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Chemical Weapons

By James Madsen, MD, MPH, Adjunct Associate Professor of Preventive Medicine and Biometrics; Chief, Consultant Branch, Chemical Casualty Care Division, Uniformed Services University of the Health Sciences; US Army Medical Research Institute of Chemical Defense, Aberdeen Proving Ground South, MD

Chemical weapons are developed by governments for wartime use and include

  • Toxic agents (intended to cause serious injury or death)

  • Incapacitating agents (intended to cause only temporary, non–life-threatening effects)

  • Incendiary agents (intended to produce light and flame)

Toxic industrial chemicals, as produced for industry, are also capable of causing mass casualties. Some chemicals (such as chlorine, phosgene, and cyanide compounds) have both industrial and chemical warfare uses.

Toxic agents are divided into four major classes:

  • Pulmonary agents

  • Systemic asphyxiants (blood agents)

  • Blistering agents

  • Nerve agents

Incapacitating agents are divided into

  • Anticholinergic agents

  • Riot-control agents (often incorrectly called tear gas) dispersed as solid aerosols or as solutions

Opioids, especially potent fentanyl derivatives such as those reputedly used by Russia against Chechnyan terrorists in 2002, can be considered incapacitating. Although their use is not typically intended to cause serious injury or death, they can easily cause death by stopping breathing when they are used as MCWs. In mass-casualty situations, an aerosolized form of opioids will most likely be used. Larger-than-usual doses of naloxone, the rescue drug for opioids, may be needed to reverse the effects of fentanyl derivatives.

In high doses, incapacitating agents can cause serious injury or death.

Incendiary agents, designed to create light and flame, may also cause burns in large numbers of casualties.

Pulmonary Agents

Pulmonary agents affect the lungs and airways. They include traditional “choking” agents, such as chlorine, phosgene, diphosgene, and chloropicrin, and some blistering agents, such as sulfur mustard, Lewisite, and phosgene oxime (which also affect the skin), as well as military smokes, products of combustion, and many toxic industrial chemicals. Most of these compounds are gases or highly volatile liquids.

Agents are divided into two types depending on which part of the respiratory tract is largely affected:

  • Type 1 agents: Affect large airways

  • Type 2 agents: Affect small airways and the small air sacs of the lungs (alveoli)

Mixed-effect agents can affect large airways, small airways, and the alveoli.

Type 1 agents include ammonia, hydrogen chloride, hydrogen fluoride, riot control agents, most smokes, sulfur dioxide, and sulfur mustard.

Type 2 agents include chloropicrin, methyl isocyanate, phosgene, and carbon tetrachloride.

Mixed-effect agents act in both large airways and alveoli in low to moderate doses. They include chlorine, HC (hexachloroethane plus zinc oxide) smoke, and Lewisite.


Initial exposure to type 1 agents causes sneezing, coughing, and spasm of the windpipe, which can block the airway. Eye irritation can also occur. People with windpipe spasm are hoarse, have wheezing, and make a gasping sound as they breathe in. This sound is called stridor. However, with high doses of type 1 agents, delayed-onset chest tightness or shortness of breath (type 2 effects) may also occur.

With type 2 agents, victims usually feel well at first except for some initial coughing and irritation, which then resolve. However, several hours later they develop chest tightness or shortness of breath due to fluid buildup in the lungs (pulmonary edema). Shortness of breath that develops within 4 hours of exposure is a sign that the person may have been exposed to a potentially lethal dose.


  • A doctor's evaluation

  • Chest x-ray

  • Frequent evaluation for deterioration

  • Sometimes bronchoscopy

Doctors and first responders base the diagnosis of exposure to a chemical weapon on the person's symptoms. They listen to the person's breathing. People with an initially noisy chest and prominent symptoms were likely exposed to a type 1 agent. People with a relatively quiet chest and whose shortness of breath is delayed were probably exposed to a type 2 agent.

Chest x-ray may initially appear normal but later on develop characteristic abnormalities. Sometimes doctors insert a flexible tube with a camera into the airways (bronchoscopy) to see the extent of airway damage. Bronchoscopy can confirm damage done by type 1 agents but may miss early damage done by type 2 agents.

Laboratory testing is not helpful to doctors as they make an initial diagnosis, but they usually monitor the oxygen level in the person's blood to help determine whether the person is deteriorating.


  • Treatment of specific symptoms

  • Oxygen (through a face mask or breathing tube)

  • Often, admission to an intensive-care unit

  • For type 1 effects: Bronchodilators, sometimes inhaled corticosteroids

  • For type 2 effects: Oral corticosteroids, treatments to remove fluid from the lungs

Because mixed effects are common, doctors base treatment on the person's symptoms rather than on the specific agent. Decontamination is not usually necessary for people exposed to vapor or gas, and there are no specific antidotes for these agents.

For people whose symptoms mainly involve the large airways (type 1 effects), doctors give warm, humidified 100% oxygen by face mask. They may need to remove debris from the person's large airways using bronchoscopy. Doctors may need to place a breathing tube in the person's windpipe, and they may give the person bronchodilators, a type of inhaled drug that widens the airways (similar drugs are used for asthma). Inhaled corticosteroids may be given to help decrease the inflammation that often accompanies lung damage.

People exposed to a possible type 2 agent are admitted to an ICU and given oxygen. Sometimes oxygen is given under pressure through a special tight face mask or through a breathing tube placed in the windpipe. Doctors give medicine to remove fluid from the lungs and may give oral corticosteroids depending on the type of damage they suspect.

Systemic Asphyxiants

Systemic asphyxiants include

  • Cyanide compounds

  • Hydrogen sulfide

Systemic asphyxiants have also been called blood agents because they are distributed through the blood. However, they damage cells throughout the body, not just blood cells.

Hydrogen cyanide or cyanogen chloride are highly volatile liquids or gases at room temperature. The combustion of many household and industrial chemicals can produce cyanides, and people suffering from smoke inhalation from any kind of industrial or household fire may also have cyanide poisoning. Although cyanide has a characteristic odor of bitter almonds, about half of people lack the ability to detect it.

Hydrogen sulfide is always a gas at room temperature, so exposure to it is usually by inhalation. Hydrogen sulfide can be produced by mixing sulfur-containing household chemicals with acids. Residual gas can affect rescuers, causing many additional casualties. Hydrogen sulfide is also produced when manure decomposes. Large farm manure pits often contain lethal quantities of the gas. Hydrogen sulfide has a characteristic rotten egg odor, but high concentrations damage a person's ability to detect the odor.


Cyanide initially causes gasping, a rapid heart rate, and high blood pressure. People may have seizures and lose consciousness in as little as 30 seconds. They may display signs that are similar to those of tetanus, including lockjaw, grimacing, and arching of the neck. Their skin may appear flushed, but about half of people have a blue tinge to their skin.

Hydrogen sulfide at high doses also can cause people to have seizures and lose consciousness. They may sustain heart damage. Continued exposure to low doses of hydrogen sulfide may irritate the eyes and membranes lining the nose and throat and cause headache, weakness, incoordination, nausea, vomiting, chest tightness, and hyperventilation.


  • A doctor's evaluation

Severely affected people must be treated immediately, so doctors base the diagnosis on the person's symptoms and history. After exposure to hydrogen sulfide, any coins that the person is carrying may have a green discoloration or darkening, which could increase the doctor's suspicion of hydrogen-sulfide exposure. Commonly ordered blood tests may suggest exposure to hydrogen cyanide or hydrogen sulfide, but only specialized tests can confirm it.


  • Ensuring person can breathe

  • Decontamination of skin

  • Antidotes if available

  • 100% oxygen

Doctors give immediate attention to the person's airway, breathing, and circulation. Skin can be decontaminated using water with or without soap.

Cyanide antidotes are available and include amyl nitrite, sodium nitrite, sodium thiosulfate, and hydroxocobalamin. If the antidotes are not available, doctors give the person 100% oxygen. Unprotected mouth-to-mouth resuscitation may expose the rescuer to cyanide in the person's breath.

People exposed to hydrogen sulfide are usually given 100% oxygen. Glucose and bicarbonate given by vein (IV) may be helpful.

Blistering Agents

Blistering agents include

  • Mustards, including sulfur mustard and nitrogen mustards

  • Lewisite

  • Phosgene oxime

Blistering agents, which cause the skin to blister, can also damage the lungs and airways. Mustards can also affect the ability of the bone marrow to produce white blood cells that fight infection and sometimes cause cancer of the skin or airways long-term.

Sulfur mustard has been variously described as smelling like mustard, garlic, horseradish, or asphalt. Lewisite may have a geranium-like odor, and phosgene oxime has been described simply as irritating. The perceptions of these odors are so subjective that they are not reliable indicators of the presence of these compounds.


Mustard compounds cause intense skin pain and redness. A few hours after exposure (sometimes as long as 36 hours later), blisters form. Blisters caused by sulfur mustard sometimes resemble a string of pearls around an unaffected area. Blisters caused by nitrogen mustard are less likely to show this pattern. Blisters may become large and full of fluid. The eyes may be painfully inflamed, and the corneas may become cloudy. People cough and have hoarseness, wheezing, gasping, and windpipe spasms. They may feel tightness in their chest and be short of breath. Nausea may develop.

Lewisite causes pain within a minute or so of skin exposure. Skin redness is often noticeable within 15 to 30 minutes, and blisters develop after several hours. The blisters usually form at the center of the reddened area and spread outward. Pain begins to subside after the blisters form. Irritation of airways occurs soon after inhalation and leads to coughing, sneezing, wheezing, and shortness of breath from fluid leaking from small blood vessels into the alveoli (tiny air sacs in the lungs). After a few hours, people may feel tightness in their chest and be short of breath.

Skin contact with phosgene oxime causes intense, stinging ("nettling") pain and whitening within 5 to 20 seconds. The affected skin then turns gray with a red border. Within 30 minutes of exposure, pale, slightly elevated swellings called wheals (similar to those in hives) develop. During the next 7 days, the skin becomes dark brown and then black as the skin and underlying tissues die. If not surgically removed, wheals may persist for more than 6 months.


  • A doctor's evaluation

  • Sometimes special laboratory tests

Pain occurring at or shortly after exposure suggests to first responders that Lewisite or phosgene oxime is the chemical agent involved. Delayed onset of pain (sometimes a day after exposure) suggests exposure to sulfur mustard. Tests available only in special laboratories can confirm the diagnosis.

People exposed to mustard should have regular blood tests for 2 weeks to monitor for changes in their white blood cells.


  • Decontamination of eyes and skin

  • Treatment of blisters

  • Sometimes supplemental oxygen

First responders quickly try to decontaminate peoples' eyes and skin. They use a specially formulated commercial topical skin decontamination product (called Reactive Skin Decontamination Lotion, or RSDL®). Soap and water may smear sulfur mustard rather than remove it, but they can still be used when there are no other options for the rapid decontamination of mass casualties. High-flow low-pressure water (for example, from a garden hose) alone can also be used to decontaminate the eyes and skin.

Doctors treat blisters as if they were regular burns from heat or fire, give the person fluid by vein, and cover the burns with sterile dressings. Scrupulous hygiene is important to prevent infection. Antibiotic ointment is applied to the edges of the eyelids to prevent the lids from sticking together.

Supplemental oxygen is needed for people who have trouble breathing. Nausea can be treated with drugs such as atropine.

Nerve Agents

There are two types of nerve agents:

  • G-series agents

  • V-series agents

G-series agents, or G agents, include GA (tabun), GB (sarin), GD (soman), and GF (cyclosarin), which were developed by Nazi Germany before and during World War II. V-series agents include VX. V-series compounds were synthesized after World War II. Nerve agents are similar to organophosphate pesticides but are far more potent.

At room temperature, G agents are watery liquids that vaporize easily. G agents are dangerous both by skin contact and by inhalation. VX is a liquid with the consistency of motor oil that evaporates relatively slowly. None of these agents has a pronounced odor or irritates the skin.

Nerve agents work by blocking an enzyme that breaks down one of the types of chemicals that nerve cells use to send signals to other nerve cells and to muscles (neurotransmitters). Because the signaling chemical, acetylcholine, is not broken down normally, it accumulates and excessively stimulates nerves, muscles, and glands (including tear glands, salivary glands, and sweat glands) throughout the body. At first the stimulated muscles twitch and contract uncontrollably, but later they become fatigued and weaken.

Exposure to nerve agents can cause long-term neurologic and neurobehavioral problems including anxiety, depression, irritability, and memory problems.


Exposure to a nerve agent causes various symptoms depending on the agent, route of exposure, and dose.

Vapor acts quickly. Exposure of vapor to the face causes constricted pupils, runny nose, and chest tightness within seconds. If vapor is inhaled, the person may collapse within seconds.

Liquid nerve agents act more slowly. Exposure to the skin first causes twitching and sweating at the site of exposure. Bodywide effects occur after a delay that can be as long as 18 hours after exposure to a very small droplet. Even fatal doses usually take up to 20 to 30 minutes to cause symptoms and signs, which may include sudden collapse and seizures without warning.

Nerve agents stimulate nerve cells in the brain, so people become agitated and confused, and they may develop seizures or become unconscious. Stimulation of nerve cells outside the brain causes nausea, vomiting, and excessive tearing, nasal secretions, salivation, lung secretions, wheezing, digestive secretions (such as diarrhea and vomiting), and sweating. Stimulation of muscle cells causes cramping followed by weakness and paralysis. Weakness of breathing muscles and disruption of the breathing center within the brain is usually the cause of death.


  • A doctor's evaluation

Doctors base the diagnosis of nerve agent exposure on the person's symptoms and history of exposure. Special laboratory tests can confirm exposure.


  • Injections of atropine and pralidoxime

Two drugs, atropine and pralidoxime, can be given for exposure to a nerve agent. Atropine blocks the effects of excessive amounts of the neurotransmitter, acetylcholine, which builds up as the result of exposure. Thus, atropine is termed an anticholinergic drug. Pralidoxime helps reactivate the enzyme that breaks down acetylcholine.

Before reaching a hospital, prehospital providers can use an autoinjector containing both these drugs to inject the drugs into a large muscle (such as the thigh). Subsequent doses of the drugs are given intravenously.

The skin is decontaminated as soon as possible using a specially formulated commercial topical skin decontamination product (called Reactive Skin Decontamination Lotion, or RSDL®), a dilute solution of household bleach, or soap and water. First responders inspect any possibly contaminated wounds, remove all debris, and flush the wound with plain or salt water. Severe symptoms and death may still occur because decontamination may not completely remove nerve agents that have already started to pass through the skin.

Anticholinergic Agents

Although anticholinergic drugs are used to treat poisoning by nerve agents, anticholinergic drugs can themselves be used as incapacitating agents. Incapacitating agents are designed not to cause serious injury or death but rather to disorient military personnel and keep them from carrying out their missions. One such agent is called BZ.

BZ is a solid that can persist in the environment for 3 to 4 weeks. Mass casualties would likely result from inhalation of aerosolized BZ, although the compound can also be dissolved and placed on a surface in the environment from which it can be absorbed through the skin.


People exposed to BZ have dry mouth and skin,dilated pupils (causing blurring of vision), and usually rapid heartbeat. Their body temperature may also become dangerously high (hyperthermia). They may become lethargic and then develop hallucinations in which they see or hear things. The hallucinations are typically concrete and easily describable (for example, voices of people they know, imaginary television programs, sharing of imaginary cigarettes, or odd shapes). Speech may be slurred, and people often pick at their skin or clothes. Stupor and coma may last hours to days, but people gradually recover.


  • A doctor's evaluation

BZ exposure cannot be detected through laboratory tests. Doctors suspect exposure in people who develop symptoms without having taken a drug that has anticholinergic side effects (see Anticholinergic: What Does It Mean?).


  • Lowering of elevated body temperature

  • Physostigmine for agitation and hallucinations

People exposed to an anticholinergic agent such as BZ are usually quiet but may become disruptive and may need to be restrained. Doctors must cool people who have an elevated body temperature (see Heatstroke : Treatment). They give the drug physostigmine to people who are disruptive or who are markedly distressed by the hallucinations.

Incendiary Agents and Hydrogen Fluoride (HF)

Military incendiary agents are designed to illuminate the battlefield, to start fires, and to create smoke to obscure terrain and personnel. Agents include thickened gasoline (napalm), thermite, white phosphorus, and magnesium. Any of these compounds can cause mass casualties.

Napalm has a jelly-like consistency. The other incendiary agents are usually weaponized as powdered solids. Many incendiary agents are used in exploding projectiles or bombs. White phosphorus may continue to burn on skin or clothing as long as it is exposed to air. Because magnesium can burn under water, it will continue to burn within tissue.

Hydrofluoric acid, used in industry and in other commercial applications, is often confused with hydrochloric acid (the acid used in swimming pools). For this reason, it is referred to as HF. HF can exist at room temperatures as a liquid or a vapor. The most common routes of exposure are through the skin, eyes, and lungs. HF penetrates deeply through the skin. In addition to causing severe burns, HF can cause a serious imbalance of body chemicals (electrolytes) that sometimes causes an abnormal heart rhythm and death.


Burns caused by an incendiary agent are similar to those of other burns caused by heat or fire.

HF exposure may not cause pain or visible burns right away. Pain may appear within an hour but typically occurs only after 2 or 3 hours. However, once pain occurs, it is often deep and intense. Affected skin gradually becomes reddened but does not appear as severely affected as the intense pain would suggest.


  • A doctor's evaluation

Burns from an incendiary agent are readily apparent to first responders. However, because burns caused by HF (particularly in low concentrations) take time to cause symptoms, medical personnel remain vigilant for injury done to the person's deep tissues and organs. Burns caused by white phosphorus may glow or smoke when exposed to air.


  • Decontamination of the skin

First responders flood areas of skin affected by white phosphorus with water, or they smother the areas to block exposure to air. Particles of white phosphorus are removed (they often adhere tightly to skin) and placed in water. Smoking trails may be good indicators of the location of small particles. Particles of burning or smoking magnesium in the skin are removed as quickly as possible. Wounds can be covered with oil until particles can be removed.

For HF exposure, prompt decontamination is needed. Burns are flushed with lots of water. However, because HF penetrates the skin quickly, significant problems may occur even after thorough decontamination. Doctors usually apply a paste containing calcium or inject calcium into the exposed area. People with significant exposure are hospitalized to undergo cardiac monitoring and additional treatment.

Riot-control agents

Riot-control agents are compounds that were initially developed for crowd control but that have also been used in military conflicts. The term tear gas is sometimes used, but the term is incorrect because it is not a gas. Instead, riot-control agents are solids that can be dissolved and dispersed as liquids or as aerosols (small particles are released explosively or as smoke). Riot control agents are intended to incapacitate people, not cause serious injury or death, although deaths have occurred. Military versions of these agents include chloroacetophenone (CN, also marketed as Mace®), chlorobenzylidenemalononitrile (CS), dibenzoxazepine (CR), and diphenylaminoarsine (adamsite, or DM, a so-called vomiting agent). Oleoresin capsicum (OC, pepper spray) is a more recently developed riot-control agent used primarily for law enforcement and personal protection.


Most riot-control agents cause nearly immediate irritation and pain to the eyes, mucous membranes, and skin. People who inhale the agents develop coughing, sneezing, wheezing, and sometimes shortness of breath.

People typically recover from the effects within a half an hour, but agents left on the skin may cause blisters. Some people develop a permanent lung complication called reactive airways dysfunction syndrome, which causes episodes of shortness of breath and wheezing, similar to that caused by asthma.


  • A doctor's evaluation

  • Sometimes chest x-rays

Doctors base the diagnosis on the person's symptoms and history of exposure. People with shortness of breath may need chest x-rays, but other tests are not needed.


  • Removal from exposure

  • Decontamination of affected areas

At the first sign of exposure or potential exposure, masks are applied when available. People are removed from the affected area when possible.

First responders remove the agent by brushing, washing, or rinsing the affected area. Water may temporarily worsen the pain caused by certain riot-control agents (such as pepper spray) but is still effective. Oils or soapy liquids are probably more effective against pepper spray. Eyes are decontaminated by copious flushing with sterile plain or salt water.

Most effects resulting from riot-control agents are short-lasting, and most people do not need to go to the hospital. Even most people with more severe symptoms need to be observed in a hospital for only a few hours.

The views expressed in this article are those of the author and do not reflect the official policy of the Department of Army, Department of Defense, or the U.S. Government.

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