Alice H. Suter
Alice Suter and Assoc., 575 Dogwood Way, Ashland, OR 97520
Terms such as ``doubling rate'' and ``time-intensity trading relation'' have given way to the ``exchange rate'' in recent years, which is the number of decibels permitted in a standard or criterion for each doubling or halving of exposure duration. Whereas most European nations, several Canadian provinces, and some U.S. agencies use the 3-dB exchange rate, the Department of Labor's 5-dB exchange rate is widely used in the U.S. Many of the premises on which the 5-dB rule were based have proven to be faulty, and although it supposedly takes intermittencies into account, it actually allows uninterrupted exposures at relatively high sound levels. Evidence from studies of laboratory animals indicates that there is some reduction of threshold shift from intermittent exposures, yet epidemiological data do not support this concept in actual working conditions. The likely reason for this discrepancy is that industrial working conditions do not provide sufficient opportunity to recover from TTS. An analysis of the origins of the 5-dB rule, as well as evidence from field and laboratory studies supports the adoption of the 3-dB rule, with the possible addition of a small adjustment in the permissible exposure limit for certain outdoor occupations.