No gas is fine the way it is. Gas was extremley OP before gas masks came out. The standard gas mask and VIP mask should be placed at 7.5k and the others should have a time of invunerability.
Red gas needs a buff though. Red gas says it makes your blood boil. So my guess is that ANY type of exposures will result in boiling. To make it more realistic red gas should act like teir gas idea of it slows you down while in it and drains hp. To counter it though you would by a hazmat suit. This suit is the only gasmask that protects against red gas. Needs to be body and head. Head = 7.5K acts as standard mask. And body = 2.5K and only protects against red gas exposure to skin. Also no gas mask will work against it except for the hazmat suits.