I have always used plywood to mount equipment wherever I am also using loomex to
wire (resi mostly). I work industrial now and it is the same as what Frank stated,everything straight on to the concrete or block.I have never taken fireproofing into consideration and have never had a violation for doing it this way.
Who knows maybe I have been missing something but I can't check for code rules as I am in a hotel in Winnipeg with no code book.(What was I thinking..lol)
