Fire Safety Science Digital Archive

If it is assumed that the primary decomposition of wood is exothermic and depends only on the temperature and the concentration of decomposing material in the solid phase, the heat balance and reaction kinetic equations show that it is possible to find a steady state where the rate of decomposition in one direction and hence the loss in weight becomes constant in time. This may be expected to represent a limiting value after burning has been in progress for a long time. The numerical results obtained are very sensitive to the value of the heat of reaction and since this is not known within narrow enough limits, it is not possible yet to make a proper comparison between experiments and theory, but the calculated results are of the same order of magnitude as those measured. If the primary reaction is endothermic or if oxygen is required, the rate of propagation must eventually tend to that given by a diffusion law and cannot be constant in time. Experiments are in progress to study the rate of charring at long times.