Rule 75. The use of riot-control agents as a method of warfare is prohibited.
State practice establishes this rule as a norm of customary international law applicable in situations constituting military hostilities during international and non-international armed conflicts, as opposed to domestic riot control.
Before the adoption of the Chemical Weapons Convention, there was disagreement as to whether riot-control agents are prohibited under the Geneva Gas Protocol. The vast majority of States are of the opinion that the Geneva Gas Protocol prohibits the use of all asphyxiating and poisonous gases and analogous materials, including riot-control agents, and apply it as such.
In the late 1960s and early 1970s, Australia, Portugal and the United Kingdom changed their earlier positions, stating that the Geneva Gas Protocol did not apply to certain riot-control agents.
A consistent exception to the majority view is that of the United States, which maintains that the customary prohibition of chemical weapons does not apply to agents with temporary effects.
During the Vietnam War, when it was not yet a party to the Geneva Gas Protocol, the United States declared that it had applied the Protocol’s provisions, which did not stop it from using riot-control agents.
However, the United States is now a party to the Chemical Weapons Convention, which prohibits the use of riot-control agents as a method of warfare and which allows no reservations. The United States has therefore renounced “first use of riot control agents in war except in defensive military modes to save lives” because, according to the United States, use in such modes would not constitute a “method of warfare”.
During the negotiations leading to the adoption of the Chemical Weapons Convention, the vast majority of States, including Australia and the United Kingdom, were of the view that riot-control agents must not be used in hostilities. The final wording of the treaty makes a distinction between use during hostilities as a method of warfare, which is prohibited, and use for purposes of law-enforcement, which is permitted.
This distinction has been confirmed by State practice since then. In particular, the prohibition of the use of riot control agents as a method of warfare is set forth in several military manuals.
It is also included in the legislation of several States.
Although the use of riot control agents has been reported in the Greek and Spanish civil wars and by South Vietnam in the Vietnam War,
the trend has been towards a prohibition of their use in all armed conflicts. This is reflected in the fact that the prohibition of the use of riot-control agents as a method of warfare contained in the Chemical Weapons Convention applies to all conflicts. It is significant that States did not consider making a general exception in the Convention allowing for the use of riot-control agents in non-international armed conflicts.
The prohibition of the use of riot control agents as a method of warfare in non-international armed conflicts is also set forth in several military manuals.
The United States has stated that the prohibition of the use of riot control agents as a method of warfare “applies in international as well as internal armed conflict”.
No official contrary practice was found with respect to either international or non-international armed conflicts. No State has claimed the right to use riot control agents as a method of warfare in military hostilities. As explained in the military manual of the Netherlands, the prohibition of the use of riot control agents as a method of warfare is inspired by the fact that use of tear gas, for example, in armed conflict “runs the danger of provoking the use of other more dangerous chemicals”.
A party which is being attacked by riot control agents may think it is being attacked by deadly chemical weapons and resort to the use of chemical weapons. It is this danger of escalation that States sought to avert by agreeing to prohibit the use of riot control agents as a method of warfare in armed conflict. This motivation is equally valid in international and non-international armed conflicts.