A Sniff in Time

After airline passengers walked through the metal detectors at Albuquerque airport last fall, some volunteered to be scrutinized one more time by a device that “sniffed” them to detect chemical explosives. One by one, they stepped into a portal about the size of two shower stalls, where nozzles puffed jets of air from their shoulders to their knees. A few seconds later, a computer screen handed down the verdict: “clean” or “dirty.”

The explosives-detection portal work- ed so well that researchers at Sandia National Laboratories, who developed the device with funding from the Federal Aviation Administration (FAA), are now seeking partners to commercialize it.

The FAA gave the researchers $2 million three years ago to develop a way to ferret out people who are carrying or have recently handled chemical explosives, including so-called plastic explosives, which conventional methods cannot detect. “We’re trying to cover any and all possible ways an explosive could get on a plane,” explains Paul Jankowski, manager of the FAA’s trace detection program, inaugurated in 1992 to stay a technological step ahead of terrorists.

The device is based on technology Sandia scientists developed to protect nuclear weapons facilities from bomb threats and to prevent people inside the facilities from smuggling out restricted chemical devices. It sprays several cubic feet of air over a person’s hands and clothes to dislodge any chemicals adhering to them. The air is sucked into a device below the traveler’s feet and passes through a chemical sensor called an ion mobility spectrometer that can identify the chemical signatures of many different types of explosives. The quantity and type of chemicals detected then appear on a computer screen.

The challenge for Sandia’s research team was to develop the preconcentrator technology-the part of the device that aggregates the air molecules quickly enough so that the ion spectrometer can analyze them. The team succeeded so well that the device can detect very small concentrations of all “explosives of interest” to the FAA, according to project leader Kevin Linker, a mechanical engineer. Naturally, given the task at hand, neither Sandia nor the FAA will reveal what types of explosives the device detects or its sensitivity.

Although the initial test, on 2,500 volunteers, worked well, members of the research team say the process-at 12 seconds per customer-still takes too long.

“Our goal is 6 to 10 seconds,” says chemical engineer Chuck Rhykerd. “That’s the current speed of metal detectors. It doesn’t seem that long, but once you take your keys out of your pocket, put your bags on the conveyor belt, walk through slowly, and pick up your bags, that’s how long it takes.”

Reducing the speed will be a challenge, he admits. “Five seconds to collect the air. Five seconds to do the analysis. We can probably cut the analysis time by one to two seconds. But cutting the sample time may reduce the device’s sensitivity. It’s a trade-off.”

Another glitch that researchers hope to fix before the device can go into production is that the machine occasionally sounds a false alarm. As for what causes the false positives, the security-minded Rhykerd says: “I have a suspicion, but I can’t tell you.”

Rhykerd believes that ultimately, the rate of false positives can be held to 5 percent, “well below” that of metal detectors. In addition to improving its accuracy, Rhykerd and his colleagues hope to overcome two other technical challenges: decreasing size and cost. The machine is bound to be expensive, but the benefits could also be high. By way of comparison, the FAA’s Jankowski notes, the CTX5000, a million-dollar machine designed to inspect luggage, is already in use at some airports. “And this device is nowhere near that expensive,” he adds.