Julia D. Royster
Environmental Noise Consultants, Inc., P.O. Box 30698, Raleigh, NC 27622
Larry H. Royster
North Carolina State Univ., Raleigh, NC 27607
Four HPDs, three plugs and one muff, were tested in four labs to identify a protocol that would estimate the real-world attenuation obtained in field studies of workers in hearing conservation programs. Audiometrically experienced subjects who had never worn HPDs regularly used each device, following the manufacturers' instructions without any supplemental experimenter training (subject-fit condition). Subsequently, after the experimenter demonstrated the use of each device, the subject used each HPD again (informed-user-fit condition). Attenuation was measured in two trials with each HPD in each instruction condition. Practice within a condition yielded no significant improvement in achieved attenuation. Experimenter instruction significantly increased the attenuation subjects obtained with earplugs (but not earmuffs). The subject-fit condition approximated the upper quartile of real-world attenuation, and the range of standard deviations of attenuation across labs was no greater than for the informed-user-fit condition, indicating acceptable reproducibility. Testing earmuffs worn with safety glasses only slightly increased the range of standard deviations.