Asymptotic behavior of temporary threshold shift and recovery from 24- and 48-hour noise exposures.

Temporary hearing loss (TTS) from long-duration noise exposure reaches an asymptote between 8 and 16 h and does not increase further during continued exposure for durations of at least 48 h. Potential auditory hazards of long-duration exposures are examined in terms of growth and recovery patterns of TTS. TTS growth and recovery patterns were compared during 24- and 48-h exposures of humans to continuous pink noise at a level of 85 dB A-weighted. Results indicate similar patterns of acquisition and relatively equal amounts of TTS for the two exposure durations. However, recovery of preexposure hearing at 4000 Hz following termination of the 48-h noise exposure differed somewhat from that which followed the 24-h exposure. The implications of these findings for long missions in noisy environments are discussed.