selection of passive hearing protection · 2019. 12. 17. · selection of passive hearing...
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2018
DepartmentofDefenseHearingCenterofExcellence3/1/2018
Selectionofpassivehearingprotection
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Table of Contents SelectionofPassiveHearingProtection......................................................................................................4
1.0 Introduction.................................................................................................................................4
2.0 Background..................................................................................................................................4
3.0 Posterelements...........................................................................................................................5
A. Continuousnoiseattenuation.....................................................................................................5
B. Impulsivenoise............................................................................................................................7
C. Spatialawareness(localization)...................................................................................................8
4.0 SelectingHearingProtection.......................................................................................................9
A. Considerationsinselectingappropriatehearingprotection.......................................................9
B. DeterminingHazardousNoiseRequirements............................................................................11
C. DeterminingSpatialAwarenessNeeds......................................................................................11
5.0 Conclusion.................................................................................................................................11
References.................................................................................................................................................12
AnnexA.Acronyms....................................................................................................................................13
Acknowledgements...................................................................................................................................14
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Selection of Passive Hearing Protection
1.0 Introduction ThepurposeofthisguidebookistoexplainelementsoftheEvaluatedPassiveHearingProtectionDevice(HPD)postertoenablehearinghealthprofessionals,industrialhygienists,andsafetyprofessionalstobetterselecthearingprotectionappropriateforthenoiseenvironmentandhearingcriticaltasksServiceMembersperform.TheHPDslistedinthisguidebookhavebeenthoroughlyevaluatedforperformancebutdonotconstituteanapprovedHPDlist.
Goodhearingiscriticaltowarfighterperformance.Allwarfightersrelyonhearingtocommunicateamongindividuals,withinandbetweenunits,withhigherheadquarters,andoftenbetweenbattlespacesandotherServices.Warfightersalsorelyonhearingforsituationalawareness,suchasdeterminingthedirectionofgunfireorwhetheranenemyisapproaching.Manywarfightersworkinhazardousnoiseenvironmentseverydayoftheirmilitarycareer.Exposuretohazardousnoise,continuousand/orimpulsive,maycausesignificanthearinglossand/orhearingrelateddisabilities.Reducingtheriskofhearinglossisessential;whenengineeringandadministrativecontrolsarenotpossible,HPDsarerequired.
TraditionalpassiveHPDsaredesignedtoreducetheamountofhazardousnoisereachingtheinnerear.WhileprotectinghearingisanessentialqualityofallHPDs,somewarfightersrequireHPDsthatallowcriticalsoundstopassthroughthedevicetoallowforcommunicationcapabilitiesandsituationalawareness.Forexample,forceprotectionpersonnelmustbeabletocommunicatewithapproachingpeople,detectandidentifysounds,localizethedirectionofthesound,andworkwithintermittentnoisefromapproachingvehiclesorevengunfire.Assuch,researchersdesignedassessmentmethodstodeterminehowwellHPDsfunctiononthreefronts:continuousnoisesuppression;impulsivenoisesuppression;andsoundlocalization.
TheposterprovidesanoverviewofperformancecharacteristicsofpassivehearingprotectivedevicesthatincludesattenuationforcontinuousandimpulsivenoiseandtheeffecttheHPDhasontheuser’ssoundlocalizationperformance.Inthisguide,section2hasbackgroundinformation,section3reviewstheposterelements,andsection4providesguidanceonselectingproperhearingprotection.
2.0 Background WhenselectingHPDs,theworkingenvironment,typeofworkperformed,andthehearingcriticaltasksoftheworkmustbeconsidered.First,HPDsmustprovidetheappropriatelevelofprotectionforthenoiselevel.Louderenvironmentsdemandgreaterlevelsofattenuation,butoverprotectionmaymaketheuserfeelisolatedfromtheenvironmentanddecreasetheuser’ssituationalawareness.Whenselectinghearingprotection,factorsotherthannoiseattenuationmaybeconsideredsuchashowadeviceaffectshearingcriticaltasks,comfort,compatibilitywithotherequipmentandothernon-acousticalfactorslikeeaseofuseandcost.
Hearingcriticaltasksaretasksinwhichhearingistheonlysensethatcanperformthosetasks.Responsetothedetection,identification,locationofsound,orunderstandingspeechisoftentimesensitive,isusuallyrelatedtothesafetyofanoperation,andleadstothesuccessfulcompletionofanoperation.Examplesofhearingcriticaltasksaretalkingoverthetelephoneorradio,detectingenemy
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presenceinlowvisibilityenvironmentsorwhenvisionisobscured,anddeterminingthedirectionofenemygunfire.
TheEvaluatedPassiveHearingProtectionDevicesposterpresentspassiveHPDsthatdonotcontainnorallowconnectiontoelectronicsthatcansuppressnoise,connecttoradiosystems,orenhancehearingcriticalsounds.HPDshavebeendevelopedwiththosecapabilities;however,thesedevicesarenotnecessaryformanyjobsinthemilitary.Audiologists,industrialhygienists,andsafetyprofessionalscanassessworkplacesandmakerecommendationsforappropriateHPDsforeachtask.ThemostexpensiveormosttechnologicallyadvancedHPDisnotalwaysnecessary.ThebestHPDprovidesthenecessarylevelofprotection,fitswell,iscomfortabletowear,andallowsuserstohearcriticalsoundsnecessaryforthejob.Mostimportantly,itisusedbytheemployeeandworncorrectly.
3.0 Poster elements MarineCorpsSystemsCommandprovidedfundingforthestudyandselectedallthepassive
insertHPDs.TheAirForceResearchLaboratory(AFRL)performedtheHPDassessmentthatincludedcontinuousnoiseattenuation,impulsivenoiseattenuationandsoundlocalizationmeasurementsbywayofanaurallyguidedvisualsearchtask.EachHPDontheposterisdescribedwithaproductname,apictureofthedevice,andaNationalStockNumber(NSN)whenapplicable.TheperformancemetricsarealsodisplayedforeachHPDbywayofacoloredratingscale.Asquareisusedtorepresentthecoloredratingforcontinuousnoiseattenuation;acirclerepresentsthecoloredratingforimpulsivenoiseattenuation;andapentagonisusedtorepresentthecoloredratingforspatialawareness.
A. Continuous noise attenuation 1. ContinuousnoiseattenuationdatawascollectedinaccordancewithANSIS12.6-2008MethodA,
trained-subjectfit.a. NoiselevelreductionstatisticsforA-weighting(NRSA)versusNoiseReductionRating
(NRR)i. NRR,asinglenumberdescriptor,isawell-knownwayofestimatingthenoise
levelunderaHPD.EPAregulationsrequiremanufacturerstodisplaytheNRRon
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HPDlabels.However,theNRRwasdesignedtobesubtractedfromC-weightednoiselevelsandrequiresa7-dBspectraladjustmentbeappliedpriortosubtractingitfromA-weightednoiselevels.
ii. NoiselevelreductionstatisticsforA-weighting(NRSA)wasdesignedtobesubtracteddirectlyfromthemeasuredA-weightednoiseleveltoestimatethelevelofsoundattheearunderthehearingprotector.Themethodoffersseveraladvantagesoverthewell-knownNRR.Asstatedabove,theNRRwasdesignedtobesubtractedfromC-weightednoiselevels.NRSAeliminatesthisproblemwiththeNRRbysubtractingfromtheA-weightednoiselevels,whicharetypicallyknown.NRSAshouldnotbeusedwithnoiseenvironmentsthathavehighlevelsoflowfrequencycontentoriftheoverallsoundpressurelevelexceeds100dBA.AnotheradvantageofNRSAisthatitcalculatestwolevelsofprotectiontoindicatetherangeofperformanceachievedduringtheevaluation.Thisrangereflectsthevariationacrossthesubjectsinthetestpanel,providinginsightintohowhard/easythedevicemaybetofit.Themajorityofusers(80%)willachievetheperformancespecifiedbythelowervalueintherange,withonlythemostmotivatedproficientusers(20%)abletoachieveorexceedthehighervalue.
iii. PosterdisplaystheNRSAviaacolorcodeforthemajorityofusers(80%).1. Blue–30dBorgreater2. Green–20-30dB3. Yellow–10-20dB4. Red–10dBorless
HearingProtector
NRSA PosterRatings80% 20%
3MEARUltraFit 19 30 YellowAllenSoundSensor 17 30 YellowEarPlugzPCwithcord 17 31 YellowEarPlugzPCwithoutcord 16 29 YellowEtymoticER20ETY 14 20 YellowHearDefendersDF 19 29 YellowHearingArmor 16 30 YellowHowardLeightMax 29 29 GreenMoldexBattlePlugsClosed 19 30 YellowMoldexBattlePlugsOpen 10 19 RedMoldexPuraFit 33 41 BlueSensGardSG26 19 31 YellowSensGardSG31 23 33 GreenCombatArmsGen4Closed 23 29 GreenCombatArmsGen4Open 10 17 YellowSonicDefendersEP3Closed 18 31 YellowSonicDefendersEP3Open 12 20 YellowSonicDefendersEP4Closed 23 28 GreenSonicDefendersEP4Open 12 20 Yellow
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SonicDefendersEP7Closed 28 34 GreenSonicDefendersEP7Open 16 30 Yellow
2. ConsultserviceguidancewhenusingtheNRR.
B. Impulsive noise 1. Whenanticipatingexposuretoimpulsivenoisesuchasonafiringrange,personnelshould
choosehearingprotectionthathasbeenevaluatedforitscapabilitytoprotectagainstimpulsivenoisehazards.M16susuallygeneratemid-150dBPrangeattheshooter(buthighertothesides)anda105mmHowitzerexposescrewtolevelsfromthemid-160dBPrangetothelow-180dBPrangedependingonfiringconditions.WhenselectingHPDstoprotectagainstimpulsivenoise,choosethepeaksoundpressurelevelclosesttotheexpectedexposure.
a. Note:ImpulsivenoiseisthetermusedinMIL-STD-1474E,theDepartmentofDefenseDesignCriteriaStandardNoiseLimits.Thetermismorecurrentandissynonymouswithimpulsenoise.
b. Thebelowtablelistsdevicesandtheaverageimpulsivepeakinsertionlossdatafromblastmeasurements.ANSIS12.42-2010wasusedforthetestingmethodology.Theinsertionlossforeachearatimpulsivenoiselevelsat170dB,185dBand195dBiscontainedbelow.
c. Theposterdisplaysviaacolorcodetheimpulsivenoiseattenuationat170dB.i. Blue–30dBorgreaterii. Green–20-30dBiii. Yellow–10-20dBiv. Red–10dBorless
HearingProtector
PeakSoundPressureLevel PosterRatings170dB 185dB 195dB
3MEARUltraFit 36 35 36 BlueAllenSoundSensor 10 21 33 YellowEarPlugzPCwithcord 35 36 33 BlueEarPlugzPCwithoutcord 34 35 41 BlueEtymoticER20ETY 25 28 32 GreenHearDefendersDF 41 38 39 BlueHearingArmor 35 36 30 BlueHowardLeightMax 41 41 41 BlueMoldexBattlePlugsClosed 36 BlueMoldexBattlePlugsOpen 30 GreenMoldexPuraFit 54 41 41 BlueSensGardSG26 31 27 33 BlueSensGardSG31 28 20 29 GreenCombatArmsGen4Closed 40 BlueCombatArmsGen4Open 33 BlueSonicDefendersEP3Closed 28 28 33 GreenSonicDefendersEP3Open 26 28 32 GreenSonicDefendersEP4Closed 35 Blue
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SonicDefendersEPOpen 28 GreenSonicDefendersEP7Closed 41 41 41 BlueSonicDefendersEP7Open 28 34 40 Green
C. Spatial awareness (localization) 1. Spatialawarenesswasassessedusinganaurallyguidedvisualsearch.Thistaskdemonstrates
theimpactHPDshaveonthetimerequiredtoaccuratelylocatetheoriginofasound.Inthetest,subjectsaretestedinthreeconditions,(1)visualtargetwithoutauralguide,(2)visualtargetwithauralguide,nohearingprotector,and(3)visualtargetwithauralguideandhearingprotector.Withoutanauralguide,subjectsaverage12.2secondstofindthetarget.Withhearingprotection,subjectstakelongertofindatargetuntiltheauralguidepresentationlevelsarearound80dB.
a. Posterdisplaysthesearchtimewhenthepresentationlevelwasat40dBviaacolorcode.
i. Blue–4secondsorlessii. Green–4-7secondsiii. Yellow–7–10secondsiv. Red–10secondsorgreater
HearingProtector
TargetLevel(dBSPL) Total(30,40,60)
PosterRating15 30 40 60 80
3MEARUltraFit 12 11 5 4 28 RedAllenSoundSensor 10 8 5 5 22 YellowEarPlugzPCwithcord 13 11 5 5 29 RedEarPlugzPCwithoutcord 11 9 5 4 25 YellowEtymoticER20ETY 12 9 6 3 18 GreenHearDefendersDF 12 11 5 4 28 RedHearingArmor 10 9 5 3 24 YellowHowardLeightMax 12 12 8 6 33 RedMoldexBattlePlugsClosed -- -- -- -- -- --MoldexBattlePlugsOpen -- -- -- -- -- --MoldexPuraFit 12 13 12 6 37 RedSensGardSG26 10 7 4 5 21 GreenSensGardSG31 9 7 5 4 21 YellowSonicDefendersEP3Closed 12 8 4 4 24 YellowSonicDefendersEP3Open 12 11 6 4 21 GreenSonicDefendersEP4Closed -- -- -- -- -- --SonicDefendersEP4Open -- -- -- -- -- --SonicDefendersEP7Closed 13 12 5 4 30 RedSonicDefendersEP7Open 12 12 10 4 26 Red
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4.0 Selecting Hearing Protection Thechartbelowisadecisiontreethatwillassistinselectingthebesthearingprotectionfortheexpectednoiseexposureandthejobtask.TheHPDsdepictedintheposterandinthisguidebookarepassiveearplugsonly.Ifcommunicationinanoisehazardousenvironmentisessential,deviceswithadditionalcapabilitiesshouldbeusedasopposedtotheHPDsinthisdocument.
A. Considerations in selecting appropriate hearing protection
1. Noise environment a. Ahazardouscontinuousnoiseenvironmentiswheretheambientnoiselevellastsfor1
secondormore(usuallymuchlonger),butwhichcanbevariable,steadyorintermittentovertime.DoDI6055.12defineshazardoussteadystatenoiselevelsat85dBAtimeweightedaverage(TWA)orgreateroveran8-hourtimeframe.Shipboardengineeringspaces,generatornoiseandhelicopternoiseareexamplesofcontinuousnoise.i. Singlehearingprotectionshallbewornwhennoiselevelsmeetorexceed85dBA,
regardlessofduration.ii. TheDoDnoiseexposurecriteriontoreducetheriskofhearinglossorhearing
relateddisabilitiesis85dBAforadurationof8hourswitha3dBperdoublingexchangerate.Therefore,ifthenoiselevelincreasesto88dBAtheallowabledurationoftimeinnoise,ifunprotected,isreducedto4hours.
iii. Guidanceontheuseofearplugandearmuffcombinations,commonlyreferredtoasdoublehearingprotection,differsamongtheServices.Theterm“double”hearingprotectionismisleadingastheattenuationfromearplugandearmuffislessthan
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thearithmeticsumoftheirindividualattenuationvalues.Whenguidanceindicatesdoublehearingprotectionisneeded,theOccupationalSafetyandHealthAdministrationrecommendsadding5dBtothederatedNRRofthehearingprotectorwiththehighestNRRtodeterminetotalattenuationprovidedbytheearplugandearmuffcombination.Regardlessofwhetherusingsingleordoubleprotection,theservicemembersoremployee’stotalexposureshallbereducedtobelow85dBATWAforan8-hourworkday.
1. TheArmyHearingProgramrequiresuseofearplugsandhelmetorearplugsandearmuffswhensteadystatenoiselevelsare103dBATWAandupto108dBATWA.
2. TheRevisedInterimNavyMedicineHearingConservationProgramGuidancestatesareasorequipmentwheresoundpressurelevelsare96dBAorgreatershallrequiretheuseofdoublehearingprotectionthatattenuatesworkernoiseexposurebelowan8-hourTWAor85dBA.TheNavybasesdoublehearingprotectionupontheeffectivefieldderatedupperlimitofmostearplugsandearmuffs.
3. FortheAirForce,thehearingprotectorsprovidedmustbecapableofattenuatingworkernoiseexposurebelowaTWAof85dBA.Thethresholdforusingdualhearingprotectiondependsontheprotectorsselected.PerAirForceInstruction48-127,3dBshouldbeaddedtothehighestNRRoftheplugormufftoestimatecombinedprotectiverating.ConsultthelocalbioenvironmentalunitortheAirForceEnvironment,SafetyandOccupationalHealthService(ESOH)Centerforassistanceindeterminingtheappropriatehearingprotection.
3. Impulsivenoiseisashortdurationsoundlastinglessthan0.5seconds,containingoneormorepulses.Impulsivenoiseisconsideredhazardousifoneormoreofthepulsesexceeds140decibelspeak(dBP)orgreater.Gunshotsandmanualhammeringareexamplesofimpulsivenoise.
a. Impulsivenoisegreaterthan140dBPrequireshearingprotection.b. PertheArmyHearingProgramandtheNavyHearingConservationProgramGuidance
exposuretolevelsabove165dBPrequiresdoublehearingprotectionunlessthesingleprotectioncanbedemonstratedtoreduceat-earlevelstobelow140dBP.
c. FortheAirForce,contactthelocalbioenvironmentalunitorESOHCenterforassistanceinselectingHPDsforimpulsivenoise.
4. Hearing Critical Tasks a. Soundlocalization,whichisdefinedastheabilitytodeterminetheapparentdirection
and/ordistanceofasoundsource,asmeasuredbythetimeittakestofixateonthesource.NOTE:Atthistime,wehavenotestablishedthepointatwhichittakestoomuchtimetoperformamilitarytask.
i. Theposterdepictssoundlocalizationasspatialawareness.b. SpeechIntelligibilityreflectstheabilitytounderstandtransmittedwords.Whenthistask
isimportant,itmayrequirethespeechbeelectronicallytransmittedtobypassthe
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attenuationofthehearingprotectororuseoflevel-dependenthearingprotectorsthatselectivelysuppressunwantedsounds.
5. Wearability a. Includeswhetheradevicecanbewornwithoutinterferingwithotherrequired
equipmentsuchasbattlehelmetand/oreyeprotection.b. Wearerfindsitcomfortablewhenworn.Comfortmaydependonhowlongtheproduct
hastobewornandtheenvironmentinwhichtheproductisused(suchasambienttemperature).
B. Determining Hazardous Noise Requirements TheServicesusenoisesurveysconductedbyoccupationalsafetyandhealthprofessionals,
occupationalaudiologists,industrialhygienists,andbioenvironmentalengineerstodeterminelocationsandequipmentthatarenoisehazardous.Noisesurveysreportsoundpressurelevels(SPLs)andcharacterizethesoundsourceaseithercontinuousorimpulsivenoise.HPDsshouldbeselectedtoprovidetheadequateprotectionagainsttheidentifiednoisehazard.
C. Determining Spatial Awareness Needs Spatialawarenessistheabilitytoaccuratelylocatetheoriginofadetectedsoundinanydirection.Theconceptisillustratedbythequestions‘CanIhearthesound?’and‘CanIdeterminethedirectionofthesound?’Inthemilitary,theabilitytoanswerthesequestionsisimportanttomanyjobsandmissionsandcertainhearingprotectioncaninterferewiththesecapabilities.Jobsthatrequirelocalizationincludedismountedoperations,specialoperations,andforceprotection.Byunderstandingtheperformanceofdevicesandtheimpactontheuser’sabilitytolocatesounds,warfighterscanselectadevicethatwillhaveminimalimpactonspatialawarenesswhileprotectingfromhazardousnoise.
5.0 Conclusion Theinformationprovidedinthisguideistoassistaudiologists,industrial
hygienists/bioenvironmentalengineers,andsafetyprofessionalsinselectingpassivehearingprotectiondevices.QuestionsontheinformationinthisguideorhowtouseitshouldbeaddressedtotheServicePublicHealthCommands/Centers,theESOHServiceCenterortotheDoDHearingCenterofExcellence(https://hearing.health.mil/).
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References
1.Gallagher,H.L.,McKinley,R.L.,Theis,M.A.,Swayne,B.J.,Thompson,E.R.PerformanceAssessmentofPassiveHearingProtectionDevices.AFRL-RH-WR-TR-2014-0148,October2014.
2.DepartmentofDefenseDesignCriteriaStandardNoiseLimits,MIL-STD-1474E,dtd15APR2016.
3.DepartmentofDefenseInstruction6055.12,HearingConservationProgram,dtd3DEC2010.
4.DepartmentoftheArmy.Pamphlet40-501.ArmyHearingProgram.2015.
5.ChiefofNavalOperationsInstruction5100.23GNavyOccupationalSafetyandHealthAshore,dtd21JUL2011.
6.BureauofMedicineandSurgeryNote6260,RevisedInterimNavyMedicineHearingConservationProgramGuidance,dtd24APR2014.
7.AirForceInstruction48-127.OccupationalNoiseandHearingConservationProgram,dtd26FEB2016.
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Annex A. Acronyms ANSI–AmericanNationalStandardsInstitute
ASA–AcousticalSocietyofAmerica
AFRL–AirForceResearchLaboratory
dB–decibel
dBA–decibelA-weighted
dBP–decibelPeak(measuredunweightedorusingtheC-weightedscale)
DoDI–DepartmentofDefenseinstruction
EPA–EnvironmentalProtectionAgency
ESOH–AirForceEnvironment,SafetyandOccupationalHealthOffice
HPD–hearingprotectivedevice
NRR–noisereductionrating
NRSA–noisereductionstatisticA-weighting
SPL–soundpressurelevel
TWA–timeweightedaverage
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Acknowledgements
ThisguidebookwasauthoredbyamultidisciplinaryteamfromtheDoDHearingCenterofExcellence,U.S.Army,U.S.Navy,U.S.AirForceandU.S.MarineCorps.TechnicalcontentwasprovidedbytheAirForceResearchLaboratory,ArmyResearchLaboratory,U.S.ArmyAeromedicalResearchLaboratory,NavalSubmarineMedicalResearchLaboratoryandCaptainWilliamJ.Murphy,Ph.D.fromtheNationalInstituteofOccupationalSafetyandHealth.Specialappreciationisgiventothefollowingindividualswhoprovidedguidance,feedback,orcommentstothedocument(listedinalphabeticalorder):
• WilliamAhroon• KariBuchanan• JeremyFederman• HilaryGallagher• MajorShannonHunt• CommanderPaulaJohnston• CharlesJokel• MajorElizabethMcKenna• RichardMcKinley• LieutenantColonelJohnMerkley• CaptainWilliamMurphy• LieutenantColonelMartinRobinette• AngeliqueScharine• BrianSimpson• EarlStefanson• EricThompson• RobertWilliams• KurtYankaskas