Could the next airline terrorist be wearing cargo pants?
At American airports, passengers are inspected, tested and searched, and now they can't even bring a latte on board. But terrorists armed with liquid or plastic explosives can still make it onto planes because there's little technology to stop them from smuggling bombs on their bodies or in their clothes, experts say.
"When you travel, you are not protected against terrorists who bring explosives on their person or in in carry-on luggage," said Hans Weber, a San Diego aviation security consultant. "It's a bigger problem than liquids."
To make detection even more challenging, there are more than 100 types of explosives, and the actual number is higher because many come in different varieties, said James O'Bryon, an aviation security consultant in Maryland who formerly served as an official in the Department of Defense.
Why can't bombs be stopped? For one thing, ordinary metal detectors are designed to detect weapons, not explosives, and X-ray machines that expose what people are carrying aren't used because of radiation concerns.
That means someone wearing cargo pants could easily smuggle in a bottle of an explosive ingredient without being detected, Weber said.
The alleged British smugglers were reportedly planning to blow up planes by using a combination of acetone and hydrogen peroxide to create a high explosive. Scientists first figured out their explosive potential in the 19th century and both are easy to obtain from chemical supply stores, although a third chemical like an acid might be needed, said Walter Rowe, professor of forensic science at George Washington University.
The chemicals could be mixed on board in a kind of "al fresco chemistry" and then detonated using a spark generated by a battery-powered device like an iPod or cell phone, Rowe said. Or the ingredients might have blown up when mixed without an electric detonator.
The terrorists would have faced challenges, like adding water and keeping the chemicals cold, Rowe said. But not much of liquid would have been needed, perhaps not more than a few ounces of each.
Plastic explosives -- like C4 or RDX -- are another airborne threat, and they easily could be carried onboard too, Weber said.
"You could put them in slabs under your clothing, or you could wear a belt," he said. "Some people have money belts; you could have an explosive belt." And in a jacket, a packet of plastic explosives might look like a sandwich to a screener at an X-ray machine, he said.
There are also problems with the rarely used devices specifically designed to detect bombs or bomb makers.
At some airports, passengers must pass through "trace portal" chambers where puffs of air knocks off molecules that are instantly tested for telltale particles leftover from bomb-making.
But a bomber who keeps himself clean of residue won't raise an alarm, and the detectors might miss certain kinds of ordinary bomb-making components.
The devices "are all set up to recognize specific compounds and specific materials," Rowe said. "If it's not programmed to pick up that material, it misses it."
And there's another problem: According to Weber, there are only about six of the machines in U.S. airports.
Security officials can run some suspicious belongings like laptops through a mass spectrometer; a worker rubs the item with a swab and puts it through the analyzer.
But "if you’re really good and you know what you're doing, and you’ve got a tightly sealed container and you've cleansed it and anything that’s touched it," the machine won't detect trouble, said Terry O'Sullivan, a terrorism analyst with the University of Southern California Center on Homeland Security.
One solution would be to make the devices more sensitive, but then they'll spew out more false positives, causing even more airport delays. (False positives are a common problem: They're estimated to plague checked-baggage scanners a third of the time.)
Checked baggage appears to be better protected from explosives. It goes through different kinds of screening than carry-on baggage; special machines are designed to help screeners detect the unique shape and density of potential bombs.
But there's another false alarm problem: "A big salami or big piece of cheese looks like an explosive in density," said Weber, who serves on a scientific advisory committee of the Transportation Security Administration.
What's next? The TSA "hasn’t gotten around to deciding what to do" regarding better explosive-detection technology, Weber said, but this week's events should speed things up.
Meanwhile, many companies are developing new explosive-detection technology, and Weber suggests that existing devices -- such as one using technology like that in MRI machines -- - could be put into wider use.
While he doubts that the alleged bombers would have gotten past security with their liquid explosives, O'Bryon agrees that there's room for improvement.
Ideally, new technology would analyze baggage in several different ways at once, looking at everything from density and chemical makeup to atomic number analysis and "offgassing," he said.
"It's called a layered defense," he said. "We're starting to develop it, but we're still not there yet."
An even better idea, many security experts argue, is to give extra screening to passengers who look suspicious. But that raises questions of profiling.
"As long as we are determined to handle the threat by looking for bad things, like bombs and knives, we are in a race we can't win," Weber said. "What we have to do is start looking for bad people, but that’s unacceptable."


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