Experimental Study on the Influence of Thermal Feedback on the Burning Behavior of Flexible Polyurethane

A series of experiments were carried out to study the effect of thermal feedback on the flame spread rate and the heat release rate for a horizontally positioned slab of polyurethane under pre-flashover conditions. Two experiments were performed in a slightly modified ISO 9705 Room Corner Test facility with a compartment measuring 2400 mm wide x 2800 mm deep x 2400 mm high. The room had a rectangular vent (opening under a calorimeter hood) measuring 740 mm wide x 1500 mm high that was located in one of the 2400 mm walls. In each of the two experiments, the room was lined with a material that had a different thermal inertia. The third experiment was performed as a free burn under a hood. The experiments showed that the flame spread rate increased in the room experiments as compared with the free burn experiments. Also, the experiments showed that the thermal feedback may increase the heat release rate and lead to flashover conditions, something which may not be predicted based on free burn experiments. Given the profound difference between the results from the different experimental conditions, it is recommended to take detailed room effects, such as thermal feedback, into considerations for the selection of design fires.