Transcript Exposure of Law Enforcement Officers to Gunfire Noise Disclaimer

Exposure of Law Enforcement Officers
to Gunfire Noise
Chucri A. Kardous, M.S., P.E.
William J. Murphy, Ph.D.
U.S. Department of Health and Human Services
Centers for Disease Control and Prevention
National Institute for Occupational Safety and Health
Cincinnati, Ohio
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 Problem
Federal, 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, Aduration, 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
130
Spectrum Level (dB)
Shotgun
Pistol
120
110
100
90
80
31
63
125
250
500 1000 2000 4000 8000
One-third Octave Spectrum (Hz)
Contribution of Secondary Sources
Spherical Spreading
Multiple Reflections
Air 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 Health
4676 Columbia Parkway, C27
Cincinnati, Ohio 45226
513-533-8146
[email protected]