Fire Safety Science Digital Archive

This report which will be mainly of interest in theoretical calculations on ignition and the spread of fire deals with two aspects of the ignition of wood. In the first a conventional approximation is used in calculating the ignition hazard. It is shown that an effective constant heat transfer coefficient can be defined to accommodate the theoretical temperature dependent coefficient. Computer calculations confirm that the approximation is satisfactory for the range of conditions of most practical interest. The second aspect concerns the rate at which volatiles are emitted at ignition. This is some guide to the phase when, after ignition, the burning wood itself acts as a fuel assisting further fire spread. Recently published data of Koohyar are analysed. This analysis shows that, although perhaps less precise than defining ignition by the attainment of a critical surface temperature, a critical rate of emission of volatiles of the order of 6 g m^-2s^-1 is a suitable alternative criterion.