apollo experience report detection and minimization of ignition hazards from water glycol...

8/8/2019 Apollo Experience Report Detection and Minimization of Ignition Hazards From Water Glycol Contamination of Silver-

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N A S A T E C H N I C A L N O T E NASA TN D-8177

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APOLLO EXPERIENCE REPORT - DETECTIONA N D M I N I M I Z A T I O N OF I G N I T I O N H A Z A R D SF R O M W A T E R / G L Y C O L C O N T A M I N A T I O N OFSILVER-CLAD ELECTRICAL CIRCUITRYW, Richard DownsLyndon B. Johnson Sdce CenterHouston, Texas 77058N A T I O N A L A E R O N A U TI C S A N D S PA CE A D M I N I S T R A T I O N W A S H I N G T O N , D. C. MARCH 1976


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1 Report No 2 Government Accession NoN A S A T N D-8177

4 Ti t le and Subt i t leA P O L L O E X P E R I E N C E R E P O R T : DETECTION AND MINIMI-ZATION OF IGNITION H A Z A R D S FRO M WA T E R/G L Y CO LCONTAMINATION O F SILVER-CLAD ELECTRICAL CIRCUITRY7 Author(s1

W . R i c h a r d D ow n s9 Performing Organizat ion Name and Address

Lyndon B. J o h n s o n S p a c e C e n t e rH o u s t o n , T e x a s 770582 Sponsoring Agency Name and Address

N a t i o n a l A e r o n a u t i c s a n d S p a c e A d m i n i s t r a t i o nW a s h i n g t o n , D . C . 2 0 5 4 6

3 Recipient's Catalog No

5 Report DateMarch- 976

6 Performing Organizat ion CodeJSC-099 118 Performing Organizat ion Report No

JS C S-44910 Work Uni t No

9 8 6 - 1 5 - 3 1 - 0 1 - 7 211 Contract or Grant No

13 Type of Report and Period CoveredT e c h n i c a l N o t e

14 . Sponsoring Agency Code

19. Security Classif. (o f th is repo r t )

I5. Supplementary Notes

20 . Security Classif.

6. AbstractT h e p o t e n t i a l f la m m a b i l i t y h a z a r d w h e n a w a t e r / g l y c o l s o l u t i o n c o n t a c t s d e f e c t i v e l y i n s u l a t e ds i l v e r - c l a d c o p p e r c i r c u i t r y or e l e c t r i c a l c om p o n en ts c a r r y i n g a d i r e c t c u r r e n t is d e s c r i b e d .T h e c h e m i c a l r e a c t i o n s a n d m e a n s f o r d e t e c t i n g t h em are e x p l a i n e d . M e t h o d s f o r d e t e c t i n ga n d c l e an i n g c o n t a m in a t e d a r e a s a n d th e u s e of i n h i b i t o r s to a r r e s t c h e m i c a l r e ac t i v i t y a r ea l s o e x p l ai n e d .

U n c l a s s i f i e d Unc l a s s i f i e d 20 $3 . 25

~~~18. D is t r ibut ion Statement

S T A R S u b j e c t C a t e g o r y :12 ( A s t r o n a u t i c s , G e n e r a l )

I 21 . NO. of Pages 22. Price'Ihis page)


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A P O L L O E X P E R IE N C E R E P O R TEDITORIAL CO MM I TTEE

T h e m a t e r i a l s u b m i tt e d f o r t h e A p o llo E x p e r i e n c e R e p o r t s(a series of NASA T e c h n i c a l N o t e s ) w a s r e v i e w e d a n d a p -proved by a NASA Edi tor i a l Review Board at t he Lyndon B .J o h n so n S p a c e C e n t e r c o n s i s t i n g of the fo llo w in g m e m b e r s :S c ott H . S i m p k in s o n ( C h a i r m a n ) , R i c h a r d R . Bal dwi n ,J a m e s R . B a t e s , W i ll i a m M . B l a n d , J r . , Al eck C . Bond ,Rober t P. B u r t , C h r i s C . C r i t z o s , J o h n M. E g g l e st o n ,E . M . Fi e l ds , Dona l d T. G r e g o r y , E d w a r d B . H a m b l e t t, J r . ,Kenneth F. Hecht , David N . H o l m a n ( E d i t o r / S e c r e t a r y ) ,and C a r l R . H u s s . T h e p r i m e r e v i e w e r for t h i s r e p o r twas Donald T. Gregory.


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CONTENTS

SectionSUMMARY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .INHIBITING FLUID-METAL REACTIONS . . . . . . . . . . . . . . . . . . . .CLEANING UP SPILLS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .DETECTING CHEMICAL REACTIONS . . . . . . . . . . . . . . . . . . . . . .TEST RESULTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .CHEMICAL REACTION A N D PREVENTION . . . . . . . . . . . . . . . . . . .MINIMIZING HAZARDS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

General Procedure s fo r Removing Glycol Contamination . . . . . . . . . . .Detailed Cleanup Pro ced ure s . . . . . . . . . . . . . . . . . . . . . . . . . .Clean lines s Verification . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

CONCLUSIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .REFERENCE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .APPENDIX- HEMICAL SPOT TEST PROCEDURE . . . . . . . . . . . . . .

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Figure1

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F I G U R E S

PageRecorder tra ce of c ur re nt s produced when water/glycol solution

contacts silver-clad wi res ca rryin g 28 volts direct cur ren t . . . . . .Recorder tr ac e of cu rr en ts produced when RS 89-a solution con-tacts silver-clad wires carrying 28 volts direct curre nt . . . . . . . .Specimenof sil ver-c lad coaxial cable carr yin g 28 volts dir ect cu rr en t afterR S 89-a w a s drippedondefe ct inins ulati on. The burned condition of thecable is shown . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Photomicrograph of formation of si lv er hydroxide and hydrogen whena water/glycol solution fir st contacts silver-clad copper wire s . , . .Photomicrograph of conglomeration of si lv er oxide in which cen te rsof explosive energy rele as e can be seen . . . . . . . . . . . . . . . .Photomicrograph of initiation of smoke and stea m and a region ofmass ive dehydration of ethylene glycol to fo rm ethylene oxideand ethylene . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Photomicrograph of copious liberation of st ea m and generaliz eddecomposition of ethylene glycol along the wi re su rf ac es . . . . . . .Photomicrograph of a bu rs t of fla me at the wir e su rfac e of thenegative pole caused by ignition of ethylene oxide and hydrogen and

of ethylene with oxygen in air . . . . . . . . . . . . . . . . . . . . . .

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APOLLO EXPERIENCE REFORTDE TEC TIO N AN D M I N I M I Z A T I O N OF I G N I T I O N H A Z A R D S F R OM

WATERIGLY COL C ON TAM I N AT lO N OF S I LVER-CLAD ELECTR I C A L C IRCU I TRYB y W. R i c h a r d DownsL y n d o n B . J o h n s o n Space C e n t e r

S U M M A R YFollowing the Apollo-Saturn 204 incident i n Janua ry 1967, it was discovered inlaboratory work that ba re o r defectively insulated silver-cl ad copper wir es carr yin g adi rect -cur rent potential produced ignition, evidenced by a small self-sustaining flame,when contacted by water/glycol fluids.Mechanisms for inhibiting water/glycol-induced react ions with met als we re inves-tigated with par tic ula r re fe renc e to the Apollo coolant fluids. Measur ements of mil li-am pe re cur rent flow during the react ion of water/glycol with s il ve r and the utilizationof a tra nsi sto riz ed amplitude-modulation recei ver fo r detecting radiofrequency emi s-sio ns wer e found effective as a means of locating circu itr y defects leading to flameproduction.Becau se water/glycol coolant fluids cannot easily be remove d fro m contaminatedcircu itry, use of a sil ver chelating agent in the water/glycol coolant to a r re s t chemicalreactivity and thereby minimize the hazar ds of flammability was proposed. Whenspillage of water/glycol oc cu rs on elect ric al equipment, the circu it eleme nts must bewashed and the pa rt s test ed for fr eedom fr om contamination before the sys tem can bequalified a s hazar d fr ee . Techniques fo r flushing elect rical circ uit ry a s a part of qual-ity assur ance procedures are described.

INTRODUCTIONSince World Wa r II, silve r-cl ad copper wires (Military Specifications

MIL-W-7139 and MIL-W-8777) have been used i n electrical circu its in military aircra ftbec aus e of the e as e and reli abili ty with which sil ver (Ag) can be so lde red to producehigh-quality e lec tri c cir cui ts. Consequently, spacecraft engin eers and build ers speci-fied silver -clad copper wir es in spacecraft construction. U s e of silve r-cla d wi re s,swi tch es, and disconnec ts seemed sound, not only because of the ease of joining butal so beca use of the protect ion afforded copper by the res is ta nce of si lv er to oxidationwhen high-melting pol yme rs for ele ctr ica l insulation coverings wer e extruded o ver the


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conductor. Becau se of occasional bleedthrough of copper to the sur fa ce of the si lverand fo r mechanical strength, som e aerospa ce desig ners specify nickel-covered copperwi re s instead of silve r-c lad copper wir es. The ground-support-equipment wiring andauxiliary wiring are usually ins ulat ed and a r e composed of p ure copper o r tin-platedcopper.

Solutions of ethylene glycol and water (call ed water/glycol) have been used incooling syste ms of land and amphibious vehicles, in the therm al tran spo rt sys tem s ofair cra ft and spacecraft, and a s a deicer fluid for airc raf t for many yea rs. Water/glycsolutions ar e used in a var iet y of applications because el the high heat capacity, therelatively nontoxic components, the exceptional pro per tie s at low tempe rat ure s, and thlow pumping pre ss ur es and flow ra te s over the opera ting the rma l rang e of the radia torsys tem . Because they have low solidification tem per atu res , low vapor pr es su re s, andlow viscos ities as a function of t emp era tur e, water/glycol solutions ar e also excellentdeic er agents for preventing and removing fr ost and ice fr om most surfa ces.

When mixed with wate r, ethylene glycol low ers the freezin g point and r a i ses theboiling point of the mixtu re without significantly affecting i t s specifi c heat . Water/glycol solutions, the ref ore , a r e efficient th erm al trans por t fluids for closed-loop s y s -te ms and a r e used in the aerosp ace and automotive indus tries as deice r agen ts. Excepfo r instances of corr osi ve action on metal s, the chemical react ivity of water/glycolsolutions w a s not fully recognized until aft er the Apollo-Saturn 204 f i re in 1967 whenstu die s were made a t the NASA Lyndon B. Johnson Space Cente r (J SC) (fo rmerly theManned Spacecraft Center (MSC)) to dete rmine the possibl e ha zardous c har act eri sti csof water/glycol. The se stud ies led to the dis clo sur e that ethylene glycol solutions incontact with silver w i r e circuitry carrying direct curre nt react chemically to produceignition; if the reacti ng solution is left undisturbed, the flammability is self -sustaininga s long as glycol fluid is present.

During the laboratory investi gations, it wa s obser ved that a defectively insulatedspacecraft coaxial silver-clad copper cable carrying 28 volts direct c urrent in all5-kN/m ( 1 6 . 7 psia) pure oxygen atmosphere r esulted in a small self-sustainingfla me when water/glycol the rma l tra nsp ort fluids dripped over the cables. The timerequ ired to attain ignition afte r onset of the water/glycol exposure was an in ver se function of the drip ra te ; that is , the slower the drip rate, the more rapidly ignition oc-cu rr ed . Fur the r observation showed that defectively insulate d pur e copper cable s ex-posed to water/glycol coolant in oxygen did not neces sa ri ly produce f ire .

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An examination w a s made of the water/glycol-induced corr os io n of me ta ls , of themechanisms f or inhibiting corro sio n, and of the reas ons why si lve r-c lad copper wir esreac ted differently than pure copper o r nickel-c overed copper wi re s when exposed towater/glycol solutions. Th is rep ort dis cus ses the us e of additive reage nts found eff ective in inhibiting reactivity of water/glycol solutions on wir e ci rcu itr y, the mea ns ofdetecting chemically induced ignition haz ards of glycol fluids in the Apollo s ys te ms , anthe methods recommended for minimizing th ese ha zar ds.

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Th e objective s of t his Apollo experi ence repor t are to delineate chemically in-duced ignition ha zar ds of glycol solutions resulting fr om spilla ges and leakag es, todescribe methods of detecting these hazards, and to show what can be accomplished tominimize them.

A s an aid to the reader, where ne ce ss ar y the origin al units of me as ur e have beenconver ted to the equivalent value in the SystGme International d'Unit6s (SI). Th e SI uni tsare written firs t, and the original units are written parenthetically the rea fte r.

I NH IB IT i NG FLU1D-METAL REACT1O NSIn the pre sence of air or oxygen (0 )at ambient or higher tem per atu res , ethylene2glycol in solution tends to oxidize to glycolic acid, and the mixture bec ome s mo re andmor e corr osi ve to aluminum alloys in contact with the solution. Once cor ros ion st ar ts ,the r at e of attack incr ea se s rapidly, and the effects of corros ion become increasingly

serious. A number of inhibitors, however, can be added to reduce the rat e of co rr o-sio n of m eta ls. One common inhibitor is a mixture of phosphate and potassium tetra-borate, another is bor ic acid, and another - especially suitable for aluminum alloysystems - is a mixtu re of t rieth anola mine phosphate (TEA P), a pH buffering agent, andsodium mercaptobenzothiazole (NACAP), a copper chelating agent.

The inhibito r sy ste m found sup eri or for the Apollo spa cecraf t environmental con-trol units was termed "NAA Type 11" and consisted of TE AP and NACAP. Th e TEAPin NAA Type 11 ha s thr ee functions: (1 ) o draw copper atoms fro m the surf ace of thealloy into solution, allowing the chelating agent (NACAP) to r ea ct with the co pper io nsto for m an undis socia ted copper che late (organometallic complex); (2) to supply phos-phate i ons to produce a uniform coating of aluminum phosphate ove r the meta l su rf ac es ,thereby protecting the n atural oxide coating; and (3) to s er ve a s a phosphate sa lt bufferfo r maintaining the hydrogen-ion concentration of the solution a t approximately pH 7and preventing wide loc al excurs ions of the hydrogen-ion concentration.

Th e choice of a n inhibitor s ys te m fo r water/glycol solutions depends on the m eta lsuse d in the coolant loop const ructi on. The Apollo environmental contr ol sy st em utili zedNAA Type 11 in a eutectic mixture (a mixture that h a s thft lowest fre ezing point possible)of 62 pe rcen t ethylene glycol and 38 percen t water . This mixture c arr ie s the t radename "RS 89-a. t v l The RS 89-a mixtu re is not a fire hazard in a 103-kN/m (15 ps ia)oxygen atmosphere, in which its autoignition temperature was demonstrated to behigher than 505 K (450" F); in a i r , this point was 694 K (790" F) for RS 89-a and 672 K(750" F) fo r pure ethylene glycol. The flashpoint temper atu re of R S 89-a is between383 and 389 K (230" and 240" F).

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RS 89-a is compounded to the following proportions: 566 gr ams of ethyleneglycol, 339.5 gr a m s of dis tille d wa te r, 14.18 gra ms of TEAP , and 1 . 4 1 gr ams ofNACAP (50-p ercen t solution) fo r a to ta l of 921.09 gram s.

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Certain prope rti es of inhibited water/glycol solutions contribute to the h aza rd s offlammability and complicat e cleanup pr oc ed ur es when these solutions contact elec tr ic alcircui try. Such proper ties are the high conductance of glycol so lut ions and the lowvapor pr es su re s im pa rt ed by the ethylene glycol constituent. The RS 89-a mixture, forexa mple, yields an ionic concentration of approximately 243 p/m a t 296 K (23" C);laboratory-distilled water yields 0.5 to 1.0 p/m at 296 K (23" C) . Thi s means that thesolution will read ily conduct electri city, and mat eri al tra nsp ort will then occur betweenoppositely charged conductors exposed i n the solution. Becau se ethylene glycol ha s alow vapor pres sure at room tempera ture, it is imp rac tic al to remov e water/glycol solu-tions fro m contaminated surf ace s by eva porative pro ces ses .

C L E A N IN G U P S P I L L SA se ri es of labor atory e xperi ments was p erfor med a t MSC to deter mine the phys-ical proper ties of RS 89-a and it s effects on wire circui try so that a method could bespecified f o r cleaning contaminated cir cui t elemen ts. The laboratory distilled water atambient tem peratu re (296 K (23" C)) ha s an ion concentration of appro ximately 0.74

p/m. By con tra st, RS 89-a fluid at ambient t emp era tur e produces an ion concentrationof 243 p/m becaus e of the phosphate and sodium ions in the inh ibi tors.The RS 89-a .mixture cannot, within practical time limits, be completely evapora-ted by vacuum techniques be cause of t he pre se nc e of the ion s and becaus e of the lowvapor pre ss ur es of the ethylene glycol and undissociated amines . Exc ess tert ia ry

amine and its phosphate, o n evaporation of the solvent , rem ain a s hygroscopic mat eri aland a re deliquescent. They tend to att ra ct moistu re from the surroundings to producean electrically conductive, cor ros ive fluid. The sodium ions present will rem ain asthe sal t sodium mercaptobenzothiazole. The sodium ion s, t he undis socia ted alkal ineamine, and the ethylene glycol re ma in when RS 89-a is spilled around ele ctrica l cableso r onto electrical connec tors, despite eff orts to evapor ate the spillage by drawing avacuum.

Flammability haza rd s ar e induced by the chemical reactivi ty of water/glycol solu-tions with silve r wire c irc uit ry because of accidental spillage o r leaka ge onto defectiveelectrical w i r e insulation o r an incorrectly designed wire har nes s. If a practical meansof dFtecting glycol contamination w er e esta bli she d to identify possible rea cti on s it es andi f a procedure were establi shed fo r minimizing the effec ts of contamination, fla mma -bility haz ard s induced by the che mic al react ivity of water/glycol solut ions with si lv erci rc ui tr y could be substantially reduced .

DETECT IN G C H E M IC AL REACTIO NSThe chemical re activ ity of ethylene glycol with s il ve r w i r e circui try c an be ob-ser ved in sev era l ways, pri mar ily in the production of smoke, pungent odor s, andfl ame.

Fl am e production is self-sustaining as long as glycol solution is presen t to fuel the fir e.

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Another mea ns of detecting chemical reactivity is the detection of radiofrequency( r f ) sta tic di stu rba nce s produced on an amplitude-modulation (AM) re ce iv er place d nearthe defective circu it where rea ction is occ urr ing. Thi s detection method see med suf-ficiently imp ortant to justi fy an investigation of the phenomenon of t hi s technique.

T e s t s were conducted to determine the nature of the rf distur bances producedfro m voltage used on spacecr aft. A silver-shielded twisted p air of insulated silve r-clad copper wires was used in the test s. This specimen w a s nicked through the shieldand also through the insulation of the two cen te r conductors so that the ce nte r conduc-to rs wer e exposed near the shield. On one end of the te st s ampl e, the two centerwi re s we re tied together and then attached to one termi nal of a voltage source; theshield wa s tied to the oth er termin al of the voltage sou rce . The RS 89-a mixture wasallowed to dri p onto th e defect i n the shield and through t he insulation.

The te sts indicated that the electrochemical reacti ons produced a broadband rfnoise (14kilohertz to 30 megahertz) and that the rf intensity generated by the r eactio nsvaried irregu larly with time. This timevariat ion wa s found to be an inherent charac-te ri st ic of the reac tio ns. Most of the noi seintens ities wer e too low for accu rat e meas-ure ment s. However, only short wire spec-imens (several centimeters) were tested;i f longer wi re lengths (approaching thelengths used in a ircr aft and spacecraftcircuits) had been tested, it is believedthat a significant increase in radiated lev-el s would have res ulted. A characterist icunique to the rf disturbance is the slowbuildup of amplitude with time . Duringele ct ri ca l checkout of a spacecraft or air-craft electrical system, the backgroundnoise lev els might mas k the rf disturbances.For this reason, i f measur ements of rfdisturbances are made a s a means of de-tecting incipient hazards, the me asu re men tsshould be perf orm ed on single-poweredcircui ts.

A third method of detecting chemicalreactivity is to obser ve the cu rren t flow inan open circu it as the chemical reactionscommence and a re maintained. Te st s wer econducted i n a n oxygen atm osph ere onsilver -clad coaxial cables in which a defectwas produced by grinding a groove to ex-pose the cen ter conductor. The tes t fluid( R S 89-a) was dr ipped onto the defect at ara te of one dro p every 5 minutes. A po-tential of 28 volts di rec t cur ren t was ap-plied ac ro ss the cable, and the current

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Current, rnAFigure 1. - Recorder trac e of cur ren ts

produced when water/glycol solutioncontacts silver-cl ad wires carrying 2 8volts dir ect cur rent.

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5.0

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Figure 2. - Recorder tra ce of cur ren tsproduced when RS 89-a solution con-tact s silver-clad wire s carrying 2 8volts direct current.Figure 3. - Specimen of silver-clad co-axial cable carrying 28 volts directcurr ent after R S 89-a was dripped ondefect i n insulation. The burned con-dition of the cable is shown.

flow was recorded. The cur rent w a s highly irr eg ul ar and was much l ar ge r than wouldbe expected on the bas is of the solution conductivity alone. Typical portions of the re-cor der tr ac es fo r the cable tes ts conducted with RS 89-a a r e shown in figures 1 and 2.Ignition occurred between 9 and 10 hours when the water/glycol fluid was used and atapproximately 5 hours when the RS 89-a solution was tested. Figur e 3 shows t h e burnedcondition of the cable af ter the test with RS 89-a.Because of the hygroscopic nature of the amine resi dues and the existence ofions, a corrosive, electrically conductive moist locale is produced, commencing withthe admission of air o r moist oxygen to equipment soaked in RS 89-a. The attraction

of moisture to regions stained with RS 89-a is time dependent and cumulative.

TEST RESULTSObservations showed that ba re o r defectively insulated silver-clad copper wi re s(carrying a direct-current potential) exposed to water/glycol solutions produced smoke

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and fire i n oxygen or i n air. Also, it w a s found that pu re c opper wi re s or nickel-cov ered coppe r wi re s under conditions of electri cal potential and oxygen exposureidenti cal to those of sil ver -cla d wi re s did not exhibit chem ical reactiv ity to water /glycol solutions and did not produce ignition. 2

Silver-clad copper wire wa s completely strip ped of i t s insulation. Two pie ces,each about 5 cen timet ers long, we re taped to cardb oard so that approximately a1-milli meter space sepa rat ed the two wires. A 22.5-volt dry- cel l battery supplieddirect current, and a milliammeter was placed in series. The R S 89-a solution wasdripped slowly into the 1 -mi llimete r space between the wir es . Elec trol ysi s beganimmediately; in 4 to 5 seconds, a black deposit w a s observe d on the si lver wir e con-nected to the positive te rmi nal of the battery. The millia mper e curr ent flow fluctuatedbetween 10 and 80 mil liam pere s, and the needle of the me ter fluctuated constantly.In a f e w minutes , copious white smoke and flame ensued. The se phenomena occ urr ed2whether the reaction was car ri ed out in ai r o r in 100-percent oxygen at 103 kN/m(15 psia).

A transistorized A M rece iver (covering the commer cial broa dcast band fr om600 to 1400 kilohertz) placed n ear the electrolysis sta rte d to click and emit stat ic,which, as the electrolysis proceeded, built up to a constant static noise that drownedout al l other reception on t h e receiver. The rf disturbance w a s observe d on the re-ceiv er when it wa s held as far away as 1 meter ( 3 fee t) , an d the intensity of the noiseincreased as the rec eiv er was moved toward the react ion sit e. The application of th eA M receiver to detect a reactio n between the water/gly col solution and the si lv erwiring w a s found to be more convenient than using a milliammeter in the circuit. Theslow er the application of water/glycol solution aft er the fi r st drop o r two, the louderthe rf disturbance over the receiv er became. Eventually, the chemical reaction s de-tect ed by the AM rec eiv er produced smoke and flam e.Nickel-covered copper wires, pure copper wires, and tin-plated copper wires

did not show evidence of cnemical reactivity when subjected to a direct-c urrent poten-tia l and exposed to the water/glycol solution. In such inst anc es, the solution simplyele ct ro lyz ed with mild generation of hea t, with no rf radiation emission, and with notendency to flammability.It makes little difference in reactivity whether the water/glycol fluid is simplyethylene glycol solution in wate r o r whether the fluid contains inhibitors such as N A A

Type I1 o r Type 111. Chemical reaction of silver with water/glycol solution oc cu rs onlywhen the silv er is connected to the positive terminal. Thi s signifies that the silv erunde rgoe s anodic oxidation, which oc cu rs readily a t a &volt potential but is barelyapparent a t a 1.55-volt potential.

-~2D. . Elliot (ref. 1) rep or ts on so-called wet-wire fires produced f rom insu-late d wi re s of va riou s metal compositions when the wir es a r e exposed to direc t cur -re nt and to aqueous conducting solutions. The work of Elliot di sc us se s a different sortof phenomenon, the formation of metall ic dendrites leading to an elec tr ica l sho rt ci r -cu it , followed by ignition and burning of the wi re insu lat ion .7


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Reaction occ urs as soon as water/glycol contacts the current -car rying silv er-clad wire s and is indicated initially by electrolysis between the wires and by the forma-tion of a black deposit. Steps in the chemical mechanism leading to ignition are shownin figures 4 to 8. These fig ure s are stereoscopic photomicrographs produced fr omfra mes of a motion picture of the reaction resulting when RS 89-a fluid w a s placedbetx.t7ee~wo silver-clad w i r e s separated 5s a distznce of 1 millimeter and impressedwith 2 2 .5 volts of direc t cur ren t. The action occ urr ed over a span of approximately1 minute, during which the cu rren t did not exceed 80 milliamperes and the averagecurrent w a s 50 milliamperes. In the photographs, the upper wire is negative and thelower wire is positive.

Figure 4. - Photomicrograph of forma-tion of si lv er hydroxide and hydrogenwhen a water/glycol solution firstcontacts silver-clad copper wires.

Figure 5. - Photomicrograph of con-glomeration of si lver oxide in whichce nt er s of explosive energy re leasecan be seen.

Figure 6. - Photomicrograph of initia-tion of smoke and st eam and a regionof m assive dehydration of ethyleneglycol to form ethylene oxide andethylene.

Figure 4 hows hydrogen ( H 2 )bubblesforming at the negative pole and st re am er sof brown sil ver hydroxide (AgOH) issuingfrom the positive pole. This reaction oc-curred a s soon as the current was im-pressed.

A s seeninfigure 5 , within a f e w sec-onds, the silver hydroxide conglomeratedto black sil ve r oxide (Ag20). Cent ers ofexplosive energy re lea se s a r e visible inthe mass of silver oxide as ethylene glycolcommenced to dehydrate.

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Figure 7. - Photomicrograph of copious liberation of stea m and generalized decom-position of ethylene glycol along the wir e sur faces.

Figure 6, a view taken sev eral seconds af ter the view in figure 5 , shows an ex-tensive region of glycol oxidation (indicated by an intense blue light) accompanying thedecomposition of the ethylene glycol, the rearrangement to for m ethylene oxide, and theformation of ethylene. Steam and smoke a r e observed rising fr om the negative-poleregions.Figure 7 shows generalized reaction all along the w i r e sur fac es and copious liber-ation of smoke and ste am , indicative of energy releases in excess of the energy drain

fr om the battery. The total power from the battery, if the maximum cu rren t ra te weremaintained f o r 1 minute, would be 108 joules (approximately 26 gram-calories), suffi-cient to produce sil ver oxide and hydrogen, as noted i n figure s 4 and 5.In figure 8, a burst of flame, caused by the reac tions of ethylene oxide with hydro-gen and of ethylene with air , is visible in the negative-pole region. Another burs t is

seen at the r ight side . Analysis showed that the washed and dried black deposit con-tained si lv er , carbon, oxygen, and nitrogen.

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Pu re copper wires or nickel-coveredcopper wires, in contrast to the reaction ofthe silver-clad copper wir es, do not re ac twhen exposed to water/glycol solutions,ei ther inai r o r in pu re oxygen atmospheres.On these types of wir es , the water/glycolsolution evaporates (f rom the heat of e lec-tr ol ys is ) without producing incandescenceo r sparks. It ha s proved impossible underthe te st conditions, even in a 100-percentoxygen atmosphere at 103kN/m (15 psi a) ,to produce ignition from nickel-covered o rpure copper wires carrying direct-currentvoltage on exposure to water/glycol s o h -tions.

2

Flame burst at h ydr qen -producing pole as ethyleneI xide and hvdrwen combine-

Figure 8. - Photomicrograph of a burstof flame at the w i r e surface of thenegative pole caused by ignition ofethylene oxide and hydrogen and ofethylene with oxygen in air.

C H E M I C A L R EA C T I O N A ND P R E V E NT IO NA chain-reaction mechanism involving the action of water/glycol solution on sil-ve r wi re begins with the anodic reactions

2AgOH- g20 + HOH ( 3 )The chain-reaction mechanism may be prevented i f a sil ver chelating agent

exists in a solution to immobilize the Ag' ion before i t can form s il ve r oxide. Such achelating agent is benzotriazole (BZT). It was experimentally confirmed that BZT inconcentrations of 2000 to 5000 p/m in water/glycol solutions inhibits the chemicalreactions of silver and glycol under an im pr es se d dir ect -cu rr ent potential. N o blackdeposits form on the si lve r electrode, no rf radiation is detectable on an A M receivernear the reaction site , the reactants do not tend to flame, and the cu rre nt flow issteady and decr eases with time. The interact ion of BZT de cr ea se s the activity of sil-ve r toward water/glycol solutions to a point at which the silver-clad copper wir es be-have simi larly to nickel-covered o r pure copper wire s; that is, a simple electrolysis

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occ urs between the s hort-c ircuit ed wi res and gradually ceases a s the solution evapo-rat es. The BZT interaction produces a greenish-white, gelatinous prec ipi tat e aroundthe s il ver conductors. This precip itate presumably is an or ganosi lver chelate hydrox-ide that remove s the silv er ion and thereby prevents formation of silv er oxide. Thecur ren t flow between the wi res is impeded by the precipitate, and the reaction ra te sare noticeably slowed. The chain reacti on leading to flammability is interr upted andprevented.

MINIMIZING H A Z A R D SOnce contamination of e le ct ri cal circu its occ ur s, the effects should be minimized

by removing the contaminant and cleaning up the ci rc uit ry or by using water/glycolflu ids containing a chemical chelating agent that is capable of b reaking the chain re ac -tion of ethylene glycol with sil ve r.

G e n e r a l P r o c e d u r e s f o r R e m o v i n g G l y c o l C o n t a m i n a t i o nThe source of glycol spillage must be located and prompt ly co rr ec te d. Runoff ofglycol fr om the spillage sit e must be prevented. Personn el activi ties in the spillagearea must be minimized.Once spillage o r leakage of glycol solution h a s occurred, the contaminationshould be cleane d up at once by proceeding as follows.1. Est ima te the amount of spilla ge and deter min e the region s contaminated.2. Follow an or der ly sequence of equipment cleaning, concentrating first on

el ec tri ca l wirin g, then on ex te ri or s ur fac es of black boxes, and finally on plumbingand st ru ctu ra l components.3 . Dis ass emb le the equipment and wire bundles.4. Execute specific cleaning procedures.5. Verify that all glycol contamination h a s been removed from contaminatedareas.

D e t ai le d C l e a n u p P r o c e d u r e sAs c onstru ction of the Apollo modules (command and se rv ic e modules and lun armodules) pro gres sed i n the Apollo Pro gra m, spillages and leakages of water/glycolfluid wer e encountered fr om time to time. It w a s necessa ry to clean the spacecraftthoroughly aft er ea ch suc h incident in a manner that would not jeopardize the qualityassu ranc e cri ter ia of spacecraft components o r of the spacecr aft. The procedu resdescribed in subsequent pa ragr aph s were evolved and wer e applied successfully to

water/glycol cleanup of lun ar modules LTA-8 and L M - 5 and of command and se rv ic emodule 2TV- 1.

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Elec tric al components. - The fi r st step in the cleanup of ele ctr ica l componentswas to wipe excess glycol solution from wires, black boxes, o r st ruc tur es using clean,dry cloths. For wire bundles and har nes ses , the tapes o r ties were removed, andal l chafe guards were s et aside at l east 1 5 centimeters (6 inc hes ) beyond the contami-nated region. Cable bundles wer e cleaned in sepa rat e 46-centimeter (18 inch) sec-tions. Each cleaned section overlapped the precedin g sect ion by a minimum of 10centimeter s (4 inches). Each w i r e w a s wiped individually at lea st t hr ee t ime s with acloth dampened with dist ill ed wat er. (The ion content of the wat er did not exceed 2p/m. ) The wiped wir e w a s then r ins ed with distilled wat er dispense d with a jet-typespr ay bottle, and the r in se fluid was caught in a container fo r meas ureme nt of ionicconcentration. Th e flow of wat er w a s directed over all sur fac es being cleaned. Ca rew a s taken to ens ure that the ri ns e fluid did not dri p, run, o r splash, except into thecatc h container. After the flushing was repeated, the wires were drie d using a cleanwipe r. The dry wi re s wer e cleansed using an applicator moistened with isopropylalcohol and were then wiped with pr eci sio n cleaning fluid (e.g. , Freon TF). (Flushingwith solvent and us e of solvent on connec tors wer e not permit ted . ) After cleansing,the wir es and connectors we re dr ied using dry nitrogen g as heated to 322 to 344 K(49" to 71" C ) . The warm nitrogen gas w a s carefully directed over the wire ca bles toavoid damaging any pa rt of the assem bly. The clean wi re har ne ss w a s then reassem-bled.

Black boxes. - Cleaning up glycol spill age on ex te ri or s of black boxes included(1)wiping exce ss fluid fr om the su rfa ces of the boxes, fr om joints and overl aps in theboxes, and fr om points of i ng re ss to the boxes; (2 ) wiping the black-box su rf ac es withcloths moistened with isopropyl alcohol; and (3) drying each su rf ace .Fixtures and stru cture s. - Cleanup of glycol solution fr om plumbing fi xtur es o rstr uct ura l elem ents included removal of e xc es s spillage with wiper cloth s, final clean-ing with wiper cloths moistened with isopropyl alcohol, and drying.

C l e a n I in e s s V e r i f i c a t i o nIt is important , in the ca se of sil ver- clad e lec tri cal components, to remo ve ever ytr ac e of contamination. Contamination rem ova l, as previously described, w a s accom-plished by rinsing the components with je ts of dist illed wat er, After use, the rin se

wate r must be test ed fo r the efficacy of the rins ing pro ce ss by meas urin g the ionicconcentration in the ri ns e water with a conductance-measuring instrument. Alterna-tively, by using a method involving chem ical spot checking, the cle anl ine ss of the com-ponents can be determined. These methods of testing the rinsing technique are de -scribed i n subsequent paragraphs.The pre sence of ionic contamination is easily dete rmin ed by u se of a conductance-measurin g instr ume nt. Solution conductivity is proportional to the ionic concentration.The te mperature of the solution being tested mu st be determined, and the instrument

must be compensated for tem per atu re. The ion content of a sam ple of distilled water ismeasured; an acceptable level fo r a supply of d ist ille d wat er is 2 . 0 p/m at room temp-erature. The same procedure is repeated using approximately 100 cubic centimetersof r in se solution. Rinsing should be continued until the rin se water t es ts no mo re than2 p/m over that of the disti lled wat er (a to tal of 4 p/m) .

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Th e chemi cal spot-check method for verifying clea nline ss is as sensitive as con-ductivity measurements, but it is more difficult t o perform. For this test , a piece offi l ter paper is moistened with distilled water and wiped ove r the a re a to be checked fo rresidu al glycol contamination. The fil ter paper is then tr ea te d with dr ops of a chemicalsolution. The pap er contains an indic ator that turn s blue o r violet i f glycol is presenton the filt er paper. (See the appendix fo r the detailed chemical procedures . )

CONCLUSI ONSExperiments at the NASA Lyndon B. Johnson Space Cen ter (fo rme rly the Manned

Spacecraft Cen ter) and NASA- spons ored con tract work following the Apollo-Saturn 204accident in Januar y 19 67 demonstrated that bare or defectively insulated sil ver-c ladcopper wires carrying direct current could produce ignition when contacted bywater /glyc ol solutions. Th is phenomenon constitutes a disti nct haz ard of flammability(wher ever ethylene glycol soluti ons for heat tr ans fer or deicer purposes are usedaround silve r-cla d ele ctr ica l circu itry) . Hazards fro m chemically induced ignition canbe detected by noticing th e following.

1 . Pr ese nc e of smoke, pungent odor s, o r flame2. Radiofrequency sta tic on an amplitude-modulation re ce iv er placed nea r theelectr ical circuit defect3 . Micro ampere cur ren ts and their fluctuations in the wiring cir cui t as deter-mined by a sensitive microammeter mounted in se ri es in the circuitThe ha za rd s can be minimized by observing the following preca ution s.1. Avoid spi llage and leakage of water/glycol fluid s and defe cts in the el ec tr ic al

wirin g by a dhering to workmanship and sound engineering princi ple s.2. Rigorously clean glycol-contaminated areas (especially silver-clad wiringcircuits) .3 . U s e water/glycol solutions to which a r e added sma ll amounts of chemicalagents (such as benzo triaz ole) capable of chelating, o r immobili zing, the sil ve r ion.The following conclusions, there fore, ar e drawn fr om this study.1 . Water/glycol solutions cannot effectively be eva por ated fr om a region on

which spillag e has o ccu rre d because the ions contained in the cor ros ion inhibitors of thefluid re ma in af ter evaporation of the low-vapor-pressure-produ cing glycol.2. The ionizable amine-containing materials remaining after evaporation of

water /glyc ol coolant fluid f r o m equipment su rfa ces w i l l absorb moisture from thesurrou nding s and thus become progre ssivel y more alkaline a s the amines are hydro-lyzed by the ab sorbe d moisture.

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3 . Water/glycol solu tions with o r without inhibitor additions (except fo r theaddition of benz otriazo le) produce flam mabl e reactio ns accompanied by e asil y detectabl eradiofrequency radiation upon contacting sil ver- clad copper w ir es on which a direct-cu rre nt potential is impressed.

4. Pu re copper, nickel-covered copper, o r tin-plated copper wir es do not showevidence of chemical reactivity toward water/glycol solutions.

5. Silver-clad copper wiring in cir cui try exposed o r likely to be exposed towater/glycol coolant should be recognized as a potentially danger ous ignition s our ce.6 . If contamination of s ilv er-w ire cir cui tr y oc cu rs , rin sing with distil led wate r

until only a nominal ion pickup is indicated in the rins e water constitutes the reco m-mended decontamination procedure.7. A sil ver chelating agent, benzotr iazole, when added to water/glycol coolantfluids in concentrations f ro m 2000 to 5000 p/m , completely inhibi ts reacti vity of wate r/glycol solutions to silver-wire circuitry.8. An amplitude-modulation rec eiv er cov ering the co mme rci al broa dcas t bandfrom 600 to 1400 kilohe rtz will pick up a constant radiofrequency stat ic noise as thechemical reacti on of glycol with sil ver pr og re ss es . Such a receiver, therefore, shouldserve as a ready detector of incipient trouble in wire circ uitr y during test s and check-

out.

Lyndon B. Johnson Space CenterNational Aeron autics and Space Administrat ionHouston, Texas, October 24, 1 9 7 5986- 5- 31-01- 2

REFERENCE1. Elliot, D . K . Wet-Wire Fir es. Conference on Electrical Insulat ion, Annual Report .National Research Council Publication 1141, 1964, pp . 1 2 4 - 1 2 7 .

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APPEND IXCHEM l CAL SPOT TEST PROCEDURE

The chemical spot test for ethylene glycol contamination is essentially a tes t foraldehydes. The tes t is per for med by concentrating the ethylene glycol on a piece offilter paper used as a wiper ove r the contaminated area and oxidizing the glycol toaldehyde. The prep arat ion of the reag ent s and the procedu re t o us e fo r conducting thetest are as follows.

1. Ten grams of

P R E P A R A T I O N OF REAGENTSeagent-grade potassium periodate r e dissolved in 200 milli-li te rs of di stilled water to give a satu rate d solution at room tempe ratur e. The solution

is filtered j ust before use to remove undissolved p otassium periodate.2 . Twenty mi ll il it er s of concentrated sulfu ric aci d are added to 180 mil lil ite rsof d isti lled water to give a 10-percent solution.3 . One gr am of rosa nili ne hydrochloride (bas ic fushine) is dissolved in approx-imately 800 mil lil ite rs of distil led wat er. Sulfur dioxide ga s is then bubbled throughthe solution until a pale-orange color is obtained. The solution is then filt ered into a1-liter volumetric flask, and the flask is filled to the mark with distilled water. Thi s

solution is allowed to s tand overnight be fore being used a s an indicato r solution.4 .distilled wat er. The us e of fr es h, unsaturated sulfurous acid is mandatory.Concentrated sulfurous acid is pre par ed by bubbling sulfur dioxide through

PROCEDURE1. Moisten a piece of fil ter paper with distilled water . Wipe the moistened f i l -te r paper over the area to be tested fo r water/glycol res idu e. For a standard, place a

dr op of water/glycol on the moistened fi lt er pape r.2 . Place the filter paper on a clean watchglass and add two or thr ee dr ops offil ter ed, sat ura ted potassium periodate solution; then add an identical amount of

10-percent sulfuric acid.3 . Wait 5 minutes to allow oxidation of the glycol to occ ur.4 . Add five drop s of f reshl y prepa red sulfu rous acid solution to destr oy theexc ess periodic acid. A fain t tan colo r indicates unde stroyed acid . Any undestroyedacid must be eliminated with sulfurous acid before proceeding.

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5 . Add two o r three drops of indicator solution and wait for a color to develop.A positive test f o r glycol is indicated by a blue o r violet color on the filter pape r.It is advisable to run a standard at the same time as the test sample. Becausethe blue color take s time to develop, running the standa rd at the s am e tim e enable s adetermination of the tim e req uir ed before a conclusion can be made that the tes t is

negative. Negative re su lt s should not be decl are d until one-half hour h as elapsed fr omthe addition of the indicator. A pink color i ndic ates that a mistake has been made andthe test must be rerun.

apollo experience report detection and minimization of ignition hazards from water glycol...

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