Claims must be treated with caution, warn chemists.

Widespread speculation on the chemistry of liquid explosives, following news of a terrorist plot to blow up transatlantic flights from the UK, must be treated with caution, warn leading chemists. 

Wildly differing media reports suggest that nitroglycerine, a liquid explosive, could be easily smuggled onto a plane, while others prefer the idea that terrorists were planning to make the solid explosive triacetone triperoxide, (TATP) from liquid ingredients, in aircraft toilets. TATP was used in the London Underground bombing campaign of 7 July last year.

The frenzy followed an announcement from the Metropolitan Police Service, London, UK, on 10 August, that it had successfully disrupted ’a major terrorist plot to allegedly blow up an aircraft in mid-flight’. The Department for Transport followed suit with an alert detailing hand baggage restrictions for air passengers - all cabin baggage was to be treated as hold baggage; only the barest essentials were allowed into the cabin, not even drinking water. ’Any liquids discovered must be removed from the passenger,’ it instructed. 

’The measures that are in place are appropriate,’ said Sean Doyle, head of chemistry and research at the forensic explosives laboratory of the Defence Science and Technology Laboratory (DSTL), Fort Halstead, UK. Doyle’s team analysed samples taken from the explosive device that failed to detonate in London last year. ’There is a real threat’, he told Chemistry World, adding that his team was ’very much at the heart of the investigation.’ Doyle would not comment on whether he was currently analysing samples from the latest terrorist plot, and indeed security officials have not confirmed whether any explosive materials have been recovered.

However, the identity of the alleged explosive liquid is far from clear. ’It’s very ambiguous to use the word "liquid" explosive,’ said Gerry Murray, of the Forensic Science Agency of Northern Ireland. ’There are liquid explosives, there are materials that are liquid that you could mix to make explosives, and there are liquids that you can combine to produce something like TATP.’

Mixing two liquids into an explosive combination is possible - a company in the US markets a two-liquid system for blasting rock, based on hydrazine and concentrated nitric acid. This is not available in the UK, but this would not deter would-be terrorists, said Murray. ’If someone was aware that this type of explosive could be made by mixing two liquids, the materials themselves are relatively easy to get,’ he said. But Alfa Aesar, chemicals supplier based in Heysham, Lancashire, UK, pointed out that it would not supply chemicals, including nitric acid, to individuals without good reason, and the company performs stringent checks on anyone not from a university or the chemical industry.

Nitroglycerine, touted as a possible liquid explosive candidate for the foiled attack, would cause terrorists a big practical challenge if they wanted to get enough on board to explode an aeroplane, said John Wyatt, a former bomb disposal officer and security consultant. Wyatt was head of counter-terror search operations in the UK during the era that followed the Brighton hotel bombing in 1984.

’You literally just have to drop [nitroglycerine] and it’ll explode,’ he said. ’The impact of going through an X-ray machine or the impact of a body search is likely to set the stuff off.’

Wyatt said that while various combinations of fuels and oxidisers could be used to produce an explosive, preparing them is an extremely delicate process. One of the best known combinations is nitric acid and nitrobenzene: ’but to suggest that someone’s going to walk on to an aircraft and mix these two together to get an explosive liquid is, to put it bluntly, nonsense.’

Reports of making TATP in the toilets are equally far-fetched. ’It would be extremely difficult to make [TATP] on a plane,’ said Murray, not least because the process must be carried out at low temperature. ’The problem with TATP is that even if you do manage to produce the stuff, you’re producing it in aqueous solution,’ said Murray. ’It’s not just a question of mixing A and B and getting the stuff out at the end.’

Peter Fielden of the University of Manchester, UK, who works on explosives detection with DSTL, agreed that it would be tricky to make TATP on an aeroplane, and said he was concerned about the media attention the explosives were receiving. ’There’s an awful lot of unknowns and a great deal of speculation,’ he said.

Fielden warned that terrorists might get new information from news reports. ’This is an obvious danger. I’ve already seen two so-called experts on the telly, even one giving a demonstration of how to blow a hole in a piece of metal,’ he said. ’Just suppose that what was actually intended by the terrorists was incredibly crude, extremely difficult to handle and produced huge hazards to the terrorist - now they’ve got some other possibilities.’

Bea Perks  and Katharine Sanderson