Tear gas (also called CS, CN, or CX) and pepper spray (OC) are chemical compounds that are weapons designed to be used by the military and police to disperse crowds and subdue individuals. They are mucous membrane (the inside of your mouth and nose, among other places, are lined with mucus membrane) and skin irritants. They are mixed with solvents, and delivered through the use of propellants. Some people think some of these can cause cancer, birth defects and genetic mutations. In Seattle, one batch of tear gas contained methylene chloride, a highly toxic solvent which can cause mental confusion, headache, tingling of the limbs, rapid heartbeat, visual and auditory hallucinations, menstruation cycle disruption, spontaneous abortion, and varying effects on lungs and the digestive system.
Tear gas and pepper spray can be sprayed from small hand-held dispensers or large fire-extinguisher size tanks. Tear gas is most commonly deployed via canisters, which are fired into crowds, sometimes directly at people. Don't pick up the canisters without gloves as they are extremely hot. Be aware that the time it takes you to throw it will allow you to be heavily exposed.