Pubdate: Mon, 10 Jul 2000 Source: New York Times (NY) Copyright: 2000 The New York Times Company Contact: Address: 229 West 43rd Street, New York, NY 10036 Fax: (212) 556-3622 Website: Forum: Author: Sabra Chartrand


Each human body generates a column of slightly warm air that originates at the tops of the feet, swirls and rises, gathering speed and increasing in volume, staying with us as we move through the day and ascending the length of our torsos until it flows from the tops of our heads in an invisible geyser of air altered by movement and body temperature.

As this envelope of warmer air surrounds us and rises, it carries with it the skin particles that are continuously shed from our bodies.

Gary Settles has named this phenomenon the "human thermal plume." Mr. Settles, a scientist at the Penn State Research Foundation, says all people produce such an air column. And he has patented a system for sampling each person's plume to detect the presence of illegal drugs, or chemicals that might be used in weapons or explosives.

He has designed a portal similar to the metal detectors common at airports and courthouses. As people pass through, a sample of the air from each thermal plume would be analyzed to see if the person was carrying a bomb or other contraband.

Mr. Settles says his invention produces a socially acceptable, equal-opportunity inspection because it can sample molecules around every passenger in an airport without singling out individuals according to race or other characteristics. The system makes it practical to inspect everyone, he says, instead of selecting only a random number of travelers. That's because everyone continuously sheds microscopic flakes of skin.

"It has been found that the entire outer layer of skin is shed every one or two days," his patent application explains. "It turns out that some millions of skin flakes are shed by the average person every minute."

The flakes, he says, are tiny enough to pass through the weave of clothing and light enough to be swept up immediately into the air plume. "The air heated by the skin, being warmer and less dense than the surrounding air, rises naturally according to Archimedes' Principle," he says. "This generates a human boundary layer. For a standing person, the boundary layer begins at the ankles and travels up the legs and torso, growing thicker and faster as it moves." By the time it reaches the chest area, this layer of air is several centimeters thick and moving quickly. It forms the same way regardless of height, weight, or the amount or style of clothing, and every surface of the body contributes skin flakes to the moving air.

"Thus, any location where explosives might be concealed, such as the ankles, legs, thighs, waist, arms," he says, "all contribute about equally to the buoyant airstream which eventually rises above the body to form the thermal plume."

Mr. Settles' detector is a partly enclosed structure with a funnel-shaped collector above the heads of people who pass through and pause a few seconds. A fan or blower would draw the human thermal plume into a filter or particulate separator, where it would be analyzed in an ion mobility spectrometer, a device measuring electrons, for the presence of explosive molecules.

The sensor would be able to detect minute traces of plastic explosives that are imperceptible to metal detectors. Currently, specially trained dogs can sniff those small amounts, and hand-held wands or treated cloths wiped across a suspect surface can also isolate them.

But Mr. Settles thinks that neither wipes, wands nor dogs can realistically inspect the great number of travelers in an airport. He says his system would not require any contact with people being tested.

Mr. Settles says his invention could also be used to detect smuggled money, narcotics, chemical or biological warfare agents, nuclear substances like uranium, or other hazardous material. And he maintains that the skin flakes could provide samples of human DNA, though his patent says nothing about the privacy concerns that would be raised by such a feature. Mr. Settles received patent number 6,073,499.