To combust, a human body needs two things: intensely high heat and a flammable substance. Under normal circumstances, our bodies contain neither, but some scientists over the last several centuries have speculated on a few possible explanations for the occurrence.
In the 1800s, Charles Dickens ignited great interest in spontaneous human combustion by using it to kill off a character in his novel "Bleak House." The character, named Krook, was an alcoholic, following the belief at the time that spontaneous human combustion was caused by excessive amounts of alcohol in the body.
Today, there are several theories. One of the most popular proposes that the fire is sparked when methane (a flammable gas produced when plants decompose) builds up in the intestines and is ignited by enzymes (proteins in the body that act as catalysts to induce and speed up chemical reactions). Yet most victims of spontaneous human combustion suffer greater damage to the outside of their body than to their internal organs, which seems to go against this theory.
Other theories speculate that the fire begins as a result of a buildup of static electricity inside the body or from an external geomagnetic force exerted on the body. A self-proclaimed expert on spontaneous human combustion, Larry Arnold, has suggested that the phenomenon is the work of a new subatomic particle called a pyroton, which he says interacts with cells to create a mini-explosion. But no scientific evidence proves the existence of this particle.
As of March 2005, no one has offered scientific proof of a theory explaining spontaneous human combustion. If humans can't spontaneously combust, then what is the explanation for the stories and pictures of people who have seemingly burned from within?
What Science Says
If spontaneous human combustion isn't real, then what really occurred in the many pictures that exist of the charred bodies? A possible explanation is the wick effect, which proposes that the body, when lit by a cigarette, smoldering ember or other heat source, acts much like an inside-out candle.
A candle is composed of a wick on the inside surrounded by a wax made of flammable fatty acids. The wax ignites the wick and keeps it burning. In the human body, the body fat acts as the flammable substance, and the victim's clothing or hair acts as the wick. As the fat melts from the heat, it soaks into the clothing and acts as a wax-like substance to keep the wick burning slowly. Scientists say this is why victims' bodies are destroyed yet their surroundings are barely burned.
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And what about the images of a burned body with feet or hands left intact? The answer to that question may have something to do with the temperature gradient -- the idea that the top of a seated person is hotter than the bottom. This is basically the same phenomenon that occurs when you hold a match with the flame at the bottom. The flame will often go out without provocation because the bottom of the match is cooler than the top.
Finally, how does science account for the greasy stains left on walls and ceilings after a "spontaneous combustion"? They could simply be the residue that was produced when the victims' fatty tissue burned.
No one has ever conclusively proven or disproven the truth of spontaneous human combustion, but most scientists say that there are more likely explanations for the charred remains. Many of the so-called victims of spontaneous human combustion were smokers who were later discovered to have died by falling asleep with a lit cigarette, cigar or pipe. A number of them were believed to have been under the influence of alcohol or to have suffered from a movement-restricting disease that prevented them from moving quickly enough to escape the fire. Another possibility is that some of the fires and strange states of the victims' bodies were the result of a criminal act and subsequent cover-up.