Tear gas

As with all non-lethal or less-lethal weapons, there is some risk of serious permanent injury or death when tear gas is used.[4][5][2] This includes risks from being hit by tear gas cartridges that may cause severe bruising, loss of eyesight, or skull fracture, resulting in immediate death.[6] A case of serious vascular injury from tear gas shells has also been reported from Iran, with high rates of associated nerve injury (44%) and amputation (17%),[7] as well as instances of head injuries in young people.[8]

While the medical consequences of the gases themselves are typically limited to minor skin inflammation, delayed complications are also possible. People with pre-existing respiratory conditions such as asthma are particularly at risk. They are likely to need medical attention[3] and may sometimes require hospitalization or even ventilation support.[9] Skin exposure to CS may cause chemical burns[10] or induce allergic contact dermatitis.[3][11] When people are hit at close range or are severely exposed, eye injuries involving scarring of the cornea can lead to a permanent loss in visual acuity.[12] Frequent or high levels of exposure carry increased risks of respiratory illness.[2]

In the 2019–20 Chilean protests various people have suffered complete and permanent loss of vision in one or both eyes as result of the impact of tear gas grenades.[13][14][15]

TRPA1 ion channels expressed on nociceptors have been implicated as the site of action for CS gas, CR gas, CN gas (phenacyl chloride) and bromoacetone in rodent models.[16][17]

During World War I, various forms of tear gas were used in combat and tear gas was the most common form of chemical weapon used. None of the belligerents believed that the use of irritant gases violated the Hague Convention of 1899 which prohibited the use of "poison or poisoned weapons" in warfare. Use of chemical weapons escalated during the war to lethal gases, after 1914 (during which only tear gas was used).

The US Chemical Warfare Service developed tear gas grenades for use in riot control in 1919.[18]

Use of tear gas in warfare, as with all other chemical weapons, was prohibited by the Geneva Protocol of 1925: it prohibited the use of "asphyxiating gas, or any other kind of gas, liquids, substances or similar materials", a treaty that most states have signed. Police and civilian self-defense use is not banned in the same manner. [19]

Tear gas was used in combat by Italy in the Second Italo-Ethiopian War, by Japan in the Second Sino-Japanese War, Spain in the Rif War and by the United States in the Vietnam War.[20]

Tear gas exposure is an element of military training programs, typically as a means of improving trainees' tolerance to tear gas and encouraging confidence in the ability of their issued protective equipment to prevent chemical weapons exposure.[21][22][23]

Certain lachrymatory agents, most notably tear gas, are often used by police to force compliance.[5] In some countries (e.g., Finland, Australia, and United States), another common substance is mace. The self-defense weapon form of mace is based on pepper spray which comes in small spray cans. Versions including CS are manufactured for police use.[24] Xylyl bromide, CN and CS are the oldest of these agents. CS is the most widely used. CN has the most recorded toxicity.[3]

Typical manufacturer warnings on tear gas cartridges state "Danger: Do not fire directly at person(s). Severe injury or death may result."[25] Tear gas guns do not have a manual setting to adjust the range of fire. The only way to adjust the projectile's range is to aim towards the ground at the correct angle. Incorrect aim will send the capsules away from the targets, causing risk for non-targets instead.[26]

A variety of protective equipment may be used, including gas masks and respirators. In riot control situations, protesters sometimes use equipment (aside from simple rags or clothing over the mouth) such as swimming goggles and adapted water bottles.[27]

Activists in United States, the Czech Republic, Venezuela and Turkey have reported using antacid solutions such as Maalox diluted with water to repel effects of tear gas attacks,[28][29][30] with Venezuelan chemist Mónica Kräuter recommending the usage of diluted antacids as well as baking soda.[31] There have also been reports of these antacids being helpful for tear gas,[32] and for capsaicin-induced skin pain.[33]

During the 2019 Hong Kong protests, frontline protesters became adept at extinguishing tear gas: they formed special teams that spring into action as soon as it is fired. These individuals generally wear protective clothing, including heat-proof gloves, or cover their arms and legs with cling film to prevent the painful skin irritation. Canisters are sometimes picked up and lobbed back at police or extinguished straight away with water, or neutralised using objects such as traffic cones. They share information about models of 3M respirator filters which have been found to be most effective against tear gas, and where those models could be purchased. Other volunteers carry saline solutions to rinse the eyes of those affected.[34] Similarly, Chilean protesters of Primera Línea have specialized individuals collecting and extinguishing the tear gas grenades. Others act as tear gas medics, while yet another group, the so-called shield-bearers, protect the protesters from the direct physical impact of the grenades.[35]

Vinegar, petroleum jelly, milk and lemon juice solutions have also been used by activists.[45][46][47][48] It is unclear how effective these remedies are. In particular, vinegar itself can burn the eyes and prolonged inhalation can also irritate the airways.[49] Though vegetable oil and vinegar have also been reported as helping relieve burning caused by pepper spray,[40] Kräuter suggests the usage of baking soda or toothpaste, stating that they trap the particles emanating from the gas near the airways that are more feasible to inhale.[31] A small trial of baby shampoo for washing out the eyes did not show any benefit.[39]