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It is a requirement in the Korean standard that breakthorough time at 5 ppm should be at least 50 min with the challenge concentration at 300 ppm against carbon tetrachloride for small cartridge respirator for gas and vapor. However, this requirement may not a good index for the adsorption capacity of the carbon at the field situation where concentration level is much lower than the test challenge concentration. Maximum concentration where air purifying respirator can be applied is the 10 times of the workplace standard. Thus, working concentration for carbon tetrachloride is 5-50ppm. In this range, the adsorption capacity mush have different characteristics from those at 300 ppm since the adsorption capacity is also a function of challenge concentration. This study was initiated to evaluate validity of the challenge concentration level of the current cartridge performance test regulated by the Korean ministry of labor and to provide useful information for the respirator cartridge performance test protocol. The breakthrough curves were obtained for two types of 3M respirator cartridges (model #7251, and #7168(AX)) against carbon tetrachloride. The adsorption capacities of carbons were calculated using mass transfer balance equation derived from the curve fitting to the breakthrough curves experimentally obtained. Adsorption isotherms were derived from these data. Much higher adsorption capacity of carbon at 300 ppm challenge concentration was shown in the cartridge #7251. On the contrary, the cartridge #7168(AX) showed higher adsorption capacity than the cartridge #7251. The cartridge #7251 or similar types have been widely used in general industries because of higher adsorption capacity. The AX cartridge (#7168) has been developed for lower molecular vapors in the Europe. The carbons of this type have smaller micropore size compared to the traditional cartridge carbon. Due to this characteristics, the adsorption capacity at lower concentration level was increased and, thus, performance was improved. From these results, it is concluded that the current challenge concentration level is not proper to evaluate the cartridge performance and the performance tests should be made at the similar concentration range with the field situation. Otherwise, performance tests at two concentration levels are recommended to estimate the adsorption capacity at lower concentration range.
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