Ukraine Symposium – Russia’s Use of Riot Control Agents in Ukraine

Russian forces are reportedly using non-lethal chemical weapons known as riot control agents (RCA) to flush combatants out of trenches in eastern Ukraine before attacking them with conventional munitions. According to a report published by Reuters on April 17, the Ukrainian military has “recorded around 900 uses of riot control agents by Russia in the past six months out of over 1,400 since the Feb. 2022 invasion.”

Russia has denied previous claims of RCA use (and it has accused Ukraine’s military of using RCAs on the battlefield). However, Ukraine’s latest claims are difficult to dispute. For example, in December 2023, Forbes released a drone video of Russian forces dropping munitions, which release a white smoky substance, into a Ukrainian entrenchment before attacking two soldiers who are clearly affected. According to the latest U.S. Department of State Annual Report on Compliance with the Chemical Weapons Convention, the video depicts Russia’s 88th Brigade dropping Cheremukha (“Bird Cherry”) tear gas grenades into Ukrainian trenches. Finally, in a video posted by the State-controlled Russian Channel One, soldiers assigned to Russia’s 810th Naval Infantry Brigade openly admitted to dropping RCA grenades into Ukrainian trenches “in order to smoke them out from fortified positions.” The United States and Ukraine have each described this Russian tactic as illegal. Specifically, each State has accused Russia of violating the Chemical Weapons Convention.

In this post, I describe what RCAs are and how they typically impact the human body and psyche. I briefly explain why law enforcement agencies and militaries employ them. Next, I reiterate the treaty provisions and customary legal rules applicable to RCAs during armed conflict. Finally, I conclude that Russia’s use of RCAs in Ukraine is an unlawful method of warfare.

What Are Riot Control Agents?

Riot control agents, according to the U.S. Centers for Disease Control and Prevention, are “chemical compounds that temporarily make people unable to function by causing irritation to the eyes, mouth, throat, lungs, and skin.” The most common RCAs are “tear gas” and “pepper spray.” They are sometimes referred to as “lacrimators” (because they cause tear formation) or “sternutators” (because they may cause exposed people to sneeze).

Like everyone in the U.S. Army, I have been exposed to tear gas (during a training event intended to build confidence in the M50 gas mask), and it is completely, albeit temporarily, incapacitating. Riot control agents burn mucous membranes, including the eyes, tongue, and skin. Exposure to RCAs can also induce fright and anxiety (see this video of U.S. Army recruits being exposed to CS gas (at the 2:00 minute mark)). As one Ukrainian infantryman explained to Reuters, exposure to the Russian tear gas “disturbs and knocks you out. It makes it very difficult to carry out your duties once you’ve inhaled it.”

Common tear gases include the chemicals o-Chlorobenzylidene Malononitrile (CS), Chloroacetophenone (CN), or dibenzoxazepine (CR). According to the head of the Ukrainian military’s atomic, biological, and chemical defense forces, Russian forces have used various types of hand-grenade “loaded with CS, CN, and other gases.” However, the term “gas” is a misnomer. According to this training video presented by the U.S. Army’s Chemical Casualty Care Division in 2000, tear gases are, in fact, dispersals of aerosolized solid materials (e.g., powder) containing one or more of the chemicals listed above.

Pepper sprays include oleoresin capsicum (OC), which is derived from plants (e.g., chili pepper oil), or pelargonic acid vanillylamide, a synthetic version of OC. Interestingly, according to the online Weapons Law Encyclopedia, less common RCAs include the chemical N-nonanoylmorpholine, which is “manufactured predominantly in the Russian Federation and Ukraine.”

Finally, rare forms of RCAs include chloropicrin, “which induces severe vomiting and excessive tear formation.”Ukraine and the United States have accused Russian forces of conducting anti-personnel attacks with chloropicrin, a chemical compound used throughout the First World War. According to the Merck Manual, chloropicrin “is occasionally regarded as a riot-control agent, although it is more properly classified as a pulmonary agent.”

Why Use Riot Control Agents?

Modern RCAs were originally developed for domestic law enforcement purposes. The Parisian police were the first to deploy them; they did so to dispel anti-war rioters just before the First World War. Today, law enforcement organizations around the world use pepper sprays and tear gases lawfully to subdue violent people, disperse protestors, and control dangerous crowds (e.g., rioting inmates). Riot control agents are particularly attractive tools in domestic settings because a miniscule amount (i.e., 5 mg-min/m³) will temporarily incapacitate a person. It requires a substantial amount (i.e., 61,000 mg-min/m³) to kill a person.

Many States also maintain RCAs for military use. As Lieutenant Colonel Matt Montazzoli correctly noted in 2021, during armed conflict, “RCA may not lawfully be deployed to deliberately target combatants, but it is misleading to claim they can never be employed during combat.” In accordance with U.S. law (Executive Order 11850), members of the U.S. military can employ RCAs “in war . . . in defensive modes to save lives.”

Thus, according to the U.S. Department of Defense (DoD) Law of War Manual (§ 6.16.2) the U.S. military may lawfully employ RCAs during armed conflict:

– in riot control situations in areas under direct and distinct U.S. military control, including controlling rioting prisoners of war;

– in situations in which civilians are used to mask or screen attacks and civilian casualties can be reduced or avoided;

– in rescue missions in remotely isolated areas, of downed aircrews and passengers, and escaping prisoners; and

– in rear echelon areas outside the zone of immediate combat to protect convoys from civil disturbances, terrorists, and paramilitary organizations.

One author surmised that RCAs could have been used during the Battle of Mogadishu in October 1993 in a defensive mode as U.S. military personnel were maneuvering from Bakara Market to Mogadishu International Airport. Theoretically, RCAs might have been useful to U.S. forces attempting to disperse crowds at Hamid Karzai International Airport during the final withdrawal from Afghanistan. And in a previous post for Articles of War, Major Kevin Coble and I discussed how RCAs may be used to save hostages taken in the context of an armed conflict.

Treaty Law and Customary International Law

The United States does not consider RCAs to be “chemical weapons” banned by customary law or the 1925 Protocol for the Prohibition of the Use of Asphyxiating, Poisonous or Other Gases, and of Bacteriological Methods of Warfare (see also, International Committee of the Red Cross (ICRC), Customary International Law Study, Rule 75).

However, the 1993 Convention on the Prohibition of the Development, Production, Stockpiling and Use of Chemical Weapons and on their Destruction (the Chemical Weapons Convention or CWC), which is applicable in both international and non-international armed conflicts, specifically regulates RCAs. Article II(7) of the CWC defines RCA as, “[a]ny chemical . . . which can produce rapidly in humans sensory irritation or disabling physical effects which disappear within a short time.”

Article I(5) of the CWC, prohibits the “use [of] riot control agents as a method of warfare” (emphasis added). Russia and Ukraine are both party to the CWC.

The CWC does not define the phrase “as a method of warfare.” However, the term generally refers to warfighting tactics (see the DoD Law of War Manual, § 5.1.1). For example, as the Manual on International Law Applicable to Air and Missile Warfare makes clear, “methods of warfare” include “attacks and other activities designed to adversely affect the enemy’s military operations or military capacity” (p. 5). The relevant question, then, considering the reports described above is whether Russia’s use of RCAs to flush Ukrainian soldiers out of trenches (and then attack them) constitutes a “method of warfare.”

In my view, it does. In other words, the use of RCAs to flush combatants from defensive positions for the purpose of subsequently attacking them constitutes a “method of warfare” prohibited by the CWC. Many others agree. For example, during testimony taken as part of the CWC ratification process in the U.S. Senate, Dr. Amy Smithson, an expert on chemical and biological weapons, explained,

The law of war describes a method of warfare as a way to attain military objectives . . . . According to this definition, flushing enemy soldiers from foxholes into the line of fire, or launching an RCA attack on an enemy command post easily qualify as method of warfare uses.

In a 2001 article for the Naval Law Review, then-Major Ernest Harper, noted that, “[e]mployment of RCA in advance of lethal weapons, whether chemical or conventional, against enemy troops, positions and equipment is the archetypal use as a method of warfare.”

Finally, in a 2007 article for the University of New Hampshire Law Review, Professor Joseph Tessier argued convincingly that the use of chemical agents to flush enemy fighters from defensive positions so that they may be killed (the so-called tactic of “shake and bake”) is a method of warfare. Therefore, Russia’s use of RCAs in Ukraine violates Article I(5) of the CWC and customary international law.

However, it would be somewhat disingenuous to ignore the fact that many militaries, including the U.S. military, have used chemicals (most notably white phosphorous) to flush combatants out of enclosed spaces for the purposes of attacking them. It is an ancient tactic. For example, between 431 and 404 B.C., the Spartans “saturated wood with pitch and sulphur and burned it under the walls of Platea and Belium . . . in the hope of choking the defenders and rendering the assault less difficult.”

In modern times, the U.S. Army relied on white phosphorous to defeat German forces in the Second World War. According to one U.S. Army officer quoted in Time Magazine in 1943 (reportedly at the conclusion of the Sicilian campaign),

The Germans are very allergic to [white phosphorus]. We would root them out of their foxholes with well-placed rounds of phosphorus and when we had them above ground we plastered them with HE [high explosives].

The British Army used white phosphorous against the Argentinians for similar purposes during the Falklands War. Of course, these examples pre-date the CWC, which came into effect in April 1997. But the U.S. and British armies relied on “shake and bake” tactics again in Iraq between 2004 and 2005 after ratifying the CWC. According to Colonel Tim Collins of the British Special Air Service (discussing operations in Basra),

The star of the show was the new grenade which had only been on issue since the previous summer. It absolutely trashed the inside of the room it was put into. I directed the men to use them where possible with white phosphorus, as the noxious smoke and heat had the effect of drawing out enemy from cover, while the fragmentation grenade would shred them.

Additionally, as Pentagon spokesperson Lieutenant Colonel Barry Venable explained in 2005,

When you have enemy forces that are in covered positions that your high explosive artillery rounds are not having an impact on and you wish to get them out of those positions, one technique is to fire a white phosphorus round into the position because the combined effects of the fire and smoke—and in some cases the terror brought about by the explosion on the ground—will drive them out of the holes so that you can kill them with high explosives.

The important factual distinction is that white phosphorous is not an RCA and, therefore, not explicitly regulated by Article I(5) of the CWC. As others have noted, white phosphorous falls outside of the CWC’s purview because it is not “specifically designed to cause death or other harm” by means of a “toxic chemical.” Thus, as the DoD Law of War Manual makes clear, “white phosphorous may be used as an anti-personnel weapon” (§ 6.14.2.1).

Conclusion

While the distinction between RCAs and white phosphorous may not be satisfying, there is a distinction, nonetheless. The CWC and customary international law strictly prohibit the use of RCAs like tear gases and pepper spray as a “method of warfare” during armed conflict. The Russian Army’s use of CS and CN gases to irritate entrenched Ukrainian soldiers before attacking them with conventional munitions is, therefore, a violation of the law of armed conflict.

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Major John C. Tramazzo is an active-duty Army judge advocate and a military professor in the Stockton Center for International Law in Newport, Rhode Island.

Photo credit: Marines from Arlington, VA