Abstract:
Studies were undertaken to determine the maximum safe-exposure levels in a reverberant wave environment like that produced by firing an antiarmor weapon from a small room. The approach was first, to establish a threshold of injury for organs other than the ear then to determine whether these levels were safe for the ear. Using sheep as an animal model, the threshold of nonauditory injury was found to be approximately 190 dB peak SPL (65 kPa) with a B duration longer than 200 ms for one impulse and approximately 187 dB peak SPL (46 kPa) for three impulses. Two groups of 40 animals were used to establish statistical confidence in the ``no injury levels.'' The auditory effects were investigated using human volunteers exposed to a progression of levels from 168 to 185 dB at the ear for one impulse and then, to two and three impulses at 183 dB. A temporary threshold shift (TTS), determined 2--4 min post exposure, was used as an indicator of auditory effect. The volunteers wore an earmuff modified to simulate a poor fit, during the exposures. No significant TTS in 59 volunteers was observed, indicating no effects on hearing up to the maximum safe-exposure levels for other organs.