Why Don’t Dictators Premix Their Chemical Weapons?

Answers to your questions about the news.
Dec. 3 2012 5:52 PM

Why Is Syria Mixing Sarin?

A mini-Explainer on the process of making chemical weapons.

Syrian protesters dance during a demonstration against the regime.
Syrian protesters dance during a demonstration against the Bashar al-Assad regime in Aleppo on Nov. 9.

Photo by Achilleas Zavallis/AFP/Getty Images.

U.S. intelligence sources indicate that the Assad regime is “mixing chemicals” to make sarin gas for use against Syrian rebels. Secretary of State Hillary Clinton said chemical warfare was a “red line,” and the United States would take action if the Assad regime deployed sarin. Why don’t dictators premix their sarin?

Because it’s dangerous, volatile, and corrosive. There are several recipes for sarin, but they all require mixing together some combination of chemicals, such as hydrochloric acid, isopropyl alcohol, hydrogen fluoride, phosphorous trichloride, and difluoromethylphosphonate. Kept separately, some of these chemicals pose minimal threat to handlers or the public. Once mixed, one drop of sarin can kill a person in a matter of minutes. That’s why the United States and other countries have historically maintained the unmixed components of sarin in separate buildings. Sarin is also highly corrosive. The Nazis used solid silver containers to mix sarin, and today’s despots use specialized corrosion-resistant metal alloys to concoct the deadly mixture.

Mixing sarin is actually a rather simple process. In fact, during the 1960s, the United States developed a projectile called the M 687 GB that featured two containers. One container was filled with difluoromethylphosphonate and the other with a combination of isopropyl alcohol and a chemical catalyst called isopropylamine. When the projectile was fired, the launch caused the membrane separating the two substances to break and the spinning action of the flight stirred together the chemicals. By the time the canister reached its destination, the chemical reaction was complete. The United States successfully tested the M 687 with sarin in 1969 and conducted thousands of additional tests with nonlethal chemicals.

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The technical challenge for users of sarin is the dispersal. When the Japanese terrorist cult Aum Shinrikyo released sarin on the Tokyo subway in 1995, the attack could have killed hundreds of people. However, the group packaged the chemical in lunchbox-like containers and broke them open with umbrellas. The leaking fluid managed to kill 12 people and hospitalize thousands, but the death toll on the crowded, rush-hour subways would have been far higher had the chemical been aerosolized.

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Brian Palmer writes about science, medicine, and the environment for Slate and the Natural Resources Defense Council. Email him at explainerbrian@gmail.com. Follow him on Twitter.