Criteria for autoignition of combustible fluids in insulation materials

Criteria have been investigated for the conditions at which a 'lagging fire ' may occur when a flammable liquid penetrates and is dispersed within insu lation material surrounding a hot pipe. The conditions at which a Frank-Kam enetskii thermal ignition criterion should be replaced by one derived from the heat release rate versus fluid evaporation rate were deduced. These con ditions were related to the decreasing enthalpy of vaporization of the flui d. Practical investigations were based on formal 'cube test' methods for th ermal ignition. The theory was tested against the behaviour of n-C16H34, n- C18H38 and n-C20H42, which represent alkanes of mid-range volatility, and a lso with reference to squalane (C30H62), which is representative of highly involatile alkanes.