The National Institute for Occupational Safety and Health, Hearing Loss Prevention Team has conducted hearing protector real-ear attenuation at threshold measurements for 228 workers. Each worker's A-weighted noise exposure was known and the hearing protector attenuations were assessed several times during the course of a year. Initial assessments were restricted to 125, 500 and 2000 Hz one-third octave noise-band frequencies. Subsequent evaluations tested 125, 250, 500, 1000, 2000, 4000, and 8000 Hz noise bands. The attenuations from the reduced set of frequencies were used to predict the protected exposure level for each worker based upon the A-weighted noise exposure level and assuming a flat noise spectrum. From these estimates, additional counseling was provided to the workers with respect to the type of protector and technique(s) used to fit the hearing protection devices. This paper will report the attenuation data, unprotected and protected exposure levels for the workers, as well the differences between the labeled Noise Reduction Rating and the noise reduction delivered by the devices tested in this study.
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