David C. Byrne

Working in Noise with a Hearing Loss: Perceptions from Workers, Supervisors, and Hearing Conservation Program Managers

Objective: Workers with hearing loss face special problems, especially when working in noise. However, conventional hearing conservation practices do not distinguish between workers with normal hearing versus impaired hearing. This study collected information from workers with self-reported noise exposure and hearing loss, supervisors of such workers, and hearing conservation program managers through focus groups and in-depth interviews to evaluate their perspectives on the impact of hearing loss on safety and job performance, the use of hearing protection, and information needed to appropriately manage hearing-impaired workers who work in noisy environments. Results: Concerns about working in noise with a hearing loss could be grouped into the following 10 categories: impact on job performance, impact on job safety, impaired ability to hear warning signals, impaired ability to monitor equipment, interference with communication, stress and/or fatigue, impaired communication caused by hearing protector use, reduced ability to monitor the environment as the result of hearing protector use, concerns about future quality of life, and concerns about future employability. Mostly, there was an agreement between the perceptions of workers, supervisors, and hearing conservation program managers regarding difficulties associated with hearing loss and consequent needs. These findings suggest that noise-exposed workers with hearing loss face many of the same problems reported in the literature by noise-exposed workers with normal hearing, with additional concerns primarily about job safety as the result of a reduced ability to hear environmental sounds, warning signals, and so forth. Conclusions: The study outlines potential challenges regarding job safety and hearing conservation practices for noise-exposed, hearing-impaired workers. Awareness of these issues is a necessary first step toward providing appropriate protective measures for noise-exposed, hearing-impaired workers.

Effects of training on hearing protector attenuation

The effect of training instruction, whether presented as the manufacturers printed instructions, a short video training session specific to the product, or as a one-on-one training session was evaluated using four hearing protection devices with eight groups of subjects. Naïve subjects were recruited and tested using three different forms of training: written, video, and individual training. The group averages for A-weighted attenuation were not statistically significant when compared between the video or the written instruction conditions, regardless of presentation order. The experimenter-trained A-weighted attenuations were significantly greater than the written and video instruction for most of the protectors and groups. For each earplug, the noise reduction statistic for A-weighting (NRS A ) and the associated confidence intervals were calculated for the 80 th and 20 th percentiles of protection. Across subject groups for each protector, the differences between NRS A ratings were found to be not statistically significant. Several comparisons evaluating the order of testing, the type of testing, and statistical tests of the performance across the groups are presented.

Relationship between comfort and attenuation measurements for two types of earplugs.

Noise-induced hearing loss is almost always preventable if properly fitted hearing protectors are worn to reduce exposure. Many individuals choose not to wear hearing protection because it may interfere with effective communication in the workplace or it may be uncomfortable. Hearing protector comfort has not received the same amount of attention as noise reduction capability. The present study was conducted to evaluate the comfort level of two different types of insert earplugs as well as the attenuation levels achieved by the earplugs. Attenuation levels were obtained with a commercially available earplug fit-test system, and the comfort ratings were obtained by questionnaire. The primary research objective was to determine whether hearing protector comfort was related to measured attenuation values. A linear mixed effects model provided evidence for an inverse relationship between comfort and attenuation.

Results of the National Institute for Occupational Safety and Health—U.S. Environmental Protection Agency Interlaboratory Comparison of American National Standards Institute S12.6-1997 Methods A and B

The National Institute for Occupational Safety and Health and the Environmental Protection Agency sponsored the completion of an interlaboratory study to compare two fitting protocols specified by ANSI S12.6-1997 (R2002) [(2002). American National Standard Methods for the Measuring Real-Ear Attenuation of Hearing Protectors, American National Standards Institute, New York]. Six hearing protection devices (two earmuffs, foam, premolded, custom-molded earplugs, and canal-caps) were tested in six laboratories using the experimenter-supervised, Method A, and (naive) subject-fit, Method B, protocols with 24 subjects per laboratory. Within-subject, between-subject, and between-laboratory standard deviations were determined for individual frequencies and A-weighted attenuations. The differences for the within-subject standard deviations were not statistically significant between Methods A and B. Using between-subject standard deviations from Method A, 3-12 subjects would be required to identify 6-dB differences between attenuation distributions. Whereas using between-subject standard deviations from Method B, 5-19 subjects would be required to identify 6-dB differences in attenuation distributions of a product tested within the same laboratory. However, the between-laboratory standard deviations for Method B were -0.1 to 3.0 dB less than the Method A results. These differences resulted in considerably more subjects being required to identify statistically significant differences between laboratories for Method A (12-132 subjects) than for Method B (9-28 subjects).

Comparison of speech intelligibility measures for an electronic amplifying earmuff and an identical passive attenuation device

Elderly individuals often complain of difficulties in understanding speech, especially when heard against a background noise or when there are multiple speakers. One of the hypothesized reasons for these complaints is the reported age-related decline in auditory temporal processing (Schneider & Pichora-Fuller, 2001; Schneider, Daneman, & PichoraFuller, 2002). The rationale underlying this hypothesis is that the appropriate use of speech cues relies on several types of auditory temporal resolution, which research has shown is age-related (Gordon-Salant, 2005; Pichora-Fuller & Souza, 2003; Schneider & Pichora-Fuller, 2001; Schneider et al., 2002). A large number of studies have compared young and elderly subjects on a variety of auditory temporal resolution tasks and reported poorer resolution by the elderly as compared to the younger individuals. Elderly adults perform poorer than younger adults in gap detection tasks and need longer silent intervals to identify the presence of a gap when the marker signal is 250 msec or shorter (Fink, Churan, & Wittmann, 2005; Fitzgibbons & Gordon-Salant, 2001; Grose, Hall, & Buss, 2006; Lister & Roberts, 2005; Lister & Tarver, 2004; Roberts & Lister, 2004; Schneider & Hamstra, 1999; Schneider, Speranza, & Pichora-Fuller, 1998; Snell, 1997; Snell & Frisina, 2000; Snell, Mapes, Hickman, & Frisina, 2002; Strouse, Ashmead, Ohde, & Grantham, 1998). Other studies have reported that older subjects have difficulty in correctly identifying temporal order in a tonal sequence (Fitzgibbons & Gordon-Salant, 1998; Gordon-Salant & Fitzgibons, 1999). Furthermore, a number of studies have reported that older individuals require larger differences in duration between two tones in order to detect a difference (Abel and Hay, 1996; Fitzgibbons & GordonSalant, 1994, 1995, 1996). Similar results, indicating poorer discrimination by the elderly, were found when comparing older and younger adults on binaural temporal processing tasks such as locating a tone in the frontback plane (Abel and Hay, 1996), tone localization (Abel, Giguère, Consoli, & Papsin, 2000) and click lateralization (Babkoff, Muchnik, Ben-David, Furst, Even-Zohar, & Hildesheimer, 2002; Strouse et al., 1998). Traditionally, most of the studies of age-related decline in temporal resolution have used the gap detection task, in which the duration of the silent interval within a tone is manipulated until the participant (young or elderly adult) is able to detect a non-continuous tone (Ezzatian , PichoraFuller , & Schneider, 2010; Fink et al., 2005; Fitzgibbons & Gordon-Salant, 2001; Grose, Hall, & Buss, 2006; Lister & Roberts, 2005; Lister & Tarver, 2004; Roberts & Lister, 2004). Other researchers have used the duration discrimination task, in which the duration of a tone is manipulated and changes in duration are detected (Abel and Hay, 1996; Gordon-Salant & Fitzgibbons, 1999; Fitzgibbons & Gordon-Salant, 1994, 1995). Taken together, the results of these studies have shown that the elderly require larger gaps and longer tone durations than the young adults to attain the same levels of discrimination. In general, the common feature in these and other tasks that were used to measure temporal resolution is that the discrimination may be accomplished by one ear only. Consequently, the temporal cue may not necessarily be central, although some evidence points to the involvement of higher order processes in the temporal range associated with gap detection (Ross, Schneider, Snyder, & Alain, 2010). In our studies we have used a different method for studying auditory temporal resolution among the elderly, and other populations of interest, the dichotic temporal order judgment (TOJ) task. This task involves the identification of the order of two sounds that are equal in frequency and intensity (Ben-Artzi, Fostick & Babkoff, 2005; Babkoff, Zukerman, Fostick, & Ben-Artzi, 2005). The tones are delivered to each ear and are separated by a range of inter-stimulus intervals (ISI). The listener is required to judge the order of presentation of the tones to the two ears (left-right or rightleft). This paradigm eliminates the possible use of spectral cues for order judgment and depends on central mechanism(s) for the temporal resolution of information received from both ears. The elimination of spectral cues reinforces the conclusion that the judgment is based on the temporal domain. Two temporal parameters are manipulated when a tone is presented to each ear separated by an inter-stimulus interval: i) the silent interval (i.e., the inter-stimulus interval); and ii) the stimulus onset asynchrony (SOA) (i.e., the time from the onset of the tone to the first ear and the onset of the tone to the second ear. The contribution of each of the two parameters to performance level can be studied by manipulating tone duration, while keeping ISI constant. The main purpose of the current study was to identify the temporal parameter that explains most of the variance associated with the judgment of temporal order.The purpose of this study was to identify any differences between speech intelligibility measures obtained with MineEars electronic earmuffs (ProEars, Westcliffe, CO, USA) and the Bilsom model 847 (Sperian Hearing Protection, San Diego, CA, USA), which is a conventional passive-attenuation earmuff. These two devices are closely related, since the MineEars device consisted of a Bilsom 847 earmuff with the addition of electronic amplification circuits. Intelligibility scores were obtained by conducting listening tests with 15 normal-hearing human subject volunteers wearing the earmuffs. The primary research objective was to determine whether speech understanding differs between the passive earmuffs and the electronic earmuffs (with the volume control set at three different positions) in a background of 90 dB(A) continuous noise. As expected, results showed that speech intelligibility increased with higher speech-to-noise ratios; however, the electronic earmuff with the volume control set at full-on performed worse than when it was set to off or the lowest on setting. This finding suggests that the maximum volume control setting for these electronic earmuffs may not provide any benefits in terms of increased speech intelligibility in the background noise condition that was tested. Other volume control settings would need to be evaluated for their ability to produce higher speech intelligibility scores. Additionally, since an extensive electro-acoustic evaluation of the electronic earmuff was not performed as a part of this study, the exact cause of the reduced intelligibility scores at full volume remains unknown.

Early prognosis of noise-induced hearing loss: prioritising prevention over prediction

Moshammer et al 1 have recommended routine implementation of a temporary threshold shift (TTS) screening test to identify workers particularly at risk of developing noise-induced hearing loss (NIHL) from occupational exposure to hazardous noise. Their work addresses an important occupational health problem. NIHL ranks among the most common work-related injuries in many countries, with an estimated global annual incidence of 1.6 million cases, and accounts for approximately 16% of disabling adult hearing losses worldwide.2 ,3 Individuals vary in their susceptibility to the damaging effects of noise and no suitable method currently exists to predict the susceptibility of a particular worker. In their study, Moshammer et al measured TTS in newly hired employees following exposure to a 20 min, high-intensity, low-frequency experimental noise. They then followed the workers over time to see who ultimately developed a permanent threshold shift (PTS). The authors report that a TTS of 14 dB or more measured 2.5 min after the experimental exposure identifies workers at greater risk for PTS. They recommend routinely using this procedure to screen for susceptibility to noise in workplace hearing loss prevention programmes. However, this recommendation is premature in view of the study results. The TTS measure had a sensitivity of 82%, meaning that 18% of those who developed PTS were not identified by the TTS screening—a …

Acceptance of a semi-custom hearing protector by manufacturing workers.

Workers complain about wearing hearing protection for two primary reasons: comfort and communication.(1) Employers are concerned about hearing protection costs. Recent advances in hearing protector technology seemed to address those issues through a semi-custom earplug. This new device was designed to prevent overprotection by incorporating only enough attenuation to bring the worker down into the safe exposure zone. Although initially more expensive than disposable hearing protection devices (HPDs), the semi-custom hearing protector would be expected to last several years. The Hearing Loss Prevention Team of the National Institute for Occupational Safety and Health (NIOSH) was invited by a major auto manufacturing company and the union (UAW) to supervise a longitudinal trial of a semi-custom hearing protector (SonoCustom by Sonomax Technologies, Inc.,Montreal, Canada). This protectorwas advertised as (1) being more comfortable since each plug was custom molded for each worker, and (2) more effective because each plug’s noise reduction rating was tuned to that worker’s particular job. The company’s hearing conservation contractor partnered with NIOSH by recruiting volunteers for the study and providing follow-up usage reports. The study was conducted over the course of 1 year with NIOSH site visits at the start, at 1 month, at 4 months, and at 1-year time intervals. The goal of this trial was to determine worker acceptance of the semi-custom earplug. Compared with the non-custom earplugs used in this study, the SonoCustom ear plugs were relatively new to the market and have not been extensively investigated in the literature. Initial studies have focused on a new way to measure and model the acoustical performance.(2–4) Wagoner et al.(5) studied speech intelligibility and attenuation while subjects wore the SonoCustom earplugs or two other non-custom, commercially available hearing protectors in laboratory tests and in the field. In the laboratory they were not able to find any statistically significant difference, between the three earplugs, for speech intelligibility or attenuation. Regarding comfort issues, they briefly mentioned that the two non-custom HPDs were judged by the workers to be more comfortable and easier to use than the SonoCustom earplug.

Analysis of Nonstandard Noise Dosimeter Microphone Positions

This study was conducted as part of a project involving the evaluation of a new type of noise exposure monitoring paradigm. Laboratory tests were conducted to assess how “nonstandard” dosimeter microphones and microphone positions measured noise levels under different acoustical conditions (i.e., diffuse field and direct field). The data presented in this article reflect measurement differences due to microphone position and mounting/supporting structure only and are not an evaluation of any particular complete dosimeter system. To varying degrees, the results obtained with the dosimeter microphones used in this study differed from the reference results obtained in the unperturbed (subject absent) sound field with a precision (suitable for use in an ANSI Type 1 sound level meter) 1/2-inch (12.7 mm) measurement microphone. Effects of dosimeter microphone placement in a diffuse field were found to be minor for most of the test microphones/locations, while direct field microphone placement effects were found to be quite large depending on the microphone position and supporting structure, sound source location, and noise spectrum.

Inter-laboratory comparison of three earplug fit-test systems

ABSTRACT The National Institute for Occupational Safety and Health (NIOSH) sponsored tests of three earplug fit-test systems (NIOSH HPD Well-Fit, Michael & Associates FitCheck, and Honeywell Safety Products VeriPRO). Each system was compared to laboratory-based real-ear attenuation at threshold (REAT) measurements in a sound field according to ANSI/ASA S12.6-2008 at the NIOSH, Honeywell Safety Products, and Michael & Associates testing laboratories. An identical study was conducted independently at the U.S. Army Aeromedical Research Laboratory (USAARL), which provided their data for inclusion in this article. The Howard Leight Airsoft premolded earplug was tested with twenty subjects at each of the four participating laboratories. The occluded fit of the earplug was maintained during testing with a soundfield-based laboratory REAT system as well as all three headphone-based fit-test systems. The Michael & Associates lab had the highest average A-weighted attenuations and smallest standard deviations. The NIOSH lab had the lowest average attenuations and the largest standard deviations. Differences in octave-band attenuations between each fit-test system and the American National Standards Institute (ANSI) sound field method were calculated (Attenfit-test - AttenANSI). A-weighted attenuations measured with FitCheck and HPD Well-Fit systems demonstrated approximately ±2 dB agreement with the ANSI sound field method, but A-weighted attenuations measured with the VeriPRO system underestimated the ANSI laboratory attenuations. For each of the fit-test systems, the average A-weighted attenuation across the four laboratories was not significantly greater than the average of the ANSI sound field method. Standard deviations for residual attenuation differences were about ±2 dB for FitCheck and HPD Well-Fit compared to ±4 dB for VeriPRO. Individual labs exhibited a range of agreement from less than a dB to as much as 9.4 dB difference with ANSI and REAT estimates. Factors such as the experience of study participants and test administrators, and the fit-test psychometric tasks are suggested as possible contributors to the observed results.

Comparison sound-field measurements of hearing protector attenuation and fit-test systems

The American National Standards Institute (ANSI), accredited S12 standards committee for noise, working group 11 is developing a standard to characterize the performance of hearing protector fit test systems. An inter-laboratory study was conducted to compare sound field measurements of real-ear attenuation at threshold (REAT) tests of hearing protection with three hearing protection fit-test systems. The draft ANSI standard for personal attenuation ratings from fit-test systems includes adjustments to the fit test system personal attenuation rating for the accuracy and precision of the measurement. As well, adjustments are proposed for the effect of fitting and for spectral variability of effective attenuation. In the inter-laboratory study, two fit-test systems exhibited precision of about 2 dB while the third system had a precision of about 4 dB. The third system underestimated the sound field attenuation by about 2 dB. Because the inter-laboratory study tested two fittings of the hearing protector with each fit-test system, the variability of individual fitting is described as an average of the differences of first and second tests. This paper will also evaluate the effect of the noise spectrum for the three fit-test systems.