AUTOCORRELATION OF SHORT-TERM AND DAILY AVERAGE EXPOSURE LEVELS IN WORKPLACES

Based on workplace exposure data for 16 worker-chemical combinations, the degree of autocorrelation in a series of short-term time-weighted average (TWA) exposure concentrations (7.5-min, 15-min, 30-min, and 60 -min TWAs) was investigated. For 7.5-min and 15-min TWAs, consecutive values generally exhibited no correlation or positive correlation, but not negative correlation. Consecutive 30-min TWAs and 60-min TWAs sho wed either positive correlation, negative correlations, or no correlat ion. Autocorrelation functions displayed various patterns that depende d on the exposure time series. The mean of the autocorrelation coeffic ients across all worker-chemical combinations was similar to an expone ntial function, which signifies that the degree of autocorrelation, on average, decreased as the interval between two averaging periods incr eased. Autocorrelation in a series of 8-hr TWAs also was analyzed for 10 worker-chemical combinations. In general, little autocorrelation wa s observed. Based on this analysis, the authors discuss a sampling str ategy that, on average, would minimize the degree of correlation betwe en measurements of short-term TWAs.