Actually the ISS and space shuttles air is 80 percent nitrogen and 20 percent oxygen at 1 atmosphere and the astronauts pre breathe 100 percent oxygen to flush nitrogen from their tissues before suiting up to reduce the chances of getting bent due to the decreased pressure in their suits.
How Low can U GO ?
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I stand corrected... ours were 5psi at least through Apollo.
Rick
k4sdi
Contributor
Yea, after Apollo 1 the US stopped using pure oxygen. Too many chances with it. All it took was a little spark.......
Mark
Mark
OP
Devjr,
I have absolutely NO use for this info. It was simply a question I was curious ABOUT. There have been dozens of people now to acheive Mt. Everest without the use of O2 and they came out fine. Granted they could stay up there long but they have done it. Most climbers do use O2 to climb but some do not. You claim you can't breath above 25,000. Mt. Everest is almost 30,000. Even Kramer from Seinfeld climbed Mt. Everest decades ago.
I've been diving for 19 yrs. Instructor for YMCA, CMAS, PADI and NAUI. I do not wish to apply any of this info to climbing, flying, diving or anything at ALL. Just curious. Have you ever just been curious about anything?
I thought it was interesting info. that the space suits NASA uses are pressurized to 4.3 psi. What is the space shuttle pressurized at?
I have absolutely NO use for this info. It was simply a question I was curious ABOUT. There have been dozens of people now to acheive Mt. Everest without the use of O2 and they came out fine. Granted they could stay up there long but they have done it. Most climbers do use O2 to climb but some do not. You claim you can't breath above 25,000. Mt. Everest is almost 30,000. Even Kramer from Seinfeld climbed Mt. Everest decades ago.
I've been diving for 19 yrs. Instructor for YMCA, CMAS, PADI and NAUI. I do not wish to apply any of this info to climbing, flying, diving or anything at ALL. Just curious. Have you ever just been curious about anything?
I thought it was interesting info. that the space suits NASA uses are pressurized to 4.3 psi. What is the space shuttle pressurized at?
Dr Deco
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Dear bengals
The Shuttle and the Space Station are both pressurized to 14.7 psi a standard atmosphere. The space suits are pressurized with 100% oxygen at 4.3 psi equivalent to 30,000 feet. It requires oxygen prebreathing to prevent decompression sickness during the depress.
The development of decompression sickness at low pressure is dependent on the duration of exposure. In the film 2001, astronaut Bowman was forced to exit his space pod and enter the sir lock of the ship, all without his space helmet. He was exposed to the vacuum of space for only about 15 seconds. While this has not been tested with humans, monkeys have performed decompressions of this sort and survived.
This is always a short time delay involved with DCS. At high altitude (greater than 55,000 feet) this is several seconds and can be used for some type of emergency action in specific cases. An example might be the pilot of the Concord putting the plane into a dive from 60,000 feet.
Dr Deco
:doctor:
The Shuttle and the Space Station are both pressurized to 14.7 psi a standard atmosphere. The space suits are pressurized with 100% oxygen at 4.3 psi equivalent to 30,000 feet. It requires oxygen prebreathing to prevent decompression sickness during the depress.
The development of decompression sickness at low pressure is dependent on the duration of exposure. In the film 2001, astronaut Bowman was forced to exit his space pod and enter the sir lock of the ship, all without his space helmet. He was exposed to the vacuum of space for only about 15 seconds. While this has not been tested with humans, monkeys have performed decompressions of this sort and survived.
This is always a short time delay involved with DCS. At high altitude (greater than 55,000 feet) this is several seconds and can be used for some type of emergency action in specific cases. An example might be the pilot of the Concord putting the plane into a dive from 60,000 feet.
Dr Deco
:doctor:
The Iceni
Medical Moderator
All totally irrelevant to diving but;
As long as you can extract sufficient oxygen from the atmosphere to keep vital tissues oxygenated it would be possible to survive at very low pressures, but gaseous exchange in the lungs requires a pressure gradient.
Alveolar air is saturated with water vapour, which is about 48 mmHg (0.06 bar) at body temperature.
The avelolar pp O2 is reduced by this amount (in proportion to FO2) So even if you were to breath 100% oxygen at that low pressure, there would be no gaseous exchange whatsoever as the lungs would be entirely saturated with water vapour.
In fact of course, almost by definition, at a pressure of 48 mmHg 37 degrees Celcius is the boiling point of water.
I doubt exposure to even a partial vaccuum is such a good idea.
I most certainly would not like to try it!
Would you find this annoying? It would be enough to make your blood boil! (Play on an English figure of speech, Apologies!)
=-)
As long as you can extract sufficient oxygen from the atmosphere to keep vital tissues oxygenated it would be possible to survive at very low pressures, but gaseous exchange in the lungs requires a pressure gradient.
Alveolar air is saturated with water vapour, which is about 48 mmHg (0.06 bar) at body temperature.
The avelolar pp O2 is reduced by this amount (in proportion to FO2) So even if you were to breath 100% oxygen at that low pressure, there would be no gaseous exchange whatsoever as the lungs would be entirely saturated with water vapour.
In fact of course, almost by definition, at a pressure of 48 mmHg 37 degrees Celcius is the boiling point of water.
I doubt exposure to even a partial vaccuum is such a good idea.
I most certainly would not like to try it!
Would you find this annoying? It would be enough to make your blood boil! (Play on an English figure of speech, Apologies!)
=-)
Dr Deco
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Dear Paul:
In aviation, crews wear masks to obtain 100% oxygen. At 40,000 feet, this is the same oxygen one would get if breathing air at 10,000 feet. At 42,000, pressure breathing (6 inches of water pressure) is employed. Above this, the pressure makes breathing difficult except for short periods.
Dr Deco
:doctor:
In aviation, crews wear masks to obtain 100% oxygen. At 40,000 feet, this is the same oxygen one would get if breathing air at 10,000 feet. At 42,000, pressure breathing (6 inches of water pressure) is employed. Above this, the pressure makes breathing difficult except for short periods.
Dr Deco
:doctor:
The Iceni
Medical Moderator
Dr Deco,
Somewhere on your forum I am sure there is a thread listing the atmospheric pressure at various altitudes but I cannot find it.
However Bengal asked an interesting question.
The point I was making, (my physiology training keeps raising its ugly head) is that even when you breath 100% oxygen on the surface the alveolar pp O2 is not 1 bar. It is 1 bar less the saturated water vapour pressure at 37 degrees C AND the pp CO2, which is normally about 40 mmHg, I believe.
In healthy lungs the blood in the pulmonary circulation equalises with the pp O2 in the alveoli, not in the airways.
If 100% oxygen is breathed on the surface the airway pp O2 is 760 mmHg - 48 mmHg = 712 mmHg or 0.93 bar but carbon dioxide is also present in the alveoli to dilute the pp O2 even further by 40 mmHg to 672 mmHg or 0.88 bar
When air is breathed the inspiratory pp O2 is 0.21 bar; 0.21 x 760 mmHg = 159 mmHg and the alveolar pp O2 is 0.21 x 672 = 141 mmHg (0.21 x 0.88 = 0.17 bar).
If I remember correctly 1 atmosphere is 29 inches of water so 6 inches of water is 0.2 bar (157 mmHg). Thus your high altitude fast jet pilots are breathing oxygen with a partial pressure very close to the pp O2 of air at the surface.
Let's take the example of a fast jet pilot having to eject into a very thin atmosphere a quarter normal of 0.25 bar (3.7 psi) WITHOUT oxygen.
He is beathing air at 190 mmHg with with an inspiratory pp O2 of 0.21 x 190 = 40 mmHg (0.05 bar) but what about water vapour and carbon dioxide?
This guy's alveolar pp O2 is 0.21 x (190 - 48-40) = 21.5 mmHg.
The oxygen reaching his circulation is reduced to about a half that available in the outside air due to the water vapour and carbon dioxide produced by the body.
At this partial pressure the arterial haemoglobin is only about 30% saturated.
As Piscean has shown elswhere, at http://www.mtsinai.org/pulmonary/ABG/PO2.htm the blood of a healthy fit male contains up to 15 g of haemoglobin per decilitre, each gram of which can carry 1.34 ml of oxygen.
This pilot's arterial blood will carry only 15 x 1.34 x 30% = 6 ml of oxygen per decilitre all of which will be needed for metabolism.
I suspect that not all of this oxygen can be freed from haemoglobin for metabolic neeeds at the tissues so this pressure could be well below the minimum required to support life.
I thought it was generally accepted that a ppO2 of less than 0.1 bar is deadly, which is why the BSAC do not advocate the use of any diving mix with a FO2 of less than 0.12 since it would lead to unconciousness or death if breathed on, or close to, the surface.
No doubt a physiology text book would provide a definitive answer.
Somewhere on your forum I am sure there is a thread listing the atmospheric pressure at various altitudes but I cannot find it.
However Bengal asked an interesting question.
The point I was making, (my physiology training keeps raising its ugly head) is that even when you breath 100% oxygen on the surface the alveolar pp O2 is not 1 bar. It is 1 bar less the saturated water vapour pressure at 37 degrees C AND the pp CO2, which is normally about 40 mmHg, I believe.
In healthy lungs the blood in the pulmonary circulation equalises with the pp O2 in the alveoli, not in the airways.
If 100% oxygen is breathed on the surface the airway pp O2 is 760 mmHg - 48 mmHg = 712 mmHg or 0.93 bar but carbon dioxide is also present in the alveoli to dilute the pp O2 even further by 40 mmHg to 672 mmHg or 0.88 bar
When air is breathed the inspiratory pp O2 is 0.21 bar; 0.21 x 760 mmHg = 159 mmHg and the alveolar pp O2 is 0.21 x 672 = 141 mmHg (0.21 x 0.88 = 0.17 bar).
If I remember correctly 1 atmosphere is 29 inches of water so 6 inches of water is 0.2 bar (157 mmHg). Thus your high altitude fast jet pilots are breathing oxygen with a partial pressure very close to the pp O2 of air at the surface.
Let's take the example of a fast jet pilot having to eject into a very thin atmosphere a quarter normal of 0.25 bar (3.7 psi) WITHOUT oxygen.
He is beathing air at 190 mmHg with with an inspiratory pp O2 of 0.21 x 190 = 40 mmHg (0.05 bar) but what about water vapour and carbon dioxide?
This guy's alveolar pp O2 is 0.21 x (190 - 48-40) = 21.5 mmHg.
The oxygen reaching his circulation is reduced to about a half that available in the outside air due to the water vapour and carbon dioxide produced by the body.
At this partial pressure the arterial haemoglobin is only about 30% saturated.
As Piscean has shown elswhere, at http://www.mtsinai.org/pulmonary/ABG/PO2.htm the blood of a healthy fit male contains up to 15 g of haemoglobin per decilitre, each gram of which can carry 1.34 ml of oxygen.
This pilot's arterial blood will carry only 15 x 1.34 x 30% = 6 ml of oxygen per decilitre all of which will be needed for metabolism.
I suspect that not all of this oxygen can be freed from haemoglobin for metabolic neeeds at the tissues so this pressure could be well below the minimum required to support life.
I thought it was generally accepted that a ppO2 of less than 0.1 bar is deadly, which is why the BSAC do not advocate the use of any diving mix with a FO2 of less than 0.12 since it would lead to unconciousness or death if breathed on, or close to, the surface.
No doubt a physiology text book would provide a definitive answer.
Dr Deco
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Dear Paul:
All of what you have written is correct. At altitude you would need to deduct the water vapor and carbon dioxide partial pressures since these are generated by the body and are constant diluents.
The dangers of bailout at high altitude are many fold. There is of course the problem of low pressure and hypoxia. In addition, the ambient air temperature is very low. Some standard numbers for these pressures and temperatures are:
30,000 feet [sp][sp] 4.27 psi [sp][sp] -50 F
40,000 feet [sp][sp] 2.72 psi [sp][sp] -70 F
50,000 feet [sp][sp] 1.68 psi [sp][sp] -70 F
To counter these problem, parachutes do not open until the aviator reaches a low altitude. The individual will free fall and the chute will open automatically. If one is very high, a pressure suit is required.
Dr Deco
:doctor:
All of what you have written is correct. At altitude you would need to deduct the water vapor and carbon dioxide partial pressures since these are generated by the body and are constant diluents.
The dangers of bailout at high altitude are many fold. There is of course the problem of low pressure and hypoxia. In addition, the ambient air temperature is very low. Some standard numbers for these pressures and temperatures are:
30,000 feet [sp][sp] 4.27 psi [sp][sp] -50 F
40,000 feet [sp][sp] 2.72 psi [sp][sp] -70 F
50,000 feet [sp][sp] 1.68 psi [sp][sp] -70 F
To counter these problem, parachutes do not open until the aviator reaches a low altitude. The individual will free fall and the chute will open automatically. If one is very high, a pressure suit is required.
Dr Deco
:doctor:
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