Liquid Explosives among Terrorist Tools Israel Has Guarded against for Years

Airports have the technology to detect liquid explosives, but it's a time-consuming process and must be coupled with passenger profiling to narrow the pool of suspects, Israeli aviation security experts said.

Security engineers are racing to devise new defenses against the ingenuity of dedicated bombers. But even if the latest threat to passenger aircraft is eventually neutralized, terrorists have many more ways to blow up an airplane, the experts warned.

In the plot foiled by British authorities this week, the planners sought to use common electronic devices to detonate liquid explosives to bring down U.S.-bound planes.

"There are all kinds of ways to smuggle in explosives," said Yoram Schweitzer, terrorism expert at the Jaffee Center for Strategic Studies in Tel Aviv. "In this case, the only reason they were caught was because of good intelligence."

In the aviation world, the Israeli national airline El Al has been the No. 1 target for terrorists ever since one of its airliners was hijacked in 1968 to Algeria. Since then, Israel's planes, airline personnel and its traveling citizens have been attacked by gunmen, bombers and more hijackers.

Former El Al security chief Tuvia Livneh said would-be bombers have been caught with liquid explosives in the past. "This is not new at all," said Livneh, now head of a private security company, Sital International.

He said countermeasures have been developed, but are rarely used because they are complicated and take too much time, requiring checks of tens of thousands of passengers processed through a major airport every day.

Ehud Keinon, an explosives expert at the Technion Research Institute in Haifa, said the peroxide-based liquid chemical compound uncovered by British authorities was probably triacetone triperoxide, or TATP.

"The raw materials to make this compound are available anywhere, in hardware stores, agricultural stores, pharmacies, supermarkets," he said. "And they're really cheap. I have calculated that to bring down an airplane it will cost you, at retail prices, $35."

Keinon has developed a single-use disposable peroxide detector, which is unsuitable for use on a massive scale, at a cost of $20 a unit. Still, he said, airline security companies have shown an interest in his tester, and he plans to develop it for large-scale use in coming months. "There's a long line of customers," he said.

El Al refuses to discuss specific equipment employed to sniff out potentially dangerous chemicals, which can be part of an explosive chain of innocent looking material. Even duty-free liquor is highly combustible and can be used to fuel an explosion.

One device on the market, developed by the U.S. company Guardian Technologies of Herndon, Va., uses image-analysis software attached to existing X-ray screeners and circles items matching the density of known explosives.

"If we detect any explosive items, it will put a big red box over the image so the screener can take a better look and do more screening," said Steven Lancaster, the company's vice president. The software costs $50,000 to $100,000 per unit, he said.

"Explosives look the same as any other organic items. You can mold it into any shape, so you can't do shape recognition," he said in a telephone interview. "We basically bombard the image with algorithms that allow us to begin to separate the items and look at unique areas of interest. It takes only a few seconds and we are able to establish unique signatures," he said.

But Israeli security experts still put their faith in the human factor.

"In the end, for the attackers and the defenders, the main issue is not the equipment. It's what quality of humans they have," said Leo Gleser, of the security consultancy firm ISDS. A highly trained security agent who can spot a suspicious passenger is the best defense against a would-be bomber ready to kill himself.

"In Israel, we use profiling. That means you learn your enemy, learn the way he is going to attack you, and once you know that, you build up your system," said Gleser, a former sky marshal and El Al security officer.

Profiling goes beyond racial appearances. "Your behavior is different when you know this is your last day," he said.

Livneh says the greatest threat to civil aviation is not from on-board bombs but from sophisticated anti-aircraft weapons, some of which are easily obtainable on the international arms market. Terrorists with missile launchers don't have to pass through airport security, he said.

Three years ago, an Israeli civilian flight had a narrow escape when two missiles missed it as it took off from Mombassa, Kenya.

The latest anti-missile deflection device was put on the civilian market last December, based on a missile warning system and diversion flares. Called Flight Guard, it is in wide use with the Israeli military and has been bought by several countries for use by their heads of state, Livneh said.


Associated Press Reporter Benjamin Harvey in Jerusalem contributed to this report

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