Growth and recovery of temporary threshold shifts from 24 hour continuous, 48 hour continuous, and 48 hour intermittent noise exposure

Abstract

The effects on human hearing of 24 and 48 hour continuous and 48 hour intermittent exposures to pink noise at an Leq of 85 dB were measured by pure tone audiometry to address two questions. First, previous studies have demonstrated an asymptotic temporary threshold shift (ATTS), i.e., growth of TTS ceases, after 8–16 hours of exposure to sound. On the assumption that these effects on hearing are the same once asymptote is reached, there should be no difference between the growth of TTS, level of ATTS and recovery from the two exposure durations. Second, if the equal energy concept is appropriate to exposure durations of 48 hours then the effects found for the interrupted conditions should also demonstrate some similarity with the effects from continuous noise exposures. For instance, results of earlier work has shown similar recovery times between 24 hour interrupted and continuous noise exposures. Present results demonstrate that (1) for the 24–48 hour continuous exposures, TTS growth patterns and ATTS levels are similar. However, recovery from the 48 hour exposure was significantly longer than for the 24 hour condition, and (2) for the 48 hour interrupted exposures, growth and recovery patterns are similar to those of continuous exposures, although the magnitude of the TTS was less and the recovery to pre-exposure hearing more rapid than for continuous exposures.