MICHELE NORRIS, host:
Officials haven't said precisely what type of bombs were to be used in the alleged terrorist plot, but Homeland Security Chief Michael Chertoff did offer a general description today.
Mr. MICHAEL CHERTOFF (Department of Homeland Security): The terrorists planned to carry the components of the bombs, including liquid explosive ingredients and detonating devices, disguised as beverages, electronic devices or other common objects.
NORRIS: Experts say that's not surprising. Terrorists have used liquid explosives before.
NPR's Jon Hamilton reports.
JON HAMILTON reporting:
The U.S. government has focused on the threat of liquid explosives since at least 1995. That's when they learned about a plot in the Philippines to plant bombs on 11 airliners bound for the U.S. The plotters apparently wanted to use liquid nitroglycerin. They planned to smuggle it aboard in bottles made for contact-lens solution.
But the plan came apart when there was a fire in the apartment where the bombs were being made. Greg Bower(ph), of the International Association of Bomb Technicians and Investigators, says nitroglycerin is usually too unstable to handle safely.
Mr. GREG BOWER (International Association of Bomb Technicians and Investigators): For nitroglycerin to be transportable, it has to be kept very cold, not freezing, but very col.
HAMILTON: Bower says it appears that the terrorists have now moved on to a different type of liquid explosive. It's called a binary explosive, which means it comes as two separate components. Neither will blow up by itself, but when the two are combined, the end product is easy to detonate.
Bower says bomb squads often keep these explosives on-hand to destroy suspicious packages, and he says terrorists might well have chosen to use a binary explosive for the sort of plot described today.
Mr. BOWER: The binary explosive, if this is what in fact they were using, would be relatively easy to separate out, bring in two separate people, bring in two separate components, and mix it in the cabin of the plane. Yeah, I can see that happening.
HAMILTON: Experts say the components of binary explosives can be difficult to detect in a passenger's baggage. Chris Ronay used to run the FBI Explosives Unit. Now he's the president of the Institute of Makers of Explosives. Ronay says that until now, airport screeners haven't had much experience looking for liquids that might create a bomb.
Mr. CHRIS RONAY (President, Institute of Makers of Explosives): It might be less detectable because people aren't used to looking for liquids, plus the fact that some of these materials are common.
HAMILTON: Nitrates, for example, are used in shampoos and suntan lotions, as well as in bombs. Bomb experts say that security checks are probably more likely to find the device that detonates a liquid bomb than the liquid explosive itself.
But detonators are also tricky to spot. They can look like any other battery-powered electronic device. Ronay says the problem for airports these days is that you can no longer just look for obvious things like timers and sticks of dynamite.
Mr. RONAY: There are just a myriad of possibilities of what you can make a bomb out of. There's no limit except the imagination of the guy who's doing it.
HAMILTON: And this most recent incident suggests terrorists are trying new approaches.
Jon Hamilton, NPR News.
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