For other uses, see Airlock (disambiguation).
An airlock on board the Space Shuttle.

An airlock is a device which permits the passage of people and objects between a pressure vessel and its surroundings while minimizing the change of pressure in the vessel and loss of air from it. The lock consists of a small chamber with two airtight doors in series which do not open simultaneously.

An airlock may be used for passage between environments of different gases rather than different pressures, to minimize or prevent the gases from mixing.

An airlock may also be used underwater to allow passage between an air environment in a pressure vessel and the water environment outside, in which case the airlock can contain air or water. This is called a floodable airlock or an underwater airlock, and is used to prevent water from entering a submersible vessel or an underwater habitat.


Before opening either door, the air pressure of the airlock—the space between the doors—is equalized with that of the environment beyond the next door to open. This is analogous to a waterway lock: a section of waterway with two watertight gates, in which the water level is varied to match the water level on either side.

A gradual pressure transition minimizes air temperature fluctuations (see Boyle's law), which helps reduce fogging and condensation, decreases stresses on air seals, and allows safe verification of pressure suit and space suit operation.

Where a person who is not in a pressure suit moves between environments of greatly different pressures, an airlock changes the pressure slowly to help with internal air cavity equalization and to prevent decompression sickness. This is critical in scuba diving, and a diver may have to wait in an airlock for some hours, in accordance with decompression tables.


US Navy submarine diving lock out, 2007.

Airlocks are used in

Similar mechanisms

Fictional airlocks

A four-door airlock (with three interior chambers) was proposed by science fiction writer H. Beam Piper in his novel Uller Uprising. The atmosphere inside the fictional structure was human-breathable, while the outside atmosphere was highly toxic. Only one door of the airlock opened at a time, and the middle chamber of the three would always contain a vacuum to minimize traces of the exterior atmosphere reaching the habitat.

Airlocks are also used in the Bioshock game series for entrance and exit into water environments.

Airlocks are commonly used in science fiction as a form of execution, often referred to as "spacing" or "airlocking". Battlestar Galactica and the Honorverse books both make frequent use or reference to it.

In the film Moonraker, James Bond dispatches of the villain Hugo Drax aboard his own space station by first shooting him in the chest with a cyanide dart, then pushing him out an airlock into space ("Take a giant leap for mankind.").

In Star Trek, Star Wars and some other fiction genres, conventional airlocks may be replaced by forcefields which hold in air while allowing solid matter like spacecraft to pass through. Airlocks of this type usually have pressure doors as a backup.

Airlocks play a somewhat important role in The Martian, as the failure of Mark Watney's Mars Habitat airlock and the subsequent depressurization of the environment kills the potato crops he was growing, exacerbating his situation of being marooned on Mars.

See also


External links

Media related to Airlocks at Wikimedia Commons

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