Why Liquid Explosives May Be Terror's Secret Weapon

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Much of the speculation during the last five years over how al-Qaeda might construct a sequel to 9/11 has centered on unconventional weapons: Could Bin Laden's men acquire a nuclear weapon, or even more easily, build a radioactive "dirty bomb"? Or might they seek to use poison gases or anthrax to kill thousands of Americans? But the plot revealed by British security services on Thursday suggests that al-Qaeda — prime suspects, according to Homeland Security Secretary Michael Chertoff — still sees plenty of mileage to be gained from using conventional explosives, which are far more accessible, and can be just as effective in spreading carnage and terror.

Explosives remain a primary concern of those guarding U.S. flights. The several thousand U.S. Federal Air Marshals who fly on scores of domestic and international flights each day routinely search the aircraft's lavatories for bomb-making components — although the marshals tend to sit in only one section of the aircraft. Although these security agents are armed, and there are also now more armed pilots authorized to use deadly force to stop an attack than there are marshals in American skies, their weapons may be of no use against explosives.

And the latest plot seems to have validated the assumption that terrorists would be more likely to try and confound airport security measures by smuggling a bomb on board in pieces and assembling it in mid-flight. The particularly devious innovation of the London plotters was their alleged use of liquid explosives or explosive components, which are easily concealed in many of the items found in most travelers' hand luggage — perfume, hair gel, deodorant, medicines, drinks, toothpaste, lotions, and so on — and are extremely difficult to detect. Metal detectors will obviously miss them. While there have been some "puffer" explosive-detection machines placed in some U.S. airports, they are few and far between — and aren't made to detect liquid explosives in sealed containers.

Liquid explosives also attack airline security's weakest point — the Transportation Security Administration screeners. They are the burger-flippers of the entire security system, and the chances of even the best of them visually identifying a liquid explosive in an innocuous bottle are slim — that's why Israel's Ben Gurion airport has a laboratory in the basement to conduct instant tests of liquids found on suspect passengers. If the U.S. system lacks sufficient technology to detect liquid explosives, and if it relies on the TSA screeners to ID possible terrorists, it is, at best, a wire mesh fence.

AP reports that a number of analysts are warning that the new types of threat may dictate a radical change in the security regime governing air travel, in which passengers may be required to subject themselves to substantially longer delays for pre-flight scrutiny. The potential to hide explosive components in everything from toothpaste and contact-lens solution to laptop computers and other personal electronic devices may also demand rules that make air travel even less comfortable than it currently is.

A passenger at Washington's National Airport Thursday morning described passengers crowding around the trashcans dumping anything that could be considered liquid, even toothpaste. But he passed unchecked through security with toothpaste and lotion in his hand luggage, showing the difficulties of enforcing tighter measures in a country with 700 million passengers a year.

The answer, say security experts, highlights the need for a security system based on sophisticated profiling: It may be more important for the security system to be geared towards detecting passengers with intent to do harm rather than relying on detecting the specific means they've chosen. Boston's Logan Airport is currently testing a version of profiling called the SPOT program, but it avoids the ethnic profiling that many security experts say, despite its objectionable political connotations, would have to be the focus of an effective system.