Ninjin, the gas used in Russia was "sleeping" gas which from all accounts is some type of secret nerve gas, lethal without antidote.
CS is an irritant, and
generally will not cause death, except under certain specific concentrations and circumstances. CS is used in civilian law enforcement, during riot control, and in fact, is what is prepared for military trainees in the US for exposure to chemical agents. And yes, it is still used for that purpose.
In RA286, Duke/Toad made a WP 40mm round, which was pretty neat.......it just set you on fire, and you either had to low crawl or get into water to put it out.
The problem with development of a chemical agent in game, is how to differentiate between the appearance of regular smoke and the chemical agent. Although, I generally like the idea, esp for spawncamping spots, hehe. In addition, someone would say it isn't realistic, because a soldier would have a mask and MOPP gear and I for one, don't want to see someone trying to model either of those.