Machines used in U.S. airports today generally examine bags from only one angle. Government audits have shown that it is sometimes difficult for screeners to detect banned items or weapons, depending on where they are placed in a carry-on.
Security officials are seeking new technology to counter the threat of liquid explosives, a month after British authorities said they uncovered a plot to blow up transatlantic flights. The upgraded machines would not identify explosive compounds but would help screeners pick up shapes of items that could contain liquid explosives, officials said.
"What gives me the capability to find explosives now?" Kip Hawley, head of the Transportation Security Administration, asked in an interview. "The answer is X-rays. We're looking at where we can get the biggest bang for the buck."
Hawley declined to discuss specifics of the proposal to divert money from the purchase of puffers, which analyze bursts of air blown at passengers to determine whether they have come into contact with explosives.
The puffers break down too often because their sensors get clogged with dust in the busy airport environment, TSA officials said. The $160,000 devices also can't detect liquid explosives, they said.
Authorities have installed 93 puffers at more than 30 airports. The TSA has stopped taking delivery of the devices, which are built by General Electric Co. and Smiths Detection, until improvements are made, TSA officials said.
The officials said they did not plan to pull puffers out of service. Just a month ago, the TSA called the devices "state-of-the-art machines" in a press release.
The X-ray proposal highlights a problem identified by many outside experts after arrests in the alleged plot in Britain were announced on Aug. 10: The TSA has no reliable tool to find liquid or gel explosives. After the arrests, officials banned nearly all liquids and gels from the passenger cabins of commercial aircraft because they were concerned that a terrorist might be able to slip a liquid bomb onto a plane.
Officials said a decision on the reallocation was weeks or months away, and it was not clear how the new machines would affect the ban on gels and liquids. TSA officials said they were reviewing the ban to see whether they might be able to lift some restrictions based on the size and shape of containers.
Several outside experts said improving X-ray technology would be a smart decision. But others said that they worried the TSA was losing focus and that the proposal under consideration highlighted the agency's continuing struggle to find better ways to uncover threats.
"This seems like another attempt to bring on new technology when we have had a series of failures, and I have no confidence that the redirected funds are going to be better spent than the funds they have spent already," said Michael Greenberger, director for the Center of Health and Homeland Security at the University of Maryland School of Law.
At a New Mexico laboratory, the Department of Homeland Security is testing 10 devices that contractors think can detect liquid explosives, said James Tuttle, who oversees much of the department's explosive-detection effort.
The government has been evaluating those devices for months. It has received about 50 proposals from vendors since it issued its initial request last month, Tuttle said.
Officials and outside experts said most of the devices were probably several years away from widespread deployment in airports. The devices would not only have to be able to detect explosives but also survive the wear and tear of busy airports -- a lesson that officials have learned from their experience with the puffers.
"When you put them in a commercial environment, with people taking shoes off and whatever they are doing, a nice clean sensor is one thing," Tuttle said. "Once it is in there for six months and you dirty that sensor up, it's like dirtying up a car. It just doesn't perform as well. We need to test these things in an operational environment."