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#1
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hi alt oxygen
Im just wondering why pure oxygen is used for high altitude flying
instead of regular air. I thought prolonged exposures to breathing pure oxygen can be harmfull as you can become oxygen dependant. |
#2
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"Arquebus257WeaMag" wrote in message m... Im just wondering why pure oxygen is used for high altitude flying instead of regular air. I thought prolonged exposures to breathing pure oxygen can be harmfull as you can become oxygen dependant. http://www.batnet.com/mfwright/hypoxia.html Hypoxia Hypoxia is a state of oxygen deficiency in the body which is sufficient to cause an impairment of function. Hypoxia is caused by the reduction in partial pressure of oxygen, inadequate oxygen transport, or the inability of the tissues to use oxygen. In brief, being drunk is kind of the same as being exposed to high altitude. In both cases, oxygen to your brain and muscles is reduced. |
#3
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You live off off something called the "partial pressure of oxygen" in the
medium you are breathing. As altitude increases, the partial pressure of oxygen in air decreases. Therefore, you must "enrich" the breathing medium with more oxygen in order to achieve the *same* partial pressure of oxygen that exists at lower altitudes. Two solutions: 1) increase the relative percentage of oxygen inht e medium, or 2) pressurize hte medium. 1) is much less expensive than 2). Steve Swartz (The partial pressure of oxygen is what gets the O2 across your lung tissue into your bloodstream. As total pressure decreases, the partial pressure of oxygen decreases. Eventually, as ambient pressure goes down, you would need to breathe pure *pressurized* [3.2 psi IIRC] oxygen in order to make up the deficit.) "Arquebus257WeaMag" wrote in message m... Im just wondering why pure oxygen is used for high altitude flying instead of regular air. I thought prolonged exposures to breathing pure oxygen can be harmfull as you can become oxygen dependant. |
#4
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Thank you for the information. Very interesting! On Wed, 10 Mar 2004 11:46:52 -0500, "Leslie Swartz" wrote: You live off off something called the "partial pressure of oxygen" in the medium you are breathing. As altitude increases, the partial pressure of oxygen in air decreases. Therefore, you must "enrich" the breathing medium with more oxygen in order to achieve the *same* partial pressure of oxygen that exists at lower altitudes. Two solutions: 1) increase the relative percentage of oxygen inht e medium, or 2) pressurize hte medium. 1) is much less expensive than 2). Steve Swartz (The partial pressure of oxygen is what gets the O2 across your lung tissue into your bloodstream. As total pressure decreases, the partial pressure of oxygen decreases. Eventually, as ambient pressure goes down, you would need to breathe pure *pressurized* [3.2 psi IIRC] oxygen in order to make up the deficit.) "Arquebus257WeaMag" wrote in message om... Im just wondering why pure oxygen is used for high altitude flying instead of regular air. I thought prolonged exposures to breathing pure oxygen can be harmfull as you can become oxygen dependant. all the best -- Dan Ford email: (requires authentication) see the Warbird's Forum at www.warbirdforum.com and the Piper Cub Forum at www.pipercubforum.com |
#5
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Here's some quick and dirty info on oxygen - normally about 1/5 of
'air'. So the 'partial pressure' is 1/5 of 29.92 inches/760 mm Hg equalling 152mm O2. The ambient air pressure drops by 1/2 every 18,000 feet (roughly). So at sea level you get 1/5 of 760mm; at 18,000 you get 1/5 of 380mm. At about 34000 you get the equivalent of sea level oxygen partial pressure breathing 100% oxygen. If you keep going on up pretty soon you reach a dangerously low level of partial pressure - that's at about 41,000. So modern diluter-demand O2 regulators start feeding you oxygen under pressure. Easy to inhale - you have to work to exhale. This gets worse as you keep going up. At 50,000 cabin pressure it is physically demanding to exhale and the mask has to be very tightly strapped on your face. Not to mention painful. Note that so far we don't have any 'cabin pressure' - air bled from the engine(s) to remedy the situation. Also as you keep climbing into areas of lesser pressure water boils at progrssively lower temperatures. At 63,000 ambient pressure water boils at 98.6F/37C - body temp. That means your lungs are now filled with water vapor and you can no longer absorb oxygen. Hence pressure cabins and pressure suits over 50,000 feet. Breathing pure oxygen for extended periods of time is a hassle. First, there is no water in Aviator's oxygen - can't take the chance of water freezing in the lines. Therefore every breath you're becoming more and more dehydrated. Second, oxygen can flood the inner ears (through the eustachian tubes) and late at night in bed that oxygen gets absorbed by the blood and you wake up with giant earaches. Third, if you're breathing pure O2 and pulling lots of G - the lower airsacs in your lungs tend to stick together because with pure O2 you're not breathing as deeply. Back on the ground when you take a deep breath it feels as if someone just knifed you. This is termed 'atelactasis'. Now, oxygen is used to keep pilots crew and passengers functioning at more or less an efficient level. Rule of thumb - O2 over 10,000 feet. There is a 'cheat' where one can got to 12 for 30 minutes. But the brain needs O2 to function properly. With hard training one can function adequately at higher altitudes. But even the best can screw up - read 'Into Thin Air'. FWIW I used to teach this stuff. Walt BJ |
#7
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There is a 'cheat' where one can got to 12 for 30 minutes. But the
brain needs O2 to function properly. With hard training one can function adequately at higher altitudes. Pensacola. Low pressure tank. 30,000 feet pressure. Instructor asks for volunteer. (I tend to do dumb things) I said OK. "Please take this pencil and write your name on this clipboard." "How many times?" "Don't worry. I'll tell you when to stop." Off comes mask. I write and I write and at the 4th perfect signature I stop -- wondering why am I doing this. "Hell, I can do this for the rest of my life." (30,00 feet. Yeah) Instructor slams mask back on. My vision instantly changed from looking down a soda straw to wide open, COLOR!, side vision. Wow! Last signature was a straight line. (Hmmmm. Looked OK at the time.) At 30K, one has about 4 seconds of useful consciousness -- unless one holds one's breath. That may net one a couple of seconds more. No pain. No strain. Quite pleasant. Been there. Done that. Fast and almost fun. Humans need a constant supply of oxygen and we store almost none. Lack of oxygen doesn't hurt. What hurts and gives the feeling of strangulation is an overabundance of carbon dioxide. Want to know what too much CO2 feels like? Hold your breath for 3-4 minutes. Throw in a little exhaust gas and the ceiling easily drops to 20K or lower. Quent |
#8
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On Wed, 10 Mar 2004 11:46:52 -0500, "Leslie Swartz"
wrote: You live off off something called the "partial pressure of oxygen" in the medium you are breathing. As altitude increases, the partial pressure of oxygen in air decreases. Therefore, you must "enrich" the breathing medium with more oxygen in order to achieve the *same* partial pressure of oxygen that exists at lower altitudes. Two solutions: 1) increase the relative percentage of oxygen inht e medium, or 2) pressurize hte medium. 1) is much less expensive than 2). Steve Swartz (The partial pressure of oxygen is what gets the O2 across your lung tissue into your bloodstream. As total pressure decreases, the partial pressure of oxygen decreases. Eventually, as ambient pressure goes down, you would need to breathe pure *pressurized* [3.2 psi IIRC] oxygen in order to make up the deficit.) "Arquebus257WeaMag" wrote in message om... Im just wondering why pure oxygen is used for high altitude flying instead of regular air. I thought prolonged exposures to breathing pure oxygen can be harmfull as you can become oxygen dependant. Same basic idea of the PPO2 is why SCUBA divers going down need to cut the oxy levels of their breathing gas down to avoid PPO2 levels above 1.4 ATA... so you can find divers using as low as 5% oxy in a deep dive Trimix (Oxy, Nitrogen, and Helium) bottom gas |
#9
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On 10 Mar 2004 21:12:59 -0800, (WaltBJ) wrote:
Rule of thumb - O2 over 10,000 feet. It used to amuse me, in the days before the Eisenhower Tunnel, that the highway over Loveland Pass in CO took the driver above the altitude at which the USAF wanted pilots to use oxygen masks. At Aspen of course we skied all winter at above 11,000 feet. (At Loveland, the parking lot was higher than that.) Do you suppose that's why ski bums are famously so unstable? all the best -- Dan Ford email: (requires authentication) see the Warbird's Forum at www.warbirdforum.com and the Piper Cub Forum at www.pipercubforum.com |
#10
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Cub Driver wrote:
On 10 Mar 2004 21:12:59 -0800, (WaltBJ) wrote: Rule of thumb - O2 over 10,000 feet. It used to amuse me, in the days before the Eisenhower Tunnel, that the highway over Loveland Pass in CO took the driver above the altitude at which the USAF wanted pilots to use oxygen masks. At Aspen of course we skied all winter at above 11,000 feet. (At Loveland, the parking lot was higher than that.) Do you suppose that's why ski bums are famously so unstable? The difference being the rate at which you ascend from lower altitudes, although the military's 10,000 foot rule seems very conservativ. IIRR, even the FAA allows pilots to fly between 12,500 and 14,000 ft. for 1/2 an hour without O2, and pax can do it indefinitely. Pity the poor fighter pilots in WW1, who used to climb up to 17-20,000 feet without O2 and patrol there for an hour or so in open, unheated cockpits. And suffered massive headaches as a result. Guy |
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