This follow up story on airport security measures examines the existing–but often not yet implemented–devices that can help identify liquid explosives. It comes from Celeste Biever of the New Scientist. Here are some highlights.
“It’s not the case that we absolutely cannot identify liquid explosives,” says John Parmeter, an explosives expert at Sandia National Laboratories in Albuquerque, NM. Joe Reiss of American Science and Engineering (AS&E) in Billerica, MA, which makes baggage-screening technology explains, “Analysts are trained to look for suspicious combinations of things. A solid explosive by its nature does not have a defined form and can take a variety of shapes and sizes. With liquids at least you know you are looking for a container.”
AS&E’s Gemini device (not yet installed in most airports) can detect X-rays that are scattered by objects rather than those that are transmitted, allowing it to image even low-density organic materials such as the liquid explosives TATP and nitroglycerine.
Rapiscan of Los Angeles, CA, which makes a large number of the X-ray machines used in airports, has added quadrupole resonance imaging to its X-ray devices. This technology, similar to magnetic resonance imaging, can identify specific molecules that might indicate the presence of explosives.
Existing Ion Mobility Spectrometer (IMS) machines look for certain nitrogen-containing compounds, including liquid explosives such as nitroglycerine and explosive slurries made of ammonium nitrate. The UK-based company Smiths Detection of Bushey, Hertfordshire, and Thermo Electron in Waltham, MA, have developed IMS machines capable of spotting TATP, although these are not yet in use.
Devices to scan passengers for hidden explosives are also being developed. Scanners that measure the way objects absorb and reflect terahertz waves, which lie between microwaves and infrared on the electromagnetic spectrum, can detect explosives, as the reflected signal reveals characteristic spectral signatures. TeraView, based in Cambridge, UK, is developing small scanners that can be used to screen passengers for concealed devices as they pass by.