Disclaimer: I am not a prepper. I think being prepared for things like fires, tornadoes, and other events is a good thing. I have a cellar where I live, but I think something like any of the Tornado or Fire Shelters offered by Atlas is something I would prefer to my cellar as a fire in my house would make my cellar a potential death trap.
Atlas offers safe cellars, fire shelters, bomb shelters, and tornado shelters.
I ran across Atlas Survival Shelters a while back. Here’s an example of one of their shelters – Garage Floor Tornado Shelter: https://www.youtube.com/watch?v=PDRv9Vu1Plo (about 1:14 minutes long).
Here’s their YouTube channel: https://www.youtube.com/channel/UCPf0hMaIoO2dyf3MDUTcCOg
Official Website: www.atlassurvivalshelters.com
Flickr: https://www.flickr.com/search/?text=Atlas%20Survival%20Shelter (have to look around as it also includes things related to Atlas missiles)