Cabin pressurization 1488888 225781707 2008-07-15T11:05:09Z SmokeyJoe 901576 /* Pressurized flight */ "cabin altitude". was undefined Jargon from the source. Reword. '''Cabin pressurization''' is the active pumping of [[air]] into an [[aircraft cabin]] to increase the air pressure within the cabin. It is required when an [[aircraft]] reaches high altitudes, because the natural [[atmospheric pressure]] is too low to allow people to absorb sufficient [[oxygen]], leading to [[altitude sickness]] and ultimately [[Hypoxia (medical)|hypoxia]]. ==Unpressurized flight== A lack of sufficient oxygen will bring on hypoxia by reducing the [[Pulmonary alveolus|alveolar]] oxygen tension. In some individuals, particularly those with heart or lung disease, symptoms may begin as low as 1500&nbsp;[[Metre|m]] (5000&nbsp;[[foot (unit of length)|ft]]) above [[sea level]], although most passengers can tolerate altitudes of 2500&nbsp;m (8,000&nbsp;ft) without ill effect. At this altitude, there is about 25% less oxygen than there is at sea level.<ref name="02_calc">{{cite web | author=K. Baillie and A. Simpson | title=Altitude oxygen calculator | url=http://www.altitude.org/calculators/airpressure.htm | accessdate=2006-08-13}} - Online interactive altitude oxygen calculator</ref> Passengers may also develop fatigue or [[headaches]] as the plane flies higher. As the operational altitude increases, reactions become sluggish and unconsciousness will eventually result. Sustained flight operations above 3,000&nbsp;m (10,000&nbsp;ft) generally require supplemental oxygen (through a [[nasal cannula]] or [[oxygen mask]]) or a [[pressure suit]]. ==Pressurized flight== [[Image:Bottle.jpg|thumb|right|Empty water bottle, closed during a commercial transatlantic flight at a cruising altitude of 30,000 ft. Photo taken back on the ground.]]Aircraft that routinely fly above 3000&nbsp;m (10,000&nbsp;ft) are generally equipped with an oxygen system fed through masks or canulas (typically for smaller aircraft), or are pressurized by an [[environmental control system]] (ECS) using air provided by [[Gas compressor|compressors]] or [[bleed air]]. Bleed air extracted from the engines is compressively heated and extracted at approximately 200&nbsp;[[Celsius|°C]] (392&nbsp;[[Fahrenheit|°F]]) and then cooled by passing it through a [[heat exchanger]] and [[air cycle machine]] (commonly referred to by aircrews and mechanics as 'the packs system').Most modern commercial aircraft today have a dual channel electronic controller for maintaining pressurization along with a manual back-up system. These systems maintain air pressure equivalent to 2,500&nbsp;m (8,000&nbsp;ft) or below, even during flight at altitudes above 13,000&nbsp;m (43,000&nbsp;ft). Aircraft have a positive pressure relief valve in the event of excessive pressure in the cabin. This is to protect the aircraft structure from excessive loading. Normally, the maximum pressure differential between the cabin and the outside air is 7.5–8&nbsp;[[pounds per square inch|psi]]<!-- "psid" is redundant: "the difference is X psid" = "the difference is a difference of X" --> (52–55&nbsp;[[Pascal (unit)|kPa]]). If the cabin were maintained at sea level pressurization and then flown to 35,000 feet (10.7&nbsp;km) or more, the pressurization differential would be greater than 9&nbsp;psi (60&nbsp;kPa) and the structural life of the airplane would be limited.The traditional method of bleed air extraction from the engine comes at the expense of powerplant efficiency. Some aircraft, such as the [[Boeing 787]], use electric compressors to provide pressurization. This allows greater propulsive efficiency.As the airplane pressurizes and decompresses, some passengers will experience discomfort as trapped gasses within their bodies expand or contract in response to the changing cabin pressure. The most common problems occur with gas trapped in the [[gastrointestinal tract]], the [[middle ear]] and the paranasal sinuses. Note that in a pressurized aircraft these effects are not due directly to climb and descent, but to changes in the pressure maintained inside the aircraft. It is always an emergency if a pressurized aircraft suffers a pressurization failure above 3000&nbsp;m (10,000&nbsp;ft). If this occurs, the plane must begin an emergency descent, and [[oxygen mask]]s are activated for everyone aboard. In most passenger jet aircraft (such as the Boeing 737<ref>[http://www.b737.org.uk/emergency_equipment.htm Emergency Equipment<!-- Bot generated title -->]</ref>), passenger [[oxygen mask]]s are automatically deployed if the cabin pressure falls below the equivalent pressure of the atmosphere at 14,000 feet (i.e. if "cabin altitude" exceeds 14,000 feet).<ref>[http://www.usatoday.com/travel/columnist/getline/2006-05-15-ask-the-captain_x.htm USATODAY.com - When oxygen masks mysteriously appear<!-- Bot generated title -->]</ref> ==History and usage of cabin pressurization== Prior to World War II the [[Boeing 307]] Stratoliner had a pressurized cabin, though only ten such aircraft were produced. While the piston fighters of [[World War II]] often flew at very high altitudes, they were not pressurized; instead pilots used oxygen. However, in a larger bomber where crew moved about the cabin, this was considerably less practical. Therefore, the first bomber with cabin pressurization (though restricted to crew areas), was the [[B-29 Superfortress]]. The cabin pressure control system was designed for the B-29 by [[Garrett Systems|Garrett AiResearch Manufacturing Company]], drawing in part on licensing of patents held by Boeing for the Stratoliner.<ref>Seymour L. Chapin, "Garrett and Pressurized Flight: A Business Built on Thin Air," ''Pacific Historical Review'' 35 (August 1966): 329-343.</ref> Post-war piston airliners such as the [[Lockheed Constellation]] expanded the technology to civilian service, and as jet airliners were always designed for high-altitude operation, every jetliner features the technology. Most [[turboprop]] aircraft also feature cabin pressurization due to their medium to high altitude operation. A very few piston-engined small private planes also do so; most do not routinely fly high enough to justify such a system. ==Loss of pressurization== One consequence of cabin pressurization is that the pressure inside the airplane might be 70&nbsp;kPa (10&nbsp;psi), while the pressure outside is only 15&nbsp;kPa (2&nbsp;psi). An otherwise-harmless pinhole under these pressure differences will generate a high-pitched squeal as the air leaks out at [[supersonic]] speeds{{Fact|date=February 2007}}. A hole a metre and a half (5 feet) across will depressurize a jetliner in a fraction of a second. Rapid decompression is a change in cabin pressure where the lungs can decompress faster than the cabin. [[Explosive decompression]] is a change in cabin pressure faster than the lungs can decompress (less than 0.5 seconds). This type of decompression is potentially dangerous and often results in lung damage and unsecured items / debris flying around the cabin.{{Fact|date=June 2007}} Rapid decompression of commercial aircraft is extremely rare, but dangerous. People directly next to a very large hole may be forced out or injured by flying debris. Floors and internal panels may deform. Gradual or slow decompression is dangerous because it may not be detected. The [[Helios_Airways_Flight_522|Helios Airways]] 2005 accident is a good example <ref name="Helios Airways 2005">{{cite web | author=J. Laming | title=Helios out of oxygen. Flight Safety Australia magazine - Nov-Dec 2005, pp 27-33| url=http://www.casa.gov.au/fsa/2005/dec/27-33.pdf | }} </ref>. Warning systems may be ignored, misinterpreted or fail and self-recognition of the subtle effects of hypoxia really depends upon previous experience and [[hypoxia familiarization]] training. Unfortunately, in most countries this has been largely restricted to military hypobaric chamber training with its risk of [[decompression sickness]] and [[barotrauma]]. Newer reduced oxygen breathing systems <ref name="Hypoxia familiarization training by the reduced oxygen breathing method">{{cite web | author=R. Westerman | title= Hypoxia familiarization training by the reduced oxygen breathing method. ADF Health 2004; 5 (1): 11-15 | url=http://www.defence.gov.au/health/infocentre/journals/ADFHJ_apr04/ADFHealth_5_1_11-15.pdf | }} </ref> are more accessible, safer and provide valuable practical experience <ref name="Hypoxia symptoms in military aircrew: long-term recall vs. acute experience in training.">{{cite web | author=AM. Smith | title= Hypoxia symptoms in military aircrew: long-term recall vs. acute experience in training. Aviat Space Environ Med. 2008 Jan;79(1):54-7. | url=http://www.ncbi.nlm.nih.gov/pubmed/18225780?ordinalpos=1&itool=EntrezSystem2.PEntrez.Pubmed.Pubmed_ResultsPanel.Pubmed_RVDocSum| }} </ref> . Adding such practical training to knowledge required by regulatory authorities is likely to increase hypoxia awareness and aviation safety. [[Hypoxia (medical)|Hypoxia]] will result in loss of consciousness without emergency oxygen. The [[Time of Useful Consciousness]] varies depending on the altitude. Additionally, the air temperature will plummet due to expansion, potentially resulting in [[frostbite]]. *Contrary to Hollywood myth, as seen in the [[James Bond]] film, [[Goldfinger (film)|Goldfinger]], people just a few feet from the hole are more at risk from [[Hypoxia (medical)|hypoxia]] than from being forced out. ==Effects of cabin pressurization on an aircraft fuselage== As the airplane is pressurized and depressurized, the metal skin of the airplane expands and contracts, resulting in [[metal fatigue]]. Modern aircraft are designed to resist this compression cycle, but some early jetliners (see [[De Havilland Comet]]) had fatal accidents due to underdesign for fatigue. ==Effects of cabin pressurization on the human body== *[[Ear]] and [[paranasal sinus]]es: One needs to adjust to the pressurized cabin air from the beginning. 1 in 3 passengers suffer ear discomfort, pain and temporary hearing loss on takeoff or landing, called "aerotitus" by the [[House Ear Institute]] in [[Los Angeles]]. Rapid changes in air pressure cause the air pocket inside the ear to expand during takeoff and contract during descent, stretching the [[eardrum]]. To equalize pressure, air must enter or escape through the [[Eustachian tube]]. "''If a passenger has serious congestion, they risk ear drum damage''", says [[Sigfrid Soli]], [[Ph.D.]], head of the HCSD Department at the [[HSI]].{{Fact|date=July 2007}} *[[Tooth]]: Anyone with gas trapped in an infected tooth may also experience [[barodontalgia]], a toothache provoked by exposure to changing atmospheric pressure. *[[Pneumothorax]]: Anyone who has suffered a pneumothorax is recommended not to fly (even in a pressurised cabin) for at least 1 month and should obtain an x-ray prior to travelling. As well as the more acute health effects experienced by some people, the cabin pressure altitude of 2,500&nbsp;m (8,000&nbsp;ft) typical in most airliners contributes to the fatigue experienced in long flights. The [[Boeing 787]] airliner (in development) will feature pressuration to the equivalent of 1,800&nbsp;m (6,000&nbsp;ft), which Boeing claims will substantially increase passenger comfort. The [[Airbus A350]] may go even further, with pressurising to 1,500&nbsp;m (5,000&nbsp;ft) being considered.{{Fact|date=October 2007}} Some people may still experience symptoms of [[altitude sickness]] despite the cabin pressure. ==Noted incidents== * [[BOAC Flight 781]]: In-flight metal fatigue failure caused an [[explosive decompression]], a form of cabin depressurization, in 1954, which killed 35 people. This was the first of a series of [[de Havilland Comet]] accidents that would require extensive redesign of the aircraft. * [[American Airlines Flight 96]]: A [[DC-10]] lost its rear cargo door in flight due to a problem with the latch mechanism. The ensuing decompression collapsed the cabin floor, severing hydraulic lines which allowed control of the tail surfaces and one of the engines. The aircraft was saved without loss of life by the pilot's ([[Bryce McCormick]]) use of differential thrust from the aircraft's wing engines to establish limited pitch and yaw control. * [[Turkish Airlines Flight 981]]: A [[DC-10]] lost its rear cargo door in flight due to a problem with the latch mechanism. The severity of the depressurization damaged hydraulic controls causing the flight crew to lose control. All 346 on board were killed. * [[Japan Airlines Flight 123]]: A [[Boeing 747]] had its rear pressure bulkhead fail, resulting in a decompression. The damage to the aircraft severed hydraulics, and the flight crew were unable to maintain control. 520 passengers died with only 4 survivors. * [[Aloha Airlines Flight 243]]: A [[Boeing 737]] explosive decompression, resulting in the death of one [[flight attendant]]. * [[United Airlines Flight 811]]: A Boeing 747-122 lost its forward cargo door, resulting in the loss of several seats from the business class cabin and the deaths of 9 passengers. * Golfer [[Payne Stewart]] and five others died in a [[1999 South Dakota Learjet crash|Learjet accident]] as a result of loss of cabin pressure. * [[Helios Airways]] [[Helios Airways Flight 522|Flight 522]]: A [[Cypriot]] [[Boeing 737]] crashed in Greece on [[August 14]] [[2005]], killing all 121 people aboard. It is believed that the plane failed to pressurize and the pilots fell unconscious. * [[China Airlines Flight 611]]: A [[Boeing 747]] disintegrated while climbing to cruising altitude on May 25, 2002, killing all 225 passengers aboard. This was caused by metal fatigue (caused by a faulty repair 22 years earlier) leading to the cabin's decompression. == In Fiction == * In the movie [[Snakes on a Plane]], decompression forces helped to remove the offending snakes from the aircraft through "open" windows. ==See also== *[[Atmosphere (unit)]] *[[Compressed air]] *[[Rarefaction]] *[[Space suit]] ==First Airliners with pressurization systems== *[[Boeing 307]] *[[Avro Tudor]] *[[Lockheed Constellation]] *[[Douglas DC-6]] ==Notes== {{reflist|2}} ==General references== *Seymour L. Chapin, "Garrett and Pressurized Flight: A Business Built on Thin Air," ''Pacific Historical Review'' 35 (August 1966): 329-343. *Seymour L. Chapin, "Patent Interferences and the History of Technology: A High-flying Example," ''Technology and Culture'' 12 (July 1971): 414-446. *Portions from the [http://www.vnh.org/FSManual/01/07RapidDecompress.html United States Naval Flight Surgeon's Manual] *[http://www.cnn.com/2005/WORLD/europe/08/14/greece.crash/index.html CNN: 121 Dead in Greek Air Crash] *"Explosive Decompression" segment of ''[[MythBusters]]'' episode 10, [[January 11]] [[2004]] **also shown as a segment of ''[[Beyond 2000|Beyond Tomorrow]]'' episode 12 [[Category:Aerospace engineering]] [[Category:Aviation terminology]] [[de:Druckkabine]] [[nl:Drukcabine]]