Fire Safety Science Digital Archive

An approximate theory of the growth to flashover of fires in compartments is described for those situations where there are no effective breaks in the continuity of the fuel. The essence of the theory is the assumption that the instantaneous rate of spread depends on the surface temperature of the fuel. It is shown that heat loss through the walls is of negligible importance on the heat balance and that the gas temperature may be regarded as responding immediately to changes in the burning rate. It is not sufficient however to regard the gases as uniformly mixed and the effect of stratification appears important. The observed differences between the behaviour of compartments fully lined with fibre insulating board and only half lined - upper walls and ceiling being brick, is consistent with the view that the fuel is heated by radiation and that because brick heats up more slowly than fibreboard it does not begin to reradiate heat to the fuel surface so soon. The calculations demonstrate the importance of the thermal properties of the walls and ceiling etc., in determining the rate at which the fuel surface itself rises in temperature, and so controlling the fire growth.