Fire Safety Science Digital Archive

The present work is dedicated to building up an ignition model for evaluating the fire risk of a structural component exposed to the external radiant heat flux sourced from bushfires. Based on the theory of one-dimensional heat transfer, analytical correlations for determining the ignition delay time and the energy absorbed by the targeted solid are worked out, which are a function of external radiation heat flux, wind speed and the solid thermal properties. Ignition delay times for various types of materials are then computed and compared with the available experimental data. Energy absorbed by the solids during their ignition process is also quantified, which decreases with increasing incident heat flux and is also a function of wind speed in general. Based upon the energy balance between energy uptake by a solid and the energy required for the thermal boundary layer on the solid surface to reach ignition status, a simplified ignition criterion is derived for an undried solid with fixed apparent thermal properties. Testing of the model with two independent experimental data sets shows that it may provide convenient and reliable predictions on the ignition delay times for moist materials located in the flowing environment. This model has application in engineering practice for predicting the ignition potential of a solid intercepting radiant heat sourced from a developing bushfire.