Timeline for Why is the breathing atmosphere of the ISS a standard atmosphere (at 1 atm containing nitrogen)?
Current License: CC BY-SA 4.0
15 events
| when toggle format | what | by | license | comment | |
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| Jun 8 at 2:26 | comment | added | uhoh | @StevePemberton ya we agree that most people "tend to think of humidity as a separate property of a gas mixture", but I missed that "balance" bit in the question, so I'm wrong :-) | |
| Jun 8 at 2:07 | comment | added | Steve Pemberton | @uhoh - I think in most contexts people are referring to the gas proportion not including water vapor. That seemed to be the case with the original question, which states "(ISS) atmosphere: 21% oxygen, balance nitrogen at 101.3 kPa". I doubt that they were implying that the ISS sea-level atmosphere contains no water vapor. The OP of this answer posits that one reason that ISS does not use 100% oxygen is because it does not contain water vapor. I was pointing out that while yes purely 100% oxygen (as well as 21% oxygen with balance nitrogen) contains no water vapor, humidified versions do. | |
| Jun 7 at 22:28 | comment | added | uhoh | @StevePemberton I think the point the OP wants to make is that, strictly speaking "100% oxygen has zero water vapor in it." We tend to think of humidity as a separate property of a gas mixture, instead of water being a gas mixture constituent, but strictly speaking as soon as it's humidified, it's no longer 100% pure O2. I guess a 0.21 bar atmosphere at 50% relative humidity would be 95% O2 and 5% H2O. | |
| Jun 7 at 18:51 | comment | added | Steve Pemberton | Pure oxygen gets dried out as part of the production process, but it can afterwards be humidified. | |
| Jun 7 at 18:39 | comment | added | Nick T | Breathing mixes are always referenced "dry". @MikeJones as mentioned by me and many others, problems with oxygen toxicity are often caused by its partial pressure (e.g. 0.21 atm in normal air, 1.0 atm if on pure oxygen in a hospital [which can be bad over time], or >1.4-1.6 atm if diving with EAN32+ [which can cause seizures and other acute neurological problems]) | |
| Jun 7 at 17:13 | comment | added | Hobbes | The Apollo cabin atmosphere was maintained at 50% humidity. So technically it's not 100% oxygen, but oxygen plus water vapor. | |
| Jun 7 at 17:07 | comment | added | fyrepenguin | I mean, for one, the EVA suits use 5 psi 100% O2 atmospheres, much like the LM did for Apollo. The “death zone” is regarding supplemental, not pure oxygen breathing. Sea level oxygen partial pressure is actually lower than pure O2 at 5 psi. | |
| Jun 7 at 16:53 | comment | added | Hobbes | Apollo definitely had a pure oxygen environment, not a mixed atmosphere. | |
| Jun 7 at 16:51 | comment | added | Hobbes | Mt Everest has 0.3 bar pressure, and a 80/20 nitrogen/oxygen mix, or 1/5 the oxygen partial pressure that Apollo had, which is lethal. | |
| Jun 7 at 16:20 | comment | added | Mike Jones | Apollo had to have been an air environment and not pure oxygen. Pure oxygen has no water vapor in it. Also, .3 bar is Everest Summit pressure. that's a death zone if you stay there for more than a few hours even with supplemental oxygen. | |
| Jun 7 at 15:48 | comment | added | Mike Jones | That's fascinating. Why does the medical establishment not know that all they need to do is put people in hypobaric chambers with pure oxygen and they will thrive for long periods of time? I'd love to see the clinical trials that were conducted in the 60s showing the safety of this. Do you know of any? | |
| Jun 7 at 15:24 | comment | added | Hobbes | That is true when breathing 100% oxygen at 1 bar ambient pressure. The Apollo spacecraft ran a 100% oxygen atmosphere at about 0.3 bar, and the crews remained healthy during the flights that took up to two weeks. Oxygen toxicity is an issue when the partial pressure of oxygen is a lot higher than the 0.2 bar you normally get. | |
| Jun 7 at 14:33 | review | Late answers | |||
| Jun 7 at 15:56 | |||||
| S Jun 7 at 14:17 | review | First answers | |||
| Jun 7 at 15:46 | |||||
| S Jun 7 at 14:17 | history | answered | Mike Jones | CC BY-SA 4.0 |