Extremely dangerous chemical weapons are not deployed by spraying them directly at people manually at close proximity while walking through a thick fog of the substance. That would be extremely risky, considering that only 5-10 mg of agents such as VX can kill an average-sized man by skin contact. But if somebody did choose to do immerse themselves into thick clouds of the deadliest poison for some reason, unless they had a death wish, they would use a fully sealed protective suit, not just a simple respirator.