A blast shelter is a place where people can go to protect themselves from blasts and explosions, like those from bombs, or in hazardous worksites, such as on oil and gas refineries or petrochemical facilities. It differs from a fallout shelter, in that its main purpose is to protect from shock waves and overpressure instead of from radioactiveprecipitation, as a fallout shelter does. It is also possible for a shelter to protect from both blasts and fallout.
Blast shelters are a vital form of protection from nuclear attacks and are employed in civil defense. There are above-ground, below-ground, dedicated, dual-purpose, and potential blast shelters. Dedicated blast shelters are built specifically for the purpose of blast protection (see bunker). Dual-purpose blast shelters are existing structures with blast-protective properties that have been modified to accommodate people seeking protection from blasts. Potential blast shelters are existing structures or geological features exhibiting blast-protective properties that have potential to be used for protection from blasts.
Design
Blast doors in a missile control bunker at Minot Air Force Base, North Dakota.The 25-ton blast door in the Cheyenne Mountain nuclear bunker is the main entrance to another blast door (background) beyond which the side tunnel branches into access tunnels to the main chambers.
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 psi (20 kPa) of overpressure, blast shelters are regularly constructed to survive several hundred psi. This substantially decreases the likelihood that a bomb can harm the structure.
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 radiation shielding, and the negative pressure is usually only 1/3 of the overpressure.
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.
The door of a light civil defense shelter in Finland
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 Kearny Air Pump, or KAP, named after the inventor Cresson Kearny.[citation needed]) Kearny asserts, based on field testing, that air filtration is not normally needed in a nuclear shelter. He asserts that fallout is either large enough to fall to the ground, or so fine that it will not settle and thus has little bulk to emit radiation. However, if possible, shelters should have air-filtration to stop chemical, biological and nuclear impurities which may abound after an explosion.
Ventilation openings in a bunker must be protected by blast valves. A blast valve is closed by a shock wave, but otherwise remains open. If the bunker is in a built-up area, it may include water-cooling or an immersion tube and breathing tubes to protect inhabitants from fire storms. In these cases, the secondary exit is also most useful.
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 125μm), 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 fiber-reinforced plastic shells. Compressive protection may be provided by inexpensive earth arching. The overburden is designed to shield from radiation. To prevent the shelter from floating to the surface in high groundwater, some designs have a skirt held-down with the overburden. A properly designed, properly installed home shelter does not become a sinkhole in the lawn. In Switzerland, which requires shelters for private apartment blocks and large private houses, the lightest shelters are constructed of stainless steel.[citation needed]
Stations of the Pyongyang Metro in North Korea, constructed 110 metres (360ft) below ground in the 1960s and 1970s, are designed as nuclear blast shelters and each station entrance has thick steel blast doors.[1][2]
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.
A bomb is an explosive weapon that uses the exothermic reaction of an explosive material to provide an extremely sudden and violent release of energy. Detonations inflict damage principally through ground- and atmosphere-transmitted mechanical stress, the impact and penetration of pressure-driven projectiles, pressure damage, and explosion-generated effects. Bombs have been utilized since the 11th century starting in East Asia.
Nuclear fallout is the residual radioactive material propelled into the upper atmosphere following a nuclear blast, so called because it "falls out" of the sky after the explosion and the shock wave has passed. It commonly refers to the radioactive dust and ash created when a nuclear weapon explodes. The amount and spread of fallout is a product of the size of the weapon and the altitude at which it is detonated. Fallout may get entrained with the products of a pyrocumulus cloud and fall as black rain. This radioactive dust, usually consisting of fission products mixed with bystanding atoms that are neutron-activated by exposure, is a form of radioactive contamination.
A nuclear bunker buster, also known as an earth-penetrating weapon (EPW), is the nuclear equivalent of the conventional bunker buster. The non-nuclear component of the weapon is designed to penetrate soil, rock, or concrete to deliver a nuclear warhead to an underground target. These weapons would be used to destroy hardened, underground military bunkers or other below-ground facilities. An underground explosion releases a larger fraction of its energy into the ground, compared to a surface burst or air burst explosion at or above the surface, and so can destroy an underground target using a lower explosive yield. This in turn could lead to a reduced amount of radioactive fallout. However, it is unlikely that the explosion would be completely contained underground. As a result, significant amounts of rock and soil would be rendered radioactive and lofted as dust or vapor into the atmosphere, generating significant fallout.
A bunker is a defensive military fortification designed to protect people and valued materials from falling bombs, artillery, or other attacks. Bunkers are almost always underground, in contrast to blockhouses which are mostly above ground. They were used extensively in World War I, World War II, and the Cold War for weapons facilities, command and control centers, and storage facilities. Bunkers can also be used as protection from tornadoes.
A bomb shelter is a structure designed to provide protection against the effects of a bomb.
The effects of a nuclear explosion on its immediate vicinity are typically much more destructive and multifaceted than those caused by conventional explosives. In most cases, the energy released from a nuclear weapon detonated within the lower atmosphere can be approximately divided into four basic categories:
Air raid shelters are structures for the protection of non-combatants as well as combatants against enemy attacks from the air. They are similar to bunkers in many regards, although they are not designed to defend against ground attack.
"Duck and cover" is a method of personal protection against the effects of a nuclear explosion. Ducking and covering is useful in offering a degree of protection to personnel located outside the radius of the nuclear fireball but still within sufficient range of the nuclear explosion that standing upright and uncovered is likely to cause serious injury or death. In the most literal interpretation, the focus of the maneuver is primarily on protective actions one can take during the first few crucial seconds-to-minutes after the event, while the film of the same name and a full encompassing of the advice also cater to providing protection up to weeks after the event.
The Diefenbunker, formerly known by its military designation, Canadian Forces Station Carp (CFS Carp), is a large underground four-storey reinforced concrete bunker and nuclear fallout shelter located in the rural area of Carp, Ontario approximately 30 km (19 mi) west of downtown Ottawa. Between 1957 and 1961, during the Cold War the Government of Canada led by then Prime Minister John Diefenbaker authorized the Diefenbunker to be designed and built as the Central Emergency Government Headquarters (CEGHQ Carp) in an attempt to ensure the continuity of government subsequent to a nuclear weapons attack by the Soviet Union. In 1994, CFS Carp was decommissioned and closed.
A blast valve is used to protect a shelter, such as a fallout shelter or bunker, from the effects of sudden outside air pressure changes. A nuclear weapon creates a shock wave, which may produce sudden pressure changes of more than an atmosphere even several kilometres from the detonation point. After the shock wave passes, a sudden negative pressure follows.
Explosives safety originated as a formal program in the United States in the aftermath of World War I when several ammunition storage areas were destroyed in a series of mishaps. The most serious occurred at Picatinny Arsenal Ammunition Storage Depot, New Jersey, in July, 1926 when an electrical storm led to fires that caused explosions and widespread destruction. The severe property damage and 19 fatalities led Congress to empower a board of Army and Naval officers to investigate the Picatinny Arsenal disaster and determine if similar conditions existed at other ammunition depots. The board reported in its findings that this mishap could recur, prompting Congress to establish a permanent board of colonels to develop explosives safety standards and ensure compliance beginning in 1928. This organization evolved into the Department of Defense Explosives Safety Board (DDESB) and is chartered in Title 10 of the US Code. The DDESB authors Defense Explosives Safety Regulation (DESR) 6055.9 which establishes the explosives safety standards for the Department of Defense. The DDESB also evaluates scientific data which may adjust those standards, reviews and approves all explosives site plans for new construction, and conducts worldwide visits to locations containing US title munitions. The cardinal principle of explosives safety is expose the minimum number of people for the minimum time to the minimum amount of explosives.
The Kearny air pump is an expedient air pump used to ventilate a shelter. The design is such that a person with normal mechanical skills can construct and operate one. It is usually human-powered and designed to be employed during a time of crisis. It was designed to be used in a fallout shelter, but can be used in any situation where emergency ventilation is needed, as after a hurricane.
Nuclear War Survival Skills or NWSS, by Cresson Kearny, is a civil defense manual. It contains information gleaned from research performed at Oak Ridge National Laboratory during the Cold War, as well as from Kearny's extensive jungle living and international travels.
A safe room or panic room is a fortified room that is installed in a private residence or business to provide a safe shelter, or hiding place, for the inhabitants in the event of a break in, home invasion, tornado, terror attack, or other threat. Safe rooms usually contain communications equipment, so that law enforcement authorities can be contacted.
The Sonnenberg Tunnel is a 1,550 m (5,090 ft) long motorway tunnel, constructed between 1971 and 1976 and located in Lucerne, Switzerland. At its completion it was also the world's largest civilian nuclear fallout shelter, designed to protect 20,000 civilians in the eventuality of war or disaster.
A rupture disc, also known as a pressure safety disc, burst disc, bursting disc, or burst diaphragm, is a non-reclosing pressure relief safety device that, in most uses, protects a pressure vessel, equipment or system from overpressurization or potentially damaging vacuum conditions.
Operation Sailor Hat was a series of explosives effects tests, conducted by the United States Navy Bureau of Ships under the sponsorship of the Defense Atomic Support Agency. The tests consisted of two underwater explosions at San Clemente Island, California in 1964 and three surface explosions at Kahoʻolawe, Hawaii in 1965. They were non-nuclear tests employing large quantities of conventional explosives to determine the effects of a nuclear weapon blast on naval vessels, and the first major test of this kind since Operation Crossroads in July 1946.
Abo Elementary School in Artesia, New Mexico, United States, was the first public school in the United States constructed entirely underground and equipped to function as an advanced fallout shelter. Designed at the height of the Cold War and completed in 1962, the school had a concrete slab roof which doubled as the school's playground. It contained a large storage facility with room for emergency rations and supplies for up to 2,160 people in the event of nuclear warfare or other catastrophe. The building was listed on the National Register of Historic Places in 1999.
An overpressure protection system is one designed to protect an individual or group of individuals in a chemical, biological, radiological and nuclear (CBRN) environment. The two parts of the system are a safe area which as far as possible is sealed from possible contaminated air and an air filtration system which will filter out all possible toxins. Air pumps force clean air through the filters into the safe area such that the air pressure within the safe area will always be higher than that outside of the safe area. This pressure differential means that any flows of air will always be from the safe area to the outside, preventing the ingress of toxins.
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