Basement SheltersIt is next to impossible to retrofit a basement shelter into an existing basement and achieve the proper shielding and blast protection needed to meet minimum Swiss standards for 15 psi. The maximum blast protection achieved is usually well under 5 psi., as the shelter walls and ceiling must be self supporting and independent of the building in order to reach protection from those blast levels. Significant radiation protection factors, however, can be achieved, by placing enough mass overhead and around the shelter. Some areas of low blast may receive high levels of radiation from rain out, local winds, or fast moving prevailing winds. To reach a minimum PF of 100, place at least 14 inches of concrete (or 18 inches of dirt) overhead. The walls receive radiation from windows and door openings. They must, therefore, be thicker than the ceiling. There are formulas for figuring the thickness, according to the number of openings, but a good approximation would be 18 inches of concrete (24 inches dirt equivalent). You may want to frame a 24-inch wide wall with wood and fill the interior of the wall with dry sand.
Be sure to provide adequate ventilation in your shelter. See the sub-title, 'Ventilation' under 'Shelter Components' on our web site. Carbon dioxide builds very quickly and may drive you out of your shelter before it is safe to leave.
You can find a basic plan for a basement shelter under 'Pricing'. These plans are meant only to guide you, and are not engineered to a specific size. Walls, ceilings and floors of homes came in many sizes, thickness and strengths of materials. It is mandatory that you consult a civil engineer to draw your engineered plans, before beginning the construction of any basement shelter and before cutting into foundation walls.