The authors used a mixed-effects model on a cohort of 258 randomly chosen workers in 7 fuel-distribution facilities to examine the association between airborne benzene exposure and task and timing factors. During an 8-y period, 692 repeated personal measurements were performed. Filler task, warm month, Tuesday, credit day, and time period (1992-1996) were associated significantly with higher exposures to benzene. The authors controlled for the time period, and task type strongly affected the between-worker variance; therefore, two exposure groups (i.e., fillers and nonfillers) were adequate for purposes of exposure grouping strategy. Timing factors (after controlling for task and period effects) strongly affected the high within-worker variance (> 2 than between-worker variance). Long-term exposure would be better represented if the sample was stratified by warm/non-warm months and if measurement days were selected randomly.
- Fuel distribution