Hazardous Noise Exposure Research Articles

High frequency audiometric notch: An outpatient clinic survey

It is a common misconception that high frequency audiometric notches are diagnostic of noise induced hearing loss. The aim of this study was to identify the prevalence of high frequency notch (HFN) in an audiovestibular medicine outpatient clinic population at a district general hospital. One hundred and forty nine consecutive adult patients were assessed. According to standard practice at the audiovestibular clinic, a full clinical history with particular emphasis on neuro-otological symptoms, noise exposure, and medical risk factors for sensorineural hearing loss was taken. After standard 8-frequency pure tone audiometry, subjects were divided into those with HFN and those without. There were 84 (56%) females and 65 (44%) males with a mean age of 45 years (range: 19 to 91 years). A total of 39.6% had notches not attributable to noise (occupational or recreational) or any other known risk factor. In 29 (49.2%) and 15 (25.4%) the HFN was present in the left and right ear respectively whereas 15 (25.4%) were bilateral. The frequency least affected was 3 kHz while 4 kHz and 6 kHz were affected in almost equal proportions. In 53 ears (71.6%), the notch depth was less than 20 dBHL (10–19 dB) compared to 21 ears (28.4%) with a depth of 20 dBHL or more. This study concludes that high frequency notch without excessive noise exposure or any other known factor is common. It is neither diagnostic of, nor invariable with NIHL unless a convincing history of hazardous noise exposure is elicited from the history.SumarioEs un concepto comúnmente equivocado que las muescas audiométricas en frecuencias altas implican el diagnóstico de pérdida auditiva inducida por ruido (NIHL). El objetivo de este estudio fue identificar la prevalencia de muescas de frecuen-cias altas (HFN) en pacientes ambulatorios de medicina audio-vestibular en un hospital general distrital. Fueron evaluados ciento cuarenta y nueve pacientes adultos consecutivos. De acuerdo con la práctica normal de una clínica audio-vestibular, se hizo una historia clínica completa, con énfasis particular en los síntomas neuro-otológicos, exposición a ruido y factores de riesgo médico de pérdidas auditivas sensorineurales. Tras una audiometría estándar de tonos puros en ocho frecuencias, los sujetos fueron divididos según si tenían o no HFN. Fueron 84 (56%) mujeres y 65 (44%) hombres con edad media de 45 años (rango: 19-91 años). El 39.6% tenían muescas no atribui-bles a ruido (ocupacional o recreativo) o a otros factores de riesgo conocidos. En 29 (49.2%) y en 15 (25.4%) la HFN estuvo presente en oído izquierdo o derecho, respectivamente, mientras que en 15 (25.4%) fue bilateral. La frecuencia menos afectada fue 3 kHz mientras que 4 kHz y 6 kHz estuvieron casi igualmente afectadas. En 53 oídos (71.6%) la profundidad de la muesca fue menor de 20 dBHL (10-18 dB) comparada con 21 oídos (28.4%) en los que fue de 20 dBHL o mayor. Este estudio concluye que es común la HFN sin exposición exce-siva a ruido o a otros factores de riesgo y que no es un signo diagnóstico ni invariablemente una consecuencia de la NIHL, a menos que existan antecedentes convincentes de exposición peligrosa a ruido, derivados de la historia clínica

Exposure to hazardous workplace noise and use of hearing protection devices among US workers—NHANES, 1999–2004

To estimate the prevalence of workplace noise exposure and use of hearing protection devices (HPDs) at noisy work, NIOSH analyzed 1999-2004 data from the National Health and Nutrition Examination Survey (NHANES). A total of 9,275 currently employed workers aged > or =16 years were included in the weighted analysis. Hazardous workplace noise exposure was defined as self-reported exposure to noise at their current job that was so loud that the respondent had to speak in a raised voice to be heard. Industry and occupation were determined based on the respondent's current place and type of work. Twenty-two million US workers (17%) reported exposure to hazardous workplace noise. The weighted prevalence of workplace noise exposure was highest for mining (76%, SE = 7.0) followed by lumber/wood product manufacturing (55%, SE = 2.5). High-risk occupations included repair and maintenance, motor vehicle operators, and construction trades. Overall, 34% of the estimated 22 million US workers reporting hazardous workplace exposure reported non-use of HPDs. The proportion of noise-exposed workers who reported non-use of HPDs was highest for healthcare and social services (73.7%, SE = 8.1), followed by educational services (55.5%). Hearing loss prevention and intervention programs should be targeted at those industries and occupations identified to have a high prevalence of workplace noise exposure and those industries with the highest proportion of noise-exposed workers who reported non-use of HPDs.

A comparison of “Train‐the‐Trainer” and expert training modalities for hearing protection use in construction

Few assessments have been conducted on the impact of a "Train-the-Trainer" (T3) approach for training delivery. The present study compared the effectiveness of a noise induced hearing loss (NIHL) prevention training delivered using "Train-the-Trainer" and expert trainer modalities. Participating construction companies were assigned to the Train-the-Trainer or expert trainer modalities. Workers were recruited from each company and then trained. The effectiveness of the modalities was assessed through the use of surveys. The accuracy of self-reported hearing protection device (HPD) use was also evaluated through on-site observation. Post-training scores for hearing conservation knowledge, perceived barriers, and current and intended future use of HPDs improved significantly for both training modalities. Subjects trained by T3 trainers significantly increased their beliefs regarding general susceptibility to NIHL, desire to prevent NIHL, and ability to recognize, and control hazardous noise exposures. The expert-trained groups significantly increased their beliefs regarding the benefits of HPD use and ability to ask for help with HPDs. The only changes that were significantly different between modalities were in general susceptibility to NIHL and effective use of HPDs. However, these beliefs differed significantly between subjects in the two-modality groups prior to training. Self-reported HPD use was poorly correlated with observed use, calling into question the validity of survey-based HPD use measures in this context. The training improved beliefs regarding HPD use, increased workers' hearing conservation knowledge, and increased self-reported HPD use. The effectiveness of the training was not found to be dependent on training modality.

Can otoacoustic emissions indicate susceptibility to noise‐induced hearing loss in individual ears?

Otoacoustic emissions (OAEs) can potentially be used to identify normal‐hearing individuals who are susceptible to imminent noise‐induced hearing loss. Until now, there has been no way to monitor an individual’s susceptibility dynamically as it varies due to physiological and environmental factors. Although it is known that groups of normal‐hearing noise‐exposed people have lower than average levels of OAEs, such data have never been used to predict future hearing loss in the same individuals. Here, we discuss two studies where the OAEs and hearing thresholds of individuals were measured before and after hazardous noise exposure. Individuals with normal hearing and low‐level or absent OAEs at baseline were at increased risk for acquiring noise‐induced hearing loss after the noise exposure. This supports the theory that OAEs can reflect incipient inner‐ear damage undetected by standard behavioral hearing tests. Furthermore, OAE efferent strength measures may be predictors of NIHL in humans. The animal data are promising, but developing an efficient OAE test that reliably distinguishes a strong efferent reflex from a weaker one in humans is challenging. [Work supported by ONR & USAMRMC].

Where We Work: Naval Submarine Medical Research Laboratory

Where We Work: Naval Submarine Medical Research Laboratory

Real-world performance of headset active noise reduction systems

Active noise reduction (ANR) in headsets promotes the electro-acoustic cancellation of sound within the ear cups of a hearing protector. Operating at frequencies below 1000 Hz, ANR augments attenuation where passive protection is minimal. Personal ANR can reduce the potential for hazardous noise exposure and can facilitate auditory communications. ANR system performance has been characterized to assist purchasing departments in making informed decisions about commercial devices suitable for use in high-noise environments such as helicopters and tracked vehicles. Test methods were developed to assess: (a) active attenuation properties, (b) issues of fitting integrity, (c) speech discrimination performance, (d) saturation or overload threshold limit, and (e) general suitability for long-term use. When properly designed and applied, personal ANR can enhance the listening environment for the user. Nonetheless, performance limitations have been identified in certain devices. Some tended to overload easily or to cease operating under adverse conditions, and others became unstable when the seal around the ear was broken. Proper fitting is pivotal to satisfactory ANR operation, particularly in units with low overload tolerance. Ultimately, the function of any ANR system must be understood in relation to its intended operating environment.

Sampling strategy for noise dosimetry measurements

The U.S. Army has adopted most of the new ACGIH TLVs as criteria in its hearing conservation program. Most significant to the Army program was the change from a non-time-weighted inclusion criterion to the 8-h time-weighted average noise exposure level (TWA). The TWA must now be identified for all Army civilian personnel subjected to hazardous noise exposure and for soldiers working in noise-hazardous industrial operations. This can be accomplished without making noise dosimetry measurements on every single individual suspected of being exposed to hazardous noise. The U.S. Army Environmental Hygiene Agency Technical Guide 181 on noise dosimetry and risk assessment was developed as a guide for evaluating types of noise exposure patterns and includes sampling strategies for dosimetry measurement of TWAs. The statistical basis of the sampling approach will be discussed in some detail. Other changes in the Army hearing conservation program resulting from the adoption of the TLVs will be outlined.

The application of frequency and time domain kurtosis to the assessment of hazardous noise exposures

Five computer synthesized broadband noises, each having the same average spectrum and the same unweighted Leq of 100 dB SPL but very different temporal structures were used to produce hearing loss in chinchillas. Despite the same exposure energies and spectra, each noise exposure produced a different magnitude and frequency distribution of hearing loss and sensory cell loss. The results indicate that the statistical properties of a signal are important in the determination of hearing loss. When the audiometric and histological results are compared to a metric based upon kurtosis measured in the time and the frequency domain for each exposure, there is a strong indication that these matrices are good predictors of the magnitude and frequency distribution of the acoustic trauma. [Research sponsored by NIOSH Grant 2R010H02317.]

Delayed Temporary Threshold Shift Induced by Impulse Noises (Weapon Noises) in Men

Most of the available information on the effects of impulse noise on hearing is derived from temporary threshold shift (TTS2) measurements performed 2 min after a single exposure to small-weapon noises. TTS is known to recover as a linear function of the logarithm of time when it is induced by a continuous noise of moderate intensity. Following the exposure to impulse noise, several investigators have reported individual exceptions to the log-time relation, e.g. increases in TTS during the first hour of recovery. These authors observed a 'rebound recovery function' for most of the exposed men, and they conclude that this phenomenon '... has implications for the use of TTS in the construction of damage risk criteria for hazardous noise exposure ..., a single measure, such as the widely used TTS2 may not be an adequate index of the magnitude of the TTS'. In order to thoroughly investigate in man the existence of 'delayed' TTS following the exposure to actual weapon noises, the 'French Committee on Weapon Noises' carried out the following study. Three groups of soldiers (28 subjects) wearing no hearing protection were exposed in the free field over 2 days to impulse noises produced by a rifle. Békésy audiograms were obtained from each subject just before the exposure, and at 5 min, 1 h and 4 h after exposure. All audiometric tests were carried out even when no TTS was observable in the first postexposure audiogram. A significant number of subjects showed a 'delayed TTS' and/or 'rebound recovery'. The maximum TTS was observed at 1 h after exposure, but the observation of a delayed recovery and a rebound recovery indicate that audiometric tests should be performed in all cases at least up to 4 h after the exposure. More detailed work is necessary to establish what changes may be necessary in the present damage risk criteria for impulse noises of a very high level.

The Hazardous Noise Exposure to Which Airline Passengers are Subjected

Babies and children, in particular, and adults should not be exposed to the noise levels inside commercial aircraft. The passenger cabin noise levels during flight equal or exceed even the inappropriately high legal limits which have been shown not to protect hearing and health. Studies have shown that airline pilots have above normal hearing loss. Thus, each day (in the U. S.) about 400,000 airline passengers are exposed to long periods of excessive and hazardous noise radiation. This unfunded study shows that cruise flight noise levels inside Boeing 737 and 727, Lockheed L-1011, and McDonnell-Douglas DC-10 aircraft are in the 85 to 100+ dBC (or 80 to 90+ dBA) range. A few data released by the EPA indicate there are similar noise levels in all commercial aircraft. Despite the seriousness of the problem, the Cumulative Indices for JASA and contemporary literature on acoustics for the years 1948 to 1972 show no published reports on jet aircraft cabin noise. Consequently, airline passangers have not been informed about the noise levels and effects, and have been deprived of information necessary for making rational judgments about the acceptability of air travel noise environments.

Auditory Temporary Threshold Shift in Snowmobile Users

It has been determined that the noise levels of many snowmobiles and other all-terrain-vehicles frequently exceed criterion values of safe exposure as a function of time. However, there are obvious limitations to the use of the CHABA criteria for determining hazardous noise exposure, since typical snowmobile use does not approximate the extent of exposure implied by the “working-lifetime” concept. Thus, the empirical determination of the amount of TTS resulting from “typical” exposures, whatever they may be, seemed to provide a more relevant approach to the question of whether snowmobile noise poses a hazard to hearing acuity of operators and passengers. TTS measurements were obtained on a number of individuals of all ages under field conditions (within 1–15 min of termination of exposure). Significant amounts of TTS were observed to be occurring in a large proportion of the persons tested. The implications of this study are discussed in terms of the users, the manufacturers, and the CHABA criteria for hazardous noise exposure.

Development of Realistic A-Weighted Auditory Risk Criteria for Aerospace Operations

Attempts directed at identifying potentially hazardous noise exposures have been vigorous. Unfortunately, unanimity of opinions relative to establishment of such criteria has not been achieved. The authors have previously proposed adoption of CHABA Work Group 46 criterion for steady-state-type noises for assessing degrees of auditory risk associated with aerospace operations. The authors review the salient features of various damage risk criteria and primary and secondary compromises are discussed. The authors, using noise data representative of ground and airborne operations, evaluate and critique the different criteria relative to degree of stringency imposed by each. A simple criterion using A-weighted sound levels is proposed for broadband and narrow-band steady-state-type noises.