Environmental Engineering Reference
In-Depth Information
where. WBGT. =. Wet. Bulb. Globe. Temperature. Index,. NWB. =. Nature. Wet-Bulb.
Temperature,.DB.=.Dry-Bulb.Temperature,.and.GT.=.Globe.Temperature.
Exposure. limits. are. valid. for. employees. wearing. light. clothing.. They. must. be.
adjusted.for.the.insulation.from.clothing.that.impedes.sweat.evaporation.and.other.
body. cooling. mechanisms.. Ventilation,. air. cooling,. fans,. shielding,. and. insulation.
are.the.ive.major.types.of.engineering.controls.used.to.reduce.heat.stress.in.hot.work.
environments.. Heat. reduction. can. also. be. achieved. using. power. assists. and. tools.
that.reduce.the.physical.demands.placed.on.a.worker..However,.for.this.approach.to.
be.successful,.the.metabolic.effort.required.for.the.worker.to.use.or.operate.these.
devices. must. be. less. than. the. effort. required. without. them.. Another. method. is. to.
reduce.the.effort.necessary.to.operate.power.assists..The.worker.should.be.allowed.
to.take.frequent.rest.breaks.in.a.cooler.environment.
The. human. body. can. adapt. to. heat. exposure. to. some. extent.. This. physiologi-
cal.adaptation.is.called.acclimatization..After.a.period.of.acclimatization,.the.same.
activity. will. produce. fewer. cardiovascular. demands.. The. worker. will. sweat. more.
eficiently.(causing.better.evaporative.cooling),.and.thus.will.more.easily.be.able.to.
maintain.normal.body.temperatures..A.properly.designed.and.applied.acclimatiza-
tion.program.decreases.the.risk.of.heat-related.illnesses..Such.a.program.basically.
involves.exposing.employees.to.work.in.a.hot.environment.for.progressively.longer.
periods..NIOSH.(The.National.Institute.for.Occupational.Safety.and.Health).stated.
that,.for.workers.who.have.had.previous.experience.in.jobs.where.heat.levels.are.high.
enough.to.produce.heat.stress,.the.regimen.should.be.50.percent.exposure.on.day.1,.
60.percent.on.day.2,.80.percent.on.day.3,.and.100.percent.on.day.4..For.new.workers.
who.will.be.similarly.exposed,.the.regimen.should.be.20.percent.on.day.1,.with.a.
20 percent.increase.in.exposure.each.additional.day.
Cool.(50°F.to.60°F).water.or.any.cool.liquid.(except.alcoholic.beverages).should.
be.made.available.to.workers.to.encourage.them.to.drink.small.amounts.frequently.
(e.g.,. one. cup. every. twenty. minutes).. Ample. supplies. of. liquids. should. be. placed.
close.to.the.work.area..Although.some.commercial.replacement.drinks.contain.salt,.
this.is.not.necessary.for.acclimatized.individuals.because.most.people.add.enough.
salt.to.their.summer.diets.
Engineering.controls,.such.as.general.ventilation,.are.used.to.dilute.hot.air.with.
cooler.air.(generally.cooler.air.that.is.brought.in.from.the.outside)..This.technique.
clearly. works. better. in. cooler. climates. than. in. hot. ones.. A. permanently. installed.
ventilation.system.usually.handles.large.areas.or.entire.buildings..Portable.or.local.
exhaust.systems.may.be.more.effective.or.practical.in.smaller.areas..Air.treatment/air.
cooling.differs.from.ventilation.because.it.reduces.the.air.temperature.of.the.air.by.
removing.heat.(and.sometimes.humidity).from.the.air..Air.conditioning.is.a.method.
of.air.cooling.but.it.is.expensive.to.install.and.operate..An.alternative.to.air.condi-
tioning.is.the.use.of.chillers.to.circulate.cool.water.through.heat.exchangers,.over.
which.air.from.the.ventilation.system.is.then.passed;.chillers.are.more.eficient.in.
cooler.climates.or.in.dry.climates.where.evaporative.cooling.can.be.used..Local.air.
cooling.can.be.effective.in.reducing.air.temperature.in.speciic.areas..Two.methods.
have. been. used. successfully. in. industrial. settings.. One. type,. cool. rooms,. can. be.
used.to.enclose.a.speciic.workplace.or.to.offer.a.recovery.area.near.hot.jobs..The.
second.type.is.a.portable.blower.with.a.built-in.air.chiller..The.main.advantage.of.a.
