Damage Risk Criteria Research Articles

Acoustic reflexes are common but not pervasive: evidence using a diagnostic middle ear analyser

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.

Occupational Hearing Loss from Non-Gaussian Noise.

For millennia, we have known that loud noise can harm hearing. However, defining the specific hearing risk posed by a specific noise for a specific individual is still elusive. Many factors influence whether or not a given noise is harmful. Attempts to quantify this potential harm began in earnest after World War II, when many veterans returned to their civilian lives with service-connected hearing loss. Database analyses, laboratory studies of permanent and temporary threshold shifts in animals, and laboratory studies of temporary threshold shifts in humans led to the first recommended hearing damage-risk criteria and corresponding hearing conservation programs in the 1950s. Not unexpectedly, as our ability to measure and monitor both noise exposures and their effects on humans and animals has evolved, recommended hearing damage-risk criteria and hearing loss prevention practices also have evolved.

Acoustic reflexes are common but not pervasive: evidence from the National Health and Nutrition Examination Survey, 1999–2012

Objective: To determine whether acoustic reflexes are pervasive (i.e. sufficiently prevalent to provide 95% confidence of at least 95% prevalence) and might be invoked in damage-risk criteria (DRC) and health hazard assessments (HHA) for impulsive noise.Design: Cross-sectional analyses of a nationally-representative study.Study sample: National Health and Nutrition Examination Survey (NHANES) data collected between 1999 and 2012 were used. Over 60 thousand reflex traces obtained from 15,106 NHANES participants were used in the study, along with demographic, audiometric, health and exposure variables obtained in that study.Results: Acoustic reflexes were not sufficiently prevalent to be deemed pervasive by any detection method or in any subgroup defined by age or audiometric characteristics. The odds of observing acoustic reflexes were greater for women, young adults, and people with better hearing sensitivity. Abnormally high tympanometric admittance and “Other” race/ethnicity (i.e. people who do not self-identify as exclusively Non-Hispanic White, Non-Hispanic Black, Mexican–American, or Hispanic) were associated with lower odds.Conclusions: Acoustic reflexes are not sufficiently prevalent to be included in DRC and HHA for impulsive noise.

Auditory risk of air rifles

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.

Effect of personal music system use on sacculocollic reflex assessed by cervical vestibular-evoked myogenic potential: A preliminary investigation.

Listening to music through a portable personal music system (PMS) is a growing trend, especially among the youth. The preferred listening level in such kinds of PMS has been reported to cross the safe levels and its impact on the auditory system was demonstrated in several previous investigations. Owing to the commonality in several aspects between the auditory and the vestibular systems, it appears likely that the deleterious effects of PMS use could also be impinging on the vestibular system, which has never been investigated. The present study therefore, aimed at evaluating the effects of PMS use on the sacculocollic reflex assessed by the cervical vestibular-evoked myogenic potential (cVEMP) technique. Thirty-two regular PMS users and 32 nonregular PMS users underwent cVEMP testing using alternating polarity 500 Hz tone bursts. The results revealed no significant group difference in latencies and interaural asymmetry ratio. However, the cVEMP was significantly reduced in the group of individuals in whom the diffused field equivalent sound pressure levels (SPLs) were above the damage risk criteria (DRC) compared to those with diffused field equivalent SPLs below it (P < 0.01). Therefore, the use of PMS at high levels of volume controls could be deleterious to the vestibular well-being of an individual.

Measurement of high level impulse noise for the use with different damage risk criteria

On the battlefield, but also during training, a soldier is continuously exposed to various types of noise (impulse and continuous). This exposure is not only noise generated by his own weapon but also by weapons or vehicles of close by troops. The exposure levels are between 160 dB peak for small arms and 190 dB peak at the soldier's ear for some anti tank weapons, with A-durations from 0.3 ms (small caliber) to 4 ms for large caliber weapons (e.g., Howitzers). In order to protect the soldier to noise exposures which may induce hearing loss, damage risk criteria (DRC) are implemented, and proposed for the prediction of the potential risk due to a certain noise exposure. Depending on the type of criteria (Pressure-Time-History or A-weighted Energy based), the recording and evaluation of different physical signal parameters has to be done in accordance to the used DRC. The paper will present the problems which may arise when recording impulse (weapon) noise with very high peak pressure levels and discuss measurement techniques compatible with the used DRCs. The paper will also discuss problems which may arise during the use and development of portable noise dose meters for the use in the military environment.

LIAeq100ms, An A-duration adjusted impulsive noise damage risk criterion

Impulsive noise damage risk criteria (DRCs) have been the subject of much debate nationally and internationally for more than 30 years. Several approaches have been used in proposed DRCs including: curves defining exposure based on peak level and A or B duration; auditory hazard units based on the analytical auditory model known as AHAAH; and LAeq metrics based on the equal energy concept. Each of the approaches has positive and negative attributes. One of the issues with LAeq metrics has been the over estimation of hazard with long duration impulses such as those coming from blasts, artillery, large mortars, or shoulder launched missiles. The presentation will describe and discuss the LIAeq100ms impulsive DRC which includes an adjustment based on the A-duration of the impulsive noise and a method of computing protected impulsive noise exposures using impulsive insertion loss data from hearing protectors measured with methods defined in ANSI S12.42.

Noise exposure criteria for continuous noise: A case for reducing the 8 hour open ear exposure level

Personnel working in hazardous noise environments can be protected from noise induced hearing loss (NIHL) or other hearing related disabilities when their exposures are limited. Limiting noise exposures can be accomplished by engineering controls, administrative controls, and/or with the use of personal protective equipment. Damage risk criteria (DRC) were developed as a guide to limit personnel noise exposure in order to reduce the risk of NIHL. With the exception of the US Occupational Safety and Health Administration (OSHA), the US and many European countries accepted the DRC of 85 dB for 8 hours with a 3 dB per doubling exchange rate. Recent studies of the auditory response to noise dose, conducted at the Air Force Research Laboratory, found that A-weighted open ear exposures may be more hazardous (i.e., have a higher effective noise dose) than equal A-weighted level protected ear exposures. A potential conclusion of these studies is that hearing protectors are more effective than previously thought and reducing the open ear exposure criteria may be needed in order to minimize NIHL. This presentation will describe the pros and cons of reducing the 85 dBA DRC.

Prevalence of acoustic reflexes in the United States

The acoustic reflex is a contraction of the middle ear muscles in response to high-level sounds. Acoustic reflexes are invoked as a protective mechanism in some damage-risk criteria (DRC). However, acoustic reflexes are not always observed among people without auditory dysfunction, and should not be included in DRC unless there is 95% certainty that 95% of the population have acoustic reflexes. In the current study, we present the prevalence of acoustic reflexes among people 12 years and older (N &amp;gt; 11,400), using data from the National Health and Nutrition Examination Survey (NHANES). The NHANES can be used to produce prevalence estimates generalizable to the non-institutionalized U.S. population. Ipsilateral reflexes were screened at two elicitor frequencies and detected using Frequentist methods and via Kalman filtering of the reflex trace. Reflexes are pervasive only among those with hearing thresholds better than 15 dB HL at all frequencies, and fall below the criterion certainty with poorer sensitivity even at lower frequencies. Age and tympanometric variables are also related to reflex detection. Reflex prevalence is generally high among young people with adequate hearing sensitivity for unrestricted military duty, but the prevalence is not uniform among audiometric configurations within this hearing profile.

Assessing acoustic reflexes for impulsive sound

The acoustic reflex is an involuntary contraction of the middle ear muscles in response to a variety of sensory and behavioral conditions. Middle ear muscle contractions (MEMC) have been invoked in some damage-risk criteria for impulsive noises for over 40 years and one damage-risk criteria proposes that MEMC precede the impulse for a warned listener via response conditioning. However, empirical data describing the prevalence, magnitude, and time-course of reflexive MEMC elicited by impulsive stimuli as well as non-acoustic stimuli and behaviors are scant. Likewise, empirical support for anticipatory MEMC is limited and studies often fail to control for attention or concomitant muscle activity. The current study is a large-scale, multi-experiment project designed to address these limitations in a laboratory and field environment. MEMC are detected using click train stimuli as probes. Reflexive MEMC are elicited using tones, recorded gunshots, and non-acoustic stimuli (e.g., controlled release of compresse...

Evaluation of high-level noise exposures for non-military personnel

Noise-induced hearing loss is often attributed to exposure to high-level impulsive noise exposures from weapons. However, many workers in industries such as mining, construction, manufacturing, and services are exposed to high-level impulsive noise. For instance, construction workers use pneumatic tools such as framing nailers that can produce impulses at levels of 130 dB peak sound pressure level or greater. Miners have exposures to roof bolters and jack-leg drills that produce more of a continuous, but highly impulsive noise. In some areas of manufacturing the exposures include drop forge processes which can create impacts of more than 140 dB. Finally, in the services sector, law enforcement personnel who maintain proficiency with firearms experience the full gamut of small-caliber firearms during training. This paper will examine the noise exposures from recordings that the NIOSH Hearing Loss Prevention Team have collected. The noises will be evaluated with different damage risk criteria for continuous and impulse noise where appropriate.

A biomechanically based auditory standard against impulse noise

This paper addresses two critical issues in developing a damage risk criteria against impulse noise injury, namely, (1) difficulty in setting a threshold for large weapon noise involving hearing protecting devices (HPDs) and small arms noise involving no HPDs; and (2) having a standard procedure to account for the effects of HPDs. The rational way to resolve these issues is to develop biomechanical-based standard using a physics-based model. The Auditory Hazard Assessment Algorithm for the Human (AHAAH) is a biomechanical model that simulates the transmission of sound energy from free field through the ear canal and middle ear to the cochlea. Extensive research has been performed by subjecting the AHAAH to a rigorous verification and validation process. Findings show that the AHAAH middle ear is overly compressive and corrections were made to the annular ligaments parameters. The human data from the historical Albuquerque walk-up study with volunteers wearing HPDs were used to validate the model and develop the dose-response curve for the injury threshold. Calculations were then performed for the German rife noise tests with volunteers not wearing HPDs, and the predictions show excellent comparison with the injury outcomes, hence providing an independent validation of the revised model.

Damage risk criteria for high-level impulse noise and validation data

The existing DRCs for high-level impulse noise will be briefly described along with their relative merits. Classical DRCs (CHABA, Mil-STD 1474D Z-curves, Pfander, Smoorenburg...) overestimate the hazard of large weapons, do not assess the actual efficiency of the HPs, and are not compatible with the occupational DRCs. The AHAAH model is potentially very powerful. However, the model needs to “know” the exact pressure-time history of the impulse at the subject's ear and the human middle ear transfer function for high-level impulses. Unexpected artifacts of measurements send the model on wrong tracks! Last but not least the “parameters” of this model need to be “adjusted” to be in agreement with the experimental results obtained on a large number of soldiers (to be presented). The LAeq8 method with a limit of 85 dB allows a limitation of the hearing hazard comparable to that aimed at by the other DRCs. It allows the assessment of the hazard for all kinds of weapon noises (free field and/or reverberant conditions) and for combined exposures (impulse and continuous noise) either on protected or unprotected ears. Finally, the auditory hazard is evaluated along the same rules in the military and in occupational exposures (ISO 1999).

Review of weapon noise measurement and damage risk criteria: considerations for auditory protection and performance.

Noise-induced hearing loss resulting from weapon noise exposure has been studied for decades. A summary of recent work in weapon noise signal analysis, current knowledge of hearing damage risk criteria, and auditory performance in impulse noise is presented. Most of the currently used damage risk criteria are based on data that cannot be replicated or verified. There is a need to address the effects of combined noise exposures, from similar or different weapons and continuous background noise, in future noise exposure regulations. Advancements in hearing protection technology have expanded the options available to soldiers. Individual selection of hearing protection devices that are best suited to the type of exposure, the auditory task requirements, and hearing status of the user could help to facilitate their use. However, hearing protection devices affect auditory performance, which in turn affects situational awareness in the field. This includes communication capability and the localization and identification of threats. Laboratory training using high-fidelity weapon noise recordings has the potential to improve the auditory performance of soldiers in the field, providing a low-cost tool to enhance readiness for combat.

Comparison of impulse peak insertion loss measured with gunshot and shock tube noise sources

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 the earmuff reduces the shock wave and reduces the effective level experienced by the earplug. For the double protection conditions, bone conduction presents a potential limiting factor for the effective attenuation that can be achieved by hearing protection.

Auditory risk estimates for youth target shooting

Objective: To characterize the impulse noise exposure and auditory risk for youth recreational firearm users engaged in outdoor target shooting events. The youth shooting positions are typically standing or sitting at a table, which places the firearm closer to the ground or reflective surface when compared to adult shooters. Design: Acoustic characteristics were examined and the auditory risk estimates were evaluated using contemporary damage-risk criteria for unprotected adult listeners and the 120-dB peak limit suggested by the World Health Organization (1999) for children. Study sample: Impulses were generated by 26 firearm/ammunition configurations representing rifles, shotguns, and pistols used by youth. Measurements were obtained relative to a youth shooter's left ear. Results: All firearms generated peak levels that exceeded the 120 dB peak limit suggested by the WHO for children. In general, shooting from the seated position over a tabletop increases the peak levels, LAeq8 and reduces the unprotected maximum permissible exposures (MPEs) for both rifles and pistols. Pistols pose the greatest auditory risk when fired over a tabletop. Conclusion: Youth should utilize smaller caliber weapons, preferably from the standing position, and always wear hearing protection whenever engaging in shooting activities to reduce the risk for auditory damage.

Noise exposure profiles for small-caliber firearms from 1.5 to 6 meters

Small caliber firearms (rifles, pistols and shotguns) are commonly used at outdoor firing ranges for training in shooting skills, job qualification and for recreation. Firearm noise from fifty-four weapons was measured at an outdoor range in the near field (6 meters and closer) of the weapons using a radial array of 18 microphones centered on the shooter’s head. Each weapon was fired five times and the microphone array was sampled at 200 kHz with at least 16-bit resolution. Peak sound pressure levels and damage risk criteria (e.g. MIL-STD 1474D, 8-hour Equivalent A-weighted Level (LAeq8), and Auditory Hazard Assessment Algorithm for Humans (AHAAH)) were computed for each microphone and compared across weapon type, caliber and load. The acoustic propagation from the muzzle to the microphone was modeled using a simple image source over a reflecting plane. The impedance of the ground was estimated from the observed data and was used to compare the measured waveforms with the estimated waveforms. These data will be used to model the exposures for multiple shooters and observers standing at or behind the firing line.

Continuous and impulsive noise attenuation performance of passive level dependent earplugs

Level dependent hearing protectors, earplugs and earmuffs, have advanced in technology due to the needs of military personnel and others to reduce the risk of hearing damage from impulsive noise. These hearing protectors were developed to preserve ambient listening capabilities therefore improving situational awareness while reducing the risk of noise induced hearing loss by attenuating both continuous and impulsive noise. Four commercially available passive level dependent earplugs were assessed for both continuous noise attenuation and impulsive insertion loss performance. The continuous noise attenuation results were collected using American National Standard Institute (ANSI) S12.6-2008 Methods for Measuring the Real-Ear Attenuation of Hearing Protectors while the impulsive insertion loss results were collected using ANSI S12.42-2010 Methods for the Measurement of Insertion Loss of Hearing Protection Devices in Continuous or Impulsive Noise Using Microphone-in-Real-Ear (MIRE) or Acoustic Test Fixture Procedures. The presentation will include the passive noise attenuation performance of level dependent earplugs for both continuous and impulsive noise. The impulsive insertion loss results for these particular hearing protectors will be applied to impulsive noise damage risk criteria for an estimate of allowable impulsive noise exposure.

A case for using A-weighted equivalent energy as a damage risk criterion for impulse noise exposure

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.

Using impulsive peak insertion loss of hearing protectors with impulsive damage risk criteria

Impulsive noise presents special challenges for hearing conservation. The scientific community continues to search for an impulsive noise exposure criterion which accurately assesses the hearing damage risk for both short and long duration impulses. Other factors, such as the use of hearing protectors, earmuffs and earplugs, also affect the hearing damage risk but the current criteria do not address methods for using the attenuation of hearing protectors in impulsive noise. The relatively new ANSIS12.42-2010 “Methods for the Measurement of Insertion Loss of Hearing Protection Devices in Continuous or Impulsive Noise using Microphone-in-Real-Ear or Acoustic Test Fixture Procedures” describes methods for measuring the peak insertion loss of a hearing protector in impulsive noise. This paper will describe a method to apply the peak insertion loss data to impulsive noise damage risk criteria for an estimate of allowable impulsive noise exposure when using hearing protection.