The efficiency of commercially available air purifying respirators in adsorbing methyl-isocyanate (624839) was evaluated. Respirator cartridges obtained from two manufacturers were tested as received. An airstream containing methyl-isocyanate vapor was pulled through the cartridge cell housing that contained either a single cartridge or a pair of cartridges, depending upon the design of the respirator from which they were removed. Breakthrough data for the tested organic vapor cartridges from both manufacturers showed that at high methyl-isocyanate concentrations such as might be encountered during emergency situations, methyl-isocyanate was very poorly absorbed on organic vapor cartridges. At the lowest challenge concentration studied (300 parts per million), a breakthrough time of only 30 minutes was observed. The breakthrough concentration encountered was approximately 20 times higher than the threshold limit value for methyl-isocyanate (0.02 parts per million). While acid gas and organic vapor/acid gas cartridges gave breakthrough times in excess of 60 minutes under dry conditions, at increased humidity instantaneous breakthrough of methyl-isocyanate was observed. No commercially available air-purifying cartridge tested provided protection against methyl-isocyanate breakthrough at the high challenge concentrations that might be encountered under emergency conditions. The authors conclude that only supplied air respirators should be used (even for escape purposes only) when methyl- isocyanate is the suspected environmental contaminant.
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