The blast lock is like an airlock in a spaceship. There is an outer door and an inner door, and (when the silo was operational) both doors could not be opened together. The door locking pins can be seen at left and right on the door frame.
The blast lock walls are about 4 feet (1.2 m) thick, while the floor and ceiling are 5 feet (1.5 m) thick. The entire structure is steel plated.
The initial viewpoint looks into the blast lock through blast door 6, as seen from the foot of the access portal stairway.