Student Research: Gregory Frick
Passive monitors fulfill a valuable role in industrial hygiene sampling. Although operation of the monitors in mixed chemical environments has been reviewed, the effect of each additional chemical in the mixture on monitor accuracy has not been evaluated. If individual chemical attributes (such as vapor pressure and polarity) predictably alter monitor performance, this information will assist industrial hygienists in assessing applicability of these devises.
To address this issue, passive monitors were challenged with mixtures of three common industrial solvents (methyl ethyl ketone, o-xylene, and trichloroethylene) in a bench-scale sampling system. In a series of eight, 8-hour randomized experiments, filtered air, at a constant humidity, temperature, and velocity was injected with a solvent mixture and continuously fed into a sampling chamber containing fifteen passive monitors (five each, from three different manufacturers). All possible combinations of the three solvents were represented in the eight experiments; one control, three single chemical runs, three double chemical runs, and one run with all three chemicals. Chamber concentrations for each mixture component were set at the Threshold Limit Value and verified with a set of MIRAN 1A instruments.
Monitor performance was influenced by mixture composition. When o-xylene recovered from all badges to average chamber o-xylene concentration (termed accuracy ratio) was 0.89 (0.06) (mean (standard deviation)). However, when methyl ethyl ketone was present with o-xylene, the accuracy ratio for o-xylene dropped to 0.80 (0.06) (p<0.01). Surprisingly, some chemical combinations actually enhanced monitor performance. Additionally, the relationship between mixture composition and monitor performance was influenced by an interaction between the two for two out of three study chemicals. This information can guide the industrial hygienist in selecting passive monitors based on mixture composition and monitor characteristics.