People should have the time to go from not having a mask on, to having to quickly get it on or be hurt.
My input would be to make the gases kill you a lot slower, especially the less lethal one which to me seems like its supposed to just be more like teargas than lethal poison. Unprotected units die in about 4-5 seconds of direct exposure, and I expected the less lethal gas to work more slowly, but it pretty much does the same thing if you dont have a mask on, it hurts you, knocks you out and kills you in about 6 seconds. I like this mechanic, though I feel like both gasses kill you way too quickly. The other gas is supposed to just hurt you if you don't have a gas mask.
The nerve agent gas hurts a unit if he doesn't have the special chemical suit on and a mask. I tried it out breifly, and while its a neat concept, I think it still needs work.