An application of exposure modeling in exposure assessments for a university chemistry teaching laboratory

Chemical exposures in a university teaching lab were assessed using a tiered approach to modeling. Zero ventilation and well mixed room models estimated air concentrations of ethyl ether, n-hexane, and methylene chloride during distillation and extraction exercises. A simple, zero ventilation model determined that health risks from the ethyl ether exercise were minimum. N-hexane and methylene chloride exposures were evaluated with higher tiered, well mixed room models. An assumption that all of the solvent evaporated during the lab resulted in estimated n-hexane concentrations well below the occupational exposure limit. Methylene chloride concentration estimates using this approach were only one-half the occupational exposure limit, so the model was refined using information on the actual amount of solvent that evaporated. This resulted in a concentration estimate approximately one-fifth of the occupational exposure limit. Air sampling was done to evaluate model performance. Measured concentrations were higher than modeled concentrations by up to a factor of two but were still below applicable occupational exposure limits. The exposure models selected were deemed useful in the assessment of exposure acceptability in these labs.