Here's what I learned shooting riots in South Korea.

1. Wet handkerchief over mouth saves you from inhaling the powder.
2. Swim goggles keep the gas out of your eyes.
3. DON'T TOUCH ANYTHING NEAR YOUR FACE UNTIL YOU HAVE WASHED YOUR HANDS TWICE.
4. Your cameras will stink, but it will eventually go away.
5. Wipe down any hard surfaces with a lightly wet rag when you're back from shooting.
6. DON'T TOUCH ANYTHING NEAR YOUR FACE UNTIL YOU HAVE WASHED YOUR HANDS TWICE.

If you can get a gas mask with large eyepieces, it will make your experience much better. If you cannot aquire a gas mask, then the swim goggles and wet handkerchief tied around your head will do pretty good.