First things first - yes, it turns out that spontaneous combustion of humans might actually be a real thing. I know what you're thinking: no, it's not. It's just a fire no one caught, or something sparking, or some other very logical and reasonable explanation. And trust me, I'm with you. Or at least I was. But it turns out that, maybe, just maybe, it's a real thing.
Last year, a man in Ireland was found near the furnace of his apartment. But the coroners determined that the furnace was not the source of the fire. There were burn marks on the floor and ceiling directly above and below the body, but no where else in the apartment. And, io9 says that the only case of spontaneous combustion that has a witness comes from a father taking care of his mentally disabled daughter. They write:
One day he saw a flash out of the corner of his eye, and turned to find her on fire. Despite the flames, she continued to quietly sit in a chair, not reacting and not giving any indication she was in pain. The man's attempts to put the fire out left him with burned hands. The woman lived through the combustion, but slipped into a coma and died shortly afterwards. This indicates one of the strangest parts of human combustion. It takes a very hot flame to reduce a human body to ash. Crematoriums have special chambers designed for it. However, in almost all combustions, there's no burns in the room around the body, indicating that the person simply stayed in one place. Whatever the cause of this combustion, it seems to knock people out first.
People explode. One minute they may be relaxing in a chair, the next they erupt into a fireball. Jets of blue fire shoot from their bodies like flames from a blowtorch, and within half an hour they are reduced to a pile of ash. Typically, the legs remain unscathed, sticking out grotesquely from the smoking cinders. Nearby objects (a pile of newspapers on the armrest, for example) are untouched. Greasy fat lies on the floor. For centuries, this gruesome way of death has been debated, with many people discounting it as a myth. But spontaneous human combustion is real and we think we can show how it happens.
Now, that feature was written by a man named Brian J. Ford. He's a biologist who researches spontaneous combustion. So, of course, he thinks it's real. And he's trying to figure out why it happens. Here's a video of Ford explaining his latest experiment. It involves blowing up a pig. Ford is using these pigs as human proxies. The idea is that humans build up too much acetone in their bodies, which can ignite. New Scientist:
In this video, two miniature dummies burn in about 30 minutes until only their protruding legs are left, a classic hallmark often observed in human victims. Ford thinks the limbs remain unscathed because they contain less fat and so can't absorb as much acetone.
If you'd rather read, than watch, here's Ford explaining:
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 Ford can prove that these pigs ignite when they've got too much acetone, he'll be one of the first people to suggest a probable, and experimentally validated explanation for the infamous phenomenon.