Environmental Engineering Reference
In-Depth Information
tABle 24.5
Permissible noise exposure limits
sound level dBA
slow response
duration per day (hours)
8
90
6
92
4
95
3
97
2
100
1-1/2
102
1
105
½
110
1/4.or.less
115
Source: . Courtesy.of.United.States.Department.of.
Energy.
FIgure 24.10
Workers.wearing.ear.muffs.as.hearing.protection.
Single-use.earplugs.made.of.waxed.cotton,.foam,.or.iberglass.wool.are.self-forming.
and,.when.properly.inserted,.work.as.well.as.most.molded.earplugs..Preformed.and.
molded.earplugs.can.be.reusable.or.at.times.single.use/disposable;.this.type.of.plug.
must.be.individually.itted.by.a.professional..Nondisposable.plugs.should.be.cleaned.
after.each.use.
Earmuffs.require.a.perfect.seal.around.the.ear.(see.Figure 24.10)..Glasses,.long.
sideburns,.long.hair,.and.facial.movements.such.as.chewing.may.reduce.the.protec-
tive.value.of.earmuffs..It.is.possible.to.purchase.special.earmuffs.designed.for.use.
with.eyeglasses.or.beards.
Hearing. protectors. only. reduce. the. amount. of. noise. that. gets. through. to. the.
ears..The.amount.of.this.reduction.is.referred.to.as.attenuation..Attenuation.differs.
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