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Sunday, March 3, 2024

PERSPECTIVE: Determining Reasonable and Proportional Use of Tear Gas

Recent deployments of tear gas in law enforcement settings have raised questions about its use managing riots and public-order incidents. Recent controversy has centered upon the deployment of tear gas against migrants rushing the U.S.-Mexico border fence by U.S. Border Patrol agents and its deployment by French gendarmes and police to quell violent ‘gilet jaunes’ protests in Paris and other cities across France. While the legality of the deployment of tear gas across international frontiers is contested, its use as a riot-control agent has also been questioned in the media.

Why Is Tear Gas Controversial?

The use of tear gas has a long and controversial history. As Anna Feigenbaum describes in her book Tear Gas: From the Battlefields of World War I to the Streets of Today police use of tear gas, which was first used by French troops during World War I, has become a stable of riot control and managing disorder worldwide. Despite this broad usage, its use in border control and policing riots and public assemblies (protests and demonstrations) is subject to criticism due to human-rights concerns. Indeed, the Organization for Security and Co-operation in Europe (OSCE) Office for Democratic Institutions and Human Rights cautions while widely employed there are situations where chemical agents should never be used. In their guidance, these include dispersal of peaceful assembly and situations involving vulnerable populations such as the elderly or children.

The human rights concerns surrounding the use of chemical agents – known as Riot Control Agents (RCAs) – have been voiced in both border and protest situations. Domestic use charts back to 1932 when National Guard troops deployed tear gas against the Washington, D.C., encampments of World War I veterans known as the “bonus army,” resulting in at least two deaths (a third death of an infant through asphyxiation was disputed). While the recent tear gas use at the border with Tijuana has been criticized by many observers and is under review by Customs and Border Protection (CBP) officials, tear gas has been deployed at the border many times in recent years. Other controversial contemporary uses include demonstrations ranging from Ferguson, Mo., to Gaza. Opposition to the use of tear gas by police centers on analogies to prohibitions on its battlefield use and health risks to vulnerable populations.

Tear Gas and Riot Control Agents (RCAs) Banned on Battlefield

Critics of tear gas use in civil settings are right in stating that chemical irritants, including tear gas (mostly CS) and other riot-control agents (RCAs), including pepper sprays such as OC and PAVA, are prohibited as a method of warfare. Frederick R. Sidell, MD, in his discussion on the medical aspects of riot-control agents, notes, ”Riot control agents are compounds that cause temporary incapacitation by irritation of the eyes (tearing and blepharospasm), causing them to close, and irritation of the upper respiratory tract. They are often called irritants, irritating agents, and harassing agents; the general public usually calls them tear gas.” Sidell observes that “more research is needed to illuminate the health consequences of riot control agents.” SIPRI (the Stockholm International Peace Research Institute) shares this assessment, noting that while the most commonly known RCAs – chloroacetophenone (CN), ortho-chlorobenzylidene-malononitrile (CS), dibenz (b,f)-1,4-oxazepine (CR) and oleoresin capsicum (OC, or pepper spray) – have short-lived acute effects, some cases of serious and irreversible effects have been documented. These effects can contribute to fatalities and are most pronounced when agents are used in high concentrations or against vulnerable populations (including infants, children, the elderly, asthmatics, persons with sickle cell traits, and persons with respiratory and heart disease).

Legal Status of Riot Control Agents (RCAs)

The prohibitions on chemical weapons are a customary international norm for both International Armed Conflicts (IACs) and Non-International Armed Conflicts (NIACs). These prohibitions are summarized in Customary International Humanitarian Law (IHL) Rule 74. Chemical Weapons. Specifically, the use of chemical weapons is prohibited in IACs in a series of treaties, including the Hague Declaration concerning Asphyxiating Gases, the Geneva Gas Protocol, the Chemical Weapons Convention and the Statute of the International Criminal Court. In addition, the Chemical Weapons Convention prohibits the use of chemical weapons in all warfare situations, including NIACs. Poison and poisoned weapons are also proscribed under customary international law (Customary IHL Rule 72). Law enforcement purposes outside armed conflict (both IACs and NIACs) are not prohibited by international law. That is, while Customary IHL Rule 74. Chemical Weapons and Customary IHL Rule 75. Riot Control Agents as well as state practice prohibit their use as a method of warfare during military hostilities, situations of civil strife or unrest such as domestic riot control are excluded.

In addition, the use of other toxic chemical agents (like the use of sleeping gas to immobilize terrorists as seen in Moscow’s Dubrovka theater siege) other than RCAs is likely prohibited via international human rights law (IHRL). The ICRC position on the use of toxic chemicals as weapons for law enforcement is summarized as: “The International Committee of the Red Cross (ICRC) believes that the use of toxic chemicals as weapons for law enforcement purposes should be limited exclusively to riot control agents, which have long been accepted as legitimate means for law enforcement. Riot control agents are defined in the 1993 Chemical Weapons Convention as ’[a]ny chemical not listed in a Schedule, which can produce rapidly in humans sensory irritation or disabling physical effects which disappear within a short time following termination of exposure.’”

Assessing the Situation

State practice confirms that states find the use of tear gas and riot-control agents (RCAs) a valuable tool in managing violent outbreaks, containing riots, and ensuring public order. Yet their use remains controversial. In the border control setting, the recent use of tear gas by CBP agents against migrants seeking asylum at the San Ysidro port of entry has been criticized by the American Civil Liberties Union (ACLU), among others. The cross-border issues are also controversial and Mexico has demanded an investigation into the use of non-lethal weapons in the Tijuana incident. The outcome of that investigation and the findings on the legal status of the cross-border use of tear gas and other RCAs remain to be seen. In the interim, public scrutiny on the use of non-lethal riot control agents continues.

In any event, this scrutiny demands transparency and potentially revisiting the rules of engagement governing the deployment of riot-control agents in both border and urban riot-control situations. The OSCE Human Rights Handbook on Policing Assemblies and the California POST (Commission on Peace Officer Standards and Training) guidelines on Crowd Management, Intervention, and Control are a good place to start when framing the training and operational preparations necessary before a police or border control force deploys riot-control agents. Both emphasize the need for democratic policing, implementation of an Incident Command System (ICS), risk assessment informed by intelligence, strategic, operational, and tactical planning for policing assemblies and managing disorder and violence.


Knowledge of crowd behavior and guidelines for the use of force and deployment of non-lethal weapons – including tear gas and RCAs – is essential. Warnings and dispersal orders should be given when feasible per Deorle v. Rutherford, 272 F.3d 1272, 1284 (9th Cir. 2001). Training to deploy RCAs must include legal issues, command decision-making, risk management, tactical considerations, and the need to assess weather conditions and crowd composition prior to deployment. Like all uses of force, the deployment of non-lethal RCAs must be objectively reasonable (under the totality of circumstances per Graham v. Connor, 490 U.S. 386 (1989) and proportional to the threat.

Public scrutiny demands measured use of RCAs commensurate with the threat faced. The use of force can at times appear brutal even when necessary and objectively reasonable. This places a premium on transparency, adherence to standards, training and exercising to enhance command capabilities and experience. Mitigating negative optics in the community is an essential ingredient of using non-lethal capabilities to address the “Strategic Challenge of Riots” for urban police in cities and for border security forces at the frontier.

The views expressed here are the writer’s and are not necessarily endorsed by Homeland Security Today, which welcomes a broad range of viewpoints in support of securing our homeland. To submit a piece for consideration, email [email protected]. Our editorial guidelines can be found here.

Dr. John P. Sullivan
Dr. John P. Sullivan
Dr. John P. Sullivan was a career police officer, now retired. Throughout his career he has specialized in emergency operations, terrorism, and intelligence. He is an Instructor in the Safe Communities Institute (SCI) at the University of Southern California, Senior El Centro Fellow at Small Wars Journal, and Contributing Editor at Homeland Security Today. He served as a lieutenant with the Los Angeles Sheriff’s Department, where he has served as a watch commander, operations lieutenant, headquarters operations lieutenant, service area lieutenant, tactical planning lieutenant, and in command and staff roles for several major national special security events and disasters. Sullivan received a lifetime achievement award from the National Fusion Center Association in November 2018 for his contributions to the national network of intelligence fusion centers. He has a PhD from the Open University of Catalonia, an MA in urban affairs and policy analysis from the New School for Social Research, and a BA in Government from the College of William & Mary.

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