Explosives in Your Shoes
For those who fly the ritual of standing barefoot waiting to be scanned as your shoes are intimately examined for explosives, is a common airport mishap. The ability to efficiently and unobtrusively screen for trace amounts of explosives on airline passengers could improve travel safety — without invoking the ire of inconvenienced fliers. Toward that end, mechanical engineer and fluid dynamicist Matthew Staymates of the National Institute of Standards and Technology in Gaithersburg, Maryland, and colleagues have developed a prototype air sampling system that can quickly blow particles off the surfaces of shoes and suck them away for analysis.
Travelers are screened by metal detectors. Explosive detection machines used include X-ray machines and explosives trace-detection portal machines (a.k.a. "puffer machines"). In the United States the TSA is working on new scanning machines that are still effective searching for objects that aren't allowed in the airplanes but that don't depict the passengers in a state of undress that some find embarrassing. Explosive detection machines can also be used for both carry on and checked baggage. These detect volatile compounds given off from explosives using gas chromatography.
A technology released in Israel in early 2008 allows passengers to pass through metal detectors without removing their shoes, a process required as walk-though gate detectors are not reliable in detecting metal in shoes or on the lower body extremities. Alternately, the passengers step fully shod onto a device which scans in under 1.2 seconds for objects as small as a razor blade.
The NIST engineers developed several different versions of the system. "One particular device is a kiosk-style instrument that people step into, never having to physically remove their shoes for sampling," Staymates explains. "Air jets are located in strategic locations and used to dislodge particles from the shoe surface, and a large blower establishes a bulk flow field that ensures all liberated particles are transported in the appropriate direction."
In order to be used commercially, the sampling system — which can collect particles in just 6 to 7 seconds — would have to be combined with a particle collection device and a chemical analyzer, Staymates says: "Incorporating a particle collection device and chemical analyzer would certainly be possible in the current prototype, but it was outside of the scope of the project. NIST's role was to uncover the fundamental connection between fluid dynamics and trace aerodynamic sampling, and use our findings to help in the development of next-generation sampling approaches."
For further information: http://www.physorg.com/news/2011-11-sampling-amounts-explosives.html