[Assessment of occupational exposures to industrial hazardous substances. III. On the frequency distribution of daily exposure averages (8-h TWA)].

A method based on interday fluctuation of contaminant concentrations for evaluating employee's exposure averages (8-h TWAs) was proposed in our previous report. The method was established on the assumption that daily exposure averages of the workers are lognormally distributed in actual workplaces. The study was conducted to elucidate whether the distribution of daily exposure averages is statistically lognormal or not and to examine the relationship between sample geometric standard deviation (sg) of worker's daily exposure averages and its estimate (sg2) calculated by measurements for two consecutive days. These are critical for our proposed method. The data on daily exposure concentrations over five to six weeks were collected from workers exposed to cobalt, acetone, n-hexane, toluene, xylene, ethylbenzene and ethylacetate. The data on organic lead, inorganic lead and mercury exposures reported by Cope et al. and Lindstedt et al. were also used for the study. The result can be summarized as follows: 1. Lognormal distribution of daily exposure averages was confirmed by plotting on normal probability paper and chi 2-test. 2. Median of sg2 on daily exposure averages obtained from individual worker was smaller than sg. 3. sg calculated by a set of measurements for two consecutive days in every worker can be corrected by the equation: (sg2) 1.48 in obtaining a better estimate of sigma g. 4. Statistical analysis on daily exposure averages of all workers showed that median of sg2 was smaller than that of sg, and 88% upper limit of sg2 was equal to that of sg. 5. Therefore, in evaluating TWA obtained by only single day's measurement using the proposed method, median of sg representative of industrial hazardous substance exposure workplaces could be also corrected by the equation described above. However, correction of 90% upper limit of sg2 is not necessary.