Development of hearing loss during long-term exposure to occupational noise. A 20-year follow-up study.

Occupational noise-induced hearing loss is still responsible for the majority of occupational ailments and injuries, with very large sums being paid in compensation. Repeated hearing tests over a 20-year period have been performed on 319 employees of a timber processing firm, working in sawmills and paper pulp production, exposed to mean noise levels of around 95-100 dB (A) and in a chemicals division with mean noise exposure levels of 80-90 dB (A). During the observation period, mean hearing levels deteriorated slowly, especially at 4 kHz, but no dramatic changes from one year to another were seen. We therefore propose 3-year intervals between regular hearing tests in this type of industry where noise exposure is predominantly of the continuous type, thus releasing resources for more active measures against noise-induced hearing loss. Cases of manifest hearing loss or otherwise at risk must of course be followed up at shorter intervals. A remarkably large proportion of the employees in the chemicals division suffered a hearing loss corresponding to 10% disablement according to Swedish criteria, which raises the question of a possible relation between exposure to industrial solvents and hearing loss.