The reduction of gunshot noise and auditory risk through the use of firearm suppressors and low-velocity ammunition

Quantification of suppressor effects on breech and action noise from AR-15 pattern firearms and its implications for the protection of human hearing

Noise from firearms is well known to be harmful to human hearing. This problem has been addressed by various military units through the use of muzzle suppressors. However, as suppressor technology has advanced, shooters report hearing the mechanical action of gas-operated semi-automatic rifles (ArmaLite Rifle Model 15 style aka AR-15) as being louder than the suppressed muzzle noise. This study aims to evaluate if harmful noise is present in the shooter's ear, even when impulse noise emanating from the muzzle is suppressed. To characterize the impulse noise of the firearm action caused by the reciprocation of the bolt carrier group (BCG) and subsequent impact when it returns to battery (the forward locked position), the muzzle of a rifle was placed through a constructed plywood wall, and the noise of the action/breech was measured independently from the muzzle noise. This research finds that the impact of the BCG returning to battery (132 dBZ) has the potential to be harmful to the shooter's hearing even when the noise from the muzzle is effectively suppressed.

Impulse noise measurement in view of noise hazard assessment and use of hearing protectors

Experience shows the occurrence of situations when the measurements of impulse noise parameters are made with measurement equipment unsuitable for such conditions. The results of using such equipment were compared with the results of using equipment with a sufficiently large upper limit of the measurement range. The analysis was carried out on the example of noise generated during shots from a Mossberg smooth-bore shotgun and AKM rifle, as well as produced in the forge. The use of the unsuitable equipment allowed to indicate the exceeding of the exposure limit value of the peak value of the signal (L_Cpeak), but this is not always possible when determining the energy properties of the signal (L_EX,8h). While the inadequate properties of the measurement equipment will generally not prevent the conclusion that noise in a particular workplace is hazardous to hearing, the results of measurements cannot be used to select hearing protectors.

Cohort difference in the association between use of recreational firearms and hearing loss: findings from the HUNT study

OBJECTIVES

The risk of noise injury from recreational firearm use is well known. Despite preventive measures it is uncertain whether it has become less harmful. We assessed whether the association between recreational firearm use and hearing has changed during the last two decades.

DESIGN

We used a repeated cross-sectional design and determined hearing thresholds by pure-tone audiometry. Frequency-specific associations between recreational firearm use and hearing thresholds were assessed by multivariate linear regression stratified by sex and adjusted for age and other covariates.

STUDY SAMPLE

Two cross-sectional population-based cohorts 20 years apart (1998 and 2018) comprised 27,580 (53% women, mean age 53 years) and 26,606 individuals (56% women, mean age 54 years), respectively.

RESULTS

Recreational firearm use was reported by 28% in 1998 and 30% in 2018. The proportion that reported wearing hearing protection increased. Exposure to recreational firearms was associated with elevated thresholds at 3-6 kHz in both cohorts. The association increased with the number of lifetime shots. The associations increased by age and were substantially smaller in the most recent cohort.

CONCLUSIONS

Analyses of two cohorts revealed a reduction in the association between recreational firearm use and hearing over 20 years, coinciding with the introduction of hearing preservation measures.

Systematic Review of Interventions to Prevent Occupational Noise-Induced Hearing Loss - A Follow-up

PURPOSE

To conduct a systematic review of the effectiveness of interventions to prevent occupational hearing loss, following up on the findings of the most recent version of Cochrane systematic review on the same topic.

RESEARCH STRATEGY

Searches were carried out in PubMed, Web of Science and Scopus databases.

SELECTION CRITERIA

The following interventions were considered: engineering/administrative controls; hearing protection devices (HPD); and audiological monitoring.

DATA ANALYSIS

For bias risk analysis, each study was assessed according to randomization, allocation, blinding, outcomes, other sources of bias.

RESULTS

475 references were obtained. Of these, 17 studies met the inclusion criteria: one randomized, one interrupted time series, and 15 before and after studies. Most studies were conducted in industries; three in military and/or shooting training environments; one in an orchestra, and one in construction. Most studies showed a high risk of bias. Six studies found a reduction in short-term exposure to noise through engineering/administrative controls; one found a positive impact due to changes in legislation; five studies have found positive effects of HPD in reducing exposure to noise and of educational trainings in the use of HPD; lastly, two studies found a reduction in noise levels and an increase in the using of HPD due to the implementation of hearing conservation programs.

CONCLUSÃO

Todos os estudos analisados concluíram que as intervenções utilizadas resultaram em efeitos positivos sobre a audição e/ou sobre a exposição ao ruído. Em relação aos efeitos de longo termo, a grande maioria dos estudos limitou-se a avaliar efeitos imediatos ou de curto termo, reforçando que estudos incluindo follow-up de longo termo devem ser desenvolvidos.

Toward an improved hearing safety standard for impulse noise exposure in the Canadian Armed Forces

Introduction: Current hearing safety standards for the Canadian Armed Forces (CAF) do not adequately address exposure limits for mitigation of noise-induced hearing loss (NIHL) from weapon noise. Recommendations for updating the hearing safety standard are being formulated by the recently initiated Noise Health Hazard Working Group (NHHWG). In this article, we aim to provide a way forward for the NHHWG. Methods: On the basis of experience with auditory research, noise measurement, acoustic standards development, interactions with CAF members, and a review of the literature, we present an overview of the current state of knowledge regarding impulse noise. The topics include impulse noise measurement, engineering and administrative controls for noise exposure, and use of personal hearing protection devices (HPDs). Results: Although technology for impulse noise measurements and ways to account for HPDs have improved substantially in recent years, not much has changed in hearing damage risk criteria. Energy-based metrics can account for the impulse duration and frequency-dependent characteristics of the HPD, which are important considerations in calculating allowed exposures. Discussion: The NHHWG is recommended to focus on measurements of current weapons systems in various configurations and training environments and to evaluate the use of energy-based metrics, together with frequency-dependent HPD insertion loss.

Force and Sound Pressure Sensors Used for Modeling the Impact of the Firearm with a Suppressor

In this paper, a mathematical model for projectiles shooting in any direction based on sensors distributed stereoscopically is put forward. It is based on the characteristics of a shock wave around a supersonic projectile and acoustical localization. Wave equations for an acoustic monopole point source of a directed effect used for physical interpretation of pressure as an acoustic phenomenon. Simulation and measurements of novel versatile mechanical and acoustical damping system (silencer), which has both a muzzle break and silencer properties studied in this paper. The use of the proposed damping system can have great influence on the acoustic pressure field intensity from the shooter. A silencer regarded as an acoustic transducer and multi-holes waveguide with a chamber. Wave equations for an acoustic monopole point source of a directed effect used for the physical interpretation of pressure as an acoustic phenomenon. The numerical simulation results of the silencer with different configurations presented allow trends to be established. A measurement chain was used to compare the simulation results with the experimental ones. The modeling and experimental results showed an increase in silencer chamber volume results in a reduction of recorded pressure within the silencer chamber.

Noise of military weapons, ground vehicles, planes and ships

Noisy equipment and processes are found throughout military operations, exposing service members to risks of hearing damage due to hazardous noise levels. This article provides an overview of the military noise environment for the non-expert and provides a general characterization of the noise by source type and operational category. The focus of the article is primarily related to the Army, but the same, or similar, equipment is used by the Navy, Marine Corps, and Air Force. Damage risk criteria used by the Army Public Health Command are discussed. In addition, the important role of hearing protection to mitigate the hazards of noise exposure is provided.

Cumulative noise exposure model for outdoor shooting ranges

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.

Noise-induced hearing loss and its prevention: Integration of data from animal models and human clinical trials

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.

Selection of Level-Dependent Hearing Protectors for Use in An Indoor Shooting Range

The high sound pressure level generated by impulse noise produced in an indoor shooting range makes it necessary to protect the hearing of the people it affects. Due to the need for verbal communication during training at a shooting range, level-dependent hearing protectors are useful. The objective of this study was to answer the question of whether it is possible to properly protect the hearing of a shooting instructor using level-dependent hearing protectors. The noise parameters were measured in the places where the instructor was present at the shooting range. The division of a specific group of trained shooters into subgroups consisting of three or six simultaneously shooting individuals did not significantly affect the exposure of the shooting instructor to the noise. An assessment of noise reduction was carried out for eight models of earmuffs and two variants of earplugs, using computational methods for the selection of hearing protectors. Among the noise parameters, both the A-weighted equivalent sound pressure level and the C-weighted peak sound pressure level were taken into account. Depending on the assessment criterion adopted, a sufficient reduction in impulse noise was provided by either four or six out of the 10 hearing protectors included in the study.

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.