To compare the safety of underground shelters versus basement fallout shelters within target areas, the kill probability from nuclear weapons has been analyzed. This was estimated by relating the calculated lethal radii for various weapon yields and the distance from the target point to a current ICBM aiming error. Curves were constructed showing kill probability at varying distances from the target point for selected megaton yields with specified degrees of protection. For example, a comparison showed that a person 4 miles from a 5 megaton ICBM target point would have a 97% risk of being killed within a basement fallout shelter, or an 8% risk within the specified underground shelter.
Russell PW, Kimbrel LG. Estimates of the Kill Probability in Target Area Family Shelters. JAMA. 1962;180(1):25-29. doi:10.1001/jama.1962.03050140027006