Determination of the critical conditions leading to the ignition of decking slabs by flaming firebrands

Abstract

This study investigates the ignition by flaming firebrands of two decking slabs used in French dwellings located in Wildland–Urban Interface. The first decking slab was made of pine and the second one was a thermoplastic composed of polypropylene and calcium carbonate. Flaming firebrands were produced by heating and igniting wood chips of different shapes (square, longitudinal and rectangular) with a cone calorimeter. The firebrands generated preserved their shape during their heating. Their projected area was between 0.07 and 12.00 cm2 and their mass ranged from 0.57 mg to 2.66 g. The location of flaming firebrands, the minimal mass and the minimal number of firebrands needed to ignite the slabs were analysed in order to determine the critical conditions of ignition. The ignition of the decking slab only occurred when the firebrands were positioned at the interstices of the wooden slabs and against the leg of the thermoplastic slabs. No ignition occurred when the firebrands were located on the surface of the decking slab. A minimum mass of firebrands of 0.31 g and 0.80 g was necessary to ignite the wooden slabs and the thermoplastic ones, respectively. Less firebrands were needed to ignite wooden slabs than thermoplastic ones.