HHE Report No. HETA-2002-0131-2898, Fort Collins Police ...exposure guideline from NIOSH. # Radio...

NIOSH HEALTH HAZARD EVALUATION REPORT:

DEPARTMENT OF HEALTH AND HUMAN SERVICESCenters for Disease Control and Prevention

National Institute for Occupational Safety and Health

HETA #2002-0131-2898Fort Collins Police ServicesFort Collins, Colorado

March 2003

This Health Hazard Evaluation (HHE) report and any recommendations made herein are for the specific facility evaluated and may not be universally applicable. Any recommendations made are not to be considered as final statements of NIOSH policy or of any agency or individual involved. Additional HHE reports are available at http://www.cdc.gov/niosh/hhe/reports



This Health Hazard Evaluation (HHE) report and any recommendations made herein are for the specific facility evaluated and may not be universally applicable. Any recommendations made are not to be considered as final statements of NIOSH policy or of any agency or individual involved.


applicable. Any recommendations made are not to be considered as final statements of NIOSH policy or of any agency or individual involved. Additional HHE reports are available at http://www.cdc.gov/niosh/hhe/reports

http://www.cdc.gov/niosh/hhe/reports

ii

PREFACEThe Hazard Evaluations and Technical Assistance Branch (HETAB) of the National Institute forOccupational Safety and Health (NIOSH) conducts field investigations of possible health hazards in theworkplace. These investigations are conducted under the authority of Section 20(a)(6) of the OccupationalSafety and Health (OSHA) Act of 1970, 29 U.S.C. 669(a)(6) which authorizes the Secretary of Health andHuman Services, following a written request from any employer or authorized representative of employees,to determine whether any substance normally found in the place of employment has potentially toxic effectsin such concentrations as used or found.

HETAB also provides, upon request, technical and consultative assistance to Federal, State, and localagencies; labor; industry; and other groups or individuals to control occupational health hazards and toprevent related trauma and disease. Mention of company names or products does not constitute endorsementby NIOSH.

ACKNOWLEDGMENTS AND AVAILABILITY OF REPORTThis report was prepared by Randy L. Tubbs of HETAB, Division of Surveillance, Hazard Evaluations andField Studies (DSHEFS) and William J. Murphy of the Hearing Loss Prevention Section (HLPS), Divisionof Applied Research and Technology (DART). Field assistance was provided by Carol Goetz and PatriciaLovell, Certified Occupational Hearing Conservationists of HETAB, and Mark Little, Audiologist of HLPS.Desktop publishing was performed by Ellen Blythe of HETAB. Review and preparation for printing wereperformed by Penny Arthur.

Copies of this report have been sent to employee and management representatives at the Fort Collins PoliceServices. This report is not copyrighted and may be freely reproduced. Single copies of this report will beavailable for a period of three years from the date of this report. To expedite your request, include a self-addressed mailing label along with your written request to:

NIOSH Publications Office4676 Columbia ParkwayCincinnati, Ohio 45226

800-356-4674

After this time, copies may be purchased from the National Technical Information Service (NTIS) at5825 Port Royal Road, Springfield, Virginia 22161. Information regarding the NTIS stock number may beobtained from the NIOSH Publications Office at the Cincinnati address.

For the purpose of informing affected employees, copies of this report shall beposted by the employer in a prominent place accessible to the employees for a periodof 30 calendar days.

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Highlights of the NIOSH Health Hazard Evaluation

Evaluation of Weapon Noise and its Effects on Hearing of Police Officers

NIOSH investigators were requested to evaluate the customized hearing protectors used by the SWAT teamduring training exercises. We used temporary changes in hearing following weapons firing on the indoor andoutdoor ranges as an estimate of noise overexposure. We also made thorough measurements of the noisefrom the weapons used by the department as well as measurements of the noise reduction from all the hearingprotectors worn by the Fort Collins officers.

What NIOSH Did

# We tested the hearing of officers before and afterfiring their weapon on indoor and outdoor ranges.# We measured the noise from all pistols, shotguns,and rifles used by the department.# We use an artificial ear to evaluate the hearingprotectors used by the officers on the firing ranges.# We handed out a questionnaire to employeesabout their work history and self evaluation of theirhearing.

What NIOSH Found

# Officers did not show poorer hearing followingshooting.# Most officers have normal hearing patterns.# Weapon noise was found to be between 159 and169 dB peak which is greater than a 140 dB peakexposure guideline from NIOSH.# Radio transmissions were not incorporated intothe customized protectors used by the SWATofficers.

# The hearing protection devices lowered noiseabout 30 dB peak. Double protection (plugs plusmuffs) added 15-20 dB peak protection.

What Fort Collins Police ServiceManagers Can Do

# The department should research new hearingprotection devices that incorporate radiocommunications into the device and are stillcompatible with other protection devices such ashelmets and glasses.# The department should begin a hearingconservation program with annual hearing tests.

What the Fort Collins PoliceService Officers Can Do

# Officers should wear hearing protectionwhenever they are at the firing ranges.

What To Do For More Information:We encourage you to read the full report. If you

would like a copy, either ask your health andsafety representative to make you a copy or call

1-513-841-4252 and ask for HETA Report #2002-0131-2898

Highlights of the HHE Report

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Health Hazard Evaluation Report 2002-0131-2898Fort Collins Police Services

Fort Collins, ColoradoMarch 2003

Randy L. Tubbs, Ph.D.William J. Murphy, Ph.D.

SUMMARYThe National Institute for Occupational Safety and Health (NIOSH) received an employee request for a healthhazard evaluation of the Fort Collins Police Service in Fort Collins, Colorado, in January 2002. Thedepartment was concerned about noise exposures and potential hearing damage from weapons training ontheir indoor and outdoor firing ranges. One specific concern was the Special Weapons And Tactics (SWAT)team of the Fort Collins Police Services and the type of customized hearing protection that they had recentlypurchased for the team members to use during training and deployment. To address these concerns, NIOSHconducted a temporary threshold shift (TTS) study of officers’ hearing following weapons firing on astandard qualification course on the indoor and outdoor firing ranges. NIOSH investigators also used anacoustic mannequin head to measure noise levels produced by all weapons used by this department. Thisallowed for the measurement of noise levels when different hearing protection devices were placed on themannequin, simulating the noise from weapons on protected and unprotected ears.

The hearing test results showed almost no temporary loss of hearing among officers following weapons firingfor the qualification course used in the evaluation. Also, the pre-exposure hearing tests revealed normalhearing patterns for the majority of the department, with only the oldest group of officers (> 45 years)showing a mild hearing loss pattern at the higher test frequencies. The noise measurements for the variousweapons ranged from 159-169 decibels (dB) peak which is greater than a 140 dB peak exposure guidelinefrom NIOSH. The peak reductions afforded by the ear plugs, ear muffs, and customized SWAT team hearingprotectors were all in the 30 dB range. Double hearing protection (plugs plus muffs) added 15–20 db moreof peak reduction.

Based on the measurements and observations made during the evaluation, NIOSH investigatorsdetermined that a potential health hazard does exist for officers of the Fort Collins Police Servicebecause the noise levels produced by their weapons are sufficient to put them at risk for occupationalhearing loss. However, the hearing protection used by these officers does seem to offer protection asevidenced by the lack of TTS following a qualification course with pistols, shotguns, and rifles and bythe normal hearing thresholds measured in nearly all of the officers.

Keywords: SIC 9221 (Police Protection), noise, weapons, firing range, hearing protection devices,audiometry, hearing loss, temporary threshold shift, TTS, noise spectra

TABLE OF CONTENTSPreface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ii

Acknowledgments and Availability of Report . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ii

Highlights of the HHE Report . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iii

Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iv

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2TTS and Hearing Loss . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2Noise Measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Equipment and Calibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3Weapons and Protectors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3Data Processing and Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Evaluation Criteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4Noise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5Noise-Induced Hearing Loss . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7TTS and Hearing Loss . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7Noise Measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Peak Exposure Levels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8Weapons Spectra . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9Spectral Difference Plots . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9David Clark Model 27 Earmuff Plus EAR Classic Earplug Attenuation . . . . . . . . . . . . . . . . . . . 9Electronic Shooter Protection Elite . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10TTS and Hearing Loss . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10Noise Measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Peak Exposure Levels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11David Clark Model 27 Earmuff Attenuation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12Performance of the ESP Elite Devices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12Performance of the EAR Classic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Recommendations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Health Hazard Evaluation Report No. 2002-0131-2898 Page 1

INTRODUCTIONThe National Institute for Occupational Safety andHealth (NIOSH) received an employee request fora health hazard evaluation (HHE) from employeesand management of the Fort Collins PoliceServices in Fort Collins, Colorado, in January2002. The department was concerned about noiseexposures and potential hearing damage fromweapons training on their indoor and outdoorfiring ranges. One specific concern was theSpecial Weapons And Tactics (SWAT) team ofthe Fort Collins Police Services and the adequacyof customized hearing protection that they hadrecently purchased for the team members to useduring training and deployment.

NIOSH investigators spent the week of May 12,2002, with the Fort Collins Police to test thehearing ability of several members of theirdepartment along with officers from other area lawenforcement agencies and to measure the soundspectra for various weapons they use. Hearingtests were administered at the indoor firing rangeon Monday, Tuesday, and Friday and at theoutdoor range on Wednesday and Thursday.Noise measurements were collected on the indoorrange on Wednesday and on the outdoor range onThursday. Individual hearing test results weresent to each participant along with an explanationof the audiogram in July 2002. For those whospecified on the informed consent sheet, thesame results package was sent to their designatedphysician or audiologist.

BACKGROUNDThe Fort Collins Police Services patrols nearly 47square miles in the city of Fort Collins, Colorado,which has an estimated population of 118,652.There are 148 sworn police officers in thedepartment, which includes a 21-member SWATteam. In 2000, the department investigated128,684 police incidents.

Each SWAT team member was issued a .223caliber, short-barreled rifle for use in SWATdeployments approximately 2–3 years ago. Theyare also exposed to many different explosivedevices used in training exercises and actualincidents. Their training schedule calls formonthly activities with weapons and explosivedevices. A SWAT team from a nearby lawenforcement agency had reported an incidentwhere weapons similar to those used by the FortCollins Police Services were fired inside anenclosed space during a deployment and teammembers suffered permanent hearing losses. Thisled the Fort Collins SWAT team to purchasespecialized hearing protection devices (HPDs) foruse in training exercises and in SWAT teamdeployments—Electronic Shooters Protection(ESP) Elite devices. The company’s literaturedescribes these devices as custom earmolds withanalog electronics that amplify sounds under 90decibels (dB), but damaging sounds above 90 dBare limited to safe levels by miniaturizedcompression circuitry. Two models of the deviceswere issued to the officers, a completely in theear mold and a behind the ear model with threesizes of ear buds. These devices offered hearingprotection in high noise conditions andamplification of signals in low noise situations,and they allowed the officers to wear helmets andgoggles without interference as would be the caseif ear muffs, for example, were used.

The regular training schedule and the high-powered weapons and explosive devices used withthe electronic HPDs was an area of concern formembers of the SWAT team. They wanted someassurance that the HPDs would protect them frompermanent hearing loss resulting from the use ofweapons and explosives in training and actualfield situations. A temporary threshold shift(TTS) study was designed to investigate the risk ofhearing damage from the SWAT team noiseexposure situations. The TTS approach would notonly identify any change in hearing followingweapons’ exposure, it would also documentcurrent levels of hearing. In addition to the TTSinvestigation, measurements of the noise signaturefrom the weapons used by the Fort Collins Police

Health Hazard Evaluation Report No. 2002-0131-2898

Services were made on the indoor and outdoorfiring ranges. Simultaneous measurements of theprotection offered by various HPDs and the levelsproduced by the weapons were collected with anacoustic mannequin as part of the evaluation.

TTS is a transient loss of hearing exhibited afterexposure to brief, intense noise that dissipates overa short period of time. The parameters of TTShave been investigated by many researchers.1 Ithas been consistently observed that higherfrequency hearing (2–6 kilohertz [KHz]) is moreeasily affected by noise exposures than lowerfrequency.2,3 The results from many experimentalstudies indicate that TTS recovers at a rate of 3 dBper doubling of recovery time.4 The Committeeon Hearing, Bioacoustics, and Biomechanics(CHABA) of the National Research Council usedthe TTS index of 2 minutes (TTS2) following thetermination of a noise exposure in its attempt toderive damage-risk contours for noise.5,6

METHODS

TTS and Hearing LossAll patrol officers of the Fort Collins PoliceService were eligible for the hearing tests. Also,other local law enforcement officers from theSheriff’s Department and other local departmentswere invited to participate in the NIOSHinvestigation by the officer in charge of FortCollin’s SWAT operations. Officers reported toeither the indoor or outdoor firing range whenthey were available during their work shift.Informed consent was obtained from eachparticipant before a short questionnaire aboutwork history and self-assessment of their hearingability was given to them for completion.Audiometric tests were administered to each of theparticipants prior to the use of their weapon on therange. While on the range, the officer wasinstructed by the range officer to fire astandardized qualification course for the weaponbeing used. The three courses chosen by the FortCollins Police Services were (1) qualificationpistol - 1 which fires 24 rounds, (2) qualification

shotgun - X which fires 12 rounds, and (3) Phase1 of the SWAT operations standard drill for a 2shooter-contact team which fires 20 rounds. Thefirst two courses were used on the indoor rangeand the third course was used on the outdoorrange. The pistol and shotgun qualification coursewere usually completed with two shooters on theindoor range, however, a few times only oneshooter was available. As the outdoorqualification course states, two shooters werealways present. Immediately upon completion ofthe qualification course, a stopwatch was startedand the officer was escorted back to theaudiometric test booth for a post-exposure hearingtest. The time at which the left ear and right eartests were finished was recorded on the person’squestionnaire. The amount of TTS was calculatedby subtracting the pre-qualification test from thepost-qualification test resulting in a positive valueif the officer’s hearing got worse and a negativenumber if it got better.

Two Tracor Instruments (Austin, Texas) ModelAR-200EC Audiometric Booths provided anacoustic environment for hearing testing. Thebooths were set up in an adjacent classroom atthe indoor firing range and in a storage shed atthe outdoor range. Conversations and otherextraneous noises were controlled during testing.The booths were moved from the indoor to theoutdoor range on Wednesday morning andreturned to the indoor range on Friday for the lastday of testing. Since electrical power was notavailable at the outdoor location, an electricalgenerator on the department’s SWAT vehicleprovided power to the shed. It was parked morethan 100 yards from the storage shed withelectrical extension cords running from thegenerator so that there was no noise impact on thetest environment. Hearing tests were collectedwith Tremetrics (Eden Prairie, Minnesota) ModelRA500 Audiometers that had received anexhaustive calibration check within the past year.Hearing tests were conducted by technicianswho have current certification from the Councilfor Accreditation in Occupational HearingConservation (CAOHC). For the pre-weaponsqualification test, the audiometer tested the


pure-one frequencies of 500, 1000, 2000, 3000,4000, 6000, and 8000 Hertz (Hz) in thecomputerized mode in each ear, left ear first. Thepost-qualification hearing test only used thefrequencies of 2000, 3000, 4000, and 6000 Hz, thefrequencies most sensitive to noise exposure,to reduce the time necessary to collect all of thedata. These frequencies were also tested in thecomputerized mode.

Noise Measurements

Equipment and Calibration

Acoustic recordings of the gunshots werecollected for both the indoor and outdoor firingranges. Recordings were made using a TascamDA-P1 Digital Audio Tape (DAT) recorder thatdigitized the microphone signals at 48000samples per second. An external microphone andmannequin were positioned one meter to the leftof the shooter. The mannequin was built by theFrench German Research Institute de Saint Louis(ISL) specifically for measuring impact andimpulse noise.7 The mannequin consists of thehead, acoustic pinnae, and ear canals, Brüel andKjær 4157 middle ear simulator, and a Brüel andKjær 4165 ½-inch microphone. The maximumpeak sound pressure level (SPL) that could bemeasured with the mannequin was 148 dB (dBSPL re 20 micropascals [µPa]). Since all of themannequin measurements were performedunder hearing protection, the maximum SPLwas not exceeded. The sound outside the hearingprotector was sampled by a Brüel and Kjær4136 ¼ inch microphone which had a maximumsound pressure of 172 dB, sound pressure level(dB SPL). The 4136 microphone was positioned6 centimeters from the right side of the mannequinhead with the microphone pointed verticallyupwards and was not touching the stand thatsupported the mannequin. The diaphragm of themicrophone was visually aligned with the axis ofthe ear canal of the mannequin. The height ofboth the mannequin’s ear canal and externalmicrophone were adjusted to the same height as

the shooter, 6 feet 2 inches, so that they were inthe same plane as the shooter’s ear canal.

Both the mannequin microphone and the externalmicrophone were calibrated with a Brüel and Kjær4228 piston-phone that produces a 124 dB SPLtone at 250 Hz. With the piston-phone running,the recording levels for the right (mannequin) andleft (4136 microphone) channels of the DAT wereadjusted to approximately 50 dB below theexpected maximum signal levels, 150 and 170 dBSPL, respectively. Because the DAT recordingshad to be transferred to computer for post hocanalysis, the recording settings were approximateand recordings of the calibration tones werecollected at the beginning and end of each day’smeasurements. The calibration tone recordingswere used to normalize the digital voltage levelsinto Pascals for the data analysis.

Weapons and Protectors

In Table 1, the 10 weapons that were tested withhearing protectors are listed. The weapons were arepresentative cross section of those used bythe Fort Collins police officers. Specifically, thecalibers were selected and then long and short-barreled models were chosen to address a concernthat short-barreled weapons produced louderimpulses than long-barreled weapons. In additionto the weapons in Table 1, measurements werecollected for a group of 10 SWAT officers usingHeckler and Koch (H&K) 53 and H&K 36 assaultrifles. The H&K weapons used a .223 caliberfrangible bullet. The expense of frangibleammunition prohibited the comprehensivemeasurements with hearing protectors at theindoor range. At the outdoor range, sevenweapons were tested with hearing protectors andare listed in Table 2. Only the long-barreledmodels of the pistols were measured. Althoughthe H&K 53 had a fully-automatic setting, theweapon was used with the single-shot setting.

Several types of hearing protectors were testedat both firing ranges. The protectors that will bediscussed in this report are the David ClarkCompany (Worcester, Massachusetts) Model 27


earmuffs, Electronic Shooters Protection (ESP;Brighton, Colorado) Elite, and the Aearo™Corporation (Indianapolis, Indiana) EAR®Classic® earplugs. Other protectors weremeasured for the purpose of developing areference database of the impulse response of theprotectors when measured on the ISL mannequin.For the David Clark earmuffs, three conditionswere measured: earmuff alone, earmuff plusEAR Classic earplug together, and earmuff withsafety glasses producing a leak under the earmuffcushion. The ESP Elite was essentially an in-the-ear assistive listening device with a wide spectrumgain function and compression circuit to limit theoutput of the device to nominally 90 dB SPL in a2 cubic centimeter (cm3) coupler. The ESP Elitedid not have a Noise Reduction Rating (NRR) asrequired by the U.S. Environmental ProtectionAgency (EPA) for all hearing protection sold inthe United States.8

Prior to the HHE, NIOSH researchers hadElectronic Shooter Protection manufacture an ESPElite protector for the ISL mannequin. The ESPdevice had approximately 3 millimeters betweenthe end of the device in the ear canal and the gridfor the ear simulator. The ESP device was testedat three gain settings: off, unity, and maximum.The unity gain was determined by performing aloudness match between the ESP and air-conducted sound in a double-walled sound roomin the NIOSH Taft Laboratories. Three NIOSHresearchers judged the unity output of the deviceand the mean setting was marked on the face ofthe device.

For each weapon, five shots were fired for eachhearing protector condition. The shots werespaced approximately 2 seconds apart. Eachprotector condition was announced at thebeginning of the recording. The weapons wereannounced to the external microphone beforefiring and were always tested in the orderpresented in Tables 1 and 2. The recording wasstopped after each set of weapons. The recordingtimes and any misfires or weapon malfunctionswere recorded in a lab notebook.

Data Processing and Analysis

The DAT tape recordings were digitallytransferred to .wav files using a Lexicon Core32sound card. Each set of recordings were separatedinto a .wav file and directory. Next, the five-shotgroups were isolated and saved as .wav files foranalysis. The calibration tones were edited toselect only the final portions of each channel’ssample of the calibration signal. The calibrationlevels were calculated for each microphone andused in the subsequent analysis.

A Matlab program was developed to examinethe average signal level as a function of time,permitting the researcher to identify the beginningof each gunshot within the sample. Once the startof each gunshot was identified, a time window of42.67 or 170.67 milliseconds (ms) was analyzedfor the peak protected and unprotected noiselevels, the third-octave band spectra and theattenuation spectrum of the hearing protector. Theshorter time window, 42.67 ms, was used with theoutdoor measurements. The protected andunprotected equivalent levels, dB Leq, weredetermined for linear weighting. The one third-octave unprotected spectra from each weaponwere averaged across recordings to estimate themean spectra for each weapon.

EVALUATION CRITERIAAs a guide to the evaluation of the hazards posedby workplace exposures, NIOSH field staffemploy environmental evaluation criteria for theassessment of a number of chemical and physicalagents. These criteria are intended to suggestlevels of exposure to which most workers maybe exposed up to 10 hours per day, 40 hours perweek for a working lifetime without experiencingadverse health effects. It is, however, important tonote that not all workers will be protected fromadverse health effects even though their exposuresare maintained below these levels. A smallpercentage may experience adverse health effectsbecause of individual susceptibility, a pre-existingmedical condition, and/or a hypersensitivity


(allergy). In addition, some hazardous substancesmay act in combination with other workplaceexposures, the general environment, or withmedications or personal habits of the worker toproduce health effects even if the occupationalexposures are controlled at the level set by thecriterion. These combined effects are often notconsidered in the evaluation criteria. Finally,evaluation criteria may change over the years asnew information on the toxic effects of an agentbecome available.

The primary sources of environmental evaluationcriteria for the workplace are: (1) NIOSHRecommended Exposure Limits (RELs),9 (2) theAmerican Conference of Governmental IndustrialHygienists’ (ACGIH®) Threshold Limit Values(TLVs®),10 and (3) the U.S. Department of Labor,Occupational Safety and Health Administration(OSHA) Permissible Exposure Limits (PELs).11

Employers are encouraged to follow the OSHAlimits, the NIOSH RELs, the ACGIH TLVs, orwhichever are the more protective criteria.

OSHA requires an employer to furnish employeesa place of employment that is free fromrecognized hazards that are causing or are likely tocause death or serious physical harm[Occupational Safety and Health Act of 1970,Public Law 91–596, sec. 5(a)(1)]. Thus,employers should understand that not allhazardous chemicals have specific OSHAexposure limits such as PELs and short-termexposure limits (STELs). An employer is stillrequired by OSHA to protect their employeesfrom hazards, even in the absence of a specificOSHA PEL.

NoiseThe A-weighted decibel [dB(A)] is the preferredunit for measuring sound levels to assess workernoise exposures. The dB(A) scale is weighted toapproximate the sensory response of the humanear to sound frequencies near the threshold ofhearing. The decibel unit is dimensionless, andrepresents the logarithmic relationship of themeasured sound pressure level to an arbitrary

reference sound pressure (20 :Pa, the normalthreshold of human hearing at a frequency of1000 Hz). Decibel units are used because of thevery large range of sound pressure levels whichare audible to the human ear. Because the dB(A)scale is logarithmic, increases of 3 dB(A), 10dB(A), and 20 dB(A) represent a doubling, 10-fold increase, and 100-fold increase of soundenergy, respectively. It should be noted thatnoise exposures expressed in dBs cannot beaveraged by taking the simple arithmetic mean.

The OSHA standard for occupational exposure tonoise (29 CFR 1910.95)11 specifies a maximumPEL of 90 dB(A) for a duration of 8 hours perday, expressed as a time-weighted average(TWA). The regulation, in calculating the PEL,uses a 5 dB time/intensity trading relationship, orexchange rate. This means that a person may beexposed to noise levels of 95 dB(A) for no morethan 4 hours, to 100 dB(A) for 2 hours, etc.Conversely, up to 16 hours exposure to 85 dB(A)is allowed by this exchange rate. The duration andsound level intensities can be combined in order tocalculate a worker's daily noise dose according tothe formula:

Dose = 100 X (C1/T1 + C2/T2 + ... + Cn/Tn ),

where Cn indicates the total time of exposure at aspecific noise level and Tn indicates the referenceduration for that level as given in Table G-16a ofthe OSHA noise regulation. During any 24-hourperiod, a worker is allowed up to 100% of hisdaily noise dose. Doses greater than 100% are inexcess of the OSHA PEL.

The OSHA regulation has an additional actionlevel (AL) of 85 dB(A); an employer shalladminister a continuing, effective hearingconservation program when the 8-hour TWAvalue exceeds the AL. The program must includemonitoring, employee notification, observation,audiometric testing, hearing protectors, training,and record keeping. All of these requirements areincluded in 29 CFR 1910.95, paragraphs (c)through (o). Finally, the OSHA noise standardstates that when workers are exposed to noise


levels in excess of the OSHA PEL of 90 dB(A),feasible engineering or administrative controlsshall be implemented to reduce the workers'exposure levels.

NIOSH, in its Criteria for a RecommendedStandard,12 and the ACGIH,10 propose exposurecriteria of 85 dB(A) as a TWA for 8 hours, 5 dBless than the OSHA standard. The criteria also usea more conservative 3 dB time/intensity tradingrelationship in calculating exposure limits. Thus,a worker can be exposed to 85 dB(A) for 8 hours,but to no more than 88 dB(A) for 4 hours or 91dB(A) for 2 hours. Twelve hours exposures haveto be 83 dB(A) or less according to the NIOSHREL.

Noise-Induced Hearing LossNoise-induced loss of hearing is an irreversible,sensorineural condition that progresses withexposure. Initially, the noise exposure may causea TTS, that is, a decrease in hearing sensitivitythat typically returns to its former level within afew minutes to a few hours. Repeated exposurescan lead to a permanent threshold shift. Althoughhearing ability declines with age (presbycusis) inall populations, exposure to noise produceshearing loss greater than that resulting from thenatural aging process. This noise-induced loss iscaused by damage to nerve cells of the inner ear(cochlea) and, unlike some conductive hearingdisorders, cannot be treated medically.13 Whileloss of hearing may result from a single exposureto a very brief impulse noise or explosion, suchtraumatic losses are rare. In most cases, noise-induced hearing loss is insidious. Typically, itbegins to develop at 4000 or 6000 Hz (the hearingrange is 20 Hz to 20000 Hz) and spreads to lowerand higher frequencies. Often, materialimpairment has occurred before the condition isclearly recognized. Such impairment is usuallysevere enough to permanently affect a person'sability to hear and understand speech undereveryday conditions. Although the primaryfrequencies of human speech range from 200 Hzto 2000 Hz, research has shown that the consonant

sounds, which enable people to distinguish wordssuch as "fish" from "fist," have still higherfrequency components.14

Audiometric evaluations of workers are conductedin quiet locations, preferably in a sound-attenuating chamber, by presenting pure tones ofvarying frequencies at threshold levels, i.e., thelevel of a sound that the person can just barelyhear. Audiograms are displayed and stored astables or charts of the hearing levels (HL) atspecified test frequencies.15 Zero dB HLrepresents the hearing level of the average, normalhearing individual. In OSHA-mandated hearingconservation programs, thresholds must bemeasured for pure-tone signals at the testfrequencies of 500, 1000, 2000, 3000, 4000, and6000 Hz. Individual employee’s annualaudiograms are compared to their baselineaudiogram to determine the amount of standardthreshold shift (STS) that might have occurredover the time period being evaluated.Specifically, OSHA states that an STS hasoccurred if the average threshold values at 2000,3000, and 4000 Hz have increased by 10 dB ormore in either ear when comparing the annualaudiogram to baseline audiogram.11 The NIOSHrecommended threshold shift criterion is a 15-dBshift at any frequency in either ear from 500–6000Hz measured twice in succession.12 Practically,the criterion is met by immediately retesting anemployee who exhibits a 15-dB shift frombaseline on an annual test. If the 15-dB shift ispersistent on the second test, a confirmatoryfollowup test should be given within 30 days ofthe initial annual examination. Both of thesethreshold shift criteria require at least twoaudiometric tests. In cases where only oneaudiogram is available, a criterion has beenproposed for single-frequency impairmentdeterminations.16 It employs a lower fence (theamount of HL necessary before a hearinghandicap is said to exist) of 25 dB. With thiscriterion, any person who has a hearing level of26 dB HL or greater at any single frequency isclassified as having some degree of hearing loss.The degree of loss can range from mild (26–40 dBHL) to profound (>90 dB HL).


RESULTS

TTS and Hearing LossA total of 93 hearing tests were given over the fivedays of the site visit. Of this total, 71 tests weregiven to Fort Collins Police Services officers, 18tests were given to officers of neighboringdepartments, and 4 tests were repeats for SWATofficers who were tested on Monday on the indoorrange and on Wednesday at the outdoor range.The hearing test results figures include only theFort Collins’ officers; the other officers’ data areincluded in the table listing the TTS values foundfollowing the firing of the various weapons. Onthe indoor range, participants fired either theirservice revolver or a 12-gauge shotgun. On theoutdoor range, .223 caliber rifles were used.Hearing protection devices used on the indoorrange were generally David Clark Model 27earmuffs or custom-molded earplugs. For the 20Fort Collins Police Services SWAT officers testedon the outdoor range, all but 4 wore the ESP Elite(14) or the behind-the-ear model Pro-Elite (2)custom-molded electronic devices. The other fourwore EAR Classic earplugs (3) or EAR plugs plusAearo Peltor® Model Tactical™ 7 earmuffs (1).

The mean hearing test results for the Fort CollinsPolice Services’ officers who participated in theevaluation are shown in Figure 1. The graphshows the mean hearing levels for all 71 officersfrom the audiograms obtained before any weaponswere fired by the officer. The left ear results areslightly poorer at the higher test frequencies, butoverall, the mean results fall into a normal (<25dB HL) hearing range for both ears. Sixty-three ofthe seventy-one officers were male. The mean agefor the group is 37.2 years (range = 29–52 years).These officers have been in law enforcement for amean of 12.9 years with a mean time of 10.4 yearswith the Fort Collins Police Services. The resultswere separated into age brackets to see the hearingprofile trends over time, and are shown in Figure2 for the left ear and Figure 3 for the right ear.These data show that all age groups of less than 46years of age have mean levels that are in a normal

hearing range for both ears. It is only the oldestgroup of officers that have mean hearing loss as agroup in the higher test frequencies, 4000 Hz andabove. The high frequency loss is classified as amild loss.16 When the SWAT officers arecompared to the rest of the department, there islittle difference between the two groups in theirmean hearing levels (Figure 4). The mean age ofthe SWAT officers is 36.6 years with a mean timeas an officer of 10.5 years. The remainder of theFort Collins Polices Services have a mean age of38.4 years and time in service of 13.8 years.

As previously noted, after completing the firstaudiometric examination, the officers weremoved to the firing range and were instructed tofire their weapon using a standard firearmqualification course under the direction of therange instructor. Under most circumstances, twoofficers completed the course simultaneously intwo adjacent lanes on the firing range.Immediately after completion of the qualificationcourse, a stopwatch was started and the officerswere quickly returned to the audiometric testbooth for the modified audiometric examination ofhigh-frequency pure tones. Elapsed times wererecorded when the left ear test and right ear testwere completed. TTS values were determined bysubtracting the pre-qualification hearing test fromthe post-qualification test for each frequencytested.

The mean TTS values for each weapon type(pistol, rifle, or shotgun) and for the SWATcustom-made hearing protector are given in Table3. The majority of the mean TTS values arenegative numbers, meaning that the officersactually heard better following the qualificationcourse on the firing range. Mean completiontimes on the indoor range for the left ear tests wereslightly greater than 2 minutes and the right earswere finished in 3.25 minutes. On the outdoorrange the officers were tested further away fromthe firing line and it took nearly 3.5 minutes tofinish the left ears and 4.5 minutes to finish theright ears. The mean TTS values for SWATofficers wearing the ESP hearing protectors andfiring .223 cal rifles were less than 1.0 dB, with


the majority being 0.0 dB or less. Inspection ofindividual results shows only one instance wherethe change in hearing was +10 dB at a testfrequency of 6000 Hz. When the three types ofweapons used by the officers are looked atseparately, the mean TTS values are all less than1.0 dB. For the .223 cal rifle used on the outdoorrange, there were two individuals out of 26 testedthat had TTS values of +10 dB, one at 4000 Hzand the other at 6000 Hz. On the indoor range, thepistol qualification course resulted in 11 of 52officers exhibiting a TTS of +10 dB or greater.Two of the 11 officers had +10 dB shifts at twoseparate test frequencies. Ten of the shiftsoccurred at the 6000 Hz test frequency. Theshotgun qualification course resulted in only oneofficer out of 14 that had a +10 dB shift at 4000Hz. No individual TTS exceeded +20 dB.

Noise Measurements

Peak Exposure Levels

Figure 5 shows the mannequin’s protected ear andthe unprotected waveforms for a Smith & Wessonrevolver recorded at the outdoor firing range. Themeasurements at the outdoor range provided abetter approximation to what one might expectin an anechoic environment, one with fewerreflected sound waves. Particularly, the firstimpulse of the shockwave from the muzzle of theweapon was extracted for analysis. The recordingconditions (drizzling rain) required that we use afabric tent over the shooting area. The ground,ISL mannequin, tent, shooter, shooter’s assistant,picnic table, and weapons were potential reflectivesurfaces. Of these, the side of the mannequin’shead reflected the most energy (see the doublepeak at 1.82 ms). Peaks at 3.58 and 4.23 msprobably correspond to reflections from the tentand the shooter. The peak at 6.24 ms is consistentwith the path length difference between the directand ground-reflected paths.

The protected waveform (solid blue line) for theSmith & Wesson 586 and David Clark Model 27earmuffs yielded a peak protected level of 137.5

dB SPL. The waveform was less sharply peakedthan the unprotected waveform (solid red line).This difference was primarily a function of thehearing protector. Earmuffs generally yielded alow-pass filter that smoothed the jagged natureof the waveform. Earplugs, such as the EARClassic, had more low frequency attenuationthan the earmuff. Consequently, the resultingprotected waveforms were not dominated by thelow-frequency signal and more closely resembledthe unprotected waveform.

Figure 6 shows a pair of bar graphs indicating theaverage and standard deviation of the maximumpeak sound pressure level in decibels referenced to20 µPa measured at the indoor and outdoor firingranges. For the indoor range (upper panel), theSmith & Wesson 586 and 686 revolvers had soundpressures of 167.9 and 167.1 dB SPL,respectively. The Colt Pocket9 and Par-OrdinanceP10 pistols had the next greatest peak pressures of162.3 and 162.4 dB SPL, respectively. Theremaining weapons at the indoor range had peakpressures that ranged from 158.6 to 160.8 dB SPL.For the outdoor range (lower panel), the Smith &Wesson 586 revolver and the H & K 53 rifle hadthe highest peak pressures of 168.6 and 166.8 dBSPL, respectively. The other weapons rangedfrom 159.0 to 161.5 dB SPL.

Weapons Spectra

In Figure 7, the a-octave band spectra of theweapons tested on the outdoor range are displayedin staircase plots. The horizontal lines are spacedin 10 decibel intervals and the dark bar at thecenter of each spectrum is the 1000 Hz band. Formost of the weapons, the maximum level isbetween 500 and 800 Hz. With the exception ofthe Glock 22 and Colt 1991-A1, the maximumband exceeded 130 dB SPL. The maximumenergy of the Smith & Wesson 586 was at2000 Hz.

One point should be clarified about the a-octaveband analysis. The estimate of the peak impulselevel is based upon the instantaneous soundpressure. The third-octave analysis represents the


average of the signal over the analysis window(42.67 ms for the outdoor data). One mayvisualize spreading the instantaneous peak overthe analysis window. If a single gunshot issampled with both a short and long time window,the long-window third-octave analysis will yieldlower estimates of the band levels. For thisreason, the peak sound pressure levels are listedon the weapon spectra in Figure 7 rather than thelogarithmic sum of the a-octave bands.

Spectral Difference Plots

To better examine the differences betweenweapons, the .450 caliber Colt 1991 A1 pistol wasused as a reference spectrum and was subtractedfrom the spectra of the other weapons shown inFigure 8. The spectra for the Glock 22, Sig SauerP228 and Colt 1991-A1 were similar except at thehigh frequencies. The Colt AR-15 levels wereapproximately 7-10 dB/band greater below 200Hz. From 400 to 1000 Hz, the AR-15 levels were3-5 dB/band higher. The Remington 11-87shotgun was greater by 5-14 dB/band below 400Hz. Above 4000 Hz, the shotgun was slightlygreater than the Colt 1991-A1. The Smith &Wesson 586 levels were 5-15 dB/band higherin almost every band. Above 250 Hz, the 586was not more than 10 dB/band greater than theColt 1991-A1. The peak level from the Smith &Wesson 586 in Figure 7 was also evident in thedifference plot at 2000 Hz. The H & K 53exhibited the greatest spectral differences at 20 of27 third-octave band frequencies. Below 500 Hz,the H&K 53 exceeded the Colt 1991-A1 by 10-15dB/band. Above 500 Hz, the H&K 53 was greaterby about 5-10 dB/band.

David Clark Model 27 EarmuffPlus EAR Classic EarplugAttenuation

Figure 9 shows the attenuations measured for theDavid Clark Model 27 earmuff, EAR Classicearplug, and David Clark Model 27 with EARClassic. The David Clark muffs exhibitedattenuations of about 10 dB/band at 100 Hz and

below. From 100-500 Hz, the attenuationincreased to about 35 dB. The attenuation above500 Hz varied between 28 and 40 dB/band. TheClassic earplug increased in attenuation from 18dB at 25 Hz to 38 dB at 800 Hz. Above 800 Hz,the attenuation ranged from 30 to 52 dB/band.

The combination of the David Clark and Classicprotectors were measured at both firing ranges.The indoor range data below 250 Hz exhibitedattenuations close to the sum of the David Clarkand Classic measured separately. Above 250 Hz,the attenuations varied over a range of 40 decibels.The differences were likely due to resonances intransmission through the protectors andresonances of the enclosed volumes of the earmuffand earplug.

The results with David Clark Model 27 whenworn with safety glasses are presented in Figure10. Two features are prominent in the figure: theattenuation is negative below 200 Hz; theattenuation at 2000 Hz varies more than theadjacent frequencies. The variability at 2000 Hzcorrelates with the output of various weapons atthat frequency. The low-pass filtering of theearmuff will yield greater exposure underneaththe earmuffs for weapons with significant low-frequency content such as the H & K 53, ColtAR-15, Remington 11-87 and the Smith andWesson 586.

Electronic Shooter ProtectionElite

The ESP Elite was tested at both firing ranges forthree gain settings—off, unity, and maximumgain. In Figure 11, the off setting is shown withgray symbols, unity with green, and maximumwith red symbols. The outdoor attenuations areshown with squares and the indoor with circles.The indoor and outdoor attenuations differedconsiderably between 100 and 400 Hz. Above2500 Hz, the outdoor and indoor attenuationsdiffered by as much as 10 dBs. When the ESPElite was turned off, the attenuations above 2500Hz are within 4 dB for the indoor and outdoormeasurements. The disparity between the indoor


and outdoor results suggest that the ESP may besensitive to how well it was fit in the mannequinear canal.

In Figure 12, the summary analysis of 24 ESPElite protectors performed with the Frye FP40Hearing Aid Analyzer is shown.17 In the upperpanel, the histogram of the maximum SPL outputof the ESP exhibited a wide range of levels from90 to 105 dB SPL. In the lower panel, thehistogram of the average of the saturated SPLdetermined as the average of 1000, 1600 and 2500Hz is shown. The upper histogram seems to havetwo groups centered at 92 and 102 dBs. Thelower histogram is centered about 88 dB and hasone group.

The data from Figure 12 suggest that officerswearing the ESP Elite could be exposed to levelsof noise above the NIOSH recommended limitof 85 dB if they use the maximum gain. The ESPElite measured on the mannequin exhibited moreattenuation at the low frequencies and comparableattenuation at the high frequencies when comparedto the David Clark Model 27 earmuffs. While themeasured peak impulse levels of gunshotsunderneath the ESP were approximately 128 to138 dB, the highest saturated sound pressureoutput of the ESP device was limited to about 105dB (the average of 1000, 1600 and 2500 Hz witha 90 dB input). The exposure to the weapon posedthe greatest risk of noise exposure. The averages of the peak reduction are shown inFigure 13 for the various hearing protector, safetyglasses, and range conditions. The earmuffs withsafety glasses had a reduction of 12 and 18 dBs.The earmuffs alone reduced the peak energy by 29and 32 dB. The peak energy reduction of the EARClassic was 29 dB. The peak reductions for thecombined earmuff and earplug were 46 and 50 dB.The peak reductions for the ESP Elite protectorwere approximately 30-31 decibels regardless ofthe volume setting.

DISCUSSION

TTS and Hearing Loss

The weapon qualification courses fired by theofficers did not result in significant amounts ofTTS. The mean values were consistently less than0 dB, meaning that the HPDs used during thisevaluation seems to have prevented temporarychanges in hearing for the officers firing theirweapons under these circumstances. These dataare somewhat different from previously presentedresults of TTS in officers who wore doublehearing protection on an indoor firing range andwere found to exhibit an average TTS of 9 dB at6000 Hz when the ear plug was not properlyinserted into their ears.18 The pre-noise exposureaudiometric examinations also showed that theaverage Fort Collins Police Service officer testeddid not show hearing loss patterns consistentwith noise over-exposures. Only the oldest groupof officers (> 45 yrs.) had mean hearing levelsthat fell into a mild hearing loss category forthe higher test frequencies (4000, 6000, and8000 Hz). One finding in the hearing data,however, does raise some concern. For theindividual officers tested who exhibited temporaryshifts of 10 dB or more, nearly all of the changeswere at 6000 Hz, the test frequency where theolder officers were found to have mild hearingloss.

Noise Measurements

Peak Exposure Levels

Several issues need to be considered with respectto these data. First, the mannequin was designedto estimate the airborne transmission path for anexternal sound attenuated by a hearing protector.In the human, the acoustic energy can reach thecochlea through several pathways: through the air,through the hearing protection, through leaksaround the hearing protection, through the oral-nasal cavities (transmitted into the middle earcavities), and through bone conduction. Theattenuations measured at the high frequencieswith the mannequin are not representative ofthe attenuations measured using the real-earattenuation at threshold method for humans


subjects. The mannequin has more isolation of themicrophone and thus does not recreate the bone-conduction and oral-nasal pathways. However,the peak level reductions may be reasonableestimates for what a human subject wouldexperience.

Second, the attenuation of a protector used inimpulsive noise may not be the same when used incontinuous noise. Newton’s first law of motionstates, “Every body persists in its state of rest or ofuniform motion in a straight line unless it iscompelled to change that state by forcesimpressed on it.”19 An acoustic shock wave willimpart energy to the protector, but may not be aseffective in causing the protector to oscillate orvibrate as a low-amplitude continuous waveform.Protector attenuations are tested using continuousthird-octave band noise at or near the threshold ofhearing. An impulsive waveform will excite theprotector at effectively all frequencies, but theenergy is transmitted over a short time period. Ifthe device being excited behaves in a nonlinearmanner, the transmission of a high-level impulsemay be affected by the nonlinearity while thetransmission of low-level continuous noise willnot be affected. Acoustic nonlinearities becomeimportant at signal levels above 120 decibels.Acoustic shock waves can be formed at levels of140 dB and greater when the impedance of theair becomes nonlinear. The attenuation forcontinuous noises remains constant as a functionof level over a wide range of signal levels. Thepeak reduction data in Figure 13 were presented asbar graphs because the peak reduction wasconstant within the error limits over the range ofweapons tested. The only device that was notconstant was the earmuff with safety glasses. Thesafety glasses will be discussed in a later sectionof this report.

Third, the audiology, occupational safety andhealth, and military communities have not reacheda consensus regarding the risk of hearing losswhen it comes to impulse noise. Particularly, theU.S Military Standard 1474D yields estimates ofthe daily allowed number of rounds fired thatseem to be unacceptably high (one calculation

using a protected waveform under an earmuffyielded 3000 shots for a Colt AR-15 rifle).20

Other calculations suggest that 100 to 1000 shotsis the recommended number of shots. NIOSH hasproposed the following formula for evaluating therisk of impulsive noise,

N = 10(140 - PI dB)/10

where N is the total number of shots and PI dB isthe peak impulsive level in dB SPL.21 Using thisformula and the peak levels in Figure 6 and thepeak reductions in Figure 13, the officers wouldbe exposed to peak impulse levels of 130–140 dBSPL. Applying this formula yields an allowablenumber of shots of 1 to 10 shots per day. Thisproposed formula is a conservative estimate andmakes no compensation for the duration of theimpulse.22,23,24 Applying the NIOSH formula tothe double-protected data increases the allowablenumber of shots from 100 to 1000. Even thoughonly a few of the officers experienced a small shiftin this evaluation, properly-fit, double protectionshould minimize TTS and potential permanentthreshold shifts.

David Clark Model 27 EarmuffAttenuation

The David Clark Model 27 earmuffs yieldedpeak reductions that are typical of other earmuffsmeasured with these methods.25 A peak reductionof 30 decibels is typical of other earmuffs thatwere measured for 9mm and .223 caliber weapons.Two areas of concern should be addressed withthe earmuff usage by the Fort Collins PoliceService SWAT officers: the use of HPDs withsafety glasses; and the use of the devices withhelmets.

During the HHE, the mannequin measurementswere performed with and without safety glasses.As shown in Figure 13, the peak reductions werediminished when the safety glasses disruptedthe seal of the earmuff cushion with the side of thehead. The small opening around the earpiece ofthe glasses lowered the effective peakreduction by 20 to 30 dBs. Using the peak levels


from Figure 6, the officer with a comparable leakcould be exposed to 156 to 150 dB peak SPL. Ifthe officers could wear the safety glasses over thetop of the earmuff cushions, or use glasses with astrap or low profile stem rather than a high profilestem, the size of the leak could be reduced oreliminated. Ideally, the safety glasses should bean integral part of the earmuff or the helmet.

The peak level reduction for the earmuff withsafety glasses exhibited a slight increase in peakreduction as the peak SPL increased. This effectis consistent with nonlinear acoustic impedanceof shockwaves that impinge upon an orifice. Infact, nonlinear impedance forms the basis ofseveral hearing protection devices, such as theEAR Combat-Arms earplug, Bilsom ISL earplug,and the EAR Ultra 9000 shooters earmuff.

The second issue is using earmuffs with theSWAT officers helmets. The officers had Kevlarhelmets that had attachment points for faceshields but not hearing protectors. Also, thehelmets covered the upper half of the pinna.Consequently, the current helmet could not beused with the circumaural earmuffs used by theFort Collins Police Service. However, Peltor nowmakes a hearing protection device that permits theuse of a helmet with an earmuff (Peltor® COM-TAC and SWAT•TAC). There is also researchbeing conducted for the U.S. military on the useof earplugs with communication capabilities forimpulsive and steady-state noise environments.26

Performance of the ESP EliteDevices

The ESP Elite exhibited inconsistent attenuationwithin the measurements collected at both firingranges, which may have been a function of howwell the device was fit. At each location, thedevice was inserted fully into the mannequin’s earcanal and pinna. The insertion is not difficult andshould not have caused any effect between the tworanges. The data in the lower panel of Figure 12suggests that the ESP device yields a consistentsaturated SPL, the average of the output at 1000,

1600 and 2500 Hz in response to a 90 dB SPLinput.

One of the issues which applies more to hearingaids and sound-restoration earmuffs is theperformance in intermittent noise. Typically adevice will use either a level-limiting,compression, or automatic gain control circuit tolimit the maximum SPL output of the electronics.For lower SPL, these devices are able to amplifythe sound and reproduce the signal at a levelwhich is above the attenuated SPL and below itsmaximum output level. The output of the ESPElite, or other electronic hearing protectors, inresponse to high amplitude impulsive sounds,will not be reproduced by these devices due tomechanical and electrical limitations. In otherwords, an intermittent peak of 80 dB mightbe attenuated by 20 dB resulting in anunaided/unamplified sound pressure level of60 dB. When the device amplifies that sound by20 dB, the output would be restored to the 80 dBlevel. For a high amplitude impulsive sound(160 dB), the device might attenuate by 20 dB, butthe amplification cannot restore the sound level to160 dB because it exceeds the capability of thecircuitry. This shortcoming is good, because thedevice will not reproduce harmful sound pressurelevels that exceed the capability of the circuitry.For intermittent noise, these devices also havesome recovery time after a loud sound occurs.The recovery time can adversely affectcommunication by cutting of the speech during aloud sound. The manufacturer lists the releasetime as 400 ms. The hearing aid analyzer that wasused in the field to assess the performance of theESP Elite protectors was not equipped to measurethe attack and release times. For an intermittentnoise, a short recovery time might have less of aneffect on communication.

Another issue that should be considered with theofficers using the ESP device is how well theearpiece fits. Every officer using the ESP shouldhave the fit of the device tested to determinewhether they are achieving an effective seal ofthe ear canal. A poor seal could increase the noiseexposure that officers receive. FitCheck is a


product which can be installed on a personalcomputer running Windows software.27 FitCheckmeasures the attenuation of earplugs usingnarrow-band noise signals. If an officer does notreceive a reasonable amount of attenuation (15–30decibels in every frequency band), the deviceshould be remade. Unfortunately, the ESP Eliteprotector does not have an EPA NRR.8 If it hadan NRR, consumers would know what attenuationto expect if fit testing were performed.

Performance of the EAR Classic

The EAR Classic earplug yielded a peak levelreduction of 30 dBs. Again this number seemsto be typical for a well fit protector on themannequin. The Classic earplug exhibits aconsistent performance across subjects and is notas susceptible to acoustic leaks as other earplugs.28

For a human, the Classic earplug can be insertedanywhere from 10 to 100 percent of the length ofthe earplug into the ear canal. With respect to realear attenuation at threshold, the attenuation isaffected by how much of the earplug has beeninserted. For the ISL mannequin, a maximum of60 percent of the earplug could be inserted into theear canal. The peak reduction in a human earcanal may be more or less depending upon howmuch of the earplug is inserted. Real-worldstudies of hearing protector devices have shownthat they do not achieve the manufacturer’smeasured attenuations for experimenter fitearplugs.29,30

CONCLUSIONSUsing the NIOSH REL as a guideline, the officersshould not be exposed to noise impulses above140 dB for any amount of time.12 The unprotectedpeak noise levels measured on the acousticmannequin were found to range from 159 to 169dB. The results from the TTS study indicate thatthe weapons’ noise is not great enough to result ina temporary loss of hearing while firing a singlestandard qualification course on either the indooror outdoor range with the HPDs used during theevaluation. The baseline hearing tests for the

police service revealed normal hearing patterns forall but the oldest group of officers. It is possiblethat the mild hearing loss measured in the oldestgroup is the result of different work practices usedby the police service when these officers were justbeginning their careers and that the current groupof young officers will not necessarily accrueoccupational hearing loss. Or these results mayshow that the amount of sound energy from theirweapons is intense enough to eventually resultin hearing loss. It is not possible to answer thisquestion with the data collected during thisevaluation.

The measurements of the protection afforded bythe HPDs were consistently in the 30 dB range(Figure 13), unless the earmuff seal with the sideof the mannequin was broken by the safetyglasses.

These peak reduction results along with the peaknoise levels measured for the weapons indicatethat the officers should consider using dualhearing protection during weapons trainingexercises for maximum protection. To overcomethe inability to communicate when double-protected, the officers should be provided withelectronic level-limiting earmuffs and a choice ofearplugs. The earplugs can provide an additional15–20 dB of peak reduction while the electronicearmuffs can compensate for the reduced speechintelligibility due to double protection. If theprotected peak SPL are in the 120–130 dB range,then the NIOSH formula suggests that 100 to 1000shots per day would be allowed. Recognizing thatthis is a conservative estimate, officers will not beexposed to an excessive risk of hearing loss withdouble protection. In addition to the electronicearmuffs, commercially available communicationheadsets exist that would permit the range officerto transmit instructions via short range radio to theofficer’s headset that could improve thecommunication even further. Companies such asAearo/Peltor, Baccou-Dalloz (Bilsom), DavidClark, and Hellberg make combined hearingprotector and communication systems that mightbe adaptable to the SWAT team’s needs duringtraining and during deployment.


1. Davis H, Morgan CT, Hawkins Jr. JE,Galambos R, Smith FN [1950]. Temporarydeafness following exposure to loud tone andnoise. Acta Otolaryngologica Supplement

88:1–57.

2. Hirsh IJ, Ward WD [1952]. Recovery of theauditory threshold after strong acousticstimulation. Journal of the Acoustical Society ofAmerica 24:131–141.

3. Kryter KD [1963]. Exposure to steady-statenoise and impairment of hearing. Journal of theAcoustical Society of America 35:1515–1525.

4. Kryter KD [1970]. The effects of noise onman. New York, NY: Academic Press.

5. Kryter KD, Ward WD, Miller JD, EldredgeDH [1966]. Hazardous exposure to intermittentand steady-state noise. Journal of the AcousticalSociety of America 39:451–464.

6. Ward WD [1966]. The use of TTS in thederivation of damage risk criteria for noiseexposure. International Audiology 5:309–313.

7. Franke R, Parmentier G, Buck K, Evrard G,Kronenberger G, Beck C, Brunner JJ [1994]. Teteartificielle pour l’evaluation de l’efficacite desprotecteours auditifs vis a vis bruis de niveaueleve Partie 1: Developpement et essais en regimeimpulsionnel. Research report French-GermanInstitute for Research of Saint Louis. Report R-112/94.

8. EPA [1978]. Noise labeling requirements forhearing protectors. Fed Regist 44(190), 40CFRpart 211, 56130-56147.

9. NIOSH [1992]. Recommendations foroccupational safety and health: compendium ofpolicy documents and statements. Cincinnati, OH:U.S. Department of Health and Human Services,Public Health Service, Centers for Disease Controland Prevention, National Institute forOccupational Safety and Health, DHHS (NIOSH)Publication No. 92-100.

10. ACGIH [2002]. 2002 TLVs® and BEIs®:threshold limit values for chemical substances andphysical agents and biological exposure indices.Cincinnati, OH: American Conference of

RECOMMENDATIONSBased on the measurements and observationsmade in the evaluation of weapon noise and itseffect on hearing for the Fort Collins PoliceService, the following recommendations are madeto improve working conditions for the officers.

1. The use of double hearing protection iswarrented during weapons training exercises. Thepeak noise levels measured for the weapons andthe amount of attenuation given by the HPDs aresuch that double protection will offer maximumprotection and some insurance against improperfitting of the devices or incompatibility with otherpersonal protective equipment.

2. Although the ESP device worn by the SWATofficers did not result in any TTS, the Fort CollinsPolice Service should investigate other devicesthat are available. The ESP Elite does not have anNRR rating which is required by the EPA forHPDs.8 The device also does not allow for closed-circuit radio communications which would limitthe broadcasting of radio transmissions into anenvironment that may be better protected withradio silence. HPDs that offer this are beginningto be available. These devices should be reviewedto see if they are compatible with the SWATteam’s equipment and practices.

3. The noise levels that are generated by theweapons used by the police service are intenseenough to warrant the initiation of a hearingconservation program. As a minimum, the hearingconservation program should meet therequirements of the OSHA hearing conservationamendment (29 CFR 1910.95).11 Other sourcesfor defining effective hearing conservationprograms are also available.31,32,33

REFERENCES


Governmental Industrial Hygienists.

11. CFR [1997]. 29 CFR 1910.1000. Code ofFederal Regulations. Washington, DC: U.S.Government Printing Office, Office of the FederalRegister.

12. NIOSH [1998]. Criteria for a recommendedstandard: occupational noise exposure (revisedcriteria 1998). Cincinnati, OH: U.S. Departmentof Health and Human Services, U.S. Public HealthService, Centers for Disease Control andPrevention, National Institute for OccupationalSafety and Health, DHHS (NIOSH) PublicationNo. 98-126.

13. Ward WD, Royster LH, Royster JD [2000].Anatomy & physiology of the ear: normal anddamaged hearing. Chapter 4. In: Berger EH,Royster LH, Royster JD, Driscoll DP, & Layne M,eds. The noise manual. 5th ed. Fairfax, VA:American Industrial Hygiene Association, pp101–122.

14. Suter AH [1978]. The ability of mildlyhearing–impaired individuals to discriminatespeech in noise. Washington, DC: U.S.Environmental Protection Agency, JointEPA/USAF study, EPA 550/9–78–100,AMRL–TR–78–4.

15. ANSI [1996]. American national standardspecification for audiometers. Melville, NY:Acoustical Society of America, AmericanNational Standards Institute, ANSI S3.6-1996.

16. Eagles EL, Hardy WG, Catlin FI [1968].Human communication: The public health aspectsof hearing, language, and speech disorders(NINDB monograph #7). Washington, DC:Government Printing Office, USPHS Publication1745.

17. ANSI [1996]. American national standard ofhearing aid characteristics. Melville, NY:Acoustical Society of America, AmericanNational Standards Institute, ANSI S3.22-1996.

18. Tubbs RL [1992]. Temporary thresholdshifts in hearing following exposure to gunfirenoise on firing ranges. Unpublished paperpresented at the 27th Annual Meeting of the U.S.Public Health Service Professional Association,Cincinnati, Ohio, April 25–28.

19. Newton I [1686]. Philosopiae NaturalisPrincipia Mathematica.

20. MIL-STD-1474D [1997]. Department ofdefense design criteria standard: Noise limits,AMSC, A7245.

21. NIOSH [2002]. Comments of the NationalInstitute for Occupational Safety and Health onthe Occupational Safety and HealthAdministration ANPR Hearing ConservationProgram for Construction Workers 29 CFR Part1926 Docket No. H-011G. Cincinnati, OH: U.S.Department of Health and Human Services, PublicHealth Service, Centers for Disease Control andPrevention, National Institute for OccupationalSafety and Health.

22. Smoorenburg GF [1982]. Damage risk criteriafor impulse noise. In: Hamernik R, Henderson D,Savli R, eds. New perspectives on noise-inducedhearing loss. New York, NY: Raven Press, pp471–490.

23. Pfander F, Bongartz, H, Brinkman H, Kietz H[1980]. Danger of auditory impairment fromimpulse noise: A comparative study of theCHABA damage-risk criteria and those of theFederal Republic of Germany. Journal of theAcoustical Society of America 67:628–633.

24. Pfander F [1975]. Das Knalltrauma. Berlin,Heidelberg, New York: Springer Verlag.

25. Murphy WJ, Little MB [2002]. Performanceof electroacoustic hearing protectors. Presented atthe 143rd meeting of the Acoustical Society ofAmerica, Pittsburgh, PA, June 3, 2002.

26. Mozo B [2003]. Communications & EarProtection, Inc. [http://www.cep-usa.com]. Dateaccessed: February 2003.


27. Michael KL [1998]. Comprehensive use ofhearing protectors: Integration of training, fieldmonitoring, communication and documentation.Journal of Occupational Hearing Loss 1:67–74.

28. Murphy WJ, Franks JR, Krieg EF [2002].Hearing protector attenuation: Models ofattenuation distributions. Journal of theAcoustical Society of America 111:2109–-2118.

29. NIOSH [1995]. The NIOSH compendium ofhearing protection devices. Cincinnati, OH: U.S.Department of Health and Human Services, PublicHealth Service, Centers for Disease Control andPrevention, National Institute for OccupationalSafety and Health, DHHS (NIOSH) PublicationNo. 95–105.

30. Berger EH, Franks JR, Behar A, Casali JG,Dixon-Ernst C, Kieper RW, Merry CJ, Mozo BT,Nixon CW, Ohlin D, Royster JD, Royster LH[1998]. Development of a new standardlaboratory protocol for estimating the fieldattenuation of hearing protection devices. Part III.The validity of using subject-fit data. Journal ofthe Acoustical Society of America 103:665–-672.

31. NIOSH [1996]. Preventing occupationalhearing loss–A practical guide. Cincinnati, OH:U.S. Department of Health and Human Services,Centers for Disease Control and Prevention,National Institute for Occupational Safety andHealth, DHHS (NIOSH) Publication No. 96–110.

32. Suter AH [2002]. Hearing conservationmanual. 4th ed. Milwaukee, WI: Council forAccreditation in Occupational HearingConservation.

33. Royster JD, Royster LH [1990]. Hearingconservation programs: practical guidelines forsuccess. Chelsea, MI: Lewis Publishers.


500 1000 2000 3000 4000 6000 8000Audiometric Test Frequency [Hz]

0

-10

-20

-30

-40

-50

-60

-70

-80

-90

Mea

n B

ase l

ine

Hea

ring

Leve

l [dB

HL ]

Left Ear Right Ear

Figure 1Hearing Levels - Fort Collins Police Service

Fort Collins, COHETA 2002-0131

May 2002

0

10

20

30

40

50

60

70

80


0

-10

-20

-30

-40

-50

-60

-70

-80

-90

Mea

n B

asel

ine

Hea

ring

Leve

l [dB

HL]

24-30 yrs. 31-35 yrs. 36-40 yrs.41-45 yrs. 46-54 yrs.

Figure 2Left Ear Hearing Levels by Age

Fort Collins Police ServiceFort Collins, COHETA 2002-0131

May 2002

0

10

20

30

40

50

60

70

80



0

-10

-20

-30

-40

-50

-60

-70

-80

-90

Mea

n B

a sel

ine

He a

ring

Lev e

l [dB

HL ]

24-30 yrs. 31-35 yrs. 36-40 yrs.41-45 yrs. 46-54 yrs.

Figure 3Right Ear Hearing Levels by Age


May 2002

0

10

20

30

40

50

60

70

80


0

-10

-20

-30

-40

-50

-60

-70

-80

-90

Mea

n B

asel

ine

Hea

ring

Leve

l [dB

HL]

Department, Left Ear Department, Right EarSWAT, Left Ear SWAT, Right Ear

Figure 4SWAT versus Rest of Department Hearing Levels


May 2002

0

10

20

30

40

50

60

70

80


Figure 5Outdoor Recording of the Unprotected and Protected Waveforms


May 2002

Measurements from the Bruel & Kjaer 4136 microphone and ISL mannequin. The red line is theunprotected waveform (microphone) and the blue line is the protected (mannequin). The vertical dashedlines indicate the presence of reflected pressure waves from surrounding objects.


Ft. Collins Indoor Range

Pea

k Im

puls

e Le

vel (

dB S

PL)

145

150

155

160

165

170

175

Ft. Collins Outdoor Range

Pea

k Im

puls

e Le

vel (

dB S

PL)

145

150

155

160

165

170

175

Weapon Peak Impulse Noise Levels (dB SPL)C

olt 1

991A

1

Par

Ord

inan

ce P

10

Glo

ck 2

2

Glo

ck 2

7

Rem

ingt

on 1

187

Rem

ingt

on 8

70

Sig

Sau

er P

228

Col

t Poc

ket 9

Sm

ith &

Wes

son

586

Sm

ith &

Wes

son

686

Col

t 199

1A1

Glo

ck 2

2

Rem

ingt

on 1

187

Sig

Saue

r P22

8

Smith

& W

esso

n 58

6

Col

t AR

15

Hec

kler

& K

och

53 Caliber0.4500.40012 gauge9 mm0.3570.223

Figure 6Peak impulse noise levels at the indoor and outdoor firing ranges


May 2002


70

90

110

130

70

90

110

130

70

90

110

130

70

90

110

130

70

90

110

130

70

90

110

130

Third Octave Band Frequency (Hz)

25 50 100 250 500 1000 2500 5000 10000

Sou

nd P

ress

ure

Leve

l (dB

SP

L)

70

90

110

130

Heckle

r & K

och 53

167 d

B

Smith &

Wes

son 58

6

169 d

B

Colt AR-15

161 d

B

Remington 11

-87

162 d

B

Sig Sauer

P228

160 d

B

Glock 22

158 d

B

Colt 199

1 A1

159 d

B

Figure 7One third-octave band spectra for weapons measured at the outdoor firing range


May 2002

The horizontal lines are spaced in 10 dB intervals. The dark bar in the center depicts the 1000 Hz onethird-octave band. The weapons are positioned with the lowest to highest sound pressure levels fromfront to back.


Difference in Third-Octave Pressure with 0.450 Caliber Colt 1991 A1 Pistol

Frequency (Hz)25 50 100 250 500 1000 2500 5000 10000

Diff

eren

ce (d

B)

-10

-5

0

5

10

15

20

25

30

AR-15Glock 22Heckler & Koch 53Remington 1187Sig Sauer P228Smith & Wesson 586

Figure 8One third-octave band difference spectra for weapons

measured at the outdoor firing rangeFort Collins Police Service


May 2002

The .450 caliber Colt 1991-A1 semi-automatic pistol was used as the reference weapon. The Colt 1991spectra was subtracted from the spectra of the other weapons to derive the difference spectra shownabove. Error bars are depicted on one side of the data symbols to reduce clutter.


David Clark Blue EarmuffAttenuation vs Frequency

Frequency (Hz)25 50 100 250 500 1000 2500 5000 10000

Atte

nuat

ion

(dB

)

0

10

20

30

40

50

60

70

80

90David Clark Blue IndoorDavidClark Blue OutdoorDC Blue & EAR Classic IndoorDC Blue & EAR Classic OutdoorEAR Classic Indoor

Figure 9One third-octave band attenuation results for the

David Clark Earmuff and EAR EarplugFort Collins Police Service


May 2002

The third-octave band attenuation spectra for the David Clark model 27 earmuff alone and in conjunctionwith an EAR Classic earplug on the indoor and outdoor ranges.


David Clark Blue Earmuff with Safety Glasses Attenuation by Weapon

Frequency (Hz)25 50 100 250 500 1000 2500 5000 10000

Atte

nuat

ion

(dB

)

-20

-10

0

10

20

30

40Colt 1991-A1 Colt AR15 Glock 22 Heckler Koch 53 Remington 11-87 SigSauer P228 Smith & Wesson 586

Figure 10One third-octave band attenuation results for the

David Clark Earmuff and Safety GlassesFort Collins Police Service


May 2002

The third-octave band attenuation spectra for the David Clark model 27 earmuff with a leak caused by apair of safety glasses under the earmuff. The different weapons are depicted with different coloredsymbols. The attenuations below 250 Hz are largely negative as a result of the leak. At 2000 Hz, thevariation of the attenuations is larger than neighboring frequencies.


Electronic Shooter Protection EliteAttenuation vs Frequency

Frequency (Hz)25 50 100 250 500 1000 2500 5000 10000

Atte

nuat

ion

(dB

)

0

10

20

30

40

50

60

70

Off IndoorOff OutdoorUnity Gain IndoorUnity Gain OutdoorMaximum Gain IndoorMaximum Gain Outdoor

Figure 11One third-octave band attenuation results for the ESP


May 2002

The third-octave band attenuations of the Electronic Shooter Protection Elite hearing protector for threedifferent settings: off, unity gain, and maximum gain. The measurements for the indoor and outdoorfiring ranges are different when the gain is applied whereas the off settings exhibit little difference above100 Hz.


Histogram of the Maximum SPL Output

Maximum Sound Pressure Level (dB SPL)

88 90 92 94 96 98 100 102 104 106 108

Num

ber o

f Occ

uran

ces

0

1

2

3

4

5

Histogram of the Saturated SPL Output

Saturated Sound Pressure Level (OSPL90)

78 80 82 84 86 88 90 92 94 96 98

Num

ber o

f Occ

uran

ces

0

2

4

6

8

Figure 12One third-octave band attenuation results for the ESP


May 2002

Measurements forthe ESP Elite device as tested according to ANSI S3.22-1996. The upper panel displays the histogram ofthe maximum sound pressure level (SPL) in dB along the x-axis for 24 units tested. One unit was for theISL mannequin and one officer provided only one ESP Elite device. The lower panel shows a histogramof the saturated sound pressure level (SSPL) for the same 24 devices. The manufacturer’s specificationsindicate maximum SPL of 93 dB and SSPL of 88 dB.


Peak Reductions for Protectors at Both Firing Ranges

Peak Reduction (dB SPL)0 10 20 30 40 50 60

David Clark w Glasses OutdoorDavid Clark w Glasses Indoor

EAR Classic IndoorDavid Clark Model 27 Indoor

David Clark Model 27 OutdoorDavid Clark & EAR Indoor

David Clark & EAR OutdoorESP Elite Off Indoor

ESP Elite Off OutdoorESP Elite Unity Indoor

ESP Elite Unity OutdoorESP Elite Max Indoor

ESP Elite Max Outdoor

Figure 13Peak Reductions for the Hearing Protection Devices


May 2002

The peak reductions for the protectors measured at both firing ranges. The maximum sound pressurelevel for the protected waveform was subtracted from the maximum sound pressure level for theunprotected waveform. The resulting difference is the peak reduction.


Table 1Weapons Tested at the Indoor Firing Range

Fort Collins Police ServicesFort Collins, COHETA 2002-0131

May 2002

Manufacturer Model Caliber Barrel Length Weapon Classification

Smith and Wesson 686 .357 2.5 inches revolver

Smith and Wesson 586 .357 6 inches revolver

Colt 1991A .450 5 inches semi-automatic pistol

Para Ordinance P10 .450 3.5 inches semi-automatic pistol

Glock 27 .400 3.5 inches semi-automatic pistol


Colt Pocket9 9 mm 2.5 inches semi-automatic pistol

Sig Sauer P228 9 mm 4.5 inches semi-automatic pistol

Remington 1187 12 gauge 18 inches pump shotgun

Remington 870 12 gauge 18 inches semi-automatic shotgun

Table 2Weapons Tested at the Outdoor Firing Range

Fort Collins Police ServicesFort Collins, COHETA 2002-0131

May 2002

Manufacturer Model Caliber Barrel Length Weapon Classification

Smith and Wesson 586 .357 6 inches revolver

Colt 1991A .450 5 inches semi-automatic pistol


Sig Sauer P228 9 mm 4.5 inches semi-automatic pistol

Heckler and Koch 53 .223 8.5 inches automatic rifle

Colt AR15 .223 20 inches semi-automatic rifle

Remington 870 12 gauge 18 inches semi-automatic shotgunTable 3


Mean Temporary Threshold Shift (TTS) ValuesFort Collins Police Services


May 2002

Condition EarTested

Time[sec.]

2000 Hz 3000 Hz 4000 Hz 6000 Hz

.223 cal Rifle - ESP protectors

Left 201.4 0.6 dB -2.2 dB -2.2 dB -0.3 dB

Right 263.1 0.0 dB -1.2 dB 0.0 dB -0.3 dB

.38, .40, .45 cal, 9 mmRevolvers

Left 124.6 -0.6 dB -1.7 dB -0.9 dB -1.8 dB

Right 196.7 -0.9 dB -1.4 dB -1.4 dB -0.2 dB

.12 ga Shotguns

Left 132.1 -0.7 dB 0.7 dB -0.4 dB -0.7 dB

Right 199.9 0.0 dB 0.0 dB -0.7 dB -3.2 dB

.223 cal Rifles

Left 203.2 0.2 dB -1.9 dB -2.1 dB -1.5 dB

Right 267.0 -0.2 dB -1.2 dB -0.4 dB -1.2 dB

DEPARTMENT OF HEALTH AND HUMAN SERVICESCenters for Disease Control and PreventionNational Institute for Occupational Safety and Health4676 Columbia ParkwayCincinnati, OH 45226-1998

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