An isohazard function for impulse noise

Existing criteria for safe exposure to impulse noise do not consider the frequency spectrum of an impulse as a variable in the evaluation of the hazards to the auditory system. This study was designed to determine the relative potential that impulsive energy concentrated at different frequencies has in causing auditory system trauma. One hundred and thirty (130) chinchillas, divided into 22 groups of 5 to 7 animals, were used. Pre‐ and postexposure audiograms were measured on each animal using avoidance conditioning procedures. Quantitative histology was used to determine the extent and pattern of the sensory cell damage (cochleograms). Noise exposure employed seven different computer‐generated narrow‐band impulses (approximately 400‐Hz bandwidth) having center frequencies located at 0.260, 0.775, 1.025, 1.350, 2.075, 2.450, and 3.550 kHz, presented at two to four different intensities. An isohazard weighting function derived from the audiometric and histological data demonstrates that equivalent amounts of impulsive energy concentrated at different frequencies are not equally hazardous to the auditory system. Comparison of the derived weighting function with the A‐weighting curve indicates that low‐frequency impulses are less hazardous than predicted by A‐weighted sound exposure level.