5-YEAR FOLLOW-UP-STUDY OF HEARING-LOSS AT SEVERAL LOCATIONS WITHIN A LARGE AUTOMOBILE COMPANY

This longitudinal epidemiologic study was designed to investigate hear ing loss over a 5-year period among noise-exposed employees of a large automobile company and to assess effectiveness of hearing conservatio n programs at locations representing the spectrum of operations (assem bly, light manufacturing, heavy manufacturing and machining, metal fab rication, 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 locat ions, which had maximal 8-hr time-weighted average (TWA) noise exposur es ranging from 104 to 110 dB(A). Methods presented here provide for c onsideration of age and hearing level of study subjects at baseline au diogram 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 th e follow-up period; after adjustment for presbycusis, the loss was les s than 2 dB at all but one location, which showed a loss of nearly 4 d B. In comparison to a control group of nonnoise-exposed employees, hea ring conservation programs at four of the five locations were judged t o be effective. One location, a metal fabrication plant with a large p ercentage of employees having an 8-hr TWA noise exposure over 90 dB(A) , was particularly noted for the effectiveness of its program. (C) 199 3 Wiley-Liss, Inc.