Presumed noise-induced permanent threshold shift resulting from exposure to an A-weighted Leq of 89 dB

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Abstract
The noise-induced permanent threshold shift (NIPTS) resulting from up to 10 yr of exposure to an average A-weighted sound level Leq [equivalent level] of 89 dB was investigated. Prior occupational noise exposure was controlled for by eliminating subjects with previous high-noise-level jobs or uncertain exposure histories. The final population consisted of 42 males and 58 females working in steady-state broadband noise environments. No attempt was made to screen subjects for any auditory pathology. A 222-subject control group from the same geographic area as the exposed subjects was selected such that none of its constituents had any effective industrial noise exposure. Presumed NIPTS was calculated by correcting each individual audiogram of the exposed subjects according to the aging curves developed from the control population hearing levels. The results indicated a considerable male-female difference in NIPTS, even though both groups were exposed to the same Leq. Averaging the results for all 100 subjects, in order to make comparisons to other available data, yielded results in close agreement to predictions based upon the work of Burns and Robinson, Baughn, NIOSH [National Institute for Occupational Safety and Health] and Passchier-Vermeer, indicating that 10 yr of exposure to a daily Leq of 89 dB causes measurable hearing loss at 4 kHz.

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