An Evaluation of a Hearing Conservation Program—A Five-Year Longitudinal Study

The effectiveness of a hearing conservation program was investigated by analyses of changes in hearing threshold levels over a 5-year period among 2770 male employees of the DuPont Company. The study focused on 1966 men in this group whose level of noise exposure did not change during the study period. Three categories of noise levels were established. One consisted of areas in which the level was below the hearing conservation criterion, approximately 90 dBA; the other two were above that level. The mean differences in hearing levels were essentially the same in the three noise level categories, at each test frequency, and regardless of the hearing level at the beginning of the study period. We therefore concluded that a hearing conservation program whose components include periodic audiometric testing and ear protection, and which utilizes a hearing conservation criterion of approximately 90 dBA, is capable of protecting the hearing of noise-exposed workers.