Shoot the first two mutants but prepare for a nasty surprise from behind.
All doors are locked on this floor, find the Gold Key behind the entrance elevator room to continue into this bleak and scary steel environment.
Take the second door on the left to get to the elevator, or enter the other sections. Investigate the areas behind the secret doors.
When you get to the room behind the pushwall by the dead guard in the north part of the floor, there is another set of pushwalls behind the western door. These let you get to the big ammo room and further to the elevator but at the same time block the path back to the central area.
Now open the northern door, and jump! Grab the Silver Key quickly and make it into the north-eastern part and finish off the mutants as quickly as possible. There are lots of powerups in this area, but you may need more. Venture south down the meandering corridor to get what you have left in the south-east corner. From here you can also get to the chaingun if you have not already found it.
On your way back keep your nerves under control, Schabbs may be on your tracks.