Tests of a weapon designed to heat people’s skin using a beam similar to a microwave pulse have shown that it can disperse crowds.
The Air Force Research Laboratory (AFRL), based in New Mexico have allegedly finished testing the system, known rather worryingly as the ‘Heat Ray,’ on human volunteers.
The US Air Force now wants to use this ‘Active Denial Technology (ADT)’, which it says is ‘non-lethal’, for peacekeeping or riot control use only at “a relatively long range” – possibly using low-flying drone aircraft.
ADT uses a 2 Metre direct-able dish to create a narrow microwave beam that can be scanned across a crowd or even aimed at specific individuals.
The AFRL has used infrared imaging to analyse the effects on the volunteers’ bodies.
They confidently state that the 3-millimetre wavelength radiation penetrates ‘only 0.3 millimetres into the skin’, which rapidly heats the surface above the 45 °C pain threshold.
At 50 °C, the human body’s involuntary pain reflex makes people pull away automatically after less than a second of exposure – it has been reported to feel similar to pressing your skin against a hot light bulb.
“You would have to stay in the beam for 250 seconds before it burnt the skin,” the scientists say, giving “ample margin between intolerable pain and causing a burn”.
Understandably, critics have questioned 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 scatter crowds, may be too close to the level that would injure them.
Air Force scientists (no surprise there) helped set the present skin safety threshold of 10 milliwatts per square centimetre in the early 1990s, when little comparative data was available, said 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 in the journal Health Physics has shown that exposure to 2 watts per square centimetre for three seconds irreparably damaged the corneas of the rhesus monkeys it was tested on.
On August 20, 2010, the Los Angeles Sheriff’s Department announced it’s intent to use this technology on prisoners in the Pitchess Detention Centre, and Russia are allegedly developing their very own version.