Tony Avelar/Associated Press
Allowing liquids on planes in small quantities limits risks, officials say.
Threats & Responses
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Since a London-based plot to bomb airliners was broken up seven weeks ago, aviation security officials in the United States have pushed to assess how serious that threat was and what safeguards should be taken. The revised checkpoint rules announced last week by American, Canadian and European authorities were the result of that frenzied effort, Transportation Security Administration officials said.
The new rules — which ease a ban on liquids by allowing travelers to carry three-ounce containers of toiletries in a one-quart, zip-top plastic bag — have been largely met with approval by passengers and relief by airlines overburdened with a crush of checked bags. But the changes also provoked some skepticism by the public about the reasoning behind the decision.
Aviation security officials said they were confident they had settled on a sound course. “We looked at it from the chemistry point of view, the physics point of view — which kind of operational tactics one might use, with different scenarios,” said Kip Hawley, the assistant secretary for the transportation agency. “The arrangement we came up with does have a good margin of error.”
The testing, Mr. Hawley said, confirmed that the risks posed by the London plot were real. “This was a serious, serious, serious threat — chilling is the word,” he said in an interview last week. But extensive work by government and university scientists showed that the threat could be largely counteracted by limits on the size of containers, he said.
Mr. Hawley and the deputy homeland security secretary, Michael Jackson, provided new details about the analysis of the London scheme in a joint interview last week, in part because they were aware of the skepticism over the new checkpoint rules. Officials from the F.B.I., the T.S.A., the White House domestic security office and aviation security agencies overseas concurred in the decision, Homeland Security officials said.
There was “remarkable interagency consensus,” said Russ Knocke, a Homeland Security spokesman.
Some aviation security and explosive detection experts said the new rules demonstrated that the initial ban on liquids was overkill.
“I think they overreacted,” said Penrose Albright, a former assistant secretary at the Science and Technology division of the Department of Homeland Security. “Where they are at now is where they should have been from the beginning.”
But others worry that lifting the ban might be premature. Stephen J. McHale, a former deputy T.S.A. administrator, said some security experts in Washington were concerned that with some suspects perhaps still at large, government scientists could not reliably counter unknown formulas terrorists might be developing.
Homeland Security officials said the effort to assess the threat began soon after the arrests of plot suspects by British authorities on Aug. 9. Laboratories lined up by Homeland Security and the Federal Bureau of Investigation immediately began replicating the bomb the British plotters were experimenting with. And scientists tried to build every alternative they could imagine.
Scientists tested the ingredients linked to the London plot in the Rio Grande Valley south of Albuquerque, where the canyons and mountains form a perfect explosives testing range. Based on the materials found in Britain, investigators developed a specific theory of the bomb plot, two officials who have been briefed on the inquiry said.
With the seal on a sports drink called Lucozade intact, the plotters apparently intended to remove the drink with a hypodermic needle and replace it with highly concentrated hydrogen peroxide, a syrupy liquid once used as rocket fuel. Another bottle would be filled with a common household substance, which The New York Times agreed not to disclose at the request of Homeland Security officials. After the two were mixed, a detonator hidden in a hollowed-out AA battery would be used to set off the bomb, according to this theory.
The work did not involve blowing up an airplane. Instead, ingredients were mixed in the beakers and, with the help of a robotic device, detonated while technicians were in a nearby bunker, security officials said. High-speed cameras recorded the explosions, while devices took readings so technicians could calculate the power and duration of the blasts and predict their effect on a plane.
Neither Van D. Romero, vice president for research at New Mexico Tech, which operates the explosives testing center, nor security officials would describe in detail the strength of the explosions or the quantities of liquids tested. But Mr. Romero said the blasts were of considerable force. “There are liquids that will detonate and can cause a significant amount of damage,” he said.