Cargo plane bomb plot: what is PETN?

Why the powerful plastic explosive pentaerythritol tetranitrate has become the weapon of choice for terrorists
Richard Reid
Richard Reid used PETN for his shoe bomb, which failed to go off because the fuse became damp. Photograph: AP

The bombs found in cargo planes destined for America contained the compound PETN, which is becoming the explosive of choice for terrorists.

What is PETN?

Pentaerythritol tetranitrate is an extremely powerful plastic explosive. The white powder is popular with extremists because it is available on the black market and very difficult to detect at airport checkpoints. Many countries have tight restrictions on the purchase of PETN, which can be bought in powder form or in thin plastic sheets, but it can also be made from chemicals available over the counter. PETN is used legally by the military and in industries such as mining, where it is used in detonation fuses. PETN is mixed with other chemicals to make Semtex.

How does it work?

As explosives go, PETN is reasonably stable. The substance is usually detonated by a secondary device that produces heat or a shockwave. PETN is difficult to detonate with a naked flame, as demonstrated by the shoe bomber Richard Reid, who tried to bring down an American Airlines flight in 2001 with PETN concealed in one of his boots. More often, a blasting cap is used to set it off.

Why is it hard to detect?



What went wrong with PETN previous attacks?

Richard Reid's bomb failed to go off because the fuse got damp while he waited to board the plane. Unable to light it, he attempted to set fire to the explosive itself. Abdulmutallab's chemical detonator was designed to generate enough heat to explode the PETN he was carrying. Officials have not released details of why the bomb failed to go off. Carlos the Jackal used PETN in 1983 to attack the Maison de France, the French cultural centre in Berlin.

How can PETN be detected?

Some airports have introduced advanced security measures that "sniff" passengers for explosives or analyse swabs of their clothing and belongings, all of which can carry minute residues of explosives if the person has handled them. There is no guarantee that these would catch a PETN bomb, especially if it were carried in a sealed container.

Pure PETN releases little in the way of chemicals that can be picked up by detectors, so commercial manufacturers spike it with "taggants" to make them easier to sniff out. Homemade PETN can be harder to pick up because it does not contain these chemicals. Researchers at the Centre of Excellence in Explosives Detection, Mitigation, Response and Characterisation at the University of Rhode Island have detected traces of PETN in human hair, but the technique is not used at airports.

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