If you've been watching any coverage of the Egyptian protests, you've no doubt seen the tear gas plumes as canisters are shot at protestors—often to be picked up and hurled back moments later. Many of those tear gas containers falling on the bridges and streets of Cairo aren't local products, however; they come from Jamestown, Pennsylvania, home of Combined Tactical Systems.

Several reporters in Egypt have commented on that fact this week. ABC News ran a story on the gas today in which it quotes a protestor saying, "The way I see it, the US administration supports dictators."

It's no secret that Egypt is one of the largest recipients of US foreign military funding, much of which is designated to purchase US-made weapons; it's just that Americans don't often see Egyptians holding empty tear gas canisters stamped "Made in USA" up to a TV camera.

But what's in those canisters?

The US government requires most chemical compounds to have a Material Safety Data Sheet (MSDS) outlining the ingredients, the risks of contacting those ingredients, and cleanup procedures in case of an accident. Combined Tactical Systems helpfully makes puts these MSDS files on its website.

The tear gas grenades and canisters are largely filled with a fuel mixture that burns to disperse the tearing agent. The Model 5220 CN Smoke grenade (PDF), for instance, has a small starter mixture of potassium nitrate, silicon, and charcoal. This in turn in used to light the "CN smoke"—a form of tear gas.

The CN smoke is 71 percent fuel, made up of potassium chlorate, magnesium carbonate, nitrocellulose, and sucrose. The other 29 percent of the smoke is the tearing agent, chloroacetophenone, which has been around for nearly a century and causes severe irritation of the mucous membranes. (Combined Tactical Systems also sells the commonly used "CS smoke" tear gas version, which is powered by chlorobenzalmalononitrile.)

Both kinds of tear gas have a "pungent odor," according to the MSDS. Those handling them should wear a "full face respirator with organic filter cartridge" and should "wash thoroughly after handling."

That's because, as the protestor went on to tell ABC, "Your eyes tear up a lot so you can't see, and you feel like you're suffocating. You can actually breathe but you feel like you are suffocating so you try to run, but when you run you inhale more."

As the MSDS puts it, rather more clinically, the gases cause "tearing of eyes, irritation of respiratory tract and mucous membranes," and asthma may be "aggravated by exposure."