Active Denial System

The Active Denial System (ADS) is a non-lethal directed-energy weapon developed by the U.S. military,^[2] designed for area denial, perimeter security and crowd control.^[3] Informally, the weapon is also called the heat ray^[4] since it works by heating the surface of targets, such as the skin of targeted human beings. Raytheon had marketed a reduced-range version of this technology.^[5] The ADS was deployed in 2010 with the United States military in the Afghanistan War, but was withdrawn without seeing combat.^[6] On August 20, 2010, the Los Angeles Sheriff's Department announced its intent to use this technology to control incarcerated people in the Pitchess Detention Center in Los Angeles, stating its intent to use it in "operational evaluation" in situations such as breaking up prisoner fights.^[7] As of 2014, the ADS was only a vehicle-mounted weapon, though U.S. Marines and police were both working on portable versions.^[8] ADS was developed under the sponsorship of the Department of Defense Non-Lethal Weapons Program with the Air Force Research Laboratory as the lead agency.^[9][10] There are reports that Russia^[11] and China are developing their own versions of the Active Denial System.^[12]

The ADS works by firing a high-powered (100 kW output power)^[13] beam of 95 GHz waves at a target, which corresponds to a wavelength of 3.2 mm.^[14] The ADS millimeter wave energy works on a principle similar to a microwave oven, exciting the water and fat molecules in the skin, and instantly heating them via dielectric heating. One significant difference is that a microwave oven uses the much lower frequency (and longer wavelength) of 2.45 GHz. The short millimeter waves used in ADS only penetrate the top layers of skin, with most of the energy being absorbed within 0.4 mm (1⁄64 inch),^[15] whereas microwaves will penetrate into human tissue about 17 mm (0.67 in).^[16]

The ADS's effect of repelling humans occurs at slightly higher than 44 °C (111 °F), though first-degree burns occur at about 51 °C (124 °F), and second-degree burns occur at about 58 °C (136 °F).^[17] In testing, pea-sized blisters have been observed in less than 0.1% of ADS exposures, indicating that second degree surface burns have been caused by the device.^[17] The radiation burns caused are similar to microwave burns, but only on the skin surface due to the decreased penetration of shorter millimeter waves. The surface temperature of a target will continue to rise so long as the beam is applied, at a rate dictated by the target's material and distance from the transmitter, along with the beam's frequency and power level set by the operator. Most human test subjects reached their pain threshold within 3 seconds, and none could endure more than 5 seconds.^[18]

A spokesman for the Air Force Research Laboratory described his experience as a test subject for the system:

For the first millisecond, it just felt like the skin was warming up. Then it got warmer and warmer and you felt like it was on fire. ... As soon as you're away from that beam your skin returns to normal and there is no pain.

Like all focused energy, the beam will irradiate all matter in the targeted area, including everything beyond/behind it that is not shielded, with no possible discrimination between individuals, objects or materials. Anyone incapable of leaving the target area (e.g., physically handicapped, infants, incapacitated, trapped, etc.) would continue to receive radiation until the operator turned off the beam. Reflective materials such as aluminum cooking foil should reflect this radiation and could be used to make clothing that would be protective against this radiation.^[19]

Following approximately ten thousand test exposures of volunteers to ADS beams,^[18] a Penn State Human Effects Advisory Panel (HEAP) concluded that ADS is a non-lethal weapon that has a high probability of effectiveness with a low probability of injury:^[17]

• no significant effects for wearers of contact lenses or other eyewear (including night vision goggles)
• normal skin applications, such as cosmetics, have little effect on ADSʼs interaction with skin
• no age-related differences in response to ADS exposures
• no effect on the male reproduction system
• damage was the occurrence of pea-sized blisters in less than 0.1% of the exposures (6 of 10,000 exposures).^[18]

In April 2007, one airman in an ADS test was overdosed and received second-degree burns on both legs, and was treated in a hospital for two days.^[19][20] There was also one laboratory accident in 1999 that resulted in a small second-degree burn.^[18]

ADS was developed as a non-lethal weapon. According to Department of Defense policy, non-lethal weapons "are explicitly designed and primarily employed so as to incapacitate personnel or material, while minimizing fatalities, permanent injury to personnel, and undesired damage to property and the environment."^[39] ADS has applications for crowd control and perimeter defense, and filling "the gap between shouting and shooting." Other crowd control methods – including pepper spray, tear gas, water cannons, slippery foam and rubber bullets – carry implicit dangers of temporary or permanent injury or accidental death, and often leave residue or residual material. Combinations of acoustic and optical system platforms with ADS can be used to effectively communicate to, warn of escalation of force, introduce optical and auditory deterrents and step function the escalation of transmitted force from relatively benign to ultimately forced dispersal of a crowd, or to deny them from an area or access to an area. A group of people can theoretically be dispersed or induced to leave an area in a manner unlikely to damage personnel, non-involved civilians (no stray bullets), or to nearby buildings or the environment.

Non-lethal weapons are intended to provide options to U.S. troops, for example, "to stop suspicious vehicles without killing the drivers".^[40] Although the ADS millimeter wave frequency does not affect a car's electronic components, it can be used to deter a driver in an approaching vehicle.^[41] In a broader strategic context, non-lethal weapons such as ADS have the potential to offer "precision, accuracy, and effective duration that can help save military and civilian lives, break the cycle of violence by offering a more graduated response, and even prevent violence from occurring if the opportunity for early or preclusionary engagement arises."^[42]

The Council on Foreign Relations noted that "wider integration of existing types of nonlethal weapons (NLW) into the U.S. Army and Marine Corps could have helped to reduce the damage done by widespread looting and sabotage after the cessation of major conflict in Iraq."^[43]

In Afghanistan, the need to minimize civilian casualties has led to restrictive rules of engagement on the use of lethal force by US troops. A National Public Radio correspondent in Afghanistan "witnessed troops grappling with the dilemma of whether to shoot."^[44] Non-lethal weapons such as ADS provide an option for US forces in those situations.^[32]

The effects of this radio frequency on humans have been studied by the military for years, and much, but not all of the research has been published openly in peer-reviewed journals.^[45]

A news article criticized the sheer amount of time it is taking to field this system, citing the potential it had to avert a great deal of pain and suffering in volatile areas around the world.^[46]

While it is claimed not to cause burns under "ordinary use",^[47][48] it is also described as being similar to that of an incandescent light bulb being pressed against the skin,^[14] which can cause severe burns in just a few seconds. The beam can be focused up to 700 meters away, and is said to penetrate thick clothing although not walls.^[49] At 95 GHz, the frequency is much higher than the 2.45 GHz of a microwave oven. This frequency was chosen because it penetrates less than 1⁄64 of an inch (0.40 mm),^[50] which – in most humans, except for eyelids and the thinner skin of babies – avoids the second skin layer (the dermis) where critical structures are found such as nerve endings and blood vessels.

The early methodology of testing, in which volunteers were asked to remove glasses, contact lenses and metallic objects that could cause hot spots, raised concerns as to whether the device would remain true to its purpose of non-lethal temporary incapacitation if used in the field where safety precautions would not be taken. However, these tests were early in the program and part of a thorough and methodical process to demonstrate the safety and effectiveness of the technology, which has now involved more than 600 volunteer subjects and some 10,200 exposures. As safety was demonstrated in each step of the process, restrictions were removed, and now, according to ADS proponents, there are no restrictions or precautions necessary for volunteers experiencing the effect.^[51] Long-term exposure to the beam may cause more serious damage, especially to sensitive tissues, such as those of the eyes.^[52] Two people received second degree burns after exposure to the device during testing.^[48]

Critics cite that despite the stated intent of the ADS is to be a non-lethal device designed to temporarily incapacitate, and despite that ADS had undergone legal and treaty compliance reviews by AF/JAO and determined to be in compliance with the applicable laws and treaties,^[53] that modifications or misuse by an operator could nevertheless turn the ADS into a more damaging weapon which could potentially violate international conventions on warfare.

Some have focused on the lower threshold of use which may lead those who use them to become "trigger-happy", especially in dealing with peaceful protesters. Others have focused on concerns that weapons whose operative principle is that of inflicting pain (though "non-lethal") might be useful for such purposes as torture, as they may leave little or no evidence of use, but undoubtedly have the capacity to inflict horrific pain on a restrained subject. According to Wired, the ADS has been rejected for fielding in Iraq due to Pentagon fears that it would be regarded as an instrument of torture.^[54]

Defense contractor Raytheon has developed a smaller version of the ADS, the Silent Guardian. This stripped-down model is primarily marketed for use by law enforcement agencies, the military and other security providers. The system is operated and aimed with a joystick and aiming screen. The device can be used for targets over 250 metres (820 ft) away,^[14] and the beam has a power of 30 kilowatts.^[55]

The Los Angeles County Jail installed the smaller-sized unit, under the name Assault Intervention Device, on the ceiling of the Pitchess Detention Center in 2014.^[56]

• Area denial weapons, to prevent an adversary from occupying or traversing an area
• Heat Ray
• Long-range acoustic device
• Radiation