I have a 1960s 10x12x8 ft concrete room. It was built under our concrete kitchen floor which is at ground level in 1963. The concrete is 12" thick, except for the ceiling which would be about 24" thick. I do not know if it is rebar reinforced. It has a 36 inch doorway opening in the basement and is otherwise 100% concrete. The doorway just has a simple hollow core door.
This was built in the 1960s when everyone was afraid of nukes. In recent years however we've received a lot of local tornadoes that touch down within miles of me. Last night we had one right on top of us (took out a few houses near us) and we all used this as a shelter. Is this a decent shelter or not? What should be done to it in order to make it a safe shelter? Assuming it should have some sort of shelter grade door instead of the interior hollow-core it has now? There is no venting in there either. It appears to be the start of a bomb shelter that was never finished.