NOISE-EXPOSED MALE SHEET-METAL WORKERS USING HEARING PROTECTORS - A LONGITUDINAL-STUDY OF HEARING THRESHOLD SHIFTS COVERING 15 YEARS

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.