A blast valve is used to protect a shelter, such as a
fallout shelter
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.
During ...
or
bunker
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. T ...
, from the effects of sudden outside air pressure changes. A
nuclear weapon
A nuclear weapon is an explosive device that derives its destructive force from nuclear reactions, either fission (fission bomb) or a combination of fission and fusion reactions ( thermonuclear bomb), producing a nuclear explosion. Both bom ...
creates a shock wave, which may produce sudden pressure changes of more than an atmosphere (about 1 bar) even several kilometres from the detonation point. After the shock wave passes, a sudden negative pressure follows.
If such pressure waves enter a shelter, they will likely do substantial harm to occupants and equipment. A blast valve is placed in air intake/exhaust pipes, that remains open normally, but automatically closes when strong pressure is applied in either direction.
Blast dampers operate in the same fashion and are related or identical to blast valves, the former name however is generally used to describe blast mitigation devices, for more
conventional explosive
An explosive (or explosive material) is a reactive substance that contains a great amount of potential energy that can produce an explosion if released suddenly, usually accompanied by the production of light, heat, sound, and pressure. An expl ...
events.
A typical blast valve has entries of 15–30 cm diameter, and a larger centre section. Within the centre section is a disk mounted on an axle, with weak springs that keep it centred, away from both entries. Pressure displaces the disk along the axle, until it plugs one entry or the other. After the blast, the springs return the disk to the centre, re-opening the valve.
Another type of blast valve employs rounded metal tubes held in place by springs. As pressure rises it pushes the tubes against the frame of the valve closing the opening. These valves are typically unidirectional in airflow and are employed in large wall structures where large amounts of airflow is required.
One form of blast valve, popularized by the book
Nuclear War Survival Skills
''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 liv ...
and tested by
ORNL
Oak Ridge National Laboratory (ORNL) is a U.S. multiprogram science and technology national laboratory sponsored by the U.S. Department of Energy (DOE) and administered, managed, and operated by UT–Battelle as a federally funded research and ...
is worn flat rubber
tire
A tire (American English) or tyre (British English) is a ring-shaped component that surrounds a wheel's rim to transfer a vehicle's load from the axle through the wheel to the ground and to provide traction on the surface over which t ...
treads nailed or bolted to frames strong enough to resist the maximum overpressure, with tested closing times cited as being identical to commercial grade blast valves, however the use of this form of blast valve design must also take the risk of the flammable rubber catching fire into consideration.
{{DEFAULTSORT:Blast Valve
Valves
Nuclear warfare