Maximizing communication ability in the selection of hearing protective devices

Abstract

The most common procedure for selecting hearing protective devices (HPDs) is the Noise Reduction Rating (NRR). The NRR can be misleading and often results in the selection of HPDs that either under- or over-protect the wearer. The wearer of an under-protective HPD is likely to experience noise-induced hearing loss. The use of over-protective HPDs can needlessly reduce speech communication, the ability to hear warning signals, and the ability to recognize important machine sounds. Workers fit with over-protective HPDs are also less likely to properly wear their HPDs. An articulation index (AI) based method of ranking HPDs for use in specific noise exposures was developed in conjunction with the American Iron and Steel Institute (AISI). The calculations used in the procedure incorporate the attenuation characteristics of the HPD, the spectrum of the noise source, the hearing thresholds of the wearer, the nonlinear growth of masking, and the predicted level of speech in noise. The HPD rankings are intended to insure that adequate attenuation and optimum communication ability is achieved.