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French gendarmes mobiles using tear gas

These gendarmes mobiles are ready for riot control; they carry gas masks and one has a grenade launcher for sending tear gas canisters

This gendarme mobile is shooting tear gas canisters using a Alsetex "Cougar" launcher

A riot control agent generally refers to pepper spray or OC and tear gas lachrymatory agent (or lacrimatory agent). These are chemical compounds, such as benzyl bromide, or CS gas (o-Chlorobenzylidene malononitrile) that cause the eyes to sting and water. The word "lachrymatory" comes from the Latin lacrima meaning "a tear". The term "riot control agent" is a euphemism.

Any chemical that has this effect may be called lachrymatory, but "riot control agent" or "tear gas" implies a lachrymatory chemical chosen because it is assumed to be non-lethal.

These chemicals disperse a crowd that could be protesting, in a riot, or to clear a building. They can rapidly produce sensory irritation or disabling physical effects which usually disappear 15 minutes (for tear gas) and up to 2 hours (for pepper spray) following termination of exposure. They can also be used for chemical warfare defense training, although their use in warfare itself is a violation of the Chemical Weapons Convention, Article II, Section 9 of which still authorizes their use for civilian law enforcement ^[1].

Tear gas is a non-specific term for any chemical that is used to cause temporary incapacitation through irritation of eyes and/or respiratory system. Tear gas is used as a hand-held spray or in grenades. It is widely used by police forces to subdue people in arrest or riot situations.

Popular tear gases include the eye irritants CS, CN, and CR. Another widely used chemical eye and respiratory irritant is OC pepper spray.

These gases are usually fired in canisters that heat up spewing out a 'gas' cloud at a steady rate. Technically, these clouds are aerosols, and not true gases.

Among a long series of substances, three have become of greater importance than the others. They are effective and imply low risks when used. These substances are chloroacetophenone (codename CN), ortho-chlorobenzylidene-malononitrile (codename CS) and dibenz (b,f)-1,4-oxazepine (codename CR). CN was formerly the most widely used tear gas. Today, CS has largely replaced CN and is probably the most widely used tear gas internationally.

At room temperature, these tear gases are white solid substances. They are stable when heated and have low vapor pressure. Consequently, they are generally dispersed as aerosols. All of them have low solubility in water but can be dissolved in several organic solvents. Hydrolysis of CN is very slow in water solution, also when alkali is added. CS is rapidly hydrolyzed in water solution (half-life at pH 7 is about 15 min. at room temperature) and extremely rapid when alkali is added (half-life at pH 9 is about 1 min.). CR is hydrolyzed only to a negligible extent in water solution.

CN and CR are, thus, difficult to decompose under practical conditions, whereas CS can easily be inactivated by means of a water solution. Skin is suitably decontaminated by thorough washing with soap and water. CS is then decomposed whereas CN and CR are only removed.

Decontamination of material after contamination with CS can be done with a 5-10 % soda solution or 2 % alkaline solution. If this type of decontamination cannot be accomplished (e.g., contaminated rooms and furniture), then the only other means is by intensive air exchange—preferably with hot air.

Exposed streets and sidewalks will have toxic and irritating CS powder that will be stirred into the air by traffic and pedestrians long after the cloud has dissipated, and should be washed away with water.

In contrast to human beings, domesticated animals generally have low sensitivity to tear gases. Dogs and horses can therefore be used by police for riot control even when tear gas is used.^{[citation needed]}

Backpack dispensers for riot control agents, when the intent is to use a larger quantity than possible with grenades, are one type of device used by organizations that might, for example, need to cover a prison yard ^[2] Dispensers are also made for attachment to helicopters; see CBU-19 ^[3].

Many war video games use teargas as a weapon, such as Battlefield 2, which makes the player's vision blur when inside the cloud of teargas.

• Pepper spray
• Use of poison gas in World War I
• Review about Pharmacology, Toxicology, Biochemistry and Chemistry of several riot control agents:

Olajos EJ, Salem H (2001). "Riot Control Agents: Pharmacology, Toxicology, Biochemistry and Chemistry". J Appl Toxicol 21 (5): 355-91. doi:10.1002/jat.767. PMID 11746179. 

• Riot Agents

1. ^ 9. "Purposes Not Prohibited Under this Convention" means
2. ^ Commercial Backpack Blower / Sprayer System,US Army CBDCOM,June 1998.
3. ^ Operation TAILWIND Review Extract of U.S Air Force Report,Air Force Historical Office, July 1998