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Wednesday, May 25, 2011

How To Set Someone On Fire


I've just come across a deeply disturbing paper: Attempted ignition of petrol vapour by lit cigarettes and lit cannabis resin joints

The authors set out to discover whether you could set petrol on fire by dropping a lit cigarette or hash joint onto it. It turns out, surprisingly, that you can't.
Thirty nine (39) ignition attempts that involved exposing lit commercial cigarettes, hand-rolled cigarettes and cannabis resin joints to petrol vapour were undertaken; ignition was not achieved in any of the scenarios. In addition, a single attempt to ignite petrol vapour emanating from a pool of liquid fuel was effected with a smouldering piece of cannabis resin; no ignition occurred. In all cases the petrol was clearly present within the limits of flammability since ignition was subsequently effected using a naked flame.
It's just not hot enough. Apparantly, for the "hot surface" ignition of petrol vapor to occur, you need a surface with a peak temperature of about 1000 degrees C. Puffing on a cigarette can raise the temperature at the tip to maybe 950 degrees, and while you're not puffing, it's more like 700. A cigarette lighter, however, will do it.

Well, you learn something new every day. Although I'm still not going to be lighting up in the garage any time soon. Don't try this at home.

Anyway, what makes this paper so sinister is the context. This research was done as part of a murder enquiry:
...the consideration of hot surface ignition of petrol vapour was of legitimate interest since the defence proposed the ignition of petrol vapour by “bombers” (small pieces of hot cannabis resin) falling from a lit cannabis resin joint when the smoker puffed on the joint.
The details of the murder aren't specified but reading between the lines, I guess someone burned someone else to death by covering them in petrol and lighting them, and their defence was that it was an accident caused by their joint.

It gets worse. There are pictures.

"The second set of experiments was designed to recreate circumstances specific to the murder case under investigation."

What was the murder case in question? I think I've found it, and if so, the good news is that the guy was found guilty. Stewart Blackburn, 18, was convicted of the murder of his girlfriend Jessica McCagh, in her bedroom, using petrol. The dates fit, as does the fact that the murder took place in Scotland. The paper comes from an English forensic company, but it acknowledges the help of various Scottish legal and police experts.

ResearchBlogging.orgJewell RS, Thomas JD, & Dodds RA (2011). Attempted ignition of petrol vapour by lit cigarettes and lit cannabis resin joints. Science & justice : journal of the Forensic Science Society, 51 (2), 72-6 PMID: 21605828

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