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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.

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A major cause of death or permanent injury in fires is inhalation of toxic gases. Moreover, every fire is unique, and the range of products, highly dependant on fire conditions, produces a wide variety of toxic and irritant species responsible for the most fire fatalities. Therefore, to fully understand each contribution to the toxicity it is necessary to quantify the decomposition products of the material under the test. Fires can be divided into a number of stages from smouldering combustion to early wellventilated flaming, through to fully developed under-ventilated flaming. These stages can be replicated by certain bench-scale physical fire models using different fuel-to-oxygen ratios, controlled by the primary air flow, and expressed in terms of the equivalence ratio (the actual fuel/air ratio divided by the stoichiometric fuel/air ratio). This work presents combustion product yields generated using a small-scale fire model. The Purser Furnace apparatus (BS7990 and ISO TS 19700) enables different fire stages to be created. Identification and quantification of combustion gases and particularly their toxic components from different fire scenarios was undertaken by continuous Fourier Transform Infrared Spectroscopy. The relationship between type of the fire particularly the temperature and ventilation conditions, and the toxic product yields for four bulk polymers, LDPE, PS, Nylon 6.6 and PVC are reported. For all the polymers tested, except PVC, there is a dramatic increase in the yield of products of incomplete combustion (CO and hydrocarbons) with increase in equivalence ratio, as might be expected. For PVC there is a consistently high level of products of incomplete combustion arising both from flame inhibition by HCl, and oxygen depletion. There is a low sensitivity to furnace temperature over the range 650-850°C, except that at 650°C PS shows an unexpectedly high yield of CO under well-ventilated conditions and PVC shows a slightly higher hydrocarbon yield. This demonstrates the dependence of toxic product yields on the equivalence ratio, and the lack of dependence on furnace temperature, within this range.