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Tear Gas

What Tear Gas Is and How Tear Gas Works

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This photo shows tear gas in use.

This photo shows tear gas in use during riots following the election of Nicolas Sarkozy to the presidency of the French republic, May 6, 2007.

Mikael Marguerie
Tear gas, or lachramatory agent, refers to any of a number of chemical compounds that cause tears and pain in the eyes and sometimes temporary blindness. Tear gas can be used for self-defense, but it is more commonly used as a riot control agent and as a chemical weapon.

How Tear Gas Works

Tear gas irritates the mucous membranes of the eyes, nose, mouth, and lungs. The irritation may be caused by a chemical reaction with the sulfhydryl group of enzymes, though other mechanisms also occur. The results of exposure are coughing, sneezing, and tearing. Tear gas generally is non-lethal, but some agents are toxic.

Examples of Tear Gas

Actually, tear gas agents aren't usually gases. Most compounds used as lachrymatory agents are solids at room temperature. They are suspended in solution and sprayed as aerosols or in grenades. There are different types of compounds that may be used as tear gas, but they often share the structural element Z=C-C-X, where Z denotes carbon or oxygen and X is bromide or chloride.
  • CS (chlorobenzylidenemalononitrile)
  • CR
  • CN (chloroacetophenone) which may be sold as Mace
  • bromoacetone
  • phenacyl bromide
  • xylyl bromide
  • pepper spray (derived from chili peppers and most commonly dissolved in a vegetable oil)
Pepper spray is a little different from the other types of tear gas. It is an inflammatory agent that causes inflammation and burning of the eyes, nose, and mouth. While it is more debilitating than a lachrymatory agent, it is harder to deliver, so it is used more for personal protection against a single individual or animal than for crowd control.

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