§ 131. Shafts, elevators and dumbwaiters. Every shaft shall be enclosed on all sides with fireproof walls and shall have fireproof doors and assemblies at all openings, with the doors self-closing. Not more than three elevators or dumbwaiters shall ever be placed in the same shaft. All dumbwaiter doors shall be fastened by an interior lock in the shaft operated and controlled from a central point. The doors of every elevator shaft shall be provided with an automatic device to prevent the normal operation of the elevator unless the hoistway door at which the car is standing is closed and locked, or unless all hoistway doors are locked in a closed position. Such doors, except for power-operated sliding doors, shall have a vision panel of wire glass not exceeding one square foot in area. Every elevator shall be equipped with a gate or door with an automatic device to prevent the normal operation of such elevator unless such gate or door is closed.