Presumed noise induced permanent threshold shift resulting from exposure to an Leq of 89 dBA

Abstract

The noise induced permanent threshold shift (NIPTS) resulting from up to ten years of exposure to an Leq of 89 dBA 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 with octave band spectra sloping at approximately −1.0 dB/octave. 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. Military service and nonindustrial noise exposure were common to both the control and exposed subjects. Presumed NIPTS was calculated by correcting each individual audiogram of the exposed subjects, according to the sociocusis 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, and Passchier—Vermeer, indicating that ten years of exposure to a daily Leq of 89 dBA causes measurable hearing loss at 4 kHz. [Work partially funded by a grant from the Rockefeller Foundation.]