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An airlock is a room or compartment which permits passage between environments of differing atmospheric pressure or composition, while minimizing the changing of pressure or composition between the differing environments.
An airlock consists of a chamber with two Hermetic seal doors or openings, usually arranged in series, which do not open simultaneously. Airlocks can be small-scale mechanisms, such as those used in fermenting, or larger mechanisms, which often take the form of an antechamber.
An airlock may also be used underwater to allow passage between the air environment in a pressure vessel, such as a submarine, and the water environment outside. In such cases the airlock can contain either air or water. This is called a floodable airlock or underwater airlock, and is used to prevent water from entering a submersible vessel or underwater habitat.
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 and condensation, decreases stresses on air seals, and allows safe verification of critical equipment.
When 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 underwater diving, and a diver or compressed air worker may have to wait in an airlock for a number of hours in accordance with a decompression schedule. A similar arrangement may be used for access to airtight clean spaces, Contamination spaces, or unbreathable atmospheres, which may not necessarily involve any differences in pressure; in these cases, a decontamination procedure and flushing are used instead of pressure change procedures.
During the 1969 Apollo 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 and depressurized 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 a space suit.
The first ever commercial space airlock was the Nanoracks 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. it is the largest airlock of its kind on the station, capable of fitting "payloads as large as a refrigerator."
One common use of airlock technology can be found in some , where harmful or otherwise undesired particulates 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 as , Laboratory of biochemistry, and medical centers, by keeping negative 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 and air-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 maintain electron 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 the Egyptian pyramids, to prevent the contents from beginning to Decomposition due to air contamination. Alt URL
Locking in is usually a quick procedure, taking only a few minutes, while the decompression required for locking out may take hours.
Airlocks in saturation diving are equipped with safety features such as pressure gauges, , and .
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 or lifeboat without significant pressure changes.
The Skylab orbital workshop included a manually operated trash disposal airlock to transfer trash from the pressurized habitable compartment to the unpressurized waste tank.
Other examples of airlocks used in space include the Quest Joint Airlock and the airlock on Kibō (ISS module).
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