Al-Qaeda ‘clothing bomb’? Is it serious?

According to ABC report clothes may be dipped into the liquid explosives, and become explosive themselves once the liquid dries,  So my simple question is: From your scientific point of you how real is this threat, may it work like the description says or not? Read few comments.

R. E. Benfield, Senior Lecturer in Inorganic Chemistry, School Chief Examiner, School of Physical Sciences, University of Kent

I saw various versions of this story in the British press last week, for example The Daily Telegraph and The Daily Mail.

I would agree with the opinion of Sidney Alford, quoted in the Daily Mail article: “British bomb expert Sidney Alford confirmed that the new method was possible using easily available chemicals, but pulling it off would  be tricky as the soaking process would dilute the explosive.  He  said: ‘The clothes act as a diluent and reduce the power of the explosives.'”

To explain:  the features that make an explosion so damaging are the production of large amounts of hot gas at high pressure, in an extremely rapid process.  The rapidity of the process relies on a chemical reaction propagating through the explosive substance at great speed (faster than the speed of sound), and that depends on the physical form of the explosive (high density, high degree of crystallinity etc).  If the explosive is soaked into clothing then the explosive is diluted and the reaction will not be able to propagate so quickly.  There is no doubt that clothing treated in this way and ignited with a match would burn extremely fiercely, giving some of the effects of an explosion, but this would be much less powerful than if pure explosive material was used.  The method would need extensive testing to see if it is really feasible.

I also have doubts about the claim in the Daily Telegraph article that the explosive PETN “foils sniffer dogs by having no odour”.  It is a nitro-based explosive, like many other explosives, and dogs trained to be sensitive to this type of chemical will be able to detect it, although PETN does give off less vapour than some other explosives.  See for example
http://www.defenceweb.co.za/index.php?option=com_content&view=article&id=10416:dogs-can-smell-petn-mechem&catid=3:Civil%20Security&Itemid=113

John  Goodpaster, Associate Professor, Department of Chemistry and Chemical Biology, Director, Forensic and Investigative Sciences Program, Indiana University Purdue University Indianapolis

I read the report and it is fairly vague – I am having to use my imagination a bit here.  I can think of some possible scenarios where a garment could be exposed to a solution containing a dissolved explosive, the solvent is allowed to evaporate and the explosive residue that remains could retain its explosive properties.  The explosives that I think could do this would include primary high explosives, which are shock-sensitive and if the garment was impacted, they could generate an explosion.  Examples of these types of explosives are nitrogen triiodide (which is so unstable as to be impractical for this purpose), triacetone triperoxide (TATP) and hexamethylene triperoxide diamine (HMTD).  Shock is a rather clunky way to initiate (you would have to strike the item with a hammer or something similar).  I presume you could also wire up an igniter or detonator, but those can be found in x-rays.  Of course, whatever the explosive is, it will generate volatile compounds that could be detected by a properly trained explosive-detecting canine, for example.

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