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 within 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 Article I.5 of the Chemical Weapons Convention. Article II.9 of the CWC specifically authorizes their use for civilian law enforcement .
The active ingredient in pepper spray is capsaicin, which is a chemical derived from the fruit of plants in the Capsicum genus, including chiles. A synthetic analogue of capsaicin, pelargonic acid vanillylamide (desmethyldihydrocapsaicin), is used in another version of pepper spray known as PAVA spray which is used in England. Another synthetic counterpart of pepper spray, pelargonic acid morpholide, was developed and is widely used in Russia. Its effectiveness compared to natural pepper spray is unclear and it has caused some injuries.
Pepper spray typically comes in canisters, which are often small enough to be carried or concealed in a pocket or purse. Pepper spray can also be bought concealed in items such as rings. There are also pepper spray projectiles available, which can be fired from a paintball gun. Having been used for years against demonstrators , it is increasingly being used by police in routine interventions.
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. It is used as a hand-held spray or can be fired in canisters that heat up spewing out a 'gas' cloud at a steady rate. Technically, these clouds are aerosols, and not true gases.
Popular tear gases include the eye irritants ortho-chlorobenzylidene-malononitrile (CS gas), chloroacetophenone (CN gas), and dibenz (b,f)-1,4-oxazepine (CR gas). Among a long list of substances, these three have become of greater importance than the others because of their effectiveness and low risks when used. Today, CS has largely replaced CN as 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.