Chemical agents are poisonous gases, liquids or solids that have toxic effects on people, animals or plants. Chemical incidents are characterized by the rapid onset of medical symptoms and easily observed signatures, such as colored residue, dead foliage, pungent odor and dead animals and insects. Most chemical agents cause serious injuries or death. They are classified by their effects: nerve, blood, choking or blister. These weapons kill by destruction or disruption. The infamous "gases" of World War I --mustard gas, for instance -- essentially burn away parts of the respiratory system. More modern nerve gases --Tabun, Sarin and VX -- disrupt the chemical processes through which one nerve cell communicates with another. Severity of injuries depends on the type and amount of the chemical agent used, and the duration of exposure.

Chemical agents are generally liquid when containerized but are disseminated as an aerosol or gas. To be effective, chemical agents must be dispersed in sufficient quantity to cause serious damage. These agents are heavily influenced by weather conditions, such as temperature, wind speed and direction, humidity and air stability, that make it difficult to achieve sufficient concentrations to be effective in an open-air environment. Unlike biological and radiological weapons, chemical agents are fast acting. Protection from these agents requires full respiratory and skin protection.

Were a chemical agent attack to occur, authorities would instruct residents to either seek shelter where they are and seal the premises or evacuate immediately. Exposure to chemical agents can be fatal. Leaving the shelter to rescue or assist victims can be a deadly decision. There is no assistance that the untrained can offer that would likely be of any value to the victims of chemical agents.

In this section, we discuss sarin gas, mustard gas, VX and tabun.

Sarin is a manufactured compound that is toxic to humans. It is colorless, odorless and tasteless; it also is highly volatile and highly lethal, occurring both as a liquid and vaporized as a gas. The gas, which is 26 times more deadly than cyanide gas, causes severe damage to the respiratory system, and difficulty breathing may render the victim unconscious. Sarin is rapidly absorbed through the skin, but vaporized sarin is mainly absorbed through the respiratory tract and conjunctiva. Most victims encounter vaporized sarin, which affects the eyes and the respiratory system. Six-tenths of a milligram of sarin is enough to kill an adult.

Sarin was developed by Nazi scientists in Germany in the 1930s. It was named for its four discoverers: Schrader, Ambrose, Rudriger and Van der Linde.

The United States began producing sarin in the early 1950s; production ceased in 1956. It was produced and stockpiled in large quantities by both the United States and the Soviet Union.

In 1995, the Aum Shinrikyo sect released sarin in the Tokyo subway, killing 12 and injuring 5,500 people. In that attack, sarin was transported as a liquid, in packages that resembled lunch boxes or bottled drinks. The packages were then punctured with umbrellas and began to leak a thick liquid containing sarin.

Vaporized, sarin is slightly heavier than air, so it hovers near the ground. Humidity causes sarin to degrade, but warmer temperatures increase sarin's lethal duration, despite humidity.

Early symptoms include difficulty breathing, nausea, drowsiness, convulsions and miosis (pupils in the eye shrink to the size of pinpoints). Exposure can also result in bleeding from orifices - witnesses in the Tokyo attack said that victims had blood gushing from their noses and mouths.

The pupils narrow to pinpoints, harming vision. Drooling, runny nose, tears, tightness in chest, difficulty breathing, nausea, vomiting, headache and convulsions are among other symptoms.

Death does not always come with a warning and may be caused by cardiac arrhythmia and respiratory arrest.

If sarin is released in the air, a person should try to hold his breath until a protective mask is put on. Those displaying severe symptoms would receive intravenous treatment with an antidote. If a person's breathing has stopped, CPR would be performed but not mouth-to-mouth resuscitation if the facial skin has been contaminated. If a person has difficulty breathing, oxygen would be administered. If a person's eyes have been exposed, they should be flushed with water for 10 to 15 minutes. If a person's skin has been exposed, he should don a protective mask and remove clothing, then wash the skin with copious amounts of soap and water or a solution of 5 percent household bleach. Medical attention should be sought under any of the above circumstances.

Those infected with sarin can be treated, but a potentially fatal dose requires swift treatment with injected antidotes. Recovery depends on degree of exposure to sarin and how rapidly medical treatment is provided. Death may occur within one to 10 minutes of inhalation exposure to a minute amount of sarin.

The information about sarin was compiled from the following sources:
Southern Medical Association

U.S. Army Soldier and Biological Chemical Command

Council on Foreign Relations

Centers for Disease Control

CDC Fact Sheets on Agents

Mustard gas is a colorless, oily, odorless liquid that can be vaporized to form a gas. When mixed with other chemicals, it has a brownish tint and develops a pungent, garlicky odor. Mustard gas enters the body through inhalation or skin contact, and it damages any tissue that comes into contact with it. It is more harmful to the skin on hot, humid days or in tropical climates.

Mustard gas was used in chemical warfare in World War I and World War II. It was so powerful that only small amounts had to be added to explosives for it to be effective. Once in the soil, mustard gas remains active for several weeks.

It was also used at one time in the topical treatment of psoriasis.

Mustard gas burns the skin and causes blisters within a few days. The blisters may grow quite large and may be yellowish-brown in color. The parts of the body that are sweaty are the most likely to be harmed. It makes a person's eyes burn, eyelids swell and causes blinking. It attacks the corneas and can cause blindness. If inhaled, it can cause coughing, bronchitis and long-term respiratory disease. It can cause cancer in a person's airways and lungs later in life. Some of the chemicals that are formed when mustard gas is burned or spilled into water can also be irritating to the skin.

Treatment has traditionally involved rapid decontamination and symptomatic treatment. Victims should be moved into an area with fresh air as soon as possible. Contaminated clothing should be removed as soon as possible. If a person's eyes are exposed, they must be flushed with lukewarm water for at least 15 minutes. Exposed skin should be washed thoroughly with water. Blisters should be treated as burns. If a person does not have a pulse, CPR will be administered. If a person is not breathing, artificial respiration will be provided. If breathing is labored, oxygen or other respiratory support is administered. Mustard gas changes into other chemicals in the body and those chemicals mostly leave the body in the urine within a few weeks.

If a person is exposed to a very large amount of mustard gas or exposed for a prolonged period of time, he could die.

The information about mustard gas was compiled from the following sources:
Agency for Toxic Substances and Disease Registry

Ben-Gurion University

Bristol University

Congressional Research Service

VX is a nerve agent that disrupts the transmission of nerve impulses in the body. It is an amber-colored, oily liquid that will remain in the environment until it has been properly cleaned through decontamination methods. It can be similar in appearance to motor oil. VX can enter the body through ingestion, inhalation or through the eyes or skin. VX is the most potent of all nerve agents and the least volatile, meaning it is slower to evaporate. It's approximately 50 times more toxic than cyanide gas.

It was developed by the United States and Britain in the 1950s.

Symptoms of overexposure may occur within minutes or hours, depending on the dose. The symptoms of VX exposure take longer to show up than with other nerve gases, but are similar. They include nausea, vomiting, diarrhea, constriction of the pupils or blurred vision, runny nose, chest tightness, difficulty breathing, disorientation, loss of muscle control, loss of consciousness, convulsions and eventually respiratory failure and death.

Do not induce vomiting. A person exposed to VX should immediately don a respiratory mask. The person should be thoroughly decontaminated by washing with large amounts of water and soap, sodium carbonate or bleach. This should be done gently as scrubbing will increase absorption. Emergency personnel should administer antidote. The patient may need an IV or to be placed on a ventilator to restore breathing. If there are seizures, a sedative such as Valium may help. Because symptoms may take up to 18 hours to appear, the person should be kept in the emergency room.

The dose that would be lethal to 50 percent of the people exposed is about 10 milligrams, a tiny amount that could be held on the end of a straight pin. Because the agents act slower than other nerve agents, successful treatment is possible. Once a person recovers, the symptoms are not likely to return, but the patient may suffer from the effects of oxygen deprivation for days or weeks.

The information about VX was compiled from the following sources:
Centers for Disease Control and Prevention
CDC Fact Sheets on Agents
U.S. Army Soldier and Biological Chemical Command

Fernando L Benitez, MD, Assistant Medical Director, Dallas Metro BioTel (EMS) System, Clinical Instructor of Emergency Medicine, Department of Surgery, Division of Emergency Medicine, University of Texas Southwestern Medical Center

Tabun is classified as a nerve agent that interrupts the transmission of nerve impulses in the body. For example, it binds to nerves in the spine, muscles or central nervous system depending on the manner of ingestion. It was developed in Germany in 1936 as an insecticide. Like a number of widely used insecticides, tabun is an organic compound containing phosphorus (organophosphorus compounds). It is a tasteless liquid that ranges from colorless to brown and has a somewhat fruity odor. It is volatile at room temperature and can be absorbed through the eyes or skin or inhaled as vapor.

The symptoms depend on how tabun is ingested. If inhaled or absorbed through the eyes, the first symptom to appear is usually miosis, or constriction of the pupils, and visual blurriness, combined with shortness of breath, wheezing, runny nose and tightness of the chest. If swallowed or absorbed through skin not near the eyes, pupil constriction may not occur, and nausea is the first symptom to appear. Tabun's effects also include vomiting and diarrhea, urinary and fecal incontinence, loss of muscle control, convulsions, coma, and death. Vomiting and diarrhea are symptoms of a serious exposure that must be treated immediately.

Do not induce vomiting. A person exposed to tabun should immediately don a respiratory mask. If eye contact has occurred, the patient should rinse the eyes with water for 10 to 15 minutes before putting on the mask; in the case of skin contact, wash the affected area with lots of water and soap, sodium carbonate or bleach, but not hot water, as this will speed tabun absorption. At the emergency room, medical personnel should administer a nerve agent antidote. The patient may need an IV or to be placed on a ventilator to restore breathing. A person exposed to tabun or other nerve gases should remain in the emergency room for at least 24 hours. Chances of long-term survival are high, but effects such as miosis, blurred vision and balance problems can persist for months.

Although skin absorption great enough to cause death may occur in one to two minutes, death may not occur for one to two hours. Respiratory lethal dosages kill in one to 10 minutes, and liquid in the eye kills almost as rapidly. In most cases, by the time the patient arrives at the emergency room, the agent has already taken effect. If the exposure is mild to moderate, recovery is possible if treated immediately.

The information about Tabun was compiled from the following sources:
CDC Fact Sheets on Agents U.S. Army Soldier and Biological Chemical Command Federation of American Scientists Nerve Agents, G-series: Tabun, Sarin, Soman
By Jeffrey L Arnold, MD, FACEP, FAAEM, Assistant Clinical Professor, Department of Emergency Medicine, Baystate Medical Center A Short History of the Development of Nerve Gases