Following the first wartime use of an atomic bomb by the United States in 1945, fears of nuclear retaliation by the communist Soviet Union lead many Americans to invest in a new form of self-protection called a fallout shelter. An underground fallout shelter would ostensibly protect occupants from the immediate and long-term effects of radioactive debris, or nuclear fallout, which often follows the initial detonation of a nuclear bomb.
During the 1950s and 1960s, it was not unusual for local government agencies to designate the basement of a public building as an approved fallout shelter for officials and civilians alike. A special yellow and black sign bearing three triangles and the words "fallout shelter" would be placed over the entrance to such emergency shelters, although not every designated fallout shelter actually provided the level of protection many experts considered acceptable.
Following a nuclear explosion, radioactive particles from the bomb's inner core combine with other material in the atmosphere and form a fine powder which can be carried over a significant distance by prevailing winds. This contaminated dust would contain enough radioactive material to cause radiation poisoning if inhaled or ingested. The best protection against such a health hazard is a thick barrier made from an energy-absorbing material.
In a standard fallout shelter, this material would typically be lead, concrete or compacted dirt. Once the habitable structure was completed and stocked with emergency supplies of water and food, it would be encased in a heavy layer of concrete or at least three feet of excavated dirt. The radioactive dust might settle on the surface of this material, but it would not have the ability to penetrate the shelter itself.
Sales of fallout shelters for private homeowners peaked during the 1960s, but dropped dramatically after political tensions between the Soviet Union and the United States lessened and the threat of a nuclear attack seemed far less likely. Some homeowners converted their fallout shelters into general storage buildings or weather shelters, but many allowed them to fall into disrepair or had them removed altogether.
