Respirator cartridge service-life: exposure to mixtures.

Expressions associated with a previously developed procedure to assess respirator cartridge service-life were modified to address the cartridge breakthrough properties of each of individual compounds comprising systems with more than two components. These were applied to specific ternary and quaternary test mixtures. Experimental breakthrough data were collected for (1) acetone/cyclohexane/toluene, (2) ethyl acetate/cyclohexane/toluene, (3) cyclohexane/toluene/ m-xylene, (4) ethyl acetate/cyclohexane/toluene/m-xylene, and (5) acetone/ cyclohexane/toluene/ m-xylene. Data indicate that as an exposure experiment proceeds, a compound that is adsorbed relatively weakly by the carbon bed may be displaced by a more strongly adsorbed component, which may result in a breakthrough concentration for displaced compounds that exceeds the challenge concentration in the mixture. The approach described accounts for the displacement phenomenon and can predict the ratio of the number of displaced molecules to the corresponding number of displacing molecules. Experimental data for each multicomponent system were used to determine values of three parameters (k', tau, and A(m)) for each compound in each challenge system. The value of k' characterizes the rate of adsorption of a compound under applicable experimental conditions, tau indicates the capacity of the charcoal, and A(m) describes the effectiveness of a compound in displacing a previously adsorbed compound. Parameter values were applied to calculate complete breakthrough curves for each compound of each mixture. Calculated curves were compared with corresponding experimental data; reasonable agreement justifies simplifying assumptions incorporated into the application of the approach to mixtures of more than two compounds. The time-dependence of the weight of each compound adsorbed by the carbon was calculated. The service-life of respirator cartridges exposed to multicomponent mixtures depends on the challenge concentration of each component of the system and is significantly influenced by the displacement effect. The adsorption capacity of the carbon and the breakthrough time for weakly adsorbed compounds are decreased significantly by exposure to mixtures.