<nettime> New Scientist: Microwave Crowd Dispersal Tested (ADT)

[Soenke Zehle <soenke.zehle@web.de>]

http://www.newscientist.com/hottopics/tech/heatison.jsp

New Scientist.com The World's No.1 Science & Technology News Service

Microwave beam weapon to disperse crowds

19:00   24  October  01 Jeff Hecht, Boston

Tests of a controversial weapon that is designed to heat people's skin
with a microwave beam have shown that it can disperse crowds. But critics
are not convinced the system is safe.

Last week, the Air Force Research Laboratory (AFRL) in New Mexico finished
testing the system on human volunteers. The Air Force now wants to use
this Active Denial Technology (ADT), which it says is non-lethal, for
peacekeeping or riot control at "relatively long range" - possibly from
low-flying aircraft.

ADT uses a 2-metre dish to create a narrow beam of microwaves that can be
scanned across a crowd or even aimed at individuals. AFRL is using
infrared photography to analyse the heating effect on the volunteers'
bodies.

AFRL says that the 3-millimetre wavelength radiation penetrates only 0.3
millimetres into the skin, rapidly heating the surface above the 45 �C
pain threshold. At 50 �C, they say the pain reflex makes people pull away
automatically in less than a second - it's said to feel like fleetingly
touching a hot light bulb. Someone would have to stay in the beam for 250
seconds before it burnt the skin, the lab says, giving "ample margin
between intolerable pain and causing a burn".


Little data

But critics question the AFRL's claims that the weapon's undisclosed
exposure levels are safe. John Pike of think tank Globalsecurity.org fears
that the beam power needed to scare people may be too close to the level
that would injure them. Air Force scientists helped set the present skin
safety threshold of 10 milliwatts per square centimetre in the early
1990s, when little data was available, says Louis Slesin, editor of
Microwave News.

That limit covers exposure to steady fields for several minutes to an hour
- but heating a layer of skin 0.3 mm thick to 50 �C in just one second
requires much higher power and may pose risks to the cornea, which is more
sensitive than skin. A study published last year in the journal Health
Physics showed that exposure to 2 watts per square centimetre for three
seconds could damage the corneas of rhesus monkeys.

19:00 24 October 01





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