Effects of peak levels and number of impulses to hearing among forge hammering workers.

The purpose of the study was to (1) compare measured and estimated hearing loss among forge hammering workers by applying models for risk assessment based on measurements of impulse noise, and (2) model the hazardous effects of impulse noise on hearing. Noise exposure and hearing loss among forge hammering workers were studied at two forge workshops of an automobile company, where the equivalent sound pressure levels (104 and 105 dB) were the same, but the peak levels and degree of impulsiveness were significantly different. The hearing threshold levels of selected groups of workers (97 and 235 workers) were determined. Comparison between the measured and expected hearing losses defined according to the ISO standard revealed 2 dB difference in excessive hearing loss (1 dB and 3 dB for the workers of workshop 1 and 2, respectively). The excessive hearing loss equals an increase of 3.5 years of exposure. The hearing loss of workers exposed to low impulsive noise could be predicted well using ISO 1999-1990. The hearing loss of workers exposed to high impulsive noise correlated significantly with the peak levels and the number of impulses in combination.