What legal basis do police have for using tear gas on protesters?

The use of tear gas to disperse crowds protesting the shooting of unarmed teenager Michael Brown in Ferguson, Missouri has brought new attention to the increasing militarization of U.S. police forces and a variety of civilian crowd-control tactics considered acceptable by law enforcement.

Tear gas can be a variety of chemicals turned into an aerosol for easy deployment in riot situations. Regardless of circumstances, it is a chemical that stimulates pain, tearing, and burning in the eyes and skin; in some cases it even causes lethal asphyxiation. By edict of the 1929 Geneva Protocol, this means tear gas is prohibited from use in warfare.

Of course, that hardly means it isn’t used. Sven-Eric Jordt, a nerve gas expert at Yale University School of Medicine, says the chemical agent is still “used very frequently against civilians,” a practice he calls “illogical.”

In response to the 2013 Taksim Square protests in Istanbul, Dr. Jordt told National Geographic “Law enforcement has to weigh the risk of tear gas injury of bystanders against gaining control in a riot situation, under the assumption that rioters break the law. Governments need to put in place immediate decontamination procedures for areas, and especially residences, when tear gas is used.”

The police response to civilian protests in Ferguson is a reminder that police firing tear gas at civilians has become commonplace in the United States—one useful interactive map from The Atlantic illustrates 11 nerve gas deployments in the U.S. in 2013 alone.

On August 18, Amnesty International USA announced its intent to send a 13-person human rights delegation to investigate police procedures to control civilian protests in Ferguson. The U.S. National Guard has been deployed to help diffuse tensions, but as of August 18, riot control tactics by local police remain unchanged.

Andy is a graphics editor and cartoonist at Fusion.

Daniel Rivero is a producer/reporter for Fusion who focuses on police and justice issues. He also skateboards, does a bunch of arts related things on his off time, and likes Cuban coffee.