Generation of hydrogen cyanide from flexible polyurethane foam decomposed under different combustion conditions

Experimental thermal conditions conducive to the production of high levels of hydrogen cyanide (HCN) from flexible polyurethane foam were determined. In these experiments the material was exposed to relatively low‐temperature non‐flaming oxidative conditions for a short time period, during which a char was formed. Further heating of the char to temperature above 500°C generated the increased HCN levels. Upon exposure to this same two‐step decomposition process, a fire‐retarded flexible polyurethane foam produced twice as much char and twice as much HCN. Elemental analyses indicated that the HCN concentration was directly related to the amount of char formed and its nitrogen content. Room burns of slabs of flexible polyurethane foam and chairs containing flexible polyurethane foam indicated that this same phenomenon occurs in large‐scale experiments. In these NBS tests, increased concentrations of HCN were produced when the material underwent flaming combustion following a period of smoldering, presumably from heating the char that was formed during smoldering. Investigation of the molecular mechanisms responsible for the increased HCN concentrations was attempted using ion chromatography, electron spectroscopy for chemical analysis (ESCA), Fourier transform infrared (FTIR), pyrolysis/mass spectrometry and 13C solid‐state nuclear magnetic resonance (NMR) techniques. While the molecular structures of the nitrogen‐containing compounds in the char were not elucidated, these analyses provided evidence of multiple compounds containing amine, amide, imine and nitrile functional groups as the most likely sources of the observed HCN.