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Uncontrolled decompression refers to an unexpected drop in the pressure of a sealed system, such as an aircraft cabin. Where the speed of the decompression occurs faster than air can escape from the lungs, this is known as explosive decompression (ED), and is associated with explosive violence. Where decompression is still rapid, but not faster than the lungs can decompress, this is known as rapid decompression. Lastly, slow decompression or gradual decompression occurs so slowly that humans may not detect it before hypoxia sets in.

Generally uncontrolled decompression results from human error, material fatigue, engineering failure or impact, that causes a pressure vessel either not to pressurize, or to vent into lower-pressure surroundings.

Contents

Description

The term uncontrolled decompression here refers to the unplanned depressurisation of vessels that are occupied by people, for example an aircraft cabin at high altitude, a spacecraft or a hyperbaric chamber. For the catastrophic failure of other pressure vessels used to contain gas, liquids or reactants 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.[1][2] 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 recognizes three distinct types of decompression events in aircraft:[1][2]

  • Explosive decompression
  • Rapid decompression
  • Gradual decompression
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Explosive decompression

Explosive decompression occurs at a rate faster than that at which air can escape from the lungs, typically in less than 0.1 to 0.5 seconds.[1][3] The risk of lung trauma is very high, as is the danger from any unsecured objects which can become projectiles due to the explosive force.

After an explosive decompression within an aircraft, a heavy fog may immediately fill the interior. Military pilots with oxygen masks have to pressure-breathe, whereby the lungs fill with air when relaxed, and effort has to be exerted to expel the air again.[4]

Paul Withey, an aviation expert, described an explosive decompression inside an aircraft cabin as similar to the explosion of a 500 pound (225 kilogram) bomb inside the cabin.[5]

Rapid decompression

Rapid decompression typically takes more than 0.1 to 0.5 seconds, allowing the lungs to decompress faster than the cabin.[1][6] The risk of lung damage is still present, but significantly reduced compared to explosive decompression.

Slow decompression

Slow, or gradual, decompression occurs slowly enough to go unnoticed and might only be detected by instruments.[1] This type of decompression may also come about from a failure to pressurize as an aircraft climbs to altitude. This happened on a Ryanair, Boeing 737 flight in 2001 where the pressurization system was not activated by flight crew during pre-flight checks.[7]

Pressure vessel seals and testing

Seals in high-pressure vessels are also susceptible to explosive decompression; the O-rings or rubber gaskets used to seal pressurised pipelines tend to become saturated with high-pressure gases. If the pressure inside the vessel is suddenly released, then the gases within the rubber gasket may expand violently, causing blistering or explosion of the material. For this reason, it is common for military and industrial equipment to be subjected to an explosive decompression test before it is certified as safe for use.

Fallacies

Misunderstandings of "explosive decompression" are quite likely to be a fueling factor for a persistent myth that humans would explode if exposed to the non-pressure of outer space. Extravagant depictions in media such as the film Licence to Kill, where one character's head detonates after the hyperbaric chamber he is in is rapidly depressurized, have helped to fuel the myth. This is possible with the pressures experienced in diving chambers but not with the far smaller pressure changes involved in space exploration. Accidents in space exploration research and high-altitude aviation have shown that while vacuum exposure causes swelling, human skin is tough enough to withstand a drop of one atmosphere. This assumes that the person does not attempt to hold their breath (which is likely to cause acute lung trauma), the limiting factor on consciousness then being hypoxia after a few seconds.[8][9] A sudden drop of eight atm in the Byford Dolphin accident had immediately fatal results. [10]

The term explosive decompression refers to a rapid drop in air pressure itself and does not imply a cabin or fuselage exploding due to a rapid pressure change. Using a high-pressure airplane and several scale tests, the television program Mythbusters examined the belief that a bullet shot through the hull of an airplane will cause it to "explosively decompress" outwards, sucking chairs, baggage and people out of the hole. The program's tests indicated that fuselage design does not allow this to happen. Rigorous study would still be necessary for full scientific validation of the results.

Decompression injuries

The following physical injuries may be associated with decompression incidents:

Notable decompression accidents and incidents

Decompression incidents are not uncommon on military and civilian aircraft (approximately 40–50 rapid decompression events worldwide annually[17]), however in the majority of cases, the problem is relatively manageable for aircrew.[11] Consequently where passengers and the aircraft do not suffer any ill-effects, the incidents tend not to be notable.[11] Injuries resulting from decompression incidents are rare.[11]

Decompression incidents do not only occur in aircraft—the Byford Dolphin incident is an example of violent explosive decompression on an oil rig. A decompression event is an effect of a failure caused by another problem, even though the event may worsen the initial issue.

Event Date Pressure vessel Event Type Fatalities/of # on board Decompression Type Cause
BOAC Flight 781 1954 de Havilland Comet Accident 35/35 Explosive decompression Metal fatigue
South African Airways Flight 201 1954 de Havilland Comet Accident 21/21 Explosive decompression[18] Metal fatigue
1961 Yuba City B-52 crash 1961 B-52 Stratofortress Accident 0/8 Slow/rapid decompression Fuel exhaustion following increased fuel consumption caused by having to fly below 10,000ft after depressurisation event. Two nuclear bombs did not detonate on impact.
Soyuz 11 re-entry 1971 Soyuz spacecraft Accident 3/3 Gradual decompression Damaged cabin ventilation valve
American Airlines Flight 96 1972 Douglas DC-10-10 Accident 0/67 Rapid decompression[19] Cargo door failure
Turkish Airlines Flight 981 1974 Douglas DC-10-10 Accident 346/346 Explosive decompression[20] Cargo door failure
Far Eastern Air Transport Flight 103 1981 Boeing 737 Accident 110/110 Explosive decompression Corrosion
Byford Dolphin accident 1983 Diving bell Accident 5/6 Explosive decompression Human error, no fail-safe in the design
Korean Air Lines Flight 007 1983 Boeing 747-230B Shootdown 269/269 Rapid decompression[21][22] Intentionally fired air-to-air missile after aircraft strayed into prohibited airspace; 12 minutes of flight after damage from missile shrapnel caused the cabin to decompress.[23]
Japan Airlines Flight 123 1985 Boeing 747-SR46 Accident 520/524 Explosive decompression Structural failure of rear pressure bulkhead
Aloha Airlines Flight 243 1988 Boeing 737-297 Accident 1/95 Explosive decompression[24] Metal fatigue
United Airlines Flight 811 1989 Boeing 747-122 Accident 9/355 Explosive decompression Cargo door failure
British Airways Flight 5390 1990 BAC One-Eleven Incident 0/87 Rapid decompression[25] Windscreen failure
Lionair Flight LN 602 1998 Antonov An-24RV Shootdown 55/55 Rapid decompression Probable MANPAD shootdown
South Dakota Learjet 1999 Learjet 35 Accident 6/6 Gradual or rapid decompression (Undetermined)
Australia “Ghost Flight” 2000 Beechcraft Super King Air Accident 8/8 Decompression suspected (Undetermined)
TAM flight 9755 2001 Fokker 100 Accident 1/82 Rapid decompression Window ruptured by shrapnel after engine failure[26]
China Airlines Flight 611 2002 Boeing 747-200B Accident 225/225 Explosive decompression Metal fatigue
Helios Airways Flight 522 2005 Boeing 737-31S Accident 121/121 Gradual decompression The pressurization system was set to manual for the entire flight, resulting in a failure to pressurize the cabin.[27]
Alaska Airlines Flight 536 2005 McDonnell Douglas MD-80 Incident 0/140 + crew Rapid decompression Failure of operator to report collision involving a baggage loading cart at the departure gate. Decompressed at 26,000 feet
Qantas Flight 30 2008 Boeing 747-438 Incident 0/365 Rapid decompression[28] Fuselage ruptured by explosion of an oxygen cylinder
Southwest Airlines Flight 2294 2009 Boeing 737-300 Incident 0/126 + 5 crew Rapid decompression 1 square foot (0.093 m2) hole blown in fuselage during flight.[29] Under investigation

Implications for aircraft design

Modern aircraft are specifically designed with longitudinal and circumferential re-enforcing ribs in order to prevent localised damage from tearing the whole fuselage open during a decompression incident.[30] However, decompression events have nevertheless proved fatal for aircraft in other ways. In 1974, explosive decompression onboard Turkish Airlines Flight 981 caused the floor to collapse, severing vital flight control cables in the process. The FAA issued an airworthiness directive the following year requiring manufacturers of wide-body aircraft to strengthen floors so that they could withstand the effects of in-flight decompression caused by an opening of up to 20 square feet (1.9 m2) in the lower deck cargo compartment.[31] Manufacturers were able to comply with the directive either by strengthening the floors and/or installing relief vents between the passenger cabin and aft cargo compartment.

Prior to 1996, approximately 6,000 large commercial transport airplanes were type certificated to fly up to 45,000 feet, without being required to meet high altitude special conditions.[32] In 1996, the FAA adopted Amendment 25-87, which imposed additional high altitude cabin pressure specifications, for new type aircraft designs.[33] For aircraft certified to operate above 25,000 feet (FL 250), it "must be designed so that occupants will not be exposed to cabin pressure altitudes in excess of 15,000 feet after any probable failure condition in the pressurization system."[34] In the event of a decompression which results from "any failure condition not shown to be extremely improbable," the plane must be designed so that occupants will not be exposed to a cabin altitude exceeding 25,000 feet for more than 2 minutes, nor exceeding an altitude of 40,000 feet at any time. [35] In practice, that new FAR amendment imposes an operational ceiling of 40,000 feet on the majority of newly designed commercial aircraft.[36][37][Note 1]

In 2004, Airbus successfully petitioned the FAA to allow cabin pressure of the A380 to reach 43,000 feet in the event of a decompression incident, and to exceed 40,000 feet for one minute. This special exemption allows that new aircraft to operate at a higher altitude than other newly design civilian aircraft, which have not yet been granted a similar exemption.[38]

International standards

The Depressurization Exposure Integral (DEI) is a quantitative model that is used by the FAA to enforce compliance with decompression-related design directives. The model relies on the fact that the pressure that the subject is exposed to and the duration of that exposure are the two most important variables at play in a decompression event.[39]

Other national and international standards for explosive decompression testing include:

  • MIL-STD-810, 202
  • RTCA/D0-160
  • NORSOK M710
  • API 17K and 17J
  • NACE TM0192 and TM0297
  • TOTALELFFINA SP TCS 142 Appendix H

See also

Notes

  1. ^ Notable exceptions include the Airbus A380, Boeing 787 and Concorde

References

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  2. ^ a b Dehart, R. L.; J. R. Davis (2002). Fundamentals Of Aerospace Medicine: Translating Research Into Clinical Applications, 3rd Rev Ed.. United States: Lippincott Williams And Wilkins. p. 720. ISBN 9780781728980. 
  3. ^ Flight Training Handbook. U.S. Dept. of Transportation, Federal Aviation Administration, Flight Standards Service. 1980. p. 250. http://books.google.com/books?id=ioRTAAAAMAAJ. Retrieved 2007-07-28. 
  4. ^ Robert V. Brulle (2008-09-11). "Engineering the Space Age: A Rocket Scientist Remembers" (PDF). AU Press. http://aupress.maxwell.af.mil/Books/Brulle/Brulle.pdf. Retrieved 2008-10-13. 
  5. ^ "Comet Air Crash" ("Crash of the Comet"). Seconds From Disaster.
  6. ^ Kenneth Gabriel Williams (1959). The New Frontier: Man's Survival in the Sky. Thomas. http://books.google.com/books?id=3hMZAAAAIAAJ. Retrieved 2008-07-28. 
  7. ^ "AAIU Report No. 2001/0018" (PDF). Air Accident Investigation Unit. 2001-11-30. http://www.aaiu.ie/upload/general/3496-0.pdf. Retrieved 2008-09-01. 
  8. ^ "Advisory Circular 61-107" (PDF). FAA. pp. table 1.1. http://www.faa.gov/pilots/training/airman_education/media/AC%2061-107A.pdf. 
  9. ^ "Flight Surgeon's Guide". United States Air Force. http://wwwsam.brooks.af.mil/af/files/fsguide/HTML/Chapter_02.html. 
  10. ^ Giertsen JC, Sandstad E, Morild I, Bang G, Bjersand AJ, Eidsvik S (June 1988). "An explosive decompression accident". Am J Forensic Med Pathol 9 (2): 94–101. PMID 3381801. 
  11. ^ a b c d e f Martin B. Hocking, Diana Hocking (2005). Air Quality in Airplane Cabins and Similar Enclosed Spaces. Springer Science & Business. ISBN 3540250190. http://books.google.com/books?id=KzXPJ-p75QIC. Retrieved 2008-09-01. 
  12. ^ a b Bason R, Yacavone DW (May 1992). "Loss of cabin pressurization in U.S. Naval aircraft: 1969-90". Aviat Space Environ Med 63 (5): 341–5. PMID 1599378. 
  13. ^ Brooks CJ (March 1987). "Loss of cabin pressure in Canadian Forces transport aircraft, 1963-1984". Aviat Space Environ Med 58 (3): 268–75. PMID 3579812. 
  14. ^ Mark Wolff (2006-01-06). "Cabin Decompression and Hypoxia". theairlinepilots.com. http://www.theairlinepilots.com/medical/decompressionandhypoxia.htm. Retrieved 2008-09-01. 
  15. ^ Robinson, RR; Dervay, JP; Conkin, J. "An Evidenced-Based Approach for Estimating Decompression Sickness Risk in Aircraft Operations" (PDF). NASA STI Report Series NASA/TM—1999–209374. http://ston.jsc.nasa.gov/collections/TRS/_techrep/TM-1999-209374.pdf. Retrieved 2008-09-01. 
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  17. ^ "Rapid Decompression In Air Transport Aircraft" (PDF). Aviation Medical Society of Australia and New Zealand. 2000-11-13. http://www.amsanz.org.nz/avmedia/24/am24_2Decompression.pdf. Retrieved 2008-09-01. 
  18. ^ Neil Schlager (1994). When technology fails: Significant technological disasters, accidents, and failures of the twentieth century. Gail Research. ISBN 0810389088. http://books.google.com/books?id=DH5RAAAAMAAJ. Retrieved 2008-07-28. 
  19. ^ "Aircraft accident report: American Airlines, Inc. McDonnell Douglas DC-10-10, N103AA. Near Windsor, Ontario, Canada. June 12, 1972." (PDF). National Transportation Safety Board. 1973-02-28. http://libraryonline.erau.edu/online-full-text/ntsb/aircraft-accident-reports/AAR73-02.pdf. Retrieved 2009-03-22. 
  20. ^ "FAA historical chronology, 1926-1996" (PDF). Federal Aviation Administration. 2005-02-18. http://www.faa.gov/about/media/b-chron.pdf. Retrieved 2008-07-29. 
  21. ^ Brnes Warnock McCormick, M. P. Papadakis, Joseph J. Asselta (2003). Aircraft Accident Reconstruction and Litigation. Lawyers & Judges Publishing Company. ISBN 1930056613. http://books.google.com/books?id=l5U1YwUMAJ4C. Retrieved 2008-09-05. 
  22. ^ Alexander Dallin (1985). Black Box. University of California Press. ISBN 0520055152. http://books.google.com/books?id=0XGGAAAAIAAJ. Retrieved 2008-09-06. 
  23. ^ United States Court of Appeals for the Second Circuit Nos. 907, 1057 August Term, 1994 (Argued: April 5, 1995 Decided: July 12, 1995, Docket Nos. 94-7208, 94-7218
  24. ^ "Aging airplane safety". Federal Aviation Administration. 2002-12-02. http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgFinalRule.nsf/0/ceabe3247fab85f886256c8b0058461c!OpenDocument. Retrieved 2008-07-29. 
  25. ^ "Human factors in aircraft maintenance and inspection" (PDF). Civil Aviation Authority. 2005-12-01. http://www.caa.co.uk/docs/33/cap718.pdf. Retrieved 2008-07-29. 
  26. ^ [http://www.airsafe.com/events/airlines/tam.htm "Fatal Events Since 1970 for Transportes Aereos Regionais (TAM)"]. airsafe.com. http://www.airsafe.com/events/airlines/tam.htm. Retrieved 2010-03-05. 
  27. ^ "Aircraft Accident Report - Helios Airways Flight HCY522 Boeing 737-31S at Grammatike, Hellas on 14 August 2005". Hellenic Republic Ministry Of Transport & Communications: Air Accident Investigation & Aviation Safety Board. Nov 2006. http://www.moi.gov.cy/moi/pio/pio.nsf/All/F15FBD7320037284C2257204002B6243/$file/FINAL%20REPORT%205B-DBY.pdf. Retrieved 2009-07-14. 
  28. ^ Australian Transport Safety Bureau (2008-07-28). "Qantas Boeing 747-400 depressurisation and diversion to Manila on 25 July 2008". Press release. http://www.atsb.gov.au/newsroom/2008/release/2008_24.aspx. Retrieved 2008-07-28. 
  29. ^ "Hole in US plane forces landing". BBC News. 2009-07-14. http://news.bbc.co.uk/2/hi/americas/8150346.stm. Retrieved 2009-07-15. 
  30. ^ George Bibel (2007). Beyond the Black Box. JHU Press. pp. 141–142. ISBN 0801886317. http://books.google.com/books?id=B3ng54W3sQ8C. Retrieved 2008-09-01. 
  31. ^ "FAA HISTORICAL CHRONOLOGY, 1926-1996" (PDF). Federal Aviation Authority. 2005-02-18. http://www.faa.gov/about/media/b-chron.pdf. Retrieved 2008-09-01. 
  32. ^ "Final Policy FAR Part 25 Sec. 25.841 07/05/1996". http://rgl.faa.gov/Regulatory_and_Guidance_Library%5CrgPolicy.nsf/0/90AA20C2F35901D98625713F0056B1B8?OpenDocument. 
  33. ^ "Section 25.841: Airworthiness Standards: Transport Category Airplanes". Federal Aviation Administration. 1996-05-07. http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgFAR.nsf/0/FED94F31539484AB852566720051AA5D?OpenDocument. Retrieved 2008-10-02. 
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  35. ^ "FARs, 14 CFR, Part 25, Section 841". http://www.flightsimaviation.com/data/FARS/part_25-841.html. 
  36. ^ "Exemption No. 8695". Renton, Washington: Federal Aviation Authority. 2006-03-24. http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgEX.nsf/0/9929ce16709cad0f8625713f00551e74/$FILE/8695.doc. Retrieved 2008-10-02. 
  37. ^ Steve Happenny (2006-03-24). "PS-ANM-03-112-16". Federal Aviation Authority. http://rgl.faa.gov/Regulatory_and_Guidance_Library%5CrgPolicy.nsf/0/90AA20C2F35901D98625713F0056B1B8?OpenDocument. Retrieved 2009-09-23. 
  38. ^ "Exemption No. 8695". Renton, Washington: Federal Aviation Authority. 2006-03-24. http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgEX.nsf/0/9929ce16709cad0f8625713f00551e74/$FILE/8695.doc. Retrieved 2008-10-02. 
  39. ^ "Amendment 25-87". Federal Aviation Authority. http://mrcabinpressure.com/amd25-87.htm. Retrieved 2008-09-01. 

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