The Eye-Watering Science Packed in a Can of Tear Gas

Tear gas is a relatively modern invention—a non-lethal repellant developed from the killer chemical weapons of World War I. But each canister relies on the fascinating chemistry of some ancient compounds and reactions. Wired gives us a look inside, without all the coughing and choking.

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Turns out there's a tricky balance in the equation. If the reaction goes too fast, things will get explodey, and each canister has to pack enough gas to neutralize a crowd without, uh, permanently neutralizing the crowd. Here's hoping you never get caught in cloud of tear gas, but if you do, now you'll know what's going on. Not that it'll be much comfort. [Wired]

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Tear Gas: A Personal Remembrance

In the spring of 1970 the Maryland National Guard occupied the College Park campus of the University of Maryland where I was an undergrad. Students were demonstrating to protest the Nixon administration's illegal expansion of the Viet Nam war, lying to us about it, then compelling every male to serve in the military under threat of imprisonment (see: The Draft). I imagine it's hard for young people today to appreciate the horror; flunking out could cost you your student deferment, get you drafted, shipped to Asia and killed. I vividly recall how my Physics oral exams that semester were repeatedly interrupted by guard helicopters whop-whop-whopping around campus. There was an armed soldier on every campus street corner, and clouds of tear gas rolling around everywhere.

One of the demonstrators stole a tear gas canister from the guard and, somehow associating subatomic particle research with nuclear weapons, lobbed it into the control room of the cyclotron* facility where I worked. A 350 pound post-Doc caught him by his pony tail and sat on him until the guard arrived. The gas ruined many of the controls and instruments, as well as the computer hard drives, which were of a much more open design in those days; the CS gas used at the time included an abrasive particulate element. I wasn't there when it happened, but the floor tile where the canister landed reeked for hours afterward, even after we ventilated the building. Try as we might we couldn't get the tile unstuck from the sub-floor. So, we got one of the 5 gallon dewars of liquid nitrogen we had about, and poured it on the asphalt tile, flash-freezing it. One smack with a hammer shattered it and we just swept it up. Ah, memories.

*technically, a sector-focused synchrotron, the largest of its kind at the time.