Explanation overdue for combustion of humans

How can a person burst into flames and burn almost completely while leaving the surroundings largely unscathed?

ON September 22nd this year, the west Galway coroner, Dr Ciaran McLoughlin, returned the very unusual verdict of spontaneous human combustion (SHC) after investigating the death of Michael Faherty (76), who died in a fire at his house in Ballybane, Co Galway last year. SHC is a mysterious phenomenon that has been reported many times over the past 300 years but whose explanation continues to elude science.

A Danish anatomist, Thomas Bartholin, made the first recorded report of SHC in 1663, describing how a Parisian woman "went up in smoke and ashes" while sleeping, while the straw mattress on which she lay remained unaffected. Since then, many thousands of cases have been reported. The phenomenon is well enough known to have frequently featured in literature; Charles Dickens killed off an alcoholic shopkeeper called Krook by SHC in Bleak House, and it featured in three of Nikoloi Gogol's works.

In a typical case, the victim is almost entirely consumed, usually in his/her home, but often the extremities (hands, feet) remain intact. The room in which the victim dies usually shows few, if any, signs of a fire. In Michael Faherty’s case, his body was badly burned, but otherwise in the room, only the floor below and the ceiling above the remains showed any signs of charring.

Usually in cases of SHC there is little or no evidence of any heat source that caused the body to burn. Technical experts testified that, in Mr Faherty’s case, the fire had not spread from the fireplace and that no trace of an accelerant (such as petrol) was found.

So, the mystery is – how could a human burst into flames and then burn almost completely while leaving the surroundings largely unaffected? Most scientists are sceptical about the phenomenon, in particular the “spontaneous” nature of SHC. As might be expected, hypotheses abound to explain the phenomenon.Some of the explanationsthat have been proposed include high blood alcohol, methane in the gut, static electricity, a new and undis- covered subatomic particle called pyroton, and more. None of these explanations are convinc- ing to my mind. For example, some methane, a flammable gas, is produced by bacterial action in the human gut – much more is produced in the complex guts of ruminants. In the case of SHC it is hypothesised that the methane is ignited in the gut by enzyme action or by a spark from a build up of static electricity.

Of course, instances of non-human spontaneous combustion are well known to occur. For example, piles of damp straw or hay that are left around to decompose can spontaneously combust. The bacterial induced decomposition process can generate enough heat to cause gases that are produced in the fermentation of the hay to burst into flames.

Human bodies burn up almost completely in SHC cases. How does this burning proceed? A hypothesis that seems to me to have merit – the wick effect – is used to explain this. In the absence of a convincing demonstration of how a body can spontaneously go on fire, we must assume that the fire is started by an external source of heat, such as a glowing cigarette or ember. The burning then proceeds through the wick effect with the body burning like an “inside-out” candle.

A candle is a long wick embedded in solid fat. When you light the wick, the heat of the burning wick melts some of the the fat, which soaks into the wick and starts to burn itself. As further fat melts and soaks into the wick and burns, the candle slowly burns itself completely, from the top downwards.

Now, think of the body as a candle with an external wick. The fat is located just beneath the skin, where it is stored as sub-cutaneous fat. The wick is the person’s clothing. The external initiating source of heat (perhaps a glowing cigarette or cinder) splits the skin and melts some fat that seeps out and soaks into the clothing and starts to burn. The burning then proceeds just as in a candle. Melted fat continues to soak into the clothing and to burn until the body is completely consumed. This wick effect has been demonstrated using limbs from freshly slaughtered pig carcasses.

A generally accepted scientific explanation of SHC is long overdue. Only this will allow us to identify those who are at risk and to prescribe preventive measures.

William Reville is a professor of biochemistry and public awareness of science officer at UCC. See understandingscience.ucc.ie