After terrorists attacked Paris last November, nearby Brussels, home of many of the attackers, posted heavily armed soldiers in public places. This week, terrorists calmly strolled past those patrols, then detonated bomb-laden luggage in the city’s airport and on an underground train. Dozens of people were killed and hundreds wounded.
Airport security focuses on keeping explosives off planes. Hospital-like CT scanners and X-ray diffraction machines peer into checked luggage as it moves through the bowels of airports. Passengers line up to pass through metal-detectors and be swabbed for explosives. But the Brussels attackers targeted the busy check-in area – where no security checks take place.
How do we prevent a repeat attack? Moving check-points to the front doors is one solution; metal detectors and pat-downs are ubiquitous at airport entrances across Asia. But it would mean further delays, and create new lines of people that could be targeted.
One solution, say security researchers, is to keep people moving, and scan them remotely as they pass through the building. Researchers are trying to build more nimble versions of some existing technologies, as well as entirely new ones.
In the mid-2000s, 30 US airports acquired “puffers” that wafted air past stationary passengers at standard checkpoints, then used a technique called ion mobility spectrometry (IMS) to see if it had picked up any explosives. IMS is currently used to analyse the swabs from airport pat-downs, but the puffer version was a bust: units broke down too often. They were abandoned by 2010.
Everyone going through an airport can expect to be swabbed for explosives by hand in the next few weeks, says Daniel van der Weide of the University Wisconsin. “But it is unlikely that any bomb-making material will be detected. Terrorists aren’t that foolish.”
So how else can we stop explosives getting to crowds of people? “The technologies are either imagers or sniffers,” says Brian Jenkins, a senior security expert at the Rand Corporation, a US research consultancy.
Unfortunately, imagers can be tricked. Explosives can be moulded to look like ordinary objects, for example, and cameras designed to scan for the cool areas on someone’s torso caused by a suicide vest are foiled by simply putting the bomb in a bag.
Sniffers are harder to fool. Dogs are the best, says Jenkins, but they are hard to use on a large scale. Thousands of dogs and trainers would be needed just to patrol airports, never mind train and bus stations.
Cameron Ritchie, head of technology at the US-based security firm, says puffers and IMS are still a good idea. Ritchie and Morpho are working on a “ ” that would allow passengers to walk while being scanned with an array of sensors. The enclosed space of the tunnel enhances sample collection for IMS. Imaging at the entrance could watch eye movements to detect people who seem nervous.
There are other ways to detect explosives remotely. Rather than analysing captured molecules – like the failed puffers – the Lincoln Laboratory at the Massachusetts Institute of Technology hasto “sniff” explosives from a distance.
The team behind the work says it can scan spaces for explosives from 100 metres away by sweeping them with lasers tuned to frequencies that vaporise molecules found in bombs. Material makes a tiny sound as it vaporises, which is amplified and detected.
The lab says it can “hear” explosive material on a moving car door handle, at densities as low as 200 nanograms per square centimetre. It has successfullyon homemade explosives like the TATP used in the Brussels attacks.
Lasers are also the main ingredient of a gun-shaped device called G-Scan, developed by Laser Detect Systems of Ramat Gan in Israel. This fires a green laser at a target then uses Raman spectroscopy to identify the molecules that are scattered back. It can identify anything visible, including bottle contents or surface smears, says company vice-president Adi Cooper.
The big downside of both techniques is that lasers can blind people. It isn’t clear whether one could be safely swept through a public area.
Terahertz, or millimetre-long waves, can also spot explosives from a distance, as their reflection is shifted by the characteristic crystalline structure of the explosives used in bombs. Van der Weide has foundedthat makes specialised chips that amplify terahertz signals tenfold, making detection easier. The system was tested for the first time last week.
“They will enable 20 to 30 metre stand-off,” he says. “The combination of more frequent threats and more advanced technology will eventually yield a network of security monitors whose sensitivity to explosives will allow more sophisticated tracking of bomb-making materials.”
Caught in the act
Detecting explosive material from a distance would let security services search for bombs-making materials – not just finished weapons. By scanning for telltale chemicals on people’s bodies and clothes as they move around, security services may be able to catch bomb makers before the device is finished.
“Once a bomber has a complete bomb, they are very hard to stop,” says Cooper. He thinks something like the G-Scan could have been used duringto alert police to any traces of explosives carried into the flat by people preparing bombs elsewhere in the city.
It would also allow routine inspections to reveal covert cargoes of bomb-making precursors, such as the hair bleach needed to make TATP. In theory, just scanning suspect doorknobs with a sensitive enough device might reveal explosives factories.
One problem, says Jenkins, is that a device that is too sensitive creates too many false alarms. There is also the question of how authorities responded to a positive signal from a detection quickly and effectively enough to neutralise a threat. “You can’t just yell, ‘hey you with the bomb’,” says Jenkins.
But after attacks like the one in Brussels this week, it seems probable that technology for remotely detecting explosives will continue to be developed. Using it effectively will be another matter.
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