News reports of a recent death by fire in Tulsa, OK read, “Sheriff: Oklahoma Man Died of Spontaneous Human Combustion,” and “Sheriff Rules Out Homicide, But Not Spontaneous Combustion After Autopsy.”

It’s actually not difficult to rule out spontaneous human combustion (SHC) – you can rule it out because SHC does not exist. The notion of SHC is that some process occurs in the body that causes it to heat to the point of spontaneous ignition, without an external ignition source. There simply is no known process by which this could occur.

This is not a trivial objection. While it is, of course, impossible to completely rule out the unknown, the laws of physics can make something so improbable that we can comfortably treat it as if it were impossible. At the very least the burden of proof should be extremely high – not so high that if the phenomenon were genuine we could not demonstrate it, but high enough to rule out other, even unlikely, causes.

The lack of a possible mechanism has inspired some SHC proponents to hypothesize new elementary particles as an explanation. Larry Arnold, in his book, Ablaze, posits the existence of the pyroton to explain the energy source that leads to SHC. He is not a theoretical physicist and is therefore probably not aware that you can’t just make up new particles and insert them into the standard model just to explain your alleged phenomenon. This is a rather extreme example of special pleading.

It is also curious that there are no pre or partial SHC phenomena. No one has heated up to near combustion. We also don’t see alleged cases of SHC in animals – why isn’t there spontaneous pig combustion?

Plausibility aside – what does the empirical evidence say? Are there any compelling cases of SHC, as Sheriff Lockhart seems to believe, saying:

“I think there’s only about 200 cases worldwide, and I’m not saying this happened. I’m just saying that we haven’t ruled it out.”

The hallmark of the SHC claim is that ignition occurs without an external source. It is curious, then, that one fairly consistent feature of alleged SHC cases is the presence of an external ignition source. The typical profile of a victim is an elderly or infirmed individual, or someone taking sedating medication or a heavy alcohol drinker, who lives alone and is also a smoker. Being overweight also is a common feature.

These factors lead to a very compelling scenario that seems more likely than a pyroton. Victims accidentally set themselves on fire with their cigarette or pipe, they cannot get up easily to rectify the situation, or they are unconscious from sedating medications or alcohol. They may become unconscious from smoke inhalation, and quickly die where they sit or fall.

What happens next seems curious, but has been experimentally reproduced and is not a mystery to experienced fire experts. The clothes and body fat of the victim form an inside-out candle via the wick effect. The heat of the fire liquifies the body fat, which fuels the fire. If the victim is in a closed room (also a common feature) the fire will quickly drop the oxygen content of the room so that the fire cannot spread easily or erupt into flames. The body then burns slowly without much flame until all the fuel is consumed.

The result leaves the body almost completely incinerated, usually with just the feet or arms left behind, like the ends of a log that has burned down. The surrounding room, however, is largely unscathed. Nearby objects will show heat and even smoke damage, but the room itself never caught fire.

It is understandable why, at first blush, such a scene may seem curious – the body is completely incinerated but the room has little fire damage. This is not mysterious to experts, however. Forensic biologist Mark Benecke thoroughly reviewed available cases of alleged SHC and concluded that “[t]he pictures and reports published on SHC up to now can be explained by well-known and understood mechanisms that are regularly found at the sites of burning.” In other words, there are no cases that constitute convincing evidence of SHC.

It is also understandable why there are relatively few cases that resemble what I have described above – you need the perfect storm of factors to create such a scenario. Proponents are simply engaging in anomaly hunting – looking at rare or unusual cases and then making what is essentially an argument from ignorance. In this case, however, their ignorance has already been filled in by experts.

The new case involves a 65 year old man, Danny Vanzandt, who was found in his kitchen mostly incinerated. Vanzandt was known to be a heavy drinker and a heavy smoker, and he lived alone. The autopsy found smoke and heat damage inside his trachea, which are signs that he was alive when the fire started and he breathed in the smoke, which is probably what killed him.

The Vanzandt case is likely to become another classic alleged case of SHC to fill the books and websites of proponents. At least it is a typical case – an alcoholic with an external source of ignition, and absolutely no need to postulate any combustion of the spontaneous variety.