Evaluation of occupational exposure to toluene : the influence of sampling strategy

The sampling duration and the number of measurements realized have a dramatic impact on the quality of occupational exposure assessment to toluene with regards to Occupational Exposure Limit (OEL). For evaluating this impact, a measurements database has been created, based on several campaigns realized in an industrial printing facility. Five Homogeneous Exposure Groups (HEG) have been constituted and from 120 to 290 measurements of 2 to 8 hours have been realized for each of them. With this data, a reference exposure profile is defined per HEG: the “gold standard”. This exposure profile corresponds to a log normal distribution of measurements which is characterized by three indicators: the 95th percentile category, the exceedance fraction with regards to OEL and the compliance / no compliance diagnostic with regards to OEL as defined by French regulation. Scenarios are simulated by sampling a reduced number of measurements of different duration out of the overall measurements population per HEG. For each scenario, 1000 simulated exposures profiles are computed and compared to reference exposure profile through the three indicators. The results show that the quality of exposure assessment increases with the number of measurements and with the sampling duration. Moreover, it is shown that it is possible to recommend boundaries over the number of measurements and the sampling duration in order to obtain a quite reliable exposure assessment while minimizing the sampling and analyzing effort.