Here are some things to know about tear gas that I know from personal experience, I hope it will help people:
1. If a gas mask is hard to come by, get a DUST MASK and make sure it covers your nose and mouth perfectly. It won't protect your eyes, but it will give you precious few breathes of air that you need to escape from the oncoming police beating. (Bonus: get a pair of swimming goggles if you would be comfortable with it. It will keep you from getting pain in the eyes)
2. It is terribly PAINFUL. It will burn your nose, your eyes and your skin. It sets in water and will travel with it, meaning it will stick to wet areas, your sweaty body and tears, which is unfortunate because you will realize the sides of your eyes and cheeks will also keep burning for a while when your own tears roll down on your face.
3. Tear gas is infamous for the PANIC it causes. When exposed to it, you will not have any problems getting oxygen, BUT YOUR BODY WILL THINK IT DOES. It gives a choking, suffocating sensation that will immediately have the effect of a panic. Try to stay strong, keep breathing, and leave the area as soon as possible. Help people who are under the effects.
4. Antiacids like heartburn medicines (ingestion ones) DO help. I don't know why, but mixing Gaviscon with water and keeping in a sprayer bottle REALLY REALLY helped.
5. Not about the gas itself but worth mentioning: Don't try to catch or block launched tear gas canisters. I don't know if U.S. police use them, but the police in my country uses them as projectile weapons. Many people died that way. Many others lost their eyes. It is literally a big bullet that has the force to break your bones, penetrate your body and cause trauma followed by death.
6. If you have heart condition, breathing problems or asthma, TEAR GAS CAN KILL YOU. Not directly, but the short term panic and breathing problems it causes have been known to kill people who have these problems.
7. The immediate effects of the tear gas will not exceed 30 minutes (usually) but THERE ARE LONG TERM EFFECTS. It has been over a year since I have been exposed to it and I still experience sudden loss of breath followed by irregular breathing, and heart racing once in a while. I am baffled by people who thinks this weapon is safe perfectly harmless.