Decay and residual burning in mass timber enclosures

A series of experiments were conducted to investigate the influence of enclosure parameters (ventilation size/geometry, and thermal properties and thickness of boundaries) on the decay, residual burning and extinction when mass timber panels were present on the enclosure floor and ceiling. The experiments were designed to eliminate the occurrence of stochastic phenomena such as heat-induced delamination and encapsulation failure; they were also designed to control the decay of the non-timber fuel. A range of outcomes were observed including continued flaming, continued smouldering and complete extinction. The ventilation geometry and thermal properties of the non-timber enclosure boundaries were shown to significantly influence decay and residual burning. Energy losses were dominated by convection (85 %). Conduction comprised between 0.4 and 8.3 % of the total losses for most cases – although when steel linings were used, this increased to 32.4 %. Following a scaling analysis, the residual burning was shown to scale with a characteristic time scale (${\delta }^2\rho c_p/k$) while the decay rate scaled with the thermal resistance of the linings ($k/\delta$, where δ is the thickness of the lining). A correlation was observed between residual burning and ventilation factor.