My family business is commercial real estate, in that we buy old buildings, fix them up, and rent them out.

Anyway, Years ago I can remember getting a phone call that one of our buildings was on fire (it wasn't, one of the sprinkler heads had just popped from age). They got in fine through the front door (solid wood), but were having trouble with the back door (steel door, steel frame, Medeco locks). The failed to get through it with hand tools and ended up using the cut-off saw to cut the locks out of the door.

Another time the fire department was having trouble getting through some similar steel doors on another building when I arrived. I didn't have the keys, but I did have my backhoe parked across the street. One big push from the bucket and the doors were down.

Based on those experiences, I've realized a good steel door, with good locks, set in a steel frame can offer at least a little security against brute force attacks. I mean, if the fire department is wailing on the door with a sledge hammer and they can't get it to open, than I can't see anyone kicking that door down to come inside. On the other hand, I've also seen that wood doors are essentially useless. Even solid wood doors don't really offer much more than a few seconds of security.