Fire Safety Science Digital Archive

The self-heating equation is derived in an approximate form for simultaneous thermal and mass diffusion in a symmetrically heated porous solid. This equation has already been discussed by Buben (1) and its application to the self ignition of fibre insulating board and wood is described here. Some of the numerical values of the relevant parameters are derived for fibre insulating board and wood and they show that fibre insulating board is sufficiently porous for there to be a sharp ignition point thermally controlled. The critical ignition parameters for fibre insulating board, and dust piles which are more porous but equally reactive and exothermic are theoretically little affected by whether or not the reaction is oxygen dependent. If the reaction requires oxygen there is a temperature jump to a region where oxygen availability controls the reaction. Calculated values are obtained from the theory for the temperature jump on the assumption that there is no exhaustion of reactant in the solid frame.