Introduction

The development, production, stockpiling, transfer, and use of chemical weapons are prohibited under the 1993 Chemical Weapons Convention (CWC) and international humanitarian law (IHL). However, the legal position is less clear when it comes to Riot Control Agents (RCA) which are often labelled “non-lethal”. For instance, tear gas (TG), developed during World War One, is now commonly used for crowd dispersal. Over the course of six months, more than 10,000 canisters of TG were fired by the police in Hong Kong. This has raised concerns about the long-term health risks associated with constant exposure to chemicals in one of the world's most densely populated cities.

The potential effects of TG

Theoretically, TG only causes symptoms of irritation for a maximum of 20 to 60 seconds (see). However, repeated exposure to TG over a short period without adequate ventilation can also cause breathing difficulties, nausea, and vomiting, or even the risk of death from asphyxiation (see). In Zimbabwe an incident occurred where the use of excessive quantities of TG in confined spaces resulted in multiple injuries and deaths. The direct firing of TG cartridges at protestors also resulted in several fatalities in Palestine, Venezuela, and Iraq. Nonetheless, studies on the long-term sequelae, carcinogenicity, and environmental consequences of the use of TG in the urban environment are scarce.

Prohibition of RCAs only as a method of warfare

Under the CWC, the use of RCAs in armed conflicts is explicitly prohibited – but not for domestic riot control purposes. The International Committee of the Red Cross has argued that the prohibition of RCAs as a method of warfare is prohibited under customary international law and is applicable to both international and non-international armed conflicts. The prohibition of RCAs only as a method of warfare resulted from the fear of provoking retaliation with more lethal chemical agents rather than their potentially harmful effects. As internal disturbances and tensions are seen as falling below the threshold to trigger IHL, the manner and use of TG in law enforcement operations are only governed by the rules of international human rights law (IHRL). In this regard, the following rules are applicable.

The right to life and physical integrity

The direct firing of TG cartridges at civilians or the excessive use of TG in an indiscriminate manner may violate the right to life and physical integrity of those injured or killed. While the dispersal of a crowd using TG could serve the legitimate purpose of maintaining public order, the direct firing of TG at protestors was held by the European Court of Human Rights (ECtHR) to be both unnecessary and disproportionate. The positive obligation to respect the right to life also calls for clear instructions, better training, and disciplinary measures in law enforcement operations to ensure that TG is used in a correct, safe and non-lethal manner.

The prohibition against torture and inhumane treatment

Disproportionate and excessive use of violence by law enforcement officers could also amount to torture, and cruel, degrading or inhumane treatment. The ECtHR held that the close-range spraying of pepper spray amounted to cruel and degrading treatment (Ali Gunes v. Turkey). In Tali v. Estonia, the ECtHR also held that the use of pepper spray in a confined prison cell amounted to torture and inhumane treatment. By analogy, it can be claimed that the excessive use of TG in a confined area, such as a metro station, could also amount to impermissible torture and inhumane treatment against a targeted crowd.

Rights to health and the environment

Under IHRL, States also have a positive obligation to safeguard both the right to health and to the environment of its citizens. During the protests in Hong Kong, it was alleged that TG would generate dioxins under high temperatures. The Hong Kong Police has also admitted that TG which had passed the expiry date was frequently used. A report from Venezuela also showed that toxic chemicals such as cyanide oxide were found in expired TG cartridges. Despite the lack of extensive research on the potential long-term impact of TG, this positive obligation would entail a duty on States to inform themselves of the potential consequences before using weapons that could be hazardous to health. The precautionary principle would also require States to refrain from action which might cause environmental damage.

Conclusion

The use of TG and other RCAs has raised challenges under both IHL and IHRL. Currently, the use of TG is primarily governed by soft law instruments such as the OHCHR’s Guidance on Less-Lethal Weapons in Law Enforcement. Under the CWC, State parties are also not obliged to disclose information as to the quantities of RCAs, where they are stocked, or their exact chemical compositions. This primary reliance on human rights monitoring bodies has resulted in a serious gap in the regulations on the use of RCAs in domestic law enforcement operations.