Federal regulations specify that an employee working for eight hours cannot legally be exposed to noise which has a time-weighted average greater than 90 decibels on the A scale. The industrial workforce is comprised of not only people with normal hearing acuity, but of individuals who suffer from hearing loss. While current noise regulation standards are deemed appropriate for those with normal hearing, it is difficult to apply these standards to persons wearing hearing aids on the job. The ambient, or unamplified, noise levels that fall below the maximum permitted by OSHA standards may very well be amplified to levels greater than 90 dBA, by the hearing aid. If this were the case, the company employing the hearing aid user would technically be in violation of the OSHA regulations. This study addressed the question of what noise exposure might be expected for hearing aid users on the job in different situations, as well as in non-vocational settings. The research involved two methods, conducted to determine the noise levels created by hearing aids with different amounts of gain and to determine whether the amplified noise levels exceed those requiring intervention under current regulations. For both methods, ambient and amplified noise levels for each condition were gathered in specified increments, and were compared with regard to current regulatory standards. The resultant data revealed that when ambient noise levels average between 80 and 84 dBA, amplification provided by even a mild gain hearing aid caused the eight hour time-weighted averages (TWA's) to increase to levels above the 90 dBA maximum permissible levels as delineated by OSHA. Moderate and high gain aids further increased these levels. The results of this study suggest that the hearing aid users in industrial and perhaps non-industrial settings may very well be exposed to intensity levels which exceed OSHA maximums, even when ambient levels do not. The extent to which these arc exceeded are based on the gain and output of the hearing aid in use.

Hearing protection devices (HPDs), a widely used countermeasure against noise-induced hearing loss, are laboratory-tested for their attenuation (noise reduction) capabilities. Unfortunately, laboratory tests overestimate the in-workplace performance of the devices, potentially leading to inadequate protection for the user. Many factors affect in-field effectiveness, including the physical design and "wearability" of the protector. Wearability, a highly subjective aspect which encompasses such characteristics as user comfort, ease of use, and acceptability, directly affects performance by influencing the regularity of use and the manner in which a protector is worn. This research investigated the influence of the user's work-related activities over a prolonged wearing period, and of variations in headband compression force and cushion material (liquid- or foam-filled) on achieved noise attenuation and wearability (comfort and acceptability) of earmuff hearing protectors. REAT (real-ear attenuation at threshold) testing procedures were used to collect attenuation data on 24 subjects, both prior-to and following completion of a simulated work task. Bipolar rating scales were utilized to collect pre- and post-task wearabi1ity data. Statistical analyses demonstrated that the work-related movement and wearing time significantly reduced achieved attenuation and, for higher compression earmuffs, also degraded perceived comfort and acceptability. A high headband compression force was 1inked to increased attenuation and to poorer user comfort and acceptance. The data revealed no significant difference in achieved attenuation or wearability between cushion types. The results illustrate the powerful influence of physical activity on HPD effectiveness and the criticality of certain earmuff design parameters to both attenuation and wearability. Furthermore, the existing tradeoff in earmuff design between comfort and attenuation was clearly demonstrated. / Master of Science

A study was conducted to determine the dependency of sound attenuation capabilities of earmuffs and earcaps on various application instruction techniques including: (1) no instruction, (2) no instruction with 70 dBA auditory feedback, (3) manufacturers' package instruction, (4) detailed instruction, and (5) modeled instruction. The hearing protection devices (HPDs) studied were: two earcaps (Willson #20 Sound-Ban, Flents #055 Peace & Quiet Headband), and four earmuffs (E-A-R model 1000, Siebe Norton Industrial model 4540, Peltor H6A/v, and Willson 365A Sound Barrier). HPD comfort and wearer preferences were also assessed. Furthermore, typical excessive industrial machinery noises were sampled and analyzed across the 1/3 octave frequencies. Finally, an example is provided as to how these machinery noise spectra can be matched with HPD attenuation spectra to ascertain the protector which would afford optimal protection for a given noise situation. Fifty subjects (twenty-five males and twenty-five females) participated in the experiment. Attenuation characteristics of the HPDs were evaluated utilizing the real-ear attenuation at threshold (REAT) method. A three-way mixed factorial design was used for data collection and analysis of attenuation results. Bipolar scales were used to assess individual HPD comfort, and the HPDs examined were ranked to obtain user preferences. In the analysis of attenuation results, analysis of variance CANOVA) and pairwise comparisons were utilized to detect statistical significance. The comfort scales and ranking scores were evaluated using the Friedman one-way block design. Attenuation results for the earmuffs and earcaps tested showed that they were much less susceptible than earplugs (from a previous study by Epps, 1984) to changes in user insertion/donning instruction technique and also not as dependent on user gender. The main effect of gender was not significant, and in general, any instruction was better than no instruction at all but the effects of those instructions did not differ significantly among each other. As expected, there were main effect differences among the HPDs as to their attenuation capabilities, rated discomfort, and user preference. Because the main objective was on assessing donning instruction effects on HPD attenuation, the comfort/preference assessment was based on only a short (25 minutes) wearing time during the attenuation tests. Therefore, the comfort/preference ratings could likely vary given longer wearing periods and different work environments. All results found are discussed on the basis of the sample data obtained and conclusions drawn from these results should be limited to these experimental conditions and subsequent analyses, as actual attenuation achieved in practice may differ. The example of HPD-machinery noise matching illustrates that the attenuation/spectral matching procedure may indeed be a feasible way of selecting optimal protection for workers. / Master of Science