Chemical irritants are a group of crowd-control weapons (CCWs) that include a variety of chemical compounds intended to produce sensory irritation and pain. Conventionally referred to as “tear gas” or “riot-control agents”, chemical irritants come in a variety of formulations, sizes, concentrations and delivery mechanisms, depending on the manufacturer and the context for which they are intended.
Historically categorized as non-lethal or less lethal, chemical irritants benefit from a general perception that they do not cause permanent injury or death, but instead have mostly short-term effects such as transient lacrimation (flowing of tears), ocular irritation and pain, blepharospasm (eyelid spasm), dermal pain, respiratory distress and the psychological effects of disorientation and agitation. This perception is now being challenged, with more evidence of associated moderate and permanent injuries as well as deaths.
Chemical irritants include a wide range of agents that have been developed and deployed for many decades in addition to ones that are currently under development. There are four chemical compounds that are most frequently cited in purchase orders, reports and studies in the past three decades: chlorobenzalmalononitrile (agent CS), chloroacetophenone (agent CN), oleoresin capsicum (agent OC, also known as pepper spray), and OC’s synthetic form, PAVA. Of these four, the two most commonly used by law enforcement agencies in recent years for crowd control are agents CS and OC.
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1920–1950
Agent CS is the most commonly used chemical irritant. It was developed in the 1920s in the United States …
… and was introduced as a weapon by the US military to replace agent CN in the 1950s.
1950–2000
Agent CS then became a frequently used military weapon in the second half of the twentieth century …
… and was famously deployed in the Vietnam War by the US military.
2000–present
Military use is now banned, but agent CS is widely used by law enforcement agencies in many countries.
It is often the weapon of choice in the context of protest and civilian crowd management.
Today
The US is still the largest manufacturer of agent CS, but many other countries have developed the industry …
… among them Brazil, the Republic of Korea (South Korea), India, Israel and France.
Mechanism of action
Chemical irritants are used for crowd dispersal, or for individual control or incapacitation by causing pain and sensory irritation. Agent CS and other gases can be released into the air as a fine particulate smoke, vapour or liquid spray (aerosol). They are typically deployed in two ways: in the form of spray or as a canister/grenade in crowd-control settings.
However, mechanisms of delivery vary: these include pellets and pepper-balls, used in targeting individuals, as well as water cannons, which, along with grenades and canisters, provide less discriminate means of crowd control. Pellets can be designed for a pepper spray gun, which uses a compressed gas cartridge capable of firing 21 rounds.
The spray variants of agents CS and OS, and other gases, are usually available in the form of an enclosed unit under pressure, and are released as a fine spray by means of a propellant gas. Powder forms of chemical irritants are contained in canisters or grenades and are typically triggered through a thermal explosion to disperse widely in the surrounding area.
Chemical irritants are an indiscriminate weapon by design: especially when they are delivered by firing a grenade or a canister, limiting exposure to individuals or small groups is virtually impossible, and the risk of affecting bystanders and individuals other than the intended targets is high.
Chemical irritants are an indiscriminate weapon by design: limiting exposure to individuals or small groups is virtually impossible, and the risk of affecting bystanders and individuals other than the intended targets is high.
Health effects
The health effects of chemical irritants are highly dependent on the chemical of exposure, the dose (based on quantity and time), the conditions of exposure, the deployment mechanism, and the individual’s risk factors and access to egress and care. Most exposures to chemical irritants result in temporary pain and discomfort lasting less than one hour.
Dose exposure is dependent on numerous factors that together can lead to higher or lower concentrations of the chemical in proximity to an individual.
An individual’s own health risks are related to exposure as well as their personal characteristics and access to care. For instance, certain groups that are particularly at risk from the effects of chemical irritants, and for whom they may be life threatening, include older people, children and people with respiratory problems or skin sensitivity.
More serious injuries can affect all organ types: eye injuries, lung damage, skin burns and others. Canisters and grenades directed at crowds are known to be a significant source of traumatic injury.
Case studies
What has changed?
Much of the research in the past six years amplifies the concerns presented in the original 2016 report. But there have been several new concerns raised as well.
Tear gas has continued to be used extensively across the globe. From Hong Kong to Chile, chemical irritants continue to be the primary riot-control agent used by police to repress and disperse demonstrations. In the United States, the police response to protests against police violence in the wake of George Floyd’s murder were met with tear gas use in dozens of cities.
In Colombia, the use of US-made VENOM launchers, which can deploy dozens of grenades at once from stations mounted on vehicles, shields or static installations, has rapidly increased the use of chemical irritants in protests.
Beyond the use of traditional canisters and grenades, the use of diluted chemical irritants in water cannons is a growing problem, with reports of skin irritation and pain that are difficult to investigate.
In the past six years, there have been few to no efforts from governments or regulating bodies to better understand the composition of chemical irritants or make that knowledge available to the public or to healthcare workers.
Since 2020, the ongoing Covid-19 pandemic has resulted in millions of deaths from respiratory illness.
In this context, the extensive use of chemical irritants during the pandemic has increased the risk of adverse medical effects due to Covid-19’s effects on breathing and the lungs.
The psychological impact of the use of CCWs has not been well studied or documented in the medical literature, but cases documented in this review indicate that exposure to chemical irritants may result in significant psychological symptoms and long-term disability.
An area of increasing importance, but where no clinical studies have yet been published, is the growing awareness of the effects of chemical irritants on women and reproductive health.
Mounting worries about the environment have led to more thoughtful consideration of the contamination of ground and water as a result of the deployment of chemical irritants, both in those areas and in the areas where products may run off to.
The psychological impact of the use of CCWs has not been well studied or documented in the medical literature, but cases documented in this review indicate that exposure to chemical irritants may result in significant psychological symptoms and long-term disability.
