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Fallout shelter

A sign pointing to an old fallout shelter in .
A sign pointing to an old fallout shelter in New York City.

A fallout shelter is a civil defense measure intended to reduce casualties in a nuclear war. Nuclear fallout is radioactive dust created when a nuclear weapon explodes. The explosion vaporizes any material within the fireball, including the ground if it is nearby. Much of this material is exposed to neutrons from the explosion, absorbs them, and becomes radioactive. When this material condenses in the cloud, it forms dust and light sandy material that resembles ground pumice. The fallout emits gamma rays as if each particle were a tiny x-ray machine. Much of this highly radioactive material then falls to earth, subjecting anything within the line of sight to gamma radiation, a significant hazard. A fallout shelter is designed to allow its occupants to avoid exposure to harmful fallout until radioactivity has lowered to a safer level.


Details of improvised fallout shelters

A basic fallout shelter consists of shields that reduce gamma ray exposure by a factor of 1000. Since the most dangerous fallout has the consistency of sand or finely ground pumice, a successful fallout shelter need not filter fine dust from air. The fine dust both emits relatively little radiation (because the intensity of the radiation increases as the cube of the particle size), and does not settle to the earth, where the fallout shelter is.

The required shielding can be accomplished with 10 times the amount of any quantity of material capable to cutting gamma ray effects in half. Shields that reduce gamma ray intensity by 50% (1/2) include 1 cm (0.4 inches) of lead, 6 cm (2.4 inches) of concrete, 9 cm (3.6 inches) of packed dirt or 150 m (500 ft) of air. When multiple thicknesses are built, the shielding multiplies. Thus, a practical fallout shield is ten halving-thicknesses of packed dirt. This reduces gamma rays by a factor of 1024, which is 2 multiplied by itself ten times. This multiplies out to 90 cm (3 ft) of dirt.

Usually, an expedient purpose-built fallout shelter is a trench, with a strong roof buried by ~1 m (3 ft) of dirt. The two ends of the trench have ramps or entrances at right angles to the trench, so that gamma rays cannot enter (they behave like invisible light).

To make the overburden waterproof (in case of rain), a plastic sheet should be buried a few inches below the surface and held down with rocks or bricks.

Earth is an excellent thermal insulator, and over several weeks of inhabitation, a shelter will be completely warmed by body heat. Without good ventilation, the inhabitants are likely to suffer heat prostration.

The simplest form of effective fan to cool a shelter is a wide, heavy frame with flaps that swings 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. Attach a rope, and take turns swinging it. (This is a Kearney Air Pump, or KAP, named after the inventor.)

Any exposure to fine dust is far less hazardous than exposure to the gamma from the fallout outside the shelter. Dust fine enough to pass the entrance will probably pass through the shelter.

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).

Inhabitants should plan to remain sheltered for at least two weeks, then work outside for gradually increasing amounts of time, to four hours a day at three weeks. They should sleep in a shelter for several months. Evacuation at three weeks is very impractical.

A battery-powered radio is very helpful to get reports of fallout patterns and clearance. In many countries (including the U.S.) civilian radio stations have emergency generators with enough fuel to operate for extended periods without commercial electricity.

It is possible to construct an electrometer-type radiation meter from plans with just a coffee can or pail, gypsum board, monofilament fishing line, and aluminum foil. Plans are in the reference "Nuclear War Survival Skills" by Cresson Kearny, available online at Inexpensive kits are available from KI4U. Combined with an effective fallout-shelter plan, one should also consider the use of Potassium Iodide (KI) tablets as an additional measure to protect the human thyroid gland from the uptake of dangerous radioactive iodine, a component of most fallout and reactor waste.


Substantial numbers of fallout shelters were built in the 1950s in both the Eastern and Western blocs, though not in the U.S. During the Cold War many countries built fallout shelters for high-ranking government officials and crucial military facilities. Plans were made, however, to use existing buildings with sturdy below-ground-level basements as makeshift fallout shelters, but the initial blast of a nuclear attack may have rendered these basements either buried under many tons of rubble and thus impossible to leave, or removed their upper framework, thus leaving the basements unprotected.

Switzerland, however, built an extensive network of fallout shelters (mainly through extra hardening of government buildings such as schools) of a scale to protect and feed the entire population for two years after a nuclear attack. This nation has the highest ratio of shelter space to national population of any country.

Interest in fallout shelters has largely dropped, as the perceived threat of global nuclear war reduced after the end of the Cold War. However, a renewed interest has been seen since terrorism has struck on American soil. These shelters also provide a safe haven from natural disasters such as tornadoes and hurricanes.

A fallout shelter features prominently in the Robert Heinlein novel Farnham's Freehold, the Dean Ing novel Pulling Thru, and the Walter M. Miller novel A Canticle for Leibowitz

See also

External links

  • SurvivalRing.orgThis website offers dozens of free downloadable digitized documents on fallout shelter plans, regulations, standards, technical specifications, and more, as well as US targeting info as provided by FEMA.
  • Oregon Institute of Science and MedicineThis website offers the entire online version of Nuclear War Survival Skills with full graphics and web navigation, created with the permission of the author Cresson Kearny. This manual has proven technical info on expedient fallout shelter, shelter habitation, and assorted shelter system needs that can be created from common household items. OISM also offers free downloads of other civil defense and shelter information as well.
  • FEMA Civil Defense Shelters - A state of the Art Assessment - 1986 This 25 megabyte PDF file is the complete 300 page plus report on civil defense fallout shelter and shelter systems as compiled under contract for FEMA. Includes information on the design, construction, testing and cost of blast and fallout shelters, and includes a bibliography of over 1000 documents. Hosted by
  • FEMA Fallout Shelter Management Handbook 22 page PDF document - "The safety and well-being of the people in this shelter depend on capable leadership. If a civil defense shelter manager is not present, anyone seeing this handbook who has leadership experience can and should TAKE CHARGE IMMEDIATELY." Hosted by
Last updated: 10-15-2005 12:31:04
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