The prediction of combustion products

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The basic routes leading to product formation in fires are identified and involve the thermal and thermal oxidative decomposition of the polymeric material. These products are released into the relatively mobile atmosphere of the fire where further decomposition or combustion takes place.These processes are studied at the Fire Research Station, Borehamwood, using single and two stage decomposition systems with GC-MS analysis of the products, combustion studies with a special burner system and full-scale fires.Experiments with flexible polyester and polyether foams show that the decomposition proceeds by the low temperature elimination (200° to 300°) of a nitrogen-rich material in the form of a particulate smoke which appears to be polymeric form of TDI. The smoke decomposes at high temperatures (above about 800°C) to produce a range of nitrogen-containing materials of low molecular weight and particularly hydrogen cyanide. At these high temperatures, carbon monoxide is a significant decomposition product from the polyol part of the foams.Studies of the relative yields of hydrogen cyanide and carbon monoxide in a single-stage decomposition give yields of 55 and 400 mg/g, respectively, at 1000°C.A two-stage decomposition with foam at 300°C and a secondary zone at 1000°C is necessary to simulate the relative yields of hydrogen cyanide and carbon monoxide found in fires. In this way experimental yields of hydrogen cyanide and carbon monoxide of 55 and 80 mg/g, respectively, have been obtained consistent with the relative amounts observed during the early stages of a large fire.Some recent work involving studies of the thermal decomposition of rigid polyurethane foams and the release of hydrogen cyanide is given.