Timeline for Why is the breathing atmosphere of the ISS a standard atmosphere (at 1 atm containing nitrogen)?
Current License: CC BY-SA 3.0
16 events
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| Aug 30, 2017 at 20:26 | comment | added | Nick T | @Uwe by "acutely bad" I mean you get seizures immediately. From that I was vaguely implying that you need to calculate at what depth (pressure) your chosen gas mix (Air, EAN, Trimix) you might hit certain partial pressures of certain gases: the percentage is irrelevant. | |
| Aug 30, 2017 at 20:22 | comment | added | Uwe | @NickT 1.4-1.6 atm of oxygen is acutely bad, that is only a part of the truth, more than 0.5 atm of pure oxygen may be unhealthy too, see en.wikipedia.org/wiki/Oxygen_toxicity#Lung_toxicity . But divers don't breathe pure oxygen for many hours. | |
| Jun 25, 2015 at 23:09 | comment | added | Keith Thompson | @Mehrdad: The point, I think, is that a full atmosphere of pure O2 creates the risk of an explosion (as proven by Apollo 1) as long as there are flammable substances in the area. Pure O2 at 0.21 atmosphere creates a lesser risk of explosion, but still some. | |
| Jun 25, 2015 at 23:06 | comment | added | user541686 | @KeithThompson: How about something more practical, like "may explode in the presence of oxygen with common elements"? After all, you don't call a substance an "explosive" if there's nothing around you for it to react with. I'm trying to make a very practical point here, not trying to split hairs with chemistry. Compare what would happen if they filled the rest of the 1atm of pressure with (1) oxygen, (2) nitrogen, and (3) hydrogen. The first two would not result in an "explosive" atmosphere. The third one would. It should be pretty easy to understand what I'm saying, I think. | |
| Jun 25, 2015 at 22:50 | comment | added | Keith Thompson | @Mehrdad: Neither oxygen nor hydrogen is explosive by itself (ignoring fusion). Unless the meaning of "explosive" is limited to "may explode in the presence of oxygen". | |
| Jun 25, 2015 at 22:42 | comment | added | user541686 | @KeithThompson: I literally meant that oxygen is not explosive. Hydrogen, on the other hand, is. | |
| Jun 25, 2015 at 22:11 | comment | added | Keith Thompson | @Mehrdad: Of course pure oxygen by itself is not explosive if it has nothing to react with; is that what you meant? The question is, given a fuel source, does pure oxygen at 0.21 atmosphere pressure give you more danger of explosion than 21% oxygen and 79% nitrogen at 1.0 atmosphere pressure (same partial pressure of O2 in both cases). I don't know the answer to that. | |
| Oct 25, 2014 at 14:49 | comment | added | David Hammen | Note: I am not one of the downvoters. I don't agree with this answer, but not enough to downvote it. If you downvote an answer, the only polite thing to do is to post a comment that says why. | |
| Oct 25, 2014 at 10:02 | comment | added | user541686 | -1 pure oxygen is not explosive. | |
| Oct 24, 2014 at 21:01 | comment | added | Rory Alsop♦ | I never said a pure oxygen atmosphere was unhealthy. See sentence 2 :-) | |
| Oct 24, 2014 at 19:41 | comment | added | David Hammen | With regard to the Shuttle, I suspect that it's pre-launch and post-landing concerns that drove the decision rather than on-orbit concerns. That a pure oxygen atmosphere (or even a Skylab-style mix) is "unhealthy" seems rather bogus. | |
| Oct 24, 2014 at 19:38 | comment | added | David Hammen | There are adverse safety and operational issues with using diluent gases as well. Regarding a pure oxygen atmosphere at 1/5 atmospheric pressure being "unhealthy", citation needed. I looked. No such luck. I also looked for the trade studies that made the Shuttle lean toward using a standard atmosphere. I couldn't find that, either. I found lots of trade studies that claimed to justify the pure oxygen atmosphere on Mercury, Gemini, and Apollo. | |
| Oct 24, 2014 at 18:31 | comment | added | Rory Alsop♦ | David - yes those missions did, and they stopped doing that because of the issues that arose, both pre-flight and safety. | |
| Oct 24, 2014 at 17:11 | comment | added | Nick T | As a diver it seems like a dubious claim that 0.21 atm of O2 with or without any inert component would be any different. We're taught 1.4-1.6 atm of oxygen is acutely bad and that it's the partial oxygen pressure that matters, regardless of any other gas in the mix. Do you have any links for any of your claims? | |
| Oct 24, 2014 at 15:54 | comment | added | David Hammen | The Mercury, Gemini, and Apollo programs all used a reduced pressure pure oxygen atmosphere. The Apollo 1 fire made NASA modify how that pure oxygen atmosphere was achieved, but did not alter the fact that the breathing atmosphere became pure oxygen shortly after launch. Skylab's breathing atmosphere was 75% oxygen, 25% nitrogen. Astronauts survived for 84 days breathing this "unhealthy" mix. | |
| Oct 24, 2014 at 10:07 | history | answered | Rory Alsop♦ | CC BY-SA 3.0 |