The cloud doesnt have much of a smell. It looks like fog until it’s on you and then it’s two late. A couple of sucking breaths and your chest is one fire and your eyes are bleeding. Terrible stuff, but if you think it is tough on the living, you should see what it does to the dead
PVT Thomas Quinn.
A small, primitive village has yet to discover fire, which is a good thing because there are highly flammable (but not otherwise dangerous) gasses in the air. The heroes, blissful in their ignorance, don't know that and think it a wonderful idea to show the locals open flame.