Nuclear weapons: lethal radius by bomb size and shelter type
Thereafter, populations would be subject to the nuclear radiation from both the blast and fallout, where protection is dependent on the shelter's material, thickness, and quality. The figures given are based on the assumption that the basement shelter is built from eight-inch thick unreinforced concrete blocks, whereas the underground shelter is built with 12 inches of concrete and under 30 inches of earth. Different materials offer different levels of protection, for example, a one inch layer of lead would be equal to 4.4 inches of concrete, or 17.6 inches of wood. However, due to the toxic side effects of lead exposure (which was less-understood during the cold war), most modern underground fallout shelters would be constructed with a combination of concrete and steel, with several engineering considerations, such as blast doors or entrance corridors with corners (as gamma rays travel in straight lines).