CHANGES IN THE DISTRIBUTION OF SHORT-TERM EXPOSURE CONCENTRATION WITHDIFFERENT AVERAGING TIMES

For 10 workers (16 worker-chemical combinations) exposed to organic so lvents, the distributions of 7.5-min time-weighted average (TWA) conce ntrations, 15-min TWAs, 30-min TWAs, and 60-min TWAs were examined by the Shapiro-Wilk W test and by plotting the TWA values and logarithmic values on probability paper. The hypothesis of normality of 7.5-min T WA and 15-min TWA was rejected for almost all combinations, while the hypothesis of lognormality was rejected only for a few combinations. F or 30-min TWAs and 60-min TWAs, the hypothesis of normality was reject ed for five and two combinations, respectively, while the hypothesis o f lognormality could not be rejected for any of the combinations. The probability plot also showed that TWA values with averaging times of 7 .5 to 60 min were approximately distributed in a lognormal manner. Con sequently, there was no evidence against using the lognormal distribut ion to describe the short-term exposure distribution. Results suggest that statistical methods proposed for evaluating exposure conditions b ased on lognormal distribution can be useful regardless of averaging t ime. The appropriateness of estimating exposure distribution with diff erent averaging times by Larsen's equations was also examined using 16 combinations. The geometric mean and geometric standard deviation est imated by Larsen's equations were nearly equal to those estimated by t he traditional equations' average, but the difference of the two estim ates in each case tended to be large when the ratio of the new averagi ng time to the original one was large.