Detecting liquid explosives at airports

Passengers are told by the Transportation Security Administration start ditching liquids, gels and lotions from their carry-on luggage , due to the risks of liquid explosives being activated and assembled on board aircraft. GlobalSecurity.org explains in detail how liquid explosives work, while National Public Radio has a concsise summary . Some airports , such as Tampa’s TIA have “trace portal” machines , that detect whether a passengers has handled explosives. Only a few passenagers are selected to go through the machines, which cannot detect traces in sealed containers.

X-ray scanners can’t detect explosive liquids. X-ray scanners examine density, not volatility.

Newsday reports that, until recently, most explosive detection efforts have focused on solid explosives , rather than liquids.

According to William Martel, a professor of international security studies at Tufts University , the most common explosive test -- a swipe test where a cloth or tape is wiped over luggage and put through a sensor -- is specifically designed to pick up residue from solid explosives. “We didn’t start looking aggressively for liquids until a few years ago,” he said. Some, but not all, can be picked up by “sniffer” sensors using a technique called neutron activation analysis .

Newsday explains:

The newest form of liquid explosives are so-called “binary” formulas that were developed to clear land mines in Third World countries . They’re undetectable until mixed, and also require a detonator.

There are even liquid explosive blends that don’t need a detonator, though their exact composition isn’t widely known. Methyl nitrate , which has been used in some types of antipersonnel mines including improvised explosive devices, explodes when mixed with another chemical.

Reuters says regular medicine-cabinet and cleaning supplies can be adapted to make explosions, and may not be detectable by airport security equipment. That does not mean they are easy to make into bombs, cautioned Neal Langerman, a San Diego consultant who is former chair of the American Chemical Society’s Division of Chemical Health and Safety. “I would doubt that the average layperson would successfully make triacetone triperoxide ,[one of the explosive compounds] without killing themselves,” Langerman said.

Mixing the explosives on a plane would not be easy says The Times of London .

Explosives expose aviation weak spot ( USA Today ): Thursday’s terror plot didn’t succeed in blowing up planes, but it struck at the core of a fundamental weakness in aviation security around the globe: the inability to spot explosives made from seemingly harmless ingredients.