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The Science of Detecting Liquid Explosives


One of the issues raised by today's arrest is the problem of detecting liquid explosives. Joining us to talk about that issues is Nell Boyce, NPR's technology correspondent, and Nell, I gather detecting liquid explosives is something of a problem.

NELL BOYCE reporting:

That's right. The security agencies currently have no test to check for liquid explosives. Historically, you know, technology tends to focus on threats that people have seen in the past, so you know, in early - problems would be knives and guns, and so, you know, the focus was on developing X-ray technology and things that could find those types of materials.

Then when people started thinking about solid explosives as a threat, obviously all of the technology development went to detecting and sensing solid explosives. Now it's been fairly recently that liquid explosives, particularly this type of liquid explosive, has been seen as a real threat to airlines, and companies are starting to work on technologies that could detect them. But, you know, technology development always takes time.

MONTAGNE: So what sort of things are companies looking to do in regards to detecting liquid explosives?

BOYCE: Well, they are trying a lot of things, and there's a real push for this now. I mean, I think anyone who's been through an airport security line has maybe had a cup of coffee or something like that, and they're asked to take a sip of it, and that's hardly the kind of high-tech detection device that airports would like to have.

One thing that's being tested is something called dielectric measurements. Basically, it could look through a bottle, a glass bottle, and could tell you if it was something like a water-based material like, you know, say you're bringing glass of - sorry, a bottle of wine to relatives. And if it was water-based, it wouldn't be as much of a problem if the sensor detected that the container had a petroleum-based or something like that - something that might be a solvent for an explosive.

The problem with that kind of technology is that it can't really look through metal containers. So say you were bringing an aerosol can, something like hairspray. But there are other technologies, technologies that have been previously in laboratories, that can sample a liquid and analyze its chemical structure and then compare that to a database of chemicals that might be of concern.

MONTAGNE: And then what are some of the obstacles to get these things working and also probably efficient, when you're talking about millions of people being screened in airports?

BOYCE: That's just right. I mean, scientists have technologies to analyze liquids. I mean, that's very common. It goes on in laboratories all the time. But that's very different than a device that you can put there in an airport, have it going very quickly, have it be something that people can operate with very little training. And it's especially problematic, you know, when you're looking for chemicals that are also used as common household chemicals.

So, you know, the technology development is in the works, but it hasn't been seen as much of a priority until recently.

MONTAGNE: Nell, thanks very much.

BOYCE: Thank you.

MONTAGNE: NPR's Nell Boyce is technology correspondent for NPR. Transcript provided by NPR, Copyright NPR.

Nell Greenfieldboyce is a NPR science correspondent.
Renee Montagne, one of the best-known names in public radio, is a special correspondent and host for NPR News.