Bolthole Emergency Exit

[nuke11]

Does anyone else find it strange that it is filled with sand and has to be dug out in an emergency to use it?

From what I have read about them in the Diefenbunker up here in Carp Ontario, they where filled with sand and gravel as well, but had an empty pit at the bottom of the shaft. When the hatch was opened and a lever thrown, all of the sand and gravel in the shaft very rapidly (like seconds) fell into the pit and filled it. This exposed the rung ladder in the shaft wall and allowed it to be used very rapidly.

This makes more sense that having to dig it out. But really, they never took into consideration that the shaft once opened all of the sand has to go somewhere fast, which based on the plans is inside of the bolthole.