Identification of the minimum noise level capable of producing an asymptotic temporary threshold shift.

The present study was designed to identify the minimum noise level capable of producing an asymptotic temporary threshold shift (ATTS). It was estimated that at some level below 85 dBA, probably 70-80 dBA, there existed an exposure level at which no ATTS would occur. It is assumed that if a long-duration noise does not produce temporary changes in hearing levels, then it would not produce permanent changes either. This level would then define an exposure condition below which personnel could be exposed for indefinite periods of time without adverse auditory effects. Subjects were exposed to continuous pink noise for 24 h at levels of 65, 70, 75, 80, and 85 dBA. TTS growth and recovery was measured at specific intervals throughout each condition. Results demonstrate that at the most sensitive frequency (4000 Hz), at ATTS threshold level would be predicted in the region of 75-80 dBA.