Applied Heat Flux Distribution and Time Response Effects on Cone Calorimeter Characterization of a Commercial Flexible Polyurethane Foam

The burning behavior of a commercial flexible polyurethane foam has been studied in a cone calorimeter using standard ASTM procedures. It is shown that burning takes place in two distinct stages, with the first primarily due to the release of species derived from the isocyanate used in the manufacture of the foam and the second due to species derived from the polyether component. Experiments showed that approximately 40% of the original foam mass is lost during the first burning stage. Due to the low density and high flammability of the foam, burning takes place at a high rate, and experimental times are relatively short. As a result, the heat release rates measured by the cone calorimeter are distorted by the non-uniform heat flux distribution of the cone heater over the sample volume and the instrument's finite time response. Two heat release models were developed and applied to approximately correct for the effects of finite time response and non-uniform heat flux distribution. Values reported include mass loss rate, heat release rate, heat of combustion, and heat of gasification for each of the burning stages. The measurement results are compared with earlier published findings for similar foams. The results are found to fall into two distinct classes with different heat release rate behaviors. Possible reasons for the differences are discussed.