Noise-induced hearing loss in an automobile sheet-metal pressing plant. A retrospective investigation covering 25 years.

Hearing damage suffered by male workers in an automobile sheet-metal pressing plant has been studied on five occasions during the period 1964-89. The hearing threshold data have been analysed in order to determine hearing loss due to noise in various age groups. The hearing thresholds were better on later occasions. In the youngest group of workers only 45% exhibited normal hearing in 1964, while in 1989 the corresponding figure was 88%. The same tendency towards improved hearing could also be seen in the age groups 30-39 and 40-49 years. In the oldest age group, 50-59 years, hearing handicap decreased from 58% in 1964 to 11% in 1989. With the aid of the average hearing loss, it has also been possible to estimate the equivalent noise level to which present-day workers have been exposed, as well as the reduction in level of exposure during the past 25 years. The effects of a long-term technical and medical occupational health care programme including noise-reduction measures and improved use of hearing protectors are discussed.