)): Accept in Principle SUBMITTER= Richard E. Munson, Wilmington, DE RECOMMENDATION: Insert new flow diagrams as Figures 3-4.1 and 3-4.2. Update section 3-4 Index of classification diagrams based on new flow diagrams:

Figure 3-4.1 is a flow chart which helps determine if classification is needed.

Figure 3-4.2 is a flow cbart for Class 1 classification. Note that the existing figures are deleted in another proposal and

these flow diagrams include figures and revisions described in another proposal.

SUBSTANTIATION: It is difficult to de termine if dassification is really required and if it is, to determine the extent o f division 1 and 2 areas. There is no guide for selection of figures and users must puzzle over which figure applies to their application. Wifl~ the proposed flow diagrams, a lot of the mystery in the

classification process is removed and classification becomes relatively straightforward. COMMITrEEACTION: Accept in Principle. See the Committee Action on Proposal 497A- 15 (Log #CP1).

COMMr['rEE STATEMENT: The submitter 's intent has been addressed by the Committee action on the CP1 rewrite in Sectiola 3- 7. The format used in the Proposed 497A - 15 (Log #CP1) rewrite provides a more user friendly procedure for classifying areas. NUMBER OF COMMITTEEMEMBERS ELIGIBLE TO VOTE: 24 VOTE ON COMMITFEE ACTION:

AFFIRMATIVE: 24

m q m . q = e

CI,ASS[FICATION I FLOWCHART

RGURE 3-4 .2 SHEET A

I - 11 "

CLASSIFICATION 1 FLOWCHART F I G U R E 3 - 4 . 2

SHEET B

YES [ kt ~ aq~a~ ma.,~ p~l ' i

Uu P.oum :l-4.ag

I " ' - ' " ' - " " t - - , - - - , YES ~ ; Um FlpmH) =0-4,~ CW .ZJ

I .

I t l 4 . ~ m ~,e,,#e~W t~mundaI tmh. a ~ w m ~ ' a l " w 4 ~ l e arm7 I

J ~ m ~ 4~m glll~ stolon vdm

YES le. I Um Figure ;F42S

YES ~ [ UI4 ~ :~4d~4

I " = ~ = ' " I ~ ~ I

1 =

P I . . . . ' - " - - r -

~ O, Wm ~ A I

291

N F P A 4 9 7 A - - A 9 7 R O P

CLASSIFICATION 1 FLOWCHART

v~o* ~ r ~ m tOO t=l =~ ~h*r? st*tern ~

t, uow r,to SOOgpm t* ~ h ~ N~O [

l yl~s

Anm h4m hIQh ~ T ~ eJmu

I ~ tlUm~ S4~ ~ I for

FIGURE 3-4.2 SHEET C

~mal~ o0ntah~4d? UN Ft~x. 3-4~ ~N° u~ i ~ 3-4.4 I

r̂casFstem~t ~n~lltm~orammntxdr'ea?nLXlm" IS ~ Usa F ~ 3-4.$ I ¢-

J

NOTE: F~ m,X~le te~*ge 8mxoee. m ~ ~4.tS to .le.

AREA CLASSIFICATION FLOWCHART

F I G U R E 3-4.1

i

Conskler gqulds, gasos and l v~oors proc*sted, h ~ l k J d

I o r stortd."

• Is l f l ammab l l "~

~nt kJst than lO0"g (3?.rCL vapor of Oat

t ) ,~ ~ ,a ,d .

YES

NO ~re klta4s hsvir~g flash p~nte ~ at or above t00"F(37.SoC) l i n ty

to be tmrtdl~l, ~ t a t t ~ [ . or I t m ' ~ 11 Iomperlttures atx~'o

their fhLSh polNs? /

r

Aroa ClM~I Ic I t lOn not n e ~ l ~ .

I Area may naQtt to be Oassltted.

1

Revlew $octlons I . 2, [ and 3.1 to 3,3 I

Follow Class I F1ova~iet Figure 3.4.2

" Not inclt~i*~il *t~rage in e,stl*d oomxtner

(Log #2) 497A- 9 - (Figure 3-4.1 t h rough 3-4.8, Figure 34.19, Index 3-4 (New)): Reject SUBMITTER: Richard E. Munson, Wilmington, DE RECOMMENDATION: Delete Figures 34.1 th rough 3-4.8 an d 3- 4.19 and replace them with the following sketches. Update Section 3-4 Index of classified diagrams based on the titles of the new sketches as follows:

Figure 3-4.1 is no t used. (It ks reserved for a separate proposal.) Figm:e 3-4.2 is no t used. (It is reserved for a separate proposal.) Figure 34.3 shows typical normally contained systems in low hazard

a r e a s .

Figure 34 .4 shows typical nornaally open systems in low haz~trd areas.

Figure 3-4.5 shows typical normally contained systems in modera te hazard areas.

Figure 34 .6 shows typical normally open systems in modera te hazard areas.

Figure 34 .7 is no t used. Figure 34 .8 is no t used. Figure 3-4.19 shows an outdoor storage tank.

SUBSTANTIATION: Exisdng diagrams listed above cannot be related to existing text sections 3-3.2.1 and 3-3.9.2. The text sections provide a logical basis for establishing a Division 1 or 2 classified area, bu t these diagrams do not illustrate application of the text. They do no t show Division 1 areas, except in below grade or poorly ventilated locations. The result is that the classification process is very difficult and people following the r e c o m m e n d e d practice can reach widely varying conclusions. U n d e r g r o u n d tank application are not currently covered.

The proposed sketches have been used by the DuPont Company for many years to successfully classify areas. They show clearly where a Division 1 and 2 classification apply based on the criteria in the text and us ing the descriptors "normally open" and "normally contained." They also show the impact of vapor density and location - open vs. enclosed, well ventilated vs. enclosed, no t well ventilated.

With the proposed sketches, the text will relate direcdy to those diagrams used for general applications. COMMITTEE ACTION: Reject. COMMITTEE STATEMENT: There is no technical substantiat ion to replace the exisdng figures. NUMBER OF COMMITTEE MEMBERS ELIGIBLE T O VOTE: 24 VOTE O N COMMITTEE ACTION:

AFFIRMATIVE: 24

(Log #14) 497A- 10- (Figures 3-4.2, 34.5, 3-4.6, 3-4.13, 3-4.15, 34.16): Reject SUBMITTER: J o h n Propst, Shell Oil Company RECOMMENDATION: Ch,'mge the he igh t of the ex tended classified area f rom a source f rom "18 in." or "36 in." to "24 in." to be consistent with each o ther and with many of the other figures. SUBSTANTIATION: The variation in he igh t of the ex tended port ion of classified areas has historically varied mosdy as a result of the source for the various figures. Dispersion mode l ing of releases clearly shows tha t a 6 in. differentiation is well beyond the accuracy for predic t ing vapor clouds. Therefore, we should use c o m m o n sense, and past practice as a guide, bu t we should also a t t empt to be consistent. Technically we could pick 18 in., 24 in., or 36 in. as the norm. As we increase the he igh t we decrease the risk but we also increase facility cost a n d potentially reduce reliability an d maintain- ability. I would suggest that 24 in. is a reasonable compromise for mos t outdoor well venti lated applications. COMMITTEE ACTION: Reject. COMMITTEE STATEMENT: The various dep ths shown in the figures are no t arbitrary. Selecting a single dep th as a good compromise is arbitrary. The d imens ions in these existing diagrams are f rom other NFPA documen t s that have control of the area classification d imens ions for these particular locations. NUMBER OF COMMITTEE MEMBERS ELIGIBLE T O VOTE: 24 V O T E O N COMMITTEE ACTION:

AFFIRMATIVE: 24

292

N F P A 4 9 7 A ~ A 9 7 R O P

3 ' _~_ t

®

t__ 3 '

F igure dA -- O u t d o o r s

c Div is ion i

= O l v i s ; o n 2 (see 5 . 2 . ) )

• E m ; u ; ~ aource

Grede

15' 15'

i

• .-,.~.~-. . .: -"....~: -

. ~ ~ Dlv l l i en 1 If vepor density I,O te 1.2

~ - - Grude

Figure 40 - Outdoors

8ulldin~l wall

. / ~ O m m U n l c e t i n g ol:ewl Ing

2t.. / - °,, 4,

Figure 4G - Indoors (Adeqveto|y Yemtila0ed, see 6,3)

" ~ ~ u i i d l n g '~.a | i

~--'-~'-'~--_,,/ Ing opening - t i-~ , f T . "I,

i 11 t" i / - ° ' ' "

O i v ; J | o n | I I vopo, " ~ l e s e t f l e d urea oE- - - ~ - C l a s s i f i e d urea exven<Js *uo- densi ty 1.0 to t .2 doors up, *e 10 ' but ne more to.~ds ou~loo,s up re tkun ~ from era|sale. ]S t but ~ tq~ore thQh I O u ~ e , see F;gum diA 25 J [r~m e m J l t i o .

source, ;oo FIQ. 4D Figure 4 E - - Indoors (Adequetoiy Yent i la fed. see 6,3)

I d e

Figure dC - Indoors (l~adequqt~oiy Ventilotod0 see 6.3)

V & P O R D E H S I T Y ~" "1.2

Figure 4F ~ indeers (Inodectuateiy Vonriteted, tee 6.3)

YAPOR DENSITY < 1,2

Figure 3-4.3 Normally contained systems (low hazard areas).

~ 3

N F P A 4 9 7 A - - A 9 7 R O P

®

Division 1

s; Olv i t i o~ 2 {see 5.2.1)

Fml8 slort source

l i l u l e SA - Ouldoor i

Grade

| If vapor .O to 1.2

FI~)uro SO o Ougdoore

,el l

Classi f ied area extends outdoors up to 10 1 hut Mot mort t ~ e 2S m fl~m omisoion soureoe ooo P ; g ~ SA

Figure SD - Indoors (Adequately Yqmtileted, see 6.3)

Dlvlel d e n s l .

; I t - ~g

Fiouro S~ - |ndoers (AdJoquotQiy Voet l lo tod,

l,~, 6.3)

eli

*" aa'nam~neu e I; w w J rvll

opening

Pigure $C -- |ndeot ; (Inadeq~oeely Yent i leted, ;e~ 6.3)

V A P O R D l i N $ I T Y ~ 1.2

15' I0'

Ptgum SP -- I n d ~ r s ( Inedeqve~ iy Ventlleeod, s e e &. ] )

V & P O R D E N S I T Y ~ 1.2

Figure 3-4.4 Normally open systems (low hazard areas).

294

N F P A 4 9 7 A ~ A97 R O P

u D l v l s i ~ t !

" D i v i * l e : ( j * * 5.2.1)

~D .¢ ~miss ion seurc .

, , - -a . l ' D i v i s i ~ I i f ~,,epe~ - ~ densi ty 1.0 ~* 1.2

V lgum 6D - Out4eer ,

, , " " Bv i |d tng roll ~ d~- - -Bu l l d i ng yell

n*! mince then 15 ft |rein 1.0 Io i.2 25 I t but net me~t emiss ion aMP~trco, ooQ I ~ f l ~0 ~/ (Tom mrnis~

t le~ o~Jqr~e, seq Fi lpwe 6A I:t l)vro 6D

P l l l vm IIm - |ndeers (Ade41vetely Yqmtl let~[~ l e e 6.3~ Figure 6E -- le&eers (Adequomly Vmt t l le led , hem 6.$)

Pisluwm 6C -- |ndeers ( Inedeqvete ly vim011eted, see 6.3)

VAPOR O E N S I T Y ~ | . 2

Fiipv~* 6P - Indeerw (Ine, lequetel l r ¥en t l |~ed~ • . * 6.3)

VAPOR D E N S I T Y < ~o2

Figure 3-4.5 Normally contained systems (moderate hazard areas).

295

[---q ®

Pigvea 7A - 0 u l d o o r s

N F P A 497A - - A97 R O P

D ; v ; s i a n I

Oi- |s io ,~ 2 (sec 5.2.11

[= m;s s ;o,, source i )

I

!

density 1.0 to 1.2

Figvee 7D - OuqdQ~,r$

' I '~0' i , i=

w~'--- Bu ; id in9 ,.,oil

b-t !

|

• . . # " ' G ,a d • I

I i

~ 1 0 $ 1 1 f i e d area ex lends ou tdoors vp I ° 2S |t but nQt , - o r e ,her , S0 i , f , , .~ Qmiill~el,1 IOVFI£4Po 111e F igure 7A

F;guee 7 B - - Indoors (Adequo~ei lr V e n t i l o t l d . see 6.3)

8u ; |d i~g - o i l / !

~ C o m m u n i c a t i ~ g

-

vel ~ I f d t ~ £ i ty "

1.0 to I .~

Figvee ;rE - indoors (Adeq~/ale iy Yent~lqted, see 6.3}

F igure 7C - I n d ~ r s ( Inedeqvo~e iy Vent l la t0d , see 6.3)

V A P O R D E N S I T Y ~ 1.2

o v-e

F' lgvre 7[ I: - Indooqs ( Inodequete l r Ven t i l a ted , see 6.3)

VAPOR DENSITY < 1.2

Figure 3-4.6 Normally open syste!ns (moderate hazard areas).

~ 6

N F P A 4 9 7 A - - A 97 R O P

• Divis ion I [ ~ = Divi, lo. 2 (see S,2. l )

Note:

~d;us

See

Liquid level

-.-When no dlkB

f G,•de

~'--Sump or . ° a c h ~0~ F:l/~.,re 10A - Above Gf@dl Teaks (For FIDDling-Roof Tanks, th• Area Abo.e rb• Float ing Roof

and within ~ • Ski l l te b• Classi f ied Division 1) (NEC 515)

Where dikes are higher than 61 a.g., h igh-w•l l •d cane•hart©ally diked tanks, pockert may be creat©d whlck cer~ Qcco- mulete f|ammable vapors. This may roquire lho! the • r •a within the dike b• ©lass;fi•d as Div is ion 1.

Hetardous enly durln~ f i l l in 9

op•rat lon

F i l l opening

__Liquid i • ve l

Vapor

Figure |0B - Buried Tanks (NEC S14)

VAPOR DENSITY > i .2

* 5 toad 3 I¢odl l for t ight |111 co~.•¢ i lon. F i r I • a t • f i l l conniel lon, radii b•come |0 'and 5 '

*" s tand 3 aradi l for vent dts~h0rglng upward. For downward discharge the Dlvi' i iQn 2 • re• •xtends horizontal ly lo 10' r a d i u s and to a t • d e

F'~rure ~-4.19 S to rage tanks .

297

N F P A 4 9 7 A ~ A 9 7 R O P

(Log #10) 497A- 11 - (Hgure 3-4.13): Reject SUBMITTER: J o h n Propst, Shell Oil Company RECOMMENDATION: Delete reference to "valves" and "pumps" and indicate as "source." SUBSTANTIATION: T he wording on Figure 3-4.13 implies at the very least that valves and p u m p s are to be considered hydrocarbon sources. This is a generalizat ion dlat canno t be suppor t ed by fact. A canned p u m p is certainly one example. Sources should be indicated as sources and it shon ld be left up to die j udgmen t and good engineer ing practice of die eng ineer to de te rmine what consti tutes a source in a particular facility. COMMITTEE ACTION: Reject. COMMITTEE STATEMENT: T h e figures are no t l imiting die area classification to jus t the areas a round valves and pumps but indicate o ther potential mult iple leak sources. Section 3-7.4.1 of Proposal 497A - 15 (Log #CP1) does provide a list of sources of potential leaks and tile figures simply show one possible scenario. NUMBER OF COMMITTEE MEMBERS ELIGIBLE T O VOTE: 24 VOTE O N COMMITTEE ACTION:

AFFIRMATIVE: 24

(Log #11) 497A- 12 - (Hgure 3-4.14): Reject SUBMITTER: J o h n Propst, Shell Oil Company RECOMMENDATION: Delete reference to "valves" and indicate as "source." SUBSTANTIATION: The wording on Figure 3-4.14 implies at the very least dlat valves are to be considered hydrocarbon sources. This is a generalization that canno t be suppor ted by fact. A well ma in ta ined low emissions control valve is one example. Sources should be indicated as sources and it shou ld be left up to the j u d g m e n t and good engineer ing practice of the eng ineer to de te rmine what constitutes a source in a particular facility. COMMITrEE ACTI ON: Reject. COMMITITEE STATEMENT: The figures are no t l imiting the area classification to jus t the areas a round valves and p u m p s but to indicate o ther potential mult iple leak sources. Section 3-7.4.1 of Proposal 497A - 15 (Log #CP1) does provide a list of sources of

~ otential leaks and die figures simply show one possible scenario. ection 3-3 of Proposal CPI also provides for condit ions unde r

which classification is no t required due to proper m, 'dntenance tocedures.

BER OF COMMITTEE MEMBERS ELIGIBLE T O VOTE: 24 VOTE ON COMMITTEE ACTION:

AFFIRMATIVE: 24

(Log #12) 497A- 13 - (Figure 3-4.15): Reject SUBMITTER: J o h n Propst, Shell Oil Company RECOMMENDATION: Delete reference to "valves" a n d "manholes" and indicate as "source." SUBSTANTIATION: The wording on Figure 3-4.15 implies at the very least that valves and manho les are to be considered hydrocarbon sources. This is a generalization tha t canno t be suppor ted by fact. In a well ma in ta ined m o d e r n petrochemical facility many users do not consider either valves or manways as sources unless specific eng ineer ing data would suggest otherwise. Sources should be indicated as sources and it should be left up to the j u d g m e n t and good engineer ing practice of file engineer to de te rmine what constitutes a source in a particular facility. COMMITTEE ACTION: Reject. COMMITTEE STATEMENT: Same Commit tee S ta tement as Proposal 497A - 12 (Log#11) . NUMBER OF COMMITTEE MEMBERS ELIGIBLE T O VOTE: 24 VOTE ON COMMITTEE ACTION:

AFFIRMATIVE: 24

(Log #13) 497A- 14- (Figure 3-4.16): Reject SUBMITTER: J o h n Propst, Shell Oil Company RECOMMENDATION: Delet e reference to "valves," "tanks," and "manholes" and indicate as "source." SUBSTANTIATION: The wording on Figure 3-4.16 implies at the very least that valves, tanks, and manho le s are to be considered hydrocarbon sources. This is a generalization that cannot be suppor ted by fact. In a well ma in ta ined modern petrochemical facility many users do no t consider either valves, tanks or manways as sources unless specific eng ineer ing data would suggest otherwise. Sources shou ld be indicated as sources and it should be left up to the j u d g m e n t and good engineer ing practice of the eng ineer to

de te rmine what constitutes a source in a particular facility. COMMITrEE ACTION: Reject. COMMITTEE STATEMENT: Same Commit tee Sta tement as Proposal 497A- 12 (Log #11). NUMBER OF COMMITTEE MEMBERS ELIGIBLE T O VOTE: 24 VOTE ON COMMITTEE ACTION:

AFFIRMATIVE: 24

(Log #CP 1 ) 497A- 15 - (Entire Document) : Accept SLIBMITTER: Technical Commit tee on Electrical Equ ipmen t in Chemical Awaospheres, RECOMMENDATION: The Technical Commit tee on Electrical I ~ m e n t in Chemical Atmospheres r e c o m m e n d s that the text of

497A, R e c o m m e n d e d Practice for Classification of Class I Hazardous (Classified) Locations for Electrical Installations in Chemical Process Areas, 1992 edition, and the f lammable liquids, Cg]Sl es and vapor informat ion f rom NFPA 497M, Manual for

assification of Gases, Vapors, and Dusts for Electrical Equ ipmen t in Hazardous (Classified) Locations, 1991 edition, be combined into a single document , r e n u m b e r e d and redes ignated as NFPA 497, Classification of Flammable Liquids, Gases or Vapors an d of Hazardous (Classified) Locations for Electrical Installations in Chemical Process Areas. SUBSTANTIATION: This is one of three proposals, developed by the Electrical Equ ipmen t in Chemical Atmospheres (EECA) Ad Hoc Task Group consisting of Ed Briesch, Underwri ters Laboratories; William Lawrence, Factory Mutual; Richard Masek, Bailey Controls; Richard Munson, E.I. DuPont; and David Wechsler, Union Carbide Corp. The EECA Commit tee directed the Ad Hoc Task Group to evaluate NFPA 497A, B, and M, and to de te rmine if diese document s could be developed into two unders tandab le and usable documents . Tills Study was made and the results discussed with the membersh ip of die EECA Committee. From d/at meet ing, it was agreed that the Ad Hoc Task Group should move forward and combine NFPA 497A, 49713 and 497M, into two documents ; one address ing NEC Class I, f lammable gases/vapors and combust ible liquids, and the other address ing NEC Class II combustible dusts. This proposal will incorporate NFPA 497A and NFPA 497M r e n u m b e r and redesignate the d o c u m e n t as NFPA 497, Classification of Flammable Liquids, Gases or Vapors and of Hazardous (Classified) Locations for Electrical Installations in Chemical Process Areas, which contains all die per t inent informat ion conta ined in the two separate documents .

The EECA Ad Hoc Task Group compiled a mul t i -column documen t to compare the individual texts of NFPA 497A, an d 497M. This compilat ion was then fised to editorially create a single document , NFPA 497. By proceeding in this way the Ad Hoc Task Group was able to retain as m u c h of the or ig ina l tex t as possible. A copy of dlis 57 page compilat ion has been submi t ted with this proposal. (NOTE: This compilat ion d o c u m e n t is provided for informat ion only. The proposed NFPA 497 d o c u m e n t should take p recedence over any text differences.)

It is est imated tha t abou t 95 percent of the con ten t of the NFPA 497 d o c u m e n t is simply editorially manipu la ted text, while most of the balance is fur ther deve lopment of existing material that was ei ther unc lear or not complete. The Ad Hoc Task Group strongly resisted efforts to in t roduce new material into die technical re- combin ing ass ignment . However, file subcommit tee felt that there were s trong reasons for in t roduct ion of the new information discussed below.

Examples of editorial manipula t ion can be seen: (a) In the t rea tment of the individual scope s ta tements of NFPA

497M and NFPA 497A. In essence, the one NFPA 497M scope s ta tement was combined with the five NFPA 497A scope statements, p roduc ing six s ta tements in the scope section of NFPA 497. The same m e t h o d was used for die "purpose" s ta tements where the text was extracted from each of the base 497M and 497A documents .

(b) In cases where NFPA 497M and NFPA 497A contained similar, bu t slightly different statements, the more correct of the two was used in NFPA 497. For example, NFPA 497M used the National Electrical Code (NEG) definit ion for Class I, Division l, while NFPA 497A used an abbreviated version. The text incorporated into NFPA 497 contains the NEC definition.

(c) By the creation of a formal definit ions section in NFPA 497, this permit ted no t only better identification of impor tan t terms, but also simplified some of the text. For example, the te rm "combustible material" was developed to el iminate the continual need to specify "f lammable gas, f lammable vapor, combust ible liquid p roduced vapor, that could be mixed with air and bum" . Adequate ventilation was m e n t i o n e d in NFPA 497A (2-6.2) with both a reference and a need. In NFPA 497, it has been made a def ined te rm dlat agrees with its NFPA reference.

(d) In clarifying die in tent of the subject material, the NFPA 497 text has been reorganized. For example, good informational

298

N F P A 4 9 7 A - - A 9 7 R O P

intentions, such as that contained in NFPA 497A, 2-1.4, was moved to Appendix 2-1.9 as a me,am of providing additional guidance to the s tatement in NFPA 497, 2-1.9.

(e) By using a more correct term, as for example; "unclassified" vs. "nonclassified" as meaning die port ion of the area that is nei ther Class I, Division 1, nor Class 1, Division 2. The correct term presented in NFPA 70, National Electrical Code, is "unclassified".

NFPA 497M was a documen t tiaat addressed the Groupings of various selected chemicals, while NFPA 497A provided guidance on how to develop and apply area electrical classification criteria. Wben these documents were combined, it became obvious that if more information about the physical proper t ies of selected materials was provided, that dais data could be better applied to develop appropriate area electrical classifications. The following acdons were undertaken for the reasons stated:

1. The tables in NFPA 497M contained limited information and for the purpose of applying this document for NEC Group determina- tion and Area Electrical Classification, dais material was deemed to be incomplete. Additionally, it became clear that some of the chemical names provided in NFPA 497M were synonyms and not "pure" chemical n a m e s To resolve these problems, in d e v e l o p i n g replacement tables for die new NFPA 497 from those in NFPA 497M, a new single table of selected Class I combustible materials, listed in arldPuhabetical order, was created. Supplement ing NFPA 497M table

es of "Chemical," "Group," and "AIT", the following were added: the material Chemic~d Abstract Service (GAS) number, die NFPA "liquid" definitions (Class I, II, Ill, etc.) die flash point, die lower (%LFL) and upper (%UFL) flammable limits, die vapor density, the vapor pressure, die Minimum Ignition Energy (MIE), the Maximum Experimental Safe Gap (MESG), and the Minimum Ignition Current (MIC) ratio.

As an aid in f inding materials, a supplementary table containing a numerical ranking of CAS numbers vs. Claemical names was added. The data for the chemicals was derived from NFPA documents and odler sources that the EECA Committee considered technically correct.

2. The suggested procedure for classifying areas was re-written to eliminate die seemingly simple "yes" questions and provide sound guidance that addressed cridcal aspects of electrical classification, such as the need for gathering process information data and secnring equipment layout drawings. Additional wording was provided on how m develop the electrical classification drawing and odler support documentat ion for die electrical classification methodology.

3. To assist in locating the appropriate Classification figures, a new table ilas been developed that presents die conditions addressed by the fignres.

4. With the addition of more physical property chemical information and improved clas,dfication procedures, a new appendix article was developed to aid in providing guidance on how process equipment and proc~,sing conditions may affect die extents of the electrical classifications. The information for dais appendix is based on study work published by Institute of Petroleum ([P) Area Classification Code for Petroleum Installations of Detailed Engineer- ing (Copyright 1990, ISBN O 471 92160 2). This information provides a medlodology diat permits die incorporation of die concept of flash point into die area classification analysis, that was not addressed in NFPA 497A. Further NFPA 497M provided information about die various classes of flammable and combustible liquids, but this information was really no t used in NFPA 497A. For example, die only volatility criteria provided in NFPA 497A, is die statement referring to atmospheres with NFPA Class II and Class IlI combustible (not to be confused with die NEC Classifications of Class I, Class II, etc.) liquids that are handled below their flash points, classification may not be required. All other flammable gases, vapors and combustible liquid producing vapors in NFPA 497A, ,are considered equal and die volatility issue is addressed only in the differentiation of the table of small, medium and large releases. Because this appendix material provides degrees of latitude based on reasonable unders tanding of die chemical process, die materials used, the equipment incorporated into the process design and process operating conditions that before had not been

~7 addressed by NFPA 49, A or 497M, it is considered of sufficient merit to be included as appendix information in this NFPA 497 document. As was ment ioned above, the Task Group strongly resisted efforts to

introduce new materiall into the body of NFPA 407 as part of the technical recombining assignment. However, die Task Group felt that the recent action by the NFPA Standards Council which ruled that the EECA Committee was the responsible NFPA technical body for defining die NEC Groups that were established by NEC Code Panel 14, required p rompt action. A sub-Task Group consisting of Ed Briesch, UL; BillLawrence, FM; and David Wechsler, Union

Carbide, was established to develop technically correct definitions for the NEG "Class I" Groups. This Task Group extensively reviewed not only the data presented in NFPA 497M and in other relevant publications and technical papers, but also the testing methods used to arrive at the data. The importance of this work necessitated the need to evaluate the global work effort being conducted. The resultant research has provided data that supports the Group definitions that laave been included in Section 1-$ of NFPA 497. For historical information the topic of Hazardous (Classified) Locations first appeared in the National Electrical Code (NEC) in 1923, when a new article entitled "Extra-Hazardous Locations" was accepted. Tiffs article addressed rooms or compartments in which highly flammable gases, liquids, mixtures or other substances were manufactured, used or stored. In 1931, "Classifications" consisting of Class I, Class II, etc., for the hazardous locations were defined. However it was not until 19~5 that "Groups" were introduced into the NEC. (NOTE: "Divisions" were int roduced into the NEC in 1947.) The four gas Groups, (GroupsA, B, C, and D) complemen ted the desi~a of electrical equipment used in hazardous (classified) locations and were def ined based on the level o f hazard associated with explosion pressures of specific atmospheres and the likelihood the effects of that explosion could be transmitted outside the enclosure. Group A was def ined as atmospheres containing acetylene. Group B was def ined as atmospheres containing hydrogen or gas or vapors of equivalent hazard. Group C was def ined as atmospheres containing ethyl e ther vapor; and Group D was def ined as atmospheres containing gasoline, petroleum, naphtha, alcohols, acetone, lacquers solvent vapors, and natural gas. Despite the fact that the introduction of these Groups was done without standardized testing and without the advantage of today's technological advances or equipment, these definitions have changed little since that time. The first major testing, in fact, was only conducted in the late 1950s when engineers at Underwriters Laboratories, developed a test apparatus that provided a means to determine how various materials behaved with respect to explosion ptiressures and transmission when the specific material was ignited in

ae test vessel. This apparatus, called the Westerberg Explosion Test Vessel, provided standardized documentat ion of a factor called the "Maximum Experimental Safe Gap" (MESG) and permitted other materials to be "classified by test" into one of the four gas groups. The results of these tests are contained in Underwriter Laboratories (UL) Bulletin Nos. 58 and 58A (reissued in July, 1993, as UL Technical Report No. 58). In 1971, the International Electrotechnical Commission (IEC) published IEC 79-1A, defining a different . t~e of apparatus for obtaining MESG results. While the two "MESG' test apparatus are physically different in both size and shape, the results are statistically comparative, althougil in some cases differences have been observed. A sample of values are shown in the table below.

Material Westerberg apparatus, IEC apparatus, MESG, mm MESG, mm

Propane .92 .94 Ethylene .69 .65

Butadiene .79 .79 Diethyl e ther .30 .87

Hydrogen .08 .29

Papers have been written to a t tempt to explain the reasons for this difference in the test data. One, by H. Phillips, entitled "Differences Between Determinations of Maximum Experimental Safe Gaps in Europe and U.S.A.", appeared in a 1981 edition o f t h e ~ Hazardous Materials and cited a condition of spontaneous combustion in one portion of the Westerberg Apparatus, which was reflected in materials like dieflayl ether, having low ignition temperatures. Additionally, testing on the WesterbergApparatus has demonstrated that tiffs theory was true and the MESGvalue for diethyl etlaer more than doubled. Further, Westerberg apparatus testing has also shown that the hydrogen MESG value is .23 mm. While acetylene remains segregated in Group A because of die

ltigh explosion pressure which results from its very fast flame speed, newer test methodologies have defined other types of protection methods that now consider acetylene and hydrogen to be of equivalent hazard. One such method examines the "Minimum Ignition Current" required to ignite a specific combustible material. This testing produced more variability when the results of specific combustible materials were compared. However, it was found that the minimum ignition currents of one test could be favorably compared with those of other tests if a ratio value based on methane was applied. This testing has resulted in the generation of MIC ratio data.

Otller testing has been performed when it was incorrectly assumed that a factor called "Minimum Ignition Energy" (MIE) and "Auto Ignition Temperature" (AIT) were related and could be used to place materials into Groups. The fact that these were independen t factors resulted in deletion of AITs as a basis for Group determina-

299

N F P A 4 9 7 A I A 9 7 R O P

tion in the 1971 NEC. While MIEs have been found to exhibit theoretic~al results, these values do no t translate into practical designs that can be applied to actual electrical devices with their associated energy levels.

Since the pr imary concern is to have electrical devices tha t can safely operate when used in locations classified by Class, Group and Division, the definit ions for the four gas groups have been def ined on the basis o f the parameters providing the most significant basis for tha t design; ME.SG, and MIC ratio. Lacking these values, exper ience based u p o n data indicating equivalency to a tmospheres providing similar hazards can be used.

On dais basis, defini t ions for NEC Groups A, B, C, and D have been provided. While in some cases, applying these definit ions will result in Groupings that may differ f rom the historic Groups, the Task Group considers these as being technically correct and appropriate for use.

Lastly, with the exception of r e n u m b e r i n g tile Chassification diagrams, no changes have been made to the diagrams.

The Ad Hoc Task Group wishes to express its appreciat ion to the member s of the Electrical Equ ipment in Chemical Atmospheres Commit tee for their suppor t and assistance provided us dur ing this two year effort.

NOTE: Suppor t ing material is available for review at NFPA Headquarters . COMMITTEE ACTION: AccepL NUMBER OF COMMITTEE MEMBERS ELIGIBLE TO VOTE: 24 VOTE ON COMMITTEE ACTION:

AFFIRMATIVE: 24 COMMENT ON AFFIRMATIVE:

LATAILLE: The phrase "combustible materials" now used t h roughou t NFPA 497 is potentially confusing. I consider dusts and fibers combust ible materials, but the in ten t of NFPA 497 is to cover only liquids, vapors and gases. "Combust ible fluids" would be a better phrase. Granted the te rm "combustible" is def ined dais way for the purpose of NFPA 497, but I would ra ther see file phrase "combustible fluid" so defined.

The new titles of NFPA 497 and NFPA 499 are potentially confusing. First for no t us ing file new term "combustible materials" (or fluids, as I would prefer), second for referr ing to chemical process areas. A newspaper pr int ing p lan t has classified areas a round the pr int ing presses, but few would consider these chemical process areas. Ditto for a plan~ that gr inds flour. I suggest dais title:

NFPA 497 - - Classification of Combust ible Fluids and of Hazardous (Classified) Locations for Electrical Installations in Areas Conta in ing Combustible Fhtids. WECHSLER: Appendix A-3-7.3 should be replaced with the revised

text which is provided. The informat ion provided in Appendix A-3-7.3 contains valuable

advice and should be a part of this document . However in its cur ren t fom], it lacks clarity, provides data that is conflicting in some cases, and does not do a good job of expand ing on file information conta ined in the body of the document - The suggested revision provides in clearer language, a simpler "hazardous indice" rather than tile more confilsing hazard radius, with a single figure that complemen t s several figures in main document - Confus ing tables and texts have been removed to focus on the core aspect o f being able to apply volatility concerns to the extent of the area electrical classification. The revised appendix material, contains no new data or information.

A-3-7.3 The user may wish to use the methodology discussed here, which is

based n p o n the Institute of Petroleum, Area Classification Code for Pet ro leum Installations, Part 15, March 1990, to fu r ther assess the hydrocarbon 's volatility as an added measure of deriving the extent of the classification for ventilated, Class I, Division 2, electrically classified areas. In the event tiffs me thodo logy is employed the user should fully d o c u m e n t the rational and the considerat ions as part of the area electrical classification process.

The methodology begins by placing the hydrocarbon of interest into one of four categories, as shown in Figure A-3-7.3.1.

Category 1 is considered the most volatile materials a n d includes LPG and f lammable gases. Category 2 includes NFPA 30 Class 1A Flammable Liquids plus all materials with a vapor pressure exceeding 750 m m Hg. Category 3 includes NFPA 30 Class 1B, 1C, 2 and 3 combust ible liquids tha t are above their flash point. Category 4 includes NFPA Class 2 and 3 combust ible l iqmds that are below their flash points which would fall into a category no t likely requi r ing the use of special electrical equ ipment .

Once the source category 1, 2, 3, or 4, is selected, the methodology then relates the category of volatility of the hydrocarbon to the flow rate, as shown in Figure A-3-7.3.2, to different hazard indice, in a m a n n e r similar to that def ined in dais practice us ing the low, med ium, ltigh criteria. While the Hazard lndice Matrix has 9 indice shown for the various

combinat ions of material category and flow rate, it is actually a

c o n t i n u u m in which engineer ing j u d g m e n t shou ld be applied when ei ther the category or the flow rate is near the interface. For example if the material is located near the Category 2-3 interface and the flow rate is on the low to m e d i u m interface, a hazard indice o f 5 to 10 may be used.

Figure A-3-7.3.4 and its char t (Figure A-3-7.3.3) demons t ra te how the Hazard Indice value would be applied to open air (adequately ventilated) sources of heavier than air materials.

Having de t e rmined the material volatility, and assessed the flow rate, specific details of the processing e q u i p m e n t can be evaluated to derive a family of hazard indices. These can then be utilized to develop an overall area electrical classification.

ST. ONGE: 1.3 Definitions The Group definitions are new. Presumably, other NFPA standards

will have to adopt them. Appendix A in A-l-3 ough t to have an explanat ion of the basis for

the specific values of MESG and MIC selected. Tile few references 1 have indicated they are not the same but not much different than values used in European standards.

2-1 National Electrical Code Criteria. Tile Division 2 definit ion is no t an equivalent to the Division 1

definition. It cites only one of the condit ions of the NEC definition. A more appropriate s t a tement is: "Division 2 in which die combustible material is present unde r abnormal conditions".

Tables 2-1 and 2-2 This is a classification s tandard and the first serious use of the

tables is at 3-7.1. The tables ough t to be moved to the end of Chapter 3 or even Chapter 4 where they will cause less interrupt ion in the text and classification process.

3-7.2.2 Existin~ Facility History. 1 don ' t th ink it s good policy for an NFPA s tandard to r e c o m m e n d

this type of quest ion format- The informat ion is need ed but the m e t h o d ought to be left up to the individual doing the work. I th ink a more appropriate second sen tence would be: "Experience of leakage or o ther releases occurr ing dur ing normal or abnormal operat ions or dur ing ma in tenance should be obtained".

These commen t s are submi t ted for considerat ion at the appropriate t ime in the s tandard cycle. I th ink they should be considered before issue for public comment-

t4 ~q ~q

t~

o

P r o c e s s o r S t o r a g e T e m p e r a t u r e

Figure A-3-7.3.1 shows a plot of temperature versus vapor pressure with four volatility categories (Note: 750 mm Hg = "14.5 psi)

300

" l q F P A 4 9 7 A - - ~ A 9 7 R O P

J T m

s s-~'s 2 s - s o

3 ~3-5 S-2S i

Paw I t m

Figure A-3-7.~,2 Category~Fiow rate. Haim~ Indice: clb~lays how the flow rate is divided int~ the three categorim ofiow, medium, and high as follows: Low is less than 100 . ~ . . ~ per minute; Medium is 100 to 500 gaHom per minute;High is greater than ~ to 1000 gallons per minute.

$ $ $ S 5 S 10 10 10 IS iS LS 2S 2O 30 S0 '25 25 100 ]5 25

0 NA ? 15 0 HA ]tO " " 0 NA W 2 G" NA 10 - 5 10 20 2

3 2S 25 2S* ]S 50 2

lr, gure A-S-7.&.~ f3san (above) ~ m e ~ Im~cewhh me extents of the mre~electrlcld clMdflcalioa (lrJgmm A-S-7.S.4) (located to the rk, h0

suca t s ~ m oR x ~ s ~ .

301

N F P A 4 9 7 A i A 9 7 R O P

NFPA 497

Recommended Practice for the Classification of Flammable Liquids, Gases, or Vapors and of

Hazardous (Classified) Locations for Electrical Installations in Chemical Process Areas

1997 Edition

Notice: An asterisk (*) following the n u m b e r or letter des ignat ing a paragraph indicates explanatory material on tha t paragraph in Appendix A.

Informat ion on referenced publications can be f o u n d in Chapter 4 and Appendix B.

Chapter 1 General

1-I Scope.

1-1.1 This r e c o m m e n d e d practice applies to those locations where f lammable gases or vapors, f lammable liquids, or combust ible liquids are processed or hand led and wbere their release into the atmosphere may result in their ignition by electrical systems or equip- menL

1-1.2 This r e c o m m e n d e d practice provides informat ion on spedf ic f lammable gases a n d vapors, f lammable liquids, and combust ible liquids whose relevant combus t ion propert ies have been sufficiently identified to allow thei r classification into the groups established by NFPA 70, NationalElectrical Cod~ (NEC) for p roper selection o f electrical equ ipme n t in hazardous (classified) locations. T h e tables in this d o c u m e n t are no t in t ended to be all-inclusive.

1-1.3 This r e c o m m e n d e d practice applies to chemical process areas. As nsed in tills documen t , a chemical process area may be a large, in tegrated chemical process p lan t or it may be a part of such a plant. It may be a part o f a manufac tu r ing facility where f lammable gases or vapors, f lammable liquids, or combust ible liquids are p roduced or used in chemical reactions or are hand l ed or used in certain un i t operat ions such as mixing, filtration, coating, spraying, and distillation.

1-1.4 This r e c o m m e n d e d practice does no t apply to si tuations tha t may involve catastrophic failure of or catastrophic discharge f rom process vessels, pipelines, tanks, or systems.

1-1.5 This r e c o m m e n d e d practice does no t apply to enr iched oxygen a tmospheres or py rophonc materials.

1-1.6 This r e c o m m e n d e d practice is no t in tended to supersede or conflict with the NFPA s tandards listed in Appendix C~

NOTE: It is no t the in tent of tiffs edit ion to fully address issues associated with Article 505 in the NEC.

1-2 Purpose .

1-2.1 The purpose of this r e c o m m e n d e d practice is to provide the user with a Imsic unde r s t and ing of the parameters tha t de te rmine

t h e degree and file ex ten t of the hazardous (classified) loc~tion. This r e c o m m e n d e d practice also provides the user wid'~ examples of the applications of these parameters .

1-2.2 Informat ion is provided on specific f lammable gases and vapors, f lammable liquids, and combust ible liquids, wllose relevant . . . . . prop erties de te rmine their classification into group.s This will assist m the selection of spectal electrical e q m p m e n t for hazardous (classified) locations where such electrical e q u i p m e n t is required.

1-2.3 This r e c o m m e n d e d practice is i n t ended as a guide and should be applied with sound engineer ing j u d g m e n t . Where all factors are properly evaluated, a consistent area classification s cheme can be developed.

1-3 Definitions.

For the purpose of this r e c o m m e n d e d practice, the following terms shall have the mean ings given below. T h r o u g h o u t the document , def ined terms are identified us ing bold letters (or when in titles, bold and under l ined) .

Adequate Ventilation. A ventilation rate that affords ei ther six air changes per hour , or 1 cfm per square foot of floor area, or o ther similar criteria tha t prevent the accumula t ion o f significant

quanti t ies o f vapor-air concentra t ions f rom exceeding 25 percent of the lower f lammable limit.

Autuignit ion Tempera tu re . The m i n i m u m tempera tu re requi red to initiate or cause sett-sustained combus t ion of a solid, liquid, or independent ly o f the hea t ing or hea ted element . (SeeNFPA 325, Guide to Fire Hazard Properties of Flammable Liquids, Gases, and Volatile Solids.)

C_AS. Chemical Abstract Service.

Class I, Division 1. A location: (1) in which ignitable concentra- t ions o f f lammable gases or vapors exist unde r normal opera t ing conditions; or (2) in which ignitable concent ra t ions of such gases or vapors may exist f requent ly because of repair or ma in tenance operat ions or because of leakage; or (3) in which breakdown or faulty operat ion of e q u i p m e n t or processes migh t release ignitable concentra t ions of f lammable gases or vapors and migh t also cause s imul taneous failure of electrieal equipment . See Section 500-5(a) of the NEC.

Class I, Division 2. A location: (1) in which volatile f lammable liquids or f lammable gases are handled, processed, or used, but in which the liquids, vapors, or gases will normally be conf ined within closed containers or closed systems f rom which they can escape only in case of accidental rup ture or breakdown of such containers or systems, or in case of abnormal operat ion of equipment ; or (9) in which ignitable concentyations of gases or vapors are normally prevented by positive mechanical ventilation, and which migh t become hazardous th rough failur~ or abnormal operat ion of the venti lat ing equipment ; or (3) that is adjacent to a Class l, Division 1 location, and to which ignitable concent ra t ions of gases or vapors migh t occasionally be commun ica t ed unless such communica t ion is prevented by adequate positive-pressure venti lat ion f rom a source of clean air and effective safeguards against ventilation failure are provided. (See Section 500-5(b) of the NEt72.)

Combust ib le Liquid. A liquid having a flash po in t at or above 100°F (37.8°C).

Combust ib le liquids are subdivided as follows:

Class II liquids are those having flash points at or above 100°F (37.8°C) and below 140°F (60°C').

Class III liquids are those having flash points at or above 140 F (60°C), and are subdivided as follows:

Class IlIA liquids are those having flash points at or above 140°F (60°C) a n d b e l o w 200°F (93.4°C).

Class IIIB liquids are those having flash points at or above 200°F (93.4°C).

Combust ible Material.* A gener ic te rm used to describe a flammable gas, f lammable l iquid-produced vapor, or combustible liquid- p roduced vapor mixed with air tha t may burn or explode.

Class I combustible materials are divided into four groups:

Group A - - Acetylene or gases or vapors of equivalent hazard.

Group B i Combust ible materials havin~ eidler MESG values less tlian or equal to 0.45 nun, or MIC ratio less than 0.4, or gases or vapors of equivalent hazard.

Group C - - Combust ible materials having ei ther MESG values between 0.45 m m and 0.75 m m , or MIC ratio between 0.4 an d 0.80, a n d / o r gases or vapors of equivalent hazard.

Group D - - Combustible materials having MESG values greater than 0.75 m m or MIC ratio greater than 0.80, or gases or vapors of equivalent hazard.

The group designat ion is listed in Table 2-1.

Flammable Liquid. A liquid des ignated as Class I, having a flash poin t below 100°F (37.8°C) and having a vapor pressure no t exceeding 40 psia at 100°F (37.8°C). Class Hiquids are subdivided as follows:

Class IA liquids are those having flash points below 73°F (22.8°C) and having boiling points below 100°F (37.8°C).

Class IB liquids are those having flash points below 73°F (22.8°C) and having boiling points at or above 100°F (37.8°C).

302

Chemical MIC MESG Ratio (ram)

Gasoline n-Heptane n-Heptene n-Hexane Hexanol 2-Hexanone

CAS No.

8006-61-9 142-82-5

81624-04-6

110-54-3 111-27-3 591-78-6

Group

D* D •

D b

D*b D D

Type b

I I I I

Il iA I

Flash Point (°C) -46 -4 -1

-23 63 35

AIT (°C) %LFL %UFL Vapor Densi ty (Aa~-l)

280 1.4 7.0 3.0 204 1.0 6.7 3.5 204 3.4 225 1.1 7.5 3.0

3.5 424 1,2 8.0 3.5

Vapor MIE Pressure 7 (m J) tram I-Ifi)

45.5 0.24 0.88 0.91 0.97

152 0.24 0.88 0.93

0.8 10.8

0.98

Hexene 592-41-6 D I -26 245 1.2 6.9 sec-Hex]d Acetate 108-84-9 D II 45 5.0

186

H~'drazine H) 'drosen

302-01-2 C II 1333-74-0 B* GAS

38 23 98.0 1.1 520 4.0 75.0 0.1

14.4 0.019 0.25 0.28

Hydrogen C)ranide H),drogen Selenide Hydrogen Sulfide Isgamyl Acetate,

74-90-8 C* GAS 7783-0%5 C I 7783-06-4 G* GAS 123-92-2 D I

-18 538 5.6 40.0 0.9 7793

260 4.0 44.0 1.2 25 560 1.0 7.5 4.5 6.1

0.80

0.068 0.90

Isoam)'l Alcohol Isobutane !sobut)'l Acetate Isobut),l Acrylate Isobut),l Alcohol Isobutyraldehyde Is,odecaldeh~,de Isohexane Isopentane Isooctyl Aldehyde Isophorone Isoprene

123-51-3 D 75-28-5 D b

110-19-0 D* 106-63-8 D 78-83-1 D* 78-84-2 C 112-31-2 C 107-8 3-5 D 5 78-78-4 D b

123-05-7 C 78-59-1 D 78-79-5 D*

II 43 350 1.2 9.0 3.0 3.2 GAS 460 1.8 8.4 2.0

I 18 421 2.4 10.5 4.0 17.8

1.02

I 427 4.4 7.1 I -40 416 1.2 10.9 2.5 10.5 0.92 0.98

GAS -40 196 1.8 10.0 2.5 IIIA 5.4 0.09

264 211.7 1.00

II 420 688.8 197 1.9

84 460 0.8 3.8 4.8 0.4 I -54 220 1,5 8.9 2.4 550.6

Isoprop),l Acetate 108-21-4 D I 460 1.8 8.0 3.5 60.4 Isgpropyl Ether 108-20-3, D* I -28 443 1.4 7.9 3.5 148.7 1.14 0.94 Isopropyl Glycidyl Ether Isopropylamine Kerosene Liquified Petroleum Gas Mesit~l Oxide Methane Methanol

4016-14-2 C I 75-31-0 D GAS -26 402 2.3 10.4 2.0 2.0

8008-20-6 D II 72 210 0.7 5.0 68476-85-7 D 1 405

141-97-9 D* I 31 344 1.4 7.2 3.4 47.6 74-82-8 D* GAS -223 630 5.0 15.0 0.6 0.28 1.00 67-56-1 D* I 12 385 6.0 36.0 1.1 126.3 0.14 0.82

1.12 0.92

Methyl Acetate Methyl Acrylate Methyl Alcohol Methyl Amvl Alcohol

t Methyl Chlbride Methyl Ether Methyl Ethv! Ketone Methyl Formal

79-20-9 D GAS -10 454 3.1 16.0 2.6 1.08 96-33-3 D GAS -$ 468 2.8 25.0 3.0 , 0.98 67-56-1 D* I 385 6.0 36.0 1.1 126.3

108-11-2 D II 41 1.0 5,5 3.5 5.3 74-87-3 D GAS -46 632 8.1 17.4 1.7 115-10-6 C* GAS -41 350 3.4 27.0 1.6 0.85 78-93-3 D* I -6 404 1.4 11.4 2.5 92.4 0.55 0.92

534-15-6 C* I 1 238 3.1

0.99 0.85 0.91 1.01 1.00 0.84 0.84

Z

I

O

C h e m i c a l

Meth]4 Formate 2-Methylhexane Meth)~ Isobutyl Ketone Methy Isocyanate Meth)s Mercapatan Meth)s Methacrylate Meth]J N-Amyl Ketone Meth~ Tertiary But~'l Ether

No.

107-31-3 31394-54--4

141-79-7 624-83-9 74-93-1 80-62-6

NEC Croup

Type b Flash AIT (°C) %LFL %UFL Vapor Vapor Point Density Pressure 7 (°C) (Air=l) (ram Hg)

D GAS -19 ~ 9 4.5 23.0 2.1 D b I 2 ~ D* I 31 440 1.2 8.0 3.5 11 D GAS -15 534 5.3 26.0 2.0 C D

GAS -18 3.9 21.8 1.7 I 10 422 1.7 8.2 3.6 37.2

110-43-0 D II 49 393 1.1 7.9 3.9 3.8 1634-04-4 D I -80 435 1.6 8.4 0.2 250.1

MIE (mJ)

MIC Ratio

MESG (ram)

0.94

0.95

2-Meth~,loctane 3221-61-2 2-Methylpropane 75-28-5

220 6.3 D 5 I 460 2639

Methyl-l-Propanol 78-83-1 Methyl-2-Propanol 75-65-0 2-Meth),l-$-Eth),l Pyridine 104-90-5 Meth~'lacet'ylene 74-99-7 Meth]dace~lene-Propadiene 27846-30-6 lVleth~'lai 109-8%5

D* D*

I -40 416 1.2 10.9 2.5 10.1 I 10 360 2 . 4 8.0 2.6 42.2

0.98

D C*

74 1.1 6.6 4.2 I 1.7 1.4 4306 0.11

C C I -18 237 1.6 17.6 2.6 398

0.74

/vleth)'lamine 74-89-5 2-Methylbutane 78-78-4 Meth~icTclOhexane 208--87-2 Meth),/c~ciohexanol 25630-42-3 2-Me th)tc),clohexano ne 583-60-8 2-Methylheptane

D GAS 430 D 5 -56 420 1.4 D I -4 250 1.2

4.9 ~ . 7 1.0 1.10 8.3 2.6 688.6 6.7 3.4 0.27

D 68 296 3.9 II 3.9

420 280 61.5 3-Methyihexane 589-34-4

$-Methylpentane 94-140 2-Methylpropane 75-28-5 2-Meth),l-l-Propanol 78-83-1 2-Methyl-2-Propanol 75-65-0 2-Methyloctane 221 6-32-2 $-Methyloctane 2216-33-3 4-M~thvlnct~me 2216-34-4

14143-5 78-96-6

D D 5 D 5

D b D b D* D* D b

D b D 5

278 I 460 2639 I -.40 223 1.2 10.9 2.5 10.5 I 478 2.4 8.0 2.6 42.2

220 220 6.3 225 6.8

D D

85 410 2.1 0.4 77 374 2.6 1.1

100-61-8 C 60-34-4 C

482 0.5 I 23 194 2.5 92.0 1.6

110-91-8 C* 8030-30.-6 D 8050-30-6 D,4 463-82-1 D b 98-95-$ D

II 35 310 1.4 11.2 3.0 10.1 0.95 II 42 277 I 42 2 ~ 1.1 5.9 2.5

-65 450 1.4 8.3 2.6 1286 88 482 1.8 4.3 0.5 0.94

7%24-3 C 75-52-5 C

I 28 414 3.4 2.6 20.7 I 35 418 7.3 2.1 36.1 0.92

0.87 1.17 0.84

Z

,-,I

I

1-Nitropropane 108-03-2 C I 34 421 2.2 3.1 10.1 2-Nitropropan e 79-46-9 C* I 28 428 2.6 11.0 3.1 17.1

Chemical CAS No. NEC Type b Flash AIT (°C) %LFL %UFL Group Point

(°C) i 42.84-7 C 1 17 299

M1E " MIC " MESG

[ Di-N-Prol~ylamFne 1,4-Dioxane Dipentene Dipropylene Glycol

blethyl Ether

V~ o r P. Density (Air=l)

Vapor Pressure 7 (ram Fig)

27.1

(mJ) Ratio (ram)

123-91-1 C* I 12 180 2.0 22.0 3.0 38.2 138-86-3 D II 45 237 0.7 6.1 4.7

34590-94-8 C I I IA 85 1.1 3.0 S. 1 0.5

0.19 0.70 1.18

D!!sopropylamine 108-18-9 C GAS -6 316 1.1 7.1 3.5 Dodecene 6842-1 5-5 D II IA 100 255 Epichlorohvdr in 3132-64-7 C* I 33 411 3.8 21.0 3.2 Ethane 74-84-0 D* GAS -29 472 3.0 12.5 1.0

13.0

Ethanol 64-17-5 D* I 13 363 3.3 19.0 1.6 59.3 0.24 0.82 0.91

0.88 0.89 E 75-04-7 D* I -18 385 3.5 14.0

74~5-1 C* GAS 0 450 2.7 36.0 1.6 1048 2.4 1.0 0.070 0.53 0.65 Ethylene

Ethylenediamine 107-1 5-3 D * I 33 385 2.5 12.0 2.1 12.5 Ethylenimine Ethyle..ne Chlorohydrin Ethylene Dichloride Ethylene Glycol Monoethyl Ether Acetate Ethylene Glycol ZVlonobutyl Ether Acetate Ethylene Glycol Monobuty'l Ether Ethylene Glycol Monoethyl Ether Ethylene Glycol Mono,me[hyl Ether Ethylene Oxide

151-56-4 C* 1 -11 320 3.3 54.8 107-0%3 D I I IA 59 425 4.9 15.9

1.5 211 0.48 2.8 7.2

107-06-2 D* I 13 413 6.2 111-1 5-9 C II 47 379 1.7

16.0 3.4 79. 7 4.7 2.3 0.5~ 0.97

2-Ethylhexaldehyde 2-Ethylhexanol 2-Ethylhexyl Acrylate Ethyl Acetate Ethyl Acr~'late ' (Inhibited) Ethyl Alcohol Ethyt Sec-Amyl Ketone

112-0%2 C II IA 340 0.9 111-76-2 C I l i a 238 1.1 110-80-5 C I I 235 1.7 109-86-4 D II 285 1.8 75-21.8 , , - , ,B(C)* 1, I i 23-05-7 C II 104-76-7 D IIIA 81 '103-09-3 D '" I lIA 88 ' 141'-'78~6 D* 1 140-88-5 D* I 64-17-5 D* I

541-85-5 D II

8.5 0.9 12.7 4.1 1.0 15.6 3.0 5.4 0.84 14.0 2.6 9.2 0.85

-20 429 3.0 99.9 1.5 1314 0.065 0.47 0.59 52 191 0.8 7.2 4.4 1.9

0.9 9.7 4.5 0.2 252 0.3

-4 427 2.0 11.5 3.0 93.2 0.46 0.99 9 372 1.4 14.0 3.5 37.5 0.86 13 363 3.3 19.0 1.6 59.5 0.89 59

100-41-4 D I 21 432 0.8 6.7 3.7 9.6 97-95-0 D II 57 1 ~ 3 ~ D II 46 75-00-3 D GAS -50

1.2 7.7 3.5 1.5

5i9 ~.8 15.4 4.0 3.6 2.2

60-29-7 C* I -45 160 1.9 36.0 109-94-4 D GAS -20 455 2.8 16.0 75-08-1 C* I -18 300 2.8 18.0 100-74-3 C I 32

2.6 538 2.6 2.1 527.4 4.0

0.19 0.88 0.84 0.94

0.90 0.90

lein 645-02-5 C I I IA 68 78-10-4 D II 50-00-0 B GAS 60 64-18-6 D I I 50

8008-20-6 D I I 72 98-01-1 C IIIA 60 98-00-0 C I I IA 75

4.4 7.2

429 7.0 73.0 1.0 434 18.0 57.0 1.6 210 0.7 5.0 316 2.1 19.3 3.3

42.7 0.57 1.86

z

I

2.3 0.94 490 1.8 16.3 3.4 0.6

63O-O8.-0 107-26-0 108-90-7

2425-66-3 126-99-8

1319-77-3 4170-$0-$

98-82-8 110~2-7 108-954) 108-94-1 110-83-8 75-19-4

Carbon Monoxide Chloroacetaldeh]cde Chlorobenzene

! 1-Chloro-l-Nitropropane Chloroprene Cresol Crotonaldehyde Cumene

[ Cyclohexane O/clob-~-ol C]tcloh~'Y~none C),dohexene O/clopropane

C D

NEC "' Type ti Flash AIT (°C) %LFL %UFL Vap.or Vapor Group Point Density Premure7

(°C) (Air=- l) l a i n I-I~) C* GAS 609 700 i 2.5 74. 0.97 C I l iA 88 6B.1 D I 29 593 1.3 9)6 3.9 11.9

D C* D

"O D D D

124-4O-$ 7~3-2

I l iA GAS -20 4.0 20.0 3.0 I l iA 81 559 1.1 3.7

I 15 2s2 2.1 15.5 2.4 $$.! l $6 424 0.9 6.5 4.1 4.6 I -17 245 1.3 8.0 2.9 08.8

I l iA 68 500 3.5 0.7 II 44 245 1.1 9.4 $.4 4.$ I -6 244 1.2 2.8 89.4

~ MIE MIC M F_..S G (mJ) Ratio (ram)

0.81

0.22 1.0 0.94

0.97 0.98

~eC)~aene cene

99-87-6 872-05-9

D* D D

503 2.4 10.4 1.5 5430 II 47 456 0.7 5.6 4.8 1.5 II 235 4.8 1.7

6.1't 0.84 o.01 '

n-Dec~deh),de n-Decanol

112-31-2 112-30-1

I l i a 0.09 I l iA ' 82 288 5.$ 0.008

Dec)tl Alcohol Diacetone Alcohol Di-lsobut},lene Di-lsobut~ Ketone o-Di'ch[orobenzen'e

Chemical ' CAS No.

112-$0-1 D I l iA 82 288 5.3 0.008 123-42-2 D I l iA 64 605 1.8 6.9 4.0 1.4

25167-70-8 D* I 2 391 0.8 4.8 $.8 108-83-8 D II 60 396 0.8 7.1 4.9 1.7 955-50-1 D I l iA 66 647 2.2 9.2 5.1

3583-47-9 D* I 1.9 8.5 2.0 1300-21-6 D I 438 6,2 16.0 $.4 22i 156-59-2 D I 97 460 5.6 12.8 3.4 204 594-72-9 G I l iA 76 5.0

10061-02-6 D I 55 5.3 14.5 $.8 7%73-6 C I 32 503 2.8 10~:~-87-9 G* I -28 Si2 1.8 10.1 2.5 100-37-8 C II IA 60 320 4.0 1.6

25340-17-4 D II 57 $95 4.6 60-29-7 C* I 12 160 1.9 36.0 2.6 $8.2 112-34-5 C I I IA 78 228 0.9 24. 6 5.6 0.02 111-7%5 C I l i a 93 241 0.2 121-69-7 C IIIA 63 $71 1.0 4.2 0.7 68-12-2 D II 58 455 2.2 15.2 2.5 4,1 77-78-1 D I I IA 83 188 4,4 0.7'

1071-26-7 $1394-54-4

lO~:83-5

C GAS 400 2.8 14.4 1.6 D b I ..48 405 $19.S

D b I $96 D 5 I 325 10.8

D 5 I 438 D 5 I 355 211.7

0.96

0.25 0.98 1.07 1.82

0.91 1.15

0.19 0.88 0.85

1.08

:Z

I ",,dl

Table 2-1 Selected Chemicals

Chemical CAS No.

Acetaldehyde 75-07-0 Acetic Acid 64-19-7

. ' ' t ' Aceuc Acld-Tert.-Butyl Ester 5,t0-88-5 Acetic Anhydride 108-24-7 Acetone 67-64-1 Acetone C oh drin 75-86-5 Acetonitrile)e an )' 75-05-8 Acetylene 74-86-2 Acrolein /Inhibited / 107-02-8 Acrylic Acid 79-10-7

NEC Group

C *

D* D D D*

Type b

I II II

Flash AIT (°C) %LFL %UFL Point (°C) -38 175 4.0 60.0 43 464 4.0 19.9

1.7 9.8 54 316 2.7 10.3

465 2.5 12.8

Vapor Vapor Density pressure 7 (Alr=-l) Imm H~)

1,5 874.9 2,1 15.6 4.0 40.6 3,5 4.9 2.0 250.7

D IIIA 74 688 2.2 12.0 2,9 0.3 D I 6 524 5.0 16.0 1.4 91.1

MIE MIC MESG (mJ) Ratio (ram)

0.37 0.98 0.92 2.67 i.76

1.15 1.00 1.02

1.50 2.5 ~ .9 0,9 36~0 0.017 0.28 0.25 2.8 51,0 1.9 274.1 0.15

Acrylonitrile 107-13-1

A *

B/C ) * D

D* 54 -26

505 ~S5 438 481

2,5 4.3 1.8 108.5

2.4 5.0

8.0 17.0 0.16 0.78 0.87

Adiponitrile 111-69-3 D IIIA 93 550 Allyl Alcohol 107-18-6 C* I 22 378 2 . 5 18.0

1.0 0.002 Z0 25.4 0.84

Allyl Chloride 107-05-1

Benzyl Chloride 98-87-3 Bromopropyne 106-96-7 n-Bu .tane 3583-47-9 1,3-Butadiene 106-99-0

17Butanol 71-36-3 2-Butanol 71-36-5 Butylamine 109-73-9 Butylene 25167-67-3 n-Bu t]rraldeh)'de 122,-,72-8 n-Butyl Acetate 123.-86-4 see-Butyl Acetate 105-46-4 tert,-Butvl Acetate 540-88-5 n-But)'l ,~crylate /Inhibited) ' ' 141-32-2 n-Butyl Glycidyl Ether 2426-08-6

I n-Butyl Formal 110-62-5 Butyl Mercaptan 109-79-6 But~'l-2-Propen6ate 141-52-2 para terc-Butyl Toluene 98-51-1 n-But~ic Acid 107-92-6 ~ r b o n Disulfide 75-15-0

D -32 485 57

2.9 11.1 2,6 3 ~

574 0,8 11.0 25 360 1.1 25 1.1

70

1.33 1.17 3.9 4,1 2.7

7.5 4,5 4.2 7.5 4.5

498 15.0 28.0 0,6 7498.0 615 1.3 11.0 $,2 0.7

-11 498 1.2 D II ia 585 1.1 D

D .5

1.02

7.8 2,8 94.8 4.4 0.5

6 ~ 6.85 3.17

I 10 324 3.0 GAS 288 1.9

,

-76 420 2 56 343 1.4

0,20 1.00 0.99

D* I 36 405 D GAS -12 312 D I

C* l -12 218 D *

D 22 -8

421

8.5 2.0 12 1.9

11.2 2,6 7.0 1.7 9,8 2.0

m 1.7 9.8 2,5 92.9 1.6 10.0 1,9 2214.6 1.9 12.5 2.5 112.2 1.7 7.6 4,0 11.5 1.7 9,8 4.0 22.2

0.25 0.94 0.13 0.76

1.07 0,79

i 0.91

1.13

0.92 1.08 1.04

D D

B(C) ~ C C D D D ,5

II tl lI

I l i a I II

IliA I l i a

I

49 293

49

1.7 9,8 4,0 ~ . 6 1.7 9,9 4.4 5.5

1.7 9.9

34.3 3.1 46.4 4,4 5.5

72 ~ 3 2.0 10.0 3,0 0.8

:Z

I

O

-30 90 1.5 .50.0 2.6 358.8 0.009 0.39 0.20

N F P A 4 9 7 A I A 9 7 R O P

Class IC liquids are those havingflash points at or above 73°F (22.8°C) and below 100°F (37.8~C).

Flash Point. The minimum temperature at which a liquid gives off vapor in sufficient concentrat ion to form an ignitable mixture with air near the surface of the liquid, as specified by test.

Ignitable Mixture. A combustible material that is within its flammable range.

MESG (Maximum Experimental ;Safe Gap). The maximum clearance between two parallel metal surfaces which has been found, under specified test conditions, to prevent an explosion in a test chamber from being propagated to a secondary chamber containing the same gas or vapor at die same concentrat ion.

MIC Ratio (Minimum Igniting Current Ratio). The ratio of the minimum current required from an inductive spark discharge to ignite the most easily ignitable mixture of a gas or vapor, divided by die minimum current required from an inductive spark discharge to ignite methane under the same test conditions.

NOTE: See IEC 79-3.

M1E (Minimum Ignition Energy). The minimum ener~ , required from a capacitive spark discharge to ignite the most easily ignitable mixture of a gas or vapor.

Chapter 2 Classification of Combustible Materials

2-1" National Electrical Code Criteria.

2-1.1 Article 500 of the NEC designates as hazardous (classified) any area in which a combustible material is or may be present in the a tmosphere in sufficient concentrat ion to produce an ignitable mixture. Article 500 designates three major categories of hazardous areas"

a) Class I, in which the material is a f lammable gas or vapor;

b) Class II, in wifich the material is a combustible dust;

c) Class I!I, in which the material is an ignitable fiber or flying.

This r ecommended practice is limited to Class [ hazardous ( cl,'~ifi ed) ,'treas.

Each of the above is further subdivided into Division 1 or Division 2:

(a) Division I includes areas in which die combustible material is present normally or frequently;

(b) Division 2 includes areas in which the combustible material is present as a result of infrequent failure of equ ipment or containers.

2-1.2" The intent of Article 500 of the NEC is to prevent combustible material f rom being ignited by electrical equ ipment and wiring systems.

2-1.3 For the purpose of this r ecommended practice, areas no t classified as Division 1 or Division 2 are "unelasslfied" areas.

2-2 Behavior o f Class I (Combustible Material) Gases, Vapors, and Liquids.

2-2.1" Lighter-than-Air (Vapor Density Less than 1.0) Gases. These gases tend to dissipate rapidly in the atmosphere. They will no t affect as great an area as heavier-than-air gases or vapors. Except in enclosed spaces, such gases seldom accumulate to form an ignitable mixture near grade level, where most electrical installations are located. A lighter-than-air gas that has been cooled sufficiently may behave as a heavier-than-air gas until it absorbs heat from the surrounding atmosphere.

2-2.2 Heavier-than-Air (Vapor Density Greater than 1.0) Gases. These gases tend to fall to grade level when released. The gas may rem,xin for a significant per iod of time, unless dispersed by natural or forced ventilation. A heavier-than-air gas that has been heated sufficiently to decrease its density may behave as a lighter-than-air gas until cooled by the surrounding atmosphere.

2-2.3 Applicable to All Densities. As the gas diffuses into the surrounding air, the density of the mixture approaches that of air.

2-2.4 Compressed Liquefied Gases. These gases are stored above their normal boiling point, but kept in the liquid state by pressure.

When released, the liquid immediately expands and vaporizes, creating large volumes of cold gas. The cold gas behaves like a heavier-than-air gas.

2-2.5 Cryogenic Flammable Liquids and Other Cold Liquefied Combustible Materials. Cryogenic liquids are generally handled below-101 °C (-150 °F). These behave like flammable liquids when they are spilled. Small liquid spills will immediately vaporize, but larger spills may remain in the liquid state for an extended time. As the liquid absorbs heat, it vaporizes and may form an ignitable

mixture . Some liquefied combustible materials (not cryogenic) are stored at low temperatures and at pressures close to atmospheric pressure; these include anhydrous ammonia, propane , ethane, ethylene, and propyiene. These materials will behave as described above.

2-2.6 Flammable Liquids. When released in appreciable quantity, a Class I liquid will begin to evaporate at a rate that depends on its volatility:, the lower the flash point, the greater the volatility; hence, the faster the evaporation. The vapors of Class I liquids form ignitable mixtures with air at ambient temperatures more or less readily. Even when evolved rapidly, the vapors tend to disperse rapidly, becoming diluted to a concentrat ion below the lower flammable limit. Until this dispersion takes place, however, these vapors will behave like heavier-than-air gages. Class I liquids normally will produce ignitable mixtures that will travel some finite distance from file point of origin; thus, they will normally require area classification for proper electrical system design.

2-2.7 Combustible Liquids~ A combustible liquid will form an ignitable mixture only when heated above itsflash point.

2-2.7.1 With Class II llguids, the degree of hazard is lower because the vapor release rate is low at the normal handl ing and storage temperatures. In general, these liquids will not form ignitable mixtures with air at ambient temperatures unless heated above their flash points. Also, file vapors will no t travel as far because they tend to condense as they are cooled by ambient air. Class II liquids should be considered capable of producing an ignitable mixture near the point of release when handled, processed, or stored under conditions where the liquid may exceed its flash point.

2-2.7.2 Class IlIA liquids have flash points at or above 140°F (60°C) but below 200°F (93.4°C). These liquids do not form ignitable mixtures with air at ambient temperatures unless heated above their flash points. Furthermore, the vapors cool rapidly in air and condense. Hence, the extent of the area requiring electrical classification will be very small or nonexistent.

2-2.7.3 Class IIIB liquids have flash points at or above 200°F (93.4°C). These liquids seldom evolve enough vapors to form ignitable mixtures even when heated, and are seldom ignited by properly installed and maintained general purpose electrical equipment. A Class IIIB liquid will cool below its flash point very quickly when released. Therefore, area classification is seldom needed and Class IIIB liquids are not included in Table 2-1.

2-3 Conditions Necessary for Ignition.

2-3.1 In a Class I area, three conditions must be satisfied for the combustible material to be ignited by the electrical installation:

(a) A combustible material must be present;

(b) It must be mixed with air in die proport ions required to produce an ignitable mixture; and

(c) There must be a release of sufficient energy to ignite the mixture.

2-4 Classification of Class I Combustible Materials.

2-4.1 Combustible materials are classified into four Groups, A, B, C, ,and D, depending upon their properties.

2-4.2* An alphabetical listing of selected combustible materials, with their g roup classification and relevant physical properties, is provided in Table 2-1. Table 2-2 provides a cross-reference of these chemicals sorted by their Chemical Abstracts Service or CAS number.

2-4.3 Appendix B lists references that deal with the testing of various characteristics of combustible materials.

303

Chemical CAS No. NEC Group

Type b Vapor Vapor Density pressure 7 (Air=l) (ram l-lg)

4.4 4.4 111-84-2 D b I

2721 4-95-8 D I

Flash AIT (°C) %LFL %UFL Point (°C) 31 205 0.8 2.9

0.8 4.4

MIE MIC MF.,SG (mJ) Ratio (ram)

2.4

Nonyl Alcohol n -Octane

143-08-8 D 111-65-9 D*b

Octene n-Octyl Alcohol n-Pentane

25377-83-7 D 111-87-5 D 109-66-0 D* 5

0.8 6.1 t 3 206 1.0 6.5

I 8 230 0.9

I -40 243 1.5 7.8

5.0 0.02 3.9 14.0

3.9 4.5 0.08

0.94

1.05 2.5 513 0.28 0.97 0.93

l -Pentanol 2-Pentanone l -Pentene 2-Pentene

71-41-0 D* I 107-87,9 D I 109-6%1 D I 109-68-2 D I

33 300 1.2 7 452 1.5

-18 275 -18

10.0 3.0 2.5 8.2 ~0 35.6

1.5 8.7 2.4 639.7

4.5

0.99

626-58-0 D I 23 1.1 7.5

0.019

n - Nonane

Nonene

0.45 0.82 0.97

0.89 1.00

1.05

2-Pent},l Acetate Phenylh),drazine 100-63-0 D 89 3.7 0.03 Process Gas > 30% H2 1333-74-0 B** GAS 520 4.0 75.0 0.1 Propane 74-98-6 D * GAS -104 450 2.1 9.5 1.6 0.25 1-Propanol 71-23-8 D* I 15 413 2.2 13.7 2.1 20.7 2-Propanol 67-63-0 D* I 12 399 2.0 12.7 2.1 45.4 0.65 Propiolactone 57-57-8 D 2.9 2.5 2.2 Propionaldeh~'de 123-38-6 C I -9 207 2.6 17.0 2.0 318.5 Propionie Acid 79-09-4 D II 54 466 2.9 12.1 2.5 3.7 Propionic Anhydride 123-62-6 D 74 285 1.3 9.5 4.5 1.4 n-Propyl Acetate 109-60-4 D I 14 450 1.7 8.0 3.5 33.4 n-Prop]el Ether 111-45-3 C* I 21 215 1.3 7.0 3.5 62.3 Prop)'l Nitrate 627-13-4 B* I 20 175 2.0 100.0 Prop)'lene 115-07-1 D* GAS -108 455 2.0 11.1 1.5 0.28 Prop},lene Dichloride 78-87-5 D I 16 557 3.4 14.5 3.9 51.7 Propylene Oxide 75-56-9 B / C / , I I -37 449 2.3 36.0 2.0 534.4 0.13

P ~ d i n e 110-86-1 D* I 20 482 1.8 12.4 2.7 20.8 3.6 6.1

0.91 1.32 0.70

St~ene Te tmhydrofu ran Tet rahydronaphtha lene Tetrarnethyl Lead

100-42-5 D* I 109-99-9 C* 1 119-64-2 D I l i a 75-74-1 C II "

31 4 ~ 0.9 6.8 -14 321 2.0 11.8 2.5 161.6 0.54

1.21 0.87

38 385 0.8 5.0 4.6 0.4

9.2 To luene n-Tr idecene

108-88-3 10025-78-2

D* D

I IliA

4 480 1.1 7.1 0.6

3.1 28.53 0.24 6.4 593.4

Triethylami ne Triethvlbenzene 2,2,3-'l~rimethylbu tan e

2,2,4-Trimethylbu tan e

2,2,3-Trimethylpentane



121-44-8 252,40-18-5 D

D b

D b

D b

D ~

D 5

I -9 249 1.2 83

442 407

396

415

425

8.0 3.5 68.5 56.0 5.6

0.75

4.9 1.5 1.13

Z

~D

I ~D

O

Tripropylamine 102-69-2 D I I 41 Turpent ine 8006-64-2 D I 35 253 0.8 4.8

Chemical

n-Undecene Unsymmetrical Dimethyl

H~,drazine Valeraldeh)~de Vin},l Acetate Vinyl Chloride Vinyl Toluene Vinylidene Chloride

~ ene idine

CASNo . NEC Group

28761-27-5 _ D 57-14-7 C*

Type b Flash AIT (°C) %LFL %UFL Vapor Vapor MIE MIC MESG Point Defisity Pressure 7 (mJ) Ratio (ram) (°C) (Air=l) (mm Fig)

IIIA O.7 5.5 I -15 249 2.0 95.0 1.9 0.85

110-62-3 C 108-05-4 D*

I 280 2"22 3.0 34.$ I -6 402 2.6 13.4 3.0 113.4 0.70 0.94

GAS -78 472 $.6 33.0 2.2 0.96 52 494 0.8 11.0 4.1

I 570 6.5 15.5 3.4 599.4 3.91 I 25 464 0.9 7.0 3.7 0.2

75-01-4 D*" 25015-15-4 D

75-$5-4 D 1330-20-7 D * 121-69-7 C IIIA 53 371 1.0 4.2 0.7

Z

NOTES TO TABLE 2-1:

* Material has been classified by test.

** Fuel and process gas mixtures found by test no t to present hazards similar to those of hydrogen may be g rouped based on the test results.

1 If explosion-proof equipment is isolated by sealing all conduits 1/2 in. or larger, in accordance with Section 501-5(a) of NFPA 70, National Electrical Code, equ ipment for the g roup classification

shown in parentheses is permitted.

2 For classification of areas involving ammonia, see Safety Code for Mechanical Refrigeration, ANSI/ASHRAE 15, and Safety Requirements for the Storage and Handling of Anhydrous Ammonia, ANSI/CGA

G2.1.

$ Certain chemicals may have characteristics that require safeguards beyond those required for any of the above groups. Carbon disulfide is one of these chemicals because o f its low autoigni t ion

temperature and the small jo in t clearance necessary to arrest its flame propagation.

4 Petroleum naphtha is a saturated hydrocarbon mixture whose boiling range is 20°C to 1 $5°C. It is also known as benzine, ligroin, pe t ro leum ether, and naphtha.

5 Commercial grades of aliphatic hydrocarbon solvents are mixtures of several isomers of the same chemical formula (or molecular weight). The autoigni t ion tempera tures of the individual

isomers are significantly different. The electrical equ ipment should be suitable for the AIT of the solvent mixture. See A-2-1, Table Note 5.

6 Type is used to designate if the material is a gas, f lammable liquid, or combustible liquid. See 2-2.6 and 2-2.7.

7 Vapor pressure reflected in units of m m Hg at 25°C unless stated otherwise.

I

O

N F P A 4 9 7 A - - A 9 7 R O P

Table 2-2 Cross-Reference of Chemical CAS Numbers to Chemical Names

C~S

Number: 50-0O-O

57-14.7

57-57-8 60-2%7 60-34-4 62-53-3 64-17-5

64.17-5 64.18-6 64.19.-7 67-56-1 67-56-1 67-63-O

67-64.1 68-12-2 71-23-8 71-36-3 71-36-5 71-41-0

71-43-2 74.82-8 74-84-O

74-85-1

7486-2 74-87-3 74-8%5

74-9O-8

74-93-1 74-98-6

74-9%7 75-00-3 75-01-4 75-04.7 75-05-8 75-07-0

75-08-1

75-15-0 75-19-4

75-21-8 75-28-5

75-28-5 75-28-5 75-31-0 75-35-4

75-52-5 75-56-9 75-65-0

75-74-1 75-83-2 75-83-2 75-86-5 77-78-1

Chemical Name :

FORMALDEHYDE (GAS) UNSYMMETRICAL DIMETHYL

HYDRAZINE

PROPIOLACTONE ETHYL ETHER MONOMETHYL HYDRAZINE ANILINE ETHANOL ETHYL ALCOHOL FORMIC ACID

ACETIC ACID METHANOL METHYL ALCOHOL

2-PROPANOL ACETONE DIMETHYL FORMAMIDE 1-PROPANOL

1-BUTANOL 2-BUTANOL 1-PENTANOL BENZENE

METHANE ETHANE ETHYLENE

ACETYLENE METHYL CHLORIDE METHYLAMINE

HYDROGEN CYANIDE METHYL MERCAPATAN PROPANE METHYLACETYLENE ETHYL CHLORIDE VINYL CMLORIDE ETHYl_AMINE ACETONITRILE ACETALDEHYDE ETHYL MERCAPTAN

CARBON DISULFIDE. CYCLOPROPANE

ETHYLENE OXIDE ISOBUTANE 2-METHYLPROPANE 3-METHYLPROPANE

ISOPROPYLAMINE VINYLIDENE CHLORIDE NITROMETHANE

PROPYLENE OXIDE 2-METHYU2-PROPANOL TETRAMETHYL LEAD DIMETHYLBUTANE NEOHEXANE ACETONE CYANOHYDRIN DIMETHYL SULFATE

GAS Chemical Name : Number: 78-10-4 ETHYL SILICATE

78-5%1 ISOPHORONE 78-78-4 ISOPENTANE 78-78-4 METHYLBUTANE 78-7%5 ISOPRENE 78-83-1 ISOBUTYL ALCOHOL 78-83-1 METHYL-I-PROPANOL 78-84-2 ISOBUTYRALDEHYDE 78-87-5 PROPYLENE DICHLORIDE

78-93-3 METHYL ETHYL KETONE 78-96-6 MONOISOPROPANOLAMINE

79-09.-4 PROPIONIC ACID 79-10-7 ACRYLI C ACI D

79-20-9 METHYL ACETATE 79-24-3 NITROETHANE 79-46-9 2-NITROPROPANE 80..62.-6 METHYL M ETHACRYLATE 96-14-0 3-METHYLPENTANE 96-33-3 METHYL ACRYLATE 97.-95-0 ETHYL BUTANOL 98-00-0 FURFURYL ALCOHOL

98-01-1 FURFURAL 98-51-1 tert.-BUTYL TOLUENE 98-82-8 CUMENE

98-83-9 ALPHA-METHYL STYRENE 98-87-3 BENZYL CHLORIDE 98-95-3 NITROBENZENE

99-87-6 p-CYMENE 100-41-4 ETHYL BENZENE 100-42-5 STYRENE

100-61-8 MONOMETHYL ANILINE 100-630 PHENYUqYDRAZI NE 100-74-3 n-ETHYL MORPHOLINE

102-6%2 TRIPROPYI.AMINE 103-09-3 ETHYL HEXTL ACRYLATE 104.76-7 ETHYLHEXANOL 104-90-5 2-METHYL-5-ETHYL PYRIDINE

105-46-4 sec-BUTYL ACETATE 106-35-4 ETHYL BUTYL KETONE 106-63-8 ISOBUTYL ACRYLATE 106-88-7 BUTYLENE OXIDE 106-92-3 ALLYL GLYCIDYL ETHER 106-96-7 BROMOPROPYNE 106-99-0 1,3-BUTADIENE 107-02-8 ACROLEIN (INHIBITED)

107-05-1 ALLYL CHLORIDE 107..06-2 ETHYLENE DICHLORIDE 107-07-3 ETHYLENE CHLOROHYDRIN

107-13-1 ACRYLONITRILE 107-15-3 ETHYLENEDIAMINE 107-18-6 ALLYL ALCOHOL 107-20-0 CHLOROACETALDEHYDE 107-31-3 METHYL FORMATE

311

N F P A 497A - - A97 R O P

C~S

Number:

107-83-5

107-83-5

107-83-5

107-87-9

107-92-6

108-03-2

108-05-4

108-11-2

108-18-9

108-20-3

108-21-4

108-24-7 108-84-9

108-88-3

108-90-7

108-93-0

108-94-1

10%60-4

10%66-0

10%67-1

10%68-2

109-73-9

109-7%5

10%864 10%87-5

109-94-4

10%99-9

110-19-0 110-43-0

110-54-3

110-62-3 110-62-3 110-80-5

11 O-82-7

110-83-8 110-86-1

110-91-8

111-15-9

111-27-3 111-43-3

111-65-9 111-6%3 111-76-2

111-84-2 111-87-5 112-O7-2 112-30-1 112-31-2 112-31-2 115-07-1 115-10-6

119-64-2

121-44-8

Chemical Name :

D IMETHYLPENTANE

ISOHEXANE

2-METHYLPENTANE

2-PENTANONE

n-BUTYRIC ACID

1-N ITROI'ROPANE

VINYL ACETATE

METHYL AMYL ALCOHOL

DIISOPROPYLAMINE

ISOPROPYL ETHER

ISOPROPYL ACETATE

ACETIC AN HYDRIDE

sec-HEXYL ACETATE

TOLUENE

CHLOROBENZENE

CYCLOHEXANOL

CYCLOHEXANONE

n-PROPYL ACETATE

n-PENTANE

I-PENTENE

2-PENTENE

BUTYLAMINE

BUTYL MERCAPTAN

ETHYLENE GLYCOL MONOMETHYL ETH'ER

METHYI_AL

ETHYL FORMATE

TETRAHYDROFURAN

ISOBUTYL ACETATE METHYL N-AMYL KETONE

n-HEXANE n-BUTYL FORMAL

VALERALDEHYDE

ETHYLENE GLYCOL MONOETHYL ETHER

CYCLOH EXANE

(~CLOHEXENE

PYRIDINE

MORI'HOLINE ETHYLENE GLYCOL MONOETHYL ETHER

ACETATE HEXANOL

n-PROPYL ETHER

n-OCTANE

ADIPONITRILE

ETHYLENE GLYCOL MONOBUTYL ETHER

n-NONANE

n-OCIYL ALCOHOL

ETHYLENE GLYCOLS MONOBUTYL E' ACE n-DECANOL ISODECALDEHYDE

n-DECALDEHYDE PROPYLENE

METHYL ETHER TETRAHYD RONAPHTHALENE

T R I E T ~ I N E

CAS

Number: 123-05-7

123-05-7

123-38-6

123-51-3

123-62-6 123-72-8

123-86-4

123-91-1

123-92-2 124-40-3

126-9%8 138-86-3

140-88-5

141-32-2 141-43-5

141-78-6

141-7%7

141-97-9

142-82=5 143-08-8

151-56-4

208-87-2

302-01-2

463-82-1

463-82-1

534-15-6

540-88-5

541-85-5

58%34-4 591-78-6

592-41-6

624-83-9

626-38-0 627-13-4

628-63-7 630-08-0

645-62-5 1068-19-5

1071-26-7

1319-7%3

1330-20-7 1333-74-0

1333-74-0 1634-04-4

2216-32-2

2216-33-3 2216-344

2425-66-3

2426-08-6 3132-64-7

3221-61-2 3583-47-9

4016-14-2

Chemical Name :

ETHYLHEXALDEHYDE

ISOOCTYL ALDEHYDE

PROPIONALDEHYDE

ISOAMYL ALCOHOL

PROPIONIC ANHYDRIDE

n-BUTYRALDEHYDE

n-BUTYL ACETATE

1,4-DIOXANE

ISOAMYL ACETATE

DIMETHYIAMINE

CHLOROPRENE

DIPENTENE

ETHYL ACRYLATE (INHIBITED)

n-BUTYL ACRYLATE (INHIBITED)

MONOETHANOI_AMINE

ETHYL ACETATE

METHYL ISOBIYIYL KETONE

MESITYL OXIDE

n-HEPTANE

NONYL ALCOHOL

ETHYLENIMINE

METHYLCYCLOHEXANE

HYDRAZINE

DIMETHYLPROPANE

NEOPENTANE

METHYL FORMAL

tert. BUTYL ACETATE

ETHYL SEC-AMYL KETONE 3-M ETHYLH EXANE

HEXANONE

HEXENES

METHYL ISOCYANATE

sec-AMYL ACETATE

PROPYL NITRATE

n-AMYL ACETATE

CARBON MONOXIDE

ETHYL-3-PROPYL ACROLEIN

METHYLHEPTANE

DIMETHYLHEPTANE

CRESOL

XYLENE HYDROGEN

PROCESS GAS > 30% H2

METHYL TERTIARY BUTYL ETHER

2-METHYLOCTANE

3-M ETHYLO CTANE 4-M ETHYLOCTANE

1-CH LORO-1-NITROPROPANE

n-BUTYL GLYCIDYL ETHER EPICHLOROHYDRIN 2-M ETHYLO CTANE BUTANE

ISOPROPYL GLYCIDYL ETHER

312

N F P A 4 9 7 A ~ A 9 7 R O P

CAS _~_U_~_h~: (;heroical Name : 4170-30-3 CROTONALDEHYDE 6842-15-5 DODF, CENE 7664-41-7 AMMONIA 7783-06-4 HYDROGEN SULFIDE 7783-07-5 HYDROGEN SELENIDE 8006-61-9 GASOLINE

8006-64-2 TURPENTINE 8008-20-6 FUEL OIL 1

8008-20-6 KEROSENE 8030-30-6 NAPHTHA (COAL TAR) 8030-30-6 NAPHTHA (PETROLEUM) 10025-78-2 TRIDECENE 25013-15-4 VINYL TOLUENE

Chapter 3 Clagsification O f Class I (Combust ible Material} Areas

The decision to classify an area as hazardous is based upon the possibility that an ignitable mixture may occur. Having decided that an area shou ld be classified, the nex t step is to de termine the degree o f hazard: Is the area Division 1 or Division 2?

3-1 Division 1 Classified Area.

3-1.1 A condit ion for Division 1 is whe ther dae area is likely to have an ignitable mixture present unde r normal conditions. For instance, the presence of a combustible material in the immedia te vicinity of an open dip tank is normal and requires a Division I classification.

3-1.2 "Norm,d" does no t necessarily mean the situation tha t prevails when everything is working proper ly . For instance, there may be cases in which f r equen t ma in tenance and repair are necessary. These are viewed ,as normal and, if quanti t ies of a f lammable liquid or a combust ible material are released as a result of the maintenance, the area is Division 1. However, if repairs are no t usually required between tu rnarounds , the need for repair work is considered abnormal . In any event, the classification of the area, as related to equ ipmen t main tenance , is inf luenced by main tenance procedures and f requency of main tenance .

3-2 Division 2 Classified Areas.

3-2.1 The criterion for a Division 2 area is whether the area is likely to have ignitable mix tures p resen t only u n d e r abnormal conditions. The term "abnormal" is used here in a limited sense and does not include a major catastrophe.

3-2.2 As an example, consider a vessel conta in ing liquid hydrocarbons ( the source) that releases combust ible mater ia l only unde r abnormal conditions. In this case, there is no Division 1 area because the vessel is normally tight. To release vapor, the vessel would have to leak, and that would no t be normal. Thus , the vessel is s u r r o u n d e d by a Division 2 area.

3-2.3 Chemical process e q u i p m e n t does not fail often. Further- more, the electrical installation r equ i r emen t of NFPA 70 for Division 2 areas is such that an ignition-capable spark or hot surface will occur only in the event of abnormal operat ion or failure of electrical equipment . Odlerwise, sparks and hot surfaces are no t present or are contained in enclosures. On a realistic basis, the possibility of process equ ipmen t and electrical equ i pmen t failing s imultaneously is remote.

3-2.4 The Division 2 classification is also applicable to condit ions no t invo lv ingequ ipment failure. For example, consider an area classified ,as Division 1 because of normal presence of an ignitable mixture. Obviously, one side of the Division 1 boundary canno t be normally hazardous and the opposite side never hazardous. When there is no wall, a su r round ing transition Division 2 area separates a Division 1 area f rom an unclassified area.

3-2.5 In cases in which an unpie rced barrier, such as a blank wall, completely prevents fl~e spread of the combust ible material, area classification does no t extend beyond the barrier.

313

Number: Chemical Name: 25167-67-3 BUTYLENE 25340-18-5 TRIETHYLBENZENE 25377-83-70CTENE 25630-42-3 METHYLCYCLOHEXANOL 26952-21-6 ISOOCTYL ALCOHOL 27214-95-8 NONENE 27846.-30-6 METHYLACETYLENE-PROPAD IENE 28761-27-5 UNDECENE 31394-54-4 DIMETHYLHEXANE 31394-54-4 2-METHYLHEXANE 34590-94-8 DIPROPYLENE GLYCOL METHYL ETHER 68476-85-7 LIQUIFIED PETROLEUM GAS 81624-04-6 HEPTENE

3-3 Unclassified Areas.

3-3.1 Experience has shown that the release of ignitable mixtures f rom some operat ions and apparatus is so in f requent that area classification is no t necessary. For example, it is not usually necessary to classify the following areas where combustible materials are processed, stored, or handled:

(a) Areas dlat have adequate ventilation, where combustible materials are conta ined within suitable, well-maintained, closed piping systems;

(b) Areas that lack adequate ventilation, but where p ip ingsys tems are without valves, fittings, flanges, and similar accessories that may be prone to leaks; and

(c) Areas where combustible materials are s tored in suitable containers.

3-3.2 Areas considered to have adequate ventilation include:

(a) An outside area.

(b) A building, room, or space that is substantially open and free of obstruction to the natural passage of air, ei ther vertically or horizontally. Such areas may be roofed over with no walls, may be roofed over and closed on one side, or may be provided with suitably des igned windbreaks.

(c) An enclosed or partly enclosed space provided with ventilation ec~uivalent to natural ventilation. The ventilation system mus t have

equate safeguards against failure.

3-3.3 O p e n flames and hot surfaces associated wifll the operat ion of certain equipment , such as boilers and fired heaters, provide inhe ren t thermal ignition sources. Electrical classification is not appropriate in the immedia te vicinity of these facilities. However, it is p ruden t to avoid installing electrical equ ipmen t that could be a primary ignition source for potential leak sources in pumps, valves, etc., or in waste product and fuel feed lines.

3-3.4 Experience indicates that Class IIIB liquids se ldom evolve enough vapors to form ignitable mixtures even when heated, and are se ldom ignited by properly installed and main ta ined general purpose electrical equipment .

3-3.5 Experience has shown that some ha logena ted liquid hydrocarbons, such as trichloroethylene; 1,1,1-trichloroethane; methylene chloride; and 1,1-dichloro-l-fluoroeflaane (HCFC-141b), which do no t have flash points, bu t do have a f lammable range, are for practical purposes nonf lammable and do not require special electrical equ ipmen t for hazardous (classified) locations.

3-4 Extent of Classified Areas.

3-4.1 The extent of a Division 1 or Division 2 area requires careful considerat ion of the following factors:

(a) The combust ible material; (b) The vapor density of the material; (c) The t empera tu re of the material;

N F P A 4 9 7 A - - A 9 7 R O P

(d) The process or storage pressure; (e) The size of release; and (f) The ventilation.

3-4.2* Tile first step is to ident ifythe materials being handled and their vapor densities. Hydrocarbon vapors and gases are generally heavier than air, while hydrogen and methane .are lighter than air. The following guidelines appl)c

(a) In the absence of walls, enclosures, or odler barriers, and in the absence of air currents or similar disturbing forces, the combustible material will disperse. Heavier-tilan-air vapors will travel primarily downward and outward; lighter-than-air vapors will travel upward and outward. If the source of the vapors is a single point, the horizontal area covered by the vapor wil/be a circle.

(b) For heavier-than-air vapors released at or near grade level, ignitable mixtures are most likely to be found below grade level; next most likely at grade level; with decreasing likelihood of presence as height above grade increases. For lighter-than-air gases, the opposite is true: there is little or no hazard a t a n d below grade but greater hazard above grade.

(c) In cases where the source of the combustible material is above grade or below grade or in cases where the combustible material is released under pressure, the limits o f die classified area are altered substantially. Also, avery mild breeze may extend these limits. However, a s t ronger breeze may accelerate dispersion of the combustible material so that the extent of the classified area is

ently reduced. Thus, dimensional limits r ecommended for vision 1 or Division 2 zones must be based on experience rather

than relying solely on the theoretitYal diffusion of vapors.

3-4.3 The size of a building and its design may influence considerably dm classification of the enclosed volume. In the case of a small, inadequately ventilated room, it may be appropriate to classify the entire room as Division 1.

3-4.4 When classifying buildings, careful evaluation of prior experience with the same or similar installations s h o u l d b e made. It is no t enough to merely identify a potential source of the combustible material within the building a n d p r o c e e d immediately to defining the extent o f a Division 1 or Division 2 area. Where experience indicates that a particular design concept is sound, a more hazardous classification for similar installations may not be

justified. Furthermore, it is conceivable that an area might be reclassified from Division 1 to Division 2, or from Division 2 to unclassified, based on experience.

3-4.5 Correctly evainated, an installation will be found to be a multiplicity of Divisinn l areas of very limited extent. Probably the most numerous of offenders are packing glands. A packing gland leaking a quart per minute (360 gallons per day) (0.95 liter per minute) would certainly not be commonplace. Yet, i f a quart bottle were emptied each minute outdoors, the zone made hazardous would bedi t t icul t to locate with a combustible gas detector.

3-4.6 Tile volume of combusti hie material released is o f extreme importance in de termining die extent o f a hazardous area, and it is this consideration that necessitates the greatest application o f sound englneer ing judgmenL However, one cannot lose sight o f the purpose of this judgment ; the area is classified solely for the installation of electrical equipment .

3-5 Discussion o f Diagrams and Recommendations.

3-5.1 This chapter contains a series of diagrams that illustrate how typical sources of combustible material should be classified and the r ecommended extent of the various classifications. Some of the diagrams are for single-point sources; others applyto multiple sources in an enclosed space or in an operating area. Tile basis for the diagrams are explained in Section $.0.

3-5.2 The in tended use of the diagrams is to aid in developing electrical classification maps of operating units, process plants, and buildings. Most o f the maps will be plan views. Elevations or sectional views may be required where different classifications apply at different levels.

3-5.$ An operating unit may have many interconnected sources of combustible material, including pumps, compressors, vessels, tanks, and heat exdlangers. These in turn present sources of leaks such as flanged and screwed connections, fittings, valves, meters, etc. Thus, considecable j u d g m e n t will be required to estahlisl~ the boundaries of Divlsion 1 and Division 2 areas.

314

3-5.4 In some cases, individual classification of a multitude of point sources widlin an operating unit is nei ther feasible nor economical. In such cases, the entire unit may be classified as a single-source entity. However, this should be considered only after a thorough evaluation of the extent and interaction of the various sources, both within the uni t and adjacent to it.

$-5.5 In developing these diagrams, vapor density is generally assumed to be greater than that of air. Lighter-than-air gases, such as hydrogen and methane, will quite readily disperse, and the diagrams for lighter-than-air gases should be used. However, if such gases are being evolved from the cryogenic state (i.e., liquefied hydrogen or LNG), caution must be exercised because, for some finite period of time, these gases will be heavier than air due to their low temperature when first released.

3-6 Basis for Recommendations.

$-6.1 The practices of the petroleum refining industry are published in die American Petroleum Institute's RP 500, Classification-of Locations for Electrical Installations in Petroleum Refinenea. These practices are based on a survey and an analysis of the practices of a large segment of the industry, experimental data, and careful weighing of per t inent factors. Refinery operations are characterized by the handling, processing, and storage of large quantities of materials, often at elevated temperatures. The r ecommended limits o f classified areas for refinery installations may therefore be stricter than are warranted for more traditional chemical processing facilities that handle smaller quantities.

3-6.2 Various codes, standards, and r ecommended practices of the National Fire Protection Association include recommendat ions for classifying hazardous areas. These recommendat ions are I:msed on many years of experience. NFPA 30, F/ammab/e and C.ombuaib/e Liquids Code, a n d NFPA 58, Standard for tl~ Storage and Handling of Liquefied Petroleum Gases, are two of these documents.

3-6.3 Continuous process plants and large batch chemical plants may be almost as large as refineries and should, therefore, follow the practices of the refining industry. The volume of leakage from pump and agitator shaft packing glands, piping flanges, and valves increases proportionately with process equipment size and flow rate, as do the travel distance and area of dispersion from the discharge source. Similarly, the volume of the leakage, the travel distance, and the area of dispersion all increase as operating pressure increases.

3-6.4 In deciding whether to use an overall plant classification scheme or individual equipment classification, process equipment size, flow rate, and pressure should be taken into consideration. Generally speaking, for small or batch chemical plants, point-source diagrmm can be used; for large, high-pressure plants, the API recommendat ions are more suitable. Table 5-6 gives ranges of process equipment size, pressure, and flow rate for equipment and piping handling combustible material.

Table 3-6 Relative Magnitudes of Process Equipment and Pip/ag

Handling Combustible Materials

Process Small Large

Equipment Units (Low) Moderate II-ligh)

Size gal < 5000 5000 to 25,000 > 25,000

Pressure psi < 100 100 to 500 > 500

Flow Rate gpm < 100 100 to 500 > 500

3-6.5 Tile great majority of chemical plants fall in the moderate range of sine, pressure, and flow rate tor equipment and piping handling combustible materials. However, since all cases are not the same, sound engineering judgment is required.

8-7 Procedure for Classifying Areas. The following procedure should be used for each room, section, or area being dassified.

3-7.1 Step One ~ Determining Need for Classification. The area should be classified if a combustible material is processed, handled, or stored.

3-7.2 Step Two ~ Gathering Information.

3-7.2.1 Proposed Facility Information. For a proposed facility that exists on drawings, only a preliminary area classification can be done so that suitable electrical dquipment and instrumentation can be

N F P A 4 9 7 A ~ A 9 7 R O P

purchased. Plants are rarely built exactlyas die drawings portray them, and the area classification should be later modified based upon die actual facility.

3-7.2.2 Existing Facility History. For an existing facility, the individual plant experience is extremely important in classifying areas within die plant. Both operation and maintenance personnel in die actual plafit should be ~ k e d the following questions:

(a) Have there been instances of leaks? (b) Do leaks occur frequently? (c) Do leaks occur during normal or abnormal

operation? (d) Is the equipment in good condition,

questibn~ble condition, or in need of repair? (e) Do maintenance practices result in the formation

of ignitable mixtures? (f) Does routine flushing of process lines, changing of filters,

opening of equipment, etc., re-suit in the formatio-n of ignitable mixtures?

3-7.2.$ Process Flow Diagram. A process flow diagram showing the pressure, temperature, flow rates, composition anct quantities of various materials (i.e., mass flow balance sheets) passing through die process, is needed.

3-7.2.4 Plot Plan. A plot plan (or similar drawing) is needed showing all vessels, tanks, trenches, lagoons , sumps, building structures, dikes, partitions, levees, ditches, and slmUar item-s that would atfect d i s . p drsion of any i i . . .quid, .g as,. or vapor . The p lot plan should include the prevmhng wind direcuon.

3-7.2.5* Fire Hazard Propert ies o f Combustible Material. The propert ies needed for determining area classification are shown in Table 2.1 for rmany materials. -

NOTE: A material could be listed in Table 2.1 under a chemical name different from the chemical name used at your facility. Table 2.2 i sprovided to cross-reference the C_AS number of the material to die chemical name used in Table 2.1.

ff materials being used are not listed in Table 2.1 or in other reputable chemiCd references, die needed information may be obtained by die following:

(a) Contact the material supplier to de termine if the material has been tested or group-classified-. If tested, estimate die group classification using die criteria shown in Appendix A. - - -

(b) Have die material tested andlestimate the group classification using the criteria shown in Appendix A.

c/c) Refer to Appendix D for a medlod for determining die Group assification for some mixed combustible material streams.

3-7.3 Step Three - - Selecting the Appropriate Classification Diagram. Correlate the list of-combdsfibl/~ materials from the process flow diagram and die material mass balance data with the quantities, pressures, flow rates (see Table 3-6), and temperatures to de termine the following:

(a) Whetiler the process equipment size is low, moderate, or high;

(b) Whether the pressure is low, moderate, or high;

(c) Whether die flow rate is low, moderate, or high;

(d) Whether d ie combustible material is lighter-than-air (vapor density less dlan 1) or heavier-than-air (vapor density greater than 1);

(e) Whether the source of leaks is above or below grade; and

(f) Whether the process is a loading/unloading station, product dryer, filter press, compressor shelter, hydrogen storage, or marine terminal. - " - - - -

Use Table 3-8 and die above information to select die appropriate classification diagram(s).

3-7.4 Step Four - - Determining the Extent o f the Classified Area. The extent o f the classified area may be de termined by applying, with sound engineer ing judgment , the medlods discussed-in 3-4.2 and die diagranas contaihed in this chapter.

3-7.4.1 Locate the potential sources of leaks on the plan drawing or at die actual location. These sources may include r6tating or reciprocating shafts (pumps, compressors, and control valves), and atmospheriCdischarges from pressure relief devices.

3-7.4.2 For each leakage source, f ind an equivalent example on die selected classification diagram to determine die min imum extent of

315

classification around the leakage source. The extent may be modified by considering the following-.

a) Whether an ignitable mixture is likely to occur frequently due to repair, maintenance, or leakage;

b) Where conditions of maintenance and supervision are such that leaks are likely to occur in process equipment, storage vessels, and piping systems containing combustible material;

c) Whether the combustible material could be transmitted by trenches, pipes, conduit, or ducts; and

d) Ventilation or prevailing wind in tile specific area, and the dispersion rates of the combustible materials.

3-7.4.$ Once the minimum extent is determined, for practical reasons, utilize distinct landmarks (such as curbs, dikes, walls, structural supports, edges of roads, etc.) for the actual boundaries of the area classification. These landmarks permit easy identification of the boundaries of the hazardous areas-for electricians, instrument technicians, operators, and other personnel.

3-8 Classification Diagrams. Most diagrams in this section include a table of"suggested ap~31icability" and u~se check marks to show the ranges of pr tcess equipment size, pressure, and flow rates. (See Table 3-6.) Unless otherwise stated, thesd diagrams assume that the material being handled is a f lammable]iquid. Table 3-8 provides a summary of where each diagram is in tended to apply.

Figure 3-8.1 shows a source of leakage located outdoors, at grade. The material being handled is a f lammable liquid.

Figure $-8.2 shows a source of leakage located outdoors, above grade. The material being handled isfff lammable liquid.

Figure 3-8.3 shows a source of leakage located indoors, at floor level. Adequate ventilation is provided_ The material being handled is a flammable liquid.

Figure 3-8.4 shows a source of leakage located indoors, above floor level. Adequate ventilation is provided. The material being handled is a flammable liquid.

Figure 3-8.5 shows a source of leakage located indoors, at floor level, adjacent to an opening in an exterior wall. Adequate ventilation is provided. The material being handled is a f lammable liquid.

Figure 3-8.6 shows a source of leakage located indoors, at floor level, adjacent to an opening in an exterior wall. Ventilation is not adequate. The material being handled is a f lammable liquid.

Figure 3-8.7 shows a source of leakage located outdoors, at grade. The material being handled may be a flammable liquid or a liquefied or compressed flammable gas, or a flammable cryogenic lic]uid. - - - -

Figure 3-8.8 shows a source of leakage located outdoors, above grade. The material being handled may be a flammable liquid or a liquefied or compressed flammable gas, or a flammable c~ogenic liquid.

Figure 3-8.9 shows a source of leakage located outdoors, at grade. The haaterial being handled is a flamn'/able liquid.

Figure 3-8.10 shows a source of leakage located outdoors, above grade. The material being handled is a flammable liquid.

Figure 3-8.11 shows a source of leakage located indoors, adjacent to an opening in an exterior wall. Ventilation is not adequate_The material being handled is a f lammable liquid.

Figure 3-8.12 shows a source of leakage located indoors, adjacent to an opening in an exterior wall. Adequate ventilation is provided. The mater ia lbeing handled is a flammable liquid.

Figure 3-8.13 shows multiple sources of leakage, located both at grade and above grade, in an outdoor process area. The material being handled is a flammable liquid.

Figure 3-8.14 shows multiple sources of leakage, located both at grade and above grade, in an outdoor process area. The material being handled is a flammable liquid.

Figure 3-8.15 shows multiple sources of leakage, located both at and above grade, in an outdoor process area. The material being handled is a flammable liquid.

Figure 3-8.16 shows multiple sources of leakage, located both at and above floor level, in an adequately ventilate/] building. The material being handled is a f lammable liquid.

N F P A 4 9 7 A - - A 9 7 R O P

Figure 3-8.17 shows a product dryer located in an adequately ventilated building. The-produc t dryer system is totally eficlosed. The material being hand led is a solid wet with a f lammable liquid.

Figure 3-8.18 shows a plate and f rame filter press. Adequate ventilation is provided. The material being bafidled is a s t l id wet with a f lammable liquid.

Figure 3-8.19 shows a product storage rank located outdoors, at grade. The material bein-g s tored is a f lammable liquid.

Figure 3-8.20 shows tank car loading mad un load ing via a closed transfer system. Material is t r ans fe r r edon ly t h rough the dome. The material being t ransferred is a f lammable liquid.

Figures 3-8.21 (a) and (b) show rank car and tank truck loading and un loading via a closed transfer system. Material is t ransferred th rough the bot tom fittings. The material being transferred is a f lammable liquid. -

Figure 3-8.22 shows tank car (or tank truck) loading and un loading via an open transfer system. Material is t ransferred eifller th rough the d o m e or the bot tom fittings. T he material being t ransferred is a f lammable liquid.

Figure 3-8.23 shows tank car (or tank truck) loading and un loading via a closed transfer system. Material is t ransferred only th rough the dome. The material being t ransferred may be a liquefied or compressed f lammable gas or a f lammable cryogenic liquid.

Figure 3-8.24 sbows a d r u m filling station located ei ther outdoors or indoors in an adequately ventilated building. The material being hand led is a f lammable liquid.

Figure 3-8.25 shows an emergency impoundin, g basin, or oil/water. separator and an emergency or t emporary drainage dntch onl/water separator. The material being hand led is a f lammable liquid.

Figure 3-8.26 shows liquid hydrogen storage located outdoors or indoors in an adequately ventilated-building. This d iagram applies to liquid hydrogen only.

Figure 3-8.27 shows gaseous hydrogen storage located outdoors or indoors in an adequately ventilated building. This d iagram applies to gaseous hydrogen only.

Figure 3-8.28 shows an adequately ventilated compressor shelter. The material being bandied is a lighter-than-air gas.

Figure 3-8.29 shows an inadequately ventilated compressor sheller. The material being handled is a lighter-than-alr gas.

Figure 3-8.30 shows tanks for the storage of cryogenic and other coldl iquef ied f lammable gases. [From NFPA 59A, Standard for the Productwn, Storage, and Handling of Liquefied Natural Gas (LNG ). ]

Figure 3-8.31 shows a source of leakage from equ ipmen t handl ing liquefied natural gas or o ther cold liquefied f lammable gas, and lobated outdoors, at or above grade. (From NFPA 59A.)

Figure 3-8.32 shows a source of leakage from equ ip m en t hand l ing liquefied natural gas or o ther cold liquefied flarnmable gas and - located indoors in an adequately ventilated building. (From NFPA 59A.)

Figure 3-8.33 shows the classified zones a round liquefied natural gas opera t ing bleeds, drips, vents, and drains both outdoors, at or ab- ov tg r ade , a n d indoors in an adequately venti lated building. This diagra m also applies to o ther cold liquefied f lammable gases. (From NFPA 59A.)

Figure 3-8.34 shows the classified zones at a mar ine terminal hand l ing f lammable liquids and includes the area a rou n d the stored position of loading arms and hoses.

Table 3-8 Matrix of Diagrams Versus Material/Property/Appllcation

Diagram

3-8.1 3-8,2 3-8.3 3-8.4 3-8.5 3-8.6 3-8.7 38.8 3-8.9 3-8.10 3-8.11 3-8.12 3-8.13 3-8.14 3-8.15 3-8.16 3-8.17 38.18 3-8.19 3-8.20 3-8.21

3-8.22

3-8.23

3-8.24 3-8.25 3-8.26 3-8.27 Diagram

3-8.28 3-8.29 3-8.30 3-8.31

Special Condition

Product dryer Filter Press Storage Tank Tank car loading Tank car loading Tank truck loadin~ Tank car loading Tank truck loading" Tank c ~ loading Tank truck loading Drum fillin~ station Emer;gency basin Liquid H2 stora]ge Gaseous H2 stora~'e Special Condition

Compressor sheher Compressor sheher cryogenic storage

Marine Tennin,'d

m l m i m i IIIIIIII pa I

P; I Pi ~q E

; P; I ; ; IIII ~4

; b.~ IIIIII I P~ I

i F; ~:4 7- • m g- Illll II ~.~

~- p; [ ] |

P: P;

l / g i / i e: p; l

gl~,[ll i b:4 m,, tm K l

m

L = Large ~ G = Liquified Natural Gas M = Moderate

316

Above At Size I Pressure Flow Grade Grade

X S/M ] S/M S/M S/M [ S/M S/M

X S/M [ S/M S/M X S/M ] S/M S/M

X S/M [ S/M S/M X S/M [ S/M S/M X S/M [ / M / H S/M

X S/M [ / M / H S/M X / L [ / M / L / L

X / L [ / M / L / L X / M / L [ / L / M / L X / M / L [ / L / M / L X X S/M [ S/M S/M X X / M / L [ / M / L / M / L X X S/M I S/M S/M X X S/M [ S/M S/M X X

X / M / L I / L / M / L X X X

X X

X

X X X X X X X Above At Size ] Pressure How Grade Grade

X X X X X X X X X X X ' X

X = diagram applies S = Small

N F P A 4 9 7 A - - A 9 7 R O P

Grade 7

. [ ~ - 3 f t R

,~,.. ~/~////////////?, :

Below grade location such as a sump or tren

Figure 3-8.1 Leakage source located outdoors, at ,grade.

G r a d e - ~ ,

- - 3 f t R

s ource

Y//////~ ¢

X

J_ 1 8 in.

I TM

1Of t R

Z B e l o w grade locat ion such as a sump or trench

r I

Figure 3-8.2 Leakage source located outdoors, above grade.

Material: F lammable Liquid

Process Equip. Size

Pressure

F low Rate

Small/ Low

J

7 ,/

Moderate

V

7

7

Large/ High

Division 1

Division 2

317

N F P A 4 9 7 A - - A 9 7 R O P

Grade

r 25ftR - I

Below grade location such as a sumlo or tre

Figure 3-8.3 Leakage source located indoors, at floor level. Adequate ventilation is provided.

I - 25 f t R

Below grade location such as a sump or trench

Figure 3-8.4 leakage source located indoors, above floor level. Adequate ventilation is provided.

Material: Flammable Liquid

Large/ High

Small/ Low Moderate

Process Equip. J ~ ~ Division 1 Size

Pressure V /

Flow Rate ~/ ~ ~ Division 2

318

N F P A 4 9 7 A - - A 9 7 R O P

Grade-~

Pierced w a l l ~ Source---~ ~ - - - - 5 ft R .91----Unpierced wall

£ B i n . 3 L

~ ~ Below grade location I ~ 25 ft Max R ~1 I ~ 25 ft R ~1 such as a sump or trench

F'tgure 3-8.5 Leakage source located indoors, at floor level, adjacent to opening in exterior wall. Adequate ventilation is provided.

Pierced w a l , " - - " q l ~ Unpierced wall

Division 1 or Division 2 portion of building

F'tgure 3-8.6 Leakage source located indoors, at f loor level, adjament to opening in exterior wad]. Adequate ventilation is not provided.

NOTE: If building is small compared to size uf equipment and leakage can fill the building, the entire building interior is classified Division 1.


Small/ Moderate LOW

Process Equip. ~ # Size

Pressure ~ ¢

Flow Rate J ¢

Large/ H ig h

Division 1

Division 2

319

N F P A 4 9 7 A - - A 9 7 R O P

- - 1 5 f t R

Source

Grade 7 ~ / ' / / / / / / / / / ~

BeLow grade location s u c h / as a sump or trench

Figure 3-8.7 Leakage source located outdoors, at grade.

Source,

Grade 7

' ~ \ ~ \ \

~ 1 5 ft R

/ Below grade location such - - as a sump or trench

F'~re 3-8.8 Leakage source located outdoors, above grade.

Material: Flammable Liquid, Liquefied Ftammabte Gas, Compressed Flammable Gas, and Cryogenic Liquid

Small/ Large/ Low Moderate High

Pro~ess ~ui~. J V/ Size

Pressure V

Flow Rate 4 V

4

Division 1

Division 2

~,20

N F P A 4 9 7 A - - A 9 7 R O P

Sou-rce

/

L Below grade locat ion s u c h ~ _ . ~ as a sump or t rench

25 f t

/

50 I t ~ l

r 100 f t

Figure 3-8.9 Leakage source located outdoors, at grade.

T

_1

T 25 f t

50 f t "~1

Be low grade Io~at ion such ~ i ~ as a sump or t rench 100 f t

2 f t

Ftgure 3-8.10 Leakage source located outdoors, above grade.

Mater ia l : F lammable L iqu id

Moderate Smal l / Low

Process Equip. Size

Pressure

F low Rate

Large/ High

4

J

J

m Div is ion 1

Div is ion 2

A d d i t i o n a l Div is ion 2 locat ion, Use ext ra precaut io~ where large release o f vo la t i le products may occur,

32]

N F P A 4 9 7 A M A 9 7 R O P

2 f t i L ~

[ ~ 50 f t (Note)

[~ 100 f t

- - 1 O f t R

e

Unpierced wall


NOTE: "Apply" horizontal distances of 50 feet from the source of vapor or 10 feel beyond the per imeter of the building, whichever is greater , except that beyond unpierced vaport ight walls the area is nonclassified.

F'tgure 38.11 Leakage source located indoors, adjacent to opening in exterior wall. Adequate ventilation is not provided.

S o u r ~

[-~ 50 f t

~ Unpierced wall

~ - - ' ~ Below grade location such as a sump or trench

F'tgure 3-8.12 Leakage source located indoors, adjacent to opening in exterior waU. Adequate ventilation is provided.


Process Equip. Size

Pressure

Flow Rate

Smell/ Low

Moderate Large/ High

J

J J

Division 1

Division 2

Addi t ional Division 2 location. Use extra precaution where large release of volati le products may occur.

322

NFPA 497A - - A97 R O P

Process column

3 f t around valves

Process column

deck exchanger level

Pipeways, piping " " V / X / / / / / / r . ~ / / / d P T " 7 " 7 " / / / I r / ~

..o,.v... I II °°°1 meters, or o o o O qasketed flanges

18 in. /

Grada 7 / 0'0//0/0£ ~, ' /// I / / / / / / / / / / / / x / / / / / / / / / / /

10 f t 10 f t

- - T y p i c a l support column

3 f t R above pumps, etc.

/ / I

Pump alte' Below grade location such as a sump or trench

Material: Flammable Liquid Sources

Small/ Moderate Large/ Low High

Process Equip. ,~ ~/ Size

Flow Rate ~/ ~/ i Division 2

F'~mre 3-8.13 Multiple leakage sources, both at and above grade, in outdoor process area.

Process ~ column I----25 f t I Process column

25 f t

L

w ~ w i n = - m m ~ m m ~ m m m ~ ~ m ~

/imimm/im f t

5Of t alley Pump ~ - - 5 0 f t ~ k I 5Of t Sources

Control valves (source)

Exchanger deck solid f loor

2 f t


Small/ Moderate Large/ Low High

Process Equip. ~ Size

Pressure ~ ~

Flow Rate d 4 ~ ' ~


Division I k ~ . ~ l Additional Division 2 area where release may be large

Division 2

Figure 3-8.14 Multiple leakage sources, both at and above grade, in outdoor process area.

323

N F P A 4 9 7 A - - A97 R O P

Division 2, 5 ft R from vents (typical)

Solid floor with Opening for vessel X

Division 2, 3fnttR f r o m - "k

~ 3in., ~ ' !

Emergency / / / /

Grade

-~>,\~X\\ L J '

3 ft R around pumps (typical)

n

/ vents (typical)

13f~ RoarrOcUZsduVehsel and

IJ as manholes, valves, etc.

~/? Typical support column'

"/444xy,,/1,[////// ~/f-~- I 8 i n

~ Below grade location such as a sump or trench

Figure 3-4.15 Multiple leakage sources, both at and above grade, in outdoor process a r e a .


Small/ Earge/ Low Moderate High

Process Equip. V V ~ Division 1 Size

Pressure V V

Flow Rate J 7 ~ Division 2

Figure 3-8.15 Multiple leakage sources, both at and above grade, in outdoor process area.

324

N F P A 4 9 7 A - - A 9 7 R O P

Division 2, 5 ft R from vents (typical)

Outside wall - ~

$I~ hd of Ip°°n r, n g - -~- -~

Division 2, m R / / J ~ i 3 f t R from \ I1~ ~

Below grade location - - ~ such as a sump or trench

f--- 5 ft R around ---t

/ !e laCvkhei,°:trTr ccaesh ° ' e s. \ ~. ~/~/// - - - ~ Division 1, 3 ft R from vent (typical)

d[-~ '~ Outside wall

r ~ Grating floor with opening for vessel

_ _ ~ G rude

~ Division 2, 5 ft R around pump and tank

- - 3 ft R around tank at location shown


Small/ Low Moderate

Process Equip. J Size

Pressure V V

Flow Rate V V

Large/ H ig h

Division 1

Division 2

Figure "~-8.16 Multiple leakage sources, both at and above floor level, located indoors. Adequate ventilation is provided.

325

NFPA 497A ---.. A97 ROP

Vent ~ / / / ~ Separator ~x~o~ ~~ ,~

2,

~ l n e r t gas blanket in elevator and bin

~ E l e v a t o r

Material: SolidsWet with Flammable Liquid

Division 1 ~ Division 2

F'~ure 3-8.17 Totally enclosed product dryer located in adequately ventUated building.

326

J '~?A 497A ~ A97 ROP

~ 1 1 ~ Ve~It to soIven[ reC:overy

3 f~'f "

Hood- 'up'* position

Mate~,ial: $ol~;d~ W~: wi lh F I~mmable Liquid

Division 1 ~ D i ~ i o n 2

Fgure 3-8,18 Plate and frame f'flter p r ~ provided with adequate ventilation.

3 ft

~27

NFPA 497A - - A97 ROP

Tank w i t h i n dike ~ ~-- Tank in open (undiked) area

t Division 1, \ 5 ft R, around

vent Division 2 ~ \ lOf, R \ L

D i k e ~

Tank



Process Equip. Size

Pressure

Flow Rate

Small/ Low

Large/ Moderate High

¢ ¢ NN ,/

Division 1

Divis ion 2

Figure 3-8.19 Storage tanks, outdoors at grade.

328

N F P A 4 9 7 A - - A 9 7 R O P

Vapor return line Liquid transfer line

//~,f, ~ ~I tveRs, around

~ Grade



Figure 3-8.20 Tank car/tank loading and unloading via closed system. Transfer through dome only.

i / Vapor return i n e ~ ~ /

Liquid transfer I e

///'///~h~'v/~ 7 if~is iRO : 2ound ///'///~h~'v/~ 7 if~is iRO : 2ound

~-- Grade

,~-I ~ " ~18 in, ~ 2 ~ ( f A ~

3 f tR

Figure 3-8.21 (a) Tank car loading and unloading via closed system. Bottom product transfer only.

MATERIAL: Flammable Liquid

. O raOo---

/ ' Division 2,

/ / / - - - ~ 18 in.

Figure 3-8.21 (b) Tank truck loading and unloading via closed system.

329

N F P A 4 9 7 A - - A 9 7 R O P

/ ~ / / ~ ~ L i q u i d transfer line

A Division 2,

Division 1, / / 15 ft.R 3 ft R around / ' / valves / /

/

/ -or.de

L. Below grade location such as a sump or trench /

Figure 3-8.22 Tank car/tank truck loading and unloading via open system. Top or bottom product transfer.

MATERIAL: Rammable Liquid

Vapor return line

Division 1, 5 ft R around valves

Liquid transfer line

Division 2 15ft R

L Below grade location such as a sump or trench

Material: Flammable Liquefied Gas Flammable Compressed Gas Flammable Cryogenic Liquid

Division 1 ~ Div is ion 2

F'tgure 3-8.23 Tank car/tank truck loading and unloading via closed system. Transfer through dome only.

330

N F P A 4 9 7 A - - A 9 7 R O P

ill pipe

Division 5 f t R

Division 1, 3 f t R

Vent

/

[ ~ l O f t ~l




Figure 3-8.24 Drum f'dling station, outdoors or indoors, with adequate ventilation.

331

N F P A 4 9 7 A - - A97 R O P

G r a d e - ~

± 18 in.

15ft

Liquid

18 i n . ~ l ~

I_ N~J I- lsft __~1 Below grade location such as a sump or trench

± 18 in.

t

rl- ~ ,t -I-I PI- 15 ft _I_i _ ~

°,.°.-~ ~ / / / / / / / / / / / / / / / / / / / / ~ ,,,..

~ L i q u i d / B e l o w grade location such as a sump or trench


Division I ~ Division.2

NOTE: This diagram does not apply to open pits or open vessels, such as dip tanks or open mixing tanks, that normally contain flammable liquids.

Figure 3-8.25 Emergency impounding basin or oi l /water separator (top) and emergency or drainage ditch oi l /water separa tor (bottom).

332

N F P A 4 9 7 A m A 9 7 R O P

~ S o u r c e

Division 1 , 3ftR

Division 2, 25 ft R

G r a d e - - ~

I I

- - Division 2, 25 ft R

Point where connections are regularly made

Liquid hydrogen storage container

Division 1 Division 2

Figure 3-8.26 Liquid hydrogen storage located outdoors or in an adequately ventilated building.

Division 2 , ~ 15ftR

G rade---~

Division 2 , ~ 15ft R

C~ . I "///////////////A

1"/~ ¢/// , ~/~ °r,d.~ I orto.or

Outdoor Indoor adequate ventilation

Division 1 ~ ] Division 2

Figure 3-8.27 Gaseous hydrogen storage located outdoors or indoors in an adequately ventilated building.

333

N F P A 4 9 7 A - - A97 R O P

Bot tom ( enc I osed

Material: L igh te r - than -A i r Gas

F'tgure 3-8.28 Adequately ventilated compressor shelter.

ca at 1 5 f t or lower

Division 2 , ~ 1 5 f t R t •

/

Source---~

/.

/ /

~ " - - - 10 ft /

Material: L igh te r - than-A i r Gas

~ Division 1 ~ D iv is ion2

lrtgure 3-8.29 Inadequately ventilated compressor shelter.

334

N F P A 4 9 7 A I A 9 7 R O P

5 ft R ~ 1 5 ft R from relief valve from relief v a l v e - ~ ~ ~ j ~

, ~ / ~ 1 5 ft R all around

- L . x

I H ~ , . ~ / ~ / / / ~ Container " 4 ~ / / ~ / ~ ~---G rade

~ _ . B e l o w grade location such as a sump or trench

Dike height less than distance from container to dike (H less than X)

~ 15 ft R from relief valve

5 ft R from relief v a l v e ~ . / /~ -15 ft R all around

. _

H I ~ C°ntainer ~ / ~ e

X

Dike height greater than distance from container to dike (H greater than X)

15 ft R from relief valve

15 ft R all around

Container


Material: Liquefied Natural Gas or Other Cryogenic Flammable Liquids

Figure 3-8.30 Storage tanks for cryogenic liquids.

335

N F P A 4 9 7 A - - A 9 7 R O P

Source ,~/

1 5 f t R

Gra

/ Be low grade loca t ion such as a sump or t rench

Figure 3-8.31 Leakage source from equipment handling liquefied natural gas. Source is located outdoors, at or above grade.

Div is ion 2 , ' - ~ . / . . 15 f t B ~z////////i.///

Sourc ~ l - - - ~ D iv is ion 2 GradeVJJJJ.trJ'~JJ.,/JJJfJTL~j 15 f t R. f r o m open ing

I ndoors w i t h adequate ven t i l a t i on

Mater ia l : L ique f ied Natura l Gas or O the r Cryogenic F l a m m a b l e Gas

Div is ion 1 ~ D iv is ion 2

Figure 3-8.32 Leakage source from equipment handling liquefied natural gas in an adequately ventilated building.

336

N F P A 4 9 7 A - - A97 R O P

5 f t R ~

t//•15 ft R

~ yfE a rad e

Indoors with adequate ventilation

~ 5 ft/ R

~/~1~-~15 ft R

Outdoors at or above grade


Figure 3-8.33 Leakage source from routinely operating bleeds, equipment handling liquefied natural gas in an adequately ventilated building.

337

N F P A 4 9 7 A - - A 9 7 R O P

50 f t

25 f t

50 f t

25 f t

~ F Deck

Open sump in deck for draining lines and hoses

' uperat lng envelope and stored Position of loading arms or hoses

50 f t

2 f t

~ q ~ - S h o r e

Pier

~/ater level

Division 1 ! ~ Division 2

NOTES: I. T h e "source ol vapor" shall be the opera t ing envelope and stored position of the ou tboard flange connection of the loading a rm (or hose). 2. The berth area adjacent to tanker and barge cargo tanks is to be Division 2 to the tbllowing extent:

(a) 25 ti (7.6 m) horizontally in all directions on the pier side from that port ion of the hull containing cargo tanks. (b) From the water level to 25 tt (7.6 m) above the cargo tanks at their highest position.

3. Additional locations may have to be classified as required by the presence of o ther sources of flammable liquids or by Coast Guard or o ther regulations.

MA3~ERIAL: Flammable Liquids

F'tgure 3-8.34 Marine terminal handling flammable fiquids.

338

N F P A 4 9 7 A i A 9 7 R O P

Chapter 4 Referenced Publications

4-1 The following documents or portions thereof are referenced within this r ecommended practice and should be considered part of the recommendat ions of this document . The edition indicated for each reference is the cnrrent edition as of the date of the NFPA issuance of this document .

4-1.1 NFPA Publications. National Fire Protection Association, 1 Batterymarch Park, P.O. Box 9101, Quincy, MA 02269-9101.

NFPA 30, Flammable and Combustible Liquids Code, 1996 edition.

NFPA 58, Standard for the Storage and Handling of Liquefied Petroleum Gases, 1995 edition.

NFPA 59A, Standard for the Production, Storag~ and Handling of Liquefied Natural Gas (LNG), 1996 edition.

NFPA 70, NationalElectrical Code, 1996 edition.

NFPA 325, Gu/de to Fire Hazard Properties of Flammable Liquids, Gases, and Volatile Solids, 1994 edition.

4-1.2 ANSI Publications. Amedcan National Standards Institute, 11 West 42nd Street, New York, NY 10036.

ANSI/ASHRAE 15, Safe O Cxcle for Mechanical Refrigeratitng 1989.

ANS1/CGA G2.1, Sara 3 Reg*irements for the Storage and Handling of Anhydrous Aramonia, 1989.

4-1.3 API Publication. American Petroleum Institute, 1220 L Street, NW, Washington, DC 20005.

ANSI/RP 500, Cdassification of Locations for Electrical lnstallations in Petroleum Refineries, 1992.

4-1.4 IEC Publication. International Electrotechnical Commission Central Office, 3 Rue de Varembe, P.O. Box 131,1211 Geneva 20 Switzerland.

IEC 79-3, Electrical apparatus for explosive gas atmospheres, Part 3: Spark- test apparatus for intrinsically-safe circuits.

Appendix A Explanatory Material

This Appendix is not a part of the recommendations of this NFPA document, but is included for information purposes only.

A-l-3 Combustible Material, Groups A, B. C, and D. Historically, the topic of hazardous (classified) locations first appeared in the National Electrical Code (NEC) in 1923, when a new article entit led "Extra- Hazardous Locations" was accepted. This article addressed rooms or compartments in whida highly flammable gases, liquids, mixtures, or other substances were manufactured, used, or stored. In 1931, "classifications" consisting of Class I, Class II, etc., for the hazardous locations were defined. However, it was no t until 1935 that "groups" were int roduced into the NEC. (Note: "divisions" were int roduced into the NEC in 1947.) The four gas groups, Groups A, B, C, and D, complemented the design of electrical equipment used in hazardous (classified) locations and were defined based on the level of hazard associated with explosion pressures of specific atmospheres and the likelihood the effects of that explosion could be transmitted outside the enclosure. Group A was defined as atmospheres containing acetylene. Group B was defined as atmospheres containing hydrogen or gas or vapors of equivalent hazard. Group C was def ined as atmospheres containing ethyl e ther yap.or, and Group D was def ined as atmospheres containing gasohne, petroleum, naphtha, alcohols, acetone, lacquers, solvent vapors, and natural gas. Despite the fact that the introduction of these Groups was done without standardized testing and without the advantage of today's technological advances or equipment, these definitions have changed little since that time. The first major testing, in fact, was only conducted in the late 1950s, when engineers at Underwriters Laboratories Inc. developed a test apparatus dlat provided a means to de termine how various materials behaved with respect to explosion pressures and transmission, wben the specific combustible matedal was ignited in the test vessel. This apparatus, called the Westerberg Explosion Test Vessel, provided standardized documentat ion of a factor called the "Maximum Experimental Safe Gap" (MESG) and permit ted other materials to be "classified by test" into one of the four gas groups. The results of these tests are contained in Underwriters Laboratories Inc. (UL) Bulletin Nos. 58 and 58A (reissued in July 1993, as UL Technical Repor t No. 58). In

1971, the International Electroteclmical Commission (IEC) published IEC 79-1A defining a different type of apparatus for obtaining MESG results. While the two "MESG" test apparatuses are physically different in both size and shape, the results are statistically comparative, al though in some cases differences have been observed. A sample of values is shown in the table below.

Material Westerberg apparatus, IEC apparatus, MF.SG, mm MESG, mm

Propane .92 .94 Ethylene .69 .65 Butadiene .79 .79 DiethyI e ther .30 .87 Hydrogen .08 .29

Papers have been written to at tempt to explain the reasons for these differences in the test data. One by H. Phillips, entitled

• "Differences between Determinations of Maximum Experimental Safe Gaps in Europe and U.S~. ," appeared in a 1981 edition of the Journal of Hazardous Materials, riling a condition of spontaneous combustion in one port ion of the Westerberg Apparatus, which was reflected in materials, like diethyl ether, having low ignition temperatures. Additionally, testing on the Westerberg Apparatus has demonstra ted that this theory was true, and the MESG value for diethyl e ther more than doubled. Further Westerberg apparatus testing has also shown that hydrogen MESG value is.23 mm.

While acetylene remains segregated in Group A because of the high explosion pressure which results from its very fast flame speed, newer test methodologies have def ined other types of protection methods that now consider acetylene and hydrogen to be of equivalent hazard. One such me thod examines the "minimum

niting current" required to ignite a specific combustible material. ais testing produced more variability when the results of specific

combustible materials were compared. However, it was found that file minimum igniting currents of one test could be favorably compared with those of other tests, i ra ratio value based on methane was applied. This testing has resulted in tile generation of MIC ratio data.

Other testing has been performed when it was incorrectly assumed that a factor called "Minimum Ignition Energy" (MIE) and "Autoignition Temperature" (AIT) were related, and could be used to place materials into groups. The fact that these were independent factors resulted in deletion of AITs as a basis for group determina- tion in the 1971 NEC.

MIEs have been found to exhibit theoretical results which do not translate into practical designs that can be applied to actual electrical devices with their assodated energy levels.

Since the primary concern is to have electrical devices that can safely operate when used in locations classified by class, group, and division, the definitions for the four gas groups have been defined on the basis of the parametersproviding the most significant basis for that design; MESG and MICrat io and lacking these values, experience-based data indicating equivalency to amaospheres providing similar hazards.

A-2-1, Table Note 5. Selecting electrical equipment based on the lowest AIT shown in Table 2-1 may be unnecessarily restrictive. As an example, in an area handling a commercial grade of hexane, Table 2-1 tabulates five different isomers of hexane solvent (C6H14) with the AIT ranging from a low of 225 °C to a high of 405 °C.- Th6 AIT of the solvent mixtures should be de te rmined either experimentally or from the supplier. It would be expected that die commercial grade of hexane would have an AIT ranging from 265 °C to 290 °C.

A-2-1.2 Electrical installations for classified areas may be designed in various manners. No single manner is best in all respects for all types of equipment used in a chemical plant. Explosionproof enclosures, pressurized equipment, and intrinsically safe circuits are applicable to both Division 1 and Division 2 areas. Nonincendive equipment is permitted in Division 2 areas. Nonsparking electrical

~bq.Ul~p ment and other less restrictive equipment, as specified in A 70, NationalElectrical Code, are permit ted in Division 2 areas.

Factors such as corrosion, weather, maintenance, equipment standardization and interchangeability, and possible process changes or expansion frequently dictate the use o_f special enclosures or installations for electrical systems. However, such factors are outside the scope of dais r ecommended practice, which is concerned entirely with the proper application of electrical equipment to avoid ignition of combustible materials.

339

N F P A 4 9 7 A I A97 R O P

A-2-4.2 Combust ible materials shown in Table 2-1 have been classified in groups. Some of these combustible materials are indicated in groups tha t may not seem to agree widl def ined MESG or MIC ratio values, but have been cont inued within groups due to historical experiences and specific propert ies which ace not reflected in MESG or MIC ratio testing. For example, one source for g roup classifications was Matrix of Combustion-Relevant Properties and Classification of Gases, Vapors, and Selected Solids, NMAB 353-1, publ ished by d~e National Academy of Sciences. Those materials whose g roup classifications are marked with asterisks were previously ,assigned group classifications based on tests conduc ted in the Westerberg Appara tus at Underwri ters Laboratories Inc. (SeeAn Investigation of Flammable Gases or Vapors with Respect to Explosion-Prod[ Electrical Equipment, UL Bulletin of Research No. 58, and subsequent Bulletins Nos. 58A amt 5813, rdssuedJuly 23, 1993 as UL Technieal l~port No. 58.) All o ther materials were ass igned group classifications based on analogywith tested materials and on chemical structure, or on reputable publ ished data reflecting MESG or MIC ratio values. (See, for example, IEC 79-20.) While the classifications of daese latter materials represent the best j u d g m e n t of three groups of experts, it is conceivable dmt ti~e groupclassif icat ion of any particular un tes ted material may be incorrect. Users of these dam should be aware tha t dae data are the result of exper imenta l de terminat ion , and as such are inf luenced by variation in exper imenta l appara tus and procedures and in the accuracy of the ins t rumenta t ion . Additionally, some of the dam have been de te rmined at an above-ambient t empera ture in order tha t the vapor is within the f lammable region. Variation in the t empera tu re for the de te rmina t ion would be expected to inf luence the result of the determinat ion. Values shown generally also represent the lowest repor ted in reputable, d o c u m e n t e d studies. In certain instances, therefore, it may be advisable to submi t an untes ted material to a qu,'dified testing laboratory for verification of the ,assigned group classification. Autoigni t ion tempera tures listed in Table 2-1 are the lowest value for each material as listed in NFPA 325, Guide to Fire Hazard Properties of Flammable Liquids, Gases, and Volatile Solids, or as repor ted in an article by Hilado, c . J . and Clark, S. W., in ChemicalEngineering, September 4, 1972.

A-3-4.2 The degree to which air m o v e m e n t and material volatility combine to ,affect die extent of the classified area can be illustrated by two experiences moni to red by combust ible gas detectors. Gasoline spilled in a sizable open manifold pit gave no indication of ignitable mixtures beyond 3 ft or 4 ft (0.9 m to 1.2 m) from the pit when the breeze was 8 to 10 m p h (13 to 16 k m / h r ) . A slightly sm:dler pool of a more volatile material, blocked on one side, was moni tored dur ing a gent le breeze. At grade, wapors could be detected for approximately 100 ft (30 m) downwind; however, at 18 in. (46 cm) above grade tlvere was no indication of vapor as close as 30 ft (9 rn) f rom the pool.

These examples show die great variability tha t may be present in situations of this type, m~d point out again that careful c-onsideration ffUlSt be given to a large n u m b e r of factors when classifying.areas.

A-3-7.2.5 When fire hazard propert ies of a combust ible material are no t ,available, the appropria te g roup may be est imated us ing informat ion such as:

(a) Min imum igniting cur rent ratio (MIC ratio); (b) Ratio of uppe r f lammable limit to lower

f lammable limit; (c) Molar heat of combust ion mult ipl ied by the

lower f lammable limit; (d) Ratio of file lower f lammable limit to the

s toichiometr ic concentrat ion; (e) M a x i m u m exper imenta l saffe gap (MESG); (0 Min imum ign;tion energy (MIE); / ~ Stoichiometric f lame tempera tu re;

Knowledge of the chemical structure.

A-3-7.3 The user may wish to use tile methodology discussed here, whicla is based upon the Institute of Petroleum, Area Classification Code for Petroleum Installations, Part 15, March 1990, to fur ther assess tile hydrocarbon ' s volatility as an added measure of deriving the extent of the classification. In dae event dfis methodology is employed, the user should fiflly d o c u m e n t the rationale and the considerat ions as part of dae area electrical classification process. This methodology outlines a practice which begins by placing the hydrocarbon of interest into one of four categories, as shown in Figure A-3-1 below. Category 1 encompasses the most volatile materials and includes LPG plus all l ighter hydrocarbon gases, like methane . Category 2 includes NFPA 30, Flammable and C~mbustible Liquids Cod~ Class 1A Flammable Liquids plus all materials with a vapor pressure exceeding 750 m m Hg. Category 3 includes NFPA 30 Class 1B, 1C, 2, and 3 combustible liquids that ace above their flash point. Category 4 includes NFPA 30 Class 2, and 3-combustible liquids tha t ace below their flash points; these would fall into a

nouhazacdous category and thus would no t likely require special electrical equipment .

Once dae source category 1, 2, 3, or 4 is selected, tiae methodology dlen relates the categoi-y of volatility of the hydrocacbou to the mass release rate, as shown in Figure A-3-2, to three different hazard radii, in a m a n n e r similar to flint def ined in dais practice using the low, med ium, high criteria. The hazard radius is the largest horizontal extent of the hazardous area that is genera ted by the source.

Figure A-3-1 shows a plot of t empera ture versus vapor pressure with these four categories (Note: 750 m m Hg = 1 bar _= 14.5 psi).

~0 m

o

>

0.TS

(*C) -100 -~0 0 so l o o t s o 2Go 2so 3 0 0 3so

Pries= o~ storage T=mp,tr=t~

Figure A-3-1 Volatility categories on temperature versus vapor pressure chart.

Figure A-3-2 displays how the mass release rate is divided into the three categories of low, med ium, and h igh with n u m b e r s such as low - - equal to less than 100 gallons per minute; m e d i u m - - 100 to 500 gallons per minute ; and h igh - - releases greater than 500 to 1000 gallons per minute .

I

=

13.

I Temperature

Hazard Radius, I t ]

25 25-50 50-1 O0

5 5-25 25-50

3 3-5 5-25

F'tgure A-3-2 Category - - Release Rate - - Hazard Radius Matrix

340

N F P A 497A - - - A97 R O P

While the Hazard Rad]m Matrix has nine distinct radii shown for the various combinations of material category and release rate, it is actually a cont inuum in which engineer ing j u d g m e n t should be applied when either the category ortthe release rate b near the interface. For example, if the material is located near the Category 2-3 interface and the release rate is on the low to medium interface, a hazard radius of 5 to 10 feet may be used.

The charts below demonstrate how the hazard radius would be applied to open-air (adequately ventilated) sources of heavier- and lighter-tilan-air materials.

D2 r :

H1

-] hp--QSour<~

Source a b o w grade

D1

1

IHz

If j Ground

Hazard D1 D2 H 1 H 2 Radius

(Ft) (Ft) (Ft) (Ft) (Ft)

100 100 50 25 10

50 50 25 25 25 25 25 25 1.0 H 1 + h

3 3 3 3 H t + h

I Solid Platform

D2 LI

H1

~ ' - t source . _ _ = .

IM~ H,I I . -'-

- I L . $ ~

D1 ~

Source above elevatod Idatform

I Source - . . .JL

H2 -I I " D~ - '

Open .Air (release lighter than air)

Hazard HI D1 H2 Radms

(Ft) (Ft) (Ft) (R)

30 50 30 20

15 25 15 10

10 15 10 10

5 5 5 5

G~ound er- Solid Floor

I

Pumps

The relea~_ rate f rom proceas pumps is typically a function of the type o f pump, type of shaft sealing, size of pump, the physical size o f the pump, and pump seal chamber pressure (the pressure in the cavity internal to the pump shaft seal, sometimes referred to as the stuffing box pr~ssore).

Most horizontal-shaft pumps will have a seal chamber pressure near the pump suction pressure, whereas many vertical pumps have seal chamber pressures near pump dischargo pressure. While pump seal chamber pressure tends to be the driving force behind a release, the pump sea] technology often creates the restriction that determines the release rate. The following matrix provides guidance in determining the hazard radius for two types of pumps, I .oc~3ted in adequately ventilated areas.

t .~nw ttm-b~ ~ womw ~ - - - ~ ,( 1rio Ilpttt 100 - 100 g~nt ) 51Ogpm Flow R I l l

Pmemn

s=,=.~, , , . 12 to I . I -~ lo =6 = 15 - 13 , i ,o 1,5 5 ,o =5 ,s

.~hT.~.~,o~, ' 5 lo 15 S lo . . ,o 1o u,.e~v..~7~p I = s t 5 I ,o s 5 lo 5 to. ,o

t s "L ; ' 1 5 ~ ~o ~,.oo,,.-.-k

Medium- and Low-Pressure Restrictions (Orifices, Drains, Etc.)

The following chart applies to any type of potential source in a medium- or low-pressure system, located in an adequately ventilated process area,- that has a restriction orifice or similar restriction to reduce the release rate fTom the source.

Hazard Radius for Restrictions I Restriction Diameter (in.) ]

SI units: I in. = 25.4 mm

341

N F P A 4 9 7 A - - A 9 7 R O P

Heavier-than-air Lighter-fllan-air

SI units: 1 ft = 0.3048 m

Compressors

The following chart applies to bofl~ reciprocating and axial flow compressors, located in an adequately ventilated process area.

I azard Radius fftl 50* 15

*The radius may be reduced to 25 ft (7.62 m) for pressures below 300 psi (20 bar)and shaft diameters of 2 in. (50.8 mm) or less. For diaphragm compressors the hazard radius may be reduced to

10 ft (3.05m), provided there are no vents or drains to atmosphere at the compressor. Advanced seal technology and closed-system venting may allow

reduced hazard radius.

Instrument and Process Vents and Drains to Atmosphere

For an aunospheric process vent, located in adequately ventilated process area with heavier-than-air gas discharge velocity of 500 ft/sec (152.5 m/see) or less, the following chart may be used:

Hazard Vent Rate at Amb. Gond. Radius

(cu ft /hr) (ft) Less than 300 10

300-3000 25 3000-6000 50


Flanges and Valves

Many flanged joints are rarely disassembled, e.g., only during major maintenance work, typically at intervals of 2 years or more. Any leakage from these joints is likely to be small. Depending upon the nature of the facility, level of maintenance, and past experience, a nominal hazard radius of 0 ft to 3 ft (0 mm to 914 mm) from the periphery may be assumed for such joints on a well-maintained system, provided there are no factors that could increase leakage, e.g., pressure or thermal shock, including the effect of rain, or an excessive piping loaxl on tile flanged joint. Where these factors are present, the hazard radius is shown below:

Flanges and Valves Hazard

Fluid Radius Category (ft)

1 10 2 10 3 5


Note that this area classification methodology does not take into consideration the possibility of blowout or failure of a gasket due to freezing or overpressu ring.

Appendix B Bibliography

This Appendix is not a part of the recommendations of this NFPA document but is inctuded for informational purposes onl 3. The edition indicated for each reference is the current edition as of the date of the NFPA issuance of this document.

B-I ANSI Publications. American National Standards Institute, 11 West 42nd Street, New York, NY 10036.

ANSI/ASHRAE 15, Safety Code for Mechanical ~_ fngeration, 1989, available from the American National Standards Institute, 11 West 42nd Street, NewYork, NY 10036.

ANSI/CGA G2.1, Safety Requirements for the Storage and Handling of Anhydrous Ammonia, 1989, available from the American National Standards Institute, 11 West 42nd Street, NewYork, NY 10036.

B-2 ASTM Publications. American Society for Testing and Materials, 1916 Race Street, Philadelphia, PA 19103.

ASTM D56, Standard Method of Test for Flash Point by the Tag Closed Tester, 1987.

ASTM D93, Standard Method of Test for Flush Point by. the Pens~ Martens Closed Tester, 1985.

ASTM E659, Test for Autoignition Temperature of Liquid Chemicals, 1978.

ASTM E681, Test for Limits of Flammability of Chemicals, 1985.

ASTM D3278, Standard Method of Tests for Flash Point of Liquids by Setaflash Closed Tester, 1982.

B-3 Bureau of Mines Publication. U.S. Government Printing Office, Washington, DC 20402.

RI 7009, Minimum Ignition Ensrg 3 and Quenching Distance in Gaseous Mixture.

B-4 IEC Publications. International Electrotechnical Commission, Central Office, 3 Rue de Varembe, P.O. Box 131,1211 Geneva 20 Switzerland.

IEC 79-1A, First supplement to publication 79-1 (1971), Electrical explosive gas atmospheres, Part 1: Construction and test of

eproof enclosures of electrical apparatus, Appendix D: Method of test for ascertainment of maximum experimental safe gap.

IEC 79-3, Electrical apparatus for explosive gas atmospheres, Part 3: Spark-test apparatus for intrinsically-safe circuits.

lEG 79-12, Electrical apparatus for explosive gas atmospheres, Part 12: Classification of mixtures of gases or vapors with air according to their maximum experimental safe gaps and minimum igniting currents.

IEC 79-20, Electrical apparatus for explosive atmospheres, Part 20: Data for flammable gases and vapors, relating to the use of electrical apparatus.

I3-5 National Academy of Sciences Publication. National Materials Advisory Board of the National Academy of Sciences, 2101 Constitu- tion Avenue, NW, Washington, DC 20418.

NMAB 353-1, Matrix of Combustion-Relevant Properties and Classifica- tion of Gases, Vapors and Selected Solids.

B-6 NFPA Publications. Nadonal Fire Protection Association, 1 Batterymarch Park, P.O. Box 9101, Quincy, MA 02269-9101.

NFPA 30, Flammable and Combustible Liquids Code, 1996 edition.

NFPA 36, Standard fo~ Solvent Extraction Plants, 1993 edition.

~NFPA 70, NationalElectrical C, od~ 1996 edition.

NFPA 325, Gu/de to Fire Hazard Properties of Flaramable Liquids, Gases, and Volatile Solids, 1994 edition.

B-7 UL Publication. Underwriters Laboratories Inc., 333 Ptingsten Road, Northbrook, IL 60062.

Technical Report No. 58, An Investigation of Flaramable Gases or Vapors With Respect to Explosion-Proof Electrical Equipmeng 1993.

B-8 Other Publications.

Hilado, c.J . and Clark, S. W., "Autoignition Temperatures of Organic Chemicals," ChemicalEngineering~ Sept. 4, 1972.

Institute of Petroleum, Area Classification Code for Petwleum Installations, Part 15, March 1990,John Wiley and Sons.

Phillips, H., "Differences between Determinations of Maximum Experimental Safe Gaps in Europe and U.S.tLyJournal of Hazardous Materials, 1981.

Appendix C

This recommended practice is not intended to supersede or conflict with applicable requirements of the fotlowing NFPA stimdards: --

NFPA 30, Flammable and Combustible Liquids Code; 1996 edition.

NFPA 33, Standard for Spray Application Using Flammable or Combus- tibleMaterlals, 1995 edition.

NFPA 34, Standard for Dipping and Coating Processes Using Flammable or Combastible Liquids, 1995-edirtion.

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N F P A 4 9 7 A i A 9 7 R O P

NFPA 35, Standard for the Manufacture of O~ganie Coating~ 1995 edition.

NFPA 36, Standard for Solvent Extraction Plants, 1993 edition.

NFPA 45, Standard on Fire Protectlon for Laborato~4~s Using Chemicals, 1996 edition.

NF~A 50A, Standard.for Gaseous Hydrogen Systems at Consumer Site~ 1994 edition.

NFPA 50B, Standard for Liquefied Hydrogen Systems at Consumer Sites, 1994 edition.

NFPA 58, Standard for the Storage and Handling of Liquefied Petroleum Gases, 1995 edition.

NFPA 59A, Standard for the Production, Storag~ and Handling of Liquefied Natural Gas (LNG), 1996 edition.

Appendix D

This example is provided to show how the information in this document can help de termine an NECgroup classification. It should no t be applied with mixtures a n d / o r streams that have acetylene or its equivalent hazard.

The following materials are used in a tank having a total capacity of 100,000 kg ~s a single mixed stream having this composition:

material % by vol ethylene 45 propane 12 ni trogen 20 methane 3 isopropyl e ther 17.5 d ie thy le ther 2.5

Qwluestion: lat is the appropriate NEC group to use for file mixed stream?

From NFPA 497 Table 2-1 and other references, these materials are also known to have the following properties:

Material Mol. wt. %LFL %UFL AIT °C Ethylene 28.05 2.7 36 450 Propane 44.09 2.1 9.5 450 Nitrogen 14.0 Methane 16.04 5.0 15 600 lsopropyi e ther 102.17 1.4 21 443 Diethyi e ther 74.12 1.9 36 160

One me thod to estimate the NEC group is to de termine the MESG of the mixture by applying a form of Le Chatielier relationship shown below.

~ S G M x __ 1

i

Applying the volume percent and property information above results in the following equation:

0.45+ 0.12 , 0.20_ 0.03_ 0.175_ 0.02 1 n~or~,v - 6 ~ - 0 . - ~ " - 6 ~ " ~ " -6 -~- " 0 . - ~ L . u J o . .

Solving the equation above results in an MF_.SG mixture value of 0.95. From the definitions in Section 1-3 for Groups A. B. C and D. dais calculated MESG value would fall under Group D. Thus this mixture may be considered a Group D material.

Vapor pressure, mm Hg at 25° C

52,320 7150

463,800 148.7

38.2

NEC MESG MIC BP °C Group mm ratio -104 C 0.65 .53

-42 D 0.97 .82

-162 D 1712 1.0 69 D 0.94 34.5 C 0.83 .88

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N F P A 4 9 7 B ~ A 9 7 R O P

PART II

(Log #CP1) 49713- I - (Entire Document) : Accept SUBMITTER: Technical Commit tee on Electrical Equ ipmen t in Chemical Atmospheres , RECOMMENDATION: The Technical Commit tee on Electrical Equ ipment in Chemical Atmospheres r e c o m m e n d s that the text of NFPA 497B, R e c o m m e n d e d Practice for Classification of Class II Hazardous (Classified) Locations for Electrical Installations in Chemical Process Areas, 1991 edition, and the combust ible dus t information f rom NFPA 497M, Mamml for Classification of Gases, Vapors, ,and Dusts for Electrical Equ ipmen t in Hazardous (classified) Locations, 1991 edition, be combined into a single document , r e n u m b e r e d ,and redesignated as NFPA 499, R e c o m m e n d e d Practice for Classification of Combnst ible Dusts and o f Class II Hazardous (Classified) Locations for Electrical Installations in Chemical Processing Plants. SUBSTANTIATION: This is one of three proposals developed by the Electrical Equ ipment in Chemic,al Atmospheres (EECA) Ad Hoc Task Group consisting of Ed Briesch, Underwri ters Laboratories; William Lawrence, Factory Mutual; Richard Masek, Bailey Controls; Richard Munson, E.I. DuPont; and David Wechsler, Un ion Carbide Corp. The EECA Commit tee directed the Ad Hoc Task Group to evahtate NFPA 497A, B, and M, and to de te rmine if these documen t s could be developed into two unders t andah le and usable documents . This s tudy was made and the results discussed with the m e m b e r s h i p of the EECA Committee. From that meeting, it was agreed tha t the Ad Hoc Task Group should move forward and combine NFPA 497B and 497M, into two documents ; one address ing NEC Class I, f lammable gases/vapors and combust ible liquids, and the other address ing NEC Class II combustible dusts. T i f f s proposal will replace NFPA 497B and NFPA 497M with a redesignated document , NFPA 499, Classification of Combust ible Dusts and of Hazardous (Classified) Locations for Electrical Installations in Chemical Process Areas, which contains all the per t inent informat ion conta ined in the two separate documents .

The EECA Ad Hoc Task Group compiled a mul t i -column documen t to compare the individual texts of NFPA 497A, 497B and 497M. This compilat ion was then used to editorially create a single new document , NFPA 499. By proceeding in dais way, the Ad Hoc Task Group was able to retain as much of the original text as possible. A copy of tiffs 28 page colnpilation h a s b e e n submit ted witla this proposal. (NOTE: This compilat ion d o c u m e n t is provided for informat ion only. The proposed NFPA 499 d o c u m e n t should take precedence over any text differences.)

The content of the new NFPA 499 d o c u m e n t is simply editorially manipulated. The Ad Hoc Task Gronp strongly resisted efforts to introduce new material into the technical re-combining ass ignment .

Examples of editorial manipula t ion can be seen: (a) In the t rea tment of die individu:d scope s ta tements of NFPA

497M and NFPA 497B. In essence, the one NFPA 497M scope s ta tement was combined with the five NFPA 497B scope statements, p roduc ing six s ta tements in the scope section of the new NFPA 499. The same m e t h o d was used for the "purpose" s ta tements where die text was extracted from each of the base 497M and 497B documents .

(b) In cases where NFPA 497M and NFPA 497B conta ined similar but slightly different s tatements , the more correct of the two was used in NFPA 499. For example, NFPA 497M used the National Electrical Code (NEC) definit ion for Class II, Division 1, while NFPA 497B used an abbreviated version. The text incorporated into the new NFPA 499 contains the NEC definition.

(c) By the creation of a formal definit ion section in NFPA 499, dais permit ted no t only better identification of impor tan t terms, but also simplified some of the text. For example, the term "combustible material" was developed to el iminate the continual need to specify "a mixture of dus t in air or a mixture of dnst with a f lammable gas, f lammable vapor, combustible liquid in air". The term hybrid mixture, used in NFPP~ 497B, was also made into a definition.

(d) In clarifying the in tent of the subject material, the NFPA 499 text has been reorganized. For exanap/e, material addressing good information was moved f rom the body of the d o c n m e n t into the A~ePendix where it could be better addressed.

) By us ing a more correct term, ,as for example; "unclassified" vs. "nonclassified" as mearfing the port ion of the area that is ne i ther Class II, Division 1, nor (2lass II, Division 2. The correct te rm presented in NFPA 70, National Electrical Code, is "unclassified".

(O In developing rep lacement tables for the redesignated NFPA 499 from those in NFPA 497M, a new single table of selected Class II Combustible materials, listed in alphabetical order, was created, supplement in~ the data in the NFPA 497M combust ible dus t tables, and the material Chemical Abstract Service (CA,S) n u m b e r was added. As an aid in f inding materials, a supplementa ry table containing a numerical ranking of CaLS n u m b e r s vs. Chemical names was added.

(g) Lasdy, with the exception o f r e n u m b e r i n g the Classification diagrams, no changes have been made to the diagrams.

The Ad Hoc Task Group wishes to express its appreciat ion to the members of the Electrical Equ ipment in Chemical Atmospheres Commit tee for their suppor t and assistance provided us dur ing this two year effort.

NOTE: Suppor t ing material is available for review at NFPA Headquarters. COMMITrEE ACTION: Accept. NUMBER OF COMMITTEE MEMBERS ELIGIBLE TO VOTE: 24 VOTE ON COMMITTEE ACTION:

AFFIRMATIVE: 24

NFPA 499

Recommended Practice for the Classification of Combustible Dusts and of Hazardous (Classified)

Locations for Electrical Installations in Chemical Process Areas

1997 Edition

NOTICE: An asterisk (*) following the n u m b e r or letter des ignat ing a paragraph indicates explanatory material on that paragraph in Appendix A.

Informat ion on referenced publications can be fo u n d in Chapter 4 and Appendix B.

Chapter 1 General

1-1 Scope.

1-1.1 This r e c o m m e n d e d practice applies to those locations where combust ible dusts are produced, processed, or handled and where dus t released into the a tmosphere or accumula ted on surfaces may be ignited by electrical systems or equipment .

1-1.2 This r e c o m m e n d e d practice provides informat ion on specific combust ible dusts whose relevant combust ion propert ies have been sufficiendy identified to allow their classification into the groups established by NFPA 70, NationalElectrical Codd,_~ (NEC), for proper selection of electrical equ ipmen t in hazardous (classified) locations. The tables in this d o c u m e n t are no t in t ended to be all-inclusive.

1-1.3 This r e c o m m e n d e d practice also applies to chemical process areas. As used in this document , a chemical process area may be a chemical process plant, or it may be a part of such a plant. It may be a part of a manufac tu r ing facility where combust ible dusts are p roduced or used in chemical reactions or are hand led or used in operat ions such as mixing, coating, extrusion, conveying, drying, a n d / o r grinding.

1-1.4 Tlfis r e c o m m e n d e d practice does not apply to agricultural grain hand l ing facilities except where powdered grain is used in a chemical reaction or mixture.

1-1.5 This r e c o m m e n d e d practice does no t apply to situations that may involve catastrophic failure of, or catastrophic discharge from, silos, process vessels, pipelines, tanks, hoppers , or conveying or elevating systems.

1-1.6 This r e c o m m e n d e d practice does no t apply to oxygen-enriched a tmospheres or pyrophoric materials.

1-1.7 This r e c o m m e n d e d practice is not in tended to supersede or conflict with the NFPA standards listed in Appendix C.

1-2 Purpose.

1-2.1 The purpose of this r e c o m m e n d e d practice is to provide the user with a basic unders tand ing of the parameters that de te rmine the degree and the extent of the hazardous (classified) location. This r e c o m m e n d e d practice also provides the user with examples of the applications of these parameters.

1-2.2 Informat ion is provided on specific combust ible dusts whose relevant propert ies de te rmine their classification into Groups. This will assist in the selection of special electrical equ ipmen t for hazardous (classified) locations where such electrical equ ipmen t is required.

1-2.5 This r e c o m m e n d e d practice is i n t ended as a guide and should be applied with sound engineer ing j u d g m e n t . Where all factors are

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N F P A 4 9 7 B - - A 9 7 R O P

d P r o p e r l y e v a h m t e d , a consistent area classification scheme can be eveloped.

1-2.4" This r e c o m m e n d e d p r a c t i c e is based on the criteria established by Articles 500 and 502 of NFPA 70, NationalElectrical Code. Once an area is properly classified, tile NEC specifies the type of equ ipmen t and the wiring me thods that may he used.

1-3" Definitions.

For the purpose of this r e c o m m e n d e d practice, the following terms have the mean ings given below. T h r o u g h o u t file document , def ined terms ,are identified using bold type (or when in tides, bold and under l ined) .

Autoignition Temperature (AIT). The m i n i m u m tempera ture required to initiate or cause self-sustained combust ion of a solid, liquid, or gas independen t ly of the hea t ing or heated element. See NFPA 325, Guide to Fire ttazard Properties of Flammable Liquids, Gases, and Volatile Solids.

CAS. Chemical Abstract Service.

Class II, Division 1. A Class II, Division 1 location is a location where (1) combust ible dus t is in the air u n d e r normal operat ing condit ions in qn,'mtities sufficient to produce explosive or ignitable mixtures; or (2) where mechanical failure or abnormal operat ion of mach inery or equ ipmen t migh t cause such explosive or ignitable mixtures to be p roduced a n d migh t also provide a source of ignition th rough s imul taneous failure of electrical equipment , operat ion of protect ion devices, or o ther causes; or (3) in which combustible dusts of an electrically conductive na ture may be present in hazardous quantities.

Class II, Division 2. A Class II, Division 2 location is a location where combustible dus t is not normally in the air in quanti t ies sufficient to produce explosive or ignitable mixtures, and dust accumula t ions are normally insufficient to interfere with the normal operat ion of electrical e q u i p m e n t or o ther apparatus, bu t combustible dus t may be in suspension in the air as a result of infi 'equent malf imct ioning of hand l ing or processing equ i pmen t and where combustible dus t accumula t ions on, in, or in the vicinity of the electrical equ ipmen t may be snfficient to interfere with the safe dissipation of heat f rom electrical e q u i p m e n t or may be ignitable by abnormal operat ion or failure of electrical equipment .

NOTE: The quanti ty of combust ible dus t that may be present and the adequacy of dus t removal systems are factors that meri t considerat ion in de t e rmin ing the classification and may result in an unclassified area.

Combust ible Dust.* Arty finely divided solid material 420 microns or less in d iameter (i.e., material passing t h rough a U.S. No. 40 Standard Sieve) that presents a fire or explosion hazard when dispersed.

Combust ible Dusts are sulxtivided as follows:

Group E. Atmospheres conta in ing combustible metal dusts, including a luminum, magnes ium, and their commercial alloys, or o ther combust ible dusts whose particle size, abrasiveness, and conductivity present similar hazards in the use of electrical equipment .

Group F. Atmospheres conta in ing combust ible carbonaceous dusts that have more than 8 percen t total en t rapped volatiles (see ASTM D 3175 for coal and coke dusts) or that have been sensitized by other materials so that they present an explosion hazard. Coal, carbon black, charcoal, and coke dusts are examples of carbonaceous dusts.

Group G. Atmospheres conta in ing o ther combust ible dusts, including flour, grain, wood flour, plastic, and chemicals.

Combust ible Material. A gener ic te rm used to describe ei ther a mixture of dus t in air, or a hybrid mixture, tha t may b u m , flmne, or explode.

Explosion Severity.* A measure of the damage potential of the energy released by a dus t explosion.

Hybrid Mixture. A mixture of a dus t with one or more f lammable gases or vapors.

Ignitable Mixture. A combust ible material tha t is within its f lammable range.

Ignition Sensitivity.* A measure o f the ease bywhich a cloud of combust ible dus t may be ignited.

Chapter 2 Combustible Dusts

2-1 National Electrical Code Criteria.

2-1.1 Article 500 of NFPA 70, National Electrical Code, designates as hazardous (classified) any area in which a combustible material is or may be present in the a tmosphere in sufficient concentra t ion to produce an ignitable mixture. Article 500 designates three major categories of hazardous areas:

(a) Class I, in which the material is a f lammable gas or vapor:

(b) Class 11, in which tile material is a colnbustible dust:

(c) Class III, in wifich the material is an ignitable fiber or flying.

This r e c o m m e n d e d practice is l imited to (3lass II hazardous (classified) locations.

2-1.2 The intent of Article 500 is to prevent the use of electrical e q u i p m e n t and systems in hazardous (classified) locations that would ignite an ignitable dus t c loud or layer that may be present.

2-1.3 Within each class, Article 500 recognizes two degrees of hazard: Division 1 and Division 2. In Division 1, a combustible material is likely to be p resen t cont inuously or intermit tent ly unde r normal condit ions of operation, repair, ma in tenance , or leakage. In Division 2, a combust ible material is likely to be present unde r abnormal operat ing conditions, such as in f requent failure of process equip- m e n t or containers.

2-1.4 Electrical installations in Division 1 locations are des igned and enclosed in a m a n n e r that will exclude ignitable a m o u n t s of dusts and will no t permi t arcs, sparks, or heat genera ted or liberated inside the enclosures to cause ignition o f exterior dus t accumulations on the enclosure or of a tmospher ic dus t suspensions in the vicinity of the enclosure.

2-1.5 installations for Division 2 locations are des igned and arranged so that normal operat ion of the electrical system does not provide a source of ignition. Protection against ignition dur ing electrical breakdown is not provided. However, electrical breakdowns are sufficiently rare that the chances of one occurr ing simultaneously with accidental release of an ignitable mixture are extremely remote. Arcing and sparking devices are permit ted only if suitably enclosed or if the sparks are of insufficient energy to ignite tile mixture. Electrical installations in Division 2 locations may be designed with dust-t ight enclosures or o ther equ ipmen t enclosures as specified in Article 502.

2-1.6 Electrical installations for areas classified as hazardous may be des igned in various manners . No single m a n n e r is best in all respects or for all types of equ ipmen t used in a chemical process plant. Dust- ignit ion-proof electrical equipment , pressurized electrical equipment , and intrinsically safe electrical equ ipmen t are applicable to both Division 1 and Division 2 locations. Other dust-tight equ ipmen t enclosures, as specified in Article 502 of NFPA 70, NationalElectrical Code, are permi t ted in Division 2 locations. Types X, Y, and Z pressurized electrical equ ipmen t and intrinsically safe electrical equ ipmen t are applicable to both Division 1 and Division 2 locations. Equ ipmen t and wiring suitable for Class I, Division 1 locations are no t required and may no t be acceptable in Class lI locations.

2-1.7 Where both combustible vapors and dusts are present, electrical equ ipmen t and wiring suitable for s imul taneous exposure to both Class I and Class II condi t ions are required.

2-1.8 Where Group E dusts are present in hazardous quantities, there are only Division 1 locations. The NEC does not recognize any Division 2 areas for such dusts.

2-1.9 Factors such as corrosion, weather, main tenance , equ ipmen t standardization and interchangeabili ty, and possible process changes or expansion frequent ly dictate tile use of special enclosures or installations for electrical systems. However, such factors are outside tile scope of this r e c o m m e n d e d practice.

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N F P A 4 9 7 B - - A 9 7 R O P

2-1.10 For the purpose of this r ecommended practice, locations not classified as Division 1 or Division 2 are "unclassified" locations.

2-2 Behavior of Combustible Dusts.

2-2.1 Dispersion and Explosion.

2-2.1.1 Dust discharged or leaking from equipment into the atmosphere is acted on by gravity and will settle relatively quickly dependln!g on d ie size of particles, die internal pressure propell ing the parUcles out of the eqmpment , and any air currents m the vicinity. The result is a layer of dust that setdes on horizontal surfaces below die leak opening in a radial or elliptical manner , depend ing on tile location, of the opening on the equipment. The depth of the layer wdl be greatest under and close to the source and will taper of f to the outside of the circle or ellipse. Tile greater die height of the dust source above the surface, the greater the area covered. The internal pressure in the equipment will likewise increase the area covered. The size of file leak opening and tile elapsed time of emission also ,affect the quantity of dust on tile surface. Some dusts have particles that are extremely fine and light (have a low specific particle density). Such particles may behave more like vapors than like dusts and may remain in suspension for long periods. These particles may travel Par f rom the emitting source and collect on surfaces above the source. While horizontal surfaces accumulate the largest quantities of dust, vertical surfaces may in some instances also accumulate significant quantifies.

2-2.1.2 While a dust cloud will ignite and explode readily in the presence, of an o pen ignition . . . . source, dust layers,, if undisturbed and not in direct contact with the lgmtton source, will not explode. However, i fa small amount of dust is dispersed in the air at the

ition source, a small explosion will occur. The pressure wave from explosion blows the dust layer into die air, and a larger

explosion then takes place. It is often dais secondary explosion that does the most damage.

2-2.2* Hybrid Mixtures. The presence of tile f lammable gas or vapor, even at concentrat ions less than their lower flammable limit (LFL), will not only add to d ie violence of the dust-air combustion but will drastically reduce the ignition energy. Tiffs situation is encountered in certain industrial operations, such as fluidized bed dryers and pneumatic conveying systems for plastic dusts f rom polymerization processes where volatile solvents are used. In such cases, electrical equ ipment should be specified that is suitable for simultaneous exposure to both the Class 1 (flammable gas) and the Class II (combustible dust).

2-3" Conditions Necessary for Ignition o f a Combustible Dust.

2-$.1 In a Class I1 location, one of the following sets of conditions must be satisfied for ignition by the electrical installation.

2-3.1.1 In the first set of conditions:

(a) A combustible dust must be present.

(b) Tile dust must be suspended in the air in die proport ions required to produce an ignitable mixture. Further, within the context of dais r ecommended practice, a sufficient quantity of this suspension must be present in the vicinity of the electrical equipment.

(c) There must be a source of thermal or electrical energy sufficient to ignite die suspended mixture. Within the context of this r ecommended practice, the energy source is unders tood to originate with the electrical system.

2-$.1.2" In die second set of conditioos:

(a) A combustible dust must be present.

(b) The dust must be layered on file electrical equ ipment sufficiendy thickly to interfere with the dissipation of heat and allow the layer to reach file ignition temperature of the dust.

(c) The external temperature of die electrical equ ipment must be high enough to cause die dust to reach its ignition temperature directly or to dry out die dust and cause it to self-heat.

2-$.1.$ In the third set of conditions:

(a) A Group E dust must be present.

(b) The dust must be layered or in suspension in hazardous quantifies.

(c) Current flow through the dust must be sufficient to cause ignition. (See 2-4.1.)

2-3.2 Once ignition has occurred either in a cloud suspension or in a layer, an explosion is likely. Often the initial explosion is followed by another much more violent explosion fueled by the dust from dust accumulations on structural beams and equipment surfaces tllat are thrown into suspension by the initial blast .For this reason, good housekeeping in all areas handling dust is vitally important and is assumed throughout this r ecommended practice.

2-3.3 In classifying a particular location, the presence of a combustible dust is significant in de termining the correct division. The classification depends both on the presence of dust clouds and on tile presence of hazardous accumulations of dust in layer form. As defined in 1-3, the presence of a combustible dust cloud under normal conditions of operation, or due to f requent repair or maintenance, calls for a Division 1 classification. Abnormal operation of machinery and equipment, which may simultaneously produce a dust cloud or suspension and a source of ignition, also calls for a Division 1 classification. In other words, if a dust cl dud is present at any time, it is assumed to be ignitable, and all that is necessary for electrical ignition is failure of the electrical system. 1! dust clouds or hazardous dust accumulations are present only as a result of infrequent malfunctioning of hand l ingo r processing equipment, and ignition can result only from abnormal operation or failure of electrical equipment, tile location is designated as Division 2.

2-3.4 The presence of an ignitable dust cloud or an ignitable dust layer is important in determining the boundaries of the classified location. The quantity of dust, its physical and chemical properties, dust dispersion properties, and the location of walls and cutoffs must all be considered.

2-4 Dusts with Additional Hazards.

2-4.1 Conductive Dusts. Group E dusts may cause a short in the electrical equipment when exposed to sufficiently high voltages. Group E dusts are sensitive to a p h e n o m e n o n whereby an electric current finds the path of Mast resistance through a dust layer, heating up the dust particles in its path and thus providing a source of ignition. The resulting electric arc may ignite a dust layer or dust cloud.

2-4.2 Magnesium or Aluminum Dust. Dusts containing magnesium or a luminum are particularly hazardous, and the use of extreme precaution will be necessary to avoid ignition and explosion.

2.4.$ Low Ignition Temperature Dustr~ Zirconium, thorium, and uranium dusts have extremely low ignition temperatures [as low as 20°C (68°F)] and extremely low minimum ignition energies.

2-5 Classification of Combustible Dusts.

2-5.1 Combustible Dusts are divided into three groups; Group E, Group F, and Group G, depending upon the nature of the dust.

2-5.2* A listing of selected combustible dusts with dleir group classification and relevantphysical properties is provided in Table 2- 5. The chemicals are listedalphabetically. Table 2-5.1 provides a cross-reference of the chemicals sorted by their Chemical Abstract Service (CAS) number.

2o5.3 Appendix B lists references that deal with die testing of various ch~tracteristics of combustible materials.

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Table 2-5 Selected Combustible Materials

Layer or Cloud

NEC Ignition Temp

CHEMICAL NAME CAS # Group Code °C

s, CETAL, LINEAR G NL 440

~CETOACET-P-PHENETI DID E 122-82-7 G NL 560

~tCETOACETANILIDE 102-01-2 G M 440

~C ETYLAMINO-T-NITROTH IAZOLE G 450

~,CRYLAMIDE POLYMER G 240

~CRYLONITRI LE POLYMER G 460

~,CRYLONITRI LE-VINYL CHLORIDE-VINYLIDENE G 2 ! 0

CHLORIDE COPOLYMER (70-20-10)

~CRYLONITRILE-VINYL PYRIDINE COPOLYMER G 240

M)IPIC ACID 124-04-9 G M 550

ALFALFA M EAL G 2OO

ALKYL KETONE DIMER SIZING COMPOUND G 160

ALLYL ALCOHOL DERIVATIVE (CR-39) G NL 500

~LMOND SHELL G 200

ALUMINUM t A422 FLAKE 7429-90-5 E 320

ALUMINUM, ATOMIZED COLLECTOR FINES E CL 550

t~LUMINUM - COBALT ALLOY (60-40)

ALUMINUM- COPPER ALLOY (50-50)

ALUMINUM- LITHIUM ALLOY (15% Li)

ALUMINUM- MAGNESIUM ALLOY (DOWMETAL)

~&UMINUM - NICKEL ALLOY (58-42}

ALUMINUM- SILICON ALLOY (12% Si)

E 570

E 830

E 400

E CL 430

E 540

E NL 670

M~I INO-5-NITROTH IAZOLE 121-66-4 G 460

ANTHRANILIC ACID 118-92-3 G M 580

APRICOT PIT G 230

ARYL-NITROSOM ETHYLAM ID E G NL 490

ASPHALT 805242-4 F 510

ASPIRIN (ACETOL (2)} 50-78-2 G M 660

AZELAIC ACID 109-31-9 G M 610

AZO-BIS-BUTYRONITRILE 78-67-1 G 350

BENZETHONIUM CHLORIDE G CL 380

BENZOIC ACID 65-85-0 G M 440

BENZOTRIAZOLE 95-14-7 G M 440

BETA-NAPH THALENE-AXO-D IMETHYI.ANILIN E G 175

BIS/2-HYDROXY-5-CHLOROPHENYL ) METHANE

BISPHENOL-A

97-23-4 G NL 570

80-05-7 G M 570

BORON, COMMERCIAL AMORPHOUS (85% B) 7440-42-8 E 400

CALCIUM SILICJDE E 540

CARBON BLACK/more than 8% total entrapped volatiles} F

CARBOXYMETHYL CELLULOSE 9000-11-7 G 290

CARBOXYPOLYMETHYLENE G NL 520

CASHEW OIL~ PHENOLIC r HARD G 180

CELLULOSE G 260

CELLULOSE ACETATE G :540

CELLULOSE ACETATE BUTYRATE G NL 370

CELLULOSE TR1ACETATE G NL 430

CHARCOAL (ACTIVATED) 64365-11-3 F 180

?,47

N F P A 4 9 7 B - - A 9 7 R O P

Layer or Cloud

NEC Ignition Temp

CHEMICAL NAME CAS # Croup Code °C

.ZHARCOAL (more than 8% total entrapped volafiles) F

.ZHE RRY PIT G 220

2HLORINATED PHENOL G NL 570

ZHLORINATED POLYETHER ALCOHOL G 460

ZHLOROACETOACETANI LID E 101-92-8 G M 640

2HROMIUM (97%) ELECTROLYTIC, MILLED 7440-47-3 E 400

21NNAMON G 230

.21TRUS PEEL G 270

7.£)AL, KENTUCKY BITUMINOUS F 180

~OAL, PITTSBURGH EXPERIMENTAL F 170

73OAL, WYOMING F

?,OC~'-)A BEAN SHELL G 370

ZOC£)A, NATURAL, 19% FAT G 240

2OCONUT SHELL G 220

2,OKE/more than 8% total entrapped volatiles) "F

2ORK G 210

~ORN G 250

7£)RN DEXTRINE G 370

CA)RNC£) B GRIT G 240 I

CORNSTARCH, COMMERCIAL G 330

~:ORNSTARCH, MODIFIED G 200

2OTTONSEED MEAL G 200

2,OUMARONE-INDENE, HARD G NL 520

]RAG NO. 974 533-74-4 G CL 310

~UBE ROOT, SOUTH AMERICA 83-79-4 G 230

3I-ALPHACUMYL PEROXIDE, 40-60 ON CA 80-43-3 G 180

3IALLYL PHTHALATE 131-17-9 G M 480

)ICNCLOPENTADIENE DIOXIDE G NL 420

31ELDRIN (20%) " 60-57-1 G NL 550

31HYI)ROACETIC ACID G NL 430

3IMETHYL ISOPHTHALATE 1459-934 G M 580

3IMETHYL TEREPHTHALATE 120-61-6 G M 570

DINITRO-O-TOLUAMIDE 148-01-6 G NL 500

DINITROBENZOIC ACID G NL 460

DIPHENYL 92-52-4 G M 630

DITERTIARY-BUTYL-PARACJ(LSO L 12~37-0 G NL 420

DITHANE M-45 8018-01-7 G 180

EPOXY G NL 540

EPOXY-BISPHENOL A G NL 510

ETHYL CELLULOSE G CL 320

ETHYL HYDROXYETHYL CELLULOSE G NL 390

ETHYLENE OXIDE POLYMER G NL 350

ETHYLENE-MALEIC ANHYDRIDE COPOLYMER G NL 540

FERBAM T M 14484-64-1 G 150

~ERROMAN(-;ANESE, MEDIUM CARBON 12604-534 E 290

?ERROSILICX)N/88% Si, 9% Fe) 8049-17-0 E 800

?ERROTITANIUM t19% Ti, 74.1% Fe, 0.06% C) E CL 380

;'LAX SHIVE G 230

FUMARI C ACI D 11 0-17-8 G M 520

348

N F P A 4 9 7 B m A 9 7 R O P

Layer or Cloud

NEC Ignition Temp

CHEMICAL NAME CAS # Croup Code °C

C, ARLIC, DEHYDRATED G NL 360

GILSONITE 12002-43-6 F 500

GREEN BASE HARMON DYE G 175

GUAR SEED G NL 500

GULASONIC ACID, DIACETONE G NL 420

GUM, ARABIC G 260

GUM, KARAYA G 240

GUM, MANILA G CL 360

GUM, TRAC, ACANTH 9000-65-1 G 260

HEMP HURD G 220

HEXAMETHYLENE TETRAMINE 100-97-0 G S 410

HYDRO XYETHYL CELLULOSE G NL 410

IRON, 98% H 2 REDUCED E 290

IRON, 99% CARBONYL 13463-40-6 E 310

ISOTOIC ANHYDRIDE G NL 700

L-SORBOSE G M 370

LIGNIN, HYDROLIZED, WOOD-TYPE, FINE G NL 450

LIGNITE, CALIFORNIA F 180

LYCOPODIUM G 310

MALT BARLEY G 250

MANGANESE 7439-96-5 E 240

MAGNESIUM, GRADE B, MILLED E 430

MANGANESE VANCID E G 120

MANNITOL 69-65-8 G M 460

METHACRYLIC ACID POLYMER G 990

METHIONINE/L-METHIONINE) 63-68-3 G 360

METHYL CELLULOSE G 340

METHYL M ETHACRYLATE POLYMER 9011-14-7 G NL 440

METHYL METHACRYI_ATE-ETHYL M?,RYLATE G NL 440

M ETHYL M ETHACRYLATE~STYRENE-BUTADIENE G NL 480

MILK, SKIMMED G 200

n ,n,DIM ETHYLTHIO-FO RMAM IDE G 230

NITROPYRIDONE 100703-82-0 G M 430

NITROSAM INE G NL 270

NYLON POLYMER 63428-84-2 G 430

PARA-O XY-BENZALD E HYD E 123-08-0 G CL 380

PARAPHENYLENE DIAMINE 106-50-3 G M 620

PARATERTIARY BUTYL BENZOIC ACID 98-73-7 G M 560

PEA FLOUR G 260

PEACH PIT SHELL G 210

PEANUT HULL G 210

PEAT, SPHAGNUM 94114-14-4 G 240

!PECAN NUT SHELL 8002-03-7 G 210

?ECFIN 5328-37-0 G 200

?ENTAERYTHRITOL 115-77-5 G M 400

PETRIN ACRYLATE MONOMER 7659-34-9 G NL 220

PETROLEUM ODKE (more than 8% total entrapped volatiles F

PETROLEUM RESIN 64742-16-1 G 500

PHENOL FORMALDEHYDE 9003-35-4 G NL 580

349

N F P A 4 9 7 B - - A 9 7 R O P

Layer or Cloud

NEC Ignition Temp ~HEMICAL NAME CAS # Group Code °C

?HENOL FORMALDEHYDE, POLYALKYLENE-P 9003-35-4 G 290

?HENOLFURFURAL 26338-61-4 G 310

?HENYLBETANAPHTHYLAM INE 135-88-6 G NL 680

?HTHALIC ANYDRIDE 85-44-9 G M 650

?HTHALIMIDE 85-41-6 G M 630

?ITCH, COAL TAR 65996-93-2 F NL 710

?ITCH, PETROLEUM 68187-58-6 F NL 630

OLYCARBONATE G NL 710

?OLYETHYLENE~ HIGH PRESSURE PROCESS 9002-884 G 380

?OLYETHYLENE, LOW PRESSURE PROCESS 9002-88-4 G NL 420

?OLYETHYLENE TEREPHTHALATE 25038-59-9 G NL 500

:POLYETHYLENE WAX 68441-04-8 G NL 400

POLYPROPYLENE (NO ANTIOXIDANT) 9003-07-0 G NL 420

POLYSTYRENE LATEX 9003-53-6 G 500

POLYSTYRENE MOLDING COMPOUND 9003-53-6 G NL 560 i

POLYURETHANEFOAM, FIRE RETARDA.NT 9009-54-5 G 390

POLYURETHANE FOAM, NO FIRE RETARDANT 9009-54-5 G 440

?OLYVINYL ACETATE 9003-20-7 G NL 550

POLYVINYL ACETATE/ALCOHOL 9002-89-5 G 440

POLYVINYL BUTYRAL 63148-65-2 G 390

?OLYVINYL CHLORIDE-DIOt'YIYL PHTHALATE G NL 320

?OTATO STARCH, DEXTRINATED 9005-25-8 G NL 440

?YRETHRUM 8003-34-7 G 210

~AYON (VISCOSE) FLOCK 61788-77-0 G 250

~ED DYE INTERMEDIATE G 175

?,.ICE G 220

?,ICE BRAN G NL 490

?,ICE HULL G 220

~:OSIN, DK 8050-09-7 G NL 390

RUBBEP~ CRUDE, HARD 9006-04-6 G NL 350

RUBBER, SYNTHETIC, HARD ~33% S) 64706-29-2 G NL 320

SAFFLOWER MEAL G 210

S A L I ~ I L I D E 8%17-2 G M 610

SEVIN 63-25-2 G 140

SHALE, OIL 68308-34-9 F

SHELLAC 9000-59-3 G NL 400

SODIUM RESINATE 61790-51-0 G 220

ORBIC ACID (COPPER SORBATE OR POTASH) 110-44-1 G 460

OY FLOUR 68513-95-1 G 190

~OY PROTEIN 9010-10-0 G 260

STEARIC ACID, ALUMINUM ,S~T 637-12-7 G 300

STEARIC ACID, ZINC SALT 557-05-1 G M 510

gTYRENE MODIFIED POLYESTER.C, LASS FIBER 100-42-5 G 360

STYRENE-ACRYLONITRILE {70-30) 9003-54-7 G NL 500

;TYRENE-BUTADIENE LATEX (>75% STYRENE) 903-55-8 G NL 440

I u T ~ oNE-MALEI C ANHYDRIDE COPO LYM ER 9011-13-6 G CL 470

SE 57.-50-1 G CL 350

SUGAR, POWDERED 5%50-1 G C_~ 370

SULFUR 7704-34-9 G 220

350

NFPA 4975 ~ A97 R O P

Layer or Cloud

NEC Ignition Temp

CHEMICAL NAME ' CAS # Group Code °C

~ANTALUM 7440-25-7 E 300

IZREPHTHALIC ACID 100-21-0 G NL 680

I'HORIUM, 1.2% O 9 7440-29-1 E CL 280

FIN, 96%, ATOMIZED, t2% Pb) 7440-31-5 E

FITANIUM, 99% TI 7440-32-6 E

430

CL 330

FITANIUM HYDRIDE (95% Ti, 3.8% H 2) 7704-08-5 E CL 480

FRITHIOBISDIMETHYLTHIO-FORMAMIDE G 230

lUNG, KERNELS, OIL-FREE 8001-20-5 G 240

UREA FORMALDEHYDE MOLDING COMPOUND 9011-05-6 G NL 460

UREA FORMALDEHYDE-PHENOL FORMALDEHYDE 25104-55-6 G 240

q'ANADIUM~ 86.4% 7440-62-2 E 490

VINYL CHLORIDE-ACRYLONITRILE COPOLYMER 9003-00-3 G 470

VINYL TOLUENE-ACRYLONITRILE BUTADIENE 76404-69-8 G NL 530

VIOLET 200 DYE G 175

VITAMIN B1, MONONITRATE 59-43-8 G NL 360

VITAMIN C 50-81-7 G 280

WALNUT SHELL, BLACK G 220

WHEAT G 220

WHEAT FLOUR 130498-22-5 G 360

WHEAT GLUTENr GUM 100684-25-1 G NL 520

WHEAT STARCH G NL 380

WHEAT STRAW G 220

WOOD FLOUR G 260

WOODBARK, GROU ND G 250

YEAST~ TORULA 68602-04-8 G 260

ZIRCONIUM HYDRIDE 7704-99-6 E 270

ZIRCONIUM E CL 330

NOTES TO TABLE 2-5: 1 Normally, the minimum ignition temperature of a layer of a specific dust is lower than the minimum ignition temperature of a cloud of that dust. Since this is not universally true, the lower of the two minimum ignition temperatures is listed, lfno symbol appears between the two temperature columns, then the layer ignition temperature is shown. "CL" means the cloud ignition temperature is shown. NL" means that no layer ignition temperature is available, and the cloud ignition temperature is shown. "M" signifies that the dust layer melts before it ignites; the cloud ignition temperature is shown. "S" signifies that the dust layer sublimes before it ignites; the cloud ignition temperature is shown.

2 Certain metal dusts may have characteristics that require safeguards beyond those required for atmospheres containing the dusts of aluminum, magnesium, and their commercial alloys. For examplE, zirconium, thorium, and uranium dusts have extremely low ignition temperatures [as low as 20"C (68~)] and minimum ignition energies lower than any material classified in any of the Class I or Class II groups.

~51

N F P A 497B ~ A97 R O P

Table 2-5.1 Cross-Reference of Chemical CAS Numbers to Chemical Name

# Chemical Name

50-78-2 ASPIRIN [ACETOL (2) 1

50-813 VITAMIN C

57-50-1 SUCROSE

57-50-1 SUGAR, POWDERED

59-43.8 VITAMIN B1, MONON1TRATE

60-57-1 DIELDRIN (20%)

63-25-2 SEVIN

63-68-3 METHIONINE (L-METHIONINE)

65-85-0 BENZOIC ACID

69-65.8 MANNITOL

78-67-1 AZO-BIS-BUTYRONrrRILE

80-05-7 BISPHENOL-A

80-43-3 DI-ALPHACUMYL PEROXIDE, 40-60 ON CA

83-79-4 CUBE ROOT, SOUTH AMERICA

85-41-6 PIITHALIMIDE

85-44-9 PHTHALIC ANYDRIDE

87-17-2 SALI CYI.ANILIDE

92-52--4 DI~HENYL

95-14-7 BENZOTRIAZOLE

97-23-4 B IS (2-HYDR OXY-5-CHLOROP HE NYL) METHANE

98-73-7 PARATERTIARY BUqYL BENZOIC ACID

100-21-0 TEREPHTHALIC ACID

100-42-5 STYRENE MODIFIED POLYEStER-GLASS FIBER

100-97-0 HEXAMETHS.LENE ~ E

101-92.8 CHLOROA~OACErANKJDE

102-01-2 ACETOACETANILIDE

106-50-3 PARAPHENYI~NE DIAMINE

109-31-9 AZELAIC ACID

110-17.8 FUMARIC ACID

110-44-1 SORBIC ACID (COPPER SORBATE OR POTASH)

115-77-5 PENTAERYI'HRITOL

118-92-3 ANTHRANILIC ACID

120-61-6 DIMETHYL TEREPHTHALATE

121-66-4 AMIN O-5-NITROTHIAZOLE

122-82-7 ACETOA CET-P-P HENETID IDE

123-08-0 PARA-O XY-BE N ZALDEHYDE

124-04-9 ADIPIC ACID

128-37-0 D FfERT1ARY-BUTYL-PARACRESOL

131-17-9 DIALLYL PHTHALATE

135-88-6 PHE NYLBETANAPHTHYLAMINE

148-01-6 DINrrRo-O-TOLUAMIDE

533-744 CRAG NO. 974

557-05-1 STEARIC ACID, ZINC SALT

637-12-7 STEARIC ACID, ALUMINUM SALT

Table 2-5.1 Cross-Reference of Chemical CAS Numbers to Chemical Name

CAS # Chemical Name

50-78-2 ASPIRIN [ACETOL (2) 1

50-81-7 VITAMIN C

57-50-1 SUCROSE

57-50-1 SUGAR, POWDERED

5943.8 VITAMIN B1, MONON1TRATE

60-57-1 DIELDRIN (20%)

63-25-2 SEVIN

63-68-3 METHIONINE (L-METHIONINE)

65-85-0 BENZOIC ACID

69-65-8 MANNITOL

78-67d AZO-BIS-BUTYRO NrrRILE

80-05-7 BISPHENOL-A

80-43-3 DI-ALPHACUMYL PEROXIDE, 40-60 ON CA

83-79-4 CUBE ROOT, SOUTH AMERICA

85-41-6 PHTHALIMIDE

85-44-9 PHTHALIC ANYDRIDE

87-17-2 SALICYLANILIDE

92-52-4 DIFHENYL

95-14-7 BENZOTRIAZOLE

97-23-4 BIS (2-HYDROXY-5-CHLOROPHENYL) METHANE

98-73-7 PARATERTIAR¥ BUq'YL BENZOIC ACID

100-21-0 TEREPHTHALIC ACID

100-42-5 fflYRENE MODIFIED POLYESrER-GLASS FIBER

100-97-0 HEXAMETHYLENE qETRAMINE

101-92.8 CHLOROACETOACErAN ILIDE

102-01-2 ACETOACETANILIDE

106-50-3 PARAPHENYLENE DIAMINE

109-31-9 AZELAIC ACID

110-17.8 FUMARIC ACID

110-,t4-1 SORBIC ACID (COPPER SORBATE OR POTASH)

115-77-5 PENTAERYrHRITOL

118-92-3 ANTHRANILIC ACID

120-61-6 DIMETHYL TEREPHTHALATE

121-664 AMIN O-5-N ITR OTHIAZOLE

122-82-7 ACETOACET-P-P HENETID IDE

123-08-0 PARA-OXY-BE NZALDEHYDE

124-04-9 ADIPIC ACID

128-37-0 DITERTIARY-B UIYL-PARACRF~ O L

131-17-9 DIALLYL PHTHALATE

135-88-6 P HE NYIJ?,ErANAPHTHYI.AMINE

148-01-6 DINITRO-O-TOLUAMIDE

533-74-4 CRAG NO. 974

557-05-1 STEARIC ACID, ZINC SALT

637-12-7 STEARIC ACID, ALUMINUM SALT

352

N F P A 4 9 7 B i A 9 7 R O P

CAS # Chemical Name

12604-53-4 FERROMANGANESE, MEDIUM CARBON

13463-40-6 IRON, 99% CARBONYL

14484-64-I FERBAM rM

25038-59-9 POLYETtTIYLENE TEREPHTHALATE

2510455-6 UREA FORMALDEHYDE-PHENOL FORMALDEHYDE

26338-61-4 PHENOL FURFURAL

61788-77-0 RAYON (VISCOSE) FLOCK

61790-51-0 SODIUM RESINATE

6314865-2 POLYVINYL BUTYRAL

63428-84-2 NYLON POLYMER

64365-11-3 (MARCOAL (ACTIVATED)

64706-29-2 RUBBER, SYNTHETIC, HARD (33% S)

64742-16-1 PETROLEUM RESIN

65996-952 PffCH, COAL TAR

68187-58-6 PffCH, PETROLEUM

68308-34-9 SHALE, OIL

68441-04-8 POLYETHYLENE WAX

6851 $95-1 SOY FLO UR

68602-94-8 YEAST, TORIJI.A

76404-69-8 VINYL TOLUENE-ACRYLONrlRILE BUTADIENE

94114-14-4 PEAT, SPHAGNUM

100684-25-1 WHEAT GLUI~N, GUM

100703-82-0 N1TROPYRIDO NE

130498-22-5 WHEAT FLOUR

2-6 Ignition o f Dust Clouds.

2-6.1 The electrical equ ipm en t enclosure prevents the dus t cloud from being ignited by arcing and sparking parts or o ther ignition sources within the enclosnre.

2-6.2 The dus t cloud may be ignited by ho t snrface temperatures .

2-6.3 Some dusts that are no t normally combust ible may form explosive dus t clouds when mixed with a f lammable gas. See 2-2.2 for discussion on hybrid mixture.

2-7 Ignition of Dust Layers.

2-7.1 The ignition t empera tu re of a dus t layer is a f imc t ion of the type of dus t and its pltysical and chemical propert ies and is often less than the cloud ignition temperature . T he ignition tempera ture shown in Table 2-5 is the lower of the two.

2-7.2 The ignition ternperatnre of a layer of dus t on heat -producing equ ipmen t may decrease over t ime if the dus t dehydrates or carbonizes. For this reason, the beat -producing e q u i p m e n t should no t exceed the lower of ei ther the ignitio~ t empera tu re or 165°C (329°F).

2-7.3 Some dusts in layers may melt before reaching their layer ignition temperatures . This mel ted material may then act more like a combustible liquid than a dust.

2-7.4 Other dusts, such ,as some polymers, degrade to a lower molecular weight material or to the m o n o m e r itself. This may act more like a f lammable liquid than a dust.

2-7.5 Materials such as unplasticized polyvinyl chloride, sulfur, and zinc stearate melt, but cause only ma in tenance problems.

2-7.6 An ignited dus t layer in t roduces an open flame ignition source that can ignite a dus t cloud in the vicinity and may also stir up the dus t layer, creat ing a dus t cloud.

Chapter 3 Classification o f Class II (Combust ible DusO Locations

The decision to classify an area as hazardous is based upon the probability that a combustible mixture may be present. Having decided that an area should be classified, the nex t step is to de te rmine the degree of hazard: Is the area Division 1 or Division 2?


3-1.1 f f a dus t cloud is likely to be present unde r normal conditions, the area should be classified as Division 1.

3-1.2" ff a dus t layer greater than 1 /8 in. thick is present unde r normal conditions, the area should be classified as Division 1.

3-1.3 "Normal" does not necessarily mean the situation that prevails when everything is working properly. For instance, i fa bucket elevator requires f requen t main tenance and repair, this repair should be viewed as normal. If quanti t ies of ignitable dust are released as a result of the maintenance , the area is Division I. However, if that elevator is replaced and now repairs are not usnally required between turnarounds , the need for repairs is considered abnormal . The classification of the area, therefore, is related to equ ipmen t maintenance , both procedures and frequencies. Similarly, if the problem is the bui ldup of dus t layers without the presence of visible dust suspensions, good, f requen t cleaning procedures or the lack thereof will inf luence the classification of the ~A-ea.


3-2.1 The criterion for a Division 2 area is whether the area is likely to have ignitable dus t suspens ions or hazardous dus t accumulat ions only u n d e r abnormal conditions. The te rm "abnormal" is used bere in a l imited sense and does no t include a major catas~ophe.

3-2.2 As an example, consider the replaced bucket elevator of 3-1.3, which releases ignitable dus t only unde r abnormal conditions. In this case there is no Division 1 area because the elevator is normally tight. To release dust, the elevator would have to leak, and that would not be normal .

3-2.3 Chemical process equ ipmen t does not fall often. Fur thermore, the electrical installation r equ i r emen t of the NEC for Division 2 areas is such that an ignition-capable spark or hot surface will occur only in the event of abnormal operat ion or failure of electrical equipment . Otherwise, sparks and ho t surfaces are not present or are contained in enclosures. On a realistic basis, the possibility of process equ ipmen t and electrical equ ipmen t failing s imultaneously as remote.

3-2.4 The Division 2 classification is applicable to condit ions not involving equ ipmen t failure. For example, consider an area classified as Division 1 because of normal presence of ignitable dus t suspension. Obviously, one side of the Division 1 boundary cannot be normally hazardous and the opposite side never hazardous. Similarly, consider an area classified as Division 1 because of the normal presence of hazardous dus t accumulat ions. One side of the division boundary cannot be normally hazardous, with thick layers of dust, and the other side nonhazardous , with no dust, unless there is an intervening wall. W h e n there is no wall, a su r round ing transition Division 2 area separates a Division I area f rom an unclassified area.

3-2.5 Walls are m u c h more impor tan t in separat ing Division 1 areas f rom Division 2 and unclassified areas in Class II areas than in Class I areas. Only unpie rced solid walls make satisfactory barriers in Class I areas, while closed doors, lightweight partitions, or even partial partitions may make satisfactory walls between Class II, Division 1 areas and unclassified areas. Area classification does not extend beyond the wall, provided it is effective in prevent ing the passage of dus t in suspension or layer form.

3-5 Unclassif ied Areas.

3-3.1 Experience has shown that the release of ignitable dus t suspensions f rom some operat ions and apparatus is so inf requent tha-t area classification is no t necessary. F-or example, , i t is usually not necessary to classify the following areas where combustible dusts are processed, stored, or handled:

(a) Areas where materials are s tored in sealed containers, e.g., bags, drums, or fiber packs on pallets or racks;

(b) Areas where materials are t ranspor ted in well-maintained closed piping systems;

(c) Areas wbere palletized materials with minimal dust are bandied or used;

353

N F P A 4 9 7 B - - A 9 7 R O P

(d) Areas where closed tanks are used for storage and handling;

(e) Areas where dust removal systems prevent 1) visual dust clouds, and 2) layer accumulations that make surface colors indiscernible (see A-3-1.2);

(f) Areas where excellent housekeeping prevents 1) visual dust clouds, and 2) layer accumulations that make surface colors indiscernible (see A-3-1.2).

3-3.2 Dust removal systems that are provided to allow a nondassif ied area should have adequate s,'ffeguards and warnings against failure.

3-3.3 Open flames and hot surfaces associated with the operation of certain equipment, such as boilers and fired heaters, pro',;ide inherent thernlal ignition sources. Area classification is no t appropriate in the tmmediate vicinity of these facilities. Dust cohmining operations should be cut off by blank walls or located away from such facilities. Where pulverized coal or ~round-up solid waste is used to fire a boiler or incinerator, it is p rnoen t to avoid installing electrical equipment that could become primary ignition sources for leaks in die fuel feed lines. - - -

3-4 Extent o f Classified Areas.

3-4.1 Careful consideration of the following factors is necessary in de termining the extent of the areas:

( a ) Combustible material involved;

(b) Bulk density of the material;

(c) Particle sizes of tile material;

(d) Particle densit~

(e) Process or storage pressure;

(0 Size of the leak opening;

(g) Quantity of file release;

(h) Dust removal system;

(i) Housekeeping;

(j) Presence of any hybrid mixture.

3-4.2 The dispersal of dusts and tile influence of the above factors on this dispersal were discussed generally in Sections 2-2, 2..4, 2-5, 2- 6, and 2-7. The impo~ 'mce of dust removal and housekeeping were discussed in other paragraphs of this chapter.

3-4.3 In addition, walls, partitions, enclosures, or other barriers and strong air currents will also ,affect the distance that dust particles will travel and the extent of the Division 1 and Division 2 areas.

3-4.4 Where there are walls that limit the travel of tile dust particles, area classifications do not extend beyond die walls. Providing walls and partitions is a primary means of limiting the extent of hazardous a r e a s .

3-4.5 Wilere effective walls are not provided, the extent of the Division 1 and Division 2 areas can be estimated as follows:

(a) By visual observation of the existing area using the guidelines of A-3-L2;

(b) By experience with similar dusts and similar operations, and by taking into consideration differences in equipment, enclosures, dust remo~ml systems, and housekeeping rules f indmethods;

(c) By using the classification diagrams in dais chapter.

3-4.6 Tight equipment, ventilated hoods and pickup points, good maintenance, and good housekeeping practices should limit Division 1 areas to i]lose inside of pro/ze-ss enclosures and equipment and close to openings necessary for transfer o f material, as fro/n conveyors to grinder-s to storage bins to bags. Similarly, tile same factors will also limit the Division 2 area surrounding the Division 1 a r e a .

34.7 The size of a building and its walls will influence the classification of die enclosed volume. In the case of a small room, it may be appropriate to classify the entire volume as Division 1 or Division 2.

34.8 When classifying large buildings, careful evaluation of prior experience with the same or similar mstallations should be made. Where experience indicates that a particular design concept is sound, continue to follow it. Sound eng inee r lng judgmen~and ~ood housekeeping should be used to rhinimize-the extent of nazardous areas.

3-4.8.1 Wherever possible with large buildings, walls should be used to cut off dusty operations to minimize the hazardous area. Where walls are no t possible, use the concentric volume approach of a Division 1 area surrounded by a larger Division 2, as shown in the diagrams.

3-4.8.2 Where it is necessary to have a number of dusty operations located in a building, there could be a multiplicity of Division 1 areas, with intervening Division 2 and unclassified areas.

5-4.9 The quantity of dust released and its distance of travel is of extreme importance in determining file extent of a hazardous area. This determinat ion requires sound engineering judgment . However, one cannot lose sight of the purpose of this judgment ; the area is classified solely for the installation of electrical equipment.

3-5 Discussion o f Diagrams and Recommendations .

3-5ol This chapter contains a series of diagrams that illustrate how typical dusty areas should be classified and the r ecommended extent of classification.

3-5.2 The in tended use of the diagrams is to aid in developing electrical classification maps of operating units, storage areas, and process buildings. Most of the maps will be plan views. However, elevations may be necessary to provide the three-dimensional picture of an actual operation.

3-5.3 An operating unit may have many interconnected sources of combustible material such as storage tanks, bins and silos, piping. and ductwork, hammer mills, ball mills, grinders, pulverizers, milling machines, conveyors, bucket elevators, and bagging or other

~ ackaging machines. These in turn present sources of leaks such as anged and screwed connections, fittings, openings, valves, and

metering and weighing devices. Thus, actual diagrams of the eq pui men t may be. eqr uired so that. tile necessary., engineering... j udgmen t to estabhsh the boundaries of Dwtsion 1 and Dlvmon 2 areas may be applied properly.

3-5.4 These diagrams apply to operating equipment processing dusts when thq specific particle density is greater than 40 Ib /cu ft (640.72 kg / m° ) . When d~sts with a specific particle density less than 40 Ib /cu ft (640.72 k g / m o) are being handled, there is a pro- nounced tendency for the fine dust to drift on air currents normally Pthresent in industrial plants for distances considerably farther than

ose shown on these diagrams. In those cases it will be necessary to extend file classified area using sound engineer ing j udgmen t and experience.

3-5.5 Good engineer ing practices, good housekeeping practices, and effective dust removal systems are necessary to limit the extent of file classified areas and to minimize the chances of primary and, the often more violent, secondary explosions.

3-6 Procedure for Classifying Areas.

Tile following procedure should be used for each room, section, or area being classified.

3-6.1 Step One I Need for Classification. The area should be classified if the answer to the following question is "Yes."

(a) Is a COMBUSTIBLE DUST likely to be present?

3-6.2 Step Two - - Assignment of Division Classification. Assuming an affirmative answer to Step One, the followingquestions should be answered to determine the correct division classification.

3-6.2.1 Division 1 areas are distinguished by a Wes" answer to any one of the following questions:

(a) Is a Group E dust present in hazardous quantifies?

(b) Is a dust likely to be in suspension in air continuously, periodically, or intermittently under normal conditions in quantities sufficient to produce an ignitable mixture?

(c) Will mechanical failure or abnormal operation of machinery or equipment cause such an ignitable mixture to be produced, and might it also provide a source of ignition through simultaneous failure of electrical equipment operation of protective devices or f r o m other causes?

(d) Are there dust layers or accumulations on surfaces deeper than 1 /8 in. (3 ram)?

354

Plan View

3-6.2.2 Division 2 areas for Group F or G dusts are distinguished by a Wes ~ answer to any of file follofving questions:

(a) Is die dust not normally in suspension in file air in quantities sufficient to produce an ignitable mlxture, but could it bd thrown into suspension by infrequent malfunctioning of handling or processing equipment?

(b) Are the dust accumulations insufficient to interfere with file normal operation of electrical equipment, but could the accumulations be ignited by the abuormal-ogieration or failure of electrical equipment?

(c) Is there a dust layer that makes the colors of the surfaces indiscemi bl e?

(d) Would failure of the dust removal system allow an ignitable suspension of dust or a layer deeper than 1 /8 in. (3 ram) to accumulate?

3-6.3 Step Three - - Extent o f Classified Area. The extent of the classified area may be de termined byapplying, with sound engineer- ingjudgment , the mefllods discussed in 3-4 and the diagrams contained in this chapter.

3-7 Classification Diagrams.

This section contains classification diagrams. These diagrams assume that f l~ specific particle density is greater than 40- Ibs/cu ft (640.72 kg /m°) .

Plan View

Source

Elevation View

N Division 1 ~ Division 2

Nonclassified

Source

N F P A 4 9 7 B - - A 9 7 R O P

Elevation View

Source

~ D i v i s i o n 1 [ ~ ] D i v i s i o n 2

Description of Dust Condition

DIVISION 1 ADDITIONAL DIVISION 1

Moderate or dense dust cloud Dust layer less than I/8 in. (3.18 or dust layer greater than ram) and surface color not dis- I/8 in. (3.18 mm). cernible.

Figure 3-7.2 Group E dust - - indoor, unrestricted area, open or semlenclosed operating equipment.


DIVISION 1 DIVISION 2

No visible dus t c loud. Dust Moderate or dense (:lust cloud, layer less than 1/8 in, (3.18 mm) Dust layer greater than I/8 in. and surface color not discern- (3.18 ram). ible.

Figure 3-7.1 Group F or Group G dust - - indoor, unrestricted area, open or semienclosed equipment.

355

Plan View

~ 0 ~ Source

Elevation View

/~/ Source

onclassified

[ ~ Division 1 [ ~ Division 2



None No visible dus t cloud. Dust layer less than 1/8 in. (3.18 ram) and surface coh)r notdiscernible.

Plan View

rce

Elevation View ~ rce

E Division 1 ~ Division 2

Figure 3-7.3 Group F or Group G dus t - - indoor, unrestricted area, operating equipment enclosed.

Source


DIVISION 1 DIVISION 2 NONCLASSIFIED

None None Surface color discernible.

Figure 3-7.4 Group F or Group G dust - - indoor, unrestricted area, operating equipment enclosed.

N F P A 4 9 7 B I A 9 7 R O P


DIVISION 1 DIVISION 2 NONCLASSIFIED

None None Dust layer not apparen t . Surface color discernible.

Figure 3-7.5 Groups E, F, or G dusts - - s torage area bags, d rums, or closed hoppers .

356

NFPA 497B - - A97 R O P

Nonclassified .~

Div. 1 10' In All Directions

ource

Plan View

Wall or Source Partition with all Openings Kept Closed

Elevation View

~ D i v i s i o n 1 ~ D i v i s i o n 2

Description of Dust Condition Minimize Division 1 Cutoff Volume and Area

Description of Equipment/Area Control Maximize Confinement Maximize Dust Control

Maximize Housekeeping See ~ - 5 , ~

Figure $-7.6 Group E d u s t - inside walled-off area; operating equipment enclosed.

357

N F P A 4 9 7 B - - A97 R O P

Wall Or Closed Partitions Source

10' In All Directions

Nonclassified Plan View

~ Division 1 ~ Division 2



No visible dust cloud. Dust layer less Moderate to dense dust cloud or dust than q8 in. (3.18 ram) but surface color layer greater than 1/8 in. (3.18 ram). not discernible.

Figure 3-7.7 Group F or Group G - - indoor, walled-off area; multiple operating equipment.

Source Source Nonclassified

Plan View

Wall Or Closed Barrier i Division 1 ~ ' ~ Division 2

and Self-closing Doors



No visible dust cloud. Dust layer less Moderate to dense dust cloud. Dust than I/8 in. (3.18 mm) and surface color layer greater than I/8 in. (3.18 mm). not discernible.

Figure 3-7.8 Group F or Group G - - indoor, walled-off area; multiple operating equipment.

358

N F P A 4 9 7 B ~ A 9 7 R O P

Nonclassified

Plan View

~ D i v i s l o n I ~'-~Division2



No visible dus t cloud. Dust Moderate to dense dus t cloud layer less than I/8 in. (3.18 or dus t layer greater than I/~ ram) and surface color not in. (3.18 ram). discernible.

Figure 3-7.9 Group F or Group G - - indoor, unrestr icted area; ventilated bagging head.

Chapter 4 Referenced Publications

4-1 The following documen t s or port ions thereof are referenced within this r e c o m m e n d e d practice and should be considered part of the recommencLxtions of this document . The edit ion indicated for each reference is the cur ren t edit ion as of the date of the NFPA issuance of this document .

4-1.1 NFPA Publications. National Fire Protection Association, 1 Batterymarch Park, P O . Box 9101, Quincy, MA 02269-9101.

NFPA 70, NatitmalElectrical Code, 1996 edidon.

NFPA 325, Guide to Fire Hazard Properties of Flammable Liquids, Gases, and Volatile Solids, 1994 edition.

4-1.2 ASTM Publication. Amer ican Society for Test ing and Materials, 1916 Race Street, Philadelphia, PA 19103.

ASTM D 3175, Standard Test Method for Volatile Matter in the Analysis Sample of Coal and Coke, 1989.

Where Group E dusts are present in hazardous quantifies, there are only Division 1 areas. The NEC does not recognize may Division 2 areas for such dusts.

A-I-3 Combust ible Dust. Prior to the 1981 edition of NFPA 70, NationalElectrical Code (1978 and prior editions), ,all Group E (metal dusts such as a luminum, magnes ium, and their commercial alloys) and Group F (carbonaceous dusts such as carbon black, charcoal, or coke dusts having more than 8 percen t total volatile materials) were considered to be electrically conductive. As a result, areas containing Group E or Group F dusts were all classified Division 1, as required by the definit ion of a Class II, Division 1 area. It was only possible to have a Division 2 area for Group G dusts.

The 1984 edition el iminated Group F altogether. Carbonaceous dusts with resistivity of less than 10 ohm-cm were considered conductive andewere classified as Group E. Carbonaceous dusts with resistivity of 10 ~ ohm-cm or greater were considered nonconduct ive and were classified as Group G. This reclassification allowed the use of Gro.uj~ G, Division 2 electrical equ ipmen t for many carbonaceous materials.

Appendix A Explanatory Material

This Appendix is not a part of the recommendations of thls NFPA document but is included for informational purposes only.

A-1-2.4 Electrical installations for Class II, Division 1 areas are des igned and enclosed in a m a n n e r tha t excludes ignitable amoun t s of dusts and prevents arcs, sparks, or ho t surfaces f rom igniting exterior dus t layers or suspensions .

Electrical installations in Class II, Division 2 areas may be des igned with dust-t ight enclosures or o ther equ i pmen t enclosures as specified in Article 502.

Electrical installations for classified areas may be des igned in various manners . No single m a n n e r is best in all respects for all types o fe .qu ipment used in a chemical, plant.. Dust-ignit ion-proof e l e c t r i c a l . . eqmpmen t , pressurized electrical e q m p m e n t , and inmnslcal ly safe electrical equ ipmen t are applicable to both Division 1 and Division 2 areas. O the r dust-t ight e q u i p m e n t enclosures, as specified in Article 502 of NFPA 70, NationalElectrical Code, are permi t ted in Division 2 areas. Nonsparking electrical e q u i p m e n t and o ther less restrictive equipment , as specified in NFPA 70, NationalElectrical Code, are permit ted in Division 2 areas.

The 1987 edition of NFPA 70, Nat ionalElec~al Code, reinstated Group F because the close tolerances in Group E motors necessary for metal dusts are unnecessary for conductive carbonaceous dusts, and the low tempera tu re specifications in Group G equ ipmen t necessary for grain, flour, and some chemical dusts are unnecessary for nonconduct ive carbonaceous dusts. This imposed an unwar- ranted expense on users.

This change allowed the use of Group F, Division 2 electrical equ ipment for carbonaceous dus t with a resistivity greater than 105 ohm-cm.

Tile problem with this work was that the resistivity value, a n u m b e r that related to the dust ' s ability to conduc t an electric current, was no t a constant and varied considerably based on dus t particle size and extent of oxidation, the moisture content , voltage applied, temperature , a n d test apparatus and technique. No standardized test m e t h o d for the resistivity value consider ing long-term environmenta l effects has been developed. Finally, the resistivity value is no t directly related to file explosion hazard.

A-I-3 Explosion Severity and Ignition Sensitivity. The U.S. Bureau of M i n e s h a s def ined ignition sensitivity and explosion severity as follows:

359

N F P A 4 9 7 B ~ A 9 7 R O P

PmaaxP)2 E×P,.os oN SEVER

(Tc x E X M c ) l IGNITION SENSITMTY ¢

(Tc × E × Mo)Z

where Pmax = m a x i m u m explosive pressure;

P = m a x i m u m rate of pressure rise;

T c = m i n i m u m ignition temperature ;

E = m i n i m u m ignition energy;

M c = m i n i m u m explosive concentrat ion.

Subscript 1 refers to the appropriate values for Pit tsburgh seam coal, flae s tandard dus t usectby the U.S. Bureau of Mines.

Subscript 2 refers to the values for the specific dust in question.

NOTE: Units mus t be consistent in both numera to r s and denominators .

A-2-2.2 The presence of f lammable gas in a combustible dus t cloud drastically reduces the ignition energy. The f lammable gas n e e d no t be present in a m o u n t s sufficient to reach the lower f lammable limit (consider ing file gas phase alone) to exhibit dais p h e n o m e n o n .

A-2-3 O p e n flames and welding and cut t ing operat ions have far more energy and heat than most electrical fault sparks and arcs and are quite capable of ignit ing dusts. Hot surfaces such as those in some beaters, or those caused by con t inuous friction, may also have sufficient hea t to ignite dusts. Such sources of ignition shou ld therefore be carefully controlled.

A-2-3.1.2 When subjected to heat, dusts of the rmose t t ing plastics, such as phenol formaldehyde resins, t end to polymerize ("set up") and become hard. Con t inued heat bui ldup in the polymerized material ult imately leads to carbonization (degradat ion) of the material and a significantly lower i6nition temperature . While this p h e n o m e n o n is well known, there Js no s tandardized test to define the precise parameters . Nonplast ic materials such as sugar, cornstarch, ,and dextr ine also carbonize and ignite at lower than expected temperatures .

A-2-5.2 Tile materials, and their g ronp classifications, listed in Table 2-5, have been taken f rom Classification of Combustible Dusts in Accordance with the Natlomll Elec, trical Code, NMAB 353-3, publ ished by the National Academy of Sciences. Dusts having ignition sensitivities equal to or greater than 0.2, or explosion severities equal to or greater than 0.5, are listed. Dusts whose explosibility parameters fall below these limits are not generally considered to be significant explosion hazards and are, therefore, no t included in dais table. Selection of electrical eq t t ipment for dusts that subl ime or mel t below the operat ing t empera tn re o f the e q u i p m e n t requires addit ional considerat ion of the propert ies of the specific dust. Electrical equ ipmen t evaluated and found acceptable for use in dae presence of dusts may not be acceptable when exposed to mol ten material.

A-3.1.2 Generally speaking, the NEC indicates tha t (a) if there are explosive dus t clouds unde r normal opera t ing conditions, or (b) if such explosive dus t clouds can be p roduced at the s.'m~e t ime tha t a source of ignition is p roduced , then the area is a Division 1 area. The dus t in (b) c~m be provided directly by some malfunct ion of machinery or e q u i p m e n t or can be provided by accumula t ions of dus t that are thrown into the ,air. Presumably, if all the dus t on all surfaces in a room is sufficient to p roduce a dns t concentra t ion above file m i n i m u m explosive concentrat ion, t hen tha t quant i ty of dus t should def ine a Division 1 area.

From a practical point of view, a room with a concent ra t ion of dus t that is above die m i n i m u m explosive concent ra t ion [criterion (a)] results in an a tmosphere so dense tha t visibility beyond 3 ft to 5 it (0.9 m to 1.5 m) is impossible. Such a condit ion is unacceptable u n d e r today's s tandards for chemical plant workplaces. If such a si tuation were encounte red , accumula t ions on horizontal surfaces would build up very rapidly.

O n the o ther hand , working back f rom dus t layers on horizontal surfaces in a room to a m i n i m u m explosive concent ra t ion in the

360

room, based on laboratory dust explosion tests, shows a very thin layer of dus t in the order of 1/84 in. (0.3 ram) to be hazardous. This is an equally impractical answer, since one of the most difficult exper imenta l problems in dus t explosion test work is to obtain a reasonably un i fo rm cloud for ignition. As a result, tile test apparatus is des igned specifically to obtain uni form dus t distribution. For dust lying on horizontal surfaces in a room or factory to attain such an efficient un i form distribution dur ing an upset condit ion is obviously impossible.

A typical calculation considers cqrnstarch with a powder bulk density of approximately 2~ Ib/ i t" . The m i n i m u m explosive concent ra t ion is 0.04 oz/ i t" . In a room 10 ft (3.05 m) high by 10 ft (3.05 m) wide by 10 ft (3.05 m) long, calculate the dep th of dus t that would accumula te on the floor if the r oom were completely filled with a cornstarch cloud at the m i n i m u m concentrat ion.

3 1 lb 1 ft 3 3 x l 0 0 0 f t x I x I = 0 . 1 f t o f d u s t on the floor

l___ft . . . . . 16 oz 25 Ib . . . . . .

Evenly distr ibuted over 100 sq it, the depth of dus t would be:

0 7 D . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . - 0 . 0 0 1 f t = 0 .012 in. ( 1 / 8 4 in. th ick)

Theoretically, throwing this a m o u n t of dus t f rom the floor and ledges into file room volume would create a hazardous condition. Accompl ishing such a feat, even experimentally, would be virtually impossible.

The op t imum concentra t ion is that in which the m a x i m u m rate of pressure rise is obtained u n d e r test condit ions. Since the op t imum concentra t ion is far h igher than the m i n i m u m explosive concentra- tion, the layer thicknesses necessary to produce an op t im u m concentra t ion are f rom 0.075 in. to 0.5 in. (1.9 m m to 12.7 ram). There is t hen m u c h more dus t available to be thrown into uni form suspens ion without postulat ing a 100 percen t efficiency of dispersal anddis t r ibu t ion . In addition, there are a n u m b e r of factors such as particle size and shape, moisture content , uniformity of distribution, etc., that negatively affect the susceptibility of a dus t to ignition. Thus, dusts encoun te red in industrial plants t end to be less susceptible to ignition than those used in the laboratory to obtain explosion concent ra t ion data. The following classifications of areas are r e commended , based on a bui ldup of the dus t level in a 24-hr ~eriod on the major port ions o f the horizontal surfaces.

Thickness o f Dus t Layer Classification

Grea ter t h a n 1 / 8 in. (3 ram) Division 1

Less t h a n 1 / 8 in. (3 m m ) , b u t sur face Division 2 color no t discernible

Unclassif ied Surface color discernible u n d e r t he dus t layer

Based on these thicknesses of dust, good housekeep ing can de te rmine the difference between a classification of Division 1 and a classification of Division 2, and a classification of Division 2 and unclassified. It should be emphasized, however, that housekeep ing is a s u p p l e m e n t to dus t source el imination and ventilation, h is no t a primary me thod of dus t control.

The following table shows tiae theoretical thickness of dus t on the floor of a 10 ft (3.05 m) x 10 ft (3.05 m) x 10 ft (3.05 m) room necessary to satisfy the concentra t ion requ i rements for a uni form dus t cloud of m i n i m u m explosive concentra t ion and for a uni form dus t cloud of o p t i m u m concent ra t ion for four dusts.

Table A-3-1.2

VIaterial Minimum Depth of Optimum Depth of ]ulkDensiq

Conc. oz/ft 3 Dustin. Gonc. oz/ft ~ Dustin. lb/ft 3-

2omstarch 0.04 0.012 0.5 0.15 25-50

2ork 0.035 0.022 0.2 0.125 12-15

~uKar 0.045 0.0068 0.5 0.075 50-55

aood Flour 0.035 0.016 1.0 0.47 16-36

?olyethylene 0.020 0.0072 0.5 0.180 21-35

Low Density)

NFPA 497B- - A97 ROP

Appead~ e e~bnography

This Appm~ ~ not a pavt of tht r ~ of this NFPA ~

each ~ ~ the c,,'wnt ~ as of the date of th~ NFPA issuance of this dacurnen~

B-| ~ Publications. American Sodety for Testing and Materiah, 1916 Race Street, Philadelphia, PA 19103.

ASTM E 789, Standard Test Method for P n m ~ and Rate of Pressure Rise for Dust Explosions in a Closed Vessel 1989.

ASTM D 3175, Standard Test Method for Volatile Matter in the A Sample of Cbal and ~ 1989.

B-2 Bureau of Mines Publications. U.S. Government Printing Office, Washington, DC 20402.

R15624, Laboratory Equipment and Test Proc~ures for E ~ n g Explasibili~ of Dusts.

g15753, E ~ t o ~ of A g , ~ , ~ t ~ .

RI 5971, F_.~p/os/b///9 of Dusts Used in the Plastics t~ulustr).

RI 6516, F_,xp/os/b//~y of Melal Powders.

gl 6597, ~ t y ofC, a~nacw~D~ts.

RI 7009, Minimum Ignition Energ~ and Qtwnd6ng Distan~ i~ Gacams Mixtu~

RI 7132, Dust E~losibilig of ~ . Drugs, D,3es, and Pe~idde~,

RI 7"208, E~losi&'~ty of Misc.e~nams Dus~

B ~ NFPAPubfications. National Fire Protection Amodation, 1 Ratterymarch Park, P.O. Box 9101, Quincy, MA 0'2'209-9101.

NFPA 36, StandardforSol~ntF~tractlonPiant~ 1993 edition.

NFPA 61, Standard for the ~ of Fir~ and Dust Explosknu in Ag~cu/tura/and FoodProdu~s Fad//6~, 1905 edition.

NFPA 65, Standard for the Proemsing and Finishing of Alumimu~ 1993 edition.

NFPA 68, Guide for Venting ofDeflagration~ 1994 edition.

NFPA 69, Standard on F~/os/on F~mt /on S y s t ~ 199~ edition.

NFPA 70, N a g o n a l ~ Code, 1996 edition.

~WPA c~0, ~ n d a r d ~ P,~..,,~u~ con,,~ng s . ~ f o r ~=nd~ Combm~/~ato /a& 1990 edition.

A 651, Standard for tl~ Manufacture of Aluminum Powder, 1993 edition.

NFPA 654, Standard for tl~ ~ of Fire and Dust Expk~ons in ti~ D~t P ~ a n d P k ~ Indum/~ 1994 edition.

NFPA 655, Standard for ~ of Sulfur Fims and Exploslon& 1993 edition.

NFPA fi64, Standard fir," the Pmumtion of Fires and Explosions in Wood and W ~ Fadlities~ 1993 edition.

11-4 National Academy of Sdences Pubfication. National Materials Advisory Board of the NationalAcademy of Sciences0 2101 Constim. tion Avenue, NW, Washington, DC 20418.

NMAB 353-1, Mal~ix of Combustion-Rd~ant P ~ and Classific~- of C.a~ vq~,n, and ~ sotiaL

NMAB 353-2, Test Equ/pm~afor Use in D~erra~ning Classifications of Comb~6ble Dustt _

NMAB 353-3, ~ f i c a t i o w o f Combus6blt Dusts in Acoordanc~ tuith the N a t l o n a l ~ C o d ~

B-6 Other PublkationL

Miron, Yael and l .zzza~ C~P., "Hot Surface lgaition Temperatures of Dust Layers," F/re and Mater/a/s, Volume 12, ]988, pp 115~-126.

Appm~x ¢

This recommended practice is not intended, to mpentede or conflict with applicable requirements of the following NFPA s t a n ~ .

NFPA 36, Standard for Sol~mt F~tmc6on Plants, 1993 edition.

NFPA 61, 5ta, utard for the ~ of Fires and Dust F~losions in A ~ m l a n d F o o d P m d u c t s F a d l i 6 ~ 1995 edition.

NFPA 65, Standard for ths P m c e u ~ and Finishing of Alumlnura, 1993 edition.

NFPA 68, Gnide for ]&~ing of D ~ a t i o n s . 1994 edition.

NFPA 69, Standard on EkploFum Pwoention Systons, 1992 edition.

N~A 650, Sta~ard for P~u~=~ Con~/ng Sgs~/o , HandUng Combmt/ /~ Mato/a/s, 1990 edition. " _

NFPA 651, Standard for Manufacture Of Aluminum Powder. i 993 edition.

~PA ~4, St=u~,rd~ t~ ~ ~ r e and D=t ~ in Ckem/m/, D~, P ~ and Pktst~s.l, tdustr/a, 1994 edition.

NFPA 655, Standard for ~ of Su/fur F'rres and E xp/os:unu, 1993 edition.

NFPA 664, Standard for the ~ of Fires and Explosions in Wood ~ n g and W ~ F a d / / t / e s , 1993 edition.

861

N F P A 4 9 7 M i A 9 7 R O P

PART III

(Log #CP1 ) 497M- 1 - (Entire Document): Accept SUBMITTERa Technical Committee on Electrical Equipment in Chemical Atmospheres, RECOMMENDATION: The Technical Committee on Electrical Equipment in Chemical Amaospheres recommends the withdrawal of NFPA 497M, Manual for Classification of Gases, Vapors, and Dusts for Electrical Equipment in Hazardous (Classified) Locations, 1991 edition. SUBSTANTIATION: Tiffs is one of three proposals, developed by the Electrical Equipment in Chemic~al Atmospheres (EECA) Ad hoc Task Group consisting of Ed Briesch, Underwriters Laboratories; William Lawrence, Factory Mutual; Richard Masek, Bailey controls; Richard Munson, E.I. DuPont; and David Wechsler, Union Carbide Corp. The EECA Committee directed tile Ad hoc Task Group to evaluate NFPA 497A, B, and M, and to determine if these documents could be developed into two, understood and usable documents. Tiffs study was made and tile results discussed with the membership of file EECA Committee. From that meeting, it was agreed that the Ad hoc Task Group should move forward and combine NFPA 497A, 49713 and 497M, into two documents; one addressing NEC Class I, flammable gases/vapors and combustible liquids, and the other addressing NEC Class II combustible dusts.

This proposal will withdraw NFPA 497M as file material it contains is incorporated into the redesignated NFPA 497 and 499 documents. COMMITrEE ACTION: Accept. NUMBER OF COMMITTEE MEMBERS ELIGIBLE TO VOTE: 24 VOTE ON COMMITTEE ACTION: AFFIRMATIVE: 24

(Log #2) 497M- 2 - (Table 2-3 and, 2-3.1 (New)): Accept in Principle SUBMITTER: Richard F. Schwab, Allied Signal Inc. RECOMMENDATION: New paragraph 2-3.1:

Commercial grades of aliphatic hydrocarbon solvents are mixtures of several isomers of the same chemiGal formula (or molecular weight) . The autoignition temperature, of the. . individual isomers.are signific.antly different. Tile engineer, specifying, the proper electrical classification should select electrical equipment for the tkIT of the solvent mixture.

Example: An engineer is asked to provide the proper equipment for an area

handling a commercial grade of hexane. Reference to Table 2-3 reveals that there are five (5) different isomers of hexane solvent (C6H14) with AIT ranging from a low of 225°C to a high of 405°C. The AIT of the solvent mixtures should be determined either experimentally or from the supplier. It would be expected that the commercial grade of hexane would have an tkIT ranging from 265- 290°C. Selecting the equipment based on tile lowest AIT of the mixture

would be unnecessarily restrictive. (See NFPA 70 (1990), Section 500-3, Table 500-31 ).

Insert the following in Table 2-3:

AIT °E °G 550 288 • _G.halagg Butane to n Butane (C4H10)

Insert 2 methylpropane [isobutane] (C4H10) 860 460 ~dl&tlgg Pentane to n Pentane (C5H12) 470 243 Insert

2 Methyl buKme (isopentane) C5H12 788 420 2,2 Dimethyl propane (neopentane) C5H12 842 450

Hexane to n Hexane (C6H14) 437 225 Insert

2 methylpentane (Isohexane) (C6H14) 507 264 2,2 Dimethylbutane (Neohexane) (C6H14) 761 405 2,3 Dimethylbutane (C6H14) 745 396 3 methyl pentane (C6H 14) 532 278 _Cdlalagg Heptane to n-Heptane (C7H16) 399 204 Insert

2 methyl hexane (C7H16) 536 280 3 methyl hexane (C7H16) 536 280 2,3 dimethyl pentane (C7H16) 635 335 2,2,3 trimethyl butane (G'/H16) 774 442 2,2,4 trimethyi butane (C7H16) 765 407

"Octane to n-Octane" (C8H18) 403 206 Insert

2 methyl heptane (C8H18) 788 420 2,3 dimethyl hexane (C8H18) 820 438 2,2,3 trimethylpentane (C8H18) 745 396

362

SUBSTANTIATION: Presently an engineer specifyingelectrical equipment for an area handling an aliphatic hydrocarbon solvent would consult Table 2-3 of NFPA 497 and find listed only the "normal" isomers of tlaose compounds which in all cases are lowest AIT of the group of isonmers. For example, a commercial grade of llexane would be expected to 95 percent a mixture of C6H14 isomers with the AIT ranging from a low of 225°C to a high of 405°C. The actual mixture ranges from 265°C- 290°C. As a result the engineer would end up specifying (based on the present Table 2- 3) equipment with an identification number of T2D when he really needs T2B or higher. He first has to contend with the problem of availability plus the fact that it really isn't needed. The introduction of this new material in Table 2-3 plus the new material in paragraph 2-3.1 is intended to call this to the engineer's attention. COMMITrEEACTION: Accept in Principle. New Note 5 for Table 2-1 is already incorporated into Proposal

497A- 15 (Log #CP1) to read as follows: "Commercial grades of aliphatic hydrocarbon solvents are mixtures

of several isomers of the same chemical formula (or molecular weight). The autoignition temperature of the individual isomers are significantly different. The electrical equipment shaould be suitable for the AIT of the solvent mixture. See example in A-Table 2-1."

The following example has been inserted into Appendix A to read as follows: "A-2-1, Table 2-1, Note 5. Selecting electrical equipment based on

file lowest AIT shown in Table 2-1 may be unnecessarily restrictive. As an example, in an area handling a commercial grade of hexane, Table 2-1 tabulates five different isomers of hexane solvent (C6H14) with the AIT ranging from a low of 225°C to a high of 405°C. The AIT of tile solvent mixtures should be determined either experimentally or from the supplier. It would be expected tllat the commercial grade of hexane would have an AIT ranging from 265°C to 290°C. " An engineer is asked to provide the proper equipment for an area

handling a commercial grade of hexane. Reference to Table 2-3 reveals that there are five (5) different isomers of hexane solvent (C6H14) with AIT ranging from a low of 225°C to a high of 405°C. The AIT of the solvent mixtures should be determined eidler experimentally or from the supplier. It would be expected that the commercial grade of hexane would have an AIT ranging from 265- 290°C. Selecting the equipment based on tile lowest AIT of the mixture

would be unnecessarily restrictive. (See NFPA 70 (1990), Section 500-3, Table 500-31).

CHANGES TO TABLE 2-1 already incorporated into Proposal 497A- 15 (Log#CP1). COMMIT'FEE STATEMENT: The suggested changes have already been incorporated into Proposal 497A- 15 (Log #CP1).

(Log #!) 497M- 3 - (2-7 (New)): Accept in Principle SUBMITTER; Richard F. Schwab, Allied Signal Inc. RECOMMENDATION: Introduce a new paragraph 2-7.

2-7 Experience has shown that some halogenated liquid hydrocarbons, such as trichloroethylene, 1, 1, 1 trichloroethane, methylene chloride, and 1,1 dichloro 1 fluoroethane (HCFC-141 b) which do not have flashpoints but do have a flammable range, are for practical purposes nonflammable and do not require classified electrical equipment. (Renumber existing 2-7 to 2-8). SUBSTANTIATION: Many of these compounds have had a long history of industrial use as cleaning solvents, and vapor, degr easing operations without providing any classified electrical equipment. Experience has been excellent, simply because the material has a flammable range does not require classified electrical equipment.

Note: Supporting material is available for review at NFPA Headquarters. COMMITI'EEACTION: Accept in Principle. Add semi-coitus after each of the hydrocarbons to read as follows: "

Experience has shown that some halogenated liquid hydrocarbons, such as trichloroethylene; 1, 1, 1 trichloroethane; methylene chloride; and 1,1 dichloro 1 fluoroethane (HCFC-141 b) which do not have flashpoints but do have a flammable range, are for practical purposes nonflammable and do not require classified electrical equtpment." COMMITI'EE STATEMENT: Semi-colons have been added as separators in the sentence for clarity of separation of the specific halogenated hydrocarbons. This text has already been incorporated into Proposal 497A- 15 (Log # CP1) in new Section 3-3.5.

(Log #S) 497M- 4 - (3-3): Reject SUBMITT£Ra John Valiulis, Factory Mutual Research Corp. RECOMMENDATION: Delete Article 3-3. SUBSTANTIATION: The Explosion Severity and Ignition Sensitiv- ity indexes referred to in Article 3.3 are based on Hanmann

N F P A 4 9 7 M - - A 9 7 R O P

apparatus data. This apparatus is no longer in widespread use. Due to the development and increasing use of the 20 liter and larger test spheres over the last decade or so, the Har tmann apparatus is being used less and less. The ~)0 liter (or larger) sphere is currently considered the "state-of-the-arf' in dust explosion testing. The design and use of a 20 liter test sphere are covered by ASTM E1226.

20 liter (or larger) sphere data is the only dam currently used in NFPA 68, Guide for Venting of Deflagrations, as well as other NFPA standards dealing with the hazards of combustible dusts. It appears inappropriate for NFPA 497M to indirectly promote the use of a test me thod by referring to its results, when in fact the method no longer has widespread acceptance. Referring to and explaining the test method ' s results lend that method some degree of credibility which it otherwise might not have.

Although it is requested that the material in 3-3 be removed because it does no t represent the state of knowledge in the field of dust explosions, it is not in tended that the tabulated data presented within this standard be invalidated. The data presented in tile standard thus far is based on tests done in thepast , using a methodology that was at the time well accepted. Basedon the test method used, the criteria o f ignition sensitivity greater than 0.2 and explosion severity greater than 0.5 are no doubt fully valid. However, explaining and presenting of the severity and sensitivity indices would tend to imply that this method would be appropriate for future evaluation of materials.

It may be appropriate for the committee to seek out a new set of criteria for screening current and future explosion test data witicb nses 20 liter (or larger) sphere test data. Setting tllreshold values of Kst (de termined per ASTM E1226) and min imum ignition energy (per the upcoming ASTM smnd.ard being developed by subcommit- tee E27.05) to establish wilether a given material is a significant explosion h.~ard may be one solution. COMMITI'EE ACTION: Reject. COMMITI'EE STATEMENT: There is no technical substantiation in the proposal to delete the defined method of dust ignition sensitivity. The formula in Section 3-3 [new Section A-l-3 in Proposal 497B - 1 (Log #CPI) ] for dust ignition sensitivity is technically necessary to show the origin of the information in the existing Tables. The information in dlese Tables are based upon the Hartmann Apparatus and is still valid information. The explosion severity and ignition sensitivity test can use any size sphere but must be calibrated and compared to be consistent with any previous test apparatus.

(Log #4) 497M- 5 - (3-6, Table 3-6): Accept in Principle SUBMITrER: J o h n M. Mesina, U.S. Depar tment of Labor RECOMMENDATION: Change the listed layer Ignition Tempera- ture of Lycopodium to 374°F (190°C), and reference the source report as "Hot Surface Ignition Temperatures of Dust Layers ", ~ V o l u m e 12, 1988, pp 115-126. SUBSTANTIATION: The 590°F(310°C) Layer Ignition Tempera- ture, Listed in Table 3-6, was repor ted in 1961 in the U.S. Bureau of Mines publication R15753. Exnlosibilitv of A~ricultural Dusts. The temperature was measured us |ng a modified-Godbert-Greenwald furnace, which is described in the U.S. Bureau of Mines publication RI 5624. Laboratory Eauioment and Test Procedures for Ev~uadng Exnlosibilitv of Dusts. (Both publications are listed under B2 in A~'uPendix B of NFPA 497M, 1991)

t in 1988, a significantly lower Layer Ignition Temperature, 374°F (190°C), was measured, using the same type equipmenL This later measurement was reported by Yael Miron and Cimrles P. Lazzara in Hot Surface Ignition Temperatures of Dust Layers, and Materials. Volume 12, 1988, pp 115-126. Also, Yael Miron reconfirms this f inding in the letter i have provided from her to the submitter da tedJune 12, 1995.

Note: Support ing material is available for review at NFPA Headquarters. COMMITI'EEACTION: Accept in Principle.

Change the listed layer Ignition Temperature of Lycopodium to 190°C in Table 2-5 in Proposal 497B - 1 (Lo~[#CP1) and add the following as an addition to Appendix B-5: Other Publications. Yael Miron and Charles P Lazzara, Hot-surface Ignition Temperatures of Dust Layers, Fi re and Materials, Vol. 12, pages 115-126 (1988). COMMITTEE STATEMENT: The Committee has incorporated the change of this information in Proposal 497B - 1 (Log#CP1) and has added the reference to Appendix B in Proposal 499 - 1 (log# CP1).

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