Chucri A. Kardous, M.S., P.E.

1
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
2
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.

3
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

4
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.

5
Sample Dosimeter Record
6
Acoustic Test Fixtures

• Acoustic Isolation
• Dynamic Range
• Maximum Level
• Ear Canal Length
• Flesh Simulation
• Anthropometric Shape
• Temperature Effects

7
Impulse Characterization

• Impulses are characterized be the Peak level,
  A-duration, Reverberant decay, Spectrum and
  Energy.

8
Peak pressure level
9
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.

10
B-duration Indoor vs. Outdoor
11
B-duration Pistol vs. Shotgun
12
B-duration Different Ranges
13
Spectral Content
14
Spectral Content
15
Contribution of Secondary Sources
16
Contribution of Secondary Sources
17
Hearing protection
18
Protector Effectiveness
19
Effectiveness of Level-limiting Earmuffs
20
Damage Risk Criteria

• CHABA/Coles
• MIL-STD 1474D
• Pfander/ Smoorenburg
• A-weighted Equivalent Energy
• Auditory Hazard Assessment Algorithm for Human

21
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

22
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

23
Firing Range Alert published in 2009
24
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.

25
Contact information
Chuck Kardous National Institute for
Occupational Safety and Health 4676 Columbia
Parkway, C27 Cincinnati, Ohio 45226 513-533-8146 c
kardous_at_cdc.gov