FEATURE

Testing explosives:Consideratintrinsically ratory

Certain materials are intrinsically ofthey are handled. Examples inclu wdpropane. Industries working with ac

Laboratories working with these e lebecause of the small quantities us thesuch as ventilation fume hoods.

However, when a laboratory ro sivaccidental detonation will exist. A enmaterials. Though it may be impo d opreparation will produce a workp ard

o b ndsh em

explosive powders such as black pow-der, or explosive gases such as pro-

are rare.

ventilation fume hoods. Protectivemeasures are required only if thehazardous materials have potential

exist with non-listed materials effortsshould be taken to avoid exposingmaterials to detonation sources.

al arcsoutlets,devices,produ-protec-

areal Elec-by theciation

prevent

Cear

hazahazatheme-mail: jkbchemist@gmail.com).produce a workplace that is compati-ble with these hazardous materials.Such planning includes giving consid-eration to building design, laboratoryprocedures, and personnel behavior aswell as having contingencies in placeshould a catastrophic failure of thesesystems result in an explosion.

confusion when reviewing these guide-lines are:

Intrinsically safe: Systems, circuits,or equipment which are not capableof producing any spark or thermaleffect capable of causing ignition of amixture of flammable or combusti-

J. Keith Butler is affiliated with adefense contractor to the US Army.He resides in Tennessee, United States(Tel.: 731 414 6598; fax: 731 686 6433;

handled.

24 Division of Chemical Health and Safety of the American Chemical Society 1871-5532/$36.00of how they areElseighly regulated so accidentsIn fact most accidents in these

by routine or by accident. For examplelaboratories routinely use diethylether without incident and withoutextraordinary measures.

However, when a laboratory routi-nely manipulates materials with explo-sive hazards, an elevated risk ofaccidental detonation will exist. Anintrinsically safe laboratory is the bestenvironment to manipulate such mate-rials. Though it may be impossible for alaboratory to be safe in and of itself,careful planning and preparation will

arc from static discharge, sparing from hand tools or mhandling equipment, electricfrom infrastructure serviceelectrical arcs from electronicand thermal effects from heatcing equipment. Many of thetive measures availableincorporated into the Nationtric Code (NEC) publishedNational Fire Protection Asso(NFPA).3

Two definitions that will

rtain materialse intrinsicallyrdous they arerdous in and ofselves regardlesspane, butane, and acetylene.Industries working with these materi-

als are h

to exist in explosive concentrations Hazards to avoid include electricalks aris-aterialincludes giving consideration thaving contingencies in place

By J. Keith Butler

INTRODUCTION

Certain materials are intrinsicallyhazardous they are hazardous inand of themselves regardless of howthey are handled. Examples includevier Inc. All rights reserved.ions for ansafe labo

hazardous they are hazardous in andde explosive powders such as black pothese materials are highly regulated somaterials may not be subject to the sam

ed for laboratory scale procedures and

utinely examines materials with explon intrinsically safe laboratory is the bestssible for a laboratory to be safe in anlace that is compatible with these haz

uilding design, laboratory procedures, aould a catastrophic failure of these syst

industries are normal industrial acci-dents such as slips, trips, falls, backstrain, cuts and abrasions, etc.

Laboratories working with thesematerials may not be subject to thesame level of regulation because ofthe small quantities used for labora-tory scale procedures and the con-trolled conditions in use such asthemselves regardless of hower, or explosive gases such ascidents are rare.vel of regulation as industry iscontrolled conditions in use

e hazards, an elevated risk ofvironment to manipulate suchf itself, careful planning andous materials. Such planningpersonnel behavior as well ass result in an explosion.

STANDARDS AND REGULATIONS

Every year the U.S. Bureau of Alcohol,Tobacco, Firearms and Explosivespublishes a list of materials that areexplosive and may require these pro-tective measures.1,2 If a laboratoryworks with any of these materials orsuspects a hazardous condition maydoi:10.1016/j.jchas.2009.02.006

la

hazards. Ignition is generally more

Jonormally confined to closed systems,but could escape under accidental orabnormal conditions.vsions:

Division 1 for environments whereignitable concentrations can existunder normal conditions; and,

Division 2 for environments whereolatile flammable liquids/gases areThe petroleum and gas industries areexamples of operations where Class Ienvironments may be encountered.These environments may have flam-mable gases and vapors present in theair in ignitable concentrations. Thehazard isobvious.Any laboratory invol-ved in research or analysis may fromtime to time encounter gases such asacetylene or hydrogen or vapors fromsolvents such as ether, acetone or gaso-line. Precautions should always betaken to avoid the formation of ignita-ble concentrations. If this cannot becontrolled with absolute certainty, pro-tective measures should be taken.Within this classification are two divi- Class III ignitable fibers or flyings

Class II combustible dusts

Cfied in three ways depending on thesource of the hazard:

lass I flammable gases and vaporsHAZARDOUS ENVIRONMENTCLASSES

The NEC describes hazardous environ-ments in two ways. The North Ameri-can classification includes classes,divisions, and groups. An alternateclassification system of Europeanorigin classifies hazardous locationsby Class and Zone. The Class/Divi-sion/Group system will be presentedin more detail here. An introductionto the Zone classification system willfollow.

Hazardous environments are classi-ptuwithstand an internal explosion andto contain the burning mixture to

revent ignition of explosive mix-res in the room.dble materials in air. These shallalways be grounded and bonded toany associated equipment.Explosion proof: An enclosure

esigned with sufficient strength tournal of Chemical Health & Safety, Novemgenerated in laboratories by a numberof processes such as by grinding,scientists should give considerationto these precautions for their labora-tories. This is especially true whenworking with high carbon containingparticles or combustible metals such asaluminum or magnesium. Dusts can bezerestbs or fuels. With the increasing inter-in nanoparticles, materialsdus

usekeeping when the laboratoryt includes materials that are oxidi-Spehocial vigilance should be given to

Tsion resulting in total destruction of afacility that initially had no visibledust problems.

his could happen in a laboratory.Both divisions have the followinggroups based on the autoignition tem-perature of the hazardous substance.The group designation is most usefulwhen applied to equipment design.Heat producing machinery is oftenrated for the following groups basedupon their thermal output.

Group A Acetylene Group B Hydrogen and fuels with>30% hydrogen

Group C Ether, ethylene, etc. Group D Acetone, ammonia, ben-

zene, butane, gasoline, natural gas,methane, etc.

Class II environments may beencountered in any industry that haspotential to generate combustibledusts. News reports4 of explosionsfrom grain processing facilities andsugar refining plants are unfortunatereminders of the constant vigilancerequired in these environments.Laboratories are much less likely tohave combustible dust hazardousenvironments but these must be dis-cussed. Many catastrophic industrialaccidents caused by combustibledusts are secondary explosions thatfollow a localized initiating blast.The initial localized blast may notdestroy a building but can shake therafters, and HVAC duct work, andsuspended light fixtures, and anyother structure that allows dust tocollect with little or no housekeepingattention. Localized fires or electricalarc from damaged electrical equip-ment may ignite the newly formeddust cloud propagating a major explo-er/December 2009HAZARDOUS ENVIRONMENT ZONES

An alternative method of classifyinghazardous environments comes fromEurope and is included in the moresproduced or used.Division 2 for locations whereeasily ignitable fibers or flyings aretored.egenerate a Class II environment.There are two divisions but no sub-groups for ignitable fiber or flyingenvironments:

Division 1 for locations whereasily ignitable fibers or flyings aredifficult. A class III laboratory envir-onment likewise could develop underconditions similar to those that wouldas severe as those found with Class II

assrge to be classified as a dust. Theociated hazards are similar but notborof cotton, bulk cellulose, textiles, orother material capable of forming air-

ne suspensions of particulates toomally in the air but may occur infre-quently due to malfunctioningequipment.

Both divisions have the followingGroups based on ignition temperatureof the dust:

Group E metal dusts (Al, Mg, etc.) Group F carbonaceous dust (car-

bon, coal, charcoal, coke, etc.) Group G other dusts (flour, grain,

wood, sugar, chemicals, etc.)

Class III environments are lesscommon than Classes I and II. ClassIII environments cover easily ignita-ble fibers or flyings. These may beencountered where large quantitieswoconditions.Division 2 for environments

here ignitable concentrationsf combustible dusts are not nor-t Division 1 for environments whereignitable concentrations of combus-ible dusts can exist under normalmilling, or sieving. Any procedurerequiring a dust respirator be worncould fall into this Classification. Thereare also two divisions for combustibledust environments:25

anre

cl

ensure the greatest electrical safetyavailable.

PRACTICES AND PROCEDURES LABORATORY CONSTRUCTION

The remainder of this article willaddress specific actions to take whenworking in a Class I environment. Thefirst item to consider is the buildingitself. While avoiding an explosion isthe ultimate goal, designs to minimizethe negative impact of an explosion tothe surrounding environment shouldbe considered as a contingency for aworst case scenario. The military haspublished guidelines for design ofStructures to Resist the Effects ofAccidental Explosions.7 One of thekey features of the building design isblow-out walls and ceilings.

If an explosion occurs in a laboratory,structural damage will result. If theexplosion is large enough to cause

tion. If in a stand alone building andif real estate is available, isolate it fromother occupied areas. This is done bydistanceaswells as shielding in the formof earth or manufactured barricadesthat will direct the force of an explosionupward and away from ground activ-ities. OSHA publishes safe quantity dis-tance limits in 29 CFR 1910.1098 basedon the quantity and type of explosivebeing used. Another option is to locatethe building adjacent to an unoccupiedarea that can serve as buffer zone toabsorb the directed force of an acci-dental explosion. If the laboratory isincorporated into a multipurpose struc-ture, locating it on the top floor in acorner room would provide three direc-tions for the force to be directed awayfrom other occupants and operations.Local building codes as well as applic-able OSHA and ATF regulations shouldbe reviewed prior to locating potentiallyexplosive activities in such facilities.

Once the location is selected, the

Figure 1. A simple laboratory is constructeblow-out. There is a reinforced dividing w

ctiy sin multiple severe injuries and evendeath,4 imagine what would happen ifthe dust were an explosive such as TNTor black powder. With no other indus-try standard available, the explosivesIndustry utilizes Class I guidelines tonatent26om its Class, Division, and Groupassifications. If sugar dust can deto-

e with sufficient energy to destroy anire manufacturing facility resultingconfrments, comes much responsibilityd liability. This may be part of theason the NEC excludes environments

taining explosives and gun powdersinfronZone classifications can be found inthe 2008 NEC3 or in ANSI/ISA 60079-185 and ANSI/ISA 61241-10.6

With the authority to classify hazar-dous work environments and todevelop standards for equipment and

astructure that is safe in these envir-such as maintenance or system fail-ure.

More detailed information aboutcinZone 22 locations will have ignitableoncentrations of dust, fibers, or fly-gs only under unusual conditionssZone 21 locations will likely haveignitable concentrations presentome time during normal operations.ctions exist when ignitable concentra-tions of combustible dusts, fibers andflyings may be present.

Zone 20 locations will have ignitableoncentrations present continuously.recent versions of the NEC. This sys-tem uses multi-tiered zones.

Class I, Zone 0, Zone 1, and Zone 2hazardous locations exist where fire orexplosion hazards may exist due toflammable gases, vapors or liquids:

In Zone 0 locations a risk of fire orexplosion is present during normaloperations.

In Zone 1 locations a risk of fire orexplosion may not exist continu-ously, but will occur as part of nor-mal operations.

In Zone 2 locations hazardous mate-rials are present but they are notlikely to be found in ignitable con-centrations in the air. Many conven-tional laboratories are Class 1, Zone2 locations.

Zones 20, 21 or 22 hazardous loca-explosion hazards from less hazardous aadjacent to the building to protect near-bstructural failure, collateral damage willbe felt by near-by structures as well asbystanders in the vicinity of the labora-tory. To reduce the amount of collateraldamage and bystander injury the regionof least impact should be identified andefforts taken to direct the greatest forceof an explosion in that direction. Thefirst consideration is laboratory loca-Journal of Chemical Healthconstruction design should includeconsiderations for an accidental explo-sion.7 First, reinforced walls should beconstructed in accordance with provenengineering designs to separate thepotentially explosive work area fromother activities. Secondly, portions ofthebuilding shouldhaveweaker,break-away features designed to fail quickly

d with 3 strong walls and 1 weak wall toall to serve as a barrier that separates

vities. Also notice the earthen barricadetructures.& Safety, November/December 2009

conductive material which is properlyand allow the greatest force of theexplosion to be directed in a designeddirection to minimize collateraldamage. In Figure 1 a simple laboratoryis constructed with three strong wallsand oneweakwall. The roofmayalsobeconstructed to blow-out. There is areinforced dividing wall to serve as abarrier that separates explosion hazardsfrom less hazardous activities. Alsonotice the earthen barricade adjacentto the building to protect near-by struc-tures. This design feature was usedextensively by the DuPont powder millsnear Wilmington, Delaware as early as1804.9 This arrangement is conduciveto one of the fundamentals to safelyworking with hazardous materials:minimize the number of peopleexposed to the hazard.

Defeating static discharge shouldalso be considered when designing orupdating a laboratory to work with sta-tic sensitive materials. Similar measuresare taken by the semiconductor indus-try to protect their products. Thoseworking with static sensitive energeticmaterials also need to protect their pro-duct but more importantly to protectpeople! Everything in the laboratory,including humans, can develop a staticpotential. As two objects approach eachother a static discharge may occur fromthe object of high potential to the objectof low potential. This discharge hassufficient energy to initiate a detonationin a number of materials (natural gas,black powder, etc.) Therefore stepsshould be taken to prevent static buildup and to drain static potential fromanything, including personnel, enteringthe laboratory.

All metal components of the buildingmust be grounded to allow electricalpotential to drain to the ground. Metalcomponents should also be electricallybonded tocontact material. This is com-monly done when transferring solventsfrom a metal drum to a metal safety can.But it is also a construction considera-tion when building a facility to workwith static sensitive materials. Forexample, touching a metal door knobcan result in a static discharge under theright conditions. If both the door andperson are connected to a commonground, this should not occur. Anotherexample would be two moving parts ofthe same piece of equipment such as theJournal of Chemical Health & Safety, Novemgrounded. The grounding potentialshould be periodically verified by a qua-lifiedelectrician.This will alsoprovideaconvenient location to connect anti-static wrist straps to ground.

It is possible for regions of variableelectrical potential to develop in differ-ent parts of a person and their clothing.When working with electrostatic sensi-tive materials, conductive flooringgrounded to earth is needed in additionto the wrist strap and grounded work-stations. The flooring may be incorpo-rated into the building design andinstalled uniformly throughout thelaboratory. Or for protection in limitedareas it may be a conductive structurethe analyst stands on at specific work-stations. These may be conductive pads,metal grates, or metal platforms; all ofwhich are properly grounded.

Note that this electrically groundedarrangement allows static potential todrain from personnel and is more protec-tive than electrostatic dispersive surfaces(EDS). EDSs can prevent the accumula-tion of a static build up as one walks acrossthe floor but may not drain away a chargethat has developed in some other manner.

Conductive flooring offers no pro-tection unless the analyst is conduc-tively connected to the floor. Anti-static leg or heel straps or conductiveshoe covers can be worn by the analystthat function much like wrist straps byconnecting a conductor to skin on theleg or foot with the grounded conduc-tive floor. Disadvantages are that thetop and bottom half of a guillotine cut-ting device.

Laboratory personnel will also carryan electrostatic potential. An anti-staticwrist strap connected to a ground wireis the simplest method of draining staticfrom the body. However it is critical tohave proper contact between theground connecter and skin. Groundingshould be verified periodically. Thismay be done by a qualified electricianor by the use of special meters designedfor use with wrist straps.

Grounded workstations offer addi-tional protection. They will allow a con-ductive pathway to ground formaterialsbeing handled as well as the analyst.These may be metal sheeting or otherber/December 2009shoe covers have short life times andcan be uncomfortable to walk in. Thesolution to this is conductive shoes,most of which come with steel toes.Disadvantages include cost and theyare not one size fits all. For conductiveshoes to work, non-insulating socksmust be worn. Nylon, rayon, and othersynthetic polymers are insulators. Ifsocks are worn they should have sig-nificant cotton or wool content. Poli-cies should also be in place to forbidodor reducing insoles as these willinsulate the wearer from the ground.Foot powders should not be usedeither. Electrostatic potential willdrain from the body best when theconductivity is maximized. Having anelectrolytic solution of water and salt(a.k.a. sweat) will ensure optimumfunction and a more protected analyst.The conductivity and grounding abilityof the flooring material should bechecked and documented on a regularbasis. As a minimum, daily verificationof the conductivity of the leg stats, shoecovers, or conductive shoes should bedocumented. Manufacturers of theseprotective items will have specifica-tions for proper function. All of thetest equipment used to verify conduc-tivity and grounding of the wrist stats,work benches, shoes, and flooringshould be calibrated to ensure propercompliance to those specifications.

Additional consideration should begiven to the clothing the analyst wears.Fabric of a lab coat brushing againstunderlying garments can result in anelectrostatic potential difference thatcould produce a spark. Conductivelab coats are available. One exampleis made from Worklon Micro Statpoplin blend which is approximately20% cotton with a semiconductingfiber grid woven into the fabric. Thesecome with metal snaps that can beconnected to ground wires using thesame cables found on wrist straps.(Conductive lab coats are availablethrough most distributors of laboratorysupplies.) Again, before assuming pro-tection the conductivity should be ver-ified with a calibrated meter.

Another type of static discharge thatshould not be overlooked is lightning.Lightning rods should be installed andgrounded so that the building is onecontinuous grounded electrical con-27

ductor. As devastating as a direct strikecan be, this will keep the lightning out-side rather than allowing it inside wheresensitive materials would be detonated.

In addition to electrostatic dischargeor sparks, construction design featuresmust include measures to prevent elec-trical arc or current jumping betweentwo electrodes. This is commonly seenin electrical switches such as lightswitches, thermostats, instrumentpower switches, or when plugs con-neinalposuinci

hazardous environment. For example

28 Journal of Chemical Healtha circuit breaker box could be locatedin a room accessed from outside awayfrom the laboratory. The conduit feed-ing into the breaker box would requiresealing devices in line between thehazardous environment and the box;although explosion proof breakerboxes are available at considerableexpense. If explosion proof circuitsand standard circuits are in the samebuilding, these must be separated sothat gas and dust cannot pass from oneto the other.

A detailed discussion of this type ofconstruction is beyond the scope ofthis paper; however, some examplesare presented for consideration:

Electrical conduit (Figure 2)A. Explosion proof conduit also

known as rigid metal conduitis heavy walled and threadedwith 5 threads fully engaged.

B. Standard conduit is thin walledand clamped to service boxes.

Figure 2. These fire alarm pull stationsillustrate the difference between stan-dard service boxes and conduit andClass I, Division 1 conduit and serviceboxes. (A) is connected by engaging 5or more threads; (B) with a set screw.(A) is heavy walled (3/8 in.); (B) is thinwalled (1/16 in.). (A) is held into placeby 4 heavy one inch long screws; (B)has a snap-on cover. (A) will weigh over2 pounds; (B) only a few ounces.isol&trinsically safe devices shouldways be used. This is not alwaysssible and explosion proof enclo-res must be used. Explosion proof-g is often done by sealing exposedrcuits and locating power sources in

ated locations away from theSct to receptacles. When possible,afety, November/December 2009

Figure 4. Light fixtures: (A) fluorescent, notice the rigid conduit connections, thereinforced diffuser glass, the gasket seal between the glass and bulb compartment,the thickness of the sheet metal. (B) Incandescent, notice the heavy globe surroundedby a protective cage, the elaborate enclosure to protect from heat as well as arc, andthe label indicating that the fixture is suitable for use in hazardous locations.

Figure 3. Explosion proof light switch thick walled, assembled with large screwsweighing 2 pounds.

Jofixture is in place to prevent acci-dental breakage.

Explosion proof fixtures are avail-able for any electrical service neededincluding receptacles, exit lights, firealarm pull stations and alarms withstrobes, intercom systems, pagingsystems, telephones, flashlights, etc.These are low volume items for ven-dors. They have substantial con-struction features. Selling them forhazardous environments carries lia-bility for the vendor.plate (Figure 3). The actual switchis toggled up and down remotelyby an external lever or push buttonsystem that is sealed. Rather thanstandard knock-outs, the boxhas a heavy walled openingthreaded multiple times to receiverigid conduit.

Light fixtures Two hazards with standard fixtures

are breakage and the resultingexposed arc or heat source, andfor fluorescent bulbs, arcs thatmay occur when the lamp initiates.

Explosion proof fixtures (Figure 4)are sealed to prevent explosivegases and dusts from enteringhot zones. They are also rein-forced to withstand an explosionshould one occur. Often a guardurlong bolts connecting the facenate.Service boxes Standard light switch service

boxes are thin walled. The faceplate which is commonly madeof plastic is held on loosely withtwo small screws.

For hazardous environments, thelight switch must be enclosed in aservice box with a cover rated foruse in the working environment.Class 1 boxes are thick walled,heavy, (2 pounds) with multiplement outside the enclosure to deto-

wSome types of conduit arethreaded to take washer type nutsthat only engage about 2 threads.That will not meet the demands ofan explosion proof enclosure. Therequirement for multiple threads isto create a path of sufficient lengthto cool hot gases resulting from anexplosion within the conduit. Thegases must cool to a temperature that

ill not cause gases in the environ-nal of Chemical Health & Safety, November/December 2009 29

vendor. I am not aware of an intrinsi-cally safe moisture balance either. In

pressure must be maintained at alltimes; if it ever fails there is a risk ofdust entering the device that cannot bepurged out. The device will need to bedisassembled and physically cleanedbefore placing back in service.

Heat sources can also be proble-matic. One solution is to heat withsteam that is generated external tothe hazardous environment andplumbed to the work station.

As a result of such severe restric-tions, modern instrumental techni-

Some non-electrical equipment canalso be a source of electrostatic dis-charge. Tools used for custodialand maintenance activities should bechosen carefully when hazardousenvironments are present. For example,hundreds of nylon bristles rubbingagainst one another as a broom brushesacross a floor may generate thousandsof electrostatic discharges. Plastic dustpans used to clean a floor can be a risktoo. This would also apply to smallbalance brushes used to clean up smallmesses near a balance. A steel wrenchor screwdriver being used to open asteel pail or drum could create a spark.

Conductive/non-spark forming toolsare available for every job. Brooms andbrushes should be natural animal orplant fiber. These include boars hairor horse hair push brooms and brushes,straw brooms, conductive non-sparkdust pans, and hand tools made fromnon-ferrous alloys such as copper/ber-

will fail. As a last line of defense shield-ing should be placed between the

ts for providing electrical service to a con-ion 1 hazardous location.

onventionaliring10

Class I, Division1 wiring11

$6.49 $25.65$4.67 $554.49$4.77 $160.1022.99 $955.7012.79 $274.45the light source can be sealed and iso-lated from the hazardous environmentsuch cases adjustments must be made.If a mechanical balance is availablewith suitable accuracy and precision,You will pay for this.

It will be worth it.

For a comparison of standardparts vs. explosion proof parts seeTable 1.10,11

PRACTICES AND PROCEDURES LABORATORY FURNISHINGS

Like a chain, a safety system will onlyprotect as well as its weakest link. Onceyou have a safe facility to work in, youhave to furnish it. Each piece of equip-ment placed in the laboratory should beevaluated as a potential detonationsource either by electrical arc or bythermal effects. All devices should berated intrinsically safe which will bemarked on the instrument. Or, it may berated for a specific hazardous environ-ment such as Class I, Groups A, B, C, Dor Class II E, F, and G, etc. Manydevices are available with this designa-tion. Vent hoods, electric motors,laboratory ovens, and balances butnot analytical balances with four deci-mal places! It appears there is notenough market demand for such a bal-ance to be economically attractive to a

Table 1. Cost comparison of componenventional location and to a Class I, Divis

Cw

Conduit, 3/4 in. 10 ftReceptacleLight switchFluorescent light fixture $Incandescent light fixture $Figure 5. A double pan balance withcertified weight set can also be used,but these are difficult to procure as well.

With careful consultation with themanufacturer, many devices may bepurged with an inert gas and main-tained under positive pressure(Figure 6). This works well when thehazardous environment is a gas. Gasesare easy to purge. Explosive dusts aremore difficult. Therefore, the positive

30ques are often not safe whenmanipulating explosive materials.Therefore, classical wet chemistryanalysis techniques are often utilized.These techniques would have beenquite common for the analytical che-mist of the 1950s and 1960s. Whenundertaking tasks with these types ofhazards, new analysts may discoverthat these new techniques are reallyquite old, even classic!Figure 5. Manual analytical balance with ligsystem with a magnifying lens to focus thescale. Heat vents above the original locatioexplosive dusts out of the balance. Also notthe left of the balance.

Journal of Chemical Healthworker and the hazard whenever pos-

ht source isolated in an explosion prooflight as needed to illuminate the balancen of the bulb have been sealed to keepice the explosion proof toggle switch toyllium or aluminum/bronze alloys.

PRACTICES AND PROCEDURES PERSONNEL

Even with proper construction andequipment selection, systems can and& Safety, November/December 2009

Table 2. Quantity distance calculations.

Journal of Chemical Health & Safety, November/December 2009 31

their life. But, an accident with explo-sive materials can cause severe injuryand death to co-workers. This requiresa greater sense of responsibility forworking safe and ensuring thosenear-by are working safely.

CONCLUSIONS

Few laboratories are hazardous workenvironments which require all ofthese extraordinary measures to be inplace. However, anyone working in alaboratory has the potential to findthemselves in a hazardous situation.It is at these times that an awarenesssible. This could be an enclosure forremotely operated equipment or asmall laboratory shield used whenmanually processing materials. Safetyglasses face shields, and appropriategloves should always be used.

Engineering controls alone will notensure an intrinsically safe work envir-onment. Policies and procedures thathave been verified to be protective,that are supported by all levels ofsupervision, that are enforced withsevere penalties, and are judiciouslypracticed by everyone in the laboratoryare needed.

Examples include proper storage ofenergetic materials. Explosion proofreinforced barricade type storage cabi-nets should always be used and shouldremain closed unless adding or remov-ing materials. The amount of materialin a building should be limited to theleast amount necessary but never toexceed a maximum amount for the

Figure 6. Factory supplied purge gas optisuitable for use in a hazardous location. Noboth the upper portion holding the heatingholding the balance mechanism and electro

32locguEaoplimnediftivwhor

alwwo

1.

2.

3.

Wmathe

ontice

nication as determined by appropriateidance documents8,12,13 (Table 2).ch operation should have a standarderating procedure which shouldit the amount of hazardous material

eded for that procedure. Materials offerent hazards and different sensi-ities should always be segregatedether in storage, while being used,as a waste.

Supervisors and operators shouldays follow three fundamentals torking with hazardous materials:

Minimize amount of hazardousmaterialMinimize the number of employeesexposedMinimize employee exposure time

Attitude of the worker is important.orkers should always respect theterials they work with, but not topoint of being terrified. If the work

for a moisture balance to render ite that the inert gas is split to purgelement as well as the lower portions.

that will promote a

Journal of Chemical HealthREFERENCES1. Bureau of Alcohol, Tobacco, Firearms,

and Explosives, Department of Justice:List of Explosive Materials, 27 CFRSubchapter C Part 555.23.

safe, productive workenvironment.of these hazards and the measures thatcan be taken to prevent a fire or explo-sion become critical. These are mostuseful when considered in advance,during the planning stages of a proce-dure rather than during an actualemergency. It is hoped that this articlehas given the reader new insight topotential hazards and preventive mea-sures that will promote a safe, produc-tive work environment. Extraordinaryhazards require extraordinary caution.Intrinsically hazardous materials mustbe manipulated under conditions thatare as intrinsically safe as possible.

It is hoped that thisarticle has given thereader new insight topotential hazards andpreventive measurescauses nervousness, they should find anew job. That is important for theworker as well as for co-workers.Many industrial accidents can cost aworker a finger, a hand, an eye or even& Safety, November/December 2009

2. Federal Register Volume 73, Number251, December 31, 2008, p. 80428.

3. National Electric Code published by theNational Fire Protection Association.Most codes published by the NFPAcan be accessed online. Registration isrequired but without cost. The NFPA70: National Electrical Code starts at:http://www.nfpa.org/aboutthecodes/AboutTheCodes.asp?DocNum=70#Near the bottom of the page is theheading Additional Information aboutthis Document. Select one of thedocuments to VIEW and follow theprompts. You will not be able to copy,search or print the contents. AccessedDecember 29, 2008.

4. Johnson,; Jeff. C&EN, 2008, 86(12),3839.

5. ANSI/ISA-60079-18 (12.23.01)-2005,Electrical Apparatus for Use in Class

I, Zone 1 Hazardous (Classified) Loca-tions: Type of Protection Encapsula-tion, 2005, ISBN/ID: 978-1-55617-960-0.

6. ANSI/ISA-61241-10 (12.10.05)-2004,Electrical Apparatus for Use inZone 20, Zone 21 and Zone 22Hazardous (Classified) Locations Classification of Zone 20, Zone 21and Zone 22 Hazardous (Classified)Locations, 2004, ISBN/ID: 978-1-55617-931-0.

7. US Army manual: TM 5-1300 Struc-tures to Resist the Effects of AccidentalExplosions, November 1990.

8. Occupational Safety and Health Ad-ministration, Department of LaborRule for Explosives and Blastingagents, 29 CFR 1910.109.

9. Kelly, J. Gunpowder, Alchemy, Bom-bards & Pyrotechnics: The History of

the Explosive that Changed the World.Basic Books: New York, 2004, pp. 173,174, ISBN 0-465-03718-6.

10. Ace Hardware Store, Trenton, Tennes-see; shelf price December 30, 2008.

11. Catalog, from Dale Electric SupplyWeb site: http://www.dale-electric.com/pdf/page104.pdf, accessed De-cember 29, 2008.

12. Department of Defense Manual: DOD4145.26-M, DOD Contractors Safetymanual for Ammunition and Explo-sives, March 13, 2008, Under Secre-tary of Defense for Acquisition andTechnology.

13. Department of Defense Manual: DOD6055.9 STD, DOD Ammunition andExplosives Safety Standards, July1999, Under Secretary of Defense forAcquisition and Technology.Journal of Chemical Health & Safety, November/December 2009 33

Testing explosives: Considerations for an intrinsically safe laboratoryIntroductionStandards and regulationsHazardous environment classesHazardous environment zonesPractices and procedures - laboratory constructionPractices and procedures - laboratory furnishingsPractices and procedures - personnelConclusions