Correlation analysis of sample thickness, heat flux, and cone calorimetry test data of polystyrene foam

This paper deals with thermal and fire performance evaluation of expanded polystyrene (EPS) and extruded polystyrene (XPS) in a cone calorimeter with a piloted ignition. The correlation analysis of sample thickness, heat flux (q′)and experimental results is performed. It is found that the heat flux follows a linear function of the vertical distance from the standard horizontal level to the sample. An optimization ignition model is established considering the effects of sample thickness (or radiant distance). The modified ignition time (t¯_ig) decreases with the increase of the sample thickness. Both t¯_ig (ignition time) and t¯_ig drop as external heat flux rises. EPS's t¯_ig is more sensitive to the variation of external heat flux. Thermal thickness (δ_p) decreases with the intensifying of heat flux, and δ_p is in linear correlation with ρ/q′. When sample is quite thin or the irradiance level is low (2 cmthick PS under 35 kW m^-2 and 3 cm-thick EPS under 25 kW m^-2), single peak heat release rate (HRR) is present. Under other situations, there are at least two peak values. For EPS, the first peak value is higher than the last, while the reverse is true for XPS (exclusive of 5 cm-thick XPS at 35 kW m^-2). Both peak and mean HRR rise linearly with the increase of external heat flux. t_ig, t¯_ig, critical heat flux and δ_p of XPS are smaller than those of EPS, while the reverse is true for mean HRR. The ignition and heat release risk of PS drop with the decrease of external heat flux, and these hazards of XPS are higher than those of EPS.