What is actually happening is this (our Saturday science lesson, gentle readers). When a substance with a relatively low ignition temperature, such as the majority of those materials listed above, begins to generate heat due to exothermic internal reactions (by oxidation or bacterial fermentation), because these materials are also good thermal insulators the heat cannot escape, leading to what is called thermal runaway (i.e. rapidly accelerating temperatures as heat produced exceeds heat dissipated). Given sufficient quantities of fuel, heat and oxygen (the three sides of the 'fire triangle' many of us will have learned on fire-prevention courses) autoignition results and whoof, your hayrick, coalmine, cotton store, mountain of pistachio nuts or refuse heap is ablaze without prior warning.
The net result of my copious (and rather unsettling) research leads me to believe that in the majority of the hundreds of reported cases of human beings burning to death unexpectedly, the majority can be explained by a combination of the physical condition of the deceased prior to the conflagration and the likely presence of an external heat source.
"The body of 76 year old Michael Faherty, was found in the living room of his home in Clareview Park at Ballybane in the Irish city of Galway on 22nd December 2010. The scene was searched by forensic experts from the Gardai and the fire service. The fire investigators concluded that no accelerants were used and that the open fireplace in the room was not the cause of the fire. A post-mortem carried out by pathologist Grace Callagy noted that Faherty had suffered from Type 2 diabetes and hypertension but had not died from heart failure. Callagy concluded that the extensive nature of the burns sustained precluded determining the precise cause of death The coroner in the case could not identify the cause of the death due to extensive internal organ damage and concluded that 'this [case] fits into the category of spontaneous human combustion, for which there is no adequate explanation'."'


