I suppose it depends on the type of wire. Something like bell wire or maybe even CAT 5 has a pretty good insulation to copper ratio but the kind you want out of a building the most is mostly insulation with a tiny amount of copper. A lot of this cable was not made with flame testing in mind either.
When we actually started looking at the cables we were stringing around the computer rooms IBM quietly started replacing cables about as fast as they could. Some of our old cables were down right scary in a place that was handling environmental air like a raised floor.
Everyone cheated on 645 and as the computers shrunk, the raised floor areas started becoming class A office space but still shared AC with a lot of computer room area. Of course the cube rats discovered all of that "wasted storage space" under their desk and all manner of flammable materials ended up under there.
