One of these days I'm going to convert my master closet into a tornado safe room. I know of two different homes with in ground storm shelters right behind their houses, and neither have ever gone into them when there is a tornado warning. I know that one of the family's stood there by the door, debating when the sirens where going off, but never left the house. The way I understand it, when the storm is happening, it's already storming outside and nobody wants to deal with getting wet, and climbing into a hole in the ground in at night.
I thought about adding a cellar type room to my house that I could access from inside the house, or from my garage. The more I worked on the plans, the more absurd it got.
Then I looked into building it inside my garage. I would loose a corner, but it wouldn't take up too much room. The smaller you make it, the easier it is, but for me, getting all of us and our dogs into it made the garage a bit of a challenge.
In the last five years, I'm seeing a lot of people building new homes with the master bedroom being a tornado safe room. They have a massive metal swing in door that is always kept open, and a regular door that they use every day. There is a place to sit, they have some water and snacks in there, and even a bucket for going to the bathroom if you really have to in a cabinet. The City of Tyler has been updating their Code on this, with venting being the biggest issue. I'm not sure of the details, but it was a problem for one of my clients when they had the house built.
My current plan for building a tornado storm shelter in my master closet is to dig out my foundation for a deeper footing, then pour concrete with rebar that is bent under the existing slab. Run that rebar to the ceiling and bend it for the ceiling. All continuous rebar from under the foundation to over the roof. It will go inside cinder blocks that will be filled with concrete. The ceiling will be concrete. The door will swing in and will be built from one of the Safe Companies that offer walk in safe doors. Venting will be through pipes that bend to prevent anything from flying though the wall at that point, but also allow free flow of air into the room. Overall, the cost doesn't seem too bad except for the door. Once built, I plan on finishing it off with dog kennels and shelving for our clothes. Since it's so complex and time consuming to build, I keep putting it off for other projects that always seem more important. Eventually I'll get to it, but I really don't know when.
FEMA has a lot of stuff on their website on how to build a storm shelter. I've read up on what they require, and I'm going to built it to their specifications.