Formation of acute pulmonary toxicants following thermal degradation of perfluorinated polymers: evidence for a critical atmospheric reaction.

In some small-scale tests of combustion-product toxicity, perfluorinated polymers (FP) have been shown to be much more toxic than other common materials. These studies were conducted to determine the conditions under which highly toxic decomposition products of FP are formed. A modification of the National Bureau of Standards exposure system (Levin et al. National Bureau of Standards 1982, NBS IR 82-2532) was used, in which materials could be heated either in a cup furnace or above a small methane flame. At 700 degrees C, the approximate lethal concentrations (ALCs) of the products formed from polytetrafluoroethylene (pTFE) and from hexafluoropropylene/tetrafluoroethylene copolymer (FEP) in the CH4 flame (applied for 1 min) are approximately 850 times higher than the ALCs of the products formed in the cup furnace. Analytically, the major products formed initially from pTFE at 700 degrees C under either condition (flame or cup furnace) are similar but they disappear rapidly in the presence of continuous heat. When the cup furnace is removed 1 min after pTFE is added (a procedure temporally similar to the use of the flame) the toxicity of the products is again low. However, when heat from either the cup furnace or from a small secondary flame is applied continuously (for up to 30 min) to the initial products formed from pTFE in the flame, high toxicity is observed. These observations are supported by pathological evaluation of the respiratory tracts of exposed rats. Thus, the inhalation toxicity of FP thermal decomposition products is related to a heat- and time-dependent atmospheric reaction. Such mechanisms should be considered in estimating the fire hazard of these materials in use.