Riot control agents (and their abbreviations) discussed in this article include tear gas (CS); chloroacetophenone (CN); chloroacetophenone in chloroform (CNC); bromobenzenecyanide (CA); dibenz-(b,f)-1,4-oxazepine (CR); CN, carbon tetrachloride, and benzene (CNB); and chloropicrin (PS).
Riot control agents are chemical compounds that temporarily disable victims due to their noxious contamination of skin, eyes, mucous membranes, and respiratory tract. They are not meant to kill, but to render a victim momentarity helpless. However, in certain circumstances, they can cause long-term medical sequelae, including death.[1, 2]
No antidotes exist. Treatment is supportive and begins with removal from the site of exposure. Patients with significant exposures require decontamination.[1, 3, 4, 5, 6]
The sole purpose of irritants (also known as tear gas, riot control agents, and lachrymators) is to produce immediate dermatological, respiratory, and ocular discomfort in order to render the victim incapable of fighting or resisting. Police forces use them for crowd control, and military forces currently use them mainly for training. These agents were used before World War I, and in that war, they were the first chemical agents used—well before the better-known chlorine, phosgene, and mustard gas. The United States used them during the Vietnam War to deny tunnel access to its enemies.[1]
The United States excludes these agents from the 1925 Geneva Convention banning other chemical and biological weapons. Dispersal is allowed in specific US military operations but only by presidential order.
Tear gas (CS) and chloroacetophenone (CN) are by far the most important pulmonary irritants. The two-letter codes designating these types of compounds were assigned by the North Atlantic Treaty Organization (NATO); the abbreviation for tear gas reflects the fact that it was first synthesized by Corson and Stoughton.[7]
CN was the primary pulmonary irritant after World War I until the development of CS in 1928. CS was found to be more potent (10 times more potent as a lachrymator than CN) but less toxic. In approximately 1959, CS replaced CN as the principal military and law enforcement riot control agent.
CS is the familiar tear gas most often used by police for crowd control (eg, the police in the United Kingdom have used CS as an incapacitant for the past decade). CN has been available as Mace, a product that had been used for personal protection. Capsaicin, or pepper spray, has to some extent replaced CN as a personal protective agent, with less dangerous effects.[8]
Although CS and CN are the most important agents in this class, several others require mention. Chloropicrin (PS) and bromobenzenecyanide (CA) were developed before World War I. Both largely have been replaced, as they were too lethal for their intended effects but not lethal enough to compete with the more effective blistering and nerve agents. PS is still seen occasionally as a soil sterilant, fumigant or grain disinfectant.[3, 6]
Attempts to make CN more effective resulted in the creation of CNB (CN, carbon tetrachloride, and benzene), chloroacetophenone in chloroform (CNC), and CNS (CN, chloroform, and PS). However, CS proved more effective and less toxic than any of the CN series and largely has replaced them. While the clinical effects of a CS spray may last for days, subjects sprayed with CS have shown no convincing physical evidence of pathology for up to 10 months afterward.[9]
Dibenz-(b,f)-1,4-oxazepine (CR) is a more recent tear gas, first synthesized in 1962. It reportedly is more potent and less toxic than CS. Part of its high safety profile is due to its low volatility, which minimizes its effects deep in the pulmonary system. However, it is still is not used widely. Pepper spray, or oleoresin capsicum (OC), is also considered a riot control agent. A 1% solution is sold commercially to the public, but 10% solutions exist. OC causes the release of a neuropeptide (substance P) that causes pain and inflammation. A recent review states that the neurogenic inflammation caused by capsaicinoid in the pepper spray is the cause of the compound's irritative effects.[10] However, at high concentrations and with prolonged exposure, fatalities with capsaicinoids have been reported.[11]
The possibility of secondary contamination is very real. In one incident, CS was used to flush out possible stowaways on a cargo vehicle. When the cargo was finally delivered to 16 stores within Scotland, 21 workers experienced itching and running eyes, rhinorrhea, a burning sensation on the face and hands, and a burning throat.[12] In case studies, secondary exposures have also affected emergency department personnel and anesthetists.[2]
Onset of symptoms occurs in seconds to several minutes after exposure to pulmonary irritants. Most cases are brief and self-limited, and most persons do not seek medical care. Without continuing exposure, symptoms typically resolve spontaneously in 15-30 minutes, and most persons do not seek medical care. However, serious effects, including death, have been reported.[3, 4, 5, 6] See Presentation.
Riot control agents are solids with low vapor pressures that are dispersed as fine particles or in solution. CS and CN are SN2 alkylating agents and react at nucleophilic sites. Although the mechanism is presently unclear, injuries caused by this class of agents may be caused by inactivation of sulfhydryl-containing enzymes such as lactic dehydrogenase and a specific coenzyme in the pyruvate decarboxylase system (disulfhydryl form of lipoic acid).[2]
Research has indicated that these agents are extremely potent activators of the body's TRPA1 (a family of transient receptor potential ion channel) receptors (ie, mechanical stress sensors).[1, 13] Since anti‐inflammatory and analgesic effects have been observed for TRPA1 inhibitors in multiple models of chemical injury and inflammation, it is possible that TRPA1 inhibitors could alleviate at least some of the tear gas–induced effects. The conclusion of clinical trials using TRPA1 inhibitors in diabetic neuropathic patients is eagerly awaited with the hope that more advanced inhibitors will be made available for testing in other conditions, including irritant and tear gas agent exposures.[14]
No race- or sex-related susceptibility to pulmonary irritants exists. Chemical irritants, especially those deployed in aerosolized forms, are inherently indiscriminate and can affect not only the intended targets but also peaceful demonstrators, bystanders, nearby communities and residences, and law enforcement officers themselves. The majority of people injured are young adults, consistent with typical protest demographics. Children are more vulnerable to severe injuries from chemical toxicity. The elderly and those with chronic diseases are also prone to worse outcomes.[15]
The prognosis for patients with irritant exposure is excellent. The few reported dangerous effects occur rapidly.
Short-term effects of pulmonary irritants predominate. Fatalities, albeit few, have occurred at high concentrations and with prolonged exposure.[15] In fact, the risk of death is directly related to the agent, the concentration of the agent, the duration of exposure, the proximity to the source, and location (ie, indoors vs. outdoors).[1]
A systematic review of CS that included 90 cases of CS exposure reported the following distribution of effects[2] :
Complications include the following:
A 2015 review of 10 RCA-related deaths found that RCAs were the sole cause of death in three cases, a secondary cause in three (asthma, asphyxia), and contributory in four. Pepper spray (oleoresin capsicum; OC) was the RCA involved in eight of the cases, while chloroacetophenone (CN) and tear gas (CS) caused one apiece.[16]
Different types of symptoms tend to vary in their duration. A systematic review of CS exposure found the following typical durations[2] :
In rare cases, particular reactions may persist for much longer than usual (eg, dermatitis lasting for several months).
Upon exposure to a riot control agent, the key steps are to remove oneself from the site of dissemination as quickly as possible—the mantra is to go "uphill, upwind, upstream—and then begin the process of decontamination, should sufficent material remain in contact with eyes, skin, and clothes.
Symptoms caused by a riot control agent should subside within half an hour. Persistence of effects beyond that time suggests that the agent may, in fact, not be a relatively harmless RCA, but a more toxic substance such as lewisite or phosgene, in which case, thorough decontamination is necessary.
For patient education information, see Chemical Warfare and Personal Protective Equipment.
The timing of symptom onset after exposure to tear gas (CS) varies, depending on the duration of exposure and the organ system involved. With dermal effects, for example, erythema may develop within a few minutes, whereas acute generalized exanthematous pustulosis may have a latency period of 1-2 weeks. Similarly, respiratory effects can occur immediately (eg, cough) or develop after about 3 weeks (eg, laryngeal obstruction).[2]
Most cases are self-limited, lasting 15-30 minutes after clothing is removed and the person is in an open space.[1] Reconsider the diagnosis of riot control agents if symptoms persist longer than 30 minutes. However, in one study, the majority of subjects who were directly sprayed with CS in the face still had respiratory and oral symptoms after 1 hour.[9]
Typically, exposed persons feel a burning sensation in the eyes, nose, mouth, and even airway. The eye is the most sensitive organ involved and is the most immediately and severely affected of all the target organs. Eye involvement may include the following:
Other manifestations are as follows:
Skin contact with a riot control agent results in erythema, tingling, and burning. Blistering may also occur after exposure to higher concentrations. Skin involvement tends to be more severe with CN, and may include irritation, bulla formation, and subcutaneous edema.[17] Dermal manifestations develop within minutes of exposure and last up to 1 hour after termination of exposure.
More severe skin injuries can occur in hot, humid environments with heavily sweating or wet patients or with prolonged or close-range exposures. First- or second-degree burns and delayed allergic contact dermatitis may be seen, especially with exposure to CN and CS.
Police and bystanders may be unintended victims of riot control agents. In a study by Watson and Rycroft, six police officers and one bystander developed contact dermatitis, leukoderma, exacerbation of seborrheic dermatitis, and aggravation of rosacea following exposure to CS.[18]
Serious effects, including death, have been reported. CN has accounted for five deaths due to pulmonary injury and/or asphyxia. A case report involved a 4-week-old infant who accidentally received a discharge of pepper spray (OC), which immediately led to respiratory distress, followed by apnea. The infant was resuscitated and ultimately recovered after much intensive care, including extracorporeal membrane oxygenation (ECMO).[19]
Severe effects (eg, pulmonary edema, chemical pneumonitis) usually occur only with prolonged exposure in an enclosed space. Such exposures can damage the respiratory tree. Upper airway mucosal necrosis and pulmonary edema have been reported.
Some studies have suggested that CS may be converted into cyanide in the peripheral tissues. However, the risk of cyanide toxicity seems to be minimal.[20]
One animal study has demonstrated no adverse effects of CS during pregnancy.[20]
Unintentional oral ingestions can occur, specifically in children. Abdominal cramps and diarrhea are common, but the ultimate course usually is uneventful. The lethal dose in one half of the exposed population (LD50) in animals is 200 mg/kg, which is an amount unlikely to be ingested.
Other gases irritating to the mucous membranes and respiratory system (eg, lewisite, phosgene oxime) may be confused with pulmonary irritants. Features that help with distinguishing these include the following:
Long-term effects, usually as a result of prolonged exposure, can include ophthalmological complications such as cataracts, glaucoma, and blindness as well as pulmonary deterioration leading to respiratory failure.[6]
Physical findings in patients exposed to riot control irritants are as follows[1, 3, 4, 5, 6, 10] :
Severity of manifestations varies with the age of the victim, comorbid factors, and duration of exposure.
Short-term complications include the following[1, 3, 6] :
Long-term include the following[1, 3, 6] :
Clinicians should don appropriate personal protective equipment (PPE) before triaging and assessing patients assumed to be contaminated with a riot control agent (RCA). Victims who have RCAs on clothes and exposed body parts require decontamination as a first step.
Diagnosis of pulmonary irritant exposure is based on clinical findings. However, the following may provide useful information in some cases:
Laboratory studies are not indicated unless an exposure to a RCA was prolonged or the RCA-exposure diagnosis is in doubt.
Consider the following:
Consider the following:
Consider the following:
No antidote to riot control agents (RCAs) exists, so treatment is symptomatic and supportive. Treatment measures for RCA exposure include the following:
Most people exposed to irritants do not seek medical care, and effects are self-limited. When persons seek care, first withdraw them from exposure. Responders should wear appropriate personal protective equipment (PPE). Decontamination should then proceed as follows:
Initiate or continue care in the emergency department (ED) as follows:
Most patients with irritant exposure can safely be discharged from the ED, as the few reported dangerous effects occur rapidly.The rare patient with significant respiratory damage may require oxygen supplementation, aggressive bronchodilator therapy (if bronchospasm is present), and admission to the hospital, possibly a critical care unit.
Characteristically, hospital admission for extended medical care is not indicated. Should hospitalization be required, consider alternative diagnoses.
Victims should be made aware that initial symptoms may be minimal or that there may even be a latent period. Should any clinical deterioration occur the patient should be re-evaluated.
Medical follow-up is indicated for a minority of patients, including those with any of the following:
Consultations with one or more of the following may be indicated:
Consider the following in long-term monitoring:
In general, only decontamination with water is necessary when a patient's skin has been grossly exposed to riot control agents. Bronchodilators, analgesics, and pulmonary support may be needed, depending upon the severity of injury.
Diphoterine and vegetable oil have chelating and amphoteric properties that show some promise in managing dermal exposures, but more studies are required to prove efficacy.[22]
Antibiotics may be reserved for dermal and pulmonary complications. An antiobitic ointment may be helpful with ocular involvment.
Analgesics for pain, preferably non-steroidal agents;
Clinical Context: Beta-agonist for bronchospasm refractory to epinephrine. Relaxes bronchial smooth muscle by action on beta 2-receptors with little effect on cardiac muscle contractility.
Use only for patients with evidence of significant bronchospasm after exposure.
Clinical Context: Acts as an analgesic, antipyretic, and anti-inflammatory agent.
NSAIDs have analgesic, anti-inflammatory, and antipyretic activities. Their mechanism of action is not known, but they may inhibit cyclooxygenase activity and prostaglandin synthesis. Other mechanisms, such as inhibition of leukotriene synthesis, lysosomal enzyme release, lipoxygenase activity, neutrophil aggregation, and various cell-membrane functions, may exist as well.
Clinical Context: Drug combination indicated for relief of moderate to severe pain.
Pain control is essential to quality patient care. Analgesics ensure patient comfort, promote pulmonary toilet, and have sedating properties, which are beneficial for patients who have sustained trauma or injuries.
Clinical Context: Indicated for corneal abrasions. Aminoglycoside antibiotic used for gram-negative bacterial coverage.
Clinical Context: Indicated for corneal abrasions and infections caused by susceptible strains of microorganisms and for prevention of corneal and conjunctival infections.
Therapy must cover all likely pathogens in the context of the clinical setting.