Abstract. The heat transfer and burning behavior of intumescent fire-retardant polypropylene were studied by cone calorimeter at heat flux levels of 50 kW·m -2 to establish an essential physical model for the intumescence process in fire. A mathematical model for the burning process of fire-retardant intumescent polymer was put forward based on the assumption that an intumescent front existed between the char layer and virgin layer. The model emphasizes the thermodynamic aspect of the intumescence process and a corresponding submodel is presented. Meanwhile the thicknesses and mass loss rates of the intumescent polypropylene during burning were measured for the validation of the modeling results. Thermal conductivity and heat capacity of polymer material were also measured as input parameters of the model. The validation results showed that the intumescent thicknesses and mass loss rates predicted by the model were in good agreement with the experimental results. The model was also used to predict the temperature distribution across the sample thickness during burning. The study shows that the present model can appropriately describe the intumescent behavior of the polymer and numerically predict its mass loss rates and temperature distribution in fire.

The subject of hydrocarbon sensitization by nitrates under conditions of a heterogeneous spray has been of interest due to its applicability in promoting ignition. To gain insight into the mechanisms of the nitrate sensitization effect, the present work was limited to vapour phase studies at elevated temperatures in order to avoid the influence of heterogeneous factors. The experiments performed included studies of flammability, flame propagation, shock ignition and detonation. The mixtures used were composed of air, hexane, and isopropyl nitrate (IPN) with IPN concentrations ranging from 0 to 100 mole % in hydrocarbon-IPN. In addition, methane and propane were also included in the flame experiments. For the shock ignition and detonation experiments, the measured ignition delay and detonation cell size had minimum values for IPN-air and maximum values for hexane-air. With increases in the IPN concentration, the ignition delay and detonation cell size fell monotonically between the values for hexane and IPN. This monotonic behaviour was explained to be the result of mixing the hydrocarbon with the more sensitive nitrate whose energetics are larger than or comparable to the hydrocarbon when mixed with air. For the slow combustion mode, the results also confirmed the monotonic behavior and showed that the lean flammability limit and the flame velocity fell between those of the hydrocarbon and IPN.