The dependence of spontaneous ignition temperature on surface to volume ratio in static systems for fuels showing a negative temperature coefficient

Certain hitherto unexplained features in the observed variation of spontaneous ignition temperatures with surface-to-volume ratio are discussed in terms of chain-thermal ignition theory. They are shown to be expected for substances that exhibit cool flames and two-stage ignitions, as is a region of "two-stage instability" at higher s/v values, not yet observed. The results are relevant to the assessment of hazards associated with spontaneous ignition in enclosed compartments such as aircraft fuel tanks.