産業有害物の個人曝露量の評価

(その4)片側許容限界を用いた評価法

抄録

Occupational exposures to potentially hazardous substances may vary considerably because of interday environmental behavioral fluctuations in the contaminant concentration. Such occupational exposures including those of non-monitored days can be theoretically evaluated by the following three ways: 1) assessment of geometric mean and geometric standard deviation, 2) assessment of arithmetic mean, and 3) assessment of upper limits of daily exposure distribution. In our previous report, an evaluation method on 95% upper limit or arithmetic mean of exposures was proposed. The method is useful, particularly, in case where only one or two days are being monitored, but may provide an approximate estimate because of statistical assumption. A sampling and decision scheme using one-sided tolerance limits (OTL) proposed by Tuggle (1982) can precisely evaluate the upper limits of exposures. However, many cases would be evaluated as “no decision, ” unless the sample size is extremely large in number.
We developed a revised method based on OTL for assessment of occupational exposures. The characteristic features of this method can be summarized as follows:
1. Upper limits of lognormally distributed 8-h exposure concentrations can be evaluated in comparison with an established standard.
2. A third OTL factor was introduced into Tuggle's scheme in which two OTL factors were used. A comparison between the upper limits of exposures and the standard can be made at 50% confidence level with the factor. The factor was calculated using non-central t-distribution.
3. The usefulness of the third OTL factor in the assessment of occupational exposures was confirmed by examining the performance characteristics of the method.
4. Finally, a classification scheme of the employee's exposure situation was presented on the basis of measurements for n days (n≥3).
The general application procedure of the method and an example of employee's exposure to n-hexane are also presented. In conclusion, the method can provide a precise estimate for exposure assessment and is very useful for practical purposes.