Science

How Spontaneous Human Combustion Works

Terrifying, isn’t it? To imagine that you could be sitting in your favourite easy chair, happily reading UNIX in a Nutshell, and then your body just COMBUSTS — spontaneously — and you’re a pile of ashes. A coroner in Ireland recently ruled that’s exactly what happened to Michael Faherty, 76, who burned to death last December while minding his own business and collecting his pension.

Except for the floor below and the ceiling above the body, the apartment and furnishings surrounding Faherty’s body were left intact. The coroner couldn’t find any other explanation besides spontaneous human combustion. If something external had caused the fire, wouldn’t the rest of the house have gone up in flames as well?

It’s frightening at first blush. But don’t get too upset. Spontaneous human combustion is probably not real. Yes, approximately 200 reports of such have occurred in the past 300 years. But in 1998, scientists in UK came up with a more plausible explanation: the “wick effect“.

Come to think of it, the idea that your body could emulate a candle wick is not really comforting, either. It still reduces your humanness to pile of charcoal in short order. And just to make it a little more gruesome, your arms and legs might be left intact. But at least there is some logic behind the wick effect.

On the BBC Television program Q.E.D. (quod erat demonstrandum, which means “that which was to be demonstrated”), Dr John DeHaan demonstrated the wick effect with a dead pig. They wrapped the poor thing in a blanket, then used a small drop of gasoline and a spark. It took a while for the flame to catch, but eventually it did, and flames began burning intensely hot but with low flames. The pig burned completely — even its bones were incinerated. But the surroundings were mostly spared — only a nearby television, the floor below and the ceiling above the pig were affected by the fire. It’s exactly what the result of most reported cases of spontaneous human combustion looks like.

The theory behind the wick effect is that the spark (for a human, it might be a burning cigarette or a spark from a fireplace) burns through clothing, then splits the skin enough to access subcutaneous fat. Most victims are alone and presumed to have fallen asleep so they don’t immediately notice the spark. The fat is then absorbed into the clothing and behaves like a candle wick, fuelling the flames until no fat is left.

You might think that a pig has a lot more fat than a human. We actually have a similar fat content to our porcine friends. So it makes sense that limbs would sometimes remain intact, since they contain less fat.

As for the recent case in Ireland, perhaps the coroner hand’t heard of the wick effect. But to this layperson’s eye, Mr Faherty seems like a prime candidate. He was found next to an open fireplace, which gives a potential source for a spark.

One other interesting note: Faherty was diabetic. According to this “Material Safety Data Sheet” from ScienceLab, a firm that supplies chemical and laboratory equipment, insulin may be combustible at high temperature. Just sayin’.


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