Safety fears as US demonstrates crowd control heat-ray weapon
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Ian Sample, science correspondent
Friday January 26, 2007
The Guardian

It looks like a table top stuck on a Humvee, but to the US military it
is a revolutionary new weapon, a controversial heat-ray destined to
change the face of conflict by dispersing mobs, protecting military
bases and sorting friend from foe without inflicting injuries.

Called Silent Guardian, the prototype fires a high-intensity beam of
millimetre waves, inflicting a burning sensation like a light bulb
pressed against the skin. After 12 years in development it has been
demonstrated in public for the first time, at Moody air force base in
Georgia.

For the US defence department it marks the beginning of an era of
"non-lethal, directed energy, counter-personnel" weapons, intended to
cause temporary pain instead of killing or maiming. But critics
yesterday raised fears that the weapon could cause serious, even
life-threatening burns through accident or misuse.

During the demonstration a two-man crew used built-in rangefinders to
target volunteers playing the part of angry rioters 500 metres away.
Those hit by the beam jumped out of the way immediately to escape the
sudden flash of heat.

The beam has a range of up to 1km, 10 times that of other non-lethal
weapons such as plastic bullets or beanbag-firing guns. The waves
penetrate clothing, but travel less than half a millimetre into the
skin, where they cause water molecules to heat up. Within seconds, the
beam heats the skin to around 50C (122F). Military officials plan to use
the so-called Active Denial System to keep would-be attackers from
approaching military installations or navy ships in dock, or for
repelling mobs. It may also be useful in sorting combatants from
bystanders, who are more likely to quickly leave the scene.

Speaking from the Pentagon yesterday, Lieutenant-Colonel Brian Maka said
the device, which is not expected to be ready for deployment until 2010,
was built to "stop, deter and turn back an adversary at a distance that
lessens the potential for causing injury".

But Neil Davison, an expert in non-lethal weapons at the Disarmament
Research Centre, Bradford, said that in tests so far volunteers had been
allowed a cooling off period after being hit before being targeted
again. "There's no way of guaranteeing people won't be targeted for
longer in a real situation," he said.

Jürgen Altmann, an expert in military technology at Dortmund University,
found that if the beam is tracked on a person for longer the skin
temperature can quickly rise above 55C, and begin to burn.

"Even if they build in a mechanism that limits it to work for only a few
seconds at a time, people can immediately be re-targeted," he said. "If
more than 20% of their body receives second or third degree burns, it's
potentially life-threatening."

According to papers released under freedom of information requests,
mishaps during trials have caused blistering at least six times and one
second degree burn when the beam was fired on too high a setting.
According to the US military, the risk of injury is less than 0.1%.