Stephanie Levine
Donald Henderson
Phillip Hofstetter
Hear. Res. Lab., Univ. of Buffalo, Buffalo, NY 14214
Impulse and impact noise found in industry may be particularly dangerous for workers' hearing. This study examines the effect of the level of impact noise on hearing loss. Twenty four adult chinchillas were exposed to impact noise for 7.5 h. The subjects were divided into four groups and exposed to impulses delivered at 1/s at one of four different intensities: 113, 119, 125, and 131 dB. As the level of exposure increased, the permanent hearing loss of the animals increased. At lower levels, 113--125 dB hearing loss increased at approximately 1.8 dB for each dB of noise. These findings are consistent with studies using continuous noise which report a 1.7-dB increase in asymptotic threshold shift for every dB increase in exposure. However, as the level of the impact increases beyond a critical level, (125 dB) the resulting threshold shift increases dramatically i.e., 6 dB for each dB increase in exposure level. It has been shown in prior research [Hamernik et al., Hear. Res. 13, 229--247 (1984) and Henderson et al., Hear. Res. 76, 101--117 (1994)] that the anatomical damage to the cochlea at this critical level changes from metabolic to mechanical. [Research supported by NIOSH Grant No. 15034470.]