Armstrong limit
The Armstrong limit or Armstrong's line is a measure of
The term is named after United States Air Force General Harry George Armstrong, who was the first to recognize this phenomenon.[3]
Effect on body fluids
Location | Pressure | ||
---|---|---|---|
kPa | psi | atm | |
Olympus Mons summit | 0.072 | 0.0104 | 0.00071 |
Mars average | 0.610 | 0.0885 | 0.00602 |
Hellas Planitia bottom | 1.16 | 0.168 | 0.0114 |
Armstrong limit | 6.25 | 0.906 | 0.0617 |
Mount Everest summit[4] | 33.7 | 4.89 | 0.333 |
Earth sea level | 101.3 | 14.69 | 1.000 |
Dead Sea level[5] | 106.7 | 15.48 | 1.053 |
Surface of Venus[6] | 9,200 | 1,330 | 91 |
At or above the Armstrong limit, exposed body fluids such as
At the nominal body temperature of 37 °C (99 °F), water has a
Hypoxia below the Armstrong limit
Well below the Armstrong limit, humans typically require supplemental oxygen in order to avoid
Historical significance
The Armstrong limit describes the altitude associated with an objective, precisely defined natural phenomenon: the vapor pressure of body-temperature water. In the late 1940s, it represented a new fundamental, hard limit to altitude that went beyond the somewhat subjective observations of human physiology and the time‑dependent effects of hypoxia experienced at lower altitudes. Pressure suits had long been worn at altitudes well below the Armstrong limit to avoid hypoxia. In 1936, Francis Swain of the Royal Air Force reached 15,230 m (49,970 ft) flying a Bristol Type 138 while wearing a pressure suit.[10] Two years later Italian military officer Mario Pezzi set an altitude record of 17,083 m (56,047 ft), wearing a pressure suit in his Caproni Ca.161bis biplane even though he was well below the altitude at which body-temperature water boils.
A pressure suit is normally required at around 15,000 m (49,000 ft) for a well conditioned and experienced pilot to safely operate an aircraft in unpressurized cabins.
For modern military aircraft such as the United States' F‑22 and F‑35, both of which have operational altitudes of 18,000 m (59,000 ft) or more, the pilot wears a "counter-pressure garment", which is a g‑suit with high-altitude capabilities. In the event the cockpit loses pressure, the oxygen system switches to a positive-pressure mode to deliver above-ambient-pressure oxygen to a specially sealing mask as well as to proportionally inflate the counter-pressure garment. The garment counters the outward expansion of the pilot's chest to prevent pulmonary barotrauma until the pilot can descend to a safe altitude.[12]
See also
- Altitude sickness – Medical condition due to rapid exposure to low oxygen at high altitude
- Death zone – Altitudes above about 8,000 m (26,000 ft)
- Decompression (altitude)– Reduction in ambient pressure due to ascent above sea level
- Decompression illness – Disorders arising from ambient pressure reduction
- Effects of high altitude on humans
- Effect of spaceflight on the human body – Medical issues associated with spaceflight
- Kármán line – Proposed definition for the boundary of outer space
References
- ^ a b c Geoffrey A. Landis. "Human Exposure to Vacuum". Archived from the original on 2009-07-21. Retrieved 2016-02-05.
- ^ "NASAexplores Glossary". Archived from the original on 2007-09-27.
- ^ "NAHF – Harry Armstrong". November 18, 2007. Archived from the original on 2007-11-18.
- S2CID 27875962.
- ^ "The Dead Sea Region as a Health Resort". Dead Sea, ISRAEL: Cystic Fibrosis Center LTD. Archived from the original on 15 July 2012. Retrieved 15 May 2012.
- S2CID 250815558.
- ^ "Ask an Astrophysicist: Human Body in a Vacuum". Archived from the original on 2014-10-14.
- ^ Code of Federal Regulations (Docket 18334, 54 FR 34304 § 91.211 Supplemental oxygen, Title 14, Chapter I, Subchapter F, Part 91—General Operating and Flight Rules Subpart C—Equipment, Instrument, and Certificate Requirements). August 18, 1989. Retrieved February 6, 2016.
- ^ "Skydiver's Information Manual". United States Parachute Association. March 30, 2014. Archived from the original on 2014-03-30.
- ^ "Altitude Record". Sydney Morning Herald. 1 October 1936. Retrieved 29 September 2020.
- ^ "A Brief History of the Pressure Suit". Dryden Research Center. March 25, 2016. Archived from the original on 2016-03-25.
- ^ Sweetman, Bill (July 18–25, 2011). "Stealthy Danger: Hypoxia incidents troubling Hornets may be related to F-22 crashes". Aviation Week & Space Technology. p. 35.
External links
- "Chapter 1:Physiology of Flight". US Naval Flight Surgeon's Manual (PDF).
- "Ebullism at 1 Million Feet: Surviving Rapid/Explosive Decompression". Archived from the original on 2000-09-19.
- "Air Pressure and Altitude above Sea Level". The Engineering ToolBox. Archived from the original on 2016-11-09.