Fluorocarbonresin being used widely in industry has eminent characteristics both in thermal stability and chemical inertness which are not observed in other resins. Because of its excellent thermal stability, fluorocarbonresin are used at high temperatures, and the toxicity of its pyrolytic products has been studied in various laboratories, but as yet opinions on the mechanism of its toxicity are divergent. The author has studied the principal toxic factors with a view to establishing safety standards from the industrial medical point of view, and three kinds of fluorocarbonresin were pyrolyzed under the the same conditions. As a means to evaluate correctly the toxicities of pure gases that are identical as to several components, such as hydrogen fluoride and monomers, yielded on pyrolyzing processes of fluorocarbonresins, the author, having established an exact method of biological exposure, examined the toxicity of pyrolytic products of fluorocarbonresin. As for polytetrafluoroethylene, hydrogen fluoride is he primary lethal factor in animals used in this study which is toxic not only to respiratory organs but also to the liver. Besides the author observed more than two mortal factors which had the same toxic tendency with that of the primary factor, and yet is one fifteenth of the toxic properties of hydrogen fluoride. As for polyfluoroethylenepropylene, hydrogen fluoride is the primary lethal factor and octofluoroisobuthylene the secondary lethal factor which is fiercely toxic to lungs and the liver, and other unknown toxic factors coexist acting with the same toxic tendency as octofluoroisobuthylene. As for polychlorotrifluoroethylene, hydrogen fluoride and two kinds of unknown toxic factors affecting lungs, the liver and kidneys are coexist and act collectively. Since unknown toxic factors were observed besides hydrogen fluoride and octofluroisobuthylene of which the toxicity have been debated in various ways, the author has come to the conclusion that fluorocarbonresin should be handled with utmost care when used at high temperatures and that elucidation of these unknown toxic factors is necessary.

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