what is a fallout shelter

A fallout shelter is an enclosed space designed to protect occupants from radioactive debris or fallout resulting from a nuclear explosion. Fallout shelters were constructed as civil defense measures during the Cold War. The purpose of a fallout shelter is to allow its occupants to minimize exposure to harmful fallout until radioactivity has decayed to a safer level. A basic fallout shelter consists of shielding that reduces gamma-ray exposure. Usually, an expedient purpose-built fallout shelter is a trench with a strong roof buried by 1 m (3 ft) of earth. The two ends of the trench have ramps or entrances at right angles to the trench, so that gamma rays cannot enter (they can travel only in straight lines) . To make the overburden waterproof (in case of rain), a plastic sheet may be buried a few inches below the surface and held down with rocks or bricks. Fallout shelters are not always underground; they can be above ground as well. A prototypical fallout shelter was made of concrete and steel, and sunk in the earth for added protection. However, those who could not afford such a construction project sometimes set aside a corner of their basement or dug a makeshift shelter under the crawlspace of a house. A shelter would usually be stocked with canned food, bottled water, medical supplies, a radio, a Geiger counter, and other necessary supplies.