Airlock

For other uses, seeAirlock (disambiguation).

An airlock on board theSpace Shuttle

Anairlockis a room or compartment which permits passage between environments of differing atmosphericpressureor composition, while minimizing the changing of pressure or composition between the differing environments. "Airlock" is sometimes written asair-lockorair lock,or abbreviated to justlock.

An airlock consists of a chamber with twoairtightdoors or openings, usually arranged in series, which do not open simultaneously. Airlocks can be small-scale mechanisms, such asthose used in fermenting,or larger mechanisms, which often take the form of anantechamber.

An airlock may also be used underwater to allow passage between the air environment in apressure vessel,such as asubmarine,and the water environment outside. In such cases the airlock can containairorwater.This is called afloodable airlockorunderwater airlock,and is used to prevent water from entering asubmersiblevessel orunderwater habitat.

Operation

The procedure of entering an airlock from the external or ambient pressure environment, sealing it, equalizing the pressure, and passing through the inner door is known aslocking in.Conversely,locking outinvolves equalizing pressure, unsealing the outer door, then exiting the lock compartment to enter the ambient environment.Locking on and offrefer totransfer under pressurewhere the two chambers are physically connected or disconnected prior to equalizing the pressure and locking in or out.

Before opening either door, the air pressure of the airlock chamber is equalized with that of the environment beyond the next door. A gradual pressure transition minimizes air temperature fluctuations, which helps reduce fogging andcondensation,decreases stresses on air seals, and allows safe verification of critical equipment.

When a person who is not in apressure suitmoves between environments of greatly different pressures, an airlock changes the pressure slowly to help with internal air cavity equalization and to preventdecompression sickness.This is critical inunderwater diving,and a diver or compressed air worker may have to wait in an airlock for a number of hours in accordance with adecompression schedule.A similar arrangement may be used for access to airtight clean spaces,contaminatedspaces, or unbreathable atmospheres, which may not necessarily involve any differences in pressure; in these cases, adecontaminationprocedure and flushing are used instead of pressure change procedures.

History

See also:History of decompression research and development

19th century

The first airlockpatentwas granted in 1830toThomas Cochrane,who came up with the idea to help facilitate underground tunnel construction. It was put into use in 1879 during an attempt to dig a tunnel under theHudson river.

20th century

TheApollo programinvolved developments in airlock technology, as airlocks are critical to allow humans to enter and exit the spacecraft while on the Moon without losing too much air due to itsscant atmosphere.

During the 1969Apollo 11mission, there was no room that was primarily designed to be an airlock; instead, they used the cabin as an airlock. It had to be evacuated anddepressurizedbefore the door was opened, and then once the door was closed it had to be re-pressurized again before anyone could safely reenter the cabin without aspace suit.

21st century

When theInternational Space Station(ISS) first began to house humans in November 2000,it did not include an airlock, and allextravehicular activityhad to be facilitated by the airlock on theSpace Shuttleuntil theQuest Joint Airlockmodule was installed in July 2001.

The first ever commercial space airlock was theNanoracks Bishop Airlock,installed on the ISS in December 2020. It is "bell-shaped" and is designed to transfer payloads out from the ISS interior and into space. As of July 2023it is the largest airlock of its kind on the station, capable of fitting "payloads as large as a refrigerator."

Air environments

Airlocks are used in air-to-air environments for a variety of reasons, most of which center around either preventing airborne contaminants from entering or exiting an area, or maintaining the air pressure of the interior chamber.

One common use of airlock technology can be found in somecleanrooms,where harmful or otherwise undesiredparticulatescan be excluded by maintaining the room at a higher pressure than the surroundings, alongside other measures. Conversely, particulates are prevented from escaping hazardous environments, such asnuclear reactors,laboratoriesofbiochemistry,and medical centers, by keepingnegative room pressure- maintaining the room at a lower pressure than the surroundings, so that air (and any particulates that it carries) cannot escape easily.

A lesser-known application of an airlock is in architecture:inflatable buildingsandair-supported structuressuch as pressurized domes require the internal air pressure to be maintained within a specific range so that the structure doesn't collapse. Airlocks are generally the most cost-efficient way to allow people to enter and exit these structures.

Airlocks are utilized to maintainelectron microscopeinteriors at near-vacuum so that air does not affect the electron path.Fermentation locks,such as those used in alcohol brewing, are a type of airlock which allow gases to escape the fermentation vessel while keeping air out.Parachute airlocksare necessary because airfoil collapse due to depressurization can result in dangerous loss of altitude.

Since the 1980s, airlock technology has been used to explore newly detected chambers in theEgyptian pyramids,to prevent the contents from beginning todecomposedue to air contamination.

Underground

Civil engineeringprojects that use air pressure to keep water and mud out of the workplace use an airlock to transfer personnel, equipment, and materials between the external normabaric environment and the pressurized workplace in acaissonor sealedtunnel.The airlock may need to be large enough to accommodate a whole working shift at the same time.

Locking in is usually a quick procedure, taking only a few minutes, while the decompression required for locking out may take hours.

Underwater

US Navysubmarine diving lock out

Underwater applications include:

• Hyperbaric chambers,to allow entry and exit while maintaining pressure difference between chamber and environment;
• Submarines,closed diving bells,andunderwater habitatsthat are not at ambient pressure, to permit divers to enter and exit. In submarines and underwater habitats they may also be called diver lock-out compartments; and
• Torpedo tubesandescape trunksin submarines.

Saturation diving

Main article:Saturation diving

Insaturation diving,airlocks are crucial safety elements; they serve as pressurized gateways to safely manage the transfer of divers and support personnel between the saturation system (living quarters) and thediving bell,which shuttles divers to their underwater worksite.

Airlocks in saturation diving are equipped with safety features such aspressure gauges,manual overrides,andinterlocks.

Saturation systems typically feature a variety of airlocks, including a stores lock for the transfer of supplies and a medical lock for secure passage of medical necessities or emergency evacuations. Complex "split-level" systems, which house divers at different pressure levels for varied work depths, may necessitate additional airlocks.

Decompression post-dive is a gradual process, often taking a full week. During this time, the airlocks allow divers to shift to a decompression chamber where pressure is progressively reduced back to surface levels. In emergencies, airlocks can facilitate transfer to a hyperbaric escape chamber orlifeboatwithout significant pressure changes.

Hyperbaric treatment chambers

Main articles:Hyperbaric medicineandDiving chamber

In any hyperbaric treatment chamber capable of accommodating more than one person, and where it may be necessary to get a person or equipment into or out of the chamber while it is pressurized, an airlock is used. There will usually be a large airlock at the chamber entry capable of holding one or more persons, and a smaller medical lock for locking in medical supplies and food, and locking out waste.

Outer space

STS-103closing the airlock

Airlocks are used in outer space, especially duringhuman spaceflight,to maintain the internal habitable environment onspacecraftandspace stationswhen persons are exiting or entering the spacecraft. Without an airlock (or similar technology, such as asuitport) the air inside would be rapidly lost upon opening the door due to the expansive properties of the gases that comprisebreathable air,as described byBoyle's law.An airlock room is needed to decompress astronauts after they suit up in specializedspace suitsin preparation forextravehicular activity,and then to recompress them upon return.Airlocks such as theNanoracks Bishop Airlockalso allow payloads to be released into space with minimal air loss.

Other examples of airlocks used in space include theQuest Joint Airlockand the airlock onKibō (ISS module).

See also

• Cabin pressurization
• Dysbarism– Medical conditions resulting from changes in ambient pressure
• Mechanisms with similar functions:
  • Lock (water navigation)– Uses water levels instead of air
  • Mantrap (access control)
  • Revolving door– Regulates building air pressure and temperature
  • Sally port– Focused on security rather than air pressure
  • Suitport– Alternative technology to enable extravehicular activity
  • Vestibule– Regulates building temperature
  • "Light-locks" inplanetariumsanddarkrooms
• Crew and Science Airlock Module