Hearing impairment caused by occupational noise.

Occupational noise-induced hearing impairment is an insidiously developing injury which only becomes apparent when it affects the hearing of conversational speech. As no remedy is possible, prevention is the only answer. In view of the impending legislation in South Africa a review of the literature is presented. This is confined to the auditory effects of potentially hazardous occupational noise in industry. Two principal properties of soundintensity and frequency-are briefly discussed. In the study of exposure to noise important factors are: (a) over-all noise level, (b) exposure duration in a working day, and (c) exposure duration over a working lifetime. The data derived from studies of hearing loss and of temporary threshold shift make it possible to predict the risk-percentage (incidence) and to some extent the amount of hearing loss resulting from exposure to a certain noise environment in the exposed population of workers. This enables appropriate authorities to set acceptable limits as criteria. If these are exceeded hearing conservation programmes, aimed at reducing the hazard, are indicated. Some features of these are mentioned and the value of audiometry is pointed out, especially for attempts to establish high susceptibility to suffer hearing loss in individuals. An outline of regulations regarding hearing impairment compensation in other countries is given. A few remarks are made on the role of the medical practitioner in industrial hearing conservation programmes.