Yet in....I have no idea where it is, New Vegas Steel or something, there is some sort of, I guess molten steel, and that burns you. The inconsistency really irritated me. The big fire in Nipton could have at least burned, since didn't the Mayor get hung up and burned to death in it?
New Vegas Steel, near the Fiend Territory.
What I have noticed is the molten steel knocks you on your butt. Maybe that is the reason that the fire does not hurt. I have walked through a fire once when I was younger and suffered no ill effects, after I rolled around a bit, so it is concievable that one could approach or go through a fire without getting hurt.
What someone should not be able to do is stand in a fire and not get hurt.