How Tear Gas Works

Police and military forces around the world use tear gas for a reason: It disperses crowds effectively through the application of temporary physiological discomfort. A crowd of rioters may intend to storm a barricade one moment, but priorities have a way of changing when physical pain and irritation enter the picture. Gassed people quickly become "incapable of effective concerted action," to quote the 1969 "Police Chemical Agents Manual."

The term "tear gas" may refer to any of several riot control agents, including chloroacetophenone (CN), an ingredient in the chemical spray Mace. Collectively, we refer to these chemicals as tear producers, or lacrimators. Yet modern tear gas almost always boils down to a particular chemical agent: orthochlorobenzalmalononitrile (CS) or C₁₀H₅ClN₂, a crystalline powder with a peppery odor.

Chemists first synthesized CS in the late 1950s as a crowd suppressant. Within a few years, it quickly replaced the less-powerful CN as the go-to tear gas. It remains in use around the world to this day.

Don't let the tears fool you. Lacrimators are irritants, not mood-altering chemicals. CS gas causes a severe burning sensation upon contact with skin. Your sensory nerves sound the alarm to your brain, sending the memo, "Hey, please remove this awful chemical from your skin before it physically harms you."

And indeed, prolonged exposure to the CS can cause rashes and chemical burns. When the irritant encounters the human eye, the stakes are much higher. The sensory nerves send a signal to your brain stem, which in turn sends hormones to tear glands in the eyelids. These glands pump out a salty wash of protein, water, mucus and oil to help rid your sensitive peepers of the irritant as quickly as possible.

This is how tear gas produces tears, but the effects of exposure don't necessarily stop with the ocular immune system. Inhale CS gas and the burning sensation will kick-start similar defenses in the nose and the respiratory system: flowing mucus and hacking coughs, all in an attempt to rid the body of its irritant. Nausea and vomiting also may occur.

The good news is that in most cases, these symptoms vanish within an hour of exposure. An affected person generally flees from the source of the exposure and all that crying, coughing and vomiting helps rid the body of the chemical in no time. Then the irritation subsides.

Except when it doesn't.

Not every exposure to CS gas goes according to plan. For starters, some people exhibit varying degrees of genetic or acquired immunity to the irritant -- a reality most frequently encountered in boot camp.

Members of the U.S. Army undergo routine tear gas exposure as part of their basic training. After all, as a short-term irritant, CS gas injects a healthy dose of realism into a test aimed to boost soldiers' confidence in the gear and procedures that protect them from nuclear, biological and chemical threats.

The soldiers strap on their gas masks and enter an enclosed mask confidence chamber filled with CS gas. Then their drill sergeant orders them to remove their masks and answer questions such as, "What is your name, rank and serial number?" This helps to ensure that the solider breathes the gas-tainted surrounding air.

For most soldiers, what follows is intense burning. A small minority, however, experiences far milder symptoms -- perhaps just a mere sneeze or two, thanks to a natural immunity. Drill sergeants, on the other hand, who regularly encounter CS gas in these tests, may benefit from acquired immunity. Over time, they've simply built up a degree of tolerance in the same way you might build up a tolerance to spicy food or even poison. These veterans also know what to expect from the gas and don't panic when the symptoms pop up.

Other folks, however, exhibit heightened sensitivity to CS gas. Children, the elderly and individuals with pre-existing conditions (such as asthma or a compromised immune system) are likely to experience prolonged symptoms, the severity of which depends entirely on the method, duration and intensity of the exposure.

Tear gas exposure inside a closed space is far more intense than exposure in the open air -- and it also introduces additional dangers. As we'll discuss on the following page, heat often plays a role in the dispersal of CS gas from a canister or grenade. Studies have found that, in an enclosed space, such thermal dispersion can generate additional semivolatile organic air contaminants [source: Lenhart]. For this reason, training programs usually use specially designed CS capsules rather than tear gas canisters.

In addition, while police forces often employ tear gas to force an adversary out of an enclosed space, the gas can induce panicked behavior if an exit isn't readily accessible [source: PBS].

Long-term or heavy exposure to CS gas can result in severe symptoms or even permanent damage in the form of glaucoma or blindness. In rare cases, exposure can end in death due to serious internal chemical burns or respiratory failure. In 2011, a 36-year-old Palestinian woman named Jawaher Abu Rahmeh died from respiratory failure and then cardiac arrest following exposure at a West Bank protest [source: The Guardian].

The occasional ingestion of CS produces a certain amount of abdominal turmoil but no permanent damage.

So how does tear gas find its way to a target? Find out on the next page.

Interestingly enough, the star ingredient of tear gas, orthochlorobenzalmalononitrile (CS), is actually a solid powder. In order to disperse this tear-jerker as a gas, chemists require the help of a dispersal agent, such as the solvent methylene chloride, which carries the particles through the air. A typical tear gas grenade contains a host of additional chemicals for heat dispersal of the irritant. When the solid CS powder heats up, it vaporizes into an easily dispersed aerosol.

Methods of tear gas dispersal vary, but the irritant usually scatters into crowds as a component of an aerosol solution, explosive device or smoke. In addition to hand-thrown grenades and canisters, military and police forces also use tear gas mortars and projectiles for use in riot guns, alongside such ordnance as rubber bullets. Aircraft and vehicle dispersal devices have also seen action, as have personal ones such as hand-held sprays and even gas-emitting batons.

The dispersal method itself can prove dangerous, however, as illustrated in 2011 when a police tear gas canister fractured the skull of protester and Iraq war veteran Scott Olsen [source: McKinley].

CS gas rapidly loses its effectiveness in a given environment -- especially in the open air. To counteract this property, the U.S. Department of Defense has created at least three different CS variants [source: Lenhart]:

What should you do when you encounter tear gas? How can you prepare for scenarios where it might be deployed? Skip to the next page to find out.

Whether you're an active protester, a world traveler or an enthusiastic sports fan, you might just have a future date with a face full of tear gas. So what's a person to do if he or she wants to avoid the worst of the symptoms? Aside from experiencing exposure to CS gas in a controlled environment such as military boot camp, your best bet is to know ahead of time what to do and what not to do.

The first thing you'll want to do is follow your instincts and move away from the tear gas release point. If you're outside, that means shifting away from the billowing cloud of gas or a smoking canister. If you're lying on the ground, get up and move, because heavier-than-air CS gas will settle into a thick ground-level layer. If you're inside a building, get outside to fresh air as soon as possible. The less you're exposed to the irritant, the better off you'll be.

Next, let's worry about your eyes. Wash them with clean water as soon as possible and keep doing it for at least 15 minutes. If you wear contacts, take them out and don't stick them back in. If you wear glasses, take them off and wash them with soap and water before sliding them back on again. If medical aid is available, seek it out for additional washes and treatments that will help prevent serious eye damage.

Now let's turn to your breathing. Assuming you've made it to some fresh air, breathe in and out. Get as much fresh oxygen into your lungs and blood as possible. Medics may administer asthma medications to help with severe symptoms. If you've managed to ingest any of the irritant, drink lots of water and induce vomiting. Then seek medical attention.

Skin and clothing should get your attention next. If your garments are coated with CS, get them off as soon as possible. If you can, avoid removing clothing over your head; cut it off instead. You don't want any more of the irritant coming into contact with your face. Next, wash your body thoroughly with soap and water. If irritation persists, seek medical attention.

Finally, wash contaminated clothing separately from the rest of your laundry. Jewelry should be cleaned as well. Be sure to avoid detergents that contain chlorine bleach as they can react with CS to form even more toxic compounds.

Follow these steps, as advised by the U.S. Army Center for Health Promotion and Preventive Medicine and The New York Department of Health and Mental Hygiene, and you should survive your tear gas encounter just fine. But let's hope you never have to find out.

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