Armstrong limit: Difference between revisions
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The '''Armstrong Limit''', often called '''Armstrong's Line''', is the [[altitude]] that produces an [[atmospheric pressure]] so low (0.0618 [[atmosphere (unit)|atmosphere]]s) that water boils at the normal temperature of the human body: 37 [[Celsius|°C]] (98.6 [[Fahrenheit|°F]]). It is named after U.S. Air Force surgeon [[Harry George Armstrong]], who first described it. [http://nationalaviation.blade6.donet.com/components/content_manager_v02/view_nahf/htdocs/menu_ps.asp?NodeID=1096819117&group_ID=1134656385&Parent_ID=-1] |
The '''Armstrong Limit''', often called '''Armstrong's Line''', is the [[altitude]] that produces an [[atmospheric pressure]] so low (0.0618 [[atmosphere (unit)|atmosphere]]s) that water boils at the normal temperature of the human body: 37 [[Celsius|°C]] (98.6 [[Fahrenheit|°F]]). It is named after U.S. Air Force surgeon [[Harry George Armstrong]], who first described it. [http://nationalaviation.blade6.donet.com/components/content_manager_v02/view_nahf/htdocs/menu_ps.asp?NodeID=1096819117&group_ID=1134656385&Parent_ID=-1] |
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The altitude is variously reported as being between 18.9–19.4 km (62,000–63,500 [[Foot (length)|feet]] or about 11.8 miles)[http://www.nasaexplores.com/glossary_view_9-12.php]. At or above this altitude, exposed human fluids (such as saliva or tears, but not blood in the body) will boil without a [[pressure suit]] and no amount of breathable [[oxygen]] delivered by any means will sustain life for more than a few minutes |
The altitude is variously reported as being between 18.9–19.4 km (62,000–63,500 [[Foot (length)|feet]] or about 11.8 miles)[http://www.nasaexplores.com/glossary_view_9-12.php]. At or above this altitude, exposed human fluids (such as saliva or tears, but not blood in the body) will boil without a [[pressure suit]] and no amount of breathable [[oxygen]] delivered by any means will sustain life for more than a few minutes[http://www.newscientist.com/article/dn18427-space-diver-to-attempt-first-supersonic-freefall.html]. |
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The [[NASA]] technical report ''Rapid (Explosive) Decompression Emergencies in Pressure-Suited Subjects'', which discusses the brief accidental exposure of a human to near [[vacuum]] notes the likely result of exposure to pressure below that associated with the Armstrong Limit: "The subject later reported that ... his last conscious memory was of the water on his [[tongue]] beginning to boil."[http://space.about.com/cs/basics/a/bodyvacuum1.htm] |
The [[NASA]] technical report ''Rapid (Explosive) Decompression Emergencies in Pressure-Suited Subjects'', which discusses the brief accidental exposure of a human to near [[vacuum]] notes the likely result of exposure to pressure below that associated with the Armstrong Limit: "The subject later reported that ... his last conscious memory was of the water on his [[tongue]] beginning to boil."[http://space.about.com/cs/basics/a/bodyvacuum1.htm] |
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Revision as of 09:15, 23 January 2010
The Armstrong Limit, often called Armstrong's Line, is the altitude that produces an atmospheric pressure so low (0.0618 atmospheres) that water boils at the normal temperature of the human body: 37 °C (98.6 °F). It is named after U.S. Air Force surgeon Harry George Armstrong, who first described it. [1]
The altitude is variously reported as being between 18.9–19.4 km (62,000–63,500 feet or about 11.8 miles)[2]. At or above this altitude, exposed human fluids (such as saliva or tears, but not blood in the body) will boil without a pressure suit and no amount of breathable oxygen delivered by any means will sustain life for more than a few minutes[3].
The NASA technical report Rapid (Explosive) Decompression Emergencies in Pressure-Suited Subjects, which discusses the brief accidental exposure of a human to near vacuum notes the likely result of exposure to pressure below that associated with the Armstrong Limit: "The subject later reported that ... his last conscious memory was of the water on his tongue beginning to boil."[4]
This applies to unconfined water such as saliva and tears, but according to experiments as well as accidents not to the human blood. Contrary to the sources below this doesn't have any relation to the blood pressure as the blood pressure in the venous system is close to or even lower than zero. Alternative theories trying to explain the observation that human blood stays a fluid propose that the human skin and/ or blood vessels act as a relatively rigid container to keep the fluid fraction pressurized. [5][6] However, if a person has been breathing a nitrogen-containing atmosphere, bubbles can form due to decompression which may cause decompression sickness ("the bends"). So rather than fluids changing their state of matter it is soluble gases which could generate a gaseous phase within the blood vessels.
See also
External links
- [7] US Naval Flight Surgeon's Manual. Chapter 1 is Physiology of Flight (PDF)
- Ebullism at 1 Million Feet: Surviving Rapid/Explosive Decompression