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updated 5/11/2012 4:51:26 PM ET 2012-05-11T20:51:26

Another underwear bomb attempt failed. This week U.S. intelligence officials told the press they’d foiled a plot out of Yemen to bring down an America-bound airplane using a suicide bomber with an explosive device hidden in his underwear. Only the would-be bomber was actually a CIA informant, and the device is now in an FBI explosives lab.

Officials said it was the work of Al-Qaeda bomb-maker Ibrahim Hassan al-Asiri, who was linked to the 2009 underwear bomb as well as printer cartridges packed with military grade explosive that were pulled off cargo planes in 2010. The new device is being called more sophisticated because it would have likely made it through a pat down and a metal detector.

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Bomb plots fail even without an informant for a number of reasons, explosives experts say. They discuss those safeguards and explain how the authorities work stay ahead of creative bomb-makers.

"There are multiple ways for authorities to detect a device and the person carrying that device," said John Goodpaster, an assistant professor and director of the Forensic and Investigative Sciences Program at Indiana University -- Purdue University Indianapolis. A former law enforcement official with the Bureau of Alcohol, Tobacco, Firearms and Explosives, Goodpaster now focuses on explosives research.

Missing a Link
The latest device has been called "sophisticated" by senior officials and was sewn into custom fitted underwear. In explosives, sophistication means an increased level of complexity. These devices will have powerful "high" explosives instead of gunpowder or black powder, Goodpaster said. Unlike a simple explosive like a pipe bomb lit by a fuse, complex devices include time delays and triggers.


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"Sophisticated devices have some sort of electronic component, so either a delay that's electronic in nature or a trigger that's electronic," he said.

That same sophistication, however, can be the device's undoing. More electronic components increase the likelihood that one of those components will misfire. Connections can get lose and cause circuit failure. Or, a detonator might not fire as planned and just burn, causing the device to catch on fire instead of exploding.

"Ironically, the more simple devices are less likely to fail because there are fewer pieces and parts that go into them," Goodpaster said.

Detecting the Undetectable

The exact explosive used in this new bomb remains unknown to the public, but past devices made by al-Asiri contained pentaerythritol tetranitrate or PETN, a nitrate ester in the same family of explosives as nitrocellulose and nitroglycerin.

"I suspect it is used because among the military explosives it has a rather high availability and high sensitivity," said Jimmie Oxley, an explosives expert and chemistry professor at the University of Rhode Island. Oxley and her colleagues research explosives detection and look for ways to prevent their use in improvised explosive devices.

Goodpaster added that PETN has other qualities that make it advantageous for the military. It can be used in a detonating cord that has an actuator at one end and a device hooked into the other. PETN has versatility so it can be shaped, molded, and cut. The explosive is also relatively inert.

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"The lack of metal does not make it undetectable," Oxley said of the new device. For more than a decade, a number of airport detectors seek explosives, she added. One that passengers may be familiar with is called an ion mobility spectrometer or IMS. After a fabric pad is run over luggage handles and seams, it goes into the IMS equipment, which heats the pad to detect trace amounts of explosives.

Emerging explosive threats are added to ion mobility spectrometry capabilities and the detection threshold is continuously improving, Oxley said. Behind the scenes, checked luggage goes through all kinds of screening, she added.

Another step is bottle screening, where a machine quickly analyzes bottled liquids using a kind of spectrometry. Oxley said airports are starting to install them and she has one in her lab. "They can read that yes it is wine and you can take it on the plane."

Making a Full Sweep

Equipment like IMS and bottle screeners are considered point detectors, tools used to check point by point for explosives. Applying detection on a much larger scale remains a challenge.

One major research area for Goodpaster involves canine teams at airports. "The canine is able to sniff the air and pick up explosives that are coming off your body," he said. "There's no way to prevent that unless you're literally walking around in a full body suit. Those vapors are going to escape and will be detected."

Goodpaster also pointed to "sniffing chambers," where people pass through an area that sends out small puffs of air. The scan works by loosening any trace explosives from passengers with the air and then collecting samples in a small chamber. Extremely sensitive equipment then identifies explosives in less than a second.

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Yu Lei is an associate professor of chemical, materials and biomolecular engineering at the University of Connecticut who helped develop novel sensors for detecting explosives in water and landmines buried in fields. One sensor is a film containing a fluorescent chemical mix that reveals trace explosives in the ground.

Screening machines in the airports can show that a person might be hiding a device, but authorities still have to do more tests to characterize what's actually in it, Lei said. "If we can develop one simple technology that can identify any hidden explosive, that will be a breakthrough."

Goodpaster called the description of bomb-makers versus authorities as a cat-and-mouse game an appropriate one. Fortunately, law enforcement doesn't just rely on one type of technology.

"In this case, the underwear bomb would bypass a metal detector but it would not be able to bypass any kind of chemical sniffer or canine used to detect explosives," he said. ";We've got the advantage of having multiple tiers."

© 2012 Discovery Channel

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