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A field study assessed the actual spectral noise attenuation achieved by 40 industrial workers wearing four different hearing protection devices (HPDs) while on the job. The effect of two different HPD fitting procedures (subject fit vs. trained fit) on attenuation performance over two three-week periods of protector use was determined. Subjects were retrieved from their workplaces without prior knowledge of when they were to be tested and were not permitted to readjust the fit of their HPDs. Attenuation data were then collected using psychophysical procedures testing real ear attenuation at threshold. Statistical analyses indicated that the earplugs' attenuation significantly improved when training for proper fitting was used, whereas the earmuff and the ear canal cap were relatively insensitive to the training effect. The training was most effective for a slow-recovery foam plug over the three-week period. Results confirmed that laboratory protocols designed to simulate workplace influences on attenuation may not be relied on to yield reasonable estimates of field protection performance of HPDs, particularly for earplugs; however, the laboratory results were much better predictors of field protection for the earmuff. This study also demonstrated that the labeled manufacturers' noise reduction ratings (NRRs) substantially overestimated the actual field attenuation performance.

This study involves performing improvements in workstation specification using a three-dimensional human modeling tool and proposing well-balanced work scheduling (WBWS) to prevent work-related musculoskeletal disorders (WMSDs) in a small manufacturing plant. To analyze risk factors of WMSDs, various tasks at 10 different types of workstation were evaluated with detailed motion analysis using a customized checklist. Questionnaires were administered to 27 workers to evaluate symptoms related to WMSDs. Revised workstation specifications were suggested based on anthropometric characteristics of workers using before-after analyses as an engineering control. Additionally, WBWS was proposed as an administrative control to avoid continuous physical stress on specific body parts in repetitive tasks. A software tool for WBWS was developed for convenient and easy application. The results of the study may aid managers in applying ergonomic interventions with time and cost savings, and enhance worker satisfaction and motivation due to improvements in working conditions to prevent WMSDs.

An experiment was conducted to determine the effects of movement activities and alternative fitting procedures on protection levels afforded by four hearing protection devices (HPDs). Psychophysical attenuation measurements at nine one-third-octave bands from 125 to 8000 Hz were obtained prior to, during, and following a 2-hr wearing stint that included periods of either highly kinematic but controlled work activity or vigorous temporomandibular movement. The 40 subjects, who were nonusers of HPDs, initially fit the protectors according to either the instructions on the package (i.e., subject fit) or after receiving interactive training on proper fit (i.e., trained fit). Thereafter no further protector adjustments were allowed during the wearing period. The subject-fit condition resulted in significantly lower protection levels, from 4 to 14 dB, at 1000 Hz and below for a premolded polymer earplug, a user-molded foam earplug, and a double protector consisting of a muff over the foam plug. The muff alone was significantly more resilient to fitting effects on attenuation than were the plugs. Movement activity caused up to a 6-dB significant reduction in frequency-specific attenuation over time for the premolded plug, muff, and muff-plug combination. The compliant foam earplug was largely resistant to either type of movement effect but did benefit more than the other devices from use of the trained-fit procedure. Implications of the results for hearing protector testing protocol, device selection, and user training are discussed.

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