A task-based statistical model of a worker's exposure distribution: Part I--Description of the model.
The authors present a task-based model to describe a single worker's exposures to a single airborne chemical toxicant. The model accounts for variability in short-term time-weighted average (TWA) exposure values within a task, and for variability in arithmetic mean exposure levels 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 arising from stratified random sampling of short-term TWAs with proportional allocation by task. The model accounts for autocorrelation in the stochastic process that generates successive short-term TWA values. Due to the underlying random process, a given type of workday 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 autocorrelation in the time series of short-term TWAs. A worker's total distribution of 8-hour TWAs is a mixture of these day-specific distributions weighted by the relative frequency of each type of workday; the variance of the total distribution increases with greater day-to-day variability in the array of task times.
Nicas
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Center for Occupational and Environmental Health, School of Public Health, University of California, Berkeley 94720.
Spear
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RC
D000395:Air Pollutants, Occupational; D005663:Furans; D006801:Humans; D015233:Models, Statistical; D016273:Occupational Exposure; D010150:Paint; D012494:Sampling Studies; D012498:Sanitary Engineering; D014050:Toluene
D000395:Air Pollutants, Occupational; D005663:Furans; D014050:Toluene; C018674:tetrahydrofuran