Chucri A. Kardous, M.S., P.E.William J. Murphy, Ph.D.

U.S. Department of Health and Human ServicesCenters for Disease Control and Prevention

National Institute for Occupational Safety and HealthCincinnati, Ohio

Exposure of Law Enforcement Officers to Gunfire Noise

Disclaimer: The findings and conclusions in this report are those of the author and do not necessarily represent the views of the National Institute for Occupational Safety and Health

Genesis of a ProblemFederal, State, and Local law-enforcement

agencies requested health hazard evaluations at indoor and outdoor firing ranges to

1. Noise exposures to weapons,

2. Control of weapons’ noise,

3. Hearing damage risk criteria,

4. Adequacy of hearing protection,

5. Lead exposure,

6. Adequacy of ventilation.

Early Challenges Equipment Limitations

Dosimeters, Microphones, Test Fixtures

Measurement Characterization of Impulses

Peak Level, Total Energy, Duration, Number

Contribution of Secondary Sources

Effect of Hearing Protection

Risk Assessment Metrics

MIL-STD 1474D, LAeq8, Auditory Hazard Units

Dosimeters and Sound Level Meters Dosimeters have a maximum response, ~ 145 dB Peak response may be clipped or reduced by

inadequate sampling rate

Typical Sound Level Meters have limited response. Some SLMs record waveforms, most do not. Relevant exposure metrics are not always

provided.

Sample Dosimeter Record

Acoustic Test Fixtures Acoustic Isolation

Dynamic Range

Maximum Level

Ear Canal Length

Flesh Simulation

Anthropometric Shape

Temperature Effects

Impulse Characterization Impulses are characterized be the Peak

level, A-duration, Reverberant decay, Spectrum and Energy.

Peak pressure level

Time durations A-duration is the elapsed time of the first

shockwave .

B-duration is the time for the decay of the peak pressure and reflections to 20 dB below the peak.

B-duration: Different Ranges

Altoona, PA Ft. Collins, CO

Spectral Content

One-third Octave Spectrum (Hz)

31 63 125 250 500 1000 2000 4000 8000

Spe

ctru

m L

evel

(dB

)

80

90

100

110

120

130ShotgunPistol

Contribution of Secondary Sources

Spherical Spreading

Multiple ReflectionsAir Absorption

Contribution of Secondary Sources

Hearing protection

Effectiveness of Level-limiting Earmuffs

Damage Risk Criteria CHABA/Coles

MIL-STD 1474D

Pfander/ Smoorenburg

A-weighted Equivalent Energy

Auditory Hazard Assessment Algorithm for Human

Current Criteria No Unprotected exposures above 140 dB peak

MIL STD 1474D below 177 for single protection.

Measure Peak, B-Duration and Number of Impulses

No Spectral Differentiation

LAeq8 less than 85 dBA.

Measure Waveform, Integrate to estimate LAeq8

Exposure is A-weighted to mimic Middle Ear

AHAAH waveform evaluations less than 500 ARUs.

Measure waveform and process with AHAAH model

Nonlinear annular ligament & Acoustic reflex

NIOSH Analyses Evaluated Human Blast Overpressure Study

LAeq8 performed the best

Evaluated Chinchilla Blast Overpressure Data

LAeq8 performed the best for temporary threshold shift data.

AHAAH performed the best for permanent threshold shift data.

Both Reports will be available soon on the NIOSH survey Reports pages.

www.cdc.gov/niosh/surveyreports

Firing Range Alert published in 2009

Conclusions New instrumentation are needed to

accurately measure and assess impulse noise exposure, including under hearing protection devices.

Standardized test methods to measure impulse noise.

New guidelines and agreed-upon damage risk criteria.

Contact information

Chuck Kardous

National Institute for Occupational Safety and Health4676 Columbia Parkway, C27

Cincinnati, Ohio 45226513-533-8146

ckardous@cdc.gov