I have not seen many "safe rooms" that are built above ground that I would want to be in during an F5. We have seen many tornadoes on Oklahoma. When you consider objects the size and weight of automobile and larger being thrown around and slammed into the structure most I have seen may not stand up. External storm shelter below ground for us. Yes it is a pain to go outside to get in.
Have you seen a safe room that was in a walk out basement with 12 inch thick steel reinforced concrete walls (some backed by dirt) and a FEMA approved door facing away from the glass doors and windows and with a ceiling with a mat off N-S and E-W rebar plus monolithic beams on 24 inch centers with two each 1 inch rebars in each and a concrete thickness of 14 inches?
The above ground unit I built for my mom has 14-16 inch thick ceiling and 12 inch walls with so much rebar it is basically a steel box with some concrete around it. There are 5/8 rebar prebent 2x2 ft corners connecting all the corners together as well as connecting the floor to the walls and walls to ceiling. The floor is doweled into the garage floor slab and there are piers augered under the floor at angles with rebar tied to the floor rebar, not straight down to make pulling it up way harder. The FEMA approved HD steel door is "Improved" by the addition of multiple horizontal angle irons on both sides and there are three HD dead bolts. Oh, the 5/8 and 3/4 rebar is on 8 inch centers both vertically and horizontally with two mats in ceiling.
I live on a dead end road out in the country. I saw the movie twister but nearest 18 wheelers are a ways off but probably would not come through the ceilings of these structures anyway if dropped from orbit. The truck is bigger than the room so would have do destroy the walls as well, an unlikely event, not just the ceiling. Now if the twister stopped off at a military installation like Tinker and picked up some thermonuclear warheads then you got me, I shoulda made a shelter in the ground accessed from outside in the rain, hail, lightning, and then fret over whether or not to use it because of the rain, hail, lightning, etc.
Thanks anyway, I'll just go to bed and sleep with no worries and not stay up watching the weather on TV to see if they can scare me out into the storm to access protection.
I seriously doubt there are many safe rooms that are safer than these. There are limits. Once you reach a level of strength well in excess of the danger you are countering, more is not particularly better, i.e. overkill/over engineered. I think I am a poster child for adequate storm safety.
Underground shelters if used religiously are definitely a good way to go as they are much more cost effective than my monstrosities. They can be made as safe as mine for way less $ but... I had a promise to keep to my wife of a bedroom that was a safe room. I have confidence in the safety of all three safe rooms I built above ground. I took considerable ribbing from a friend with a masters in mechanical engineering and 35 years hands on experience but I don't mind since my wife "feels" safe and I know she is.
My mom was born and raised in Oklahoma and my dad came when he was 11. He and my mom saw exactly one tornado their whole lives, the same one, in downtown Lima, Ohio. Unless you chase them or see them on TV you sure beat the law of averages to see many.
Pat