The acute toxicity of difluoromethane is very low, the 4-hr LC50 being greater than 52% in air (3). Also, it is not mutagenic in vitro (9-11) or in vivo(12). In studies of its potential to cause sensitization of the heart to adrenaline in dogs, an exposure level of 350,000 ppm (35%) did not cause a response (4). Exposures at levels up to 50,000 ppm, the highest level tested, did not cause toxicity in rats in 4 - and 13- week studies, nor did it cause developmental effects in rats (7) or rabbits (8).
It is, therefore, recommended that an exposure level associated with good industrial hygiene practice be established for this material as has been done with CFC-11, CFC-12, HFC-134a, and HFC-125. Typically, this level has been 1000 ppm as a time-weighted average (TWA) for an 8-hr day.
8-hr TWA : 1000 ppm (2200 mg/m3)
Workplace Environmental Exposure Level Guides