a little noise about noise reduction ratings - us navy：關(guān)于噪聲降低評級的美國海軍一點噪音

ALNaboutNRR-

ALittleNoiseaboutNoiseReductionRatings

Presentedatthe2007“TidewaterLSAIHAFallPDC”onNov16,2007byChristopherD.Jones,MS,CIHNAVMEDCENPortsmouth,IHDepartmentNovember16,20071BACKGROUNDThinkback,wayback,toyourearlycareereducationinindustrialhygieneorsafety,tothetimeyoufirstheardabout"thehierarchyofcontrols"November16,2007BACKGROUNDRememberthem?Engineeringcontrols;thenAdministrativecontrols;andfinallyPersonalProtectiveEquipmentWeareallprettycomfortablewiththismethodofprioritizationtorespondtooccupationalstressorsinourworkplacewhenweareassessingpersonnelexposurestooddsandendsNovember16,2007BACKGROUNDForsomereason,itissecondnatureforustorecommendanengineeringcontrolforpaintmistbeforewejumponarespirator….November16,2007BACKGROUNDButweforgetallaboutthiswhenwearedealingwithnoise;putplugsintheirearsormuffsontheirheadisoftenchoice#1,notchoice#3November16,2007BACKGROUNDIfweputsomeoneinahalfmaskrespiratorforprotectionagainstdust,whatistheassignedprotectionfactorforthatmask/filtercombination?Ten-regardlessofrespiratormanufacturerIf,ontheotherhand,youputearplugsinsidetheearcanalofanemployee,whatisthe"assignedprotectionfactor"forthatplug?ItdependsonwhomadetheplugNovember16,2007WHAT'SANNRR?TheEPArequiresthatHPDsbelabeledwiththeirnoisereductionrating,theNRR;asinglenumberratingofthehearingprotection;thehighertheNRR,thehighertheattenuationforaspecificidealsituation("TheOccupationalEnvironment-ItsEvaluationandControl",aka.,the"WhiteBook",AIHA,1997)Twokinds,A=theoneonthebox;andB=asubject/fitNRR,aspecialone,hardtofindTestfrequencies=125,250,500,1000,2000,3150,4000,6300and8000HzNovember16,2007WHAT'SANNRR?TheNRRdoesn'tprovideanaccurateestimateofthetrueattenuationprovidedtothewearer,becauseitcanbeaffectedbyfit,insertiontechnique,andthenoiselevelintheworkenvironmentSincetheNRRisn'tasolidnumbertohangyourhaton,howdoyouuseit?"Derate"it-adjustitinsomefashiontobetterreflecta"realworld"levelofprotectionthattheHPDprovidesNovember16,2007DERATINGANNRR-theOSHAwayAdjustorderatetheNRR,thencomparethenew#toyourmeasurednoiseexposureInAppendixBofOSHA'sgeneralindustrynoisestandard,29CFR1910.95,OSHArecommendsamethodtoderatetheNRRtodeterminetheadequacyofselectedHPD:EstimatedExposure(dBA)=TWA(dBA)-(NRR-7)IfusingdBCvalues,EstimateddBA=TWA(dBC)-NRRExample:TWA=100dBA;NRR=19X=100-(19-7)=88dBANovember16,2007DERATINGANNRR-theOSHAwayHowdoyouderatedoublehearingprotection?OSHAsays5dBcanbeaddedtotheNRRofthemostprotectivedeviceExample:NoiseTWA=100dBA;NRR=19foramuff,30foraplug;theassignedNRRforthiscombois30+5=35EstimatedExposure(dBA)=TWA(dBA)-(NRR-7)X=100-(35-7)=72dBANovember16,2007DERATINGANNRR-theOSHAway,PartIIOSHAdirectsinspectorstotakeintoconsiderationtherelativeperformanceofHPDs;deratetheNRRby50%(E.A.RLog20,"TheNakedTruthAboutNRRs",CabotSafety,1993;alsofoundonOSHA'swebsiteat/dts/osta/otm/noise/hcp/attenuation_estimation.html)Thisderatinghasnorelationshiptothejustmentioned7dBcorrectionspelledoutin1910.95;thisderatingadjustsNRRsto"realworld"performance,whereasthe7dBcorrectionadjuststheNRRtoadBAmeasurementNovember16,2007DERATINGANNRR-theOSHAway,PartIISohere'showOSHAinspectorsderateHPDstodeterminetherelativeperformanceofHPDs;

theycutitinhalf!EstimatedExposure(dBA)=TWA(dBA)-[(NRR-7)X50%]Example:TWA=100dBA;NRR=19Estim.Exposure=100-[(19-7)X50%]=94dBATherelativeperformanceofanNRRof19is6November16,2007DERATINGANNRR-theNIOSHwayNIOSHhasanevenmoreexcitingwaytodeterminea"true"NRR;theNRRisadjustedbythetypeofprotectionyouaregettingreadytowear(see"CriteriaforaRecommendedStandard,OccupationalNoiseExposure,RevisedCriteria1998"NIOSH,1998)Earmuffs=subtract25%fromtheMFRNRRFormableplugs=subtract50%fromtheMFRNRRAllotherplugs=subtract70%fromtheMFRNRRNovember16,2007DERATINGANNRR-theNIOSHwaySohere'showNIOSHasksyoutoderateHPDsEffectiveA-weightednoiselevel(ENL,dBA)=dBA-(deratedNRR-7)ExampleENL:TWA=100dBA;NRR=19Muffs=100-[(19X.75=14)-7]=93dBAForm.plugs=100-[(19X.50=10)-7]=97dBAOtherplugs=100-[(19X.30=6)-7]=101dBA?Whoa,itgotlouder???November16,2007REALWORLDCYPHERIN'WITHDERATEDNRRsWe(NAVMEDCENPortsmouthIHDept)havestartedcollectingnoisedosimetrydataandpayingmoreattentiontothebrandofHPDinusebythesampledindividualWecantakeourmeasuredTWA(dBA),compareittothederatedNRR,andcalculatea"correctedTWA"ThiswillhelpusmakedeterminationsaboutHPDeffectiveness;mightcauseustopursuenewbrandsofHPDsinsteadofthebrandscurrentlyinuseNovember16,2007REALWORLDCYPHERIN'WITHDERATEDNRRsTherearemultipleOELsinourIHworldOSHA=90dBA,5dBexchangerateACGIH=85dBA,3dBexchangerateDOD=85dBA,3dBexchangerateUSNavy=84dBA,4dBexchangerateWemeasuredfiveTWAsatonefacility(anaircraftsquadron)andthreewere>NavyOELor84dBA;after

derating,twooftheexposureswerestillabovetheNavyOELLet'slook….November16,2007REALWORLDCYPHERIN'WITHDERATEDNRRsAdjustedTWAsafterderatingMFRNRRsSam#TWAdBAMFRNRRDeratedNRRAdjust.TWA192.030*1280275.2143.571.7371.1217.064.1492.0143.588.5596.3143.592.8November16,2007DERATINGANNRR-thesupercool21stCenturywayYoucanhaveanNRRthatisspecifictoyouandaparticularinsertplug-personalizedjustforyouTakesintoconsiderationthewayyouinsertedtheplug,theshapeofyourearcanal,andyourhearingthresholdsatthetestingfrequenciesAnewhardware/softwarecombo,"FitCheck"fromMichaelandAssociates()allowsyoutoinsertplugs(orwearmuffs),putonsomeheadphones,andgetanaudiometrictestwhilewearingthoseplugs;resultsgivenasapersonalattenuationrating(PAR);November16,2007DERATINGANNRR-thesupercool21stCenturywayThreeplugs,onehead(mine),fourwaysoflookingatthem;PAR=personalattenuationratingModelNRRNRR-7NRR-7X50%PARSpark-plug33261314EARUltraFit251893ElvexQuattro2518922November16,2007WHATDOESTHISALLMEAN?WeprobablyoughttotakeacloserlookatthebrandsandtypesofHPDsthatarebe