Figure 1. The peak sound pressure levels ranged between 145 and 173 dB for a microphone close to the left ear of the shooter.
William J. Murphy -- wjm4@cdc.gov
Gregory A. Flamme
Edward L. Zechmann
Caroline Dektas
Deanna K. Meinke
Michael Stewart
James Lankford
Donald S. Finan
Seleen Collins
Hearing Loss Prevention Team
National Institute for Occupational Safety and Health
4676 Columbia Parkway
Mailstop C-27
Cincinnati OH 45226-1998
Popular Version of Paper 1pNS11
Presented Monday afternoon, October 22, 2012
164th ASA Meeting, Kansas City, Missouri
BANG, BOOM, BOOM, BOOM! Gun users have felt the powerful impact of that noise in their own ears, but what is its impact on the ears of people nearby? And what happens when several guns are shot at the same time?
Hunters, sport shooters, soldiers, and police officers often fire their guns singly and in groups. Most shooters know that the noise from their own guns can damage their hearing, but they might not realize the hazard posed by noise from other guns. Bystanders also might not realize that their hearing is at risk if they are positioned too close to the person shooting.
Researchers at the National Institute for Occupational Safety and Health (NIOSH) and affiliated with the National Hearing Conservation Association decided to work together on this issue. They set up an outdoor range to measure the noise impact (or exposure) from commonly available guns. Eighteen microphones capable of measuring high-level sounds were placed around a single shooter, at distances up to 6 meters, to measure the gunfire. The shooter fired 54 different guns (pistols, shotguns, and rifles) over a flat, grassy field.
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Figure 1. The peak sound pressure levels ranged between 145 and 173 dB for a microphone close to the left ear of the shooter. |
First, researchers used the measurements to determine how far away bystanders must be to keep their hearing safe. This minimum safe distance, called the foul line, was determined for each gun fired. Then the researchers estimated the effects of more than one shooter along a firing line. They combined the data from the single shooter to predict the sound exposure from multiple (2 to 16) shooters, positioned one-half to 2 meters apart, firing the same weapon.
The peak pressure levels at the shooter's left ear were between 145 and 173 decibels. The majority of peak levels were above 159 decibels. The sound pressure measurements showed that when the distance between a single shooter and a bystander doubles, the sound energy falls off by about 5 to 7 decibels. However, as the number of shooters increases, the sound level does not decline as much with extra distance from the firing line. Since the location of the bystander relative to the shooters cannot be controlled, the timing of the gunshots from different shooters was ignored in the sound pressure analysis.
Because noise levels less than 85 decibels of 8-hour-equivalent A-weighted energy are not considered a significant hearing risk, the researchers looked for the distance needed to reach that safe exposure limit for each gun. 1-3 They set the foul line at the point containing 95% of those calculated safe distances. This approach allowed them to determine the minimum safe distance for each of the guns fired.
When each shooter fired 25 shots, the foul line was found to be about 15 meters (about 16 yards, or 49 feet) back from the firing line. For some guns?rifles over .270 caliber with muzzle brakes?the foul line was farther back (see Figure 2). Muzzle brakes are ports on the barrel that reduce recoil and barrel lift during shooting. The ports direct hot gases in the barrel to the sides and backward, thus sending sound toward the firer and other shooters off to the sides.
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The bottom line is that bystanders without hearing protection should not be within 13 meters of the firing line at an uncovered, outdoor firing range. They should wear hearing protection if
References:
1 NIOSH [1998]. Criteria for a recommended standard: occupational exposure to noise. Cincinnati, OH: U.S. Department of Health and Human Services, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health. DHHS (NIOSH) Publication No. 98–126 [http://www.cdc.gov/niosh/docs/98-126/].
2 Murphy WJ [2012]. A case for selecting equivalent A-weighted energy as a damage risk criterion for impulse noise. Masters of Engineering in Acoustics Thesis. State College, PA: The Pennsylvania State University.
3 NIOSH [2012]. In depth survey report: a case for using A-weighted equivalent energy as a damage risk criterion. Cincinnati, OH: U.S. Department of Health and Human Services, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health. EPHB Report No. 350-11a.
4 NIOSH [2003]. Health hazard evaluation report: Fort Collins Police Services?Colorado. By Tubbs RL, Murphy WJ. Cincinnati, OH: U.S. Department of Health and Human Services, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health. NIOSH HETA No. 2002−0131−2898 [http://www.cdc.gov/niosh/hhe/reports/pdfs/2002-0131-2898.pdf].
5 NIOSH [2009]. Preventing occupational exposures to lead and noise at indoor firing ranges. By Kardous C, et al. Cincinnati, OH: U.S. Department of Health and Human Services, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health. DHHS (NIOSH) Publication No. 2009–136 [http://www.cdc.gov/niosh/docs/2009-136/default.html].