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A fallout shelter is a civil defense measure used to reduce casualties in a nuclear war. Fallout is dust created when a nuclear weapon explodes. The explosion vaporizes the bomb and earth or other material within the fireball. When this material condenses in the cloud, it forms dust and light sandy material that resembles ground pumice. Fallout is initially highly radioactive. The most dangerous emission from fallout is gamma rays which travel in straight lines, like ordinary light. |
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A fallout shelter is a civil defense measure used to reduce casualties in a nuclear war. Fallout is radioactive dust created when a nuclear weapon explodes or some other event causes a [thermonuclear explosion]?. The explosion vaporizes any material within the fireball, including the ground if it is nearby. When this material condenses in the cloud, it forms dust and light sandy material that resembles ground pumice. This highly irradiated material then falls to earth, subjecting anything it touches to radiation. A fallout shelter is designed to allow its occupants to avoid this fallout while it is still dangerous. |
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Initial radiation from fallout can exceed 30,000 rads/hr immediately downwind of a groundburst. A cumulative does of 450rad-hours is fatal to half of humans. The radiation falls off exponentially (quickly) with time. Most areas become safe for travel and decontamination after three to five weeks. Fallout is distributed in a wide, usually thin ellipse downwind of the explosion. Rain can cause fallout to settle more quickly. |
Nature of Fallout |
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Initial radiation from fallout can exceed 30,000 rads/hr immediately downwind of a groundburst. A cumulative does of 450rad-hours is fatal to half of a population of humans. There have been no documented cases of survival beyond 600 rad-hrs. Most people become ill after an exposure to 100 rad-hrs or more. The fetuses of pregnant women are vulnerable and may miscarry, especially in the first trimester. Human biology resists mutation from large radiation exposure: grossly mutated fetuses usually miscarry. Civilian dose rates in peace-time range from .01 to .003 rad-hrs/year. Fallout radiation falls off exponentially (quickly) with time. Most areas become safe for travel and decontamination after three to five weeks. The ground track of fallout from an explosion is a long, thin fuzzy ellipse downwind of the explosion. It may be hundreds of kilometers long, and up to 50Km (30mi) wide from a single explosion. Rain can cause fallout to settle more quickly. This means that a rainstorm can be a very bad place just downwind of a nuclear war. The most dangerous emissions from fallout are gamma rays, which travel in straight lines, like ordinary light. The fallout particles emit the invisible, deadly gamma rays in the same way that a light bulb emits light. Gamma rays are invisible, and cannot be seen, smelt, or felt, even at very dangerous intensities. Special equipment is required to detect and measure gamma rays. The gamma rays do not contaminate people or objects. Fallout particles contaminate people or objects, and since they resemble sand, they can be brushed off, or washed off. The particles should be removed from the shelter, or shielded. Emergency drinking water can be adequately cleaned by filtering contaminated water through more than 25cm (10 in) of dirt. Food in sealed packages is not poisoned by fallout. Stored grain and exposed fruit can be cleaned and peeled. Vehicles are usually washed down with fire-hoses, into drains with removable filters, or deep trenches. Ground is usually decontaminated by bulldozing the fallout into deep, narrow trenches, and then back-filling the trenches. Details |
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The required shielding can be accomplished with 10 thicknesses of any material that reduce the radiation by half. Shields that reduce gammay ray intensity by 50% include 1cm (0.4 inches) of lead, 6cm (2.4 inches) of concrete, 9cm (3.6 inches) of packed dirt or 150m (500 ft) of air. When multiple thicknesses are built, the shielding multiplies. Thus, ten halving-thicknesses of packed dirt, 90cm (3ft) reduce gamma rays by a factor of 1024, which is 1/2 to the tenth power. |
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The required shielding can be accomplished with 10 halving-thicknesses of any material. Shields that reduce gamma ray intensity by 50% include 1cm (0.4 inches) of lead, 6cm (2.4 inches) of concrete, 9cm (3.6 inches) of packed dirt or 150m (500 ft) of air. When multiple thicknesses are built, the shielding multiplies. Thus, ten halving-thicknesses of packed dirt, 90cm (3ft) reduce gamma rays by a factor of 1024, which is 1/2 to the tenth power. |
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Inhabitants should plan to remain in the shelter 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 possible. |
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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 1.5Km (1mi). |
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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. |
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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 practical. |
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Emergency drinking water can be adequately cleaned by filtering contaminated water through more than 25cm (10 in) of dirt. Food in sealed packages is not poisoned by fallout. Stored grain and exposed fruit can be cleaned. |
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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. |
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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. Inexpensive kits are available from www.ki4u.com. |
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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 on-line at http://www.oism.org/nwss/. Inexpensive kits are available from http://www.ki4u.com. |
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