Uncontrolled decompression is an unplanned drop in the pressure of a sealed system, such as an aircraft cabin or hyperbaric chamber, and typically results from human error, material fatigue, engineering failure, or impact, causing a pressure vessel to vent into its lower-pressure surroundings or fail to pressurize at all.
Such decompression may be classed as explosive, rapid, or slow:
- Explosive decompression (ED) is violent and too fast for air to escape safely from the lungs and other air-filled cavities in the body such as the sinuses and eustachian tubes, typically resulting in severe to fatal barotrauma.
- Rapid decompression may be slow enough to allow cavities to vent but may still cause serious barotrauma or discomfort.
- Slow or gradual decompression occurs so slowly that it may not be sensed before hypoxia sets in.
The term uncontrolled decompression here refers to the unplanned depressurisation of 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, 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. 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 US Federal Aviation Administration recognizes three distinct types of decompression events in aircraft:
- Explosive decompression
- Rapid decompression
- Gradual decompression
Explosive decompression occurs at a rate swifter than that at which air can escape from the lungs, typically in less than 0.1 to 0.5 seconds. The risk of lung trauma is very high, as is the danger from any unsecured objects that can become projectiles because of the explosive force, which may be likened to a bomb detonation.
In this purpose-built explosive decompression testing system, simulated flight cabin air humidity immediately cools and condenses into visible vapor upon exposure to 60,000 feet altitude equivalent air pressure. Within 2 seconds, the vapor has warmed and evaporated back into the new, low pressure environment.
After an explosive decompression within an aircraft, a heavy fog may immediately fill the interior as the relative humidity of cabin air rapidly changes as the air cools and condenses. 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.
Rapid decompression typically takes more than 0.1 to 0.5 seconds, allowing the lungs to decompress more quickly than the cabin. The risk of lung damage is still present, but significantly reduced compared with explosive decompression.
Slow, or gradual, decompression occurs slowly enough to go unnoticed and might only be detected by instruments. This type of decompression may also come about from a failure to pressurize as an aircraft climbs to altitude. An example of this is the 2005 Helios Airways Flight 522 crash, in which the pilots failed to check if the aircraft was pressurizing automatically, eventually losing consciousness (along with most of the passengers and crew) from hypoxia.
Effect of rapid decompression through a body-size hole
In 2004, the TV show MythBusters examined if explosive decompression occurs when a bullet is fired through the fuselage of an airplane informally by way of several tests using a decommissioned pressurised DC-9. A single shot through the side or the window did not have any effect – it took actual explosives to cause explosive decompression – suggesting that the fuselage is designed to prevent people from being blown out. Professional pilot David Lombardo states that a bullet hole would have no perceived effect on cabin pressure as the hole would be smaller than the opening of the aircraft's outflow valve. NASA scientist Geoffrey A. Landis points out though that the impact depends on the size of the hole, which can be expanded by debris that is blown through it. Landis went on to say that "it would take about 100 seconds for pressure to equalise through a roughly 30.0 cm (11.8 in) hole in the fuselage of a Boeing 747." He then stated that anyone sitting next to the hole would have half a ton of force pulling them in the direction of it.
At least two confirmed cases have been documented of a person being blown through an airplane passenger window. The first occurred in 1973 when debris from an engine failure struck a window roughly midway in the fuselage. Despite efforts to pull the passenger back into the airplane, the occupant was forced entirely through the cabin window. The passenger's skeletal remains were eventually found by a construction crew, and were positively identified two years later. The second incident occurred on April 17, 2018 when a woman on Southwest Airlines Flight 1380 was partially blown through an airplane passenger window that had broken from a similar engine failure. Although the other passengers were able to pull her back inside, she later died from her injuries. In both incidents, the plane landed safely with the sole fatality being the person seated next to the window involved. Fictional accounts of this include a scene in Goldfinger, when James Bond kills the eponymous villain by blowing him out a passenger window.
Exposure to a vacuum causes the body to explode
This persistent myth is based on a failure to distinguish between two types of decompression and their exaggerated portrayal in some fictional works. The first type of decompression deals with changing from normal atmospheric pressure (one atmosphere) to a vacuum (zero atmosphere) which is usually centered around space exploration. The second type of decompression changes from exceptionally high pressure (many atmospheres) to normal atmospheric pressure (one atmosphere) as may occur in deep-sea diving.
The first type is more common as pressure reduction from normal atmospheric pressure to a vacuum can be found in both space exploration and high-altitude aviation. Research and experience have shown that while exposure to a vacuum causes swelling, human skin is tough enough to withstand the drop of one atmosphere. The most serious risk from vacuum exposure is hypoxia, in which the body is starved of oxygen, leading to unconsciousness within a few seconds. Rapid uncontrolled decompression can be much more dangerous than vacuum exposure itself. Even if the victim does not hold their breath, venting through the windpipe may be too slow to prevent the fatal rupture of the delicate alveoli of the lungs. Eardrums and sinuses may also be ruptured by rapid decompression, and soft tissues may be affected by bruises seeping blood. If the victim somehow survives, the stress and shock would accelerate oxygen consumption, leading to hypoxia at a rapid rate. At the extremely low pressures encountered at altitudes above about 63,000 feet (19,000 m), the boiling point of water becomes less than normal body temperature. This measure of altitude is known as the Armstrong limit, which is the practical limit to survivable altitude without pressurization. Fictional accounts of bodies exploding due to exposure from a vacuum include, among others, several incidents in the movie Outland, while in the movie Total Recall, characters appear to suffer effects of ebullism and blood boiling when exposed to the atmosphere of Mars.
The second type is rare since it involves a pressure drop over several atmospheres, which would require the person to have been placed in a pressure vessel. The only likely situation in which this might occur is during decompression after deep-sea diving. A pressure drop as small as 100 Torr (13 kPa), which produces no symptoms if it is gradual, may be fatal if it occurs suddenly. One such incident occurred in 1983 in the North Sea, where violent explosive decompression from nine atmospheres to one caused four divers to die instantly from massive and lethal barotrauma. Dramatized fictional accounts of this include a scene from the film Licence to Kill, when a character's head explodes after his hyperbaric chamber is rapidly depressurized, and another in the film DeepStar Six, wherein rapid depressurization causes a character to hemorrhage profusely before exploding in a similar fashion.
NASA astronaut candidates being monitored for signs of hypoxia during training in an altitude chamber
The following physical injuries may be associated with decompression incidents:
Implications for aircraft design
Modern aircraft are specifically designed with longitudinal and circumferential reinforcing ribs in order to prevent localised damage from tearing the whole fuselage open during a decompression incident. 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. Manufacturers were able to comply with the Directive either by strengthening the floors and/or installing relief vents called "dado panels" between the passenger cabin and the cargo compartment.
Cabin doors are designed to make it nearly impossible to lose pressurization through opening a cabin door in flight, either accidentally or intentionally. The plug door design ensures that when the pressure inside the cabin exceeds the pressure outside, the doors are forced shut and will not open until the pressure is equalized. Cabin doors, including the emergency exits, but not all cargo doors, open inwards, or must first be pulled inwards and then rotated before they can be pushed out through the door frame because at least one dimension of the door is larger than the door frame. Pressurization prevented the doors of Saudia Flight 163 from being opened on the ground after the aircraft made a successful emergency landing, resulting in the deaths of all 287 passengers and 14 crew members from fire and smoke.
Prior to 1996, approximately 6,000 large commercial transport airplanes were type certified to fly up to 45,000 feet (14,000 m), without being required to meet special conditions related to flight at high altitude. In 1996, the FAA adopted Amendment 25–87, which imposed additional high-altitude cabin-pressure specifications, for new designs of aircraft types. For aircraft certified to operate above 25,000 feet (FL 250; 7,600 m), it "must be designed so that occupants will not be exposed to cabin pressure altitudes in excess of 15,000 feet (4,600 m) after any probable failure condition in the pressurization system." In the event of a decompression which results from "any failure condition not shown to be extremely improbable," the aircraft must be designed so that occupants will not be exposed to a cabin altitude exceeding 25,000 feet (7,600 m) for more than 2 minutes, nor exceeding an altitude of 40,000 feet (12,000 m) at any time. In practice, that new FAR amendment imposes an operational ceiling of 40,000 feet on the majority of newly designed commercial aircraft.[Note 1]
In 2004, Airbus successfully petitioned the FAA to allow cabin pressure of the A380 to reach 43,000 feet (13,000 m) in the event of a decompression incident and to exceed 40,000 feet (12,000 m) for one minute. This special exemption allows the A380 to operate at a higher altitude than other newly designed civilian aircraft, which have not yet been granted a similar exemption.
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.
Other national and international standards for explosive decompression testing include:
Notable decompression accidents and incidents
Decompression incidents are not uncommon on military and civilian aircraft, with approximately 40–50 rapid decompression events occurring worldwide annually. However, in most cases the problem is manageable, injuries or structural damage rare and the incident not considered notable. One notable, recent case was Southwest Airlines Flight 1380 in 2018, where an uncontained engine failure ruptured a window, causing a passenger to be partially blown out.
Decompression incidents do not occur solely in aircraft; the Byford Dolphin accident is an example of violent explosive decompression of a saturation diving system on an oil rig. A decompression event is an effect of a failure caused by another problem (such as an explosion or mid-air collision), but the decompression event may worsen the initial issue.
- ^ a b c d "AC 61-107A – Operations of aircraft at altitudes above 25,000 feet msl and/or mach numbers (MMO) greater than .75" (PDF). Federal Aviation Administration. 2007-07-15. Retrieved 2008-07-29.
- ^ 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 978-0-7817-2898-0.
- ^ Flight Standards Service, United States; Federal Aviation Agency, United States (1980). Flight Training Handbook. U.S. Dept. of Transportation, Federal Aviation Administration, Flight Standards Service. p. 250. Retrieved 2007-07-28.
- ^ Robert V. Brulle (2008-09-11). "Engineering the Space Age: A Rocket Scientist Remembers" (PDF). AU Press. Archived from the original (PDF) on 2011-09-28. Retrieved 2010-12-01.
- ^ Kenneth Gabriel Williams (1959). The New Frontier: Man's Survival in the Sky. Thomas. Retrieved 2008-07-28.
- ^ Josh Sanburn (April 5, 2011). "Southwest's Scare: When a Plane Decompresses, What Happens?". Time. Retrieved April 18, 2018.
- ^ Michael Daly and Lorna Thornber (April 18, 2018). "The deadly result when a large hole is ripped in the side of an aircraft". www.stuff.co.nz. Retrieved April 18, 2018.
- ^ Lauren McMah (April 18, 2018). "How could a passenger get sucked out of a plane — and has it happened before?". www.news.com.au. Retrieved April 18, 2018.
- ^ Mondout, Patrick. "Curious Crew Nearly Crashes DC-10". Archived from the original on 2011-04-08. Retrieved 2010-11-21.
- ^ Harden, Paul (2010-06-05). "Aircraft Down". El Defensor Chieftain. Retrieved 2018-10-24.
- ^ Joyce, Kathleen (April 17, 2018). "Southwest Airlines plane's engine explodes; 1 passenger dead".
- ^ "Woman Killed, 7 Hurt in Mid-Air Exploding Engine Incident".
- ^ Stack, Liam; Stevens, Matt (April 17, 2018). "A Southwest Airlines Engine Explodes, Killing a Passenger". The New York Times. Retrieved April 18, 2018.
- ^ Ryan Dilley (May 20, 2003). "Guns, Goldfinger and sky marshals". BBC.
It's not all fiction. If an airliner's window was shattered, the person sitting beside it would either go out the hole or plug it - which would not be comfortable.
- ^ a b Michael Barratt. "No. 2691 THE BODY AT VACUUM". www.uh.edu. Retrieved April 19, 2018.
- ^ Karl Kruszelnicki (April 7, 2005). "Exploding Body in Vacuum". ABC News (Australia). Retrieved April 19, 2018.
- ^ "Advisory Circular 61-107" (PDF). FAA. pp. table 1.1.
- ^ "2". Flight Surgeon's Guide. United States Air Force. Archived from the original on 2007-03-16.
- ^ a b Harding, Richard M. (1989). Survival in Space: Medical Problems of Manned Spaceflight. London: Routledge. ISBN 0-415-00253-2.
- ^ Czarnik, Tamarack R. (1999). "Ebullism at 1 Million Feet: Surviving Rapid/Explosive Decompressionn". Retrieved 2009-10-26.
- ^ Limbrick, Jim (2001). North Sea Divers – a Requiem. Hertford: Authors OnLine. pp. 168–170. ISBN 0-7552-0036-5.
- ^ a b c d Martin B. Hocking; Diana Hocking (2005). Air Quality in Airplane Cabins and Similar Enclosed Spaces. Springer Science & Business. ISBN 3-540-25019-0. Retrieved 2008-09-01.
- ^ 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.
- ^ 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.
- ^ Mark Wolff (2006-01-06). "Cabin Decompression and Hypoxia". theairlinepilots.com. Retrieved 2008-09-01.
- ^ 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. Archived from the original (PDF) on 2008-10-30. Retrieved 2008-09-01.
- ^ Powell, MR (2002). "Decompression limits in commercial aircraft cabins with forced descent". Undersea Hyperb. Med. Supplement (abstract). Retrieved 2008-09-01.
- ^ Daidzic, Nihad E.; Simones, Matthew P. (March–April 2010). "Aircraft Decompression with Installed Cockpit Security Door". Journal of Aircraft. 47 (2): 490–504. doi:10.2514/1.41953.
[A]t 40,000 ft (12,200 m), the International Standard Atmosphere (ISA) pressure is only about 18.8 kPa (2.73 psi), and the air temperatures are about −56.5 °C (217 K). The boiling temperature of water at this atmospheric pressure is about −59 °C (332 K). Above 63,000 ft or 19,200 m (Armstrong line), the ISA environmental pressure drops below 6.3 kPa (0.91 psi) and the boiling temperature of water reaches the normal human body temperature (about 37 C). Any prolonged exposure to such an environment could lead to ebullism, anoxia, and ultimate death, after several minutes. These are indeed very hostile conditions for human life.
- ^ George Bibel (2007). Beyond the Black Box. JHU Press. pp. 141–142. ISBN 978-0-8018-8631-7. Retrieved 2008-09-01.
- ^ "FAA Historical Chronology, 1926–1996" (PDF). Federal Aviation Authority. 2005-02-18. Archived from the original (PDF) on 2008-06-24. Retrieved 2008-09-01.
- ^ US 6273365
- ^ "Final Policy FAR Part 25 Sec. 25.841 07/05/1996|Attachment 4".
- ^ "Section 25.841: Airworthiness Standards: Transport Category Airplanes". Federal Aviation Administration. 1996-05-07. Retrieved 2008-10-02.
- ^ a b "FARs, 14 CFR, Part 25, Section 841".
- ^ a b "Exemption No. 8695". Renton, Washington: Federal Aviation Authority. 2006-03-24. Retrieved 2008-10-02.
- ^ Steve Happenny (2006-03-24). "PS-ANM-03-112-16". Federal Aviation Authority. Retrieved 2009-09-23.
- ^ "Amendment 25–87". Federal Aviation Authority. Retrieved 2008-09-01.
- ^ "Rapid Decompression In Air Transport Aircraft" (PDF). Aviation Medical Society of Australia and New Zealand. 2000-11-13. Archived from the original (PDF) on 2010-05-25. Retrieved 2008-09-01.
- ^ "Woman sucked from Southwest Airlines plane died of 'blunt trauma'". Sky News.
- ^ Neil Schlager (1994). When technology fails: Significant technological disasters, accidents, and failures of the twentieth century. Gale Research. ISBN 0-8103-8908-8. Retrieved 2008-07-28.
- ^ Shayler, David (2000). Disasters and Accidents in Manned Spaceflight. Springer. p. 38. ISBN 1852332255.
- ^ "Two MSC Employees Commended For Rescue in Chamber Emergency" (PDF), Space News Roundup, Public Affairs Office of the National Aeronautics and Space Administration Manned Spacecraft Center, 6 (6), p. 3, January 6, 1967, retrieved July 7, 2012,
...the suit technician who was inside the eight-foot altitude chamber, lost consciousness when his Apollo suit lost pressure when an oxygen line let go. The chamber was at approximately 150,000 [equivalent] feet at the time of the accident...
- ^ Ivanovich, Grujica S. (2008). Salyut – The First Space Station: Triumph and Tragedy. Springer. pp. 305–306. ISBN 978-0387739731.
- ^ "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. Retrieved 2009-03-22.
- ^ "explosive decompression". Everything2.com. Retrieved 2017-08-08.
- ^ "FAA historical chronology, 1926–1996" (PDF). Federal Aviation Administration. 2005-02-18. Archived from the original (PDF) on 2008-06-24. Retrieved 2008-07-29.
- ^ Brnes Warnock McCormick; M. P. Papadakis; Joseph J. Asselta (2003). Aircraft Accident Reconstruction and Litigation. Lawyers & Judges Publishing Company. ISBN 1-930056-61-3. Retrieved 2008-09-05.
- ^ Alexander Dallin (1985). Black Box. University of California Press. ISBN 0-520-05515-2. Retrieved 2008-09-06.
- ^ 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
- ^ "Aging airplane safety". Federal Aviation Administration. 2002-12-02. Retrieved 2008-07-29.
- ^ "Human factors in aircraft maintenance and inspection" (PDF). Civil Aviation Authority. 2005-12-01. Archived from the original (PDF) on 2008-10-30. Retrieved 2008-07-29.
- ^ "Accident Description". Aviation Safety Network. 1995-08-23. Retrieved 2020-06-08.
- ^ a b "Fatal Events Since 1970 for Transportes Aéreos Regionais (TAM)". airsafe.com. Retrieved 2010-03-05.
- ^ Australian Transport Safety Bureau 2001, p. 26.
- ^ "Columbia Crew Survival Investigation Report" (PDF). NASA.gov. 2008. pp. 2–90.
The 51-L Challenger accident investigation showed that the Challenger CM remained intact and the crew was able to take some immediate actions after vehicle breakup, although the loads experienced were much higher as a result of the aerodynamic loads (estimated at 16 G to 21 G).5 The Challenger crew became incapacitated quickly and could not complete activation of all breathing air systems, leading to the conclusion that an incapacitating cabin depressurization occurred. By comparison, the Columbia crew experienced lower loads (~3.5 G) at the CE. The fact that none of the crew members lowered their visors strongly suggests that the crew was incapacitated after the CE by a rapid depressurization. Although no quantitative conclusion can be made regarding the cabin depressurization rate, it is probable that the cabin depressurization rate was high enough to incapacitate the crew in a matter of seconds. Conclusion L1-5. The depressurization incapacitated the crew members so rapidly that they were not able to lower their helmet visors.
- ^ "Aircraft Accident Report – Helios Airways Flight HCY522 Boeing 737-31S at Grammatike, Hellas on 14 August 2005" (PDF). Hellenic Republic Ministry Of Transport & Communications: Air Accident Investigation & Aviation Safety Board. Nov 2006. Retrieved 2009-07-14.
- ^ "Airline Accident: Accident – Dec. 26, 2005 – Seattle, Wash". Investigative Reporting Workshop. Archived from the original on 2018-01-20. Retrieved 2017-08-08.
- ^ "Qantas Boeing 747-400 depressurisation and diversion to Manila on 25 July 2008" (Press release). Australian Transport Safety Bureau. 2008-07-28. Retrieved 2008-07-28.
- ^ "Hole in US plane forces landing". BBC News. 2009-07-14. Retrieved 2009-07-15.
- ^ "Southwest Jet Had Pre-existing Fatigue". Fox News. 2011-04-03.
- ^ "2016-02-02 Daallo Airlines A321 damaged by explosion at Mogadishu » JACDEC". www.jacdec.de (in German). Retrieved 2018-08-05.
- ^ "Southwest Flight 1380 Statement #1 – Issued 11:00 a.m. CT". Southwest Airlines Newsroom.
- ^ "Southwest flight suffers jet engine failure: Live updates". www.cnn.com. 17 April 2018.