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.