NIOSH HEALTH HAZARD EVALUATION REPORT:

DEPARTMENT OF HEALTH AND HUMAN SERVICES

Centers for Disease Control and Prevention

National Institute for Occupational Safety and Health

HETA #2002-0131-2898

Fort Collins Police Services

Fort 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.

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
ii

PREFACE

The Hazard Evaluations and Technical Assistance Branch (HETAB) of the National Institute for

Occupational Safety and Health (NIOSH) conducts field investigations of possible health hazards in the

workplace. These investigations are conducted under the authority of Section 20(a)(6) of the Occupational

Safety and Health (OSHA) Act of 1970, 29 U.S.C. 669(a)(6) which authorizes the Secretary of Health and

Human 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 effects

in such concentrations as used or found.

HETAB also provides, upon request, technical and consultative assistance to Federal, State, and local

agencies; labor; industry; and other groups or individuals to control occupational health hazards and to

prevent related trauma and disease. Mention of company names or products does not constitute endorsement

by NIOSH.

ACKNOWLEDGMENTS AND AVAILABILITY OF REPORT

This report was prepared by Randy L. Tubbs of HETAB, Division of Surveillance, Hazard Evaluations and

Field Studies (DSHEFS) and William J. Murphy of the Hearing Loss Prevention Section (HLPS), Division

of Applied Research and Technology (DART). Field assistance was provided by Carol Goetz and Patricia

Lovell, 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 were

performed by Penny Arthur.

Copies of this report have been sent to employee and management representatives at the Fort Collins Police

Services. This report is not copyrighted and may be freely reproduced. Single copies of this report will be

available for a period of three years from the date of this report. To expedite your request, include a selfaddressed mailing label along with your written request to:

NIOSH Publications Office

4676 Columbia Parkway

Cincinnati, Ohio 45226

800-356-4674

After this time, copies may be purchased from the National Technical Information Service (NTIS) at

5825 Port Royal Road, Springfield, Virginia 22161. Information regarding the NTIS stock number may be

obtained from the NIOSH Publications Office at the Cincinnati address.

For the purpose of informing affected employees, copies of this report shall be

posted by the employer in a prominent place accessible to the employees for a period

of 30 calendar days.
iii

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 team

during training exercises. We used temporary changes in hearing following weapons firing on the indoor and

outdoor ranges as an estimate of noise overexposure. We also made thorough measurements of the noise

from the weapons used by the department as well as measurements of the noise reduction from all the hearing

protectors worn by the Fort Collins officers.

What NIOSH Did

# We tested the hearing of officers before and after

firing 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 hearing

protectors used by the officers on the firing ranges.

# We handed out a questionnaire to employees

about their work history and self evaluation of their

hearing.

What NIOSH Found

# Officers did not show poorer hearing following

shooting.

# Most officers have normal hearing patterns.

# Weapon noise was found to be between 159 and

169 dB peak which is greater than a 140 dB peak

exposure guideline from NIOSH.

# Radio transmissions were not incorporated into

the customized protectors used by the SWAT

officers.

# The hearing protection devices lowered noise

about 30 dB peak. Double protection (plugs plus

muffs) added 15-20 dB peak protection.

What Fort Collins Police Service

Managers Can Do

# The department should research new hearing

protection devices that incorporate radio

communications into the device and are still

compatible with other protection devices such as

helmets and glasses.

# The department should begin a hearing

conservation program with annual hearing tests.

What the Fort Collins Police

Service Officers Can Do

# Officers should wear hearing protection

whenever 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 and

safety 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
iv

Health Hazard Evaluation Report 2002-0131-2898

Fort Collins Police Services

Fort Collins, Colorado

March 2003

Randy L. Tubbs, Ph.D.

William J. Murphy, Ph.D.

SUMMARY

The National Institute for Occupational Safety and Health (NIOSH) received an employee request for a health

hazard evaluation of the Fort Collins Police Service in Fort Collins, Colorado, in January 2002. The

department was concerned about noise exposures and potential hearing damage from weapons training on

their 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 recently

purchased for the team members to use during training and deployment. To address these concerns, NIOSH

conducted a temporary threshold shift (TTS) study of officers’ hearing following weapons firing on a

standard qualification course on the indoor and outdoor firing ranges. NIOSH investigators also used an

acoustic mannequin head to measure noise levels produced by all weapons used by this department. This

allowed for the measurement of noise levels when different hearing protection devices were placed on the

mannequin, 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 firing

for the qualification course used in the evaluation. Also, the pre-exposure hearing tests revealed normal

hearing 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 various

weapons ranged from 159-169 decibels (dB) peak which is greater than a 140 dB peak exposure guideline

from NIOSH. The peak reductions afforded by the ear plugs, ear muffs, and customized SWAT team hearing

protectors were all in the 30 dB range. Double hearing protection (plugs plus muffs) added 15–20 db more

of peak reduction.

Based on the measurements and observations made during the evaluation, NIOSH investigators

determined that a potential health hazard does exist for officers of the Fort Collins Police Service

because the noise levels produced by their weapons are sufficient to put them at risk for occupational

hearing loss. However, the hearing protection used by these officers does seem to offer protection as

evidenced by the lack of TTS following a qualification course with pistols, shotguns, and rifles and by

the 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 CONTENTS

Preface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ii

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

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

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

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

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

Methods ........................................................................... 2

TTS and Hearing Loss ............................................................. 2

Noise Measurements .............................................................. 3

Equipment and Calibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Weapons and Protectors ........................................................ 3

Data Processing and Analysis .................................................... 4

Evaluation Criteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Noise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Noise-Induced Hearing Loss . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

TTS and Hearing Loss ............................................................. 7

Noise Measurements .............................................................. 8

Peak Exposure Levels .......................................................... 8

Weapons Spectra .............................................................. 9

Spectral Difference Plots . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

David Clark Model 27 Earmuff Plus EAR Classic Earplug Attenuation ................... 9

Electronic Shooter Protection Elite . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

TTS and Hearing Loss . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Noise Measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Peak Exposure Levels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

David Clark Model 27 Earmuff Attenuation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

Performance of the ESP Elite Devices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

Performance of the EAR Classic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

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

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

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Health Hazard Evaluation Report No. 2002-0131-2898 Page 1

INTRODUCTION

The National Institute for Occupational Safety and

Health (NIOSH) received an employee request for

a health hazard evaluation (HHE) from employees

and management of the Fort Collins Police

Services in Fort Collins, Colorado, in January

2002. The department was concerned about noise

exposures and potential hearing damage from

weapons training on their indoor and outdoor

firing ranges. One specific concern was the

Special Weapons And Tactics (SWAT) team of

the Fort Collins Police Services and the adequacy

of customized hearing protection that they had

recently purchased for the team members to use

during training and deployment.

NIOSH investigators spent the week of May 12,

2002, with the Fort Collins Police to test the

hearing ability of several members of their

department along with officers from other area law

enforcement agencies and to measure the sound

spectra for various weapons they use. Hearing

tests were administered at the indoor firing range

on Monday, Tuesday, and Friday and at the

outdoor range on Wednesday and Thursday.

Noise measurements were collected on the indoor

range on Wednesday and on the outdoor range on

Thursday. Individual hearing test results were

sent to each participant along with an explanation

of the audiogram in July 2002. For those who

specified on the informed consent sheet, the

same results package was sent to their designated

physician or audiologist.

BACKGROUND

The Fort Collins Police Services patrols nearly 47

square miles in the city of Fort Collins, Colorado,

which has an estimated population of 118,652.

There are 148 sworn police officers in the

department, which includes a 21-member SWAT

team. In 2000, the department investigated

128,684 police incidents.

Each SWAT team member was issued a .223

caliber, short-barreled rifle for use in SWAT

deployments approximately 2–3 years ago. They

are also exposed to many different explosive

devices used in training exercises and actual

incidents. Their training schedule calls for

monthly activities with weapons and explosive

devices. A SWAT team from a nearby law

enforcement agency had reported an incident

where weapons similar to those used by the Fort

Collins Police Services were fired inside an

enclosed space during a deployment and team

members suffered permanent hearing losses. This

led the Fort Collins SWAT team to purchase

specialized hearing protection devices (HPDs) for

use in training exercises and in SWAT team

deployments—Electronic Shooters Protection

(ESP) Elite devices. The company’s literature

describes these devices as custom earmolds with

analog electronics that amplify sounds under 90

decibels (dB), but damaging sounds above 90 dB

are limited to safe levels by miniaturized

compression circuitry. Two models of the devices

were issued to the officers, a completely in the

ear mold and a behind the ear model with three

sizes of ear buds. These devices offered hearing

protection in high noise conditions and

amplification of signals in low noise situations,

and they allowed the officers to wear helmets and

goggles without interference as would be the case

if ear muffs, for example, were used. 

The regular training schedule and the highpowered weapons and explosive devices used with

the electronic HPDs was an area of concern for

members of the SWAT team. They wanted some

assurance that the HPDs would protect them from

permanent hearing loss resulting from the use of

weapons and explosives in training and actual

field situations. A temporary threshold shift

(TTS) study was designed to investigate the risk of

hearing damage from the SWAT team noise

exposure situations. The TTS approach would not

only identify any change in hearing following

weapons’ exposure, it would also document

current levels of hearing. In addition to the TTS

investigation, measurements of the noise signature

from the weapons used by the Fort Collins Police
Page 2 Health Hazard Evaluation Report No. 2002-0131-2898

Services were made on the indoor and outdoor

firing ranges. Simultaneous measurements of the

protection offered by various HPDs and the levels

produced by the weapons were collected with an

acoustic mannequin as part of the evaluation.

TTS is a transient loss of hearing exhibited after

exposure to brief, intense noise that dissipates over

a short period of time. The parameters of TTS

have been investigated by many researchers.1

 It

has been consistently observed that higher

frequency hearing (2–6 kilohertz [KHz]) is more

easily affected by noise exposures than lower

frequency.2,3 The results from many experimental

studies indicate that TTS recovers at a rate of 3 dB

per doubling of recovery time.4

 The Committee

on Hearing, Bioacoustics, and Biomechanics

(CHABA) of the National Research Council used

the TTS index of 2 minutes (TTS2) following the

termination of a noise exposure in its attempt to

derive damage-risk contours for noise.5,6

METHODS

TTS and Hearing Loss

All patrol officers of the Fort Collins Police

Service were eligible for the hearing tests. Also,

other local law enforcement officers from the

Sheriff’s Department and other local departments

were invited to participate in the NIOSH

investigation by the officer in charge of Fort

Collin’s SWAT operations. Officers reported to

either the indoor or outdoor firing range when

they were available during their work shift.

Informed consent was obtained from each

participant before a short questionnaire about

work history and self-assessment of their hearing

ability was given to them for completion.

Audiometric tests were administered to each of the

participants prior to the use of their weapon on the

range. While on the range, the officer was

instructed by the range officer to fire a

standardized qualification course for the weapon

being used. The three courses chosen by the Fort

Collins Police Services were (1) qualification

pistol - 1 which fires 24 rounds, (2) qualification

shotgun - X which fires 12 rounds, and (3) Phase

1 of the SWAT operations standard drill for a 2

shooter-contact team which fires 20 rounds. The

first two courses were used on the indoor range

and the third course was used on the outdoor

range. The pistol and shotgun qualification course

were usually completed with two shooters on the

indoor range, however, a few times only one

shooter was available. As the outdoor

qualification course states, two shooters were

always present. Immediately upon completion of

the qualification course, a stopwatch was started

and the officer was escorted back to the

audiometric test booth for a post-exposure hearing

test. The time at which the left ear and right ear

tests were finished was recorded on the person’s

questionnaire. The amount of TTS was calculated

by subtracting the pre-qualification test from the

post-qualification test resulting in a positive value

if the officer’s hearing got worse and a negative

number if it got better.

Two Tracor Instruments (Austin, Texas) Model

AR-200EC Audiometric Booths provided an

acoustic environment for hearing testing. The

booths were set up in an adjacent classroom at

the indoor firing range and in a storage shed at

the outdoor range. Conversations and other

extraneous noises were controlled during testing.

The booths were moved from the indoor to the

outdoor range on Wednesday morning and

returned to the indoor range on Friday for the last

day of testing. Since electrical power was not

available at the outdoor location, an electrical

generator on the department’s SWAT vehicle

provided power to the shed. It was parked more

than 100 yards from the storage shed with

electrical extension cords running from the

generator so that there was no noise impact on the

test environment. Hearing tests were collected

with Tremetrics (Eden Prairie, Minnesota) Model

RA500 Audiometers that had received an

exhaustive calibration check within the past year.

Hearing tests were conducted by technicians

who have current certification from the Council

for Accreditation in Occupational Hearing

Conservation (CAOHC). For the pre-weapons

qualification test, the audiometer tested the
Health Hazard Evaluation Report No. 2002-0131-2898 Page 3

pure-one frequencies of 500, 1000, 2000, 3000,

4000, 6000, and 8000 Hertz (Hz) in the

computerized mode in each ear, left ear first. The

post-qualification hearing test only used the

frequencies of 2000, 3000, 4000, and 6000 Hz, the

frequencies most sensitive to noise exposure,

to reduce the time necessary to collect all of the

data. These frequencies were also tested in the

computerized mode.

Noise Measurements

Equipment and Calibration

Acoustic recordings of the gunshots were

collected for both the indoor and outdoor firing

ranges. Recordings were made using a Tascam

DA-P1 Digital Audio Tape (DAT) recorder that

digitized the microphone signals at 48000

samples per second. An external microphone and

mannequin were positioned one meter to the left

of the shooter. The mannequin was built by the

French German Research Institute de Saint Louis

(ISL) specifically for measuring impact and

impulse noise.7

 The mannequin consists of the

head, acoustic pinnae, and ear canals, Brüel and

Kjær 4157 middle ear simulator, and a Brüel and

Kjær 4165 1⁄2-inch microphone. The maximum

peak sound pressure level (SPL) that could be

measured with the mannequin was 148 dB (dB

SPL re 20 micropascals [μPa]). Since all of the

mannequin measurements were performed

under hearing protection, the maximum SPL

was not exceeded. The sound outside the hearing

protector was sampled by a Brüel and Kjær

4136 1⁄4 inch microphone which had a maximum

sound pressure of 172 dB, sound pressure level

(dB SPL). The 4136 microphone was positioned

6 centimeters from the right side of the mannequin

head with the microphone pointed vertically

upwards and was not touching the stand that

supported the mannequin. The diaphragm of the

microphone was visually aligned with the axis of

the ear canal of the mannequin. The height of

both the mannequin’s ear canal and external

microphone were adjusted to the same height as

the shooter, 6 feet 2 inches, so that they were in

the same plane as the shooter’s ear canal.

Both the mannequin microphone and the external

microphone were calibrated with a Brüel and Kjær

4228 piston-phone that produces a 124 dB SPL

tone at 250 Hz. With the piston-phone running,

the recording levels for the right (mannequin) and

left (4136 microphone) channels of the DAT were

adjusted to approximately 50 dB below the

expected maximum signal levels, 150 and 170 dB

SPL, respectively. Because the DAT recordings

had to be transferred to computer for post hoc

analysis, the recording settings were approximate

and recordings of the calibration tones were

collected at the beginning and end of each day’s

measurements. The calibration tone recordings

were used to normalize the digital voltage levels

into Pascals for the data analysis.

Weapons and Protectors

In Table 1, the 10 weapons that were tested with

hearing protectors are listed. The weapons were a

representative cross section of those used by

the Fort Collins police officers. Specifically, the

calibers were selected and then long and shortbarreled models were chosen to address a concern

that short-barreled weapons produced louder

impulses than long-barreled weapons. In addition

to the weapons in Table 1, measurements were

collected for a group of 10 SWAT officers using

Heckler and Koch (H&K) 53 and H&K 36 assault

rifles. The H&K weapons used a .223 caliber

frangible bullet. The expense of frangible

ammunition prohibited the comprehensive

measurements with hearing protectors at the

indoor range. At the outdoor range, seven

weapons were tested with hearing protectors and

are listed in Table 2. Only the long-barreled

models of the pistols were measured. Although

the H&K 53 had a fully-automatic setting, the

weapon was used with the single-shot setting. 

Several types of hearing protectors were tested

at both firing ranges. The protectors that will be

discussed in this report are the David Clark

Company (Worcester, Massachusetts) Model 27
Page 4 Health Hazard Evaluation Report No. 2002-0131-2898

earmuffs, Electronic Shooters Protection (ESP;

Brighton, Colorado) Elite, and the AearoTM

Corporation (Indianapolis, Indiana) EAR®

Classic® earplugs. Other protectors were

measured for the purpose of developing a

reference database of the impulse response of the

protectors when measured on the ISL mannequin.

For the David Clark earmuffs, three conditions

were measured: earmuff alone, earmuff plus

EAR Classic earplug together, and earmuff with

safety glasses producing a leak under the earmuff

cushion. The ESP Elite was essentially an in-theear assistive listening device with a wide spectrum

gain function and compression circuit to limit the

output of the device to nominally 90 dB SPL in a

2 cubic centimeter (cm3

) coupler. The ESP Elite

did not have a Noise Reduction Rating (NRR) as

required by the U.S. Environmental Protection

Agency (EPA) for all hearing protection sold in

the United States.8

Prior to the HHE, NIOSH researchers had

Electronic Shooter Protection manufacture an ESP

Elite protector for the ISL mannequin. The ESP

device had approximately 3 millimeters between

the end of the device in the ear canal and the grid

for the ear simulator. The ESP device was tested

at three gain settings: off, unity, and maximum.

The unity gain was determined by performing a

loudness match between the ESP and airconducted sound in a double-walled sound room

in the NIOSH Taft Laboratories. Three NIOSH

researchers judged the unity output of the device

and the mean setting was marked on the face of

the device.

For each weapon, five shots were fired for each

hearing protector condition. The shots were

spaced approximately 2 seconds apart. Each

protector condition was announced at the

beginning of the recording. The weapons were

announced to the external microphone before

firing and were always tested in the order

presented in Tables 1 and 2. The recording was

stopped after each set of weapons. The recording

times and any misfires or weapon malfunctions

were recorded in a lab notebook.

Data Processing and Analysis

The DAT tape recordings were digitally

transferred to .wav files using a Lexicon Core32

sound card. Each set of recordings were separated

into a .wav file and directory. Next, the five-shot

groups were isolated and saved as .wav files for

analysis. The calibration tones were edited to

select only the final portions of each channel’s

sample of the calibration signal. The calibration

levels were calculated for each microphone and

used in the subsequent analysis.

A Matlab program was developed to examine

the average signal level as a function of time,

permitting the researcher to identify the beginning

of each gunshot within the sample. Once the start

of each gunshot was identified, a time window of

42.67 or 170.67 milliseconds (ms) was analyzed

for the peak protected and unprotected noise

levels, the third-octave band spectra and the

attenuation spectrum of the hearing protector. The

shorter time window, 42.67 ms, was used with the

outdoor measurements. The protected and

unprotected equivalent levels, dB Leq, were

determined for linear weighting. The one thirdoctave unprotected spectra from each weapon

were averaged across recordings to estimate the

mean spectra for each weapon.

EVALUATION CRITERIA

As a guide to the evaluation of the hazards posed

by workplace exposures, NIOSH field staff

employ environmental evaluation criteria for the

assessment of a number of chemical and physical

agents. These criteria are intended to suggest

levels of exposure to which most workers may

be exposed up to 10 hours per day, 40 hours per

week for a working lifetime without experiencing

adverse health effects. It is, however, important to

note that not all workers will be protected from

adverse health effects even though their exposures

are maintained below these levels. A small

percentage may experience adverse health effects

because of individual susceptibility, a pre-existing

medical condition, and/or a hypersensitivity
Health Hazard Evaluation Report No. 2002-0131-2898 Page 5

(allergy). In addition, some hazardous substances

may act in combination with other workplace

exposures, the general environment, or with

medications or personal habits of the worker to

produce health effects even if the occupational

exposures are controlled at the level set by the

criterion. These combined effects are often not

considered in the evaluation criteria. Finally,

evaluation criteria may change over the years as

new information on the toxic effects of an agent

become available.

The primary sources of environmental evaluation

criteria for the workplace are: (1) NIOSH

Recommended Exposure Limits (RELs),9

 (2) the

American Conference of Governmental Industrial

Hygienists’ (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 OSHA

limits, the NIOSH RELs, the ACGIH TLVs, or

whichever are the more protective criteria.

OSHA requires an employer to furnish employees

a place of employment that is free from

recognized hazards that are causing or are likely to

cause 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 all

hazardous chemicals have specific OSHA

exposure limits such as PELs and short-term

exposure limits (STELs). An employer is still

required by OSHA to protect their employees

from hazards, even in the absence of a specific

OSHA PEL.

Noise

The A-weighted decibel [dB(A)] is the preferred

unit for measuring sound levels to assess worker

noise exposures. The dB(A) scale is weighted to

approximate the sensory response of the human

ear to sound frequencies near the threshold of

hearing. The decibel unit is dimensionless, and

represents the logarithmic relationship of the

measured sound pressure level to an arbitrary

reference sound pressure (20 :Pa, the normal

threshold of human hearing at a frequency of

1000 Hz). Decibel units are used because of the

very large range of sound pressure levels which

are audible to the human ear. Because the dB(A)

scale is logarithmic, increases of 3 dB(A), 10

dB(A), and 20 dB(A) represent a doubling, 10-

fold increase, and 100-fold increase of sound

energy, respectively. It should be noted that

noise exposures expressed in dBs cannot be

averaged by taking the simple arithmetic mean.

The OSHA standard for occupational exposure to

noise (29 CFR 1910.95)11 specifies a maximum

PEL of 90 dB(A) for a duration of 8 hours per

day, expressed as a time-weighted average

(TWA). The regulation, in calculating the PEL,

uses a 5 dB time/intensity trading relationship, or

exchange rate. This means that a person may be

exposed to noise levels of 95 dB(A) for no more

than 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 and

sound level intensities can be combined in order to

calculate a worker's daily noise dose according to

the formula:

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

where Cn indicates the total time of exposure at a

specific noise level and Tn indicates the reference

duration for that level as given in Table G-16a of

the OSHA noise regulation. During any 24-hour

period, a worker is allowed up to 100% of his

daily noise dose. Doses greater than 100% are in

excess of the OSHA PEL.

The OSHA regulation has an additional action

level (AL) of 85 dB(A); an employer shall

administer a continuing, effective hearing

conservation program when the 8-hour TWA

value exceeds the AL. The program must include

monitoring, employee notification, observation,

audiometric testing, hearing protectors, training,

and record keeping. All of these requirements are

included in 29 CFR 1910.95, paragraphs (c)

through (o). Finally, the OSHA noise standard

states that when workers are exposed to noise
Page 6 Health Hazard Evaluation Report No. 2002-0131-2898

levels in excess of the OSHA PEL of 90 dB(A),

feasible engineering or administrative controls

shall be implemented to reduce the workers'

exposure levels. 

NIOSH, in its Criteria for a Recommended

Standard,12 and the ACGIH,10 propose exposure

criteria of 85 dB(A) as a TWA for 8 hours, 5 dB

less than the OSHA standard. The criteria also use

a more conservative 3 dB time/intensity trading

relationship 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 91

dB(A) for 2 hours. Twelve hours exposures have

to be 83 dB(A) or less according to the NIOSH

REL.

Noise-Induced Hearing Loss

Noise-induced loss of hearing is an irreversible,

sensorineural condition that progresses with

exposure. Initially, the noise exposure may cause

a TTS, that is, a decrease in hearing sensitivity

that typically returns to its former level within a

few minutes to a few hours. Repeated exposures

can lead to a permanent threshold shift. Although

hearing ability declines with age (presbycusis) in

all populations, exposure to noise produces

hearing loss greater than that resulting from the

natural aging process. This noise-induced loss is

caused by damage to nerve cells of the inner ear

(cochlea) and, unlike some conductive hearing

disorders, cannot be treated medically.13 While

loss of hearing may result from a single exposure

to a very brief impulse noise or explosion, such

traumatic losses are rare. In most cases, noiseinduced hearing loss is insidious. Typically, it

begins to develop at 4000 or 6000 Hz (the hearing

range is 20 Hz to 20000 Hz) and spreads to lower

and higher frequencies. Often, material

impairment has occurred before the condition is

clearly recognized. Such impairment is usually

severe enough to permanently affect a person's

ability to hear and understand speech under

everyday conditions. Although the primary

frequencies of human speech range from 200 Hz

to 2000 Hz, research has shown that the consonant

sounds, which enable people to distinguish words

such as "fish" from "fist," have still higher

frequency components.14

Audiometric evaluations of workers are conducted

in quiet locations, preferably in a soundattenuating chamber, by presenting pure tones of

varying frequencies at threshold levels, i.e., the

level of a sound that the person can just barely

hear. Audiograms are displayed and stored as

tables or charts of the hearing levels (HL) at

specified test frequencies.15 Zero dB HL

represents the hearing level of the average, normal

hearing individual. In OSHA-mandated hearing

conservation programs, thresholds must be

measured for pure-tone signals at the test

frequencies of 500, 1000, 2000, 3000, 4000, and

6000 Hz. Individual employee’s annual

audiograms are compared to their baseline

audiogram to determine the amount of standard

threshold shift (STS) that might have occurred

over the time period being evaluated.

Specifically, OSHA states that an STS has

occurred if the average threshold values at 2000,

3000, and 4000 Hz have increased by 10 dB or

more in either ear when comparing the annual

audiogram to baseline audiogram.11 The NIOSH

recommended threshold shift criterion is a 15-dB

shift at any frequency in either ear from 500–6000

Hz measured twice in succession.12 Practically,

the criterion is met by immediately retesting an

employee who exhibits a 15-dB shift from

baseline on an annual test. If the 15-dB shift is

persistent on the second test, a confirmatory

followup test should be given within 30 days of

the initial annual examination. Both of these

threshold shift criteria require at least two

audiometric tests. In cases where only one

audiogram is available, a criterion has been

proposed for single-frequency impairment

determinations.16 It employs a lower fence (the

amount of HL necessary before a hearing

handicap is said to exist) of 25 dB. With this

criterion, any person who has a hearing level of

26 dB HL or greater at any single frequency is

classified as having some degree of hearing loss.

The degree of loss can range from mild (26–40 dB

HL) to profound (>90 dB HL). 
Health Hazard Evaluation Report No. 2002-0131-2898 Page 7

RESULTS

TTS and Hearing Loss

A total of 93 hearing tests were given over the five

days of the site visit. Of this total, 71 tests were

given to Fort Collins Police Services officers, 18

tests were given to officers of neighboring

departments, and 4 tests were repeats for SWAT

officers who were tested on Monday on the indoor

range and on Wednesday at the outdoor range.

The hearing test results figures include only the

Fort Collins’ officers; the other officers’ data are

included in the table listing the TTS values found

following the firing of the various weapons. On

the indoor range, participants fired either their

service revolver or a 12-gauge shotgun. On the

outdoor range, .223 caliber rifles were used.

Hearing protection devices used on the indoor

range were generally David Clark Model 27

earmuffs or custom-molded earplugs. For the 20

Fort Collins Police Services SWAT officers tested

on 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 four

wore EAR Classic earplugs (3) or EAR plugs plus

Aearo Peltor® Model TacticalTM 7 earmuffs (1).

The mean hearing test results for the Fort Collins

Police Services’ officers who participated in the

evaluation are shown in Figure 1. The graph

shows the mean hearing levels for all 71 officers

from the audiograms obtained before any weapons

were fired by the officer. The left ear results are

slightly poorer at the higher test frequencies, but

overall, the mean results fall into a normal (<25

dB HL) hearing range for both ears. Sixty-three of

the seventy-one officers were male. The mean age

for the group is 37.2 years (range = 29–52 years).

These officers have been in law enforcement for a

mean of 12.9 years with a mean time of 10.4 years

with the Fort Collins Police Services. The results

were separated into age brackets to see the hearing

profile trends over time, and are shown in Figure

2 for the left ear and Figure 3 for the right ear.

These data show that all age groups of less than 46

years of age have mean levels that are in a normal

hearing range for both ears. It is only the oldest

group of officers that have mean hearing loss as a

group in the higher test frequencies, 4000 Hz and

above. The high frequency loss is classified as a

mild loss.16 When the SWAT officers are

compared to the rest of the department, there is

little difference between the two groups in their

mean hearing levels (Figure 4). The mean age of

the SWAT officers is 36.6 years with a mean time

as an officer of 10.5 years. The remainder of the

Fort Collins Polices Services have a mean age of

38.4 years and time in service of 13.8 years.

As previously noted, after completing the first

audiometric examination, the officers were

moved to the firing range and were instructed to

fire their weapon using a standard firearm

qualification course under the direction of the

range instructor. Under most circumstances, two

officers completed the course simultaneously in

two adjacent lanes on the firing range.

Immediately after completion of the qualification

course, a stopwatch was started and the officers

were quickly returned to the audiometric test

booth for the modified audiometric examination of

high-frequency pure tones. Elapsed times were

recorded when the left ear test and right ear test

were completed. TTS values were determined by

subtracting the pre-qualification hearing test from

the post-qualification test for each frequency

tested.

The mean TTS values for each weapon type

(pistol, rifle, or shotgun) and for the SWAT

custom-made hearing protector are given in Table

3. The majority of the mean TTS values are

negative numbers, meaning that the officers

actually heard better following the qualification

course on the firing range. Mean completion

times on the indoor range for the left ear tests were

slightly greater than 2 minutes and the right ears

were finished in 3.25 minutes. On the outdoor

range the officers were tested further away from

the firing line and it took nearly 3.5 minutes to

finish the left ears and 4.5 minutes to finish the

right ears. The mean TTS values for SWAT

officers wearing the ESP hearing protectors and

firing .223 cal rifles were less than 1.0 dB, with
Page 8 Health Hazard Evaluation Report No. 2002-0131-2898

the majority being 0.0 dB or less. Inspection of

individual results shows only one instance where

the change in hearing was +10 dB at a test

frequency of 6000 Hz. When the three types of

weapons used by the officers are looked at

separately, the mean TTS values are all less than

1.0 dB. For the .223 cal rifle used on the outdoor

range, there were two individuals out of 26 tested

that had TTS values of +10 dB, one at 4000 Hz

and the other at 6000 Hz. On the indoor range, the

pistol qualification course resulted in 11 of 52

officers exhibiting a TTS of +10 dB or greater.

Two of the 11 officers had +10 dB shifts at two

separate test frequencies. Ten of the shifts

occurred at the 6000 Hz test frequency. The

shotgun qualification course resulted in only one

officer out of 14 that had a +10 dB shift at 4000

Hz. No individual TTS exceeded +20 dB.

Noise Measurements

Peak Exposure Levels

Figure 5 shows the mannequin’s protected ear and

the unprotected waveforms for a Smith & Wesson

revolver recorded at the outdoor firing range. The

measurements at the outdoor range provided a

better approximation to what one might expect

in an anechoic environment, one with fewer

reflected sound waves. Particularly, the first

impulse of the shockwave from the muzzle of the

weapon was extracted for analysis. The recording

conditions (drizzling rain) required that we use a

fabric tent over the shooting area. The ground,

ISL mannequin, tent, shooter, shooter’s assistant,

picnic table, and weapons were potential reflective

surfaces. Of these, the side of the mannequin’s

head reflected the most energy (see the double

peak at 1.82 ms). Peaks at 3.58 and 4.23 ms

probably correspond to reflections from the tent

and the shooter. The peak at 6.24 ms is consistent

with the path length difference between the direct

and ground-reflected paths. 

The protected waveform (solid blue line) for the

Smith & Wesson 586 and David Clark Model 27

earmuffs yielded a peak protected level of 137.5

dB SPL. The waveform was less sharply peaked

than the unprotected waveform (solid red line).

This difference was primarily a function of the

hearing protector. Earmuffs generally yielded a

low-pass filter that smoothed the jagged nature

of the waveform. Earplugs, such as the EAR

Classic, had more low frequency attenuation

than the earmuff. Consequently, the resulting

protected waveforms were not dominated by the

low-frequency signal and more closely resembled

the unprotected waveform.

Figure 6 shows a pair of bar graphs indicating the

average and standard deviation of the maximum

peak sound pressure level in decibels referenced to

20 μPa measured at the indoor and outdoor firing

ranges. For the indoor range (upper panel), the

Smith & Wesson 586 and 686 revolvers had sound

pressures of 167.9 and 167.1 dB SPL,

respectively. The Colt Pocket9 and Par-Ordinance

P10 pistols had the next greatest peak pressures of

162.3 and 162.4 dB SPL, respectively. The

remaining weapons at the indoor range had peak

pressures 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 had

the highest peak pressures of 168.6 and 166.8 dB

SPL, respectively. The other weapons ranged

from 159.0 to 161.5 dB SPL. 

Weapons Spectra

In Figure 7, the a-octave band spectra of the

weapons tested on the outdoor range are displayed

in staircase plots. The horizontal lines are spaced

in 10 decibel intervals and the dark bar at the

center of each spectrum is the 1000 Hz band. For

most of the weapons, the maximum level is

between 500 and 800 Hz. With the exception of

the Glock 22 and Colt 1991-A1, the maximum

band exceeded 130 dB SPL. The maximum

energy of the Smith & Wesson 586 was at

2000 Hz.

One point should be clarified about the a-octave

band analysis. The estimate of the peak impulse

level is based upon the instantaneous sound

pressure. The third-octave analysis represents the
Health Hazard Evaluation Report No. 2002-0131-2898 Page 9

average of the signal over the analysis window

(42.67 ms for the outdoor data). One may

visualize spreading the instantaneous peak over

the analysis window. If a single gunshot is

sampled with both a short and long time window,

the long-window third-octave analysis will yield

lower estimates of the band levels. For this

reason, the peak sound pressure levels are listed

on the weapon spectra in Figure 7 rather than the

logarithmic sum of the a-octave bands.

Spectral Difference Plots

To better examine the differences between

weapons, the .450 caliber Colt 1991 A1 pistol was

used as a reference spectrum and was subtracted

from the spectra of the other weapons shown in

Figure 8. The spectra for the Glock 22, Sig Sauer

P228 and Colt 1991-A1 were similar except at the

high frequencies. The Colt AR-15 levels were

approximately 7-10 dB/band greater below 200

Hz. From 400 to 1000 Hz, the AR-15 levels were

3-5 dB/band higher. The Remington 11-87

shotgun was greater by 5-14 dB/band below 400

Hz. Above 4000 Hz, the shotgun was slightly

greater than the Colt 1991-A1. The Smith &

Wesson 586 levels were 5-15 dB/band higher

in almost every band. Above 250 Hz, the 586

was not more than 10 dB/band greater than the

Colt 1991-A1. The peak level from the Smith &

Wesson 586 in Figure 7 was also evident in the

difference plot at 2000 Hz. The H & K 53

exhibited the greatest spectral differences at 20 of

27 third-octave band frequencies. Below 500 Hz,

the H&K 53 exceeded the Colt 1991-A1 by 10-15

dB/band. Above 500 Hz, the H&K 53 was greater

by about 5-10 dB/band. 

David Clark Model 27 Earmuff

Plus EAR Classic Earplug

Attenuation

Figure 9 shows the attenuations measured for the

David Clark Model 27 earmuff, EAR Classic

earplug, and David Clark Model 27 with EAR

Classic. The David Clark muffs exhibited

attenuations of about 10 dB/band at 100 Hz and

below. From 100-500 Hz, the attenuation

increased to about 35 dB. The attenuation above

500 Hz varied between 28 and 40 dB/band. The

Classic earplug increased in attenuation from 18

dB 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 Classic

protectors were measured at both firing ranges.

The indoor range data below 250 Hz exhibited

attenuations close to the sum of the David Clark

and Classic measured separately. Above 250 Hz,

the attenuations varied over a range of 40 decibels.

The differences were likely due to resonances in

transmission through the protectors and

resonances of the enclosed volumes of the earmuff

and earplug.

The results with David Clark Model 27 when

worn with safety glasses are presented in Figure

10. Two features are prominent in the figure: the

attenuation is negative below 200 Hz; the

attenuation at 2000 Hz varies more than the

adjacent frequencies. The variability at 2000 Hz

correlates with the output of various weapons at

that frequency. The low-pass filtering of the

earmuff will yield greater exposure underneath

the earmuffs for weapons with significant lowfrequency content such as the H & K 53, Colt

AR-15, Remington 11-87 and the Smith and

Wesson 586.

Electronic Shooter Protection

Elite

The ESP Elite was tested at both firing ranges for

three gain settings—off, unity, and maximum

gain. In Figure 11, the off setting is shown with

gray symbols, unity with green, and maximum

with red symbols. The outdoor attenuations are

shown with squares and the indoor with circles.

The indoor and outdoor attenuations differed

considerably between 100 and 400 Hz. Above

2500 Hz, the outdoor and indoor attenuations

differed by as much as 10 dBs. When the ESP

Elite was turned off, the attenuations above 2500

Hz are within 4 dB for the indoor and outdoor

measurements. The disparity between the indoor
Page 10 Health Hazard Evaluation Report No. 2002-0131-2898

and outdoor results suggest that the ESP may be

sensitive to how well it was fit in the mannequin

ear canal. 

In Figure 12, the summary analysis of 24 ESP

Elite protectors performed with the Frye FP40

Hearing Aid Analyzer is shown.17 In the upper

panel, the histogram of the maximum SPL output

of the ESP exhibited a wide range of levels from

90 to 105 dB SPL. In the lower panel, the

histogram of the average of the saturated SPL

determined as the average of 1000, 1600 and 2500

Hz is shown. The upper histogram seems to have

two groups centered at 92 and 102 dBs. The

lower histogram is centered about 88 dB and has

one group. 

The data from Figure 12 suggest that officers

wearing the ESP Elite could be exposed to levels

of noise above the NIOSH recommended limit

of 85 dB if they use the maximum gain. The ESP

Elite measured on the mannequin exhibited more

attenuation at the low frequencies and comparable

attenuation at the high frequencies when compared

to the David Clark Model 27 earmuffs. While the

measured peak impulse levels of gunshots

underneath the ESP were approximately 128 to

138 dB, the highest saturated sound pressure

output of the ESP device was limited to about 105

dB (the average of 1000, 1600 and 2500 Hz with

a 90 dB input). The exposure to the weapon posed

the greatest risk of noise exposure. 

The averages of the peak reduction are shown in

Figure 13 for the various hearing protector, safety

glasses, and range conditions. The earmuffs with

safety glasses had a reduction of 12 and 18 dBs.

The earmuffs alone reduced the peak energy by 29

and 32 dB. The peak energy reduction of the EAR

Classic was 29 dB. The peak reductions for the

combined earmuff and earplug were 46 and 50 dB.

The peak reductions for the ESP Elite protector

were approximately 30-31 decibels regardless of

the volume setting.

DISCUSSION

TTS and Hearing Loss

The weapon qualification courses fired by the

officers did not result in significant amounts of

TTS. The mean values were consistently less than

0 dB, meaning that the HPDs used during this

evaluation seems to have prevented temporary

changes in hearing for the officers firing their

weapons under these circumstances. These data

are somewhat different from previously presented

results of TTS in officers who wore double

hearing protection on an indoor firing range and

were found to exhibit an average TTS of 9 dB at

6000 Hz when the ear plug was not properly

inserted into their ears.18 The pre-noise exposure

audiometric examinations also showed that the

average Fort Collins Police Service officer tested

did not show hearing loss patterns consistent

with noise over-exposures. Only the oldest group

of officers (> 45 yrs.) had mean hearing levels

that fell into a mild hearing loss category for

the higher test frequencies (4000, 6000, and

8000 Hz). One finding in the hearing data,

however, does raise some concern. For the

individual officers tested who exhibited temporary

shifts of 10 dB or more, nearly all of the changes

were at 6000 Hz, the test frequency where the

older officers were found to have mild hearing

loss. 

Noise Measurements

Peak Exposure Levels

Several issues need to be considered with respect

to these data. First, the mannequin was designed

to estimate the airborne transmission path for an

external sound attenuated by a hearing protector.

In the human, the acoustic energy can reach the

cochlea through several pathways: through the air,

through the hearing protection, through leaks

around the hearing protection, through the oralnasal cavities (transmitted into the middle ear

cavities), and through bone conduction. The

attenuations measured at the high frequencies

with the mannequin are not representative of

the attenuations measured using the real-ear

attenuation at threshold method for humans
Health Hazard Evaluation Report No. 2002-0131-2898 Page 11

subjects. The mannequin has more isolation of the

microphone and thus does not recreate the boneconduction and oral-nasal pathways. However,

the peak level reductions may be reasonable

estimates for what a human subject would

experience.

Second, the attenuation of a protector used in

impulsive noise may not be the same when used in

continuous noise. Newton’s first law of motion

states, “Every body persists in its state of rest or of

uniform motion in a straight line unless it is

compelled to change that state by forces

impressed on it.”19 An acoustic shock wave will

impart energy to the protector, but may not be as

effective in causing the protector to oscillate or

vibrate as a low-amplitude continuous waveform.

Protector attenuations are tested using continuous

third-octave band noise at or near the threshold of

hearing. An impulsive waveform will excite the

protector at effectively all frequencies, but the

energy is transmitted over a short time period. If

the device being excited behaves in a nonlinear

manner, the transmission of a high-level impulse

may be affected by the nonlinearity while the

transmission of low-level continuous noise will

not be affected. Acoustic nonlinearities become

important at signal levels above 120 decibels.

Acoustic shock waves can be formed at levels of

140 dB and greater when the impedance of the

air becomes nonlinear. The attenuation for

continuous noises remains constant as a function

of level over a wide range of signal levels. The

peak reduction data in Figure 13 were presented as

bar graphs because the peak reduction was

constant within the error limits over the range of

weapons tested. The only device that was not

constant was the earmuff with safety glasses. The

safety glasses will be discussed in a later section

of this report.

Third, the audiology, occupational safety and

health, and military communities have not reached

a consensus regarding the risk of hearing loss

when it comes to impulse noise. Particularly, the

U.S Military Standard 1474D yields estimates of

the daily allowed number of rounds fired that

seem to be unacceptably high (one calculation

using a protected waveform under an earmuff

yielded 3000 shots for a Colt AR-15 rifle).20

Other calculations suggest that 100 to 1000 shots

is the recommended number of shots. NIOSH has

proposed the following formula for evaluating the

risk of impulsive noise,

N = 10(140 - PI dB)/10

where N is the total number of shots and PI dB is

the peak impulsive level in dB SPL.21 Using this

formula and the peak levels in Figure 6 and the

peak reductions in Figure 13, the officers would

be exposed to peak impulse levels of 130–140 dB

SPL. Applying this formula yields an allowable

number of shots of 1 to 10 shots per day. This

proposed formula is a conservative estimate and

makes no compensation for the duration of the

impulse.22,23,24 Applying the NIOSH formula to

the double-protected data increases the allowable

number of shots from 100 to 1000. Even though

only a few of the officers experienced a small shift

in this evaluation, properly-fit, double protection

should minimize TTS and potential permanent

threshold shifts.

David Clark Model 27 Earmuff

Attenuation

The David Clark Model 27 earmuffs yielded

peak reductions that are typical of other earmuffs

measured with these methods.25 A peak reduction

of 30 decibels is typical of other earmuffs that

were measured for 9mm and .223 caliber weapons.

Two areas of concern should be addressed with

the earmuff usage by the Fort Collins Police

Service SWAT officers: the use of HPDs with

safety glasses; and the use of the devices with

helmets. 

During the HHE, the mannequin measurements

were performed with and without safety glasses.

As shown in Figure 13, the peak reductions were

diminished when the safety glasses disrupted

the seal of the earmuff cushion with the side of the

head. The small opening around the earpiece of

the glasses lowered the effective peak

reduction by 20 to 30 dBs. Using the peak levels
Page 12 Health Hazard Evaluation Report No. 2002-0131-2898

from Figure 6, the officer with a comparable leak

could be exposed to 156 to 150 dB peak SPL. If

the officers could wear the safety glasses over the

top of the earmuff cushions, or use glasses with a

strap or low profile stem rather than a high profile

stem, the size of the leak could be reduced or

eliminated. Ideally, the safety glasses should be

an integral part of the earmuff or the helmet. 

The peak level reduction for the earmuff with

safety glasses exhibited a slight increase in peak

reduction as the peak SPL increased. This effect

is consistent with nonlinear acoustic impedance

of shockwaves that impinge upon an orifice. In

fact, nonlinear impedance forms the basis of

several hearing protection devices, such as the

EAR Combat-Arms earplug, Bilsom ISL earplug,

and the EAR Ultra 9000 shooters earmuff.

The second issue is using earmuffs with the

SWAT officers helmets. The officers had Kevlar

helmets that had attachment points for face

shields but not hearing protectors. Also, the

helmets covered the upper half of the pinna.

Consequently, the current helmet could not be

used with the circumaural earmuffs used by the

Fort Collins Police Service. However, Peltor now

makes a hearing protection device that permits the

use of a helmet with an earmuff (Peltor® COMTAC and SWAT•TAC). There is also research

being conducted for the U.S. military on the use

of earplugs with communication capabilities for

impulsive and steady-state noise environments.26

Performance of the ESP Elite

Devices

The ESP Elite exhibited inconsistent attenuation

within the measurements collected at both firing

ranges, which may have been a function of how

well the device was fit. At each location, the

device was inserted fully into the mannequin’s ear

canal and pinna. The insertion is not difficult and

should not have caused any effect between the two

ranges. The data in the lower panel of Figure 12

suggests that the ESP device yields a consistent

saturated SPL, the average of the output at 1000,

1600 and 2500 Hz in response to a 90 dB SPL

input.

One of the issues which applies more to hearing

aids and sound-restoration earmuffs is the

performance in intermittent noise. Typically a

device will use either a level-limiting,

compression, or automatic gain control circuit to

limit the maximum SPL output of the electronics.

For lower SPL, these devices are able to amplify

the sound and reproduce the signal at a level

which is above the attenuated SPL and below its

maximum output level. The output of the ESP

Elite, or other electronic hearing protectors, in

response to high amplitude impulsive sounds,

will not be reproduced by these devices due to

mechanical and electrical limitations. In other

words, an intermittent peak of 80 dB might

be attenuated by 20 dB resulting in an

unaided/unamplified sound pressure level of

60 dB. When the device amplifies that sound by

20 dB, the output would be restored to the 80 dB

level. For a high amplitude impulsive sound

(160 dB), the device might attenuate by 20 dB, but

the amplification cannot restore the sound level to

160 dB because it exceeds the capability of the

circuitry. This shortcoming is good, because the

device will not reproduce harmful sound pressure

levels that exceed the capability of the circuitry.

For intermittent noise, these devices also have

some recovery time after a loud sound occurs.

The recovery time can adversely affect

communication by cutting of the speech during a

loud sound. The manufacturer lists the release

time as 400 ms. The hearing aid analyzer that was

used in the field to assess the performance of the

ESP Elite protectors was not equipped to measure

the attack and release times. For an intermittent

noise, a short recovery time might have less of an

effect on communication.

Another issue that should be considered with the

officers using the ESP device is how well the

earpiece fits. Every officer using the ESP should

have the fit of the device tested to determine

whether they are achieving an effective seal of

the ear canal. A poor seal could increase the noise

exposure that officers receive. FitCheck is a
Health Hazard Evaluation Report No. 2002-0131-2898 Page 13

product which can be installed on a personal

computer running Windows software.27 FitCheck

measures the attenuation of earplugs using

narrow-band noise signals. If an officer does not

receive a reasonable amount of attenuation (15–30

decibels in every frequency band), the device

should be remade. Unfortunately, the ESP Elite

protector does not have an EPA NRR.8

 If it had

an NRR, consumers would know what attenuation

to expect if fit testing were performed.

Performance of the EAR Classic

The EAR Classic earplug yielded a peak level

reduction of 30 dBs. Again this number seems

to be typical for a well fit protector on the

mannequin. The Classic earplug exhibits a

consistent performance across subjects and is not

as susceptible to acoustic leaks as other earplugs.28

For a human, the Classic earplug can be inserted

anywhere from 10 to 100 percent of the length of

the earplug into the ear canal. With respect to real

ear attenuation at threshold, the attenuation is

affected by how much of the earplug has been

inserted. For the ISL mannequin, a maximum of

60 percent of the earplug could be inserted into the

ear canal. The peak reduction in a human ear

canal may be more or less depending upon how

much of the earplug is inserted. Real-world

studies of hearing protector devices have shown

that they do not achieve the manufacturer’s

measured attenuations for experimenter fit

earplugs.29,30

CONCLUSIONS

Using the NIOSH REL as a guideline, the officers

should not be exposed to noise impulses above

140 dB for any amount of time.12 The unprotected

peak noise levels measured on the acoustic

mannequin were found to range from 159 to 169

dB. The results from the TTS study indicate that

the weapons’ noise is not great enough to result in

a temporary loss of hearing while firing a single

standard qualification course on either the indoor

or outdoor range with the HPDs used during the

evaluation. The baseline hearing tests for the

police service revealed normal hearing patterns for

all but the oldest group of officers. It is possible

that the mild hearing loss measured in the oldest

group is the result of different work practices used

by the police service when these officers were just

beginning their careers and that the current group

of young officers will not necessarily accrue

occupational hearing loss. Or these results may

show that the amount of sound energy from their

weapons is intense enough to eventually result

in hearing loss. It is not possible to answer this

question with the data collected during this

evaluation.

The measurements of the protection afforded by

the HPDs were consistently in the 30 dB range

(Figure 13), unless the earmuff seal with the side

of the mannequin was broken by the safety

glasses.

These peak reduction results along with the peak

noise levels measured for the weapons indicate

that the officers should consider using dual

hearing protection during weapons training

exercises for maximum protection. To overcome

the inability to communicate when doubleprotected, the officers should be provided with

electronic level-limiting earmuffs and a choice of

earplugs. The earplugs can provide an additional

15–20 dB of peak reduction while the electronic

earmuffs can compensate for the reduced speech

intelligibility due to double protection. If the

protected peak SPL are in the 120–130 dB range,

then the NIOSH formula suggests that 100 to 1000

shots per day would be allowed. Recognizing that

this is a conservative estimate, officers will not be

exposed to an excessive risk of hearing loss with

double protection. In addition to the electronic

earmuffs, commercially available communication

headsets exist that would permit the range officer

to transmit instructions via short range radio to the

officer’s headset that could improve the

communication even further. Companies such as

Aearo/Peltor, Baccou-Dalloz (Bilsom), David

Clark, and Hellberg make combined hearing

protector and communication systems that might

be adaptable to the SWAT team’s needs during

training and during deployment.
Page 14 Health Hazard Evaluation Report No. 2002-0131-2898

1. Davis H, Morgan CT, Hawkins Jr. JE,

Galambos R, Smith FN [1950]. Temporary

deafness following exposure to loud tone and

noise. Acta Otolaryngologica Supplement

88:1–57. 

2. Hirsh IJ, Ward WD [1952]. Recovery of the

auditory threshold after strong acoustic

stimulation. Journal of the Acoustical Society of

America 24:131–141.

3. Kryter KD [1963]. Exposure to steady-state

noise and impairment of hearing. Journal of the

Acoustical Society of America 35:1515–1525.

4. Kryter KD [1970]. The effects of noise on

man. New York, NY: Academic Press.

5. Kryter KD, Ward WD, Miller JD, Eldredge

DH [1966]. Hazardous exposure to intermittent

and steady-state noise. Journal of the Acoustical

Society of America 39:451–464. 

6. Ward WD [1966]. The use of TTS in the

derivation of damage risk criteria for noise

exposure. International Audiology 5:309–313.

7. Franke R, Parmentier G, Buck K, Evrard G,

Kronenberger G, Beck C, Brunner JJ [1994]. Tete

artificielle pour l’evaluation de l’efficacite des

protecteours auditifs vis a vis bruis de niveau

eleve Partie 1: Developpement et essais en regime

impulsionnel. Research report French-German

Institute for Research of Saint Louis. Report R112/94.

8. EPA [1978]. Noise labeling requirements for

hearing protectors. Fed Regist 44(190), 40CFR

part 211, 56130-56147.

9. NIOSH [1992]. Recommendations for

occupational safety and health: compendium of

policy documents and statements. Cincinnati, OH:

U.S. Department of Health and Human Services,

Public Health Service, Centers for Disease Control

and Prevention, National Institute for

Occupational Safety and Health, DHHS (NIOSH)

Publication No. 92-100.

10. ACGIH [2002]. 2002 TLVs® and BEIs®:

threshold limit values for chemical substances and

physical agents and biological exposure indices.

Cincinnati, OH: American Conference of

RECOMMENDATIONS

Based on the measurements and observations

made in the evaluation of weapon noise and its

effect on hearing for the Fort Collins Police

Service, the following recommendations are made

to improve working conditions for the officers.

1. The use of double hearing protection is

warrented during weapons training exercises. The

peak noise levels measured for the weapons and

the amount of attenuation given by the HPDs are

such that double protection will offer maximum

protection and some insurance against improper

fitting of the devices or incompatibility with other

personal protective equipment.

2. Although the ESP device worn by the SWAT

officers did not result in any TTS, the Fort Collins

Police Service should investigate other devices

that are available. The ESP Elite does not have an

NRR rating which is required by the EPA for

HPDs.8

 The device also does not allow for closedcircuit radio communications which would limit

the broadcasting of radio transmissions into an

environment that may be better protected with

radio silence. HPDs that offer this are beginning

to be available. These devices should be reviewed

to see if they are compatible with the SWAT

team’s equipment and practices.

3. The noise levels that are generated by the

weapons used by the police service are intense

enough to warrant the initiation of a hearing

conservation program. As a minimum, the hearing

conservation program should meet the

requirements of the OSHA hearing conservation

amendment (29 CFR 1910.95).11 Other sources

for defining effective hearing conservation

programs are also available.31,32,33

REFERENCES
Health Hazard Evaluation Report No. 2002-0131-2898 Page 15

Governmental Industrial Hygienists.

11. CFR [1997]. 29 CFR 1910.1000. Code of

Federal Regulations. Washington, DC: U.S.

Government Printing Office, Office of the Federal

Register.

12. NIOSH [1998]. Criteria for a recommended

standard: occupational noise exposure (revised

criteria 1998). Cincinnati, OH: U.S. Department

of Health and Human Services, U.S. Public Health

Service, Centers for Disease Control and

Prevention, National Institute for Occupational

Safety and Health, DHHS (NIOSH) Publication

No. 98-126.

13. Ward WD, Royster LH, Royster JD [2000].

Anatomy & physiology of the ear: normal and

damaged 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, pp

101–122.

14. Suter AH [1978]. The ability of mildly

hearing–impaired individuals to discriminate

speech in noise. Washington, DC: U.S.

Environmental Protection Agency, Joint

EPA/USAF study, EPA 550/9–78–100,

AMRL–TR–78–4.

15. ANSI [1996]. American national standard

specification for audiometers. Melville, NY:

Acoustical Society of America, American

National Standards Institute, ANSI S3.6-1996.

16. Eagles EL, Hardy WG, Catlin FI [1968].

Human communication: The public health aspects

of hearing, language, and speech disorders

(NINDB monograph #7). Washington, DC:

Government Printing Office, USPHS Publication

1745.

17. ANSI [1996]. American national standard of

hearing aid characteristics. Melville, NY:

Acoustical Society of America, American

National Standards Institute, ANSI S3.22-1996.

18. Tubbs RL [1992]. Temporary threshold

shifts in hearing following exposure to gunfire

noise on firing ranges. Unpublished paper

presented at the 27th Annual Meeting of the U.S.

Public Health Service Professional Association,

Cincinnati, Ohio, April 25–28.

19. Newton I [1686]. Philosopiae Naturalis

Principia Mathematica.

20. MIL-STD-1474D [1997]. Department of

defense design criteria standard: Noise limits,

AMSC, A7245.

21. NIOSH [2002]. Comments of the National

Institute for Occupational Safety and Health on

the Occupational Safety and Health

Administration ANPR Hearing Conservation

Program for Construction Workers 29 CFR Part

1926 Docket No. H-011G. Cincinnati, OH: U.S.

Department of Health and Human Services, Public

Health Service, Centers for Disease Control and

Prevention, National Institute for Occupational

Safety and Health.

22. Smoorenburg GF [1982]. Damage risk criteria

for impulse noise. In: Hamernik R, Henderson D,

Savli R, eds. New perspectives on noise-induced

hearing loss. New York, NY: Raven Press, pp

471–490.

23. Pfander F, Bongartz, H, Brinkman H, Kietz H

[1980]. Danger of auditory impairment from

impulse noise: A comparative study of the

CHABA damage-risk criteria and those of the

Federal Republic of Germany. Journal of the

Acoustical Society of America 67:628–633.

24. Pfander F [1975]. Das Knalltrauma. Berlin,

Heidelberg, New York: Springer Verlag.

25. Murphy WJ, Little MB [2002]. Performance

of electroacoustic hearing protectors. Presented at

the 143rd meeting of the Acoustical Society of

America, Pittsburgh, PA, June 3, 2002.

26. Mozo B [2003]. Communications & Ear

Protection, Inc. [http://www.cep-usa.com]. Date

accessed: February 2003.
Page 16 Health Hazard Evaluation Report No. 2002-0131-2898

27. Michael KL [1998]. Comprehensive use of

hearing protectors: Integration of training, field

monitoring, communication and documentation.

Journal of Occupational Hearing Loss 1:67–74.

28. Murphy WJ, Franks JR, Krieg EF [2002].

Hearing protector attenuation: Models of

attenuation distributions. Journal of the

Acoustical Society of America 111:2109–-2118.

29. NIOSH [1995]. The NIOSH compendium of

hearing protection devices. Cincinnati, OH: U.S.

Department of Health and Human Services, Public

Health Service, Centers for Disease Control and

Prevention, National Institute for Occupational

Safety and Health, DHHS (NIOSH) Publication

No. 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 standard

laboratory protocol for estimating the field

attenuation of hearing protection devices. Part III.

The validity of using subject-fit data. Journal of

the Acoustical Society of America 103:665–-672.

31. NIOSH [1996]. Preventing occupational

hearing 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 and

Health, DHHS (NIOSH) Publication No. 96–110.

32. Suter AH [2002]. Hearing conservation

manual. 4th ed. Milwaukee, WI: Council for

Accreditation in Occupational Hearing

Conservation.

33. Royster JD, Royster LH [1990]. Hearing

conservation programs: practical guidelines for

success. Chelsea, MI: Lewis Publishers.
Health Hazard Evaluation Report No. 2002-0131-2898 Page 17





 



 

	

	

	 	

	

	 	

500 1000 2000 3000 4000 6000 8000

Audiometric Test Frequency [Hz]

 0

 -10

 -20

 -30

 -40

 -50

 -60

 -70

 -80

 -90

Mean Basel ni e Hear ni g Level [dB

HL]

	Left Ear Right Ear 

Figure 1

Hearing Levels - Fort Collins Police Service

Fort Collins, CO

HETA 2002-0131

May 2002

 0

10

20

30

40

50

60

70

80





 



 











 





 







	

	

	 	

	

	 	







 

 

500 1000 2000 3000 4000 6000 8000

Audiometric Test Frequency [Hz]

 0

 -10

 -20

 -30

 -40

 -50

 -60

 -70

 -80

 -90

Mean Basel ni e Hear ni g Level [dB

HL]

24-30 yrs. 31-35 yrs. 36-40 yrs.

41-45 yrs. 46-54 yrs.

 	 

 

Figure 2

Left Ear Hearing Levels by Age

Fort Collins Police Service

Fort Collins, CO

HETA 2002-0131

May 2002

 0

10

20

30

40

50

60

70

80
Page 18 Health Hazard Evaluation Report No. 2002-0131-2898





 

















 





 



 

	 	

	 	 	

	

	



  



 

500 1000 2000 3000 4000 6000 8000

Audiometric Test Frequency [Hz]

 0

 -10

 -20

 -30

 -40

 -50

 -60

 -70

 -80

 -90

Mean Basel ni e Hear ni g Level [dB

HL]

24-30 yrs. 31-35 yrs. 36-40 yrs.

41-45 yrs. 46-54 yrs.

 	 

 

Figure 3

Right Ear Hearing Levels by Age

Fort Collins Police Service

Fort Collins, CO

HETA 2002-0131

May 2002

 0

10

20

30

40

50

60

70

80





   







 



 





  

 

	

	

	 	

	

	 	

500 1000 2000 3000 4000 6000 8000

Audiometric Test Frequency [Hz]

 0

 -10

 -20

 -30

 -40

 -50

 -60

 -70

 -80

 -90

Mean Basel ni e Hear ni g Level [dB

HL]

Department, Left Ear Department, Right Ear

SWAT, Left Ear SWAT, Right Ear

	 

 

Figure 4

SWAT versus Rest of Department Hearing Levels

Fort Collins Police Service

Fort Collins, CO

HETA 2002-0131

May 2002

 0

10

20

30

40

50

60

70

80
Health Hazard Evaluation Report No. 2002-0131-2898 Page 19

Figure 5

Outdoor Recording of the Unprotected and Protected Waveforms

Fort Collins Police Service

Fort Collins, CO

HETA 2002-0131

May 2002

Measurements from the Bruel & Kjaer 4136 microphone and ISL mannequin. The red line is the

unprotected waveform (microphone) and the blue line is the protected (mannequin). The vertical dashed

lines indicate the presence of reflected pressure waves from surrounding objects.
Page 20 Health Hazard Evaluation Report No. 2002-0131-2898

Ft. Collins Indoor Range

Peak Impulse Level (dB SPL)

145

150

155

160

165

170

175

Ft. Collins Outdoor Range

Peak Impulse Level (dB SPL)

145

150

155

160

165

170

175

Weapon Peak Impulse Noise Levels (dB SPL) Colt 1991A1 ParOrdinance P10 Glock 22 Glock 27 Remington 1187 Remington 870 Sig Sauer P228 Colt Pocket 9 Smith & Wesson 586 Smith & Wesson 686 Colt 1991A1 Glock 22 Remington 1187 Sig Sauer P228 Smith & Wesson 586 Colt AR15 Heckler & Koch 53

Caliber

0.450

0.400

12 gauge

9 mm

0.357

0.223

Figure 6

Peak impulse noise levels at the indoor and outdoor firing ranges

Fort Collins Police Service

Fort Collins, CO

HETA 2002-0131

May 2002
Health Hazard Evaluation Report No. 2002-0131-2898 Page 21

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

Sound Pressure Level (dB SPL)

70

90

110

130

Heckler & Koch 53

167 dB

Smith & Wesson 586

169 dB

Colt AR-15

161 dB

Remington 11-87

162 dB

Sig Sauer P228

160 dB

Glock 22

158 dB

Colt 1991 A1

159 dB

Figure 7

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

Fort Collins Police Service

Fort Collins, CO

HETA 2002-0131

May 2002

The horizontal lines are spaced in 10 dB intervals. The dark bar in the center depicts the 1000 Hz one

third-octave band. The weapons are positioned with the lowest to highest sound pressure levels from

front to back.
Page 22 Health Hazard Evaluation Report No. 2002-0131-2898

Difference in Third-Octave Pressure with 

 0.450 Caliber Colt 1991 A1 Pistol

Frequency (Hz)

25 50 100 250 500 1000 2500 5000 10000

Difference (dB)

-10

-5

0

5

10

15

20

25

30

AR-15

Glock 22

Heckler & Koch 53

Remington 1187

Sig Sauer P228

Smith & Wesson 586

Figure 8

One third-octave band difference spectra for weapons

measured at the outdoor firing range

Fort Collins Police Service

Fort Collins, CO

HETA 2002-0131

May 2002

The .450 caliber Colt 1991-A1 semi-automatic pistol was used as the reference weapon. The Colt 1991

spectra was subtracted from the spectra of the other weapons to derive the difference spectra shown

above. Error bars are depicted on one side of the data symbols to reduce clutter.
Health Hazard Evaluation Report No. 2002-0131-2898 Page 23

David Clark Blue Earmuff

Attenuation vs Frequency

Frequency (Hz)

25 50 100 250 500 1000 2500 5000 10000

Attenuation (dB)

0

10

20

30

40

50

60

70

80

90

David Clark Blue Indoor

DavidClark Blue Outdoor

DC Blue & EAR Classic Indoor

DC Blue & EAR Classic Outdoor

EAR Classic Indoor

Figure 9

One third-octave band attenuation results for the

David Clark Earmuff and EAR Earplug

Fort Collins Police Service

Fort Collins, CO

HETA 2002-0131

May 2002

The third-octave band attenuation spectra for the David Clark model 27 earmuff alone and in conjunction

with an EAR Classic earplug on the indoor and outdoor ranges.
Page 24 Health Hazard Evaluation Report No. 2002-0131-2898

David Clark Blue Earmuff with Safety Glasses Attenuation by Weapon

Frequency (Hz)

25 50 100 250 500 1000 2500 5000 10000

Attenuation (dB)

-20

-10

0

10

20

30

40

Colt 1991-A1 

Colt AR15 

Glock 22 

Heckler Koch 53 

Remington 11-87 

SigSauer P228 

Smith & Wesson 586 

Figure 10

One third-octave band attenuation results for the

David Clark Earmuff and Safety Glasses

Fort Collins Police Service

Fort Collins, CO

HETA 2002-0131

May 2002

The third-octave band attenuation spectra for the David Clark model 27 earmuff with a leak caused by a

pair of safety glasses under the earmuff. The different weapons are depicted with different colored

symbols. The attenuations below 250 Hz are largely negative as a result of the leak. At 2000 Hz, the

variation of the attenuations is larger than neighboring frequencies.
Health Hazard Evaluation Report No. 2002-0131-2898 Page 25

Electronic Shooter Protection Elite

Attenuation vs Frequency

Frequency (Hz)

25 50 100 250 500 1000 2500 5000 10000

Attenuation (dB)

0

10

20

30

40

50

60

70

Off Indoor

Off Outdoor

Unity Gain Indoor

Unity Gain Outdoor

Maximum Gain Indoor

Maximum Gain Outdoor

Figure 11

One third-octave band attenuation results for the ESP

Fort Collins Police Service

Fort Collins, CO

HETA 2002-0131

May 2002

The third-octave band attenuations of the Electronic Shooter Protection Elite hearing protector for three

different settings: off, unity gain, and maximum gain. The measurements for the indoor and outdoor

firing ranges are different when the gain is applied whereas the off settings exhibit little difference above

100 Hz.
Page 26 Health Hazard Evaluation Report No. 2002-0131-2898

Histogram of the Maximum SPL Output

Maximum Sound Pressure Level (dB SPL)

88 90 92 94 96 98 100 102 104 106 108

Number of Occurances

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

Number of Occurances

0

2

4

6

8

Figure 12

One third-octave band attenuation results for the ESP

Fort Collins Police Service

Fort Collins, CO

HETA 2002-0131

May 2002

Measurements for

the ESP Elite device as tested according to ANSI S3.22-1996. The upper panel displays the histogram of

the maximum sound pressure level (SPL) in dB along the x-axis for 24 units tested. One unit was for the

ISL mannequin and one officer provided only one ESP Elite device. The lower panel shows a histogram

of the saturated sound pressure level (SSPL) for the same 24 devices. The manufacturer’s specifications

indicate maximum SPL of 93 dB and SSPL of 88 dB.
Health Hazard Evaluation Report No. 2002-0131-2898 Page 27

Peak Reductions for Protectors at Both Firing Ranges

Peak Reduction (dB SPL)

0 10 20 30 40 50 60

David Clark w Glasses Outdoor

David Clark w Glasses Indoor

EAR Classic Indoor

David Clark Model 27 Indoor

David Clark Model 27 Outdoor

David Clark & EAR Indoor

David Clark & EAR Outdoor

ESP Elite Off Indoor

ESP Elite Off Outdoor

ESP Elite Unity Indoor

ESP Elite Unity Outdoor

ESP Elite Max Indoor

ESP Elite Max Outdoor

Figure 13

Peak Reductions for the Hearing Protection Devices

Fort Collins Police Service

Fort Collins, CO

HETA 2002-0131

May 2002

The peak reductions for the protectors measured at both firing ranges. The maximum sound pressure

level for the protected waveform was subtracted from the maximum sound pressure level for the

unprotected waveform. The resulting difference is the peak reduction.
Page 28 Health Hazard Evaluation Report No. 2002-0131-2898

Table 1

Weapons Tested at the Indoor Firing Range

Fort Collins Police Services

Fort Collins, CO

HETA 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

Glock 22 .400 4.5 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 2

Weapons Tested at the Outdoor Firing Range

Fort Collins Police Services

Fort Collins, CO

HETA 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

Glock 27 .400 4.5 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 shotgun

Table 3
Health Hazard Evaluation Report No. 2002-0131-2898 Page 29

Mean Temporary Threshold Shift (TTS) Values

Fort Collins Police Services

Fort Collins, CO

HETA 2002-0131

May 2002

Condition Ear

Tested

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 mm

Revolvers

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 SERVICES

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