Lets look at Tornado Safe Rooms in Residential Buildings.
Requirements for the in-residence shelter
Resistance to Wind Forces
Resistance to Missile Perforation
For the in-residence shelter to be effective, it must be readily accessible from all parts of the house. The central area of the home is the favored location, for added protection as well as accessibility.
The in-residence shelter must be able to resist the forces that extreme winds of 250 mph, which accounts for virtually all tornadoes which have occurred in the U.S.
Adequate fasteners are the key to satisfactory structural performance of the shelter. The roof must be securely anchored to the walls, the walls to each other, and the walls to the foundation. These connections are necessary to insure structural integrity and to prevent the shelter from overturning.
Ventilation should be provided when the shelter is intended to provide protection from hurricanes.
Tornado-generated missiles (flying debris) create the greatest threat to occupants of homes that are struck by severe wind. These missiles, very often, perforate conventional walls and roofs. In order to provide a high degree of occupant protection, the shelter must be designed to prevent perforation by missiles on all surfaces–walls, roof, and door.
In order to minimize cost, only readily available construction materials are employed in the concepts presented. No new technology or unusual building skills are required in construction.