Gunshot Noise Research Articles

Assessing effect of ground reflections on gunshot noise exposure

Investigation of weapons noise exposure outdoors necessitates including the impact of ground reflections. When analyzing the reflections’ impact on A-weighted equivalent level (LAeq), the contribution of the reflected waveform to the total level can often be acceptably modeled using a Friedlander equation-based source model and an ideal reflection based on the measurement geometry. However, the Friedlander model does not adequately model the negative phase of a gunshot waveform, making it inaccurate for locations where the waveform of the direct blast and the waveform of the reflection begin to overlap temporally. This merging of the waveforms for locations where the direct and ground-reflected path length difference is relatively small also makes it difficult to separate the waveforms and calculate the reflected wave’s contribution to noise exposure. As such, this paper investigates different approaches to estimating the contribution of the ground reflected wave to the LAeq, using direct and reflected waveforms in regions where they are well separated and then adjusting timing and amplitude for different geometries where merging takes place. Results reveal regions where the ground reflection contributes negligibly or even negatively to the total LAeq, which is not predicted by the Friedlander model nor by simple energy-addition approaches. [Work supported by Air Force Research Laboratory through Ball Aerospace Technology Corporation.]

МЕТОДИКА ФОРМУВАННЯ ВИМОГ ДО ХАРАКТЕРИСТИК ШУМУ ПОСТРІЛУ ДЛЯ ЗАБЕЗПЕЧЕННЯ ПРИХОВАНОГО ВИКОНАННЯ ВОГНЕВИХ ЗАВДАНЬ СИЛАМИ БЕЗПЕКИ

A shot from a small-arms weapon is accompanied by a sound that helps the enemy to reveal the fact of using the weapon and unmask the location of the shooter, so sound masking is necessary in some cases. To increase the concealment of the use of small arms, devices for reducing the sound level of the shot (PZRZP) and samples of silent (low-noise) weapons are used. Existing models of low-noise weapons and devices for reducing the noise of a shot are mostly designed for defense forces and cannot provide an acceptable level of acoustic concealment in the conditions of fire missions by security forces. Modern manufacturers are proactively developing gunshot noise reduction devices and offer their products illustrating the comparative reduction of gunshot noise with and without the use of a gunshot sound reduction device. In this case, for the conscious choice of devices for reducing the sound level of a shot, it is necessary to have reasonable requirements for the characteristics of the sound of the shot, which ensure the covert use of weapons in certain conditions of the execution of the firing task. Thus, there is a need to improve the methodical apparatus for the formation of requirements for gunshot noise characteristics for the most justified choice of a gunshot sound reduction device from among those offered by the market or being developed or modernized. The article has developed a methodology for the formation of requirements for the characteristics of gunshot noise to ensure covert execution of fire missions by security forces. The specified technique allows you to form requirements for the characteristics of gunshot noise, which ensure covert execution of a firing task in certain conditions, as well as to check the possibility of implementing these requirements on the basis of one or another sample of weapons, taking into account the possibility of correcting gunshot noise parameters and applying sound masking. In addition, the developed technique can be used to form requirements for the technical characteristics of devices for reducing the sound level of a shot and low-noise weapons at the stages of their development and modernization.

Evaluation of tinnitus severity in military personnel after exposure to high intensity noise

Aim to evaluate the severity of tinnitus before and after medical treatment in military personnel exposed to high-intensity noise.
 Material and methods. The study involved 14 soldiers with complaints of tinnitus who suffered hearing damage caused by gunshot noise (AK74 gun) during military training without hearing protectors. The tinnitus severity and its dynamics during the treatment by glucocorticosteroids was assessed using the Tinnitus Functional Index (TFI). The Tinnitus Handicap Inventory (THI) was used before the treatment, on the 3rd and 7th days after the treatment.
 Results. It was found that the greatest discomfort was caused by the intrusiveness of noise and inability to control it during the day, and the least discomfort was associated with sleep. The changes in the severity of noise on the THI and TFI scales on the third and seventh days after treatment were significantly different, if compared with the pre-treatment results, and had a positive trend. The therapy provided the significant decrease of noise intrusiveness and established the sense of noise control during the day, as well as minimized its effect on relaxation, hearing and quality of life, if compared to the data before treatment.
 Conclusion. The TFI and THI scales are recommended for assessing the severity of tinnitus and monitoring the treatment of patients exposed to high-intensity noise. Particular attention should be paid to the use of personal hearing protection equipment when working in conditions of increased level of noise.

A Review of Gunshot Noise as Factor in Hearing Disorders

The impulse noise produced by personal weapons (guns, rifles, shotguns) during military activity, and while people engage in sport, training and hunting, is a threat to the auditory systems of soldiers, civilians, policemen, hunters, forest officers, sportspeople and bystanders not actively engaged in professional or recreational firing. An overview of noise levels generated by different types of weapon is provided, and potential short-term and long-term consequences for the human auditory system are described. The mean values of LC, peak sound pressure level during the shot, at the shooter's ears, for various types of weapons are approximately 160 dB SPL. These are levels that can cause permanent, irreversible negative effects on hearing (hearing loss, tinnitus, etc.) even as a result of a single shot being fired. One of the largest groups of weapon users in Poland (about 120 thousand) are hunters and field masters. They are not obligated by any regulations to protect their auditory systems from impulse noise. This means that this group of firearm users is at particularly high risk of hearing damage. On the basis of the literature review, it is shown that hearing exposure to high-level impulse noise such as a gunshot can result in such consequences as damage to the middle ear and destruction of the outer/inner hair cells in the cochlea. Especially difficult to diagnose is 'hidden hearing loss', i.e. damage to the synaptic connections between the hair cells of the inner ear and the auditory nerve fibres, which is not reflected in the results of basic audiometric testing and can cause hearing problems many years after impulse noise exposure. The wide range of negative consequences of gunfire noise clearly indicates the need for the hearing of the shooters to be protected.

Comparison of oral steroid regimens for acute acoustic trauma caused by gunshot noise exposure

There are no definite guidelines regarding the most adequate steroid regimens for acute acoustic trauma. To elucidate the dose-dependent differing benefits of oral steroids on hearing improvement following acute acoustic trauma. Twenty-nine patients treated with oral steroids following a diagnosis of unilateral acute acoustic trauma were retrospectively reviewed. Patients were sorted into two groups with an oral steroid regimen. Group 1 received a 14-day course of treatment: 60 mg prednisolone daily for 10 days, tapering off over days 11-14. Group 2 received prednisolone for a total of 10 days: 60 mg for 5 days, tapering down each day for the remainder. Multivariable linear regression analysis was performed to evaluate the factors associated with the hearing gain. In the multivariable regression (R2 = 0.51, p < 0.001), patients in group 1 showed more significant improvement in the degree of hearing gain compared to group 2 (p = 0.03). After comparing the differing benefits of oral steroids on hearing improvement by dosage, we recommend a high dose of prednisolone (60 mg per day) for 10 days, tapering over the remaining 4 days, for better hearing recovery following acute acoustic trauma.

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

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.

Effects of early intratympanic steroid injection in patients with acoustic trauma caused by gunshot noise

Conclusion: This study evaluated the efficacy of concurrent administration of ITSI and systemic steroids in delayed treatment of NIHL after gunshot noise exposure. The results showed additional hearing benefits with administration of ITSI. Further evaluation is warranted to confirm this efficacy.Objective: This investigation evaluated the effects of early administration of an intratympanic steroid injection (ITSI) in combination with systemic steroids treatment in patients with acoustic trauma caused by gunshot noise.Methods: Nineteen patients eligible under the criteria established concerning delayed treatment for noise-induced hearing loss (NIHL) were enrolled in this study. Patients were divided into two groups: those who received prednisolone (PD) only (n = 8), and those who received PD with ITSI (n = 11). ITSI treatment was initiated simultaneously alongside systemic PD administration. These patients received ITSI every other day for a total of four treatments. Pure-tone air conduction threshold audiometry, to record the pure-tone average (PTA) at 2, 4, and 8 kHz, was conducted upon each patient’s initial visit, and 1 month after starting treatment, to evaluate the degree of hearing gain (hearing gain (dB) = (initial PTA) – (final PTA)).Results: The initial PTA in PD-only and PD with ITSI groups were 52.75 ± 15.50 dB and 50.27 ± 12.01 dB, respectively. There were no significant differences in the baseline characteristics of the two groups, which include age and the number of days that treatment was delayed. In the multivariable linear regression analysis, both the initial PTA and the treatment method showed a significant association (R2 = 0.41). The unstandardized regression coefficient of the initial PTA was 0.47 (p = 0.02). Patients with additional ITSI showed significant improvement in the degree of hearing gain compared with the PD-only group (unstandardized regression coefficient =11.48, p = 0.03)

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 hearing protection. An outdoor noise propagation model based on ISO 17201-1 will be used to investigate the effect of suppressors to reduce noise in surrounding communities.

Shooting history and presence of high-frequency hearing impairment in swedish hunters: A cross-sectional internet-based observational study.

The aim of this cross-sectional study among Swedish hunters was to examine the association between shooting history and presence of high-frequency hearing impairment (HFHI). All hunters registered with an e-mail address in the membership roster of the Swedish Hunters’ Association were invited via e-mail to a secure website with a questionnaire and an Internet-based audiometry test. Associations, expressed as prevalence ratio (PR), were multivariately modelled using Poisson regression. The questionnaire was answered by 1771 hunters (age 11-91 years), and 202 of them also completed the audiometry test. Subjective severe hearing loss was reported by 195/1771 (11%), while 23/202 (11%) exhibited HFHI upon testing with Internet-based audiometry. As many as 328/1771 (19%) had never used hearing protection during hunting. In the preceding 5 years, 785/1771 (45%), had fired >6 unprotected gunshots with hunting rifle calibers. The adjusted PR of HFHI when reporting 1-6 such shots, relative to 0, was 1.5 [95% confidence interval (CI) 1.1-2.1; P = 0.02]. We could not verify any excessive HFHI prevalence among 89 hunters reporting unprotected exposure to such gunshot noise >6 times. Nor did the total number of reported rifle shots seem to matter. These findings support the notion of a wide variation in individual susceptibility to impulse noise; that significant sound energy, corresponding to unprotected noise from hunting rifle calibers, seems to be required; that susceptible individuals may sustain irreversible damage to the inner ear from just one or a few shots; and that use of hearing protection should be encouraged from the first shot with such weapons.

The biochemical and hematological parameters of patients with acoustic trauma caused by gunshot noise

The biochemical and hematological parameters of patients with acoustic trauma caused by gunshot noise

Clinical Characteristics of Acoustic Trauma Caused by Gunshot Noise in Mass Rifle Drills without Ear Protection

One of the major occupational hazards of working in military service is being subjected to intense impulse noise. We analyzed the clinical presentation of acoustic traumas, induced by mass rifle gunshot noise during military training, in unprotected patients. We evaluated 189 soldiers who had otologic symptoms after rifle shooting exercises without using any hearing protection. All soldiers had been training on the K2 rifle. We took medical histories; conducted physical examinations and hearing evaluations (pure-tone audiometry, speech audiometry, and impedence audiometry); and distributed the Newmann's Tinnitus Handicap Inventory (THI) survey. In addition, we evaluated a normal control group of 64 subjects of similar age who had never fired a rifle. In the patient group, the most common and irritating reported symptom was tinnitus (94.2%), and the average THI score in the patient group was 39.51 ± 14.87, which was significantly higher than the control group score (0.56 ± 3.94) (p < 0.001). Average outcomes of post-exposure air conduction thresholds were 21.33 ± 13.25 dB HL in the affected ears. These levels also were significantly higher than those of the control group (9.16 ± 4.07dB HL) (p < 0.001). Hearing loss was most prominent at high frequencies. An asymmetry of hearing loss related to head position during shooting was not observed. Acoustic trauma induced by gunshot noise can cause permanent tinnitus and hearing loss. Hearing protection (bilateral earplugs) and environmental reform are necessary.

A Case of Sudden Unilateral Sensorineural Hearing Loss With Contralateral Psychogenic Hearing Loss Induced by Gunshot Noise

The reasons behind sudden sensorineural hearing loss are mostly unknown, but viral infections, blood disorders, ototoxicity, noise trauma, autoimmune disease, acoustic tumor, and even mental stress may be related to the disease. In cases of hearing loss as a result of psychogenic factors, early diagnosis and adequate treatment under collaboration with the psychiatric department are crucial, since failure to take appropriate measures may result in permanent sequela. We report a case, with a review of the literature, of sudden unilateral sensorineural hearing loss with contralateral psychogenic hearing loss induced by gunshot noise.

A Study on the Effectiveness of Treatment of Acoustic Trauma Caused by Gunshot Noise

Background and Objectives : The effectiveness of many treatment regimens on acoustic trauma has been debated, but there is no established treatment yet. The purpose of this study was to evaluate the efficacy of steroid treatment in acoustic trauma caused by rifles and to find a critical time limit for the treatment to be effective. Subjects and Method : A retrospective review was conducted for 86 conscripted policemen (97 ears) who suffered acoustic trauma after rifle exercise. Pure tone audiograms were compared before and after treatment at 0.5, 1 and 2 kHz (speech-frequency pure tone average, speech-PTA) and at 4, 6 and 8 kHz (high tone pure tone average, high-PTA). Treatment consisted of drugs (steroid, ascorbic acid, gingko biloba, dextran) and carbogen therapy. The patients who came to the hospital after the first 14 days following injury were grouped as control. Hearing outcomes of patients treated within 3 days and within 7 days were compared to the control. Pre-and post-treatment hearing was compared according to the elapsed time before treatment. Results : Hearing outcomes of patients who received treatment within 3 days of acoustic trauma was better than the control group. Speech-frequency did not show any difference. Treatment within 7 days showed no statistical difference compared to the control. Hearing gain was better when treated within 7 days, especially if it was within 3 days. Speech-frequency showed significant spontaneous recovery within 3days. Conclusion : Our data showed a possible effectiveness of treatment of acoustic trauma on the recovery of high frequency hearing when started within 3 days. Speech-frequency seems to recover spontaneously within 3 days.

Ten-year longitudinal study of the effect of impulse noise exposure from gunshot on inner ear function

This longitudinal study investigated how chronic gunshot noise exposure affects cochlear and saccular function in police officers who engaged in regular target shooting practice using dual protection (ear plugs plus earmuffs) for >10 years. In 1997, 20 male police officers underwent audiometry before and two weeks after shooting. Twelve of the original subjects were re-examined by audiometry coupled with vestibular evoked myogenic potential (VEMP) test in 2007. Significant deterioration of mean hearing thresholds at frequencies of 500 Hz through 4000 Hz was noted ten years later, affecting both ears. However, only the frequencies of 4000 and 6000 Hz on the left ear revealed significant difference in mean hearing thresholds compared with healthy controls. Abnormal VEMP responses were evident in nine police officers (75%), including absent VEMPs 7 and delayed VEMPs 2. In conclusion, deterioration to hearing may occur after long term exposure to gunshots, even when double hearing protection is used. Further study is in progress regarding how to preserve both cochlear and saccular function during long term gunshot exposure.

Long-term administration of magnesium after acoustic trauma caused by gunshot noise in guinea pigs

In a previous study we observed that a 7-day post-trauma magnesium treatment significantly reduced auditory threshold shifts measured 7 days after gunshot noise exposure. However this improvement was only temporary, suggesting that it could be potentially beneficial to prolong this treatment. The aim of the present study was to evaluate the efficacy of a long-term (1 month) magnesium treatment after an impulse noise trauma, in comparison with either a 7-day magnesium treatment, an administration of methylprednisolone (conventional treatment), or a placebo (NaCl). Guinea pigs were exposed to impulse noise (three blank gunshots, 170 dB SPL peak). They received one of the four treatments, 1 h after the noise exposure. Auditory function was explored by recording the auditory brainstem response (ABR) and measuring the distortion product otoacoustic emissions (DPOAE) over a 3-month recovery period after the gunshot exposure. The functional hearing study was supplemented by a histological analysis. The results showed that a 1-month treatment with magnesium was the most effective treatment in terms of hair cell preservation. The DPOAE confirmed this effectiveness. Methylprednisolone accelerated recovery but its final efficacy remained moderate. It is probable that magnesium acts on the later metabolic processes that occur after noise exposure. Multiple mechanisms could be involved: calcium antagonism, anti-ischaemic effect or NMDA channel blockage. Regardless of the specific mechanism, a 1-month treatment with magnesium clearly attenuates NIHL, and presents the advantage of being safe for use in humans.

Clinical Characteristics of Acoustic Trauma Caused by Rifle Gunshot Noise

Background and Objectives：One of the major occupational hazards of working in the military service is being subjected to intense impulse noise, hence acoustic trauma. Acute acoustic trauma is a preventable disease, but the effective treatment modality has not been established yet. Acute acoustic traumas caused by exposure to rifle gunshot noise are common in young Korean males in the military service because of conscription policy. Through the analysis of the clinical presentation of acoustic traumas caused by rifle gunshot noise, we suggest effective preventive modalities. Subjects and Method：165 soldiers who had otologic symptoms after performing regular rifle gunshot exercise without any hearing protective measures were analyzed. They all had been tested with K2 rifle. History taking, physical examination, pure-tone audiometry, and impedence audiometry, temporal MRI, and Newmann’s tinnitus inventory questionnaire survey were performed. Results：Most common and annoying symptom was tinnitus. The average outcome of postexposure air conduction thresholds were 22.3dB HL in the affected ear and 11.8dB HL in the unaffected ear. There was no correlation between severity of tinnitus and severity of hearing loss. Asymmetry of hearing loss related to head position during gunshot was not found. This may be due to the fact that during the mass gunshot training, each patient can be influenced by the gunshot noise of the adjacent gunner’s shooting. Conclusion：Widening the distance between firing lanes and providing bilateral hearing protective devices against acoustic trauma must be taken into serious consideration. (Korean J Otorhinolaryngol-Head Neck Surg 2008;51:699-704)

Potential efficacy of early treatment of acute acoustic trauma with steroids and piracetam after gunshot noise

The purpose of this randomized study was to evaluate the early effect of the treatment of acute acoustic trauma (AAT) with steroids and piracetam in a sample of 52 young soldiers who were exposed to intense gunfire noise (G3 rifle). These patients were divided into three groups: (1) group A (20 patients) in which the treatment began within the first hour after the AAT, (2) group B (17 patients) in which the treatment started more than 1 h later and less than 16 h after the AAT and (3) group C (15 patients) in which the treatment began after 24 h or more. One month after the treatment onset, 36 (69%) patients of all the groups showed hearing improvement (complete-partial recovery) in the pure tone audiometry. The greater number of patients who showed complete recovery after AAT was noted in group A (65%) compared to group B (23.5%) and C (13.3%). Moreover, in group A, in the final audiogram, the averaged hearing threshold was statistically better (P < 0.001) than that of groups B and C. In spite of the lack of control group, our data demonstrated the possible effectiveness of the immediate onset of treatment of AAT.

Noise-Induced Hearing Loss Caused by Gunshot in South Korean Military Service

Noise-induced hearing loss is a preventive disease and yet the effective treatment modality has not been established. Acute acoustic traumas caused by an exposure to gunshot noise are common in young South Korean males in military service. Considering the significant lack of awareness on this serious issue as well as the absence of proper protective gear, an in-depth analysis is desperately needed. All 3650 soldiers performed regular periodic gunfire exercise without any hearing protective measures. Seven patients with hearing impairment after periodic gunfire visited the aeromedical squadron; all were right-handed males. Six were tested with the K-2 rifle and one was tested with a K-5 revolver. History taking, physical examination, pure-tone audiometry, and impedance audiometry were conducted. In the next periodic gunfire exercise, all 3650 soldiers performed gunfire with unilateral hearing protection. The average outcome of postexposure air conduction thresholds was 6.5 dB in the right ear and 33.1 dB in the left ear. After medical treatment, hearing impairment was much improved; however, tinnitus was not diminished. In the next periodic gunfire exercise, the result of a supplement of unilateral earplug protection proved its effectiveness on acoustic trauma caused by gunfire noise. Asymmetry in hearing loss is related to the position of the head during gunfire. A unilateral hearing protection device was enough to protect hearing from gunfire noise. At the same time, it can effectively prevent a potential firearm accident that can be caused by trainees mishearing the instruction of a firearm instructor if both earplugs are worn. Thus, providing a unilateral earplug for protection against acoustic trauma must be taken into serious consideration.

Therapeutic efficacy of intra-cochlear administration of methylprednisolone after acoustic trauma caused by gunshot noise in guinea pigs

The therapeutic efficacy of cochlear infusion of methylprednisolone (MP) after an impulse noise trauma (170 dB SPL peak) was evaluated in guinea pigs. The compound action potential threshold shifts were measured over a 14 days recovery period after the gunshot exposure. For each animal, one of the cochlea was perfused directly into the scala tympani with MP during 7 days via a mini-osmotic pump, whereas the other cochlea was not pump-implanted. The functional study of hearing was supplemented by histological analysis. Forty eight hours after the trauma, significant differences between auditory threshold shifts in the implanted and non-implanted ears were observed for frequencies above 8 kHz. At day 7, the difference was significant for only one frequency and no difference was observed after 14 days recovery. Cochleograms showed that the hair cell losses were significantly lower in the MP treated ears. This work indicates that direct infusion of MP into perilymphatic space accelerates hearing recovery, reduces hair cell losses after impulse noise trauma but does not limit permanent threshold shifts.

Therapeutic efficacy of magnesium after acoustic trauma caused by gunshot noise in guinea pigs

Conclusions. The present findings show that magnesium administration can significantly reduce threshold shift 7 days after gunshot noise exposure. However, this improvement seems to be temporary, suggesting a probable advantage in prolonging the treatment. Objective. To evaluate the therapeutic efficacy of magnesium administration after hearing loss induced by gunshot noise. Material and methods. Forty-eight guinea pigs were exposed to an impulse noise (blank shot from a rifle; 170 or 176 dB SPL peak). The therapeutic efficacy of magnesium was evaluated by administering either the treatment or a placebo to the traumatized animals for 7 days, beginning 1 h after the trauma. Auditory function was explored for up to 14 days of recovery by recording the compound action potential in the round window. The functional study of hearing was supplemented by histological analysis. Results. The threshold shifts of the 170-dB SPL group that received magnesium were significantly lower than those of controls after 2 and 7 days of recovery, but no significant difference was evidenced at 14 days in this group, nor at any time in the 176-dB SPL group. Animals treated with magnesium after the 176-dB SPL exposure had a significant reduction in hair cell loss in the basal region.