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 Noise exposures to weapons, Control of weapons’ noise, Hearing damage risk criteria, Adequacy of hearing protection, Lead exposure, 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.
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.
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 Ft. Collins, CO Altoona, PA
Contribution of Secondary Sources Spherical Spreading Multiple Reflections Air Absorption
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
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 firstname.lastname@example.org