This report extends the development of normative standards for estimating occupational hearing loss using data from the United States National Health and Nutrition Examination Survey (NHANES) conducted by the National Center for Health Statistics. A proposed revision of the International Organization for Standardization (ISO) 1999:2013 standard ("Acoustics-Estimation on noise-induced hearing loss") uses a linear interpolation of hearing threshold data to estimate the 25th and 75th percentiles for men and women at 500, 1000, 2000, 3000, 4000, 6000, and 8000 Hz. This paper revisits the NHANES data to provide these estimates, avoiding other types of interpolations that could misrepresent the population data.

For more than 50 years, the National Institute for Occupational Safety and Health (NIOSH), part of the United States (U.S.) Centers for Disease Control and Prevention (CDC), has been actively working to reduce the effects of noise and ototoxic chemicals on worker hearing. NIOSH has pioneered basic and applied research on occupational hearing risks and preventive measures. The Institute has issued recommendations and promoted effective interventions through mechanisms ranging from formal criteria documents to blogs and social media. NIOSH has conducted surveillance and published statistics to guide policy and target prevention efforts. Over the past five decades, substantial progress has been made in raising awareness of noise as a hazard, reducing the risk of occupational hearing loss, improving the use of hearing protection, and advancing measurement and control technologies. Nevertheless, noise remains a prevalent workplace hazard and occupational hearing loss is still one of the most common work-related conditions. NIOSH continues to work toward preventing the effects of noise and ototoxicants at work and has many resources to assist audiologists in their hearing loss prevention efforts. © 2023 Thieme Medical Publishers, Inc.. All rights reserved.

The National Institute for Occupational Safety and Health (NIOSH) evaluated continuous and impact noise exposures and hearing loss among workers at a hammer forge company. Full-shift personal noise exposure measurements were collected on forge workers across 15 different job titles; impact noise characteristics and one-third octave band noise levels were assessed at the forge hammers; and 4,750 historic audiometric test records for 483 workers were evaluated for hearing loss trends. Nearly all workers' noise exposures exceeded regulatory and/or recommended exposure limits. Workers working in jobs at or near the hammers had full-shift time-weighted average noise exposures above 100 decibels, A-weighted. Impact noise at the hammers reached up to 148 decibels. Analysis of audiometric test records showed that 82% of workers had experienced a significant threshold shift, as defined by NIOSH, and 63% had experienced a standard threshold shift, as defined by the Occupational Safety and Health Administration (OSHA). All workers with an OSHA standard threshold shift had a preceding NIOSH significant threshold shift which occurred, on average, about 7 years prior. This evaluation highlights forge workers' exposures to high levels of noise, including impact noise, and how their hearing worsened with age and length of employment. © 2023. Thieme. All rights reserved. Thieme Medical Publishers, Inc.

Workers rely on hearing protection devices to prevent occupational noise-induced hearing loss. This study aimed to evaluate changes in attenuation over time for properly fit devices when worn by workers exposed to hazardous noise. Earplug fit testing was accomplished on 30 workers at a brewery facility with three types of foam and three types of premolded earplugs. The personal attenuation ratings (PARs) were measured before and after a 2-hour work period while exposed to hazardous noise levels. The minimum acceptable initial PAR was 15 dB. Average decreases in PAR ranged from -0.7 to -2.6 dB across all six earplug types. Significant changes in PAR were observed for the Foam-1 (p = 0.009) and Premold-3 (p = 0.004) earplugs. A linear mixed regression model using HPD type and study year as fixed effects and subject as random effect was not significant for either fixed effect (α = 0.05). Ninety-five percent of the final PAR measurements maintained the target attenuation of 15 dB. Properly fitting earplugs can be effective at reducing worker's noise exposures over time. The potential for a decrease in attenuation during the work shift should be considered when training workers and establishing the adequacy of protection from hazardous noise exposures. © 2023 Thieme Medical Publishers, Inc.. All rights reserved.

OBJECTIVES: Studies have shown that in addition to energy, kurtosis plays an important role in the assessment of hearing loss caused by complex noise. The objective of this study was to investigate how to use noise recordings and audiometry collected from workers in industrial environments to find an optimal kurtosis-adjusted algorithm to better evaluate hearing loss caused by both continuous noise and complex noise. DESIGN: In this study, the combined effects of energy and kurtosis on noise-induced hearing loss (NIHL) were investigated using data collected from 2601 Chinese workers exposed to various industrial noises. The cohort was divided into three subgroups based on three kurtosis (β) levels (K 1 : 3 ≤ β ≤ 10, K 2 : 10 <β ≤ 50, and K 3 : β > 50). Noise-induced permanent threshold shift at test frequencies 3, 4, and 6 kHz (NIPTS 346 ) was used as the indicator of NIHL. Predicted NIPTS 346 was calculated using the ISO 1999 model for each participant, and the actual NIPTS was obtained by correcting for age and sex using non-noise-exposed Chinese workers (n = 1297). A kurtosis-adjusted A-weighted sound pressure level normalized to a nominal 8-hour working day (L Aeq,8h ) was developed based on the kurtosis categorized group data sets using multiple linear regression. Using the NIPTS 346 and the L Aeq.8h metric, a dose-response relationship for three kurtosis groups was constructed, and the combined effect of noise level and kurtosis on NIHL was investigated. RESULTS: An optimal kurtosis-adjusted L Aeq,8h formula with a kurtosis adjustment coefficient of 6.5 was established by using the worker data. The kurtosis-adjusted L Aeq,8h better estimated hearing loss caused by various complex noises. The analysis of the dose-response relationships among the three kurtosis groups showed that the NIPTS of K 2 and K 3 groups was significantly higher than that of K 1 group in the range of 70 dBA ≤ L Aeq,8h < 85 dBA. For 85 dBA ≤ L Aeq,8h ≤ 95 dBA, the NIPTS 346 of the three groups showed an obvious K 3 > K 2 > K 1 . For L Aeq,8h >95 dBA, the NIPTS 346 of the K 2 group tended to be consistent with that of the K 1 group, while the NIPTS 346 of the K 3 group was significantly larger than that of the K 1 and K 2 groups. When L Aeq,8h is below 70 dBA, neither continuous noise nor complex noise produced significant NIPTS 346 . CONCLUSIONS: Because non-Gaussian complex noise is ubiquitous in many industries, the temporal characteristics of noise (i.e., kurtosis) must be taken into account in evaluating occupational NIHL. A kurtosis-adjusted L Aeq,8h with an adjustment coefficient of 6.5 allows a more accurate prediction of high-frequency NIHL. Relying on a single value (i.e., 85 dBA) as a recommended exposure limit does not appear to be sufficient to protect the hearing of workers exposed to complex noise.

Middle ear muscle contractions (MEMCs) are most commonly considered a response to high-level acoustic stimuli. However, MEMCs have also been observed in the absence of sound, either as a response to somatosensory stimulation or in concert with other motor activity. The relationship between MEMCs and non-acoustic sources is unclear. This study examined associations between measures of voluntary unilateral eye closure and impedance-based measures indicative of middle ear muscle activity while controlling for demographic and clinical factors in a large group of participants (N=190) with present clinical acoustic reflexes and no evidence of auditory dysfunction. Participants were instructed to voluntarily close the eye ipsilateral to the ear canal containing a detection probe at three levels of effort. Orbicularis oculi muscle activity was measured using surface electromyography. Middle ear muscle activity was inferred from changes in total energy reflected in the ear canal using a filtered (0.2 to 8 kHz) click train. Results revealed that middle ear muscle activity was positively associated with eye muscle activity. MEMC occurrence rates for eye closure observed in this study were generally higher than previously published rates for high-level brief acoustic stimuli in the same participant pool suggesting that motor activity may be a more reliable elicitor of MEMCs than acoustic stimuli. These results suggest motor activity can serve as a confounding factor for auditory exposure studies as well as complicate the interpretation of any impulsive noise damage risk criteria that assume MEMCs serve as a consistent, uniform protective factor. The mechanism linking eye and middle ear muscle activity is not understood and is an avenue for future research.

Occupational and recreational acoustic noise exposure is known to cause permanent hearing damage and reduced quality of life, which indicates the importance of noise controls including hearing protection devices (HPDs) in situations where high noise levels exist. While HPDs can provide adequate protection for many noise exposures, it is often a challenge to properly train HPD users and maintain compliance with usage guidelines. HPD fit-testing systems are commercially available to ensure proper attenuation is achieved, but they often require specific facilities designed for hearing testing (e.g., a quiet room or an audiometric booth) or special equipment (e.g., modified HPDs designed specifically for fit testing). In this study, we explored using visual information from a photograph of an HPD inserted into the ear to estimate hearing protector attenuation. Our dataset consists of 960 unique photographs from four types of hearing protectors across 160 individuals. We achieved 73% classification accuracy in predicting if the fit was greater or less than the median measured attenuation (29 dB at 1 kHz) using a deep neural network. Ultimately, the fit-test technique developed in this research could be used for training as well as for automated compliance monitoring in noisy environments to prevent hearing loss. © 2021 Author(s).

Hearing loss due to high-level noise exposure remains a significant occupational health hazard that continues to increase in prevalence in industrial and military work environments despite government-mandated hearing conservation programs. The underlying assumption in current noise standards is that hearing loss over an 8-hour A-weighted equivalent continuous exposure level (often abbreviated as LAeq,8h) can be predicted by the equal energy hypothesis. This method assumes equivalent effects on hearing for a 3 dB increase or decrease in exposure intensity with a halving or doubling of exposure duration, respectively. In other words, equal amounts of hearing loss are expected regardless of how the noise exposure levels have occurred over time. The equal energy hypothesis is the basis of most noise standards and guidelines in the United States and internationally. Although this approach is generally considered appropriate for steady-state noise, it is not adequate for complex noise (Hamernik and Qiu, 2001). Some Background: Consensus has been lacking on the use of simple energy averaging to predict the effects of noise on hearing. In the United States, some government agencies use a modification consisting of a 5 dB trading relationship, whereas others use the internationally accepted 3 dB rule. Use of the 3 dB rule has been recommended by the National Institute of Occupational Safety and Health (NIOSH) since 1998, which recommendation has been validated based on additional, more recent research (Suter, 2017). Another issue with using a simple energy metric is the inability of sound energy averaging to account for the increased hazard of noise with impulsive components. Although intermittences in noise exposures may have been considered helpful to hearing in the past, this no longer seems to be the case with complex noise exposures, which are found frequently in manufacturing industries. Because the additional hazards from impulsive noise were already recognized, the earliest version of the International Standards Organization (ISO) 1999 standard (1971) suggested a 10 dB adjustment to the average exposure level when impulsive noise is superimposed on a background of continuous noise. At a 1981 meeting of noise experts in Southampton, UK, some participants proposed keeping the 10 dB adjustment, with others wanting to change it to 5 dB, and a third group proposing just using simple energy averaging (Personal Observation, Suter, 1981). The resulting report concluded that hearing conservation programs should be initiated at a 5 dB lower level as a precautionary measure whenever there are impulsive noise conditions (von Gierke et al., 1981). Consequently, the 1990 version of the standard contained a note suggesting a 5 dB correction but even that disappeared without explanation in later iterations of the ISO 1999 standard (2013). Since then, more evidence has emerged regarding the hazard to hearing from complex noise environments relative to continuous noise environments. Complex or Non-Gaussian Noise: A steady-state, continuous noise exposure typically has a normal or Gaussian amplitude distribution (see background in Figure 1). However, the temporal pattern of noise exposures often varies significantly in work environments. A complex noise environment may be described as Gaussian background noise punctuated by a series of high-level transient noises resulting in a non-Gaussian distribution (as shown in Figure 1). These transients can be brief, high-level noise bursts, impulses, or impacts with varying interpeak intervals, peak levels, and peak durations. Industrial workers are often exposed to complex noise environments. Examples include jobs involving maintenance work, metalworking, and power tools, such as impact wrenches and nail guns. Over the past several decades, a number of studies using animal models have shown that exposure to complex noise produces more hearing damage than an equivalent energy exposure to continuous Gaussian noise, in terms of both behavioral hearing loss and sensory cell loss (e.g., Lei et al., 1994). These results, along with similar findings from human data in industrial settings, have demonstrated that although acoustic energy and exposure duration are necessary metrics, they are not sufficient to evaluate the hearing loss from complex non-Gaussian noise exposure. Because many noise environments can be characterized by the same equivalent energy and spectra, a metric that describes the temporal structure of an exposure would be a useful adjunct to the equivalent sound pressure level metric. The kurtosis of a sample distribution is such a metric.

OBJECTIVES: To evaluate (1) the accuracy of the International Organization for Standardization (ISO) standard ISO 1999 [(2013), International Organization for Standardization, Geneva, Switzerland] predictions of noise-induced permanent threshold shift (NIPTS) in workers exposed to various types of high-intensity noise levels, and (2) the role of the kurtosis metric in assessing noise-induced hearing loss (NIHL). DESIGN: Audiometric and shift-long noise exposure data were acquired from a population (N = 2,333) of screened workers from 34 industries in China. The entire cohort was exclusively divided into subgroups based on four noise exposure levels (85 ≤ LAeq.8h < 88, 88 ≤ LAeq.8h < 91, 91 ≤ LAeq.8h < 94, and 94 ≤ LAeq.8h ≤ 100 dBA), two exposure durations (D ≤ 10 years and D > 10 years), and four kurtosis categories (Gaussian, low-, medium-, and high-kurtosis). Predicted NIPTS was calculated using the ISO 1999 model for each participant and the actual measured NIPTS was corrected for age and sex also using ISO 1999. The prediction accuracy of the ISO 1999 model was evaluated by comparing the NIPTS predicted by ISO 1999 with the actual NIPTS. The relation between kurtosis and NIPTS was also investigated. RESULTS: Overall, using the average NIPTS value across the four audiometric test frequencies (2, 3, 4, and 6 kHz), the ISO 1999 predictions significantly (p < 0.001) underestimated the NIPTS by 7.5 dB on average in participants exposed to Gaussian noise and by 13.6 dB on average in participants exposed to non-Gaussian noise with high kurtosis. The extent of the underestimation of NIPTS by ISO 1999 increased with an increase in noise kurtosis value. For a fixed range of noise exposure level and duration, the actual measured NIPTS increased as the kurtosis of the noise increased. The noise with kurtosis greater than 75 produced the highest NIPTS. CONCLUSIONS: The applicability of the ISO 1999 prediction model to different types of noise exposures needs to be carefully reexamined. A better understanding of the role of the kurtosis metric in NIHL may lead to its incorporation into a new and more accurate model of hearing loss due to noise exposure.

Objective: In occupational hearing conservation programmes, age adjustments may be used to subtract expected age effects. Adjustments used in the U.S. came from a small dataset and overlooked important demographic factors, ages, and stimulus frequencies. The present study derived a set of population-based age adjustment tables and validated them using a database of exposed workers.Design: Cross-sectional population-based study and retrospective longitudinal cohort study for validation.Study sample: Data from the U.S. National Health and Nutrition Examination Survey (unweighted n = 9937) were used to produce these tables. Male firefighters and emergency medical service workers (76,195 audiograms) were used for validation.Results: Cross-sectional trends implied less change with age than assumed in current U.S. regulations. Different trends were observed among people identifying with non-Hispanic Black race/ethnicity. Four age adjustment tables (age range: 18-85) were developed (women or men; non-Hispanic Black or other race/ethnicity). Validation outcomes showed that the population-based tables matched median longitudinal changes in hearing sensitivity well.Conclusions: These population-based tables provide a suitable replacement for those implemented in current U.S. regulations. These tables address a broader range of worker ages, account for differences in hearing sensitivity across race/ethnicity categories, and have been validated for men using longitudinal data.

Animal models have been used to gain insight into the risk of noise-induced hearing loss (NIHL) and its potential prevention using investigational new drug agents. A number of compounds have yielded benefit in pre-clinical (animal) models. However, the acute traumatic injury models commonly used in pre-clinical testing are fundamentally different from the chronic and repeated exposures experienced by many human populations. Diverse populations that are potentially at risk and could be considered for enrollment in clinical studies include service members, workers exposed to occupational noise, musicians and other performing artists, and children and young adults exposed to non-occupational (including recreational) noise. Both animal models and clinical populations were discussed in this special issue, followed by discussion of individual variation in vulnerability to NIHL. In this final contribution, study design considerations for NIHL otoprotection in pre-clinical and clinical testing are integrated and broadly discussed with evidence-based guidance offered where possible, drawing on the contributions to this special issue as well as other existing literature. The overarching goals of this final paper are to (1) review and summarize key information across contributions and (2) synthesize information to facilitate successful translation of otoprotective drugs from animal models into human application.

Middle ear muscle contractions (MEMC) can be elicited in response to high-level sounds, and have been used clinically as acoustic reflexes (ARs) during evaluations of auditory system integrity. The results of clinical AR evaluations do not necessarily generalize to different signal types or durations. The purpose of this study was to evaluate the likelihood of observing MEMC in response to brief sound stimuli (tones, recorded gunshots, noise) in adult participants (N = 190) exhibiting clinical ARs and excellent hearing sensitivity. Results revealed that the presence of clinical ARs was not a sufficient indication that listeners will also exhibit MEMC for brief sounds. Detection rates varied across stimulus types between approximately 20% and 80%. Probabilities of observing MEMC also differed by clinical AR magnitude and latency, and declined over the period of minutes during the course of the MEMC measurement series. These results provide no support for the inclusion of MEMC as a protective factor in damage-risk criteria for impulsive noises, and the limited predictability of whether a given individual will exhibit MEMC in response to a brief sound indicates a need to measure and control for MEMC in studies evaluating pharmaceutical interventions for hearing loss.

Reverberation time measurements were conducted in the 21-lane indoor firing range at Wright Patterson Air Force Base. Long reverberation times resulted in poor speech transmission indices (STI) which required acoustical treatments within the range. After treatment, reverberation times were significantly reduced and STI was dramatically enhanced. Standard Sabine and Eyring models failed to accurately predict the reverberation times. A computer simulation of the range was developed to predict room acoustic conditions and auralize speech performance for perceptual evaluation in the range.

An impulsive noise exposure model for outdoor military shooting ranges was created. The inputs to the model included spatial interpolation of noise exposure metrics measured from a single round of fire from a small-arms ballistic weapon. Energies from this single-shot model were spatially translated and summed to simulate multiple shooters firing multiple rounds based on the equal energy hypothesis for damage risk assessment. A validation measurement was performed, and the uncertainties associated with measurement and modeling were shown to be acceptably low. This model can predict and assess total exposures and protection measures for shooters, instructors, and other range personnel.

OBJECTIVE: Assessment of the auditory risk associated with sound from ballistic N-waves produced by a rifle bullet. DESIGN: Acoustical recordings of ballistic N-waves passing through a microphone array at 6.4 metres down range were analysed to determine (a) the trajectory of the bullet, (b) the distance between the trajectory and each microphone (less than 1.3 m), and (c) the numbers of permissible exposures according to both damage-risk criteria for impulsive noise in the current U.S. military standard (MIL-STD-1474E). STUDY SAMPLE: The gun was an AR-15 style semiautomatic rifle configured to fire a 0.50 calibre Beowulf(00AE) cartridge. Four sample shots were recorded for each of four microphone spacing conditions and five kinds of ammunition (80 shots in total). RESULTS: The ballistic N-waves recorded in this study would constitute a significant auditory risk to unprotected listeners at all distances sampled. The numbers of permissible exposures decreased as the distance to the bullet trajectory decreased, decreased with increased bullet length, and departed from linear increases as the bullet velocity increased. CONCLUSIONS: Unprotected exposure to a ballistic N-wave from a supersonic 0.50 calibre bullet presents a significant risk to hearing at distances of 6.4 metres down range and through trajectories within 1.2 metres of an ear.

As co-editors for this International Journal of Audiology (IJA) special supplement, we are pleased to introduce seven papers covering innovative, impactful research that represent a selected subset of those presented at the 42nd annual meeting of the National Hearing Conservation Association (NHCA) held in Orlando, Florida in February 2018. This conference adopted the theme ‘Happy Ears for Many Years,’ and we think you will find that the research covered in this supplement aims directly, via diverse strategic avenues, toward the objective of conserving our hearing. This supplement is enabled by the financial support of the NHCA and its partners, including the National Institute for Occupational Safety and Health (NIOSH), the Council for Accreditation in Occupational Hearing Conservation (CAOHC), and the Department of Defense Hearing Center of Excellence (DoD HCE).

Accurate quantification of noise exposure in military environments is challenging due to movement of listeners and noise sources, spectral and temporal noise characteristics, and varied use of hearing protection. This study evaluates a wearable recording device designed to measure on-body and in-ear noise exposure, specifically in an environment with significant impulse noise resulting from firearms. A commercial audio recorder was augmented to obtain simultaneous measurements inside the ear canal behind an integrated hearing protector, and near the outer ear. Validation measurements, conducted with an acoustic test fixture and shock tube, indicated high impulse peak insertion loss with a proper fit of the integrated hearing protector. The recording devices were worn by five subjects during a live-fire data collection at Marine Corps Base Quantico where Marines fired semi-automatic rifles. The field test demonstrated the successful measurement of high-level impulse waveforms with the on-body and in-ear recording system. Dual channels allowed for instantaneous fit estimates for the hearing protection component, and the device worked as intended in terms of hearing protection and noise dosimetry. Accurate measurements of noise exposure and hearing protector fit should improve the ability to model and assess the risks of noise-induced hearing loss.

Globally, one in three adults has some level of measurable hearing loss, and 1.1 billion young persons are at risk for hearing loss attributable to noise exposure. Although noisy occupations such as construction, mining, and manufacturing are primary causes of hearing loss in adults, nonoccupational noise also can damage hearing. Loud noises can cause permanent hearing loss through metabolic exhaustion or mechanical destruction of the sensory cells within the cochlea. Some of the sounds of daily life, including those made by lawn mowers, recreational vehicles, power tools, and music, might play a role in the decline in hearing health. Hearing loss as a disability largely depends on a person's communication needs and how hearing loss affects the ability to function in a job. The loss of critical middle and high frequencies can significantly impair communication in hearing-critical jobs (e.g., law enforcement and air traffic control).

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 LAeq,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.

OBJECTIVE: The objective of this study is to determine whether acoustic reflexes are pervasive (i.e. known with 95% confidence to be observed in at least 95% of people) by examining the frequency of occurrence using a friction-fit diagnostic middle ear analyser. DESIGN: Adult participants with very good hearing sensitivity underwent audiometric and middle ear testing. Acoustic reflexes were tested ipsilaterally and contralaterally in both ears across a range of elicitor frequencies. Reflex elicitors were 700 ms tones presented at maximum level of 100 dB HL. Two automated methods were used to detect the presence of an acoustic reflex. STUDY SAMPLE: A group of 285 adult volunteers with normal hearing. RESULTS: There were no conditions in which the proportion of participants exhibiting acoustic reflexes was high enough to be deemed pervasive. Ipsilateral reflexes were more likely to be observed than contralateral reflexes and reflexes were more common at 0.5 and 1 kHz elicitor frequencies as compared with 2 and 4 kHz elicitor frequencies. CONCLUSIONS: Acoustic reflexes are common among individuals with good hearing. However, acoustic reflexes are not pervasive and should not be included in damage risk criteria and health hazard assessments for impulsive noise.

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 approximately 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.

In 2016, the National Hearing Conservation Association (NHCA) (http://www.hearingconservation.org), held its annual meeting in San Diego, California, with the theme of the meeting “Making Sound Waves”. Several papers presented at that meeting were invited to be developed as contributions to this special supplemental edition of the International Journal of Audiology (IJA). The articles included here were specifically selected to highlight the diversity of research activities that are successfully generating new data that inform Best Practices and improve the success of Hearing Loss Prevention Programmes in achieving the goal of preventing the onset and progression of noise-induced hearing loss (NIHL). In many cases, these articles created widespread waves across the membership, with active discussions propagating well beyond session’s end.

OBJECTIVE: To characterise the performance of hearing protection devices (HPDs) in impulsive-noise conditions and to compare various protection metrics between impulsive and steady-state noise sources with different characteristics. DESIGN: HPDs were measured per the impulsive test methods of ANSI/ASA S12.42- 2010 . Protectors were measured with impulses generated by both an acoustic shock tube and an AR-15 rifle. The measured data were analysed for impulse peak insertion loss (IPIL) and impulsive spectral insertion loss (ISIL). These impulsive measurements were compared to insertion loss measured with steady-state noise and with real-ear attenuation at threshold (REAT). STUDY SAMPLE: Tested HPDs included a foam earplug, a level-dependent earplug and an electronic sound-restoration earmuff. RESULTS: IPIL for a given protector varied between measurements with the two impulse noise sources, but ISIL agreed between the two sources. The level-dependent earplug demonstrated level-dependent effects both in IPIL and ISIL. Steady-state insertion loss and REAT measurements tended to provide a conservative estimate of the impulsively-measured attenuation. CONCLUSIONS: Measurements of IPIL depend strongly on the source used to measure them, especially for HPDs with less attenuation at low frequencies. ISIL provides an alternative measurement of impulse protection and appears to be a more complete description of an HPD's performance.

The National Institute for Occupational Safety and Health (NIOSH) sponsored tests of three earplug fit-test systems (NIOSH HPD Well-Fit, Michael & Associates FitCheck, and Honeywell Safety Products VeriPRO(R)). Each system was compared to laboratory-based real-ear attenuation at threshold (REAT) measurements in a sound field according to ANSI/ASA S12.6-2008 at the NIOSH, Honeywell Safety Products, and Michael & Associates testing laboratories. An identical study was conducted independently at the U.S. Army Aeromedical Research Laboratory (USAARL), which provided their data for inclusion in this report. The Howard Leight Airsoft premolded earplug was tested with twenty subjects at each of the four participating laboratories. The occluded fit of the earplug was maintained during testing with a soundfield-based laboratory REAT system as well as all three headphone-based fit-test systems. The Michael & Associates lab had highest average A-weighted attenuations and smallest standard deviations. The NIOSH lab had the lowest average attenuations and the largest standard deviations. Differences in octave-band attenuations between each fit-test system and the American National Standards Institute (ANSI) sound field method were calculated (Attenfit-test - AttenANSI). A-weighted attenuations measured with FitCheck and HPD Well-Fit systems demonstrated approximately +/-2 dB agreement with the ANSI sound field method, but A-weighted attenuations measured with the VeriPRO system underestimated the ANSI laboratory attenuations. For each of the fit-test systems, the average A-weighted attenuation across the four laboratories was not significantly greater than the average of the ANSI sound field method. Standard deviations for residual attenuation differences were about +/-2 dB for FitCheck and HPD Well-Fit compared to +/-4 dB for VeriPRO. Individual labs exhibited a range of agreement from less than a dB to as much as 9.4 dB difference with ANSI and REAT estimates. Factors such as the experience of study participants and test administrators, and the fit-test psychometric tasks are suggested as possible contributors to the observed results.

OBJECTIVE: This field study aimed to assess the noise reduction of hearing protection for individual workers, demonstrate the effectiveness of training on the level of protection achieved, and measure the time required to implement hearing protector fit testing in the workplace. DESIGN: The National Institute for Occupational Safety and Health (NIOSH) conducted field studies in Louisiana and Texas to test the performance of HPD Well-Fit. STUDY SAMPLE: Fit tests were performed on 126 inspectors and engineers working in the offshore oil industry. RESULTS: Workers were fit tested with the goal of achieving a 25-dB PAR. Less than half of the workers were achieving sufficient protection from their hearing protectors prior to NIOSH intervention and training; following re-fitting and re-training, over 85% of the workers achieved sufficient protection. Typical test times were 6-12 minutes. CONCLUSIONS: Fit testing of the workers' earplugs identified those workers who were and were not achieving the desired level of protection. Recommendations for other hearing protection solutions were made for workers who could not achieve the target PAR. The study demonstrates the need for individual hearing protector fit testing and addresses some of the barriers to implementation.

OBJECTIVE: To characterize the impulse noise exposure and auditory risk for air rifle users for both youth and adults. 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 and LAeq75 exposure limit suggested by the World Health Organization (1999) for children. STUDY SAMPLE: Impulses were generated by nine pellet air rifles and one BB air rifle. RESULTS: None of the air rifles generated peak levels that exceeded the 140 dB peak limit for adults, and eight (80%) exceeded the 120 dB peak SPL limit for youth. In general, for both adults and youth, there is minimal auditory risk when shooting fewer than 100 unprotected shots with pellet air rifles. Air rifles with suppressors were less hazardous than those without suppressors, and the pellet air rifles with higher velocities were generally more hazardous than those with lower velocities. CONCLUSION: To minimize auditory risk, youth should utilize air rifles with an integrated suppressor and lower velocity ratings. Air rifle shooters are advised to wear hearing protection whenever engaging in shooting activities in order to gain self-efficacy and model appropriate hearing health behaviors necessary for recreational firearm use.

In 2006, the National Institute for Occupational Safety and Health (NIOSH) entered the second decade of the National Occupational Research Agenda (NORA). NORA is a partnership program to stimulate innovative research and improved workplace practices. NORA has served as an organizing framework to plan and conduct critical occupational research and to promote expanded partnerships between the stakeholders such as universities, large and small businesses, professional societies, other government agencies (federal, state, and local), and worker organizations. Following a review by the National Academies Institute of Medicine of the NIOSH Hearing Loss Research program, a comprehensive strategic plan was developed for the Hearing Loss Prevention cross-sector. Six strategic goals were identified: 1) improved surveillance of occupational hearing loss data; 2) reduced noise emission levels from equipment focused on mining, construction, and manufacturing; 3) development of hearing protector technology; 4) development of best practices for hearing loss prevention programs; 5) identification of hearing loss risk factors; and 6) development of updated hearing damage risk criteria that consider exposures incurred during youth, adolescence, and adulthood. This presentation will review progress towards meeting these goals and propose a research agenda for the third decade of NORA research in hearing loss prevention.

Impulse peak insertion loss (IPIL) was studied with two acoustic test fixtures and four hearing protector conditions at the E-A-RCAL Laboratory. IPIL is the difference between the maximum estimated pressure for the open-ear condition and the maximum pressure measured when a hearing protector is placed on an acoustic test fixture (ATF). Two models of an ATF manufactured by the French-German Research Institute of Saint-Louis (ISL) were evaluated with high-level acoustic impulses created by an acoustic shock tube at levels of 134 decibels (dB), 150 dB, and 168 dB. The fixtures were identical except that the E-A-RCAL ISL fixture had ear canals that were 3 mm longer than the National Institute for Occupational Safety and Health (NIOSH) ISL fixture. Four hearing protection conditions were tested: Combat Arms earplug with the valve open, ETYPlugs (R) earplug, TacticalPro headset, and a dual-protector ETYPlugs earplug with TacticalPro earmuff. The IPILs measured for the E-A-RCAL fixture were 1.4 dB greater than the National Institute for Occupational Safety and Health (NIOSH) ISL ATF. For the E-A-RCAL ISL ATF, the left ear IPIL was 2.0 dB greater than the right ear IPIL. For the NIOSH ATF, the right ear IPIL was 0.3 dB greater than the left ear IPIL.

Dobie and Clark’s recent article “Exchange rates for intermittent and fluctuating occupational noise: A systematic review of studies of human permanent threshold shift” aimed to compare the suitability of a 3-dB versus 5-dB exchange rate (ER) in predicting hearing loss from non-impulsive intermittent or fluctuating noise exposures by reviewing studies of human noise-induced permanent threshold shift. The authors concluded that 3-dB ER systematically overestimates the risk of noise-induced hearing loss for intermittent or fluctuating noise. We contend that the authors did not arrive at their conclusions through an appropriate investigation. The article used flawed methodologies in the treatment and analysis of the data/studies and drew conclusions that were not substantiated by the cited data. | The authors indicated that their review did not aim to make recommendations for regulation of occupational noise, but suggested that their review provided evidence for a re-examination of recommendations in their concluding remarks. The National Institute for Occupational Safety and Health (NIOSH) maintains its recommendation of the 3-dB ER to provide sufficient protection for the many variations of continuous, intermittent and fluctuating noise exposure scenarios encountered in the workplace. In view of the advances in noise measurement and the studies’ other weaknesses, we question the suitability of revisiting a narrow segment of the human evidence (excluding robust animal studies and temporary threshold shift studies) based on outdated methodologies to address such an important issue.

OBJECTIVE: This study examined differences in thresholds obtained under Sennheiser HDA200 circumaural earphones using pure tone, equivalent rectangular noise bands, and 1/3 octave noise bands relative to thresholds obtained using Telephonics TDH-39P supra-aural earphones. DESIGN: Thresholds were obtained via each transducer and stimulus condition six times within a 10-day period. STUDY SAMPLE: Forty-nine adults were selected from a prior study to represent low, moderate, and high threshold reliability. RESULTS: The results suggested that (1) only small adjustments were needed to reach equivalent TDH-39P thresholds, (2) pure-tone thresholds obtained with HDA200 circumaural earphones had reliability equal to or better than those obtained using TDH-39P earphones, (3) the reliability of noise-band thresholds improved with broader stimulus bandwidth and was either equal to or better than pure-tone thresholds, and (4) frequency-specificity declined with stimulus bandwidths greater than one equivalent rectangular band, which could complicate early detection of hearing changes that occur within a narrow frequency range. CONCLUSIONS: These data suggest that circumaural earphones such as the HDA200 headphones provide better reliability for audiometric testing as compared to the TDH-39P earphones. These data support the use of noise bands, preferably ERB noises, as stimuli for audiometric monitoring.