Measurement of Insert-type Hearing Protector Attenuation on the End-user: A Practical Alternative to Relying on the NRR Introduction Hearing protectors are labeled with a Noise Reduction Rating

Hearing protectors are labeled with a Noise Reduction Rating (NRR) that is derived from laboratory measurements of the attenuation provided to trained and motivated human subjects in a ‘sterile’ environment. As intended, these measurements represent a best-fit condition. The literature indicates that the average attenuation provided to end-users of hearing protectors is often only a fraction of the labeled values. Because of this, various derating schemes are employed, including the 50% derating suggested in the OSHA inspector’s Technical Manual and the variable derating according to protector-type suggested in the 1998 NIOSH criteria document on occupational noise exposure.