Experimental study of spruce wood reaction to fire in single burning item test

The aim of this work is to study and characterize the fire behavior of vertically oriented spruce wood panels using experiments conducted at the scales of cone calorimeter and single burning item tests. For this purpose, first incombustible panels were exposed to burner powers of 15, 20, 30, and 50 kW in the single burning item tests to obtain a mapping of the total heat fluxes received by the panel. Subsequently, wood panels were exposed to the same burner powers for exposure times of 15, 20, and 30 min. Very thin thermocouples were embedded inside the wood panel to measure accurately the in-depth temperatures while the lateral position of the char front on the exposed surface and the depth of the char layer were also measured for each test. The latter measurement permitted to establish a char depth map according to the burner power and exposure time. Correspondingly, it was observed that for a fixed exposure time, the degraded area on the surface grows linearly with the burner power. Moreover, the in-depth char front position deduced from the 300 °C isotherm was found to comply very well with that obtained from direct measurements. Finally, a comparison is made between the char front depths measured with the single burning item and those measured with the cone calorimeter for similar heat fluxes, showing that the corresponding charring rates from these two tests deviate from one another only at low heat fluxes.