If you've been watching the news in the past few weeks, you've heard a lot about chemical weapons: has it been conclusively proven that Syria's Bashar al-Assad used them? Should their use constitute some sort of "red line" that triggers outside intervention? What are the legal and strategic ramifications of a unilateral U.S. strike against the Assad regime as a punishment for their use?
So how do chemical weapons work? What's their purpose, and why is using them different from using more conventional weapons?
The Chemical Weapons Convention (CWC) defines chemical weapons as:
"(a) Toxic chemicals and their precursors, except where intended for purposes not prohibited under this Convention, as long as the types and quantities are consistent with such purposes;
(b) Munitions and devices, specifically designed to cause death or other harm through the toxic properties of those toxic chemicals specified in subparagraph (a), which would be released as a result of the employment of such munitions and devices;
(c) Any equipment specifically designed for use directly in connection with the employment of munitions and devices specified in subparagraph (b)."
So basically, the term chemical weapons refers to weapons that disperse a toxic chemical agent that is likely to cause injury or death to anyone exposed. In the case of situations like Syria, it generally refers to warheads or missiles that, when they explode, disperse a chemical agent.
Chemical weapons were first banned at the Hague convention of 1899, which stated that "asphyxiating or deleterious gases" in projectiles should not be used in armed conflict. That didn't stop German or Allied forces in World War I, Japan during World War II, or the U.S. in Vietnam, even after the Geneva Protocol of 1925 sought to strengthen the ban.
One key reason that countries around the world have agreed to ban the use of chemical weapons is that they are indiscriminate. Once the chemical agent is released, there is no controlling it. It will kill soldiers and civilians alike.
Since the Vietnam War, most records show that the only other time a state used chemical weapons in warfare was during the conflict between Iraq and Iran in the 1980s.
However, others have argued that the U.S. and Israel's use of white phosphorous (a substance which can, when it comes into contact with skin, can burn through to the bone) in Iraq and Gaza, respectively, constitutes chemical warfare. Officials from both countries at first countered that white phosphorous is only used to create a smokescreen for troops or to mark targets for aerial bombing, but later acknowledged that they were also being used as "incendiary weapons."
Another fun fact: while the CWC bans chemical weapons on the battlefield, it explicitly states that they can be used for "domestic riot control purposes." That is why the use of tear gas, a chemical weapon, is still fairly common, but we hear about things like the chemical weapons use in Syria much less frequently.
In the case of Syria, the chemical weapon used was sarin gas, described by the Council on Foreign Relations as "among the most toxic and fast-acting chemical weapons." It is colorless and odorless, and functions by over stimulating the muscles and glands, which can shut down the respiratory system.
However, sarin disperses quickly, meaning that to cause affect mass casualties, you would most likely need vast quantities of it.
Chemical (and biological) weapons have been described as "the poor man's atomic bomb." They require less expertise and technology to obtain, so countries trying to bone up on their ability to deter larger, stronger neighboring militaries might stockpile them as an alternative to investing in the expensive process of developing nuclear weapons.
For example, in 2004, another time the West was trying to get the Assad regime to give up their chemical weapons, Assad claimed that his country would give up their chemical weapons stockpile when Israel did the same with its nuclear weapons.
There are several potential tactical reasons chemical weapons are used. One might to flush rebels out of an area where they might be hiding. Another would something called area denial, which is just what it sounds like: making an area too dangerous for your enemy to enter. A common area denial weapon is the landmine, but chemical weapons could have a similar effect.
Finally, they can just be used to generate mass casualties.