Toolbox: Explosives Detection

The attacks of September 11 transformed aviation security in the United States.

March 01, 2005 — CSO — The attacks of September 11 transformed aviation security in the United States. Soon after, a slew of security measures were established, including a requirement by Congress that all checked baggage be screened for explosives by Dec. 31, 2002.

That set off a boom in the explosives detection systems (EDS) marketplace. According to Matthew Farr, industry analyst at Frost & Sullivan's Aerospace & Defense Group, the market surged between 2001 and 2002. After that, the market cooled off, dropping to $219 million in 2004, but Farr predicts the market will rebound to $595 million by 2009.

Most of the money that funds EDS growth has come from the federal government. (Congress appropriated $1.488 billion for EDS-related purchases and modifications to terminals through FY04.) The two devices used by the Transportation Security Administration (TSA) to screen for explosives are EDS and ETD (explosive trace detection) machines. As you've likely observed while idling away your time in airport lines, EDS devices take up a large footprint in terminals, weighing up to 17,000 pounds. The machines, which cost more than $1 million, can scan hundreds of bags an hour using CAT-scan-like technology.

ETD devices are used by TSA to check carry-on baggage for explosives. (Passengers selected by screeners for pat-downs also get their bags checked.) Screeners take a dry pad and wipe the outside of an item. The pad is then run through an ETD device, which analyzes the pad for chemical traces of explosives. The devices are about the size of a computer printer.

Nothing's Perfect

Compared to explosives detection before 9/11, when just 5 percent of checked bags were screened, the fact that 100 percent of checked bags are run through EDS machines is quite an achievement, especially given the rapid implementation. But the technology is far from perfect. A report from the House Subcommittee on Aviation notes that many common objects have similar densities to explosives, resulting in a high number of false alarms. EDS machines also can miss smaller amounts of explosives.

ETD machines boast high detection rates, but are prone to human error. A recent report by the National Academy of Sciences notes the downsides of "blind sampling"that is, screeners wiping areas thought to be the most likely to have residues. Detection could fail if the surface was cleaned or the wiping didn't come into contact with the residue. On the other hand, an alarm could go off if the person had come into contact with residue innocentlysay, they work in the commercial explosives industry or take heart medication containing nitroglycerin. False alarms, in turn, can make screeners more susceptible to an attitude that all alarms are false and can bog down the screening process.