Nuclear weapons: lethal radius by bomb size and shelter type

In the event of an air burst nuclear attack, an underground shelter provides significantly more protection to nearby populations than a basement-level shelter. For a one megaton nuclear bomb, the lethal radius for those in an underground shelter would be over eight times smaller than the lethal radius for those in basement shelters. In fact, basement shelters provide relatively little protection in comparison to underground shelters, as their lethal radii is less than 20 percent smaller than that of populations in unprotected areas, whereas underground shelters' radii are over 90 percent smaller. This is largely due to the impact of thermal radiation, as temperatures from a one megaton bomb would exceed several thousand degrees Celsius at the epicenter, and would cause third degree burns up to six miles from ground zero. Additionally, shelters must be able to withstand the blast force of the explosion.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).

在遭遇空中爆发的核攻击事件中，相较于地下室避难所，地下掩体对周边民众提供了显著更高级别的保护。以一兆吨当量的核弹为例，身处地下掩体的人群的致命半径将比地下室避难所的人群的致命半径小八倍以上。实际上，地下室避难所相较于地下掩体所能提供的保护相对有限，因为其致命半径仅比无保护区域的人群的半径小百分之二十以下，而地下掩体的半径则超过百分之九十。这一现象主要归因于热辐射的影响，一兆吨核弹在爆心处的温度将超过数千摄氏度，并能在距零点六英里范围内造成三级烧伤。此外，避难所还必须能够承受爆炸产生的冲击力。此后，民众将暴露于爆炸和放射性尘埃的双重核辐射之下，而防护效果取决于避难所的材料、厚度和质量。所提供的数值基于地下室避难所由八英寸厚的非加固混凝土块建造，而地下掩体则由十二英寸厚的混凝土和低于三十英寸的土壤建造的假设。不同的材料提供不同级别的保护，例如，一英寸厚的铅相当于四点四英寸厚的混凝土，或十七点六英寸厚的木材。然而，由于铅暴露的有毒副作用（在冷战期间理解度较低），大多数现代地下放射性尘埃避难所会采用混凝土和钢材的混合结构，并考虑多项工程因素，如防爆门或带有角落的入口走廊（因为伽马射线沿直线传播）。