A second death-penalty trial for Saddam Hussein began on Monday, this time for the 1988 massacre of thousands of Kurdish villagers. Survivors accuse Hussein's troops of using chemical weapons in the attacks. "There was greenish smoke," said a witness for the prosecution, "and minutes later, a smell like rotten apples or garlic." Another survivor described a chemical agent that smelled like perfume. Wait, can poison gas really smell that good?
Sometimes. In particular, mustard gas has a rather nice aroma. Gas victims from World War I recalled a sweet and spicy scent that brought to mind lilacs, garlic, horseradish, onions, or—you guessed it—mustard. In its yellow-brown liquid form, sulfur mustard doesn't smell like anything; the characteristic sweet aroma develops only as it evaporates.
In general, "blister agents" like mustard gas smell pretty good. Another blister agent developed around the time of the First World War, lewisite, smells intensely of geraniums. A blister agent called phosgene oxime has an unpleasant, irritating smell—but with hints of freshly mown hay. The related diphosgene smells like anise.
"Blood agents," which incapacitate or destroy your blood cells, come in a variety of flavors. The bitter-almond smell of the hydrogen cyanide in Zyklon B permeated the gas chambers at the Nazi death camps in the 1940s. (Not everyone notices the nutty aroma.) Hydrogen sulfide gives off a whiff of rotten eggs. Deadly arsine has the scent of garlic.
Not all poison gases have smells. You might not even realize you're inhaling a nerve agent until your respiratory muscles start twitching. In the years leading up to the Iraq war, some weapons experts suspected Saddam of concealing supplies of unscented VX nerve agent. The cult members who gassed the subways in Tokyo in the 1990s used odorless sarin gas. Another nerve gas called soman smells like Vicks VapoRub or rotting fruit.
Do the Kurdish accounts of the 1988 gas attacks make sense? The references to sweet perfume and rotten fruit do jibe with the theory that Saddam used a combination of mustard gas and nerve agents. What about the greenish smoke? It's hard to say, since most of these poison gases are colorless. Chlorine, which was one of the first gases to be used in World War I, does have a greenish-yellow cast, but it doesn't smell like perfume—it's got a pungent aroma reminiscent of bleach.
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