Abstract
The hearing thresholds of male sheet-metal workers have been studied in a longitudinal investigation with pure tone audiometry during three periods covering 1972–1987. Using these data, the hearing threshold shifts were calculated in various age groups. When the annual rate of mean hearing threshold shift over the frequency range 2–8 kHz was considered, it was not possible to establish a difference in the threshold shift between noise-exposed groups and an otologically normal ‘highly screened’ male population from ISO 7029, database A. The correction for ageing in the noise-exposed group according to the empirical formula in ISO 1999 (1990) is discussed. The results show that a hearing conservation programme including effective use of hearing protectors and reduction of noise emission levels can eliminate noise-induced hearing threshold shifts and progressive hearing loss.