-
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: [email protected]).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
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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
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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
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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