The full-body scanners in use at 78 U.S. 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: small amounts of marijuana wrapped in baggies, other drugs stitched inside underwear, 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 because of security concerns, has also raised concerns about the effectiveness of the full-body scanners.
Based partly on early successes, federal officials are planning to continue an unprecedented roll-out of the technology over the next year. By New Year's Day, about 500 machines will be in use across the country, including at the Washington area's three major airports. By the end of next year, 1,000 X-ray machines will be operational, accounting for roughly half of the nation's 2,000 lanes of security checkpoints.
Following the United States' lead, several nations have begun to test or install full-body scanners, including Australia, Canada, France, Germany, Japan, Russia and the United Kingdom. U.S. officials have also considered whether the machines could be used to enhance security at passenger 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 that TSA officers can spot potentially dangerous items on passengers.
"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.
They have been installed at a quicker rate since a failed 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, less frequent checkpoint feature.
Still, many security experts say the machines are expensive window dressing meant to put the traveling public at ease.
A recent paper published in the Journal of Transportation Security by two former University of California-San Francisco physicists said that images produced by the 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 kilo 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.
PETN, or pentaerythritol tetranitrate, is hard to detect. Odorless and similar to a white crystal powder, 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 "clearly" tried to trick baggage screening technologies, according to the Department of Homeland Security.
Brian Michael Jenkins, director of the Transportation Security Center at the Mineta Transportation Institute in San Jose, Calif., said he was unsure whether an advanced scanner would have discovered the explosives in Abdulmutallab's underwear. The U.S. Government Accountability Office has said it "remains unclear" whether he would have been caught by a full-body scanner. But a random assortment of security measures - and not the reliance on one technology or method - is key, Jenkins said.
"It's the mystery that drives our adversaries crazy," he said. "We need the unknown."
The Transportation Security Laboratory, a federal Homeland Security testing site created in 1992 at New Jersey's Atlantic City International Airport, began testing on full-body scanners in 2007. The detailed results of the testing performed in Atlantic City are classified because of security concerns, but interviews with more than a dozen former and current government officials and the limited release of its findings found:
- The detection of weapons and contraband varied by who was evaluating the images, indicating that some transportation security officers were less adept at spotting unusual or dangerous items.
- The "backscatter" rays can be obscured by body parts and might not readily detect thin items seen "edge-on."
- Objects hidden inside the body, in cavities, might be missed by both types of the scanning machines altogether.
"If you have someone who is rather fat or who has large breasts or buttocks, that's a factor, too," said Anthony Fainberg, a physicist and former program manager for explosives and radiation detection at Homeland Security.
Fainberg has lobbied for hand-held swabbing of hands and luggage for trace detection of explosives, especially on international flights.
"If you have something hidden behind flaps of flesh, it can be missed," he said. "I'm not worried about the safety of it at all, but I am concerned about what could be missed."
Frank Cilluffo, director of the Homeland Security Policy Institute at George Washington University, said that the technology expands the TSA's security toolbox.
"It is not going to solve the problem, but it certainly comes a long way from where we were before," Cilluffo said.
'These things take time'
To address the litany of security and privacy concerns over the full-body scanners, federal officials are testing several new technologies that will probably make their way into airports in the coming months.
Homeland Security's research and design division, the Science and Technology Directorate, is testing a software patch being developed by the two companies behind the scanning technology - Rapiscan Systems and L-3 Communications - that would produce only a generic outline of a human body accompanied by a box or colored squares indicating a hidden anomaly or specific substance. An alarm might also be used to alert screeners to potential threats.
But TSA Administrator John S. Pistole said that the software, called automated target recognition, is not scoring well in lab tests, producing too many false-positive errors.
"It is a relatively complex math problem, but we're confident we're going to solve it and solve it soon," said Peter Kant, executive vice president of Rapiscan Systems. "But these things take time."
Meanwhile, federal researchers are testing systems that would scan passengers' shoes without having to take them off; a new generation of carry-on baggage equipment, such as conveyor systems; and smaller and faster baggage scanning machines, which could check 1,500 bags per hour, up from an average of 300 to 400 per hour. Technology developed at the Department of Energy's Los Alamos National Laboratory could identify liquids through opaque containers, such as a soda can or juice pouch.