Recent developments in understanding the toxicity of PTFE thermal decomposition products

Fluropolymers, especially polytetrafluoroethylene (PTFE), have good fire‐resistance properties, but their application is limited by concerns over the toxicity of their thermal decomposition products. In experiments using a tube furnace system similar to the DIN 53 436 method, the 30‐minute (+ 14 days observation) LC50 in mass loss terms was found to be 2.9 mgI−1 (Standard Error 0.40) under non‐flaming conditions, approximately ten times as toxic as wood and most other materials. Toxicity was due to upper respiratory tract and airway irritation, and was consistent with the known effects of carbonyl fluoride and hydrogen fluoride. When decomposed in the NBS cup furnace test under‐non‐flaming conditions, PTFE evolved extreme‐toxicity products with an LC50 of approximately 0.05 mgI−1 (mass loss), approximately 1000 times as toxic as wood and most other materials. Toxicity was due to deep lung irritation and oedema. Investigations of the range of conditions under which the extreme toxicity of PTFE products occurs in both small‐scale (200‐litre) and intermediate‐scale (6 m3) experiments have shown that the highest toxicity occurs when PTFE is decomposed under non‐flaming conditions over a temperature range of 400–650°C, and when the primary decomposition products are subjected to continuous secondary heating. At higher or lower temperatures, when the sample is flaming, when decomposition products from wood are also present in the chamber, when secondary heating is curtailed, or when the molecule contains hydrogen as well as fluorine, the toxicity of the products is greatly reduced, tending towards the region of ten times the potency of most other materials. Extreme toxicity is associated with a particulate, but the particulate atmosphere is not always extremely toxic, the potency decreasing as the fumes age.