Evaluation of hearing protection used by police officers in the shooting range

Brazilian

Journal

of

OTORHINOLARYNGOLOGY

www.bjorl.org

ORIGINAL

ARTICLE

Evaluation

of

hearing

protection

used

by

police

officers

in

the

shooting

range

夽

Heraldo

Lorena

Guida

,

Carla

Linhares

Taxini

,

Claudia

Giglio

de

Oliveira

Gonc

¸alves

,

Vitor

Engrácia

Valenti

a_{UniversidadeEstadualPaulista(UNESP),CampusdeMarília,SãoPaulo,SP,Brazil} b_{UniversidadeTuiutidoParaná(UTP),Curitiba,PR,Brazil}

Received11September2013;accepted23December2013 Availableonline22August2014

KEYWORDS

Noisemeasurement; Noiseoccupational; Police

Abstract

Introduction:Impact noise is characterized by acoustic energy peaks thatlast less than a

second,atintervalsofmorethan1s.

Objective: Toquantifythelevelsofimpactnoisetowhichpoliceofficersareexposedduring

activitiesattheshootingrangeandtoevaluatetheattenuationofthehearingprotector.

Methods:Measurements were performed intheshooting rangeofa military police

depart-ment. AnSV102audiodosimeter(Svantek)wasused tomeasuresoundpressurelevels.Two

microphoneswereusedsimultaneously:oneexternalandoneinsertiontype;thefirearmused

wasa0.40Taurus®_{rimlesspistol.}

Results:Thevaluesobtainedwiththeexternalmicrophonewere146dBC(peak),anda

maxi-mumsoundlevelof129.4dBC(fast).Theresultsobtainedwiththeinsertionmicrophonewere

138.7dBC(peak),andamaximumsoundlevelof121.6dBC(fast).

Conclusion: Thefindings showed highlevelsofsoundpressureintheshootingrange,which

exceededthemaximumrecommendednoise(120dBC),evenwhenmeasuredthroughthe

inser-tion microphone.Therefore,alternativestoimprove theperformanceofhearing protection

shouldbeconsidered.

© 2014Associac¸ãoBrasileira de Otorrinolaringologiae CirurgiaCérvico-Facial. Publishedby

ElsevierEditoraLtda.Allrightsreserved.

PALAVRAS-CHAVE

Medic¸ãoderuído; Ruídoocupacional; Polícia

Avaliac¸ãodaprotec¸ãoauditivautilizadaporpoliciaisemestandedetiros

Resumo

Introduc¸ão: Oruídodeimpactoécaracterizadoporapresentarpicosdeenergiaacústicade

durac¸ãoinferioraumsegundo,emintervalossuperioresaumsegundo.

夽 _{Pleasecitethisarticleas:GuidaHL,TaxiniCL,Gonc¸alvesCG,ValentiVE.Evaluationofhearingprotectionusedbypoliceofficersinthe}

shootingrange.BrazJOtorhinolaryngol.2014;80:515---21.

∗_{Correspondingauthor.}

E-mail:[email protected](H.L.Guida). http://dx.doi.org/10.1016/j.bjorl.2014.08.003

Objetivo:Quantificarosníveisderuídodeimpactoaqueopolicialmilitarficaexpostodurante

atividadesdetirocomarmasdefogoeanalisaraatenuac¸ãodoprotetorauricularutilizado.

Método: Asmedic¸õesforamrealizadasnoestandedetirosdeumBatalhãodaPolíciaMilitar.

Paraamedic¸ãodosníveisdepressãosonorafoiutilizadoumaudiodosímetromodeloSV102

(Svantek).Foramutilizadosdoismicrofonessimultaneamente:umexternoeoutrotipoinserc¸ão,

eaarmautilizadafoiapistolacalibre40,damarcaTaurus®_.

Resultados: Osvaloresobtidosnomicrofoneexternoforamde146dBC(pico)eruídomáximo

de129,4dBC(fast).Osresultadosobtidosnomicrofonedeinserc¸ãoforamde138,7dBC(pico)

eruídomáximode121,6dBC(fast).

Conclusão:Nossosachadosevidenciaramelevadosníveisdepressãosonoranoestandedetiros,

queultrapassaramoslimitesmáximosrecomendados(120dBC),mesmoemmedic¸ãocom

micro-fone deinserc¸ão.Portanto, alternativaspara melhorarodesempenho daprotec¸ãoauditiva

devemserconsideradaspelaequipedeseguranc¸adacorporac¸ão.

©2014Associac¸ãoBrasileira deOtorrinolaringologiaeCirurgiaCérvico-Facial.Publicadopor

ElsevierEditoraLtda.Todososdireitosreservados.

Introduction

Exposuretonoise can causesignificant damage tohuman hearing,suchasnoise-inducedhearingloss(NIHL).Asthey areexposedtonoise,themilitarycanbeconsidereda pop-ulationatriskforthedevelopmentofNIHL.1

The military, especially during training in shooting ranges,areexposedtointensenoise.Studiesoftheauditory profileof the military conductedin Brazil have described the presence of hearing loss in this population, which is associatedwithexcessiveexposuretoimpactnoise.1---3 _For

thisreason,healthprofessionalshaveexpressedinterestin studyingtheeffectofimpactnoiseoninnerearfunction.4

Itisimportanttoconsiderthatthetotalnumberofmilitary personnelinthecountryincludingthemilitarypolice5_and

thearmedforcesisover700,000.6

AnnexNo.2of RegulatoryNorm15 (NR-15)establishes thethresholdforimpactnoiseat130dB(linear),measured with the response time constant for impact noise. When thistime constantis notavailable onthe meter, the NR-15reportsthattheC-weightedlevelinfastresponseshould bemeasured,andthethresholdlevelshouldbe120dB(C).7

Accordingtotheanalysisofthelawsinseveralcountries relatedtolimitsofoccupationalimpactnoiseperformedby theInternationalInstituteofNoiseControlEngineering,the criterionlevel ranges from 115dB (A)fast, to140dB(C), peak. The reference indicates that C-weighted measure-mentsarepreferable tounweighted (linear)measures, as theyaredefinedasnorms,andpeaklevelsaremore appro-priatetoassessimpulsivenoises,astheycoverawiderrange offrequencies.8

TheOccupationalHygieneNorm01(NHO-01)of FUNDA-CENTROrecommendsthatthedailyexposurelimittoimpact noiseshouldbedeterminedbythenumberofimpacts occur-ring during the workday, and that the level of maximum permissiblepeak corresponds to 140dB (linear) or 127dB (C).9

Inanexperimentalstudyofcatsexposedtoimpactnoise with peak sound pressure of 135, 140, and 145dB, the authorsidentifiedhearinglosswiththegreatestimpairment at thefrequency of 4kHz.10 _{In anotherstudy of exposure}

toimpactnoise,hearinglossesdiagnosedinchinchillasby

electrophysiologicaltestsweregreaterforfrequenciesof2 and8kHz,comparedto500Hz.11

Oneoftherequirements forthe interventionofhealth professionalsinthe preventionofhearinglossisthe pres-enceofanaccuratecharacterizationofthefirearmnoise. In this sense, a pioneer study found threshold values of 115.4dB(A)forthefiringofa9mmpistol(Beretta),andthe frequencyband ofthenoisewasmostprominent between 500 and4000kHz.12 _{In anotherstudy,themaximum peaks}

measuredatthefiringrangewere113.1dB(C)for0.40 pis-tol and116.8dB (C) for a 0.38 revolver.Additionally, the studyidentifiedthroughpsychoacousticanalysis(Praat soft-ware)thatthefrequencybandwiththegreatestenergywas between4120and4580Hz,andthattherewasa correspon-dencebetweenthisfrequencybandandcaseswithhearing loss(86.7%withlossat4kHz).13

In the Federal District of Brazil, the quantification of soundlevelsatafiringrangeofthemilitarypoliceshowed values of Lmax (maximum level) of 118 and 124dB (A) whenfiring a0.40pistol and0.38revolver,respectively.14

At measurementsperformed withthe BrazilianArmy, val-ues of 147.3dB (C) for a 7.62mm-caliber light automatic rifle (LAR) were found, and the meter display showed the word ‘‘overload’’, indicating that the level of actual sound pressure was higher than that recorded by the device.15

To protect hearing from high sound pressure levels (>80dB),theimplementationofmeasuresaimedtoreduce thenoiseatitssource isindicated;however,thisaction is not always possible; hence the use of hearing protectors is recommended.16 _{When selecting the hearing protector,}

according to NR-9,17 _{comfort, constant use, and proper}

hygienemustalsobeconsidered.Studieshavebeen devel-opedinrecentyearstoevaluatetheattenuationofhearing protectors.

Since the late 1950s, methods of measuring real-ear attenuationatthreshold(REAT)havebeenwidelyusedand describedintheliterature.18_{Anotherwaytoanalyzenoise}

Itmustbeconsideredthatthelackofusertrainingand testing methodsin thelaboratory that donotportray the conditionsof hearingprotectoruse ina real-lifesituation leadtobetter attenuationperformance inthe laboratory, whencomparedtomeasuresperformedinthefield.20

In search for a solution to hearing protection for the militaryduringrealaction, researcherscarriedoutafield experimentaimingtocomparetheperformancefor sound localization(aftershootingblanks),comparingfourmodels ofhearingprotectors(three‘‘active’’electronictypesand aspecialinsertiontypeforcombat),andunprotected hear-ing(open).Atotalof13subjectswereevaluated,incombat situationswithambientnoiseandbackground noiseofthe militaryvehicle(82dBA).Thestudyconcludedthatnoneof thetestedprotectorsmaintainedtheperformanceforsound localizationequaltotheopenear.21

Another study evaluated hearing protection in two combat situations: attack and reconnaissance missions. Army soldiers usedthreemodels of protectors (two elec-tronic devices and a special insertion type for combat). Commanding officers of the missionsassessed the perfor-manceofsoldiers,andidentifiedaslightadvantageofthe electronicprotectors in relationtotheinsertion typeand theunprotectedear.Nevertheless,theauthorssuggest fur-therstudies,astherewasmuchvariationintheresponses of soldiers in relation tothe preference of protector use (consideringcomfortversushearingcapacity).22

Recently, a comparativestudy wasconductedbetween shootingafirearmwithasoundsuppressor(silencer)in rela-tiontohearingprotection, consideringthe levelsofnoise reductionofboth.Theresultsshowedabetterperformance ofsoundsuppressorsinrelationtohearingprotection.23

Noise in the military environment is exceptionally intense; therefore, the attenuation provided by a sin-gle hearing protection device may not be sufficient. In experimental studies of noise attenuation as a function of frequency, the insertion type protector and individual clamshelltype,whenusedsimultaneously,showedthatthe combinedattenuationwasatleast 5dBgreaterthan their useindividually.24_{ResearchersinCanadaevaluatedthe}

com-bined hearingprotectionbetweentheclamshell protector andtheinsertiontypeandachievedadditionalattenuation between 4 and 18dB (SPL) in relation to individual use, dependingonthetestedfrequency.25

When evaluating the attenuation of noise emitted by shootingfirearmsbyaSpecialWeaponsAssaultTeam(SWAT) intheUnitedStates,anattenuationbetween25and35dB SPL (peak)wasdocumented usingelectronic hearing pro-tectorsalone,whereastheuseofdualprotectionincreased attenuationby15---20dBSPL.26_{Anotherstudyevaluatedthe}

attenuationwithfourdistincttypesofprotectors,andfound attenuationresultsrangingfrom20to38dBSPL(peak).27

The aimofthepresentstudy wastoquantifythenoise exposure,andtoverifywhetherthehearingprotectionused bytheseprofessionalsisappropriateforexposuretoimpact noiseduringactivitiesinthefiringrange.

Methods

Thiswasaprospectivestudyofacontemporarycohort,with across-sectionaldesign.Datacollectionwasperformedat

thefiringrangeofamilitarypolicebattalioninthe country-sideofthestateofSãoPaulo.Thisrangeislocatedinanopen space,andtheprojectile bulkheadconsistsoftires (filled withsand). The training included the participation of 12 policeofficers,dividedintotwoshootingsessions(eachwith sixofficers).Themeasurementofthefirstsessionwas per-formedforthepurposeofstandardizationofthetechnique andequipment adjustments. A validcollection wasmade duringthesecondtrainingsession,withatotaldurationof 24min.

Thetrainingsessionswerestandardized,withthefiring lineconsistingofsixpoliceofficers,eachofthemfired25 shots,totaling150 impactsduringeach session.Theshots werefiredsimultaneouslybythesixpolicemen,asdirected bytheshootinginstructorofficer.Therewasnoprior selec-tion of the officers, the choice was random, and there was no interference from the researcher on the training routine.

The sound pressurelevel dosimeter was affixed tothe vestofoneofthepoliceofficerswhowaspartofthefiring line (Fig.1). Two microphones wereused simultaneously: theexternalwasattachedtothecollaroftheuniform,ata distanceof150±50mmfromtheear;andtheinsertiontype (MIRE)wasinserted in theearcanal ofthe policeofficer, shieldedbyaclamshellprotectorwithNRRsf=24dB(subject fitNoiseReductionLevels;ApprovalCertificateCA7166).28

ThefirearmusedwasaTaurus®_{0.40caliberpistol,whichis} thestandardfirearmused.

Before each measurement, the microphones were cal-ibrated by an acoustic calibrator, CR: 514 model, Cirrus ResearchPlc.ThevaluesofthepeakandLmaxwere consid-eredwhenanalyzingtheresults;additionally,thefrequency spectrumofthenoisewasanalyzed(octaveband).

Itisimportanttoreportthatthemetershowsthesquare meanofthesoundpressurevariationswithinthespecified time (1 second for the constant ‘‘slow’’ and 0.125s for ‘‘fast’’).Thus,theLmaxrepresentsthemeanofthehighest soundintensityinthistimeperiod.Inthecaseofthepeak scale,itisnolongermeasuringthemeansquaredpressure atagiventime,butratherthemaximumvaluereachedby thesoundpressureofeachimpactnoise.29

Themeasurementusedintheanalysisofthefrequency spectrumwasLeq(A), which isdefined asthe equivalent soundpressurelevel andcorresponds toaconstantsound level,which,inthesametimeinterval,containsthesame totalenergyasthefluctuatingsound.14

Theprocedureforevaluatingtheeffectivenessofhearing protectorsin areal-lifeenvironmentwasperformedusing the ‘‘long method --- frequency analysis.’’ Information on thecertificateofapproval of theclamshellprotector was considered;in thiscase, for 98% reliabilityofthe offered protection, the values of sound levels in each frequency bandweresubtractedfromthevaluesofthestandard devi-ation,multipliedbytwo.18

Figure1 (A)Photographshowingaudiodosimeterattachedtopoliceofficer’svest(arrow);and(B)useofclamshellearprotector duringtrainingsessionintheshootingrange.

Aimingto analyzethe effectivenessof attenuation, 20 noise peaksand 20 Lmaxvalues were randomlyselected, with the descriptive analyses of these values shown in

Tables1and2.DatawereanalyzedusingtheWilcoxon statis-ticaltesttocomparethesoundpressurelevelsbetweenthe microphones(externalandinsertion).Asignificancelevelof 5%(p<0.05)wasused.

Complementarily, the difference between the values indicated by the manufacturer and the actual measured attenuation values was also calculated, with analysis by ANOVA,withasignificancelevelof5%(p<0.05).

The study was approved by the Ethics Committee in Researchof a public university (ProtocolNo. 1385/2009), andaninformedconsentwassignedbyallparticipants.

Table1 PeakmeasurementresultsindB(C),obtainedby

theexternalandinsertionmicrophones.

Statisticalmeasurement External

microphone

dB(C)

Insertion microphone

dB(C)

Mean 144.29 130.26

Median 144.35 130.2

Standarddeviation 0.90 2.62

Minimum 141.8 123.6

Maximum 146.0a _138.7

a_{Maximumoutputlimitofsoundpressurelevelmeasurement.}

Table2 LmaxdB(C)measurementresultsobtainedbythe

externalandinsertionmicrophones.

Statisticalmeasurement External

microphone

dB(C)

Insertion microphone

dB(C)

Mean 126.58 112.62

Median 126.5 112.5

Standarddeviation 1.52 2.93

Minimum 123.5 108.6

Maximum 129.4 121.6

Results

The dataobtainedbymeasuringthesoundpressurelevels while usingthe two microphones (external and insertion) allowed for analyses regarding both the values of impact noiseinthefiringrange,aswellastheactualattenuation of thehearingprotectors used,asshown in Table1(peak modality)and2(Lmaxmodality).

Table1showsthattheevaluatedhearingprotector pro-videdmeanattenuationof14.03dB(C)inthepeakmodality.

Table 2 shows the measurement data of the external microphoneandofthe insertiontypein Lmaxmodality.It wasobservedthattheaverageattenuationofhearing pro-tectorswas13.96dB(C)inthismodality.

Based on the results described in Tables 1 and 2, the Wilcoxon test was applied between the two analysis groups (internal andexternal microphone),andtheresult (p<0.001) confirmed the rejection of the nullhypothesis (H0),i.e.,therewasasignificantdifferencewhen compar-ingtheresultsbetweenthesoundpressurelevelsobtained inbothpeakandLmaxmodality.

Fig.2 shows the valuesmeasured withthe use of the externalandinsertionmicrophones,illustratingtheactual attenuationofthehearingprotector.

Fig.3demonstratestheresultsoftheassessmentofthe actualattenuationprovidedbythehearingprotectorinfield measurements, following the subtraction of twostandard deviations.

Based onthe data shown in Fig. 2, it was possible to identify the frequencies with higher sound pressure level measurements:0.5kHz(113.3dBA),1kHz(116.3dBA),2kHz (114.2dBA), and 4kHz (112.4dBA). Moreover, no statisti-cal significance was observed when analyzing the values of‘‘actualattenuationversusmanufacturerattenuation−2 SD’’,usingtheANOVAtest(p=0.193).

140.0

130.0

120.0

110.0

100.0

90.0

80.0 dB

12:46:32 12:47:52 12:49:12 12:50:32 12:51:52 12:53:12 12:54:32 12:55:52 12:57:12 12:58:32 12:59:52 13:01:12 13:02:32 13:03:52 13:05:12 13:06:32 Time (h:min:s) 13:10:32

Figure2 Soundpressurelevel(peak---C-weighted)measuredintheshootingrangeasafunctionoftime.Measurementinred withexternalmicrophone;inblue,measurementwithinsertionmicrophone(MIRE).

External microphone

Insertion microphone

Actual noise reduction

Manufacturer’s reduction 2 SD

Frequency (Hz)

125 250 500 1000 2000 4000 8000

0

20

40

60

80

100

120

140

Sound pressure level dB(A)

Figure3 Valuesofthemeasurementbyfrequency(LEQ[equivalentlevel/dBA])performedbyinsertionandexternalmicrophone. Valuesofactualnoisereductionandnoisereductionsuggestedbythemanufacturer,afterdiscountingthevaluesofthestandard deviation(SD),multipliedbytwo.

Discussion

Studies related to hearing health among the military are scarceinBrazil;thus,thisstudyverifiedtheneedtoincrease sucharesearchinordertoallowtheanalysisoftheacoustic environment inmilitary policeoperations, aswell asthat ofthemilitarypersonnelofthearmedforces(Navy,Army, andAirForce).Thetotalnumberofpersonnelinthesetwo branchesis700,596 professionalsonactiveduty, ofwhom 412,0965_{aremilitarypolice;288,500}6_{comprisethearmed}

forces.

It is noteworthy that audiological profile studies con-ducted in the states of São Paulo and Paraná identified hearinglossin27.5%and25%oftheevaluatedmilitarypolice personnel,respectively.1,3

Theresultsofthepresent studydemonstratedthatthe military police were exposed to high sound pressure lev-els,withmaximumvaluesof146dBC(peak)and129.4dBC (Lmax), with peak values at the limit of the equipment (overload). The above data showed severe and imminent riskof hearing loss,as theyexceedthe limitsof national andinternational standards, which recommend a limit of 140dBC(peak)and127dBC(fast)forimpactnoise.7---9

Otherstudieswiththemilitaryhavealsoidentifiedhigh sound pressure levels during work activities.1---4,13---15 _{It is}

knownthatthemilitaryworkenvironmentisariskfactorfor hearingloss,which hasmotivatedinternational studies to evaluatetheattenuationofhearingprotectorsinthe pres-enceofimpactnoise23---27_{;however,nosimilarstudieshave}

beenperformedinBrazil.

Table3 Comparisonofnoisereductionbyfrequencyband:noisereductionsuggestedbythemanufacturerversusattenuation

measuredinactualsituation(ANOVA).

Frequency(Hz) 125 250 500 1000 2000 4000 8000 pValue

Manufacturer’sreduction(dBA) 13.9 21.4 27.4 35.4 35.1 37.4 40 0.018

a

Actualreduction(dBA) 4.5 11.2 15 26.1 24.6 22.5 17.9

The data obtained through the insertion microphone demonstrated that the clamshell protector was effective in reducing the peak value below the criterion of 140dB (C) (maximum was 138.7dBC) level; however the highest value of Lmax (121.6dBC) was above the limit estab-lished by the NR-15.7 _{The data also demonstrate that}

althoughtheprotectionuseddidnothavethedesiredeffect according to the NR-15,7 _{it attenuated the impact noise}

significantly in the two evaluated modalities (peak and Lmax).

It is noteworthy that previous experimental10,11 _and

military13 _{studieshaveidentifiedhighfrequenciesasmore}

susceptibletodamagebyimpactnoise,particularlyat4kHz. Thus,it wasdeemednecessary tomeasurethe frequency spectrumofthefirearmnoise,asthisinformationallowed for theidentification of thereal attenuationvalueof the hearingprotector.Twostudiesperformedtheacoustic anal-ysis of the frequency spectrum; both identified that the highestlevelsofsoundpressureareconcentratedbetween 0.5and4kHz.12,13

The findings of this research confirmed the analyses describedabove,andadditionalmeasurementsperoctave bandformidentifiedtheactualattenuationofclamshellear protectors, identifyingthat thehighest levels of attenua-tionwere found in these same frequencies (between 0.5 and4kHz).Thisfindingreinforcestheimportanceofusing earprotectorsduringshootingactivities.

Moreover, regarding the assessment of hearing protec-tion effectiveness in the workplace, it was verified that the attenuation reported by the manufacturer was over-rated, and did not match the field measurement. The lack of user trainingand laboratory testing methods that do not portray the use of hearing protection in real-life situations are some factors that could explain this result.20

Thelongmethodofassessmentofhearingprotectorsin the workplace was effective, as two standard deviations fromtheattenuationvalueoftheprotectorweresubtracted fromthemeasured attenuation(octave band)toobtain a reliabilityof98%.18 _{In thiscase, the valueswere closeto}

thosemeasuredinareal-lifesituationandthus,thismethod canbeaviablealternativeforthesafety/healthstaffofthe militarycorps,asthecalculationismadebasedonthe val-uesreportedinthemanufacturer’s certificateofapproval (CA).

The difference between the actual attenuation value andthe suggested value could be corrected withthe use ofdualprotection(clamshell+insertion),whichguarantees at least a 5dB increase in noise attenuation.24 _Another

studyidentifiedincreasesfrom4 to18dBinnoise attenu-ationwithdualprotection.25 _{Thisinformationis relevant,}

since even withthe use of hearing protectors, our iden-tified Lmax value (121.6dBC) was above the safe level (120dBC).7

Recentlyresearchersevaluatedthemeanattenuationof hearing protectors used in the presence of impactnoise, andfoundmeanattenuationvaluesbetween20 and38dB SPL(peak),26,27_{whereasinthepresentstudyanattenuation}

of14.03dBC(peak)wasidentified. The datademonstrate thatinadditiontodualprotection,itispossibletoimprove theperformanceofhearingprotectionwiththeuseofnext generationprotectors.

Conclusion

These findings indicate that the sound pressure levels in a police shooting range showed values above those rec-ommended by NR-15. The clamshell protectors showed statistically significantly less real attenuation than that advertised by the manufacturer, with insufficient attenu-ation to preserve the hearing of military police officers. Thus,theuseofanotherbrand/modelofhearingprotector or thepossibilityof jointuse oftwoprotectors (clamshell andinsertion)shouldbe consideredby themilitarysafety staff.

Conflicts

of

interest

Theauthorsdeclarenoconflictsofinterest.

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