There have been many alleged cases of spontaneous human combustion in history — but such accounts tend to rouse suspicion even among the more open-minded of us. How is it possible, after all, for the human body to just simply explode into flame? Well, writing in New Scientist, biologist Brian J. Ford thinks he's found the answer.
I felt it was time to test the realities, so we marinated pork abdominal tissue in ethanol for a week. Even when cloaked in gauze moistened with alcohol, it would not burn. Alcohol is not normally present in our tissues, but there is one flammable constituent of the body that can greatly increase in concentration.
Triacylglycerol lipids cleave to form fatty acid chains and glycerol. The fatty acids can be used as an alternative source of energy through beta-oxidation, giving rise to the key metabolic molecule acetyl-CoA. This helps drive the energy-producing Krebs cycle within the mitochondria of cells.
If the body's cells are starved (which can occur during chronic illness and even during a workout at the gym), acetyl-CoA in the liver is converted into acetoacetate, which can decarboxylate into acetone. And acetone is highly flammable. A range of conditions can produce ketosis, in which acetone is formed, including alcoholism, high-fat low-carbohydrate dieting, diabetes and even teething. So we marinaded pork tissue in acetone, rather than ethanol.
This was used to make scale models of humans, which we clothed and set alight. They burned to ash within half an hour. The remains - a pile of smoking cinders with protruding limbs - were exactly like the photographs of human victims. The legs remain, we think, because there is too little fat for much acetone to accumulate. For the first time a feasible cause of human combustion has been experimentally demonstrated.
The moral of the story: People with ketosis shouldn't wear synthetic fibres on dry days.
There's lots more to Ford's story at New Scientist (free registration required), including a history of spontaneous combustion and the various scientific efforts to understand it.