HCN Yields and Fate of Fuel Nitrogen for Materials under Different Combustion Conditions in the ISO 19700 Tube Furnace and Large-scale Fires

For calculations of time-concentration curves for toxic products in full-scale fires it is necessary to know how the yields of key toxic species vary with combustion conditions and fuel composition. In this paper, the relationships between equivalence ratio (phi) and HCN yields and conversion efficiencies (mass fraction of fuel nitrogen released as HCN) are presented for ten common nitrogen-containing materials and products combusted in the ISO19700 tube furnace under steady flaming conditions at a furnace temperature of 650-700°C in air. Additional experiments were carried out at 850°C and also in 10% and 12% oxygen. Large-scale fire tests were carried out under well-ventilated and vitiated combustion conditions on three materials for comparison. For non-FR materials sigmoid relationships between phi and HCN yields were found with very low yields (0.00003-0.002 g/g) at phi 0.5 increasing to a wide range (0.0036 g/g to 0.11 g/g) at phi 2 depending upon the material. Yields from some materials were also found to be sensitive to furnace temperature and oxygen concentration. When normalised for nitrogen content, the relationships between phi and HCN recovery were more similar, falling into high (maximum HCN recovery fraction ~ 0.16) and low groups (maximum 0.085). Although the large-scale test data were more variable, a good agreement was found with the tube-furnace results.