No, they had not been banned, that was not intill after WW1, during WW1 gas was actually pretty human, it hardly ever killed you, it just sent you home for a few years (Which is all the Germans wanted, you to not be a threat anymore) only like 20% of them even died, and while thats not good, its a hell of a lot better than artillery that kills anything in its path with deadly shrapnel, i will take my chance with the gas thank you very much!
Please tell me your joking?

I presume this are just some of chemical weapons deployed.