Here's a look at what you need to know about sarin, a man-made nerve agent developed for chemical warfare.
Once evaporated, sarin becomes a gas and can spread into the environment.
Sarin's military designation is GB.
People are exposed to sarin through skin contact, eye contact, or by breathing it in through the air. Sarin can also be mixed with water or food.
Sarin is an extremely volatile nerve agent because of the ability to change from liquid to gas.
Sarin dissipates quickly, presenting an immediate but short-lived threat.
Sarin's main ingredient is methyl phosphonyl difluoride.
Mild or moderately exposed people usually recover completely. Severely exposed people are not likely to survive.
Symptoms of mild to moderate exposure include:
Small, pinpoint pupils
Drooling and excessive sweating
Nausea, vomiting, and/or abdominal pain
Slow or fast heart rate
Low or high blood pressure
Loss of consciousness
Respiratory failure possibly leading to death
Symptoms of severe exposure include:
Loss of Consciousness
Respiratory failure possibly leading to death.
Leave the area of contamination as quickly as possible. Seek fresh air if exposure occurs indoors. If exposure is outdoors, head to higher ground as sarin is heavier than air and sinks.
Removal of contaminated clothing, flushing eyes with water, and washing skin with soap and water. Medical care should be sought immediately.
If ingested, do not induce vomiting or flush with fluids. Medical care should be sought immediately.
Antidotes are available in many hospitals.
1938 - Sarin is developed in Germany as a pesticide.
April-May 1967 - The U.S. military secretly tests sarin in the Upper Waiakea Forest Reserve on the island of Hawaii. The testers detonate sarin-filled 155mm artillery shells to study how the nerve agent disperses in a tropical jungle. The test is called "Red Oak." The Pentagon confirms the Red Oak program in November 2002.
1980s - Sarin and other nerve agents may have been used in chemical warfare during the Iran-Iraq War.
March 1988 - On "Bloody Friday," the Iraqi air force attacks the northern Iraq town of Halabja with poison gases that were thought to include sarin, VX and other deadly compounds. Reports indicate that 5,000 people die in the attack. Countless others suffer eyesight loss, respiratory ailments and cancers.
June 27, 1994 - In Japan, seven people die and more than 500 are hospitalized when the Aum Supreme Truth or Aum Shinri Kyo cult release sarin from a truck driving slowly around an apartment complex in Matsumoto, Nagano Prefecture. Another victim dies in 2008.
March 20, 1995 - In Japan, the Aum Supreme Truth or Aum Shinri Kyo (now known as Aleph) cult places plastic bags of sarin on trains that converge in the government district during Tokyo's rush hour. 13 people die and more than 5,000 become ill.
May 17, 2004 - A coalition convoy in Baghdad finds sarin gas in an artillery round that had been rigged as an improvised explosive device. The IED detonates as officials attempt to defuse it. Two members of the explosive ordinance team suffer minor exposure.
June 23, 2006 - The U.S. Army releases a report to Congress stating that allied forces have recovered approximately 500 weapons munitions containing degraded mustard or sarin gas since 2003. The weapons were produced before the 1991 Gulf War, and many experts believe the sarin would no longer be dangerous.
June 15, 2012 - Katsuya Takahashi, 54, the last fugitive suspect in the 1995 sarin attacks on the Tokyo subway is captured by Japanese police, ending a 17-year manhunt.
April 25, 2013 - Defense Secretary Chuck Hagel announces that Syria has used sarin on a small scale, killing 150 people in the country.
August 21, 2013 - A new alleged chemical weapons attack kills more than 1,000 people in the countryside outside its capital Damascus. Hundreds of those killed are children.
September 1, 2013 - Secretary of State John Kerry announces that samples of blood and hair taken from eastern Damascus have "tested positive for signatures of sarin."
September 16, 2013 - U.N. weapons inspectors returned "overwhelming and indisputable" evidence of the use of sarin in Syria, Secretary-General Ban Ki-moon said, calling the findings "beyond doubt and beyond the pale."