Abstract
Intermittency is a noise exposure variable which must be considered in proposing standard limits. The Committee on Healing, Bioacoustics, and Biomechanics (CHABA) defined a noise interruption as a period in the noise exposure when the level falls below 80 dBA for more than five minutes or for “20% of the duration of the preceding noise burst.” Our previous study indicated that interruption levels below 80 dBA could have variable effects on resultant temporary threshold shifts. Thirty subjects, ten for each of the three conditions, were exposed to 45 minutes of broadband noise (103 dBA). The noise bursts were interrupted twice for five minutes by levels of 57 dBA, 67 dBA and 77 dBA. Corrected TTS2 measurements and uncorrected TTS30 measurements were taken. Subjects afforded the 67 dBA and 77 dBA interruptions (1) had significantly more TTS2 and TTS30 at 4kHz and 6kHz than those subjects afforded the 57 dBA interruptions, (2) demonstrated a slower recovery rate than the 57 dBA group, and (3) experienced seven times as many 40 dB+ TTS2's than those afforded the 57 dBA interruptions. These results imply that noise interruptions defined as 80 dBA or below afford significantly less protection than interruptions which approximate 60 dBA.