Hazardous Exposure to Industrial Impact Noise: Persistent Effect on Hearing

A survey on hearing loss due to industrial impact noise was conducted in the drop-forge industry on 70 workers with 61 non-exposed controls. Noise measurements were made with a Bruël & Kjaer Impulse Precision Sound Level Meter 2204 giving the RMS values of the impacts. Mean duration of the impacts was established by oscilloscopy. The experimental data show a significant increase of hearing loss with higher noise level and longer exposure. The mean hearing losses of six groups of workers, at frequencies of 3, 4 and 6 kHz, are in agreement with those found by Robinson (1970) in groups of subjects with equivalent exposure to continuous noise. If this is confirmed by other surveys, it is foreseeable that the damage risk criteria for continuous noise could be extended to cover industrial impact noise.