eMedicine Specialties > Emergency Medicine > Warfare - Chemical, Biological, Radiological, Nuclear and Explosives

CBRNE - Irritants - CS, CN, CNC, CA, CR, CNB, PS

Author: Paul P Rega, MD, FACEP, Associate Professor, Department of Public Health and Homeland Security, The University of Toledo College of Medicine; Director of Emergency Medicine Education and Disaster Management, OMNI Health Services
Contributor Information and Disclosures

Updated: Apr 28, 2009

Introduction

Background

The sole purpose of irritants, also known as tear gas, riot control agents, and lachrymators, is to produce immediate discomfort and eye closure 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. They were used before World War I, and, during the 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. 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. These types of compounds were assigned these 2-letter codes by The North Atlantic Treaty Organization (NATO). CN was the primary pulmonary irritant after World War I until Corson and Stoughton developed 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 gas 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 is available as Mace, an over-the-counter product used for personal protection. Capsaicin, or pepper spray, has to some extent replaced CN as a personal protective agent, with less dangerous effects.

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 or grain disinfectant. The creation of CNB (CN, carbon tetrachloride, and benzene), chloroacetophenone in chloroform (CNC), and CNS (CN, chloroform, and PS) attempted to make CN more effective. However, CS proved more effective and less toxic than any of the CN series and largely has replaced them.

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 solutions exist that have a 10% concentration. OC causes the release of a neuropeptide (substance P) that causes pain and inflammation.

The possibility of secondary contamination is very real. Recently, 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.¹

Pathophysiology

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 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).

Recent 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).²

Clinical

History

• Most pulmonary irritant exposures are self-limited. Onset of symptoms occurs in seconds to several minutes. Duration is 15-30 minutes after clothing is removed and the patient is in an open space. Reconsider the diagnosis of riot control agents if symptoms persist longer than 30 minutes. However, in one recent study, the majority of subjects who were directly sprayed with tear gas (CS) in the face still had respiratory and oral symptoms after 1 hour.³
• Typically, the eyes, nose, mouth, and even airway feel a burning sensation.
• The eye is the most sensitive organ involved and is the most immediate and severely affected of all the target organs.
  • Ocular pain, tearing, and severe blepharospasm are common. At high concentrations, chloroacetophenone (CN) is known to cause corneal epithelial damage and chemosis.
  • Conjunctival injection and periorbital edema may be noted.
  • More serious and even permanent eye injuries (eg, corneal abrasions, foreign bodies) can occur. Tear gas particles, other foreign particles, or the blast injury itself causes these injuries.
  • Patients may complain of blindness because of the intense tearing and blepharospasm, but patients who can physically open their eyes have no significant change in visual acuity.
  • Nausea, vomiting, and diarrhea may also occur.
• Rhinorrhea, sneezing, and hypersalivation often occur as agents come in contact with sensitive mucous membranes.
• Patients also may report cough, chest tightness, dyspnea, and wheezing, but pulmonary function test results typically are not changed. These agents can exacerbate a chronic pulmonary condition such as asthma or chronic obstructive pulmonary disease.
• Cardiovascular function may demonstrate an increased blood pressure and heart rate, but this effect is believed to be most likely a psychological response to the situations in which tear gases typically are used.
• Exercise exacerbates symptoms.
• Patients develop tolerance to tear gas symptoms with chronic low-grade exposures.
• Psychological effects (eg, anxiety) also provoke increased response.
• Once the skin comes in contact with a riot control agent, erythema, tingling, and burning occur. Blistering may also occur after exposure to higher concentrations. These symptoms occur 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.
  • Patients can develop first- or second-degree burns, and delayed allergic contact dermatitis may be seen especially with exposure to CN and CS.  
  • Police and by-standers may be unintended victims of riot control agents. In one study by Watson et al, 6 police officers and 1 bystander developed contact dermatitis, leukoderma, exacerbation of seborrheic dermatitis, and aggravation of rosacea following exposure to CS.⁴
• Serious effects including death have been reported. CN has accounted for 5 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).⁵
  • Usually such effects (eg, pulmonary edema, chemical pneumonitis) only occur with the combination of prolonged exposure and use 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.⁶
  • One animal study has demonstrated no adverse effects of CS during pregnancy.⁶
• 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.
  • A history of gas exposure in use by law enforcement or military training suggests tear gas use.
  • Eye symptoms are especially prominent in pulmonary irritant use.
  • Significant respiratory findings are rare but may occur in high concentrations in an enclosed space, especially in pediatric and geriatric victims with preexisting comorbidities.

Physical

Physical findings of irritants are as follows⁷ :

• Respiratory signs and symptoms may include the following manifestations: cough, chest tightness, sensation of suffocation, shortness of breath, tachycardia, increased respiratory rate, wheezing, rales, decrease in oxygen saturation, cyanosis, pulmonary edema, and respiratory arrest in young infants.
• Tachycardia, hypertension
• Skin and mucous membranes will display the following findings: erythema, pain, blistering of the skin, first (possibly second) degree burns of the skin.
• Eyes may display the following findings: conjunctival injection, redness, and irritation; corneal burns; pain; tearing; and blurry vision.
• Oropharynx may display the following findings: oral burns and irritation, sore throat, hoarseness, dysphagia, and hypersalivation.
• Nose may display the following findings: rhinorrhea, burning, irritation, and sneezing.

Severity of manifestations is dependent upon age of the victim, comorbid factors, and duration of exposure.

Causes

• Crowd control adjunct: One study appreciates the fact that law enforcement officers, as well as others, may be subjected to the effects of these irritants in the process of controlling a crowd or stemming a riot. The researchers discovered that diphoterene can be used as prophylaxis or as a decontamination agent in the event of a CS exposure.⁸
• Personal protective device

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