Environmental Engineering Reference
In-Depth Information
workers;.and.limit.worker.occupancy,.or.the.number.of.workers.present,.especially.
in.conined.or.enclosed.spaces.
Some.types.of.personal.protective.clothing.can.be.employed,.such.as.relective.
clothing,. which. can. vary. from. aprons. and. jackets. to. suits. that. completely. enclose.
the.worker.from.neck.to.feet..Such.clothing.can.stop.the.skin.from.absorbing.radiant.
heat..However,.because.most.relective.clothing.does.not.allow.air.exchange.through.
the.garment,.the.reduction.in.radiant.heat.must.more.than.offset.the.corresponding.
loss. in. evaporative. cooling.. For. this. reason,. relective. clothing. should. be. worn. as.
loosely.as.possible..In.situations.where.radiant.heat.is.high,.auxiliary.cooling.sys-
tems.can.be.used.under.the.relective.clothing.
Also,. commercially. available. ice. vests,. although. heavy,. may. accommodate. as.
many.as.seventy-two.ice.packets,.which.are.usually.illed.with.water..Carbon.dioxide.
(dry.ice).can.also.be.used.as.a.coolant..The.cooling.offered.by.ice.packets.lasts.only.
2. to. 4. hours. at. moderate. to. heavy. heat. loads,. and. frequent. replacement. is. neces-
sary..However,.ice.vests.should.not.encumber.the.worker.and.thus.permit.maximum.
mobility..Cooling.with.ice.is.also.relatively.inexpensive.
Wetted. clothing. is. another. simple. and. inexpensive. personal. cooling. technique..
It.is.effective.when.relective.or.other.impermeable.protective.clothing.is.worn..The.
clothing. may. be. wetted. terry. cloth. coveralls. or. wetted. two-piece,. or. whole-body,.
cotton.suits..This.approach.to.auxiliary.cooling.can.be.quite.effective.under.condi-
tions.of.high.temperature.and.low.humidity,.where.evaporation.from.the.wetted.gar-
ment.is.not.restricted..Water-cooled.garments.range.from.a.hood,.which.cools.only.
the.head,.to.vests.and.long.johns,.which.offer.partial.or.complete.body.cooling..Use.
of.this.equipment.requires.a.battery-driven.circulating.pump,.liquid-ice.coolant,.and.
a. container.. Although. this. system. has. the. advantage. of. allowing. wearer. mobility,.
the.weight.of.the.components.limits.the.amount.of.ice.that.can.be.carried.and.thus.
reduces.the.effective.use.time..The.heat.transfer.rate.in.liquid.cooling.systems.may.
limit.their.use.to.low-activity.jobs;.even.in.such.jobs,.their.service.time.is.only.about.
20.minutes.per.pound.of.cooling.ice..To.keep.outside.heat.from.melting.the.ice,.an.
outer.insulating.jacket.should.be.an.integral.part.of.these.systems.
Circulating. air. is. the. most. highly. effective,. as. well. as. the. most. complicated,.
personal. cooling. system.. By. directing. compressed. air. around. the. body. from. a.
.supplied. air. system,. both. evaporative. and. convective. cooling. are. improved.. The.
greatest.advantage.occurs.when.circulating.air.is.used.with.impermeable.garments.
or.double-cotton.overalls.
One. type,. used. when. respiratory. protection. is. also. necessary,. forces. exhaust. air.
from.a.supplied-air.hood.(bubble.hood).around.the.neck.and.down.inside.an.imper-
meable. suit.. The. air. then. escapes. through. openings. in. the. suit.. One. problem. with.
this.system.is.the.limited.mobility.of.workers.whose.suits.are.attached.to.an.air.hose..
Another.is.that.of.getting.air.to.the.work.area.itself..These.systems.should.therefore.be.
used.in.work.areas.where.workers.are.not.required.to.move.around.much.or.to.climb.
The. weight. of. a. self-contained. breathing. apparatus. (SCBA). increases. stress.
on.a.worker,.and.this.stress.contributes.to.overall.heat.stress..Chemical.protective.
.clothing.such.as.totally.encapsulating.chemical.protection.suits.will.also.add.to.the.
heat.stress.problem.
