A fallout shelter is an enclosed space specially designated to protect occupants from radioactive debris or fallout resulting from a nuclear explosion. Many such shelters were constructed as civil defense measures during the Cold War.

During a nuclear explosion, matter vaporized in the resulting fireball is exposed to neutrons from the explosion, absorbs them, and becomes radioactive. When this material condenses in the rain, it forms dust and light sandy materials that resemble ground pumice. The fallout emits alpha and beta particles, as well as gamma rays.

Much of this highly radioactive material falls to Earth, exposing anything within its line of sight to radiation and becoming a significant hazard. A fallout shelter is designed to allow its occupants to minimize exposure to harmful fallout until radioactivity has decayed to a safer level, over a few weeks or months.

Principle

A fallout shelter is designed to protect its occupants from:

the mechanical and thermal effects of a nuclear explosion (or nuclear accident); radioactive fallout, allowing them to survive for a period of time deemed sufficient to allow them to escape safely.

History

North America

During the Cold War, many countries built fallout shelters for high-ranking government officials and crucial military facilities, such as Project Greek Island and the Cheyenne Mountain nuclear bunker in the United States and Canada's Emergency Government Headquarters. Plans were made, however, to use existing buildings with sturdy basements below ground level as makeshift fallout shelters. These buildings were placarded with the orange-yellow-and-black trefoil sign designed by the United States Army Corps of Engineers director of the administrative logistics support function, Robert W. Blakeley, in 1961.

The National Emergency Alarm Repeater (NEAR) program was developed in the United States in 1956 during the Cold War to supplement the existing siren warning systems and radio broadcasts in the event of a nuclear attack. The NEAR civilian alarm device was engineered and tested, but the program was not viable and was terminated in 1967.

In the U.S. in September 1961, under the direction of Steuart L. Pittman, the federal government started the Community Fallout Shelter Program. A letter from President Kennedy advising the use of fallout shelters appeared in the September 1961 issue of Life magazine. From 1954 to 1961, home fallout shelter sales grew, but eventually there was a public backlash against the fallout shelter as a consumer product and the market collapsed by 1963.

In November 1961, in Fortune magazine, an article by Gilbert Burck appeared that outlined the plans of Nelson Rockefeller, Edward Teller, Herman Kahn, and Chet Holifield for an enormous network of concrete-lined underground fallout shelters throughout the United States sufficient to shelter millions of people to serve as a refuge in case of nuclear war.Fortune magazine, November 1961, Pages 112–115 et alThe United States ended federal funding for the shelters in the 1970s. In 2017, New York City began removing the yellow signs since members of the public are unlikely to find edible food and usable medicine inside those rooms. In 2026, personal fallout shelters experienced an uptick in popularity.

Atomitat The Atomitat was an underground house in Plainview, Texas, designed by Jay Swayze and completed in 1962. The house was designed in response to the fear of nuclear war during the Cold War. The house was designed to be an "atomic-habitat" which met the United States Civil Defense specifications. It was the first bunker-house to meet their specifications as a nuclear shelter. Swayze also built an underground house for the 1964 New York World's Fair: it was called the Underground World Home.

Europe Similar projects have been undertaken in Finland, which requires all buildings with area over 600 m2 to have an NBC (nuclear-biological-chemical) shelter, and Norway, which requires all buildings with an area over 1000 m2 to have a shelter.

The former Soviet Union and other Eastern Bloc countries often designed their underground mass-transit and subway tunnels to serve as bomb and fallout shelters in the event of an attack. Currently, the deepest subway line in the world is situated in St Petersburg in Russia, with an average depth of 60 meters, while the second deepest subway station is Arsenalna in Kyiv, at 105.5 meters.

Germany has protected shelters for 3% of its population, Austria for 30%, Finland for 70%, Sweden for 81%, and Switzerland for 114%.

Bosnia

The Armijska Ratna Komanda D-0, also known as the Ark, was a Cold War-era nuclear bunker and military command centre located near the town of Konjic in Bosnia and Herzegovina. Built to protect Yugoslav President Josip Broz Tito and up to 350 members of his inner circle in the event of an atomic exchange, the structure is made up of residential areas, conference rooms, offices, strategic planning rooms, and other areas. The bunker remained a state secret until after the breakup of Yugoslavia in the 1990s.

The facility is now under the authority of the Bosnian Ministry of Defense. It is managed by the country's military, guarded by a five-soldier detachment, but is designated by KONS as National Monuments of Bosnia and Herzegovina and used as exhibition space for project such as Cultural Event of Europe with strong UNESCO support, and tourist attraction.

Another underground facility is Željava Air Base, situated on the border between Bosnia and Herzegovina and Croatia under the mountain, near the city of Bihać. It was the largest underground airport and military air base in the Socialist Federal Republic of Yugoslavia (SFRY), and one of the largest in Europe. The role of the facility was to establish, integrate, and coordinate a nationwide early warning radar network in SFRY akin to NORAD in the US. The complex contained tunnels in a total length of 3.5 km (2.2 mi), and the bunker with four entrances protected by 100-ton pressurized doors, three of which were customized for use by fixed-wing aircraft; capable of housing two full fighter squadrons, one reconnaissance squadron, and associated maintenance facilities. It was designed and built to sustain a direct hit from a 20-kiloton nuclear bomb, equivalent to that dropped on Nagasaki. The underground facility was lined with semicircular concrete shields, arranged every 10 km (6.2 mi), to cushion the impact of incoming strikes. The complex included an underground water source, power generators, crew quarters, and other strategic military facilities. It also housed a mess hall that could feed 1,000 people simultaneously, along with stores of food, fuel, and arms sufficient to last 30 days. Fuel was supplied by a 20 km (12 mi) underground pipe network connected to a military warehouse on Pokoj Hill near Bihać. Nowadays, they are popular for urban exploration.

Switzerland

Switzerland built an extensive network of fallout shelters, not only by extra-hardening government buildings such as schools, but also by a building regulation requiring nuclear shelters in residential buildings since the 1960s (the first legal basis in this sense dates from 4 October 1963). Catherine Frammery, "Dans les entrailles du Sonnenberg, monstrueux témoin de la Guerre froide" , Le temps, Monday 15 August 2016 (page visited on 15 August 2015). Later, the law ensured that all residential buildings built after 1978 contained a nuclear shelter able to withstand a blast from a 12-megaton explosion at a distance of 700 metres. The Federal Law on the Protection of the Population and Civil Protection still requires that every inhabitant should have a place in a shelter close to where they live. Daniele Mariani, "À chacun son bunker", Swissinfo, 23 October 2009 (page visited on 5 August 2015).

The Swiss authorities maintained large communal shelters (such as the Sonnenberg Tunnel until 2006) stocked with enough food and fuel to last over four months. The reference Nuclear War Survival Skills declared that, as of 1986, "Switzerland has the best civil defense system, one that already includes blast shelters for over 85% of all its citizens." As of 2006, there were about 300,000 shelters built in private residences, institutions and hospitals, as well as 5,100 public shelters for a total of 8.6 million places, a level of coverage equal to 114% of the population.

In Switzerland, most residential shelters are no longer stocked with the food and water required for prolonged habitation. A large number have been converted by the owners to other uses (e.g., wine cellars, ski rooms, gyms), but a legal obligation to ensure that the shelters are properly maintained remains in effect.

United Kingdom

In the United Kingdom, a network of fallout shelters were built across the country for use by the Royal Observer Corps in its nuclear reporting role. Other shelters were built for the purposes of the ROTOR radar system and the regional seat of government scheme. The Pindar complex in London is intended to provide its inhabitants with fallout protection in the event of nuclear attack, as was the earlier Central Government War Headquarters in Corsham.

Details of shelter construction

Shielding A basic fallout shelter consists of shielding that reduces gamma-ray exposure by a factor of 1000. The required shielding can be accomplished with 10 times the thickness of any quantity of material capable of cutting gamma ray exposure in half. Shields that reduce gamma ray intensity by 50% (1/2) include of lead, of concrete, of packed earth or of air. When multiple thicknesses are built, the shielding multiplies. Thus, a practical fallout shield is ten halving-thicknesses of packed earth, reducing gamma rays by approximately 1024 times (210).

Usually, an expedient, purpose-built fallout shelter is a trench with a strong roof buried 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.

Blast doors are designed to absorb the shock wave of a nuclear blast, bending and then returning to their original shape.

Climate control Dry earth is a reasonably good thermal insulator, but over several weeks of habitation, a shelter will become dangerously hot. The simplest form of effective fan to cool a shelter is a wide, heavy frame with flaps that swing in the shelter's doorway and can be swung from hinges on the ceiling. The flaps open in one direction and close in the other, pumping air. (This is a Kearny air pump, or KAP, named after the inventor, Cresson Kearny.)

Unfiltered air is safe, since the most dangerous fallout has the consistency of sand or finely ground pumice. Such large particles are not easily ingested into the soft tissues of the body, so extensive filters are not required. Any exposure to fine dust is far less hazardous than exposure to the fallout outside the shelter. Dust fine enough to pass the entrance will probably pass through the shelter. Some shelters, however, incorporate NBC-filters for additional protection.

Locations Effective public shelters can be the middle floors of some tall buildings or parking structures, or below ground level in most buildings with more than 10 floors. The thickness of the upper floors must form an effective shield, and the windows of the sheltered area must not view fallout-covered ground that is closer than 1.5 km (1 mi). One of Switzerland's solutions is to use road tunnels through the mountains, with some of these tunnels capable of protecting tens of thousands.