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Effectiveness of airport scanners questioned

Explosives molded to body may prove difficult to detect

A passenger at Logan International Airport went through a full-body scanner last month. A passenger at Logan International Airport went through a full-body scanner last month. (David L. Ryan/ Globe Staff)
By Derek Kravitz
Washington Post / December 27, 2010

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WASHINGTON — The full-body scanners in use at 78 US airports can detect small amounts of contraband and hidden weapons, all while producing controversial images of travelers.

The “good catches,’’ federal officials say, have largely gone unnoticed amid the criticism that erupted over the ghostly X-rays and “enhanced’’ pat-downs.

The Transportation Security Administration, which intensified airport screening last month, points to several successes: finding small amounts of marijuana wrapped in baggies, other drugs stitched inside underwear, and ceramic knives concealed in shirt pockets.

But the machines could miss something far more deadly: explosive material taped to someone’s abdomen or hidden inside a cavity. Researchers and security experts question the technology’s ability to detect chemical explosives that are odorless, far smaller than previous incarnations, and easily molded to fool machines and security screeners into thinking they are part of the human body.

Government testing, which has been mostly classified, also raised concerns about the effectiveness of full-body scanners.

Based partly on early successes, federal officials are planning to continue an unprecedented rollout of the technology over the next year. By New Year’s Day, about 500 machines will be in use across the country. By the end of next year, 1,000 will be operational, accounting for roughly half of the nation’s 2,000 lanes of security checkpoints.

Following the US lead, several nations have begun to test or install full-body scanners, including Canada, Japan, Russia, and Britain. US officials have also considered whether the machines could be used to enhance security at rail stations.

Federal officials say the scanners represent the best technology that has passed both lab and field tests. But as with reading an X-ray, training is the most important factor in making sure TSA officers can spot potentially dangerous items.

“The bottom line is that we are now able to detect all types of the most dangerous weapons — nonmetallic explosive devices,’’ TSA spokesman Nicholas Kimball said. “Even in small amounts, it can be picked up.’’

Two types of scanning machines — backscatter and millimeter wave — have been installed at airports since 2007, when they were launched as part of a pilot program at Phoenix Sky Harbor International Airport. Both machines produce the same full-body images that attracted controversy; they work by bouncing X-rays or radio waves off skin or concealed objects.

Logan International Airport in Boston is among those with backscatter X-ray machines.

Machines have been installed at a quicker rate across the nation since a Christmas Day terrorist attempt last year in which Umar Farouk Abdulmutallab hid explosives in his underwear on a flight from Amsterdam to Detroit. The failed attack also prompted federal officials to use the scanners as a primary security technique at airports instead of a secondary feature.

Still, many security analysts say the machines are just expensive window dressing.

A recent paper published in the Journal of Transportation Security by two former University of California San Francisco physicists said images produced by backscatter scanners would probably fail to show a large pancake-shaped object taped to the abdomen because it would be “easily confused with normal anatomy.’’ As a result, a third of a kilogram of PETN, a type of malleable explosive, which could be discovered by a pat-down, would be missed, the scientists said.

“It’s not an explosives detector; it’s an anomaly detector,’’ said Clark Ervin, who runs the Homeland Security Program at the nonprofit Aspen Institute. “Someone has to notice that there’s something out of order.’’ Ervin was the first inspector general for the Department of Homeland Security.

Odorless PETN (pentaerythritol tetranitrate) is hard to detect. It was used in both package bombs shipped to the United States in October and the Christmas airliner attempt last year. Those who plotted the cargo attack hid the explosive in toner cartridges and tried to trick screening technologies, the Department of Homeland Security said.

Yesterday on CNN’s “State of the Union,’’ Homeland Security Secretary Janet Napolitano said the use of full-body scanners and pat-downs will not change for the “foreseeable future.’’

The Transportation Security Laboratory, a Homeland Security testing site created in 1992, began testing full-body scanners in 2007. The detailed results are classified but according to interviews with former and current government officials and the limited release of findings:

■ The detection of contraband varied by who was evaluating the images, indicating that some transportation security officers were less adept.

■ The backscatter rays can be obscured by body parts and might not readily detect thin items seen “edge-on.’’

■ Objects hidden in body cavities might be missed by both types of scanning machines.