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An Orientation to Explosive SafetyBetty W. HarrisLos Alamos National Laboratory, P.O. Box 1663,Los Alamos, NM 87545

Explosives are chemical or physical systems capable ofextremelv raoid exothermic reactions. which are eenerallvaccompahiedby high pressures a t the ;eaction zone,products, and a vast amount of heat and light. Such systemscan do a tremendous amount of work in a very short time.For this reason, explosives are used for domestic, commer-cial, and military p&poses. Explosives also are used to clearforest areas, to open canals, to build dams, to blast rock inconstruction projects, to drill for oil, to mine ore, and forsubmarine activities.Different kinds of explosives are used for different pur-poses. Initiating explosives are used to set off more stableexplosives. Low explosives are used in some ammunitionshells, blasting charges, and fireworks. High explosives(HE'S) are used as main charges, especially in weapon sys-tems.Exdosives are aenerallv svnthesized com ~o un ds r for-mulated mixturesof compou&ds. However, some very dan-aerous exnlosive systems can be accidentally created by bothprofessionals and laymen. Among these &e methane-airmixtures found in landfills or digester gas (sewage) plantslocated near residential areas , undetected explosive devicesleft by the military in areas th at have since been converted todomestic use, the dust from the storage of grain and fertiliz-ers, and misplaced or lost blasting caps or dynamites fromconstruction projects. Appropriate precautions, safeguards,and expertise must be used to eliminate the hazards arisingfrom these situations.Clasrlficatlon of Explosives

Explosives can be classified in many ways ( I ) . We havechosen to limit our classification t o the manner and t he easewith which they react.Initiating or Primary Explosives

Primary explosives are generally sensitive to light, heat,shock. snarks. and static electricitv. Thev are verv unstableand &'be detonated directly when acted upon dy externalforces. Examnles are mercurv fulminate. H e ( 0 N c ) ~ .eadazide, P~ (N &, cyanurictriazide [ c ~ N ~ ( N ~ ) ~ J , 'eadstypb-nate, [CsH(N02)30~Pb. zO], and silver acetylide, [AgzCz].These are usually packaged as disc- or capsule-type detona-tors such as blasting caps used t o stimulate (set off) enereet-icreactionsinothersystems.'~'hus,ead a ~ i d e ay he use> toinitiate a RDX- or I'KrN-(hexahydro-1.3,s.-trinitro-1,3,3-triazine and pentaerythritol tetranitrate, respectively) basecharge. Special standardized procedures and the propersafeguards must be enforced during the preparation and useof initiating or primary explosives.Low Explosives

Low exnlosives are chemical cornnositions or chemicalcompounds that deflagrate by a seif-sustaining reaction(burn slowlv. when unconfined) over a eiven neriod of time.when confined, they may react withexplosive violence.Therefore, they are used often in propellants, where con-trolled burning is important, and in blasting operations.Black powder or gunpowder is an example. Black powder iscomposed of charcoal, sulfur, an d potassium ni tra te or sodi-um nitrate.

Black powder is sensitive to flames, sparks, and friction.When confined, black nowder can be heated to a relativelvhigh temperature before an explosion will occur. However, itcan be ignited easilv by a simple snark. Black-powder firescan cause severe damage to ocher eiplosives and to individ-uals. Do not attempt to fiaht a black-powder fire.Black powder can be desensitized b; pouring it into water.Even empty black-powder containers should he washed be-fore discarding. ~ cc id en ts ave been reported t hat werecaused by contaminated black-powder containers.Hiah Exolosives (Secondarv Exolosives). . .

Highexplosives (HE'S) arechemicalcompoundsor chemi-cal com~ositionshat are much more stable than initiatineexplosives. These are used almost exclusively for maincharges. Some high explosives are insensitive to mild shock,friction, flames, and heat, and they are generally set off byblasting caps or other initiators. When initiated by a blasting-cap, the intense shock wave creates many hot spots withinth e explosive causing extremely rapid conversion of the solidinto gaseous products with the subsequent release of heatand light. The noise one hears from an explosion is the shockwave generated by t he hot, rapidly expanding gases movingthrough the air at the speed of sound. Energy release isalmost instantaneous. High explosives are generally moreeasily handled because of their added stability.Some typical HE'S a re nitroglycerin [CH2(N03)CH(N03)CHzN031, trinitrotoluene (TNT), hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), 1,3,5-triamino-2,4-trinitrobenene(TATB), pentaerythritol tetranitrate (PE TN) , dynamite(principal explosive ingredient ammonium nitrate or nitro-glycerin), and Composition B (6013911 wt% RDXITNTIwax).Dvnamite is the high exvlosive tha t t he lavman is most.likely to encounter. Its composition varies widely with itsuse. The principal explosive ingredient is ammonium nit rateor nitroglycerin. However, explosive or nonexplosive sensi-tizers often are added t o brine about its detonation. Sensitiz-ers are miatcriak that enhance the detonat ion wave propaga-tioncharacteristics. thus reducing thecritical (failure)diam-eter of the explosive. The criticai diameter i st he minimumdiameter of a cylindrical charge of high explosive required tosustain a high-order, steady-state detonation. The criticaldiameter is a function of charge confinement, charge densi-ty, material particle size, and the initial temperature of thecharge. Sensitizers can also he impurities in the explosive.Liquid sensitizers are usually added with carbonaceous ab-sorbent material to prevent leakage and to obtain a suitableoxveen balance. Ethvlene elvcol dinitra te is an examnle of asuccessful liquid sensitizer. ~ m o n ghe solid sensitizers arenitro-oraanic co m~ ou nd such as nitrotoluene. nitrostarch.and nitr&aphthaieue. Aluminum and sulfur a;e also addedas solid sensitizers. Shock and heat can cause dvnamitemixtures to explode. Some grades of dynamite al sdgive offpoisonous aases.- Figure lgives t he three basic steps in an explosive train. I talso shows the relationship between primary and secondaryexplosivrs Ulilsting caps ihemselves, common explosive de-vices, utilile this relatiunship in their constructton (2).

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Figure 1. Basic three-step explosive train.

RUBBER PLUG, IGNnlOu MIX/

SHY& LEGWIRBI SASESH' WDGE nE ' 'wGE

Figure2. Du Pont no.6 ommerciai electric blasting cap

Detonating DevicesTwo general types of devices or methods are used to se t offexplosives: igniters and detonators. Igniters carry to the ex-plosive mass a flame th at lights the explosive mass. Detona-tors deliver a shockwave that causes the explosive to dissoci-ate, detonate, or burn rapidly.Igniters are squibs (plain or electric), fuses, and delayieniters. Sauibs are small-diameter tubes of oaner or straw. .filled with a quick-burning powder; they have a relativelyslow-hurnine match head attached to one end. Althauehthey are not safe, they are still being used in some coil-mining ooerations. Fuses are usuallv fine oarticles of blackpowder wrapped in a coarse fiber forming a ropelike mater i-al. Delay igniters are a combination of igniters and fuses.They are standard and relatively safe for use in metal-min-ing and tunnel ing operations. Most detonation devices, evenelectric blasting caps, are unsafe in coal-mining operationsbecause of the probability of igniting the dust or pas oresen t. . .in the mine.Blasting caps are shells or cups made of copper or alumi-num alloy. They are closed a t one end and contain two- or

three-layered charges of explosive within. The initiating(verv sensitive) exolosive is near the ooen end of the cunkhiie the less senskive base charge is ciosest to the close2end of the cup. Th e intermediate or primary charge is in th ecenter. Figures 2-5 show representations of electrical andnonelectrical blasting caos (2).Electrical blasting cans areset off by essentiall; insiantaneous vaporizationuof bridgewires, while nonelectrical blasting caps need a fuse for igni-tion.Blasting caps are rather small and easily lost. Construc-tion an d military personnel sometimes lose live blasting capsin areas where they could be found and handled by children.They look like shiny empty rifle or pistol shells. However,they are very dangerous and could he injurious or even fatalto an individual if accidentally exploded. Therefore, laymen

ALUMiNUMALLOY CUP

/ / 1 B A ~ EHARGESuLN' IGNllION CHARGE INTBMWIAE (RDX)(LEAD 5NPHNATE CHARGEAND ?ARIUM [LEAD UlDf lFigure 3. Military Corpsof Engineers special no. 8 electric blastingcap

ALUMINUM IGNmON PRIMING BASE CHARGEALLOY S H Y WRGE, ~ A R G E ,PRNOPEN ENDINSERnONSAFEIYN

Figure 4. DuPont no. 6 commerciel nonelectric blasting cap.

OPEN END WRINSERTION OFSAFFil NSEI

COPPOl OR IGNlilON PRIMING BASE CHARGEALUMINUMSHN CHARGE CHARGE RDX

Figure 5. Military Corps of Engineers Special no. 8 nonelectric blasting cap.

are urged to he able to identify blasting caps and notify thelocal police if one is found in a resident ial environment. Donot attem pt to destroy th e blasting cap.Domestlc Explosive Systems

One very common domestic explosive system is the accu-mulation of large volumes of gas-air mixtures. Sucha systemwill ignite with explosiveviolence. Sparks from a light switchor telephone, or from static electricity, could cause suchmixtures to detonate. Some common sources found in build-ings are natural gas (meth ane),propane, or butane gas leaks,digester gas or landfill gas accumulations in residential sec-tions, and hydrogen-oxygen mixtures near life-supportequipment.Fine dust particles from grain can evenly distribu te them-selves amone the available air in a erain elevator. This he-comes a suitable fuel for a reaction-A spark can ignite thisfine erain-dust-air mixture creating a violent exolosion.Ammonium nitrate fertilizer, when stored in garages orbarns. can sometimes become contaminated with oil fromlawn mowers or production machinery. The paper bag, am-monium nitrate, and oil constitute an explosive mixture tha tcould be ignited by a cigarette, match; or even a backfirefrom equipment.Fuels and flammable solvents, such as gasoline, lanternoils, paint thinners, dry cleaning fluids, and adhesives, canbe vaporized even at room temperature. The vapors willtravel an unimaginable dis tance in a very shor t time formingan explosive air-solvent mixture. These vapors can be ignit-ed easily by cigarettes, candles, sparks , or the pilot light of agas stove or hot water heater or any other source of flames.

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Table 1. Sensitivity of Explosives Determined by Drop-WeightImnact Test

Explosive Type 12 H5. (cm) 'Lead Azide 300

eDistetancsa2.5 kg(5.5 Iblweightneeds oFall to inltistethematerial50% of the time.

Table 2. Results of Friction TestsIn the Granlte Groove Friction Apparatus Steel Slider

Loads kgExplosive 10 20 30 40 50 60 70 80 90 100 150 200Lead mid e EPETN EBlasting Gelatine ELFB-Dynamite 0 0 E EN i t ro~ e l l ~ l o~ e O O K KRDX O K EPowder 688 0 K"Borenitl' O O O K EPowder 401 0 0 KTetryl O O KGurit 0 0 0"Nitrolit" 0 0 0 00 = NOaudibleor visibleelfed:E= Explodon:K = CRickiing noiseaminor flash.

When ignited, t he system will explode with violence some-times destroying houses and killing or maiming individualsin the vicinity. For example, when confined and mixed withthe proper volume of air, one pound of gasoline can explodewith almost 10 times as much en erm liberated as would he.liberated form one pound of dynamite, see the example cal-culation in the Appendix. A gallon of gasoline would liberateabout 62 times as much energy as a pound of dynamite.These chemicals should not be brought into the house norshould they be used for anything other than their statedpurpose. Gasoline should not be used to clean soiledclothing , floors, walls, etc. For flammable solvents intend-ed for use indoors, read labels carefully. All flammahle sol-vents should be stored in a well-ventilated area.Aerosol cans are pressurized, and they contain a propel-lant that is easily vaporized. When heated, the pressurewithin th e can becomes so great that t he can explodes. Aero-sol explosions are not as energetic as those produced fromflammable solvents or fuels, but the flying pieces of metalcan be lethal.Dry chemicals used by laymen a re also potential explosivehazards. Calcium hwochlorite, a solid used to disinfectswimming pools, is % example. The compound liberateschlorine gas when it comes in contact with moisture. Chlo-rine gas is poisonous and can cause fires and explosions ifbrought in contact with compounds such as turpen tine, am-monia gas, paint, kerosene, rubber, or alcohols. As a generalrule, add only a small amount of calcium hypochlorite to alarge volume of water, never the reverse. Use a dry, cleanscoop t o ransfer th e chemical and store the original contain-er where it cannot come in contact with moisture.The pressure inside a closed container can exceed theallowable limits, causing the container to explode. A mal-functioning safety valve on a hot water heater can createsuch an explosive system. Exploding hot water heaters have

been known to penetrate both floors of a two-story building.Both thermostats and safety valves should be checked peri-odically.

Explosives are considered thermodynamically unstablesystems. The ease with which they can be made to react byexternal forces is a measure of their sensitivity toward thatforce. Heat , friction, impact, flame, and light are a few of theexternal forces known initiate explosives.Sensitivity to HeatOne of the firs t sensitivity tests performed for safety pur-poses is to burn milligram quanti ties of the explosive inloveran open flame. Many explosives will melt before reaching anexolosion temperature. Others exolode before thev melt.Th e compound mercury fulminate is an example of the lat-ter. Th e burnine process is a self-sustainina reaction. Th eoxygen needed ;lies not come from the air but is foundwithin the compound's structure. Generally, explosive typesare arranged according to their thermal stability. Therefore,primary explosives < secondary sensitive HE < secondaryinsensitive HE (e.g., lead azide < RDX < TATB). Moreprecise data can be obtained using a differential thermalcalorimeter. These d ata are useful in planning for long-termstorage of explosives.Sensitivity to Impact

An idea of the stability of an explosive to mechanicalimpact can he obtained simply by striking a few milligrams,resting on a metal surface, with a hammer. Precise drop-weight impact machines have been designed to give morereliable dat a on impact sensitivity or to establish the criticalimpact energy necessary to make the compound or mixtureexplode. Table 1gives results from tested explosives.Sensitivity toFriction

Equipment has been designed to measure the explosiveresponse to the stress and hea t generated by friction when anexplosive is rubbed between rough surfaces. Soil or sandpa-per is sometimes used as an abrasive and a force or load isnecessary in this test. Table 2 gives results with some testedexplosives (3).TATB would no t react under t he conditionsof the test; however, RDX is sensitive to friction.I t is believed th at friction causes heat to concentrate inlocalized areas creating hot spots within the explosive. Thisresults in a self-propagating reaction that could lead to adetonation.ExplosiveReactions

Explosive reactions are exothermic, fast, and give off gas-eous pri~ducts.They an be classified as ( 1 ) deflngrntions, ( 2 )explosions, and (3) etonations. Th ew can he rmtrolle d byvarying the composition and the manner in which the explo-sive is confined. Brief descriptions of these three classesfollow.DeflagrationThis is the autocombustion of explosive particles. Also, i tis usually a surface phenomenon. In t he open air a deflagra-tion is generally slow (rate-meterslsecond) with practicallyno sound. Gases, heat, and light are final products. Thedeflagration of black powder is an example.Explosions

Explosions are extremely rapid reactions characterized bya sharp increase in pressure a t the reaction site. Gaseousproducts expand into a volume much greater than the origi-nal unreacted material and can severely deform or totallydestroy objects in th e vicinity. Explosions are accompaniedby a loud sound. The confinement of black powder in ablasting cap creates this kind of a system.Volume 64 Number 6 June 1987 54 3

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DetonationsDetonations are ex~l osio ns ropagating a t a constant ratethat exceeds the speed of so&d'(rate of a few kilometers1

second) in a given substance. Detonations are almost alwaysassociated w&h a shock wave traveling a t a given ve ~ o c % ~(detonation velocity) (4). Although usually associated withhigh explosives, some less sensitive explosives such as pro-pellants and ammonium nit rate can be made to detonate ifproperly confined.The difference between an explosion and a detonation canbe shown best by describing their effects upon a physicalobject. If an explosion is made to occur inside a 5-in. X 3-in.X l-in . wooden block, using a fuse an d a metal sleeve filledwith black powder, the hlock is broken up into large chunks.Using a blasting cap and following the same procedure thesystem can he made to detonate. The wooden hlock is thenblown into sawdust-size particles. Although the energy inhoth systems is nearly the same, the effects are quite differ-ent. In the detonation, the energy is delivered in a muchshorter period of time. This results in a much higher pres-sure, which is very destructive.Emergency Response

The time and manner in which one responds to a poten-tially explosive situation or to an explosion can save hothlives and property. Most major facilities, such as factories,government laboratories, and military establishments, havestandard operating procedures (SOP'S), which outline indetail a sequence of emergency responses. For the layman,two things are basic, (1) f possible, leave the hazard area,and (2) notify the proper authorities, the police, the firedepartment, or local military ordnance group. In many ar-eas, the emergency telephone number is 911.Conclusion

For many, explosives are sources of otherwise unavailableenergy to do work. They are used by farmers instead ofmanpower to remove trees, sha tter boulders, and drill wells.To the construction worker, they are a means of weldingmetal. of hlastine for road construction. or of dieeine canals."W -To industry, explosives are big business in various aspects ofuroduction. use. and trans~ortation.The mace industrv.. .especially in the use of solid:propellants rocket boosters, is a

good example. To the military, explosives are a means ofmainta ining defense. Basic knowledge about explosive safe-ty is of a definite benefit to laymen who might accidentallycreate an explosive atmosphere, or handle explosives occa-sionally. However, no one should attempt to use explosiveswho has not been trained to do so. To recoenize a situation~involving explosives and to know how to d e z with it cansavemany lives. This brief introduction to explosives, their rec-ognition, classification, reactions, and safety aspeets, can heused in conjunction with other resource books such as th eDangerous Properties of Industria l Materials (5) ,Explo-siues (6),and Terminal Ballistics (7).

Literature Cited1. O ne example ia found in Mi l i t a ry Erp i o r i m a : Departments of the Army and Air ForceTeehniesl M anual. U.S. Government Printing Offim: Washington, DC. Nov. 1967:

1 9 7 0 : ~ 37.4. Fair, H. 0.;Walker , R. F. Ener#e tic Moteria is; Plenum: Ne w Yark, 1977: p 431.6. Sax, N. I. Dongerour Pro p e r t i e a o ( In d u d r i o 1 Mo l e r io i s ; Reinhold: New York, 1979:pp

W L C * ?....6. Meye,. R. Explosives: Verlsg Chemie: Deerfield, FL , 1981.7. Bsckman, M. E. Terminal Roi l ist ics; Naval Weapons Center: Chins Lake, CA, 1976.

Appendix: Example CaiculatlonDynamite

Detonation Energy = 1Kcallg453 gilb X 1 Kcallg = 45 3 KealflhGasoline (n-Octane)

Heat of combustion = 112,460 BTUIgal

Comparison4,325.4 Kcalflb gasoline = 9.6453 Kcalllb dynamite

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