Blast Effect ProtectionIn the detonation of a one megaton size weapon (which is roughly equivalent to 1 million tons of TNT), the fireball grows to 440 feet in just a fraction of a second. In 10 seconds, the fireball is over a mile wide. At the same time the fireball is forming and growing, a high-pressure wave develops and moves outward in all directions. This wave of air causes a huge increase in air pressure. At one-quarter mile from the crater edge, the overpressures are about 200 psi. It is not expected that nuclear weapons with a greater yield than one megaton would be used against the civilian population. We are, therefore, limiting our discussion of blast effects to that yield.
At approximately 4 miles from the epicenter, the winds are 165 mph and the overpressure is approximately 5 psi. Most homes would be destroyed, and very little blast effect protection would be found in a basement shelter at that distance. At 6 and 7 miles from the epicenter, there would be moderate damage to residences and the likelihood of surviving in a basement is increased.
People housed in hardened blast shelters and radiation shelters, such as are built by Utah Shelter Systems, would be expected to survive all NBC weapons effects at ground zero from an air burst (50 psi), and at one quarter mile from the crater edge from a one megaton yield ground burst. At that proximity, an 8 ft. diameter shelter must have at least 8 feet of dirt cover. A 10-foot diameter shelter must have at least 10 feet of dirt cover overhead. Each person must have approximately 10 square feet of shelter space for short-term survival (up to 2 weeks). Double this space requirement if the shelter must be used for longer periods.