CR gas

CR gas or dibenzoxazepine, chemically dibenz[b,f][1,4]oxazepine, is an incapacitating agent and a lachrymatory agent. CR was developed by the British Ministry of Defence as a riot control agent in the late 1950s and early 1960s.

Physical properties
CR is a pale yellow crystalline solid with a pepper-like odor. It is slightly soluble in water and does not degrade in it. CR is usually presented as a microparticulate solid, in the form of suspension in a propylene glycol based liquid. Contrary to its common name, it is not actually a gas but is solid at room temperature.

The dibenz[b,f][1,4]oxazepine moiety is present in the typical antipsychotic drug loxapine, but unlike CR, loxapine is not reactive and is not an irritant. CR was first synthesised in 1962.

These gases are usually fired in canisters (LACR) that heat up, producing an aerosol cloud at a steady rate.

Effects
CR gas is a lachrymatory agent (LA) exerting its effects through activation of the TRPA1 channel. Its effects are approximately 6 to 10 times more powerful than those of CS gas. CR causes intense skin irritation, particularly around moist areas, blepharospasm causing temporary blindness, coughing and gasping for breath, and panic. It is capable of causing immediate incapacitation. It is a suspected carcinogen. It is toxic, but less so than CS gas, by ingestion and exposure. However, it can be lethal in large quantities. In a poorly ventilated space, an individual may inhale a lethal dose within minutes. Death is caused by asphyxiation and pulmonary edema.

The effect of CR is long-term and persistent. CR can persist on surfaces, especially porous ones, for up to 60 days.

Treatment
While CS can be decontaminated with a large amount of water, use of water may exacerbate the effects of CR. Skin contaminated with CR gas may become extremely painful in contact with water for up to 48 hours after contamination.

Medical treatment is mostly palliative. The contaminated clothing has to be removed. The eyes and skin can be washed, the eye pain can be alleviated with medications.

Use
In the late 1980s, CR was used in the townships in South Africa. It caused some fatalities, particularly among children.

Republican groups in northern Ireland have alleged that British Army and Royal Ulster Constabulary units used CR gas against Republican prisoners.

Because of its alleged carcinogenic properties, the United States does not utilize CR for riot control. The U.S. military classification for this chemical agent is combat class chemical weapon causing serious side effects for humans.