Blast shelter
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Nuclear weapons |
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Background |
Nuclear-armed states |
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A blast shelter is a place where people can go to protect themselves from blasts and explosions, like those from
Blast shelters are a vital form of protection from
Design
This article possibly contains original research. (March 2024) |
Blast shelters deflect the blast wave from nearby explosions to prevent ear and internal injuries to people sheltering in the bunker. While frame buildings collapse from as little as 3
The basic plan is to provide a structure that is very strong in compression. The actual strength specification must be done individually, based on the nature and probability of the threat. A typical specification for heavy civil defence shelter in Europe during the Cold war was an overhead explosion of a 500 kiloton weapon at the height of 500 meters. Such a weapon would be used to attack soft targets (factories, administrative centres, communications) in the area.
Only the most heavy bedrock-shelters would stand a chance of surviving.[citation needed] However, in the countryside or in a suburb, the likely distance to the explosion is much larger, as it is improbable that anyone would waste an expensive nuclear device on such targets. The most common purpose-built structure is a steel-reinforced concrete vault or arch buried or located in the basement of a house.
Most expedient blast shelters are civil engineering structures that contain large buried tubes or pipes such as sewage or rapid transit tunnels. Even these, nonetheless, require several additions to serve properly: blast doors, air-filtration and ventilation equipment, secondary exits, and air-proofing.
Improvised purpose-built blast shelters normally use earthen arches or vaults. To form these, a narrow (1-2 metre-wide) flexible tent of thin wood is placed in a deep trench (usually the apex of the tent is below grade), and then covered with cloth or plastic, and then covered with 1–2 meters of tamped earth. Shelters of this type are approved field expedient blast shelters of both the U.S. and China. Entrances are constructed from thick wooden frames. Blast valves are to be constructed from tire-treads laid on thick wooden grids.
Nuclear bunkers must also cope with the underpressure that lasts for several seconds after the shock wave passes, and prompt radiation. The overburden and structure provide substantial
The doors must be at least as strong as the walls. The usual design is a trap-door, to minimize the size and expense. In dual-purpose shelters, which have a secondary peacetime use, the door may be normal. To reduce the weight, the door is normally constructed of steel, with a fitted steel lintel and frame welded to the steel-reinforcement of the concrete. The shelter should be located so that there is no combustible material directly outside it.
If the door is on the surface and will be exposed to the blast wave, the edge of the door is normally counter-sunk in the frame so that the blast wave or a reflection cannot lift the edge. If possible, this should be avoided, and the door built so that it is sheltered from the blast wave by other structures. The most useful construction is to build the door behind a 90°-turn in a corridor that has an exit for the overpressure.
A bunker commonly has two doors, one of which is convenient, and in peacetime use, and the other is strong. Naturally, the shelter must always have a secondary exit which can be used if the primary door is blocked by debris. Door shafts may double as ventilation shafts to reduce the digging, although this is inadvisable.
A large ground shock can move the walls of a bunker several centimeters in a few milliseconds. Bunkers designed for large ground shocks must have sprung internal buildings, hammocks, or bean-bag chairs to protect inhabitants from the walls and floors. However, most civilian-built improvised shelters do not need these as their structure cannot stand a shock large enough to seriously damage the occupants.
Earth is an excellent insulator. In bunkers inhabited for prolonged periods, large amounts of ventilation or air-conditioning must be provided to prevent heat prostration. In bunkers designed for war-time use, manually operated ventilators must be provided because supplies of electricity or gas are unreliable. 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. (This is a
Ventilation openings in a bunker must be protected by blast valves. A
Bunkers must also protect the inhabitants from normal weather, including rain, summer heat and winter cold. A normal form of rainproofing is to place plastic film on the bunker's main structure before burying it. Thick (5-mil or 125 μm), inexpensive polyethylene film serves quite well, because the overburden protects it from degradation by wind and sunlight. Naturally, a buried or basement-situated reinforced-concrete shelter usually has the normal appearance of a building.
When a house is purpose-built with a blast shelter, the normal location is a reinforced below-grade bathroom with large cabinets.[citation needed] In apartment houses, the shelter may double as storage space, as long as it can be swiftly emptied for its primary use. A shelter can easily be added in a new basement construction by taking an existing corner and adding two poured walls and a ceiling.
Some vendors provide true blast shelters engineered to provide good protection to individual families at modest cost. One common design approach uses
Subways
During
Stations of the Pyongyang Metro in North Korea, constructed 110 metres (360 ft) below ground in the 1960s and 1970s, are designed as nuclear blast shelters and each station entrance has thick steel blast doors.[1][2]
Further reading
- Protecting Buildings from Bomb Damage: Transfer of Blast-Effects Mitigation, 1995, pp32-33 an overview of the literature.
- FEMA Bibliography of building design documents to prevent blast hazards.
- Blast Loading and Blast Effects on Structures – An Overview, 2007. Predicting blast pressures.
- AFSWC-TDR-6Z-138 Air Force Design Manual, Principles and practices for design of hardened structures 1962. Superseded by 1987 Manual for Design and Analysis of Hardened Structures, AFWL-TR-87-57 and Army Technical Manual TM 5-855-1 (Air Force Pamphlet AFPAM 32-1147, Navy Manual NAVFAC P-1080, DSWA Manual 1997).
See also
- Air raid shelter
- Autonomous building
- Emergency preparedness
- Retreat (survivalism)
References
- ISBN 978-1-74104-558-1.
- ISBN 978-963-00-8104-7.