Just thought I would add that we recently dug out our stoop which goes down
13 feet underground and was poured with the basement walls. After
installing a drainage pipe, rather than filling it with gravel and dirt I
considered making it into a tornado shelter with a door from the basement.
The basement itself is a daylight basement with lots of steel beams and
would not be a terrific place during a tornado. In any case I dropped the
idea and fiilled it with gravel and dirt before replacing the slab over it.
Could have been my panic room.