James E. Lankford

Auditory risk to unprotected bystanders exposed to firearm noise

BACKGROUND What is the risk of hearing loss for someone standing next to a shooter? Friends, spouses, children, and other shooters are often present during hunting and recreational shooting activities, and these bystanders seem likely to underestimate the hazard posed by noise from someone elses firearm. Hunters use hearing protection inconsistently, and there is little reason to expect higher use rates among bystanders. Acoustic characteristics and estimates of auditory risk from gunfire noise next to the shooter were assessed in this study. RESEARCH DESIGN This was a descriptive study of auditory risk at the position of a bystander near a recreational firearm shooter. DATA COLLECTION AND ANALYSIS Recordings of impulses from 15 recreational firearms were obtained 1 m to the left of the shooter outdoors away from reflective surfaces. Recordings were made using a pressure-calibrated 1/4 inch measurement microphone and digitally sampled at 195 kHz (24 bit depth). The acoustic characteristics of these impulses were examined, and auditory risk estimates were obtained using three contemporary damage-risk criteria (DRCs) for unprotected listeners. RESULTS Instantaneous peak levels at the bystander location ranged between 149 and 167 dB SPL, and 8 hr equivalent continuous levels (LeqA8) ranged between 64 and 83 dB SPL. Poor agreement was obtained across the three DRCs, and the DRC that was most conservative varied with the firearm. The most conservative DRC for each firearm permitted no unprotected exposures to most rifle impulses and fewer than 10 exposures to impulses from most shotguns and the single handgun included in this study. More unprotected exposures were permitted for the guns with smaller cartridges and longer barrel length. CONCLUSIONS None of the recreational firearms included in this study produced sound levels that would be considered safe for all unprotected listeners. The DRCs revealed that only a few of the small-caliber rifles and the smaller-gauge shotguns permitted more than a few shots for the average unprotected listener. This finding is important for professionals involved in hearing health care and the shooting sports because laypersons are likely to consider the bystander location to be inherently less risky because it is farther from the gun than the shooter.

Measuring recreational firearm noise.

Recreational use of firearms in the United States is commonplace. There are 28 × 106 Americans who consider themselves hunters and 13 × 106 went hunting in 2000. Participation in the shooting sports, without the use of properly worn hearing protection, exposes the involved persons to high levels of impulsive noise which may cause hearing loss and/or tinnitus (ear ringing). The present study was initiated to gain a better understanding of the noise exposure created by contemporary firearms using state of the art instrumentation and to ultimately increase our knowledge and awareness of this unique noise hazard. The sound pressure signal created by recreational firearms as used in hunting or target practice is characterized by a high‐frequency, short duration impulsive noise. This signal is perceived by the human ear as one single, loud impulse or “shot.” However, when the firearm sound level is measured with microphones capable of sampling wide frequency ranges and combined with high‐speed data acquisition ...

Auditory risk estimates for youth target shooting

Abstract Objective: To characterize the impulse noise exposure and auditory risk for youth recreational firearm users engaged in outdoor target shooting events. The youth shooting positions are typically standing or sitting at a table, which places the firearm closer to the ground or reflective surface when compared to adult shooters. Design: Acoustic characteristics were examined and the auditory risk estimates were evaluated using contemporary damage-risk criteria for unprotected adult listeners and the 120-dB peak limit suggested by the World Health Organization (1999) for children. Study sample: Impulses were generated by 26 firearm/ammunition configurations representing rifles, shotguns, and pistols used by youth. Measurements were obtained relative to a youth shooters left ear. Results: All firearms generated peak levels that exceeded the 120 dB peak limit suggested by the WHO for children. In general, shooting from the seated position over a tabletop increases the peak levels, LAeq8 and reduces the unprotected maximum permissible exposures (MPEs) for both rifles and pistols. Pistols pose the greatest auditory risk when fired over a tabletop. Conclusion: Youth should utilize smaller caliber weapons, preferably from the standing position, and always wear hearing protection whenever engaging in shooting activities to reduce the risk for auditory damage.

Measurement of impulse peak insertion loss for four hearing protection devices in field conditions

Abstract Objective: In 2009, the U.S. Environmental Protection Agency (EPA) proposed an impulse noise reduction rating (NRR) for hearing protection devices based upon the impulse peak insertion loss (IPIL) methods in the ANSI S12.42-2010 standard. This study tests the ANSI S12.42 methods with a range of hearing protection devices measured in field conditions. Design: The method utilizes an acoustic test fixture and three ranges for impulse levels: 130–134, 148–152, and 166–170 dB peak SPL. For this study, four different models of hearing protectors were tested: Bilsom 707 Impact II electronic earmuff, E·A·R Pod Express, E·A·R Combat Arms version 4, and the Etymotic Research, Inc. Electronic BlastPLG™ EB1. Study sample: Five samples of each protector were fitted on the fixture or inserted in the fixtures ear canal five times for each impulse level. Impulses were generated by a 0.223 caliber rifle. Results: The average IPILs increased with peak pressure and ranged between 20 and 38 dB. For some protectors, significant differences were observed across protector examples of the same model, and across insertions. Conclusions: The EPAs proposed methods provide consistent and reproducible results. The proposed impulse NRR rating should utilize the minimum and maximum protection percentiles as determined by the ANSI S12.42-2010 methods.

Otolithic Evoked Potentials: A New Technique for Vestibular Studies

Evoked potentials, EP, are time-locked electroencephalographic voltages bearing temporal relation to an excitatory stimulus, recorded by scalp electrodes and an averaging computer. This paper reports the first apparent recording of otolithic EP. Thirty-nine students on a tilt table underwent head drop conditions stimulatory to the otolithic maculas. The wave-form obtained resembles neither auditory, visual, somatosensory or semicircular EP. Otolithic EP provide heretofore unavailable insights into the electrophysiology of the macular generators, VIII nerve, and related central processing.

Impulse noise generated by starter pistols

Abstract Objective: This study describes signals generated by .22 and .32 caliber starter pistols in the context of noise-induced hearing loss risk for sports officials and athletes. Design: Acoustic comparison of impulses generated from typical .22 and .32 caliber starter pistols firing blanks were made to impulses generated from comparable firearms firing both blanks and live rounds. Acoustic characteristics are described in terms of directionality and distance from the shooter in a simulated outdoor running track. Metrics include peak sound pressure levels (SPL), A-weighted equivalent 8-hour level (LeqA8), and maximum permissible number of individual shots, or maximum permissible exposures (MPE) for the unprotected ear. Results: Starter pistols produce peak SPLs above 140 dB. The numbers of MPEs are as few as five for the .22-caliber starter pistol, and somewhat higher (≤ 25) for the .32-caliber pistol. Conclusion: The impulsive sounds produced by starter pistols correspond to MPE numbers that are unacceptably small for unprotected officials and others in the immediate vicinity of the shooter. At the distances included in this study, the risk to athletes appears to be low (when referencing exposure criteria for adults), but the sound associated with the starter pistol will contribute to the athletes overall noise exposure.

Ambient noise levels in mobile audiometric testing facilities: compliance with industry standards.

Excessive ambient noise levels in audiometric test booths may elevate and therefore invalidate hearing thresholds of employees included in a hearing conservation program. This study was conducted to determine if a sample of mobile test vans and trailers operating in the Midwest met the 1983 Occupational Safety and Health Administration (OSHA) maximum permissible ambient noise levels (MPANLs), the MPANLs in the American National Standards Institute (ANSI) S3.1–1991, and the suggested National Hearing Conservation Association (NHCA) values. Ambient noise levels were measured in 13 audiometric test booths contained in 12 different industrial mobile test vans and trailers operating in the Midwest. Results indicated that all 13 (100%) of the industrial mobile test vans and trailers evaluated complied with 1983 OSHA permissible levels and the NHCA 1996 recommended levels. With regard to the 1991 ANSI MPANLs, 5 (38%) of the 13 booths were in compliance at all frequencies. Those that failed did so at 125, 250, and 500 Hz. It appears that the NHCA levels need to be used for all hearing conservation programs with respect to compliance for noise levels in mobile audiometric test booths.

Noise exposure profiles for small-caliber firearms from 1.5 to 6 meters

Small caliber firearms (rifles, pistols and shotguns) are commonly used at outdoor firing ranges for training in shooting skills, job qualification and for recreation. Firearm noise from fifty-four weapons was measured at an outdoor range in the near field (6 meters and closer) of the weapons using a radial array of 18 microphones centered on the shooter’s head. Each weapon was fired five times and the microphone array was sampled at 200 kHz with at least 16-bit resolution. Peak sound pressure levels and damage risk criteria (e.g. MIL-STD 1474D, 8-hour Equivalent A-weighted Level (LAeq8), and Auditory Hazard Assessment Algorithm for Humans (AHAAH)) were computed for each microphone and compared across weapon type, caliber and load. The acoustic propagation from the muzzle to the microphone was modeled using a simple image source over a reflecting plane. The impedance of the ground was estimated from the observed data and was used to compare the measured waveforms with the estimated waveforms. These data w...

Prevention of Noise-Induced Hearing Loss from Recreational Firearms

In the United States and other parts of the world, recreational firearm shooting is a popular sport that puts the hearing of the shooter at risk. Peak sound pressure levels (SPLs) from firearms range from ∼140 to 175 dB. The majority of recreational firearms (excluding small-caliber 0.17 and 0.22 rifles and air rifles) generate between 150 and 165 dB peak SPLs. High-intensity impulse sounds will permanently damage delicate cochlear structures, and thus individuals who shoot firearms are at a higher risk of bilateral, high-frequency, noise-induced hearing loss (NIHL) than peer groups who do not shoot. In this article, we describe several factors that influence the risk of NIHL including the use of a muzzle brake, the number of shots fired, the distance between shooters, the shooting environment, the choice of ammunition, the use of a suppressor, and hearing protection fit and use. Prevention strategies that address these factors and recommendations for specialized hearing protectors designed for shooting sports are offered. Partnerships are needed between the hearing health community, shooting sport groups, and wildlife conservation organizations to develop and disseminate accurate information and promote organizational resources that support hearing loss prevention efforts.

The reduction of gunshot noise and auditory risk through the use of firearm suppressors

Law enforcement, security, and military personnel train with small-caliber firearms that present a significant risk of noise induced hearing loss for the operator and range instructors. Measurements of three rifles and one pistol equipped with suppressors were conducted at an outdoor firing range using subsonic and supersonic ammunition. Suppressed and unsuppressed recordings were analyzed. Microphones were located to the left of the muzzle, to the right and left of the shooter’s head, and one meter behind the shooter’s head at the nominal instructor’s position. Recordings were collected with a National Instruments PXI 1082 chassis with an NI 4499 data acquisition board at a 200 kHz sampling rate. Analysis of the peak sound pressure levels (dB SPL) and 8-h equivalent A-weighted energy (LAeq8) were conducted. The suppressors reduced the peak between 15 and 25 dB SPL and the LAeq8 between 8 and 28 dB. Reduced noise levels at the source will reduce auditory risk but do not necessarily eliminate the need for ...