Presentation Abstract

Title: TWA or STEL? A Measurement Strategy for Determining VOC Exposure during use of a Mixed-hydrocarbon Solvent

Author: Marc J. Plisko, CIH

Presented at: AIHCE 2010, Denver, Colorado

Studies have shown that concentrations of volatile compounds in mixed hydrocarbon solvents decrease over time, demonstrating that lower boiling point compounds readily evaporate while the higher boiling compounds tend to stay in solution.  One such study, which evaluated the solvent vapor exposure to a worker using a parts washer solution spiked with benzene, showed that more than 35% of the benzene evaporated in four hours and more than 75% evaporated after eight hours.  These implications are significant for sampling strategy design since the highest solvent vapor concentrations may be expected during the first few minutes or hours of solvent use.  Such observations suggest that air monitoring for comparison with short term exposure limits (STEL’s) should be performed in addition to full shift or consecutive sampling when characterizing solvent exposures.  Recent studies undertaken by the authors further verified this concept.  During one representative test trial, solvent vapor measurements obtained during the evaporation of a mixed hydrocarbon solvent showed a peak VOC concentration of approximately 260 ppm during the first 15 minutes, while an average VOC concentration of approximately 14 ppm was recorded for the first 240 minutes.  Measurements obtained during additional trials yielded similar trends.  Given the disparity between the information derived from short and long term air monitoring, knowledge of the compounds used during the performance of certain job tasks is critical when developing exposure measurement strategies.

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