I just played a game with caustic and was in a 2 story bldg with a random teammate. He was in a corner of the room not gassed, I was on the staircase. There were 4 gas traps going off (2 at each door) and an ultimate gas in the middle of the room by the windows, the entire room (except that corner) was filled with gas. Robot comes in the door and stands in the middle of two gas traps and just stands there for long enough to fire off several shotgun shots off and finally kill me, then keeps standing there and finishing me through my knockdown shield, all while it ticks away 6, 6, 4, 6, etc....it's like if you had a group of 1st graders help you fight a grown man.
Suggestion, make the dmg increase over time, and also attach a d.o.t. (damage over time) effect to it that is possibly related to how high you allowed the initial damage to get.
For example, ticker starts at 5, then 10, then 20, then 40...then you leave the smoke, you get another 40 hit, then another 20 hit, then another 10 hit, then another 5 hit essentially giving the gas damage a half life.
I mean think about it, if you inhale toxic fumes you aren't healthy as soon as you walk out, it takes recuperation time and the toxic effect wears off slowly.
Make it happen!