carbons. HCFC-141b is used in the production of rigid polyurethane and polyisocyanurate or phenolic insulation foams for residential and commercial buildings. It may also be used as a solvent in electronic and other precision cleaning applications.

HCFC-141b is of low inhalation toxicity. Uptake and elimination are rapid, and most of the absorbed dose is excreted unchanged in the exhaled air. Its effects have been studied with human subjects and several animal species, including the monkey, dog, rat, mouse, and rabbit. In addition, studies addressing repeated and chronic exposures, genotoxicity, carcinogenicity, neurotoxicity, and cardiac sensitization were also available. At high concentrations, halogenated hydrocarbons may produce cardiac arrhythmias; this sensitive end point was considered in the development of AEGL values. The air odor threshold in healthy subjects is approximately 250 parts per million (ppm) (Utell et al. 1997). The ethereal odor is not unpleasant.

Adequate data were available for development of the three AEGL classifications. Inadequate data were available for determination of the relationship between concentration and exposure duration for a fixed effect. However, based on the rapidity with which blood concentrations in humans approached equilibrium, the similarity in lethality values in rats exposed for 4 or 6 hours (h), and the fact that the cardiac sensitization effect is based on a concentration threshold rather than exposure duration, a single AEGL value was used across all time periods for each AEGL classification. Some experimental exposure durations in both human and animal studies were generally long, 4 to 6 h, which lends confidence to using the same value for all exposure durations.

The AEGL-1 value was based on the observation that exercising healthy human subjects could tolerate exposure to concentrations of 500 or 1,000 ppm for 4 h with no adverse effects on lung function, respiratory symptoms, sensory irritation, or cardiac symptoms (Utell et al. 1997). The exercise, which tripled the subjects’ minute ventilation, simulates an emergency situation and accelerates pulmonary uptake. Results of the exposure of two subjects for an additional 2 h to the 500-ppm concentration and the exposure of one subject to the 1,000-ppm concentration for an additional 2 h failed to elicit any clear alterations in neurobehavioral parameters. The 4- or 6-h 1,000-ppm concentration is a NOAEL in exercising individuals, there were no indications of response differences among tested subjects, and animal studies indicate that adverse effects occur only at considerably higher concentrations, so the 1,000-ppm value was adjusted by an uncertainty factor (UF) of 1. The intraspecies UF of 1 is supported by the lack of adverse effects in patients with severe



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