Superposition of heat release rate curves for combustibles with bench-scale tests

In fire hazard assessment, the resultant heat release rate of burning different combustibles has to be known. The principle of superposition is commonly applied to estimate the total heat release rate from the individual curves measured for single items. Accuracy of such an approach will be studied with bench-scale tests in this paper. The heat release rate curves of burning each sample cube of polymethylmethacrylate (PMMA), polyvinyl chloride (PVC), polycarbonate (PC) and wood were first measured individually by a cone calorimeter. Radiative heat fluxes of 50 and 70 kW m-2were applied. After that, a PMMA cube was burnt with a cube of another material under the same heat flux. The resultant heat release rate curves of burning these two cubes were measured. Heat release rate curves of burning the single cube were used to estimate the resultant curves. The technique of fundamental analysis will be applied for comparing the predicted curves with the experiments. Importance of the parameter s for estimating the secant inner product cosine specifying the data points intervals will also be discussed. For the samples tested, it is observed that superposition gives good estimations of the total heat released curve if those for individual items were measured under the same radiative heat fluxes. However, the results will not be so good where the curves for each combustible were measured at different heat fluxes. This point is very important in estimating the possible heat release rate for a design fire.