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Laboratory attenuation of earmuffs and earplugs both singly and in combination

Laboratory attenuation of earmuffs and earplugs both singly and in combination

American Industrial Hygiene Association Journal 44(5): 321-329

For high-level noise exposures, especially when 8 h, time-weighed averages are > 105 dBA, the attenuation of a single hearing protection device may be inadequate. For such exposures, double hearing protection, i.e., muffs plus plugs, may be called for. Double hearing protection does not yield overall attenuation equal to the sum of the individual attenuation of each device due to the bone-conduction flanking paths and the acoustical-mechanical interaction between 2 closely spaced devices. The incremental performance to be gained by double protection was investigated experimentally by measuring the real ear attenuation at threshold for a number of combinations, according to ANSI S3.19-1974. All tests were conducted on 10 subjects, 3 replications/subject. Devices included foam plugs (partial, standard and deep insertions), fiberglass down, V-51R earplugs, medium and large volume commercially available earmuffs and an experimental large-volume Pb earmuff. All devices were examined singly and in combination. In all cases, plugs-plus-muffs outperformed either device individually, except at 1 kHz for 1 combination. Although the 2 pairs of commercially available earmuffs offered significantly different low frequency attenuation (125-1000 Hz), when either earmuff was combined with the V-51R or deeply inserted foam earplug, the improvements were similar. When the situation was reversed and the different inserts were examined in combination with a single earmuff, the choice of insert was important below 2 kHz; at above 2 kHz all plug-plus-muff combinations provided attenuation approximately equal to the bone-conduction limits of the skull. Double hearing protection may provide the additional noise reduction needed in high noise level environments.

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Accession: 005787507

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DOI: 10.1080/15298668391404905

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