Deanna K. Meinke

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.

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.

Awarding and promoting excellence in hearing loss prevention

Abstract Objective: To describe the rationale and creation of a national award to recognize and promote hearing loss prevention. Design: In 2007, the National Institute for Occupational Safety and Health partnered with the National Hearing Conservation Association to create the Safe-in-Sound Excellence in Hearing Loss Prevention Award™ (www.safeinsound.us). The objectives of this initiative were to recognize organizations that document measurable achievements and to share leading edge information to a broader community. Results: An expert committee developed specific and explicit award evaluation criteria of excellence in hearing loss prevention for organizations in different industrial sectors. The general approach toward award criteria was to incorporate current ‘best practices’ and familiar benchmarks of hearing loss prevention programs. This approach was reviewed publicly. In addition, mechanisms were identified to measure the impact of the award itself. Interest in the award was recorded through the monitoring of the visitor traffic registered by the award web site and is increasing yearly. Specific values and strategies common across award winners are presented. Conclusion: The Safe-in-Sound Award™ has obtained high quality field data; identified practical solutions, disseminated successful strategies to minimize the risk of hearing loss, generated new partnerships, and shared practical solutions with others in the field.

Shooting habits of youth recreational firearm users

Abstract Objective: This study surveyed youth recreational firearm users (YRFUs) regarding shooting habits, reported use of hearing protection devices (HPDs), self-assessed auditory status, and attitudes about firearm noise and hearing loss. Design: A descriptive study using a 28-item survey administered by personal interview. Study sample: Two-hundred and ten youth aged 10 to 17 years responded. Results: Seventy-eight percent of those surveyed began shooting before the age of ten. The majority reported using large caliber firearms capable of rapid fire for both hunting and target practice. Most youths in this study were not aware of, and therefore, were not utilizing HPDs specifically designed for the shooting sports. Ten percent of subjects reported constant tinnitus and 45% notice tinnitus occurred or worsened after shooting. Although the majority of YRFUs reported good or perfect hearing, a small percentage (4–5%) of youth reported having only ʽfair” hearing. Conclusion: YRFUs are putting themselves at risk beginning at a young age for noise-induced hearing loss (NIHL) and tinnitus based on self-reported shooting habits and inconsistent use of HPDs during both target practice and hunting activities. This research highlights the need for early education and intervention efforts to minimize the risk of NIHL in youth.

Distortion product otoacoustic emission level maps from normal and noise-damaged cochleae

Distortion product otoacoustic emission (DPOAE) level mapping may be useful for detecting noise-induced hearing loss (NIHL) early. Employing DPOAE mapping effectively requires knowledge of the optimal mapping parameters to use for detecting noise-induced changes. The goal of this project was to show the map regions that differ most between normal and noise-damaged cochlea to determine the optimal mapping parameters for detecting NIHL. DPOAE level maps were generated for the 2f 1 -f 2 and the 2f 2 -f 1 DPOAEs for 17 normal hearing male subjects and 19 male subjects with NIHL. DPOAEs were measured in DPOAE frequency steps of approximately 44 Hz from 0.5 kHz to 6 kHz using constant f 2 /f 1 ratios incremented in 0.025 steps from 1.025 to 1.5 using both unequal-level (L1,L2 = 65,55 dB sound pressure level (SPL)) and equi-level (L1,L2 = 75,75 dB SPL) stimulus paradigms. Maximal responses for the 2f 2 -f 1 emission at L1,L2 = 65,55 dB SPL were found at lower ratios compared to previous studies. The map regions where NIHL eliminated or reduced DPOAE magnitude were identified. DPOAE level mapping using higher-level, equi-level primaries produced significantly more detectable emissions particularly for the 2f 2 -f 1 emission. The data from this study can be used to optimize DPOAE level mapping parameters for tracking noise-exposed subjects longitudinally.

Reliability of audiometric thresholds obtained with insert earphones when used by certified audiometric technicians

Clinical audiologists and audiometric equipment manufacturers have embraced the clinical use of insert earphones; however, their use in audiometric testing in occupational hearing loss prevention programs has been limited. This study was undertaken to research whether certified audiometric technicians without practical hands-on training could reliably use insert earphones when compared to a clinically experienced audiologist. Hearing thresholds were obtained on 60 human ears by six certified audiometric technicians using insert earphones for the first time. Technician-acquired audiometric thresholds were compared to thresholds obtained under the same conditions by a clinical audiologist experienced in the use of the insert earphones. Statistical analyses of audiometric thresholds were performed to investigate the relationships between audiometric threshold values at each frequency obtained by certified technicians vs. the audiologist. These relationships were examined for the group as a whole as well as when ear tip size and earphone insertion depth varied between the audiologist and the technicians. No significant differences (p > .01) were found between mean group thresholds at any of the test frequencies (500-8000 Hz). Mean group thresholds differed by < 1.2 dB. Pearson Product-Moment correlation (PPMC) coefficients suggested that thresholds obtained by the audiometric technician were highly correlated with those obtained by the audiologist. There were no significant threshold differences (p > .01) even when the audiologist and technicians varied in their selection of ear tip size or in the amount of insertion depth achieved. This study suggests that CAOHC-certified audiometric technicians can reliably use insert earphones without practical training when testing in quiet environments by reading the earphone package directions provided by the manufacturer.

DPOAE level mapping for detecting noise-induced cochlear damage from short-duration music exposures.

Distortion product otoacoustic emission (DPOAE) level mapping provides a comprehensive picture of cochlear responses over a range of DP frequencies and f2 /f1 ratios. We hypothesized that individuals exposed to high-level sound would show changes detectable by DPOAE mapping, but not apparent on a standard DP-gram. Thirteen normal hearing subjects were studied before and after attending music concerts. Pure-tone audiometry (500-8,000 Hz), DP-grams (0.3-10 kHz) at 1.22 ratio, and DPOAE level maps were collected prior to, as soon as possible after, and the day after the concerts. All maps covered the range of 2,000-6,000 Hz in DP frequency and from 1.3 to -1.3 in ratio using equi-level primary tone stimuli. Changes in the pure-tone audiogram were significant (P ≤ 0.01) immediately after the concert at 1,000 Hz, 4,000 Hz, and 6,000 Hz. The DP-gram showed significant differences only at f2 = 4,066 (P = 0.01) and f2 = 4,348 (P = 0.04). The postconcert changes were readily apparent both visually and statistically (P ≤ 0.01) on the mean DP level maps, and remained statistically significantly different from baseline the day after noise exposure although no significant changes from baseline were seen on the DP-gram or audiogram the day after exposure. Although both the DP-gram and audiogram showed recovery by the next day, the average DPOAE level maps remained significantly different from baseline. The mapping data showed changes in the cochlea that were not detected from the DP-gram obtained at a single ratio. DPOAE level mapping provides comprehensive information on subtle cochlear responses, which may offer advantages for studying and tracking noise-induced hearing loss (NIHL).