A TASK-BASED STATISTICAL-MODEL OF A WORKERS EXPOSURE DISTRIBUTION .1.DESCRIPTION OF THE MODEL

The authors present a task-based model to describe a single worker's e xposures to a single airborne chemical toxicant. The model accounts fo r variability in short-term time-weighted average (TWA) exposure value s within a task, and for variability in arithmetic mean exposure level s between tasks. For a given workday, the 8-hour TWA value is equated with the sample mean of an appropriate number of short-term TWAs arisi ng from stratified random sampling of short-term TWAs with proportiona l allocation by task. The model accounts for autocorrelation in the st ochastic process that generates successive short-term TWA values. Due to the underlying random process, a given type of work-day with regard to the set of task times has an associated distribution of 8-hour TWA values; the variance of this distribution increases with increasing a utocorrelation in the time series of short-term TWAs. A worker's total distribution of 8-hour TWAs is a mixture of these day-specific distri butions weighted by the relative frequency of each type of workday; th e variance of the total distribution increases with greater day-to-day variability in the array of task times.