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

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 lobbies resulting from other security mandates, government and commercial aviation officials have balked at the suggestion, says Laird.

"My response to those comments is, do you want to find the bomb, or don't you?" he says. "It's not that we don't know how to do security in the United States--we're not willing to pay for it. We need to deploy the correct technology so that the screeners can find what they're looking for," he adds.

In September 2005, TSA awarded contracts totaling $7.4 million to Analogic Corporation, in Peabody, Mass., and Reveal Imaging Technology, Inc., in Bedford, Mass., for the development and delivery of small, automated explosive detection systems suitable for screening carry-on bags. The TSA in October 2006 expanded the so-called Project Cambria contract in an effort to expedite the systems. Kudwa says the TSA has been evaluating the two systems in its labs and is anticipating testing to begin at selected airports in the next several months.

Though the CT-based machines will be able to distinguish hidden threat items--including liquids--from benign ones inside carry-on baggage, they will not be able to ascertain what hazards those might pose.

Identifying the composition of potentially dangerous items requires other advanced technologies, such as quadrupole resonance and neutron scanning capabilities. Unlike CT devices, which show only the density of objects, quadrupole resonance machines can differentiate between a bar of chocolate and an explosive without requiring a person to open the bag, says Poole. Such systems bounce radio frequency beams off an object to identify its molecular structure.

"It's promising technology, but it's nowhere near fast enough to use for the volume of the people" going through security checkpoints at an airport, he says.

Before the arrest of the bomb plotters in London, the Department of Homeland Security's transportation security laboratory had begun to evaluate several commercial liquid explosives detection devices, says Christopher Kelly, a DHS spokesman.

About the size of tabletop coffee makers, the machines deploy energy through a bottle of liquid and use a variety of scanning technologies, including microwave, acoustic, ultrasonic and infrared spectroscopy, to detect a threat.

"There were 10 evaluated in the lab that showed a degree of promise, but which needed further testing against real liquid explosives in an environment that could handle those on a testing range," says Kelly. Those systems were tested at the New Mexico Institute of Mining and Technology in Socorro in the fall and the results are being shared with TSA, he tells National Defense.

Promising technologies will go to TSA for pilot program projects in various airports, he says.

DHS in September announced a "homemade explosives detection system development program" in an effort to survey new technologies for screening liquids, gels and pastes for explosives.

One such technology has been developed to detect peroxide-based explosives, which reportedly was the key ingredient the suspects in the foiled U.K. plot had planned to conceal inside toothpaste tubes. Homemade peroxide-based explosives also were used in the London transit-system bombing attacks in July 2005.

Detecting two of the most common peroxide-based explosives--triacetone triperoxide (TATP) and hexamethylene triperoxide diamine (HMTD)--is difficult, but if the explosive is converted to hydrogen peroxide, then it can be readily detected, says Joseph Wang, director of Arizona State University's Center for Biosensors and Bioelectronics at the Biodesign Institute.

That sort of detection can be accomplished in a handheld device, similar to medical glucose meters used by diabetics to monitor blood sugar levels. Glucose-sensing devices convert glucose into hydrogen peroxide using an enzyme. The monitor then detects the amount of hydrogen peroxide present.

Wang followed the same principle in developing his palm-sized "Add-Detect" device for peroxide-based explosives.

"It's the same challenge of detecting a hydrogen peroxide product, whether it's glucose in blood or it's an explosive in liquid or powder," he says.

Current liquid explosives detection technologies convert peroxide explosives into hydrogen peroxide using light or acid. But the problem is that those processes deactivate the peroxidase enzyme that commonly monitors the hydrogen peroxide product, says Wang. The "add-detect" approach uses an artificial enzyme, known as Prussian blue, which is unaffected by the harsh acidic conditions.

To detect whether a liquid--or a solid--is a peroxide-based explosive takes about 15 seconds using the device, says Wang. The estimated price of a single device is $100, with the disposable sensor unit costing about $3 apiece.

Other systems rely on technologies that don't require sampling.

A company in China, Nuctech Co. Ltd., which produces security screening systems for baggage, cargo and shipping containers, has developed a rotating CT scanner that can detect liquid explosives without opening the container.

Any bottle, regardless of its packaging material, can be placed inside the LS8016 liquid security inspection system and within five seconds, it will determine whether the liquid is flammable, explosive or safe, says James Li, CEO of EverIris Medical Systems LLC, a Philadelphia-based company that is marketing the scanner in the United States.

The LS8016 system is about the size of a two-drawer filing cabinet and sits on casters for mobility, says Bill Roedel, director of marketing at EverIris. It uses a dual-scanning process that sends two x-ray beams through the bottle at different intensities and then compares the results against a database of 10,000 materials. The system can determine with a high degree of certainty what the tested bottle may contain, he said.

"We know it works," he says. London's Heathrow International Airport recently conducted successful tests on the system, he adds.

Nuctech officials have announced plans to deploy the technology to all 147 of Chinas commercial airports in time for the 2008 Summer Olympics in Beijing.

Roedel says the price per unit falls in the $100,000 to $200,000 range.

Before any of these technologies can find their way into U.S. airports, they must meet stringent TSA requirements.

"We screen two million people a day. You need to have technology that works in a non-sterile environment, used dozens, if not hundreds of times, per day, and a throughput that does not interrupt commerce. Those are all very key aspects that we need to evaluate when we're looking to deploy technology," says TSA's Kudwa.

The U.K. plot has prompted aviation security officials to reexamine the technologies at airport checkpoints, says Poole.

He and Laird have long called for deploying the controversial x-ray backscatter technologies that would allow security check point screeners to see what might be hidden beneath passengers' clothing. The TSA has been examining such whole-body imaging technologies for several years and addressing privacy concerns. It recently began testing the technology in Phoenix Sky Harbor International Airport, says Kudwa.

But even technologies designed to streamline passenger screening processes can create more problems. A shoe scanner that was supposed to enable passengers to keep their shoes on through security checkpoints in Orlando International Airport detected harmless metal in more than half of those scanned, which required passengers to take off their shoes and undergo a second screening.

Improvements that will enable the technology to differentiate between harmful and harmless metals are underway.

"It's really important in the meantime to develop technologies that will work, and that will work effectively and efficiently to minimize those false-positives and false-alarm rates. That's what we're here to do," says Kelly.

But analysts say the nation cannot afford to wait months or years for better screening technologies.

"We have technology that's fast enough and affordable now, if we only have to deal with 10 percent, as opposed to 100 percent, of the passengers," says Poole.

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RELATED ARTICLE: Focus on checked baggage screening has detracted from aviation security.

IN A RECENT Government Accountability Office report, Congress was lauded for implementing an explosives screening requirement for all checked luggage following the 9/11 terrorists attacks.

But aviation security analysts say the measure has diverted funds, attention and resources from passenger and carry-on baggage screening checkpoints to the detriment of national security.

"We had an inconsistency between checked baggage and carry-on baggage. Either one was a threat of getting a bomb on a plane, and Congress, by mandating 100 percent screening of checked baggage, left this glaring inconsistency with carryons," says Robert Poole, director of transportation studies at Reason Public Policy Institute, a nonprofit organization headquartered in Los Angeles.

That loophole was exposed flagrantly in August, when British authorities disclosed an alleged terrorist plot to bomb at least 10 airplanes as they flew to destinations in the United States.

The nation's airports do not have any liquid explosives detection technology deployed to passenger screening checkpoints.

"We're extremely weak on the liquids side. What has saved us in the past is that people have not wanted to do liquid explosives because they tend to be very volatile," says Douglas R. Laird, president of Laird and Associates, Inc., an aviation security consulting firm.

The mastermind behind the 1994 Philippine Airlines bombing incident was caught when one of the liquid explosives being concocted for another bombing attempt caught fire in a Manila apartment. But liquid explosives have come to the forefront as weapons of choice for potential terrorists because ingredients are attainable at local stores.

The 9/11 terrorist attacks were not the result of checked bag gage security procedures, but they did shed light on the lack of screening requirements. Until Congress mandated its 100 percent screening requirement, only 5 percent of checked bags were being screened for explosives.

"Congress should not be initiating these sorts of things. The Transportation Security Administration, with access to all the intelligence data and all their modeling capabilities, ought to be the one proposing what we need to do next and where we would get the most bang for the buck," says Poole.

To meet Congress' mandate for screening all checked baggage for explosives, TSA spent millions of dollars to procure and deploy explosive detection systems at the nation's airports. While EDS systems have been deployed to the largest 85 airports in the country, explosives trace detection systems have been deployed to the rest of the airports.

"Trace is good, but trace should never be used as a primary screening device, because all it tells you is whether something is or isn't there," says Laird.

Trace technology searches for vapors or particles of explosives. The system requires security agents to handle luggage manually and swab them for testing. It's a time-consuming and labor-intensive process, and that type of technology can be fooled, he says. EDS, on the other hand, gives a vivid picture of a bag's contents down to minute detail, he says.

"The good news is, there's EDS at airports that handle 85 percent of the people. But the bad news is, 15 percent of airports use trace," he adds.

--GRACE JEAN