Comparison of toxic product yields from bench-scale to ISO room

Toxic products are the main cause of fire injuries and deaths, but available methods for measuring or calculating toxic product yields have severe limitations. Full-scale or large-scale experimental re-creations of fire scenarios are sometimes used for the assessment of toxic hazard, but such tests are expensive, while small-scale or even larger-scale tests often provide poor simulations of full-scale conditions. From a testing and engineering calculation perspective there is a need for test methods to provide data-enabling calculations of toxic product yields in defined full-scale scenarios. Full-scale and large-scale tests have demonstrated that toxic product yields are highly dependent upon the combustion conditions. Fire stages and types can be characterised either in terms of CO2/CO ratio, or preferably in terms of equivalence ratio, which provide reasonably good predictive metrics for product yields. The steady-state tube furnace (ISO TS 19700) allows individual fire stages to be replicated and shows a good general agreement with product yield data (measured for CO2, CO, HCN, NOx, total hydrocarbons and smoke particulates) obtained from large-scale ISO room tests for the five materials considered here and expressed as functions of equivalence ratio and CO2/CO ratio. The closest direct agreement between the large- and small-scale data were obtained for pool fires involving PP and nylon 6.6 product yield. For materials burned as wall linings, with varying decomposition conditions at different room locations, and/or when a propane flame is also present, direct comparison with tube-furnace data is more problematic. Nevertheless MDF, MDF-FR and PS show reasonable agreement for CO, CO2, HCN and hydrocarbon yields between the scales. Smoke yields tended to be more variable and may be influenced by the presence of different areas of flaming and non-flaming decomposition.