February 1, 2013 Features

Bigger Caliber, Bigger Boom

Skeet and trap shooting. Target practice. Cowboy action shooting. Wild game hunting. These are popular leisure-time activities in America, where the citizenry owns more firearms than in any other country in the world. An estimated 70 million Americans own more than 270 million firearms, according to a 2007 issue of Small Arms Survey. And several states have hunting laws allowing children as young as age 10 to hunt when accompanied by an adult family member.
But even as firearms provide people with recreational opportunities, they also can cause significant noise-induced hearing loss with associated tinnitus unless shooters wear proper hearing protection. According to recent studies, relatively few of them do.

Bigger Caliber, Bigger Boom

Recreational firearm users' shooting habits may increase their risk of acquiring noise-induced hearing loss. Several studies suggest many shooters put themselves at risk by firing large-bore guns numerous times per year without proper hearing protection. I conducted several studies, involving more than 1,000 firearm users, with colleagues at Central Michigan University. About 80 percent of participants reported never using hearing protection while hunting, and approximately 40 to 50 percent reported inconsistent use of protective devices during target practice.
When a user shoots rapid-fire (semi-automatic) guns, the ear has less time to recover between shots. Shooting in reverberant environments such as indoor firing ranges and hunting blinds increases the overall peak sound pressure level and duration of firearm noise. And shooting in a group—a frequent occurrence at firing ranges and on hunting expeditions—means exposure to multiple shots from the shooter's firearm and from those nearby. All these factors combine to increase the auditory hazard and risk of damage to the ear.

Guns are loud!

Firearm noise can cause permanent hearing loss because the peak sound pressure level of the impulse noise generated by a firearm is dangerously high. Recent firearm noise studies conducted by William Murphy and others have measured sound pressure levels of popular recreational firearms at 160 dB to 170dB+. A 2011 study by Gregory Flamme and colleagues found exposure levels can be hazardously high not only for the shooter, but also for bystanders.

The type of hearing loss caused by firearm noise is also an important consideration. High-level impulse noise can lead to sudden hearing loss, the result of immediate physical damage to several inner-ear structures including inner and outer hair cells, pillar cells, the stria vascularis, and capillaries. This damage is different from gradual hearing loss caused by prolonged exposure to high-level, steady-state noise, which results primarily in outer hair cell damage over time.

The intensity of firearm impulse noise is directly related to the type of firearm. A good rule of thumb is: "The bigger the bore (larger calibers), the bigger the cartridge (more gunpowder), the shorter the barrel (closer to ears), the bigger the boom." As noted, firing a gun in a reverberant environment—such as a hunting blind or enclosed shooting range—significantly increases the duration of the resulting impulse noise, increasing auditory risk. The graph on page 52 (top) details examples of impulse noise generated by a large-bore rifle fired in an open field, as opposed to the inside of a hunting blind. Even to the untrained eye, the difference is striking.

The left ear (in right-handed shooters) often suffers more damage than the right ear because it is closer to, and directly in line with, the muzzle of the firearm. Also, the right ear is partially protected by head shadow. Such hearing loss (see the audiogram on page 52) can be difficult to remediate with amplification because of the steeply sloping audiometric configuration and the severity of hearing loss in the high-frequency range. The affected person may be unaware of the hearing loss due to normal hearing in the lower frequency range, and may accuse others of mumbling or not speaking loud enough. In fact, the person's damaged ears are filtering out high-frequency consonant sounds that contribute significantly to speech clarity.

A recent study by Deanna Meinke and her colleagues found that young shooters may be at increased risk of noise-induced hearing loss from firearm use because of their shooting positions during target practice and their use of shorter guns—with muzzles closer to the ear—specifically designed for smaller shooters.

Customized intervention

Clinical audiologists can reduce their patients' risk of hearing loss from firearms by identifying people at risk, providing counseling about the hearing hazards of firearm noise (see the list at left for tips), and recommending appropriate hearing protection for specific shooting activities.

When probing the case history of a recreational firearm user—an important first step—audiologists may want to ask these questions to uncover crucial information:

  • What caliber of rifle, or gauge of shotgun, do you shoot? Most hunting rifles and shotguns generate dangerously high levels of impulse noise, and muzzle brakes and magnums increase noise levels significantly. Almost any gun except BB and pellet guns can be hazardous to hearing, especially if it is capable of rapid fire and is fired in a reverberant environment. Stress the consistent use of appropriate hearing protection.
  • How many unprotected shots are you exposed to in an average year (for each gun)? You should recommend "no unprotected exposures" to firearm noise from any gun (except BB and pellet guns). Discuss with your patient the possibilities of gradual and sudden hearing loss due to acoustic trauma.
  • Do you ever hunt in groups? Waterfowlers are a high-risk group because they often hunt in groups, may shoot multiple shots in a single hunt, and almost exclusively use rapid-fire, large-bore firearms. Caution patients about multiple shots from big-bore guns in a short period of time, and ensure they wear hearing protection.
  • Do you ever hunt in a blind? Discuss the effects of reverberant environments: higher sound pressure level and longer duration of impulse, which lead to an increased risk of hearing loss. Stress the importance of moving the gun barrel outside of the blind before firing, and always wearing
    protective devices.
  • Do you ever fire a handgun? Any caliber of handgun generates hazardous levels of impulse, which increase risk because the short barrel's muzzle is closer to the ears. Big-bore pistols (for example the .357, .44 magnum and .50), especially semi-automatics, pose the greatest danger to hearing. Recommend double hearing protection when firing big-bore handguns.
  • Do you always wear hearing protection when you target practice? Explain the benefits beyond hearing protection: Hearing protective devices can also improve accuracy because the reduced blast to the shooter's ears causes less flinching. Counsel patients about what is appropriate and available; provide websites or product information.
  • Do you wear hearing protection every time you hunt? Recommend electronic hearing protection devices, or a nonlinear device.

Many recreational firearm users are unaware of commercially available hearing protection specifically designed for use in the shooting sports. Electronic devices provide mild amplification to allow the shooter to hear soft and moderate-level sounds, but employ electronic peak clipping and passive attenuation to protect the shooter's hearing when the gun is fired. Shooters should use electronic devices to protect against high-level firearm noise when they also need to hear enough to be aware of their surroundings—during, for example, firing range instruction. Styles include circumaural headsets, custom-made in-the-ear devices, behind-the-ear devices (preferably with custom molds) and one-size-fits-all insert plugs.

Nonlinear hearing protective devices are a less-expensive alternative to electronic devices and are engineered to allow soft sounds to pass while providing attenuation of intense impulse noise. Nonlinear devices provide increased attenuation as the peak sound pressure level of the impulse increases. Conventional insert plugs in conjunction with circumaural muffs (especially those utilizing a twin cup design) should be used when firing big-bore rifles, pistols or shotguns during target practice when audibility of conversation and environmental sounds is not necessary. Double protecting with inserts and circumaural muffs provides the greatest amount of protection for the shooter.

Michael Stewart, PhD, is a professor of audiology at Central Michigan University. His research interests include industrial and recreational hearing conservation. He is an affiliate of ASHA Special Interest Group 8, Public Health Issues Related to Hearing and Balance. stewa1mg@cmich.edu.

cite as: Stewart, M. (2013, February 01). Bigger Caliber, Bigger Boom. The ASHA Leader.

Tips for Shooters to Reduce Hearing Loss Risks

  • Keep disposable hearing protective devices on hand.
  • Double-protect when using large-caliber guns or when many shots will be fired.
  • Consider smaller calibers (for example, a 7mm-08 rifle instead of a .30-.06, or a 20-gauge shotgun rather than 12-gauge).
  • Choose a single-shot or bolt-action over a semi-automatic weapon.
  • Avoid shooting in groups, especially at indoor or enclosed firing ranges.
  • Choose firearms with longer barrels (farther from the ear).
  • Consider using low-recoil (low-noise) ammo.
  • When hunting in a blind, make sure the muzzle is outside the blind before pulling the trigger.
  • Use nonlinear or appropriate electronic ear protection for hunting.


Resources

Several educational tools for clinical or classroom settings, effective in counseling recreational firearm users and motivating them to protect themselves from firearm noise, are available on the National Hearing Conservation Association website. These include:

  • National Institute for Occupational Safety and Health hearing loss simulator.
  • A tinnitus simulator.
  • Posters and slides of inner-ear structures damaged by excessive firearm noise.
  • A brochure on hearing protection devices for shooting sports.
  • A hunting and hearing video.
  • Links to other educational resources.


Sources

Coles, R. R. A., Garinther, G. R., Rice, C. G., & Hodge, D. C. (1967). Criteria for assessing hearing damage risk from impulse-noise exposure. Technical Memorandum 13–67. In: US Army Human Engineering Laboratories.

Flamme, G. A., Wong, A., Liebe, K., & Lynd, J. (2009). Estimates of the auditory risk from outdoor impulse noise II: Civilian firearms. Noise Health, 11, 231–242.

Flamme, G. E., Stewart, M., Meinke, D., Lankford, J., & Rasmussen, P. (2011). Auditory risk to unprotected bystanders exposed to firearm noise. Journal of American Academy of Audiology, 22, 93–103.

Henderson, D., Bielefeld, E. C., Harris, K. C., and Hu, B. H. (2006). The role of oxidative stress in noise-induced hearing loss, Ear and Hearing, 27(1), 1–19.

Jütersonke, O., Krause, K., & Muggah, R. (2007) Guns and the city: Urban landscapes of armed violence in Small Arms Survey. Graduate Institute of International Studies, Cambridge University Press, Geneva, Switzerland, p. 47.

Kardous, C. A., & Murphy, W. J. (2010). Noise control solutions for indoor firing ranges. Noise Control Engineering Journal, 58(4), 345–356.

Meinke, D. K., Finan, D. S., Soendergaard, J., Flamme, G. A., Murphy, W. J., Lankford, J. E. and Stewart, M. (In press). Impulse noise generated by starter pistols. International Journal of Audiology.

Meinke D. K., Lankford J. E., Flamme G. A., Stewart, M., Finan, D. S., Soendergaard J., Murphy W. J., & Jerome, T.W. (In press). Auditory risk estimates for youth target shooting. Abstracts of the National Hearing Conservation Association 38th Annual Convention, St. Petersburg, FL. NHCA Spectrum.

Murphy, W. J., & Tubbs, R. L. (2007). Assessment of noise exposure for indoor and outdoor firing ranges. Journal of Occupational and Environmental Hygiene, 4(9), 688–697.

Murphy, W. J., Flamme, G. A., Meinke, D. K., Sondergaard, J., Finan, D. S., Lankford, J. E., Khan, A., & Stewart, M. (2012). Measurement of impulse peak insertion loss for four hearing protection devices. International Journal of Audiology, 51, S31–S42.

Nakayama, J. R., Stewart, M., & Lehman, M. E. (2008). Demographic risk patterns and shooting behaviors of female recreational firearm users: Abstract. NHCA Spectrum, 25(1), 29.

National Shooting Sports Foundation (2010). Families afield: An initiative for the future of hunting. Available from: www.familiesafield.org/pdf/familiesafield_report.pdf [PDF].

Smoorenburg, G. (2003). Risk of hearing loss from exposure to impulse sounds. Report No. RTO-TR-017. Brussels, Belgium:North Atlantic Treaty Organization (NATO)

Stewart, M., Borer, S., & Lehman, M. E. (2009). Shooting habits of waterfowl hunters. Noise and Health, 11(42), 8–13.

Stewart, M., Foley, L., Lehman, M. E., & Gerlach, A. (2011). Risks faced by recreational firearm users. Audiology Today, March–April, 38–48.

Stewart, M., Flamme, G. A., Meinke, D. K., Lankford, J. E., Sondergaard, J., Finan, D. S., Murphy, W. J., Khan, A., & Lehman, M. E. (2011). Firearm noise in a hunting blind. Abstracts of the National Hearing Conservation Association 36th Annual Convention. Mesa, AZ. NHCA Spectrum, Vol. 28., supplement II. p.47.

Wagner, A., Stewart, M., & Lehman, M. E. (2006) Risk patterns and shooting habits of recreational firearm users: Abstract. NHCA Spectrum, 23(1), 28.

Weissler, P. G., & Kobal, M. T. (1974) Noise of police firearms. Journal of the Acoustical Society of America, 56(5), 1515–1522.



  

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