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Terrors deadly, elusive liquid alternative

BY LOU DOLINAR | Special to Newsday

August 11, 2006

Liquid explosives, while not undetectable in all circumstances, are far easier to conceal than their solid counterparts.

Terrorists have a broad smorgasbord from which to choose, ranging from home-brew that can be mixed in flight, to unstable but widely available nitroglycerin, to exotic blends -- the use of which could suggest involvement of a nation-state.

"We've focused for the last 10 years on solid explosives and their signatures," said William Martel, a professor of international security studies at Tufts University. "Liquid poses a different problem. Liquids are ubiquitous -- shaving cream, shampoo, bottles of water, juice, infant formula."

According to Martel, the most common detection test -- in which a cloth or tape is swiped over luggage and put through a sensor -- is specifically designed to pick up residue from solid explosives.

"We didn't start looking aggressively for liquids until a few years ago," Martel said. Some, but not all, can be picked up by "sniffer" sensors using a technique called neutron activation analysis.

Most experts say the main candidate is nitroglycerin. As far back as the 1930s, bank robbers learned to distill it from dynamite or make it directly, so the technology is well known and within reach of the average terrorist. It requires a detonator, making it somewhat complex and more readily detectable as an in-flight bomb. The other potential problem: if poorly formulated, it can explode without warning.

Nitroglycerin was the explosive of choice for Ramzi Yousef in Project Bojinka, a terror plot foiled in 1995 in which 11 U.S.-bound flights were to be bombed.

Vincent Cannistraro, former executive director of the CIA's counterterrorism center, said he believes the latest plot involved a Yousef formula.

"It's nitroglycerin (plus other things), no question about it," Cannistraro said. "We know it can't be detected by any security machines in use right now, and so it scared the hell out of everyone."

Since the Bojinka plot, terrorists have focused on hand-placing tiny bombs in critical structural parts of airplane cabins, rather than simply checking bomb-laden luggage into cargo compartments, according to John Pike, head of Globalsecurity.org, a Washington-based think tank. That's because a bomb big enough to bring down a plane would be picked up rather easily by routine baggage X-rays.

The newest form of liquid explosives are so-called "binary" formulas like FIXOR, recently developed as part of the humanitarian campaign to clear land mines in Third World countries. They're stable and undetectable until mixed, and also require a detonator.

A home-brew candidate is triacetone triperoxide, also composed of two liquids, used by Britain's July 7, 2005 subway bombers. It can be fabricated from readily available chemicals. ANFO (ammonium nitrate and fuel oil, used in the 1995 bombing of the Murrah Federal Building in Oklahoma) could also be mixed in flight, but like nitroglycerin, it can be picked up by some detection systems.

There are even liquid explosive blends that don't need a detonator, though their exact composition isn't widely publicized.