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Impulse Noise_Auditory Risks

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William James Murphy
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Recent research into the assessment of worker noise exposure has demonstrated that the combination of impulsive noise and continuous noise creates an additional risk of developing noise-induced hearing loss (NIHL). Zhang et al. (2021) demonstrated that workers exposed to non-Gaussian noise accumulated NIHL at a faster rate over their careers than workers exposed to Gaussian noise. The kurtosis statistic of the sound pressure distribution provides a means to adjust the estimated risk of hearing loss between exposure groups exposed to different types of noise. This paper will review the results from our recent studies of kurtosis and exposure level. Some unanswered questions involve the selection of a suitable sample length to estimate kurtosis (Tian et al. 2021), the selection of an applicable compensation factor (Qiu et al. 2021), and understanding the differences exhibited in short (less than 10 years) and long-term exposures and kurtosis (Zhang et al. 2021).
William James Murphy
added 5 research items
We measured impact noise, noise exposures, whole body and hand-arm vibration, and heat stress in a hammer forge. Impact noise levels at the hammers were up to 148 decibels. Nearly all employees’ noise exposures were above noise exposure limits, and noise exposures near the hammers were above 100 decibels, A-weighted. Whole body vibration was above some recommended guidelines, and hand-arm vibration at the grinders could exceed recommended limits. We did not find excessive heat stress. We recommended installing noise controls and replacing current equipment with less noisy equipment. We also recommended putting vibration isolation pads or mats on the hammer work platforms and providing antivibration gloves to employees at the grinders.
This paper describes the development of spatial maps for both peak and A-weighted equivalent sound levels from various firearms, as measured with different spatial resolutions. Two outdoor datasets that adhered to the MIL-STD-1474E weapon noise measurement standard are considered. First is an extensive measurement of the M16A4 rifle at U.S. Marine Corps Base Quantico that included several shooter configurations and a circular measurement arc with 15-deg spacing and 3.67 m radius [R. D. Rasband et al., J. Acoust. Soc. Am. 143, 1935 (2018)]. Second is a measurement of many different firearms using an array with 30-deg spacing and 3.0 m radius, performed in Rudyard Michigan [W.J. Murphy et al., J. Acoust. Soc. Am. 132, 1905 (2012)]. Using these levels and conservative estimates based on spherical spreading and symmetry, level maps are created based on shooter position, weapon used, and number of shots fired. The fidelity of the extrapolation procedure and possible future improvements is discussed. [Work supported by ONR, WTB Quantico, and AFRL through ORISE.]
Gunshot sound pressure levels are commonly measured using commercial sound level meters. The performance of commercial SLMs are compared to a field research system reference. Performance was considered in terms of peak SPL, LAeq8 and damage risk indices. Impulses were generated by a Colt AR-15 and measurements were obtained at 5 reference level locations (130-, 140-, 150-, 160- and 170 peak SPL). Peak levels displayed by SLMs underestimated exposures and peak levels were measured more accurately via SLM AC output at levels up to 150 dB pkSPL. Above 150 dB pkSPL, the downward bias increased with level. Errors were smaller for LAeq8 levels. MPEs were overestimated at higher levels, but were underestimated at lower levels, suggesting that SLM-based assessments of hazard may be too permissive at high levels and too restrictive at low levels. Differences across SLM models were complex and depended on whether the display or AC output was used.
William James Murphy
added 3 research items
Hearing loss in the construction and mining sectors has about a 25% prevalence rate based upon published NIOSH research. Dunn et al. demonstrated that impact noise was more hazardous to the hearing of chinchillas than an equal level (Leq) continuous noise [1]. Zhao et al. demonstrated that human workers exposed to high kurtosis (4 th standardized moment) noise accumulated hearing loss at faster rates than those workers exposed to lower kurtosis values [2]. Operation of machinery can be particularly hazardous when that noise contains significant peaks of high levels exceeding the average levels. Jackhammer noise is one example of a noise exposure that has both a high exposure level (107 dB SPL) and a high kurtosis (15 to 17). This study evaluated six hearing protection devices fitted on an acoustic test fixture. The average reductions of jackhammer noise level for the HPDs was between 21 and 42 dB. For traditional passive HPDs (muffs and plugs), the kurtosis values were reduced to between 3 and 12. For a filter-style earplug in the open condition, the kurtosis value was reduced from 16 to 12. For the earmuff, the kurtosis value was reduced from 15 to 3.
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.
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.
William James Murphy
added a research item
Referee whistles have been suggested as a significant contributor to noise-induced hearing loss. Thirteen models of sport whistles were tested for sound power with a 3-meter hemispherical array of 19 microphones. The whistler produced nine tweets of low, medium, and high effort with two samples of each whistle model. Sound power levels ranged between 74 and 115 dB re 1 picowatt. The low, medium, and high effort tweets had average power levels of 85±6 dB, 100±6 dB, and 110±4 dB, respectively. Preliminary damage-risk analysis of the whistle impulses yield varied estimates for the allowable number of tweets before auditory damage might be expected. For the Auditory Hazard Assessment Algorithm, between 4 and 66 tweets may exceed the daily exposure threshold. Based upon the amount of eight-hour equivalent A-weighted energy, approximately 120 to 500 tweets would exceed the daily 85 dBA exposure limit. The directivity of the sound power measurements will also be examined and risk of hearing loss will be discussed.
William James Murphy
added an update
We made measurements at an indoor firing range before and after noise treatments were installed. The reverberation times decreased significantly, greater than 4 seconds before to less than 1.5 seconds after. I hope to complete an analysis of the relative risks firing before and after treatments.
Also we have an article in preparation that will validate a model for predicting levels at an outdoor firing range. We hope to see it in press this year.
 
William James Murphy
added a research item
Presentation given at the Troy Acoustics 2019 Spring Seminar for Acousticians and Architects. This reports information about firing range measurements that we have conducted.
William James Murphy
added 2 research items
The paper describes the evaluation of 13 models of referee whistles evaluated for peak levels, 8-hour equivalent A-weighted energy and sound power at an outdoor test site. Levels ranged between peak sound pressure levels of 70 - 105, 85 - 117 and 102 - 120 dB for three different levels of blowing effort (Low, Medium and High). The LAeq8 values ranged from 30 - 60, 37 - 72 and 57 - 75 dB A-weighted. The sound power levels ranged from 110 to 124 dB. The levels correlated well with the sound powers reported by manufacturer's data that were available.
As a companion paper to the sound power evaluation of referee whistles, we conducted measurements of the whistles in the laboratory. Intraoral pressure seemed to maintain a linear relationship with the RS amplitude.
William James Murphy
added a research item
This paper compares seven damage risk criteria for impulses measured with small caliber firearms. The conclusions, at least for these data are that the DRCs are largely measuring similar results, the question is what is the acceptable level of hazard before hearing loss is incurred.
William James Murphy
added 13 research items
Hearing protection devices (HPDs) are the principal means of protecting the hearing of a person against harmful levels of noise in highly impulsive noise environments. New HPDs which utilize sound restoration circuitry were measured using a mannequin to assess the performance of these protectors in response to small‐arms weapons fire. The results for the peak reduction and attenuation were analyzed for both indoor and outdoor measurements. The performance of the protectors exhibited little dependence with level for impulses between 150 and 170 decibels. The passive performance for a single protector characterized the active performance for these high‐intensity impulses. The results were also evaluated using the US Army AHAAH cochlear model. As the peak sound‐pressure level underneath the different models of protectors increased, the estimated risk of hearing loss increased. [Work supported by EPA Interagency Agreement DW75921973‐01‐0.]
In 2012, NIOSH partnered with 3M and VIAcoustics for a field study at the 3M™ E-A-RCAL Laboratory (Indianapolis, IN) to measure Impulse Peak Insertion Loss (IPIL) with four hearing protector conditions. IPIL characterizes the noise reduction provided by a hearing protection device in response to high-level impulse signals. The IPIL value is the difference between the maximum sound pressure levels in open-ear and closed-ear conditions. Two data acquisition systems gathered readings from a blast probe and two models of the same acoustic test fixture (ATF): one model from E-A-RCAL and one from NIOSH. The ATFs and blast probe were placed in front of a horn attached to an acoustic shock tube, which produced acoustic impulses at various test levels. Four hearing protection devices (3M™ E-A-R™ Single-Ended Combat Arms™ Earplug, Etymotic Research ETYPlugs® Earplug, 3M™ Peltor™ TacticalPro Communications Headset, and a dual-protector ETYPlugs® earplug with TacticalPro earmuff) were evaluated at nominal peak impulse levels of 132, 150, and 168 decibels (dB). The data were simultaneously recorded by two acquisition systems and did not differ significantly between systems. However, statistically significant differences were observed between the IPIL estimates from the E-A-RCAL and NIOSH ATFs and between the left and right ears of each ATF. The IPIL measured by the left ear of the E-A-RCAL ATF was significantly higher than that of the right ear. The NIOSH ATF did not show such trends, even though the two ATFs were nearly identical. The orientation and location of the ATFs with respect to the wavefront expanding from the horn were significant factors on the impulse level at the two fixtures and between the ears of the fixtures. For the majority of the protectors and impulse levels, the differences between the average IPIL measurements for the two ATFs were statistically significant, indicating real differences possibly due to the fixtures’ position or construction. To ensure repeatability, the IPIL estimates were computed with two separate implementations of the ANSI/ASA S12.42-2010 standard. Analyzing the full-length waveforms recorded during the study with the NIOSH MATLAB IPIL calculator and the VIAcoustics IPILA software yielded identical IPIL estimates.
Several hearing protection devices were tested for impulse peak insertion loss (IPIL) using an acoustic shock tube according to the ANSI S12.42-2010 standard. The protector types included earmuffs with electronic level-limiting circuitry, standard earplugs and earplugs with an orifice or filter that provided increasing attenuation with impulse level. Measurements were conducted using two GRAS 45 CB test fixtures and nominal peak impulse levels of 132, 150 and 168 dB. This poster will report the results from tests of sixteen products tested at the NIOSH Impulse Noise Testing Laboratory. Nonlinear earplug IPILs ranged between about 10-15 dB for 132-dB and 25-35 dB for the 168-dB impulses. Earmuff IPILs exhibited a similar range of performance. The passive foam earplugs provided upwards of 40-55 dB IPIL.
William James Murphy
added a research item
This was a Webinar presented for the NIOSH Public Safety Sector. https://niosh-connect.adobeconnect.com/pkp2o589clrx/ Much of the same information was later presented in June 2018 for the Audiology Online ContinuED webinar. This link will allow you to hear the presentation and the Q&A at the end.
William James Murphy
added 3 research items
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 Beowulf00AE 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.
The National Institute for Occupational Safety and Health (NIOSH) received an employee request for a health hazard evaluation of a Special Weapons Assault Team (SWAT) in January 2002. The department was concerned about noise exposures and potential hearing damage from weapons training on their indoor and outdoor firing ranges. NIOSH investigators conducted noise sampling with an acoustic mannequin head and 1/4 -inch microphone to characterize the noise exposures that officers might experience during small arms qualification and training when wearing a variety of hearing protection devices provided by the department. The peak sound pressure levels for the various weapons ranged from 156 to 170 decibels (dB SPL), which are greater than the recommended allowable 140 dB SPL exposure guideline from NIOSH. The earplugs, ear muffs, and customized SWAT team hearing protectors provided between 25 and 35 dB of peak reduction. Double hearing protection (plugs plus muffs) added 15-20 dB of peak reduction.
William James Murphy
added a research item
PLEASE NOTE: This abstract was submitted to the San Antonio TX meeting. However, I was unable to attend the meeting to give the presentation. The same abstract and paper was presented at ASA meeting Baltimore MD in May 2010. The proposed U.S. Environmental Protection Agency regulation for labeling hearing protection devices (HPDs) includes an impulsive noise reduction rating. In 2009, the American National Standards Institute Subcommittee for noise approved a revised standard for measuring the impulsive insertion loss of HPDs, ANSI/ASA S12.42‐2009. The exposure at the ear in response to a forward‐propagating wave depends strongly on the orientation of the head with respect to the direction of propagation. Furthermore, the insertion loss varies with the peak sound pressure level. This paper reports the results of tests performed using an acoustic shock tube to produce peak impulses of approximately 160‐dB peak sound pressure level. Two manikins were evaluated: the GRAS KEMAR manikin equipped with 1/2‐ and 1/4‐in. microphone in a GRAS 711 IEC coupler and the Institute de Saint Louis manikin equipped with a Bruel & Kjaer IEC 711 coupler equipped with a 1/4 in. microphone. The manikin heads were rotated through ±90 deg relative to the direction of the oncoming wavefront and impulsive peak insertion loss was measured according to S12.42‐2009. [Portions of the research were supported by U.S. EPA Interagency Agreement No. 75921973‐01‐0.]
William James Murphy
added 2 research items
The 1968 CHABA recommendations to limit impulsive noise exposure to levels below 140 dB sound pressure level form the basis of current United States occupational and military standards. The U.S. military standard, MIL‐STD 1474D, estimates the number of allowable shots to which a person may be exposed using peak level, B‐duration, for varying levels of hearing protection usage. The French Weapons Noise Committee has uses the 85 dBAA‐weighted equivalent level, LAeq8 hr, as the limit for allowable exposures. The U.S. Army sponsored a series of noise exposures with chinchillas to investigate the effects of level, number of impulses, and interstimulus interval. Several types of impulses were created ranging from acoustic shock tubes to narrow band impacts reproduced by a loudspeaker. The goodness‐of‐fit and the discrimination of five noise exposure metrics were evaluated in this study: MIL‐STD 1474D, AHAAH model, LAeq8 hr, Pfander’s C‐duration metric, and Smoorenburg’s D‐duration metric. Goodness‐of‐fit was evaluated with a logistic regression and discrimination was evaluated using the area under the receiver operator characteristic curve. The LAeq8 hr was found to best predict the temporary threshold shifts and the AHAAH model was found to best predict the permanent threshold shifts. [Partial funding provided by US Army Aeromedical Research Laboratories MIPR8J07586218].
The proposed U.S. Environmental Protection Agency regulation for labeling hearing protection devices (HPDs) includes an impulsive noise reduction rating . In 2009, the American National Standards Institute Subcommittee for noise approved a revised standard for measuring the impulsive insertion loss of HPDs, ANSI/ASA S12.42‐2009. The exposure at the ear in response to a forward‐propagating wave depends strongly on the orientation of the head with respect to the direction of propagation. Furthermore, the insertion loss varies with the peak sound pressure level. This paper reports the results of tests performed using an acoustic shock tube to produce peak impulses of approximately 160‐dB peak sound pressure level. Two manikins were evaluated: the GRAS KEMAR manikin equipped with 1/2 and 1/4 in. microphone in a GRAS 711 IEC coupler and the Institute de Saint Louis manikin equipped with a Bruel & Kjaer IEC 711 coupler equipped with a 1/4 in. microphone. The manikin heads were rotated through ±90 deg relative to the direction of the oncoming wavefront and impulsive peak insertion loss was measured according to S12.42‐2009. [Portions of the research were supported by U.S. EPA Interagency Agreement No. 75921973‐01‐0.]
William James Murphy
added 3 research items
The analysis of the chinchilla impulsive noise exposures evaluated six potential noise exposure hazard indices (HIs) for goodness-of-fit and discrimination. The candidate HIs were the MIL-STD 1474D, A-weighted equivalent 8-hour level (LAeq8hr), Auditory Hazard Assessment Algorithm for Human (AHAAH) in the Unwarned and Warned condition, Pfander C-duration, and Smoorenburg D-duration. The Auditory Research Laboratory at State University of New York at Plattsburgh and the US Army Aeromedical Research Laboratory (Fort Rucker) collected auditory evoked potentials (AEP) from more than 900 chinchilla following exposure to impulsive noise exposures. For each exposure condition, a representative waveform was digitally recorded and archived along with the baseline AEP threshold, temporary threshold shift, permanent threshold shift and histological data from each animal. The exposures investigated the effects of peak level, number of impulses (1, 10, or 100) and temporal spacing of impulses (6, 60 or 600 seconds). The current analysis evaluated the goodness of fit through the use of mixed models that evaluated the immediate threshold shift (TS0) following exposure and the permanent threshold shift (PTS) evaluated approximately 4 weeks following exposure. The threshold shifts were evaluated using six different outcome variables: categorical classification for a 25 dB shift in hearing (permanent and temporary); categorical classification for a 15 dB shift in hearing (permanent and temporary); and as a continuous variable for threshold shift (permanent and temporary). Furthermore, two fixed effects were considered: frequency and baseline threshold. Goodness-of-Fit: Generally, the statistical analysis demonstrated that LAeq8hr provided the best fit to the threshold shift data for both the permanent and temporary outcomes. The Pfander and Smoorenburg models generally demonstrated the second and third best fits. The Mil-Std 1474D typically had the poorest fit. Goodness-of-fit was judged using the Akaike and Bayesian information criteria. In an analysis separate from the statistical modeling, the threshold shift data were fit at the individual frequencies against the HIs using a logistic model and the threshold shift as a continuous variable. In these fits, the LAeq8hr was also demonstrated to have the best fit as demonstrated by the Coefficient of Determination, r2. Discrimination: Discrimination was tested by analyzing the Receiver Operator Characteristic (ROC) curves for each HI and the threshold shift outcomes. In this sort of analysis greater area under the ROC curve (AUC) implies a greater ability to predict whether or not hearing loss will occur in the chinchilla. The discrimination results depended on the outcome variable. For the categorical permanent threshold shifts (25 dB and 15 dB) the Unwarned AHAAH provided the best discrimination. For the categorical temporary threshold of 25 dB the Unwarned AHAAH, Warned AHAAH, and LAeq8hr indices were better than all the rest, but did not differ significantly from each other. For the categorical outcome of a 15 dB temporary shift, the LAeq8hr index was not significantly different from the Unwarned AHAAH, but better than all the rest. The Unwarned AHAAH was better than three of the rest. Conclusions: The purpose of the interagency agreement between NIOSH and US Army Aeromedical Research Laboratories was to investigate the ability of the several hazard indices to fit the chinchilla data. The LAeq8hr index provided the best fit to the data for all outcome variables, with the Pfander and Smoorenburg indices second and third except in the case of the continuous outcome for permanent threshold shift. In the case of the continuous permanent threshold shift, the Unwarned AHAAH index provided the best fit. While the Unwarned AHAAH model exhibited better discrimination, the Warned AHAAH model did not exhibit significantly better discrimination than the LAeq8hr index.
In 2009, the US Environmental Protection Agency proposed an impulse noise reduction rating (NRR) for hearing protection devices. The impulse NRR is based the American National Standard, ANSI S12.42‐2010, and requires measurements with an acoustic test fixture for three ranges of impulse noises: 130–134, 148–152, and 166–170 dB peak SPL. Five protectors of each of five models (The Combat Arms Linear, Combat Arms Nonlinear, EAR Pod Express, Etymotic EB1, and Bilsom 707 Impact II, all in passive mode) were evaluated per the levels specified in the ANSI standard. Impulses were generated by an acoustic shock tube in the laboratory and by a 0.223 caliber rifle in the field. At each peak impulse level, protector samples were fitted on the test fixture five times and for each insertion, at least three impulses were measured. The impulse NRR 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. Relationships between the continuous noise NRR, the impulse NRR, and the increase in allowable impulse exposures due to the protector will also be presented.
The exposure at the ear in response to a forward-propagating wave depends upon the angle of incidence at the head, the nominal sound pressure level of the impulse and the attenuation of hearing protection (if worn). The unoccluded and occluded responses of an acoustic test fixture equipped with two G.R.A.S. IEC 60711 couplers ¼-inch microphones were measured in 15° increments for impulses with nominal peak sound pressure levels of 150 and 160 decibels. The attenuation was assessed in a variety of ways: Impulse Peak Insertion Loss (IPIL), change in A-weighted Equivalent Energy, and change in the Auditory Hazard Unit. Generally, the LAeq was quite similar to the (IPIL). However the change in AHUs predicted less attenuation than was actually observed. The lower performance for AHUs may be attributable to the nonlinear hazard growth for the unoccluded ear.
William James Murphy
added 3 research items
The NIOSH Health Hazard Evaluation program evaluated employee exposures to high level continuous and impact noise at a hammer forge company. Personal dosimetry data were collected from 38 employees and noise exposure recordings were collected during two facility visits. Extensive audiometric records were reviewed and trends for hearing loss, threshold shifts and risk of hearing loss were assessed. Hearing protector effectiveness was evaluated for hammer forging with an acoustic test fixture. A longitudinal analysis was conducted on the audiometric data set that included 4750 audiograms for 483 employees for the years 1981 to 2006. The analysis of the audiometric history for the employees showed that 82% had experienced a NIOSH-defined hearing threshold shift and 63% had experienced an OSHA-defined standard threshold shift. The mean number of years from a normal baseline audiogram to a threshold shift was about 5 years for a NIOSH threshold shift and was about 9 years for an OSHA threshold shift. Overall hearing levels among employees worsened with age and length of employment. The NIOSH audiometric test criteria in addition to OSHA threshold shift criteria to assess threshold shifts could provide an opportunity for early intervention to prevent future hearing loss. Disclaimer: The findings and conclusions in this report are those of the authors and do not necessarily represent the views of the National Institute for Occupational Safety and Health. Mention of any company or product does not constitute endorsement by NIOSH.
A bullet traveling at supersonic speeds produces a ballistic shock-wave that is N-shaped (N-wave) with properties that are determined by the speed and dimensions of the projectile. The sound levels of these N-waves can be hazardous, and can be comparable to the blast wave received at the shooter’s ear. The present study was undertaken to assess the noise produced by 0.50 caliber Beowulf bullets fired from a semiautomatic rifle with a 16” barrel at a distance of approximately 6.4 meters downrange from the muzzle. The width of the measurement plane ranged between 0.6 and 1.2 meters, and the nominal height of the measurement plane was 1.3 m. Bullet paths were identified using combinations of differences in arrival times of the N-wave on a 3-microphone array. Results confirmed that the sounds produced by a passing supersonic bullet are hazardous and are more hazardous than the blast noise reaching the shooter’s ear at 6.4 meters downrange and within 1.2 meters of the trajectory of the bullet. Disclaimer: The findings and conclusions in this report are those of the authors and do not necessarily represent the views of the National Institute for Occupational Safety and Health. Mention of any company or product does not constitute endorsement by NIOSH.
In-ear dosimetry for high-level impulse noise presents significant challenges. External peak sound pressure levels (>140 dB SPL) combined with hearing protection can result in earcanal levels approaching 140 dB. MIT Lincoln Laboratory has developed a modified commercial-off-the-shelf recorder that simultaneously measures signals from both ear canal and just outside the ear at a sample rate of 96 kHz. Validation measurements were conducted with a GRAS 45CB fixture and an acoustic shock tube. An exploratory study was conducted with a small sample of experimenters during a recent Navy-sponsored noise survey conducted at Quantico Marine Corps Base. Results will be presented from the nominal instructor’s position as well as from bystanders observing at a firing range. Disclaimer: The findings and conclusions in this report are those of the authors and do not necessarily represent the views of the National Institute for Occupational Safety and Health. Mention of any company or product does not constitute endorsement by NIOSH.
William James Murphy
added 2 research items
Damage risk criteria (DRCs) for continuous noise rely upon epidemiologic analyses of populations of persons exposed over several years to noise in occupational environments. In 2006, the U.S. Army proposed to update the MIL-STD 1474D to use the Auditory Hazard Assessment Algorithm for Humans (AHAAH) and discontinue using the peak sound pressure level, envelope duration and number of impulses. The National Institute for Occupational Safety and Health has conducted two separate evaluations of the data used to justify the AHAAH methodology and found that the use of the A-weighted equivalent energy LAeq8 was more suitable for the purposes of predicting the effects of temporary threshold shifts (TTS) both in humans and in chinchillas. The LAeq8 method provided best fit for the TTS outcomes and demonstrated the greatest discrimination (ability to predict TTS) when compared to AHAAH, MIL-STD 1474D and two other proposed DRCs. Similarly, LAeq8 was found to give the best-fit and greatest discrimination for the chinchilla impulse noise exposures. The LAeq8 affords the best sensitivity and specificity for discrimination of potential hazards and has the greatest level of integration with present occupational exposure standards and prospective hearing protection labeling regulations.
William James Murphy
added 2 research items
The Combat Arms Training Facility (CATF) at Wright Patterson Air Force Base in Dayton Ohio was evaluated for the effect of noise treatment to the interior of the firing range. Reverberation time measurements were conducted in the untreated and treated indoor firing ranges. The primary goal of the noise control was to reduce the reverberant energy in the range through the installation of the acoustical treatments to the walls and ceiling of the range. No modifications were made to the windows, doors connecting the range interior to adjacent rooms. Prior to the noise treatments, the reverberation times (RT60) ranged from about 3.5 seconds at 100 Hz to about 2.5 seconds at 2 kHz. Following application of the noise treatments, the RT60 was reduced to about 1.6 seconds at 100 Hz to 0.9 seconds at 2 kHz. This paper will report the measurements, analysis and implications for exposures at the CATF. The room-acoustic measurements will be reported in detail. The effect of the changes in the RT60 will be used to evaluate the speech transmission indices within the range, the critical distance and the estimated levels of sound transmission to the main control room of the range.
The National Institute for Occupational Safety and Health in cooperation with scientists from 3M and the U.S. Army Aeromedical Research Laboratory conducted a series of Impulse peak insertion loss (IPIL) tests of the acoustic test fixtures from the Institute de Saint Louis (ISL) with a 0.223 caliber rifle and two different acoustic shock tubes. The Etymotic Research ETYPlugs™ earplug, 3M™ TacticalPro™ communication headset and the dual protector combination were tested with all three impulse noise sources. The spectra, IPIL, and the reduction of different damage risk criteria will be presented. The spectra from the noise sources vary considerably with the rifle having peak energy at about 1000 Hz. The shock tubes had peak levels around 125 and 250 Hz. The IPIL values for the rifle were greater than those measured with the two shock tubes. The shock tubes had comparable IPIL results except at 150 dB for the dual protector condition. The treatment of the double protection condition is complicated because th...
William James Murphy
added 2 research items
The NIOSH health hazard evaluation program evaluated employees’ exposures to high level continuous and impact noise at a hammer forge company. Personal dosimetry data were collected from 38 employees and noise exposure recordings were collected during two visits to the facility. Extensive audiometric records were reviewed and trends for hearing loss, threshold shifts and risk of hearing loss were assessed. The effectiveness of hearing protection devices for hammer forging was evaluated with an acoustic test fixture. A longitudinal analysis was conducted on the audiometricdata set that included 4750 audiograms for 483 employees for the years 1981 to 2006. The analysis of the audiometric history for the employees showed that 82% had experienced a NIOSH-defined hearing threshold shift and 63% had experienced an OSHA-defined standard threshold shift. The mean number of years from a normal baseline audiogram to a threshold shift was about 5 years for a NIOSH threshold shift and was about 9 years for an OSHA threshold shift. Overall hearing levels among employees worsened with age and length of employment. The NIOSH audiometric test criteria in addition to OSHA threshold shift criteria to assess threshold shifts could provide an opportunity for early intervention to prevent future hearing loss.
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.
William James Murphy
added a project reference
William James Murphy
added a research item
Recreational firearm use is a popular leisure-time activity in the United States today. Millions of Americans of all ages enjoy shooting sports including target practice, competitive shooting, and hunting. While participation in the shooting sports can be an enjoyable recreational pursuit, it can also put an individual at risk for noise-induced hearing loss (NIHL) and tinnitus resulting from unprotected exposure to high-intensity firearm noise. Almost all firearms generate impulse levels in excess of 140 dB peak SPL. Hearing loss may occur gradually over time due to repeated unprotected exposure to firearm noise. Hearing loss also may occur suddenly due to acoustic trauma from a single unprotected gunshot. The hearing loss is often characterized by normal or near normal hearing sensitivity in the lower frequency range with severely impaired hearing in the higher frequency range which results in difficulty hearing speech clearly. NHCA developed this guidance document to assist hearing conservationists, audiologists, physicians and other hearing conservation professionals, in managing and mitigating the risk of NIHL associated with recreational firearm noise. Several strategies can be employed to reduce the risk of acquiring NIHL and associated tinnitus from firearm noise exposure. These include wearing hearing protection devices (HPDs), using firearms equipped with suppressors, choosing smaller caliber firearms, using subsonic ammunition, shooting in a non-reverberant environment, and avoiding shooting in groups. In addition, several commercially-available HPDs are specifically designed for the shooting sports. These include conventional passive earmuffs and earplugs, level-dependent devices that attenuate high level sound while providing audibility for lower level sound, and electronic devices that amplify low level sounds and attenuate high level hazardous sounds. The key to preventing NIHL and tinnitus secondary to excessive firearm noise exposure is to educate firearm users about the auditory hazard associated with firearm noise and provide them with strategies to protect their hearing. Educational programs may be offered through hunter safety courses, hunting clubs, or during training. A special firearm noise topic section should be included in occupational educational training for individuals who use firearms as part of their jobs. Finally, clinical audiologists should educate their patients who use firearms regarding the hazards and ways to prevent hearing loss. Several educational tools are available on the National Hearing Conservation Association website including a hearing loss simulator, a tinnitus simulator, posters and slides of inner ear structures damaged by firearm noise, a hearing protection brochure, a hunting and hearing video and links to other educational resources. Firearm NIHL is almost completely preventable if necessary precautions are taken.
Deanna K Meinke
added 11 research items
Recreational use of firearms in the United States is commonplace. There are 28 x 10(6) Americans who consider themselves hunters and 13 x 10(6) 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 andor 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 computer systems, the impulses can be resolved into a number of different acoustic signals related to different source mechanisms.
Sports officials commonly use a .22 caliber starter pistol at athletic events to generate a loud impulse sound to signal the start of the event (i.e. race) has started (Figure 1). Acoustic comparisons of the impulses generated from a typical .22 starter caliber pistol (Italian Model 314) firing blank ammunition were made to impulses generated from an actual .22 revolver (Smith & Wesson K-22 Masterpiece) firing both blanks and two types of standard velocity cartridges (.22 caliber short and long rifle ammunition). Peak sound pressure levels at the shooters left ear are higher for the starter pistol than the standard .22 caliber revolver for all types of ammunition evaluated. Hence, a typical starter pistol is not inherently less hazardous to hearing than a traditional firearm and alternative lower-level signaling devices should be considered for sporting events. The use of hearing protection devices (HPDs) by event personnel when firing a starter pistol is recommended.
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 else's 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. This was a descriptive study of auditory risk at the position of a bystander near a recreational firearm shooter. 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. 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. 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.
Deanna K Meinke
added a research item
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 (L(eqA8)), 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 athlete's overall noise exposure.