John R. Franks
Bioacoust. and Occupational Vibration Section, Natl. Inst. for Occupational Safety and Health, 4676 Columbia Pkwy., Mail Stop C-27, Cincinnati, OH 45226-1998
John G. Casali
Virginia Polytechnic Inst., Blacksburg, VA 24061
A disparity exists between the advertised and realized attenuation of noise by hearing protective devices. The disparity has been accredited to many factors, including overfitting by experimenters and misuse by workers. This study compared attenuation data for three earplugs and one earmuff obtained from an interlaboratory (IL) study using a subject-fit method with data on the same protectors reported in the literature from work-site (WS) studies where workers fitted the hearing protection and with manufacturer-reported (MR) data on NRR labels. The IL method required subjects who where audiometrically competent, but inexperienced with hearing protectors, to fit hearing protectors relying solely upon guidance from the manufacturers' written instructions. Results indicated that there were no differences in attenuations between laboratories. Confidence interval testing was performed comparing the IL mean attenuations and variances to WS means and standard deviations and to MR means and standard deviations. Results indicated that the IL data were more consistent with the WS data than with the MR data. In all cases the IL data were significantly less than the MR data. Depending upon protector type, the IL data were equivalent to or greater than the WS data.