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The thermal decomposition of various polyester and polyether flexible polyurethane foams has been carried out in air atmospheres between 300 and 1000C. It is shown that the main decomposition processes are similar to those observed in inert atmospheres, namely that the decomposition proceeds via the initial release (200 to 300Â°C) of a nitrogen-rich material which subsequently decomposes at temperatures above about 500C (800C in inert atmospheres) to give nitrogen-containing materials of low molecular weight, particularly hydrogen cyanide, acetonitrile, acrylonitrile and benzonitrile. The intermediate nitrogen-rich material has not been directly isolated from oxidative environments but the experiments of this report indicate that it is probably identical to the 'yellow smoke' observed under inert conditions. The main nitrogen-containing material observed in this work produced from the thermal-oxidative decomposition of the intermediate is hydrogen cyanide of which the yield increases with temperature from 500 up to 700Â°C, decreases at 800C then increases again at 900 and 1000C. At 700C approximately 10 to 20 per cent of the theoretically available nitrogen is released as hydrogen cyanide and at 1000C this figure rises to 35 to 40 per cent of the theoretical.