Tear gas, formally known as a lachrymatory agent or lachrymator (from lacrima meaning "tear" in Latin), is a non-lethal chemical weapon that stimulates the corneal nerves in the eyes to cause tears, pain, and even blindness. Common lachrymators include pepper spray (OC gas), CS gas, CR gas, CN gas (phenacyl chloride), nonivamide, bromoacetone, xylyl bromide, syn-propanethial-S-oxide (from onions), and Mace (a branded mixture).
Lachrymatory agents are commonly used for riot control. Their use as chemical warfare agents is prohibited by various international treaties. During World War I, more toxic lachrymatory agents were used.
Tear gas works by irritating mucous membranes in the eyes, nose, mouth and lungs, and causes crying, sneezing, coughing, difficulty breathing, pain in the eyes, temporary blindness, etc. With CS gas, symptoms of irritation usually appear after 20–60 seconds of exposure and commonly resolve within 30 minutes of leaving (or being removed from) the area. With pepper spray (OC gas), the onset of symptoms, including loss of motor control, is almost immediate, forcing the victim to abandon aggressive behavior in 90% of cases.
Lachrymators are thought to act by attacking sulfhydryl functional groups in enzymes. One of the most probable protein targets is the TRPA1 ion channel that is expressed in sensory nerves (trigeminal nerve) of the eyes, nose and mouth.
As with all non-lethal, or less-than-lethal weapons, there is some risk of serious permanent injury or death when tear gas is used. This includes risks from being hit by tear gas cartridges, which include severe bruising, loss of eyes, skull fracture, and even death. While the medical consequences of the gases themselves are typically limited to minor skin inflammation, delayed complications are also possible: people with pre-existing respiratory conditions such as asthma, who are particularly at risk, may sometimes require hospitalization or even ventilation support. Skin exposure to CS may cause chemical burns or induce allergic contact dermatitis. When people are hit at close range or are severely exposed, eye injuries involving scarring of the cornea can lead to a permanent loss in visual acuity.
Use in war
Use of tear gas in warfare (as all other chemical weapons) is prohibited by various international treaties that most states have signed. Police and private self-defense use is not banned in the same manner. Armed forces can legally use tear gas for drills (practicing with gas masks) and for riot control. First used in 1914, xylyl bromide was a popular tearing agent since it was easily brewed.
Use in riot control
Certain lachrymatory agents are often used by police to force compliance, most notably tear gas. In some countries (e.g., Finland, Australia, and the United States), another common substance is mace, which is the same as CN and is used as a self-defense weapon, in small spray cans. Xylyl bromide, CN and CS are the oldest of these agents, and CS is the most widely used.
Typical manufacturer warnings on tear gas cartridges state "Danger: Do not fire directly at person(s). Severe injury or death may result." Such warnings are not necessarily respected, and in some countries, disrespecting these warnings is routine. In the 2013 protests in Turkey, there were hundreds of injuries among protesters targeted with tear gas projectiles.
However, tear gas guns do not have a manual setting to increase or decrease the range of fire. The only way to adjust the projectile's range is to aim towards the ground at the correct angle. Incorrect aim will send the capsules away from the protesters, causing risk for ordinary citizens instead. For example, this occurred during the 2013 protests in Brazil.
The most obvious counter-measure is to prevent contact with the gas by leaving the area. Alternatively, a variety of protective equipment may be used, including gas masks and respirators. In riot control situations, protesters sometimes use a wide variety of equipment (aside from simple rags or clothing over the mouth) such as swimming goggles and adapted water bottles.
Once a person has been exposed, a variety of treatments may be used. The standard first aid for burning solutions in the eye is irrigation (spraying or flushing out) with water, and some evidence suggests that diphoterine solution, a first aid product for chemical sprays, may help with ocular burns or chemicals in the eye.
Activists in the United States, the Czech Republic, and Turkey have reported using antacid solutions such as Maalox diluted with water as a home remedy for tear gas attacks. Vinegar, vaseline, milk and lemon juice solutions have also been used by activists. It is unclear how effective these remedies are. In particular, vinegar itself can burn the eyes and prolonged inhalation can also irritate the airways.
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