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Anairlock[a] is a room or compartment which permits passage between environments of differing atmosphericpressure or composition, while minimizing the changing of pressure or composition between the differing environments.
An airlock consists of a chamber with twoairtight doors 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 contain eitherair orwater. This is called afloodable airlock orunderwater airlock, and is used to prevent water from entering asubmersible vessel orunderwater habitat.
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 out involves equalizing pressure, unsealing the outer door, then exiting the lock compartment to enter the ambient environment.Locking on and off refer totransfer under pressure where 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 suit moves 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,contaminated spaces, or unbreathable atmospheres, which may not necessarily involve any differences in pressure; in these cases, adecontamination procedure and flushing are used instead of pressure change procedures.
The first airlockpatent was granted in 1830 toThomas 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.[1][2]
TheApollo program involved 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 11 mission, 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 anddepressurized before 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.[3]
When theInternational Space Station (ISS) first began to house humans in November 2000,[4] it did not include an airlock, and allextravehicular activity had to be facilitated by the airlock on theSpace Shuttle[5] until theQuest Joint Airlock module was installed in July 2001.[6]
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 2023[update] it is the largest airlock of its kind on the station, capable of fitting "payloads as large as a refrigerator."[7]
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 undesiredparticulates can 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,laboratories ofbiochemistry, 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 buildings andair-supported structures such 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 microscope interiors 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 airlocks are 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 todecompose due to air contamination.[8]
Civil engineering projects 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 acaisson or 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.
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Underwater applications include:
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 orlifeboat without significant pressure changes.
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.
Airlocks are used in outer space, especially duringhuman spaceflight, to maintain the internal habitable environment onspacecraft andspace stations when 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 suits in preparation forextravehicular activity, and then to recompress them upon return.[5] Airlocks such as theNanoracks Bishop Airlock also allow payloads to be released into space with minimal air loss.
TheSkylab orbital workshop included a manually operated trash disposal airlock to transfer trash from the pressurized habitable compartment to the unpressurized waste tank.[9]
Other examples of airlocks used in space include theQuest Joint Airlock and the airlock onKibō (ISS module).
Media related toAirlocks at Wikimedia Commons
