How to Find Hidden Explosives at Airports

The bomb that Umar Farouk Abdulmutallab reportedly tried to set off as his flight neared Detroit on Christmas could have been detected using existing screening technologies, had they only been used. Not only could the explosives have been spotted using back-scatter X-rays or millimeter wave technology--which can see through clothes--invisible traces of the explosive could have been detected using chemical sensors. But both technologies, if used to screen all passengers, would lead to long lines at airport security checkpoints.

These images were recorded with millimeter wave technology.
Credit: TSA

The main explosive used has been identified at pentaerythritol tetranitrate (PETN). Unlike some explosives, it does not produce enough vapors to be detected through sealed containers. But it could be detected by swabbing a person's hands or the outside of a briefcase, or in devices at airports that use puffs of air to dislodge trace explosives particles, which are then sampled and tested via spectrometers. They could also be detected by new materials that glow (or stop glowing) in response to certain explosives, and can be much faster than the technology used now in airports.

A secondary explosive--a liquid--also appears to have been used in the attempt to set off the bomb. This likely would have produced enough enough vapor that it could be detected through a sealed container using handheld devices that are starting to be used in some airports. Depending on the exact explosive used, it could have been detected, for example, by this handheld sensor.

PETN would also easily show up on scanners that use X-rays or those that use 30 to 300 gigahertz electromagnetic waves (called millimeter wave scanners) that are able to distinguish between skin and other materials. Explosives should show up particularly clearly because they're typically denser than other materials, says Aimee Rose, a principle researcher at ICx Technologies, which makes explosives detection equipment. "One of the reasons that they are explosive is that they're a lot denser than typical materials. You need a lot of material in a small area."

But neither of these technologies is as fast as a standard metal detector, and they're expensive and can be difficult to operate, making it impractical to install enough of them to keep people moving quickly. "Any of these systems are likely going to slow down checkpoints," Rose says, although she notes time could be saved by eliminating the need for pat downs.

Such systems, however, could eliminate other security measures--such as being restricted to your seat for the last hour of flights or not being able to use blankets--that are both inconvenient and may not do much good. That, and the added safety, could make it worth the extra wait at airports.