ABSTRACT
In addition to the cartridge breakthrough data developed by Nelson et al. many investigators also conducted cartridge breakthrough studies. Before the creation of NIOSH, respirators were tested and approved by the Bureau of Mines (BM) under the test schedules prescribed in 30 CFR 11. The test method for chemical cartridges was listed in Schedule 23B, which prescribed carbon tetrachloride as the test agent for organic vapor. Carbon tetrachloride has a threshold limit value (TLV) of 10 ppm and an odor threshold of 50 ppm, making its use hazardous (CCl4 was not considered as a suspected carcinogen then). The Bureau searched for a safe replacement for CC14.' Halocarbons were selected because these solvents were relatively innocuous with physical properties similar to CC14. Three halocarbons, fluorotrichloromethane (Freon 11), dichloromonofluoromethane (Freon 21), and 1,1,2-trichloro-1,2,2-trifluoromethane (Freon 1 13), were selected for testing. The test conditions were: 1000 ppm challenge, 32 and 64 liters per minute (1/m) flow rate, room temperature, and 50% relative humidity. The breakthrough time was measured at 0.5% of the challenge.
