My Dad said sometimes he'd have nightmares and my poor grandmother would get a beating. He got involved in working with poison gas because he thought he was volunteering for a detail that would get him out of the front lines. Little did he realize what he was in for.
My grandfather was lucky to have survived that crap.
Yes, he was. The chemical agents used in The Great War got nastier as it progressed. Straight chlorine gas wasn't deadly enough (!!!) and could easily blow back at the people using it, so they got clever. The various phosgene, lewisite, and mustard agents were used because they were deadlier and less susceptible to weather. There were, in fact, over a dozen different chemicals, and various mixtures, employed by both sides. It was a nasty business; your grandfather's reluctance to talk about it is understandable.