The compound 2-chlorobenzalmalononitrile (also called o-chlorobenzylidene malononitrile; chemical formula: C10H5ClN2), a cyanocarbon, is the defining component of the lachrymatory agent commonly called CS gas, a tear gas used as a riot control agent, and is banned for use in warfare pursuant to the 1925 Geneva Protocol.
CR gas or dibenzoxazepine (chemical name 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. A report from the Porton Down laboratories described exposure as "like being thrown blindfolded into a bed of stinging nettles", and it earned the nickname "firegas".
In its effects, CR gas is very similar to CS gas (o-chlorobenzylidene malononitrile), but twice as potent, even though there is little structural resemblance between the two. For example, 2 mg of dry CR causes skin redness in 10 min, 5 mg causes burning and erythremia, and 20 mg—strong pain. Water usually amplifies the pain effect of CR on skin. CR aerosols cause irritation at concentrations of 0.2 mcg/L, becoming intolerable at 3 mcg/L. The LD50 of CR through air inhalation 350 mg·min/L.
Tear gas, also known as a lachrymatory agent or lachrymator (from Latin lacrima 'tear'), sometimes colloquially known as "mace" after the early commercial self-defense spray, is a chemical weapon that stimulates the nerves of the lacrimal gland in the eye to produce tears. In addition, it can cause severe eye and respiratory pain, skin irritation, bleeding, and blindness. Common lachrymators both currently and formerly used as tear gas include pepper spray (OC gas), PAVA spray (nonivamide), CS gas, CR gas, CN gas (phenacyl chloride), bromoacetone, xylyl bromide, chloropicrin (PS gas) and Mace (a branded mixture).
While lachrymatory agents are commonly deployed for riot control by law enforcement and military personnel, its use in warfare is prohibited by various international treaties. During World War I, increasingly toxic and deadly lachrymatory agents were used.
During 12–16 August 1969, there was an outbreak of political and sectarian violence throughout Northern Ireland, which is often seen as the beginning of the thirty-year conflict known as the Troubles. There had been sporadic violence throughout the year arising out of the Northern Ireland civil rights campaign, which demanded an end to discrimination against Catholics and Irish nationalists. Civil rights marches had been attacked by Protestant loyalists, and protesters often clashed with the Royal Ulster Constabulary (RUC), the overwhelmingly Protestant police force.
On 12 August, the Battle of the Bogside erupted in Derry: three days of fierce clashes between the RUC and thousands of Catholic/nationalist residents of Derry's Bogside district. The besieged residents built barricades and set up first aid posts and workshops for making petrol bombs. Police fired CS gas at rioters for the first time in the history of the UK. In support of the Bogsiders, on 13 August Catholics/nationalists held protests elsewhere in Northern Ireland, some of which led to violence. The bloodiest clashes were in Belfast, where seven people were killed and hundreds wounded, five of them Catholic civilians shot by police. Protesters clashed with both the police and with loyalists, who attacked Catholic districts. Scores of homes and businesses were burnt out, most of them owned by Catholics, and thousands of mostly Catholic families were driven from their homes. In some cases, police helped the loyalists and failed to protect Catholic areas. Both republican and loyalist paramilitaries were involved in the clashes. There were also clashes between protesters and police in Armagh, where a protester was killed by police, as well as in Dungannon and Newry.
PAVA spray is an incapacitant spray similar to pepper spray. It is dispensed from a handheld canister, in a liquid stream. It contains a 0.3% solution of pelargonic acid vanillylamide (PAVA), also called nonivamide, a synthetic capsaicinoid (analogue of capsaicin), in a solvent of aqueous ethanol. The propellant is nitrogen. This solution has been selected because this is the minimum concentration which will fulfill the purpose of the equipment: namely, to minimise a person's capacity for resistance, without unnecessarily prolonging their discomfort.
PAVA is significantly more potent than CS gas. The liquid stream is a spray pattern and has a maximum effective range of up to four metres (13 ft). Maximum accuracy, however, will be achieved over a distance of 1.25–2 metres (4.1–6.6 ft). The operating distance is the distance between the canister and the subject's eyes, not the distance between the user and the subject.