Fire Safety Science Digital Archive

Maple plywood samples were heated in an oven at 180°C to a residual weight of 70%, 50%, and 30% of the virgin weight. The virgin plywood and the thermally pretreated samples were tested in a cone calorimeter over the range of 6 to 15 kW/m² without the use of an ignitor. Tests were conducted until smoldering/glowing combustion was observed or for eight hours if ignition was not observed. The extent of thermal pretreatment of the plywood had no measurable effect on the minimum heat flux for smoldering ignition. At heat fluxes above the minimum for ignition, ignition times were reduced for thermally pretreated samples relative to virgin wood. This is consistent with the thermal pretreatment achieving the charring required as the first step in smoldering ignition and the reduction in thermal inertia resulting from charring. Samples of the virgin and pretreated wood were subjected to thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The chemical kinetics analysis of the virgin and pretreated samples showed no change in the chemical mechanism. The thermal pretreatment simply resulted in the samples being further along the reaction pathway at the start of the ignition test. The results are not consistent with the formation of a more reactive char species commonly referred to in the fire investigation lore as “pyrophoric carbon.”