I have a shelter under my back yard. It is entirely steel plate. It is both welded and in some places riveted.
Riveted. Like the Titanic!
Some folks scoff and say it is a tornado shelter. It is not.
My shelter, built in the mid 1960s, has a full 3 feet of earth between the surface and the ceiling.
Also, it has a foyer at the bottom of the stairwell with a 90 degree turn into the main room, because radiation does not go around corners, it was believed at the time.
Pretty sure that is still the case.
Unless you have a black hole down there.
Nice!
I think having a fallout shelter would be a good idea, no argument. Groundwater is way too high here, at least to go underground.