To catch a bomber: U.S. airports still lack technologies to detect liquid explosives.

• Author: Jean, Grace
• Position: HOMELAND SECURITY

DESPITE KNOWN TERRORIST THREATS, it could be years before airports in the United States are equipped with scanners to detect liquid explosives hidden on passengers and inside carry-on luggage.

A heated debate about the need to deploy liquid-explosive detectors began six months ago, when U.K. authorities thwarted a terrorist plot to blow up multiple airliners flying from London to the United States.

Supporters of installing new detectors point out that these technologies have been available in the commercial market for years. But airports have been reluctant to install them for several reasons, including questionable reliability of the equipment, high costs and logistical burdens. Critics argue that most liquid-explosive detectors are cumbersome, hard to operate, have high rates of false alarms and still require security agents to individually screen items.

"There's nothing yet that is inexpensive enough, combined with having a fast enough processing rate, to reliably identify liquid explosives on a mass basis that would be needed for passenger checkpoints," says Robert Poole, director of transportation studies at Reason Public Policy Institute, a nonprofit organization headquartered in Los Angeles.

Following the August 2006 terrorist plot announcement, the Transportation Security Administration immediately banned passengers from carrying liquids aboard flights. Later, it imposed measures to limit the amount of liquids taken onto planes using a decidedly simple technology: Ziploc bags. Passengers can carry liquids or gels in three-ounce bottles that fit inside a single quart-size plastic bag. This "3-1-1" policy, which also has been adopted by Canada, Australia and the European Union, will remain in effect for the foreseeable future, says Amy Kudwa, a TSA spokesperson.

But some officials say regulations alone are not enough to prevent would-be terrorists from smuggling explosives and other weapons aboard aircraft.

"Everything we do at the checkpoint now is just basically for show," says Douglas R. Laird, president of Laird and Associates Inc., an aviation security consulting firm.

The technologies currently deployed are not designed to find sophisticated weapons, such as liquid explosives, he points out. When hand-carried items are run through the x-ray machines, the chances of screeners finding the components for an improvised explosive device, "are remote at best," alleges Laird.

Metal detectors and even the puffer booths that pick up explosive particles or residue on passengers also are weak defenses against savvy terrorists wielding non-traditional weapons.

"Anybody with any sophistication whatsoever can carry a liquid through a screening checkpoint. You just don't carry it through in a Coke bottle. You carry it in a couple of little baggies taped to your leg," says Laird.

The TSA must give screeners better tools, he says. A step in the right direction would require TSA to look no further than the machines airports already use to screen checked luggage--the explosive detection systems which rely on computed tomography, or CT, technology to look inside bags, he says.

But with an approximate $1.2-million price tag per machine and overcrowded airport...