The cameras will be fine in tear gas. It will irritate only your mucus membranes, not the metal and plastic parts of your cameras.
Don't panic when you get gassed. You will live. It will not kill you. Just keep breathing steadily no matter how funny it feels, and walk (i.e. don't run, trip, panic, stumble, stampede, etc.) to an area with some fresh air. The gas is not lethal, but you need oxygen, so just keep breathing. You will be OK in a few minutes after reaching fresh air. If you are from a dense urban area, it may not affect you badly at all. I had to get gassed in boot camp, and it was a pain in the ass, but definitely not horrible. Some people were more heavily affected, but being from L.A. my whole life, I seemed to be less sensitive to the gas.
Everytime I find a film or paper that I like, they discontinue it. - Paul Strand - Aperture monograph on Strand