THE MAGAZINE

New Views on Airport Screening

By Joseph Straw


Trace Detection

Explosives trace detection (ETD) systems, like the name implies, are used to test for explosive residue on passengers and their effects, typically carry-ons.

The TSA’s first major attempt at ETD technology was a misfire: explosives detection trace portal machines, commonly referred to as “puffers.” Passengers stood in the portals, their arms raised. A quick puff of air dislodged solid particles from the passengers skin, hair, and clothing, which the machine then vacuumed up for analysis. The machines, however, tested in relatively sterile lab environments, were quickly fouled—and thus foiled—by the high volume of particulates in airport air, and as a result, they didn’t work. The TSA has shelved the technology indefinitely.

Meanwhile, there has been progress with other new technologies designed to detect trace elements of explosives, including liquids, which became a concern after a terrorist plot was uncovered in the United Kingdom in 2006. That plot entailed the use of liquid explosives to bring down an airplane headed for the United States.

Two Smiths Detection devices used by the TSA, the IONSCAN 400B and the SABRE 4000, rely on a process called ion mobility spectrometry to test for the presence of explosives (whether liquid or solid), illegal drugs, or chemical agents. The process is similar to that employed by many smoke detectors. Sample material is given an electrical charge, then passed through an electrical field to see how fast it moves. The speed of the material determines its composition.

The IONSCAN consists of equipment that is about the size of a microwave oven. An operator must take a sample using a swab—such as from the inside of a suspect bag—and drop it into the machine for analysis.

The SABRE miniaturizes the process into a handheld device tipped with a sensor probe that is used to “sniff” the air around a suspect object, such as the seal on a bottle containing liquid or gel. The SABRE’s key advantage is speed, due mainly to elimination of the swab step. An entire test can be conducted in as little as 20 seconds, according to Smiths.

Another new scanning device is the Fido explosives detector, which is manufactured by ICx Nomadics. It also “sniffs” around suspect areas and objects to detect explosives vapors, but it employs different technology to detect threats. The technology, licensed from the Massachusetts Institute of Technology, is based on chemiluminescence, the property that makes glow sticks glow. When explosive materials interact with Fido’s proprietary chemistry, they light up, and the device detects that luminescence.

Fido is currently in use by the TSA at 70 airports nationwide, according to Patrick Dempsey, ICx’s  vice president of direct sales. ICx hopes to expand Fido technology to detect a broader range of threats, Dempsey says.

Another product TSA plans to evaluate is called the explosives particle analysis kit (XPAK), developed by RedXDefense, initially for military applications. The portable array, the size of a flattened shoebox, features an eyepiece and a removable wand, resembling a household lint roller, that is inserted in the side.

To test for explosives, the user covers the wand with a fresh, disposable paper sleeve, swabs the test area, and inserts the wand into the device. For the test, the system sprays the inserted wand with proprietary ink. Then, the user activates an internal ultraviolet lamp, and looks through the eyepiece. The ink is fluorescent, but explosives eliminate its fluorescence. Thus, any dark areas on the wand indicate the presence of explosives.

Currently, XPAK’s ink only detects organic explosives, but the company plans to field an ink capable of detecting inorganic compounds used in some “homemade” explosives, like ammonium nitrate and urea nitrate, says Sarah Toal, RedXDefense’s chief chemist.

The Next Generation

Researchers at the government’s national laboratories are working with funding from the TSA and the Department of Homeland Security’s Directorate for Science and Technology to see whether technologies from other fields can be adapted for airport security screening.

One example is magnetic resonance imaging (MRI). A 2006 call for new technologies to detect suspect liquids and gels (in response to the U.K. terrorist plot) coincided with ongoing work at Los Alamos National Laboratory to develop an MRI-type device with a magnetic field weak enough to read the subtle electromagnetic signatures of the brain, “see” a fetal heart beat, or be used to evaluate patients with implanted medical devices containing metal, like pacemakers.

A standard-strength MRI machine, used at a security checkpoint, might rip bags containing metal items to shreds, pull bystanders’ keys from their pockets, and send nearby magnetometers haywire. But a low strentgh MRI could help TSA scan liquids without restricting the amount or requiring special packaging.

“I think that’s DHS’s ultimate goal, but we’re a long way from that,” says Michelle Espy, the researcher and team leader working on the device, called the superconducting quantum interfering device, or SQUID. Espy’s team hopes to have a prototype built by the end of the year.

MRI machines use their magnetic fields to orient the existing magnetic fields around the nuclei of hydrogen atoms, then re-orient the fields slightly with radio waves. Detection of the changes in the fields produce clear images of the body’s soft tissues, which is difficult with x-rays.

Espy explains that the SQUID device would not read densities or atomic weights like current x-ray machines but rather it would detect how different chemicals react to magnetic fields. The device would rely on fields no stronger than those present in the everyday world. Ideally, Espy explains, the SQUID device would assay a child’s juice box packed in a carry-on and determine its contents as safe despite the container’s foil liner, and without damaging anything.

Remote testing. Another futuristic idea being pursued in the lab is the potential to test substances from a distance. At Oak Ridge National Laboratory in Tennessee, researcher Thomas Thundat is pursuing an explosives detection technology that holds the promise of “standoff” explosives trace detection from 20 or more meters away.

Oak Ridge’s standoff explosives detection research is based on spectroscopy, the process by which a substance’s chemical composition is determined through analysis of how it refracts energy, sometimes visual light—in this case, infrared energy from a quantum cascade laser. A relatively new technology relying on semiconductors, quantum cascade lasers are “eye safe,” Thundat says. They have already been commercialized for industrial chemical detection.

The technology has both high sensitivity and selectivity on small chemical traces, 100 times smaller than a fingerprint, either up close or at “tens of meters.”  The technology also has the promise of hand-held portability. A likely obstacle, Thundat concedes: high cost per unit, which he attributes to a limited market for the technology, but that could change as the market grows.

Separate research at Oak Ridge holds the promise of palm-sized test devices for taking vapor samples from the air near suspect objects. The technology relies on microelectromechanical systems (MEMS), in this case cantilevers, which Thundat compares to a diving board the width of a human hair and 1/100th its thickness.

In one experiment, one side of the MEMS cantilever is coated with a chemical that automatically binds to an explosive compound present in vapor form. When that chemical reaction occurs, the cantilever bends, and the MEMS device detects the resistance. The real challenge, Thundat says, is to develop chemicals that attract specific explosive compounds selectively.

Another possible MEMS application involves what Thundat calls “deflagration,” essentially igniting trace explosive molecules present in air vapor form by heating the cantilever to 600 degrees Celsius—which is easy given its small size. Each compound’s ignition would have a specific signature, theoretically readable by the device. Thundat is still pursuing proof-of-concept for the deflagration concept, he says.

The most futuristic idea of all, however, is that screening can somehow be made effective but painless for travelers. Smiths Detection’s Laustra says forthcoming innovations are likely to include x-ray machines with alternative belts that automatically divert suspicious bags to secondary screening, so TSOs don’t have to stop the belts completely to remove suspect bags by hand. And Smiths Detection plans by 2010 to field a concept for what Laustra calls a “lane of truth,” a seamless, largely automated security checkpoint that would offer unintrusive screening that barely slows passengers’ progress from the check-in counter to the gate.

TSA shares that objective, says Howe. It could be achieved through a combination of identity verification, behavioral threat assessment, and technology, she says, adding, “I think there is a vision in which you could be going through screening and not even know it.”


Joseph Straw is an assistant editor at Security Management.

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