I was tear gassed in the late 70s. Some jerk thought it funny to set off a large military gas canister in the Griffith Park tunnel (Los Angeles). I was riding my motorcycle into the tunnel and thought it odd that 2 really tough "Hells Angels" types had dropped their bikes and were lying on the grass having a picnic. I should have known better, no one simply drops a hog onto the ground! They had just come out of the tunnel/gas. They weren't having a picnic, they couldn't see! I drove into the tunnel, and could barely see enough to "aim for the light" at the other end. I blared my horn the whole way, I couldn't tell what lane I was in! Far more gas that one would typically get in an outdoor situation. They took the two "Hells Angels" types away in an ambulance. Me, I went through a few minutes later... it had dissipated a bit... I got my eyes washed out and sent home.
I doubt typical police outdoor levels of tear gas will harm a camera or film or you. Crazy protesters and outnumbered police are what you should worry about. Be safe!