Measurement of Insert-type Hearing Protector Attenuation on the End-user: A Practical Alternative to Relying on the NRR
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.
De-rating the labeled NRR
De-rating the labeled NRR provides a better estimate of the average attenuation realized by a population of end-users. However, field measurements indicate that attenuation provided across end-users is highly variable (standard deviation > 10 dB), so many wearers will receive much greater attenuation than the average, and many will receive much less attenuation than the average. Therefore, if hearing protectors are selected according to a de-rated NRR, some individuals will still be under-protected and some will receive excessive attenuation, leading to potential communication problems. A solution to this problem is to base the selection process on objective data obtained by measuring the attenuation provided to each end-user of insert-type hearing protectors.
In this article the Steel Industry experience is examined when it comes to individual hearing protector fit-testing. In this industry Almost all HPD wearers at this plant wear insert-type devices. To learn more about the wide variability of attenuation provided by insert-type protectors a results please click here to download the entire study: DOWNLOAD PDF