First comes the staccato pop, the sound of the canister being launched into the air. Seconds later, the tear gas envelops you. A burning sensation hits the skin on your face, and then you’re crying. It’s hard to breathe, and your nose is running, and you’re struggling to see, looking for a way out of the cloud.
This has been the experience of some people in Ferguson, Mo., this week. The suburb of St. Louis has been the site of daily protests since a white police officer, whose name has been withheld, shot and killed unarmed black 18-year-old Michael Brown on Saturday. Police have employed tear gas and rubber bullets to disperse the crowds, and the scene quickly began to resemble a war zone.
Tear gas is a nonlethal chemical weapon. Its use is banned in warfare under the Chemical Weapons Convention, a 1993 arms-control treaty with 190 member nations, including the United States. But the agreement bans tear gas only in combat, not domestic riot control, which means it can be used in the U.S. to disperse crowds.
The main ingredient in the most widely used kind of tear gas, CS gas, is called 2-chlorobenzalmalononitrile. The chemical compound reacts with moisture on the skin and in the eyes, causing searing pain, uncontrollable tearing, reflexive shutting of the eyelids, overproduction of mucus and difficulty breathing.
Tear gas is meant to hurt. In an interview with Vox’s Sarah Kliff on Thursday morning, Sven-Eric Jordt, a scientist at Duke University who researches the gas, described being gassed in the 1980s as a student protesting nuclear-waste transport in Germany:
It’s extremely painful. Your face starts burning very quickly, and your eyes start tearing. The eyelids shut and you can’t do much. It’s like cutting an onion but maybe 100 times more severe. It actually is the same pain receptors being activated as what happens with an onion, except you’re dealing with something that is about 100 or 1,000 times more potent.
What happens next is you get severe pain in your nose and throat and you also get a lot of mucus and snot production, and that obstructs your breathing. It’s like a burn injury or a chemical burn that happens.
The effects of exposure are temporary, and most of the symptoms clear within a few hours. Affected people should rinse their eyes with water as the first method of treatment. Some activists have found that milk or antacid solutions, like Maalox mixed with water, also help. The long-term effects of the gas, especially on children, older people, and those with preexisting respiratory conditions, are unclear.
The demonstrations in Ferguson are likely to continue. If people gather, so will police, bringing crowd-control methods like tear gas and rubber bullets with them. During a press conference by Ferguson police on Wednesday, Missouri state Sen. Maria Chappelle-Nadal, who had been hit with tear gas during a rally, asked Police Chief Thomas Jackson if it would happen again. “I just want to know if I’m going to be gassed again,” she said.
“I hope not,” Jackson replied. Police used tear gas there Wednesday night.