A subterranean, steel-reinforced concrete vault or arch is the most prevalent form of purpose-built building. Civil engineering constructions with enormous subterranean tubes or pipelines, such as sewage or fast transit tunnels, are the most practical blast shelters. These structures can withstand pressure levels many times greater than that which would otherwise be experienced at ground level.
The walls of a bunker are usually about 6 feet thick and its roof 9 to 12 feet high. The entrance is generally about 3 feet by 4 feet. A bunker's interior is well-lit and ventilated by means of natural light and ventilation holes cut into the roof. There are usually two storage rooms: one for food and the other for water. A bunker's internal temperature varies depending on how much heat is generated by its occupants; however, it is always below freezing outside.
Bunkers were popular in Europe during World War II when protection was needed from aerial bombing attacks. Today, they are used primarily for sheltering government agencies and private companies in emergency situations where security is important but life support systems might be compromised.
There are three main types of bunkers: anti-tank, anti-aircraft, and nuclear.
An anti-tank bunker is built to protect soldiers against attack by armored vehicles such as tanks. It has thick walls for defense and includes firing ports through which soldiers can shoot back at attackers.
Blast defense This significantly reduces the possibility of a bomb (other than a bunker buster) causing damage to the structure. The fundamental concept is to build a structure that is extremely robust under physical compression. These can be found in military bases, government buildings, and even some commercial structures. They are also used as safe houses by some families who fear violence at home.
Bomb protection Most nuclear weapons are designed to destroy their target, not to injure people many miles away. However, an atomic blast produces extreme heat and pressure that can travel through solid material such as rock, destroying or damaging anything in its path. The main purpose of a bomb shelter is to protect against this kind of attack. A shelter's thickness depends on how far down it goes; the deeper the better. The recommended minimum depth for safety reasons is 20 feet (6 m). Shelters should be located as far away from cities as possible. Preferably, they should be located more than 100 miles (160 km) from major population centers.
Radiation protection Even though radiation isn't completely opaque to light, it does have a strong effect on certain elements of the electromagnetic spectrum. For this reason, lights are usually not allowed inside a nuclear fallout zone. Only essential equipment should be kept operating after a nuclear attack, since nonessential equipment would just add weight to an already overloaded power grid.
During World War II, they were primarily developed by nations such as Germany to safeguard vital industry from aircraft assault. Industrial bunkers are also used as control rooms for hazardous tasks such as rocket engine testing or explosive experiments.
In modern times, they are used again for protection against aerial attack, this time on military targets. They are also used as safe storage facilities for toxic chemicals. Civilian use includes mining bunker houses where people can work in safety while being protected from underground explosions.
During WWII, international law allowed the use of subterranean structures for defense purposes. The Germans used mines as defensive weapons long before it was officially approved under the Geneva Convention. As far back as 1915, German engineers built mine-protected factories to protect their industrial machinery from enemy attacks. These first "industrial bunkers" were simple chambers with no internal support beams or doors that could be filled with high-grade metal ore to shield it from aircraft bombs.
Soon after the war started, the British and Americans began building their own bunkers. They were needed because traditional fortifications were not giving good results against air raids. The Germans used hydrogen gas during the battle of Britain because it was invisible to radar and could travel farther than conventional explosives. This would not be possible without first encasing them in protective shells.
Bunkers are typically subterranean, whereas blockhouses are mostly above ground. They were widely employed for weapons facilities, command and control centers, and storage facilities throughout World War I, World War II, and the Cold War. Bunkers can also be utilized as tornado shelters.
Bunkers come in many forms, but they generally consist of a room with no more than 4 feet of clearance from the outside wall. They can be built into the side of a hill or mountain, under a house, or anywhere else that space allows. The walls should be at least 6 inches thick to withstand heavy artillery fire or nuclear attacks.
Blockhouses are larger, better protected structures used to guard against attack by soldiers armed with muskets or cannons. Blockhouses often included several rooms with barricaded doors for defense. They were commonly used on frontier towns during the American Revolutionary War and the French and Indian War. Blockhouses remain in use today in places such as Afghanistan and Canada.
There are three main types of blockhouses: picket, stockade, and earthwork. A picket blockhouse is simply a wooden post with a flagpole attached to it. The flag would either be plain white with red stripes (for peace) or blue with yellow stripes (for war). If the blockhouse was located on government property, then it would usually have one or more flags flying above it.