PATENTS

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.