Abstract
Smouldering can progress without flame and destroy timber structures through exothermic solid-phase oxidation reactions of porous char. Anecdotally, smouldering has been reported to be more severe in timber infrastructure treated with chromate copper arsenate (CCA), which is used to improve biological durability. Scientific knowledge on the severity and mechanisms of this phenomenon are insufficiently developed. This study investigated the boundary conditions required to induce smouldering in CCA-treated slash/Caribbean pine under laboratory conditions. Cone calorimeter and thermogravimetric analysis (TGA) showed that the presence of CCA did not affect the flaming behaviour (e.g. HRR) but affected smouldering combustion. A lower critical heat flux of smouldering ignition (~7.5 kW/m2) in CCA-treated specimens was found when exposed to radiative heat. An earlier onset and slightly higher reaction peak of oxidative pyrolysis was observed from TGA results. CCA-treated samples exhibited self-sustained smouldering after removal of an external heat source; the thermal decomposition for these was measured as more severe for lower densities and for prolonged heating times. The heat flux was found to have a minor influence on self-sustained smouldering, which was inhibited after high heat flux (50 kW/m2) exposure.