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Abstract
A group of workers exposed to 180 to 200 ppm of methylene chloride had car- boxyhemoglobin (COHb) levels of about 4.5% as measured by alveolar carbon monoxide concentrations at the beginning of their workday. This rose to about 9% after eight hours of exposure and then dropped exponentially to 4.5% by the time they started working the next day. The 24-hour time-weighted average %COHb was 7.3% compared with 2.7% for persons exposed to 35 ppm of carbon monoxide or 3.8% for persons exposed to 50 ppm of CO.
On the basis of these observations, it is proposed that the threshold limit value for methylene chloride be reduced to 75 to 100 ppm to avoid body burdens of COHb greater than those allowed persons exposed to exogenous CO.