The reduction of gunshot noise and auditory risk through the use of firearm suppressors and low-velocity ammunition

Abstract

Objective: This research assessed the reduction of peak levels, equivalent energy and sound power of firearm suppressors. Design: The first study evaluated the effect of three suppressors at four microphone positions around four firearms. The second study assessed the suppressor-related reduction of sound power with a 3 m hemispherical microphone array for two firearms. Results: The suppressors reduced exposures at the ear between 17 and 24 dB peak sound pressure level and reduced the 8 h equivalent A-weighted energy between 9 and 21 dB depending upon the firearm and ammunition. Noise reductions observed for the instructor’s position about a metre behind the shooter were between 20 and 28 dB peak sound pressure level and between 11 and 26 dB L_Aeq,8h. Firearm suppressors reduced the measured sound power levels between 2 and 23 dB. Sound power reductions were greater for the low-velocity ammunition than for the same firearms fired with high-velocity ammunition due to the effect of N-waves produced by a supersonic bullet. Conclusions: Firearm suppressors may reduce noise exposure, and the cumulative exposures of suppressed firearms can still present a significant hearing risk. Therefore, firearm users should always wear hearing protection whenever target shooting or hunting.

Key Words:

• Hearing conservation/hearing loss prevention
• instrumentation
• impulse noise
• psychoacoustics/hearing science
• noise induced hearing loss
• firearm suppressors
• damage risk criteria

Note

Acknowledgements

The findings from this article were presented at the 171st meeting of the Acoustical Society of America on 24 May 2016 in Salt Lake City, UT and at the National Hearing Conservation Association meeting on 21 February 2017 in San Antonio, TX. The authors thank Lieutenant Thomas R. Wanless with the Michigan Department of Natural Resources, Law Enforcement Division, Recreational Safety, Education and Enforcement Section for his support and cooperation with measurements collected at the Rose Lake firing range. Other Michigan DNR officers assisting with the Rose Lake suppressor measurements were Lieutenant Andrew Turner and Sergeant Steve Orange. We thank the NIOSH reviewers Rauno Pääkönen and Robert Maher and the three anonymous reviewers for the International Journal of Audiology to improve the readability and organisation of the manuscript.

Declaration of Interest: No potential conflict of interest was reported by the authors.

The findings and conclusions in this report are those of the authors and do not represent any official policy of the Centers for Disease Control and Prevention or the National Institute for Occupational Safety and Health. Mention of company names and products does not constitute endorsement by the CDC or NIOSH.

Supplementary material available online

Notes

1. Other equivalent energy metrics could have been used, Sound Exposure Level (SEL) or the new L_IAeq,100ms. To convert L_Aeq,8h to SELA, add 44.6 dB. To convert L_Aeq,8h to L_IAeq,100ms, add 54.6. All of the unsuppressed A-durations were less than 0.2 ms, which in turn requires no correction for the A-duration (MIL-STD 1474E, 2015, p 45, Eq. 3a).