Level 400
Emergency Escape Hatch
The Emergency Escape Hatch would be used if the normal entrance to the bunker (through the blast doors on Level 400) became blocked or inoperative. The hatch leads to a 30-foot vertical tunnel that emerges on the surface. The tunnel is filled with 15 tons of pea stone gravel to block radiation from entering the bunker.
There was a lever directly inside the hatch that, when pulled, would release the pea stones downward past a grate into a pit at the bottom of the tunnel.