nope not thinking of oxygen. one fire my brother in law had to go to was one where some student had brought his lunch with him to the local high school. with his greasy hands (don't know what he was eating) he was switching out the regulator to a new tank of gas in the chem lab for the teacher. the grease of his hands reacted cheically with the head and what residue was there and burst into flames.

I work with acetylene quite a bit, and oxygen. After his warning, I keep a loose plastic wrap over the head when not using them, to prevent any kind of contamination.