[Assessment of occupational exposures to industrial hazardous substances. V. A proposed method for evaluating employee's exposure averages (8-h TWAs) using a single day measurement].

Daily exposure averages (8-h TWAs) to hazardous substances may vary considerably day to day, even though a worker is engaged in the same job. Previously we proposed a method to evaluate a long-term exposure condition with interday fluctuation using some exposure measurements. As it is assumed that 8-h TWAs are log-normally distributed, geometric standard deviation (sigma g) representing true interday fluctuation of 8-h TWAs should be estimated. If a single day's 8-h TWA of a worker is measured, sigma g of his own distribution of 8-h TWAs cannot be estimated. Therefore, to evaluate a long-term condition using a single day's 8-h TWA, representative sigma g in all industrial workplaces must be determined beforehand. To investigate sigma g observed in many industrial workplaces, two days' 8-h TWAs of each worker were measured in a week on 260 workers exposed to 19 hazardous substances. Sg2 (geometric standard deviation estimated by two samples) ranged from 1.00 to 8.22 with a median of 1.47 and a 90% upper limit of 2.47. Transforming Sg2 into sigma g, median and 90% upper limit of sigma g were 1.75 and 2.47, respectively. According to a classification scheme in the proposed method, exposure levels (I to III) were calculated using sigma g of 1.75 and 2.47. A long-term exposure condition to hazardous substances can be evaluated by comparing a single day's 8-h TWA with the exposure levels.