Given: In a single family residence, the space between two floor joists is closed with a galvanized steel sheet. The space is used as a return air duct for the furnace. May a non-metallic sheathed cable NM that is not identified as LS be routed along the face of joist within this enclosed space? Why or why not?

Given: In a single family residence, the space between two floor joists is closed with a galvanized steel sheet. The space is used as a return air duct for the furnace. May a non-metallic sheathed cable NM that is not identified as LS be routed along the face of joist within this enclosed space? Why or why not?