By Aimée Turner in London

Plot suggests explosive properties are well understood

According to US Department of Homeland Security (DHS) chief Michael Chertoff, the plot to down airliners foiled by UK authorities involved carrying liquid explosives and detonation devices on board transatlantic flights from the UK.

"Terrorist cells based in the UK" were behind the plot, say authorities, and late last week 24 suspects had been arrested.

The plot to use liquid explosives suggests that terrorists understood precisely the ease of taking on board small amounts of explosive in seemingly innocuous containers. The plan bears disturbing similarities to a plot in 1995 by Ramzi Ahmed Yousef, convicted of planning to blow up the World Trade Center, to down 12 aircraft over the Pacific with liquid explosive. That was only foiled when his plans were discovered in his terrorist base in Manila, the Philippines, following a house fire.

The move by US and UK authorities last week to ban liquids, including drinks, hair gels and lotions, from carry-on baggage and to step up the use of explosives detection technologies, indicates that what explosives experts have long regarded as a relatively easy procedure has now entered the mainstream terrorist repertoire.

Dr Sidney Alford, chairman of explosives company Alford Technologies, dismisses the idea that it is only highly skilled chemists surfing the internet for arcane knowledge contained in sophisticated terrorist cookbooks who can construct highly effective liquid bombs.

"A teenage boy could do it," he says, and advises authorities not to dwell too long on so-called new types of explosive. "Nitroglycerine, nitro methane, methyl nitrate all remain devastating explosive weapons and are either easily available or require simply a basic knowledge of organic chemistry to make," he says. "You only require minimal quantities to create a destructive effect."

While all these liquid explosives are easy to make, some require electrical detonation, others require mixing to sensitise. And then there is a completely different set of chemicals that requires just the addition of what Alford calls "substance X" to form a powerful explosive.

An example is triacetone triperoxide (TATP), the explosive used by the bombers who attacked London in July last year. Explosives expert Hans Michels, a professor of safety engineering at Imperial College London, says that TATP "is not a liquid explosive itself it is made from three liquids, but the product is solid. It is unstable when still wet and might possibly already be detonatable in that state."

Source: Flight International