Editing Uncontrolled decompression (section)

==Description==
[[File:Explosive Decompression Test System.gif|thumb|In this test chamber, air pressure drops suddenly to that of the atmosphere at {{cvt|60000|ft}}. Air humidity immediately condenses into fog, which within seconds evaporates back into gas.]]

The term ''uncontrolled decompression'' here refers to the unplanned depressurisation of [[pressure vessel|vessels]] that are occupied by people; for example, a pressurised aircraft cabin at high altitude, a [[spacecraft]], or a [[hyperbaric chamber]]. For the catastrophic failure of other pressure vessels used to contain [[gas]], [[liquid]]s, or [[reactant]]s under pressure, the term [[explosion]] is more commonly used, or other specialised terms such as [[BLEVE]] may apply to particular situations.

Decompression can occur due to structural failure of the pressure vessel, or failure of the compression system itself.<ref name="FAA-OPS">{{cite web|publisher=[[Federal Aviation Administration]] |url=http://www.faa.gov/pilots/training/airman_education/media/ac%2061-107a.pdf|date=2007-07-15 |title=AC 61-107A – Operations of aircraft at altitudes above 25,000 feet msl and/or mach numbers (MMO) greater than .75|access-date=2008-07-29}}</ref><ref name=Dehart>{{cite book |title=Fundamentals Of Aerospace Medicine: Translating Research Into Clinical Applications, 3rd Rev Ed.|last=Dehart|first=R. L.|author2=J. R. Davis |year=2002 |publisher=Lippincott Williams And Wilkins|location=United States|isbn=978-0-7817-2898-0|page=720}}</ref>  The speed and violence of the decompression is affected by the size of the pressure vessel, the differential pressure between the inside and outside of the vessel, and the size of the leak hole.

The [[Federal Aviation Administration|US Federal Aviation Administration]] recognizes three distinct types of decompression events in aircraft: explosive, rapid, and gradual decompression.<ref name="FAA-OPS"/><ref name=Dehart/>

===Explosive decompression===

Explosive decompression occurs typically in less than 0.1 to 0.5 seconds, a change in cabin pressure faster than the lungs can decompress.<ref name="FAA-OPS"/><ref>{{cite book|title=Flight Training Handbook|url=https://books.google.com/books?id=ioRTAAAAMAAJ|year=1980|access-date=2007-07-28|publisher=U.S. Dept. of Transportation, [[Federal Aviation Administration]], Flight Standards Service|page=250|author1=Flight Standards Service, United States|author2=Federal Aviation Agency, United States}}</ref> Normally, the time required to release air from the lungs without restrictions, such as masks, is 0.2 seconds.<ref name="phak7-36" /> The risk of lung trauma is very high, as is the danger from any unsecured objects that can become [[projectile]]s because of the [[explosion|explosive]] force, which may be likened to a bomb detonation.

Immediately after an explosive decompression, a heavy fog may fill the aircraft cabin as the air cools, raising the [[relative humidity]] and causing sudden condensation.<ref name="phak7-36">{{Cite PHAK|year=2016|chapter=7|pages=36}}</ref> Military pilots with [[oxygen mask]]s must pressure-breathe, whereby the lungs fill with air when relaxed, and effort has to be exerted to expel the air again.<ref>{{cite web|url=http://aupress.au.af.mil/digital/pdf/book/brulle_engineering_space_age.pdf|title=Engineering the Space Age: A Rocket Scientist Remembers|author=Robert V. Brulle|date=2008-09-11|publisher=[[Athabasca University Press|AU Press]]|archive-url=https://web.archive.org/web/20110928085032/http://aupress.au.af.mil/digital/pdf/book/brulle_engineering_space_age.pdf|archive-date=2011-09-28|access-date=2010-12-01}}</ref>

===Rapid decompression===
Rapid decompression typically takes more than 0.1 to 0.5 seconds, allowing the lungs to decompress more quickly than the cabin.<ref name="FAA-OPS"/><ref>{{cite book|url=https://books.google.com/books?id=3hMZAAAAIAAJ|title=The New Frontier: Man's Survival in the Sky|author=Kenneth Gabriel Williams|year=1959|access-date=2008-07-28|publisher=Thomas}}</ref> The risk of lung damage is still present, but significantly reduced compared with explosive decompression.

===Gradual decompression===

Slow, or gradual, decompression occurs slowly enough to go unnoticed and might only be detected by instruments.<ref name="FAA-OPS2">{{Cite web |url=http://www.faa.gov/pilotos/training/airman_education/media/ac%2061-107a.pdf |title=AC 61-107A - Operations of aircraft at altitud above 25,000 feet MSL and/or mach numbers (MMO) greater than .75 |date=July 15, 2007 |work=[[Federal Aviation Administration]] }}</ref> This type of decompression may also come about from a failure to pressurize the cabin as an aircraft climbs to altitude. An example of this is the 2005 [[Helios Airways Flight 522]] crash, in which the maintenance service left the pressurization system in manual mode and the pilots did not check the pressurization system. As a result, they suffered a loss of consciousness (as well as most of the passengers and crew) due to [[hypoxia (medical)|hypoxia]] (lack of oxygen). The plane continued to fly due to the autopilot system and eventually crashed due to fuel exhaustion after leaving its flight path.