Five-year follow-up study of hearing loss at several locations within a large automobile company

This longitudinal epidemiologic study was designed to investigate hearing loss over a 5-year period among noise-exposed employees of a large automobile company and to assess effectiveness of hearing conservation programs at locations representing the spectrum of operations (assembly, light manufacturing, heavy manufacturing and machining, metal fabrication, and founding). Based on computerized audiometric test data, the study summarizes methodology developed for measuring occupational hearing loss and its application in evaluating programs at these locations, which had maximal 8-hr time-weighted average (TWA) noise exposures ranging from 104 to 110 dB(A). Methods presented here provide for consideration of age and hearing level of study subjects at baseline audiogram and clearly demonstrate the extent of hearing loss during the study period. Among five study locations, the average hearing loss at 2,000-4,000 Hz in the worst-loss ear ranged from 3.4 to 6.2 dB over the follow-up period; after adjustment for presbycusis, the loss was less than 2 dB at all but one location, which showed a loss of nearly 4 dB. In comparison to a control group of nonnoise-exposed employees, hearing conservation programs at four of the five locations were judged to be effective. One location, a metal fabrication plant with a large percentage of employees having an 8-hr TWA noise exposure over 90 dB(A), was particularly noted for the effectiveness of its program.