# What are the necessary components of air to sustain human or mammalian life? **URL:** \ **Category:** Factual Questions\ **Created:** [February 16, 2021, 6:20am UTC](https://boards.straightdope.com/t/what-are-the-necessary-components-of-air-to-sustain-human-or-mammalian-life/933009 "2021-02-16T06:20:03Z")\ **Posts on this page:** 20\ **Page:** 2
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [February 16, 2021, 6:15pm UTC](https://boards.straightdope.com/t/what-are-the-necessary-components-of-air-to-sustain-human-or-mammalian-life/933009/21 "2021-02-16T18:15:10Z")
> [@k9bfriender](#): > > Gases are weird, they aren’t liquids or solids. If you fill up a balloon with a liter of nitrogen at STP, then add the same volume of oxygen, the balloon will not inflate much, if at all. This is not true. If you take a liter of oxygen at STP and a liter of nitrogen at STP, and put all of both into a balloon, then the volume will be a little less than 2 L, because the skin of the balloon itself does exert some pressure, but only a little less, because most balloon materials exert only a very small amount of pressure (rather, they mostly stretch to increase their volume, until the pressure inside is very close to the pressure outside). ---
**Author:** ![Machine\_Elf](https://avatars.discourse-cdn.com/v4/letter/m/82dd89/32.png) [@Machine\_Elf](https://boards.straightdope.com/u/Machine_Elf)\ **Post date:** [February 16, 2021, 7:15pm UTC](https://boards.straightdope.com/t/what-are-the-necessary-components-of-air-to-sustain-human-or-mammalian-life/933009/22 "2021-02-16T19:15:10Z")
> [@k9bfriender](#): > > Gases are weird, they aren’t liquids or solids. If you fill up a balloon with a liter of nitrogen at STP, then add the same volume of oxygen, the balloon will not inflate much, if at all. This is not possible. The density of nitrogen at STP is 1 gram per cc, and the density of oxygen at STP is 1.429 grams per cc. If what you say is true, then the density of air at STP would be 2.429 grams per cc, but it’s not; it’s 1.225 grams per cc. > [@k9bfriender](#): > > Adding water vapor to a gas doesn’t increase or decrease its density. The chart on **[the page I linked to](https://www.engineeringtoolbox.com/density-air-d_680.html)** clearly shows that for any given fixed temperature, humid air is less dense than dry air. Are you saying the chart on that page, along with the numerous assertions that the amount of water vapor in air influences its density, are incorrect? > [@Chronos](#): > > Is concentration of oxygen actually a problem, or is it partial pressure of oxygen? I can’t see how diluting it (without displacing it) would make any difference to fires or metabolic processes. It’s both. increasing O2PP provides more oxidizer, and increasing concentration (removing diluent) lowers peak temperatures which can influence reaction rate and end products > [@Little\_Nemo](#): > > A morbid trivia note I’ve heard is that when people are confined in a sealed environment it isn’t a lack of oxygen that kills them. They die from an overdose of carbon dioxide while there is still a breathable amount of oxygen. This was the primary concern during the Apollo 13 mission. After the decision was made to abort, they had enough oxygen to sustain them for the trip home, but they needed to find a way to scrub CO2 out of the air along the way or they would die of hypercapnia before splashdown. They figured it out, and everybody lived happily ever after. > **[Apollo 13 | Return to Earth](https://en.wikipedia.org/wiki/Apollo_13#Return_to_Earth)** > > The LM carried enough oxygen, but that still left the problem of removing carbon dioxide, which was absorbed by canisters of lithium hydroxide pellets. > The LM's stock of canisters, meant to accommodate two astronauts for 45 hours on the Moon, was not enough to support three astronauts for the return journey to Earth. The CM had enough canisters, but they were of a different shape and size to the LM's, hence unable to be used in the LM's equipment. Engineers on the ground devised a way to br ---
**Author:** ![carnivorousplant](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/carnivorousplant/32/3563_2.png) [@carnivorousplant](https://boards.straightdope.com/u/carnivorousplant)\ **Post date:** [February 16, 2021, 7:17pm UTC](https://boards.straightdope.com/t/what-are-the-necessary-components-of-air-to-sustain-human-or-mammalian-life/933009/23 "2021-02-16T19:17:01Z")
Duct tape. ---
**Author:** ![carnivorousplant](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/carnivorousplant/32/3563_2.png) [@carnivorousplant](https://boards.straightdope.com/u/carnivorousplant)\ **Post date:** [February 16, 2021, 7:18pm UTC](https://boards.straightdope.com/t/what-are-the-necessary-components-of-air-to-sustain-human-or-mammalian-life/933009/24 "2021-02-16T19:18:01Z")
Thanks, k0bfriender. I didn’t know they were running 20 PSI during the fire. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [February 16, 2021, 7:37pm UTC](https://boards.straightdope.com/t/what-are-the-necessary-components-of-air-to-sustain-human-or-mammalian-life/933009/25 "2021-02-16T19:37:17Z")
> [@Machine\_Elf](#): > > The chart on **[the page I linked to](https://www.engineeringtoolbox.com/density-air-d_680.html)** clearly shows that for any given fixed temperature, humid air is less dense than dry air. The question you always have to ask when working with gases is, what are you keeping constant? The answer to that question is usually not obvious, so it always needs to be specified. If you add water vapor to air while keeping the volume and number of particles of other gases constant, you’ll increase its density (and also its pressure). If you add water vapor to air while keeping the total pressure constant, you’ll decrease its density (and also either increase its volume, or decrease the number of particles of other gases). ---
**Author:** ![Dark\_Sponge](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dark_sponge/32/121_2.png) [@Dark\_Sponge](https://boards.straightdope.com/u/Dark_Sponge)\ **Post date:** [February 16, 2021, 7:51pm UTC](https://boards.straightdope.com/t/what-are-the-necessary-components-of-air-to-sustain-human-or-mammalian-life/933009/26 "2021-02-16T19:51:47Z")
> [@Machine\_Elf](#): > > …When performing an EVA, an astronaut’s suit is pressurized to only 4.5 psi, which helps with dexterity (easier to flex the suit’s joints). This is equivalent to the pressure on top of Mount Everest, and yes they use pure O2 in this setting. I thought breathing pure O2 resulted in euphoria. Is this not true at lower pressures? Or is a bit of euphoria considered a plus during a space walk? ---
**Author:** ![Stranger\_On\_A\_Train](https://avatars.discourse-cdn.com/v4/letter/s/13edae/32.png) [@Stranger\_On\_A\_Train](https://boards.straightdope.com/u/Stranger_On_A_Train)\ **Post date:** [February 16, 2021, 8:22pm UTC](https://boards.straightdope.com/t/what-are-the-necessary-components-of-air-to-sustain-human-or-mammalian-life/933009/27 "2021-02-16T20:22:24Z")
> [@Napier](#): > > Air loaded with H2O will be lighter, won’t it? Water in the gas phase is only a little over half as dense as the nitrogen and oxygen it’s displacing. My error; mea culpa. > [@Dark\_Sponge](#): > > I thought breathing pure O2 resulted in euphoria. > > Is this not true at lower pressures? Or is a bit of euphoria considered a plus during a space walk? Breathing pure oxygen does not cause euphoria. You can experience [nitrogen narcosis](https://www.divein.com/articles/what-is-nitrogen-narcosis/) in breathing high pressure air (starting at about 60 psia). I’ve had divers claim that breathing nitrox (an “enriched air” combination of up to 40% oxygen with the remainder being nitrogen) makes them feel more refreshed but that has not been my personal experience. Nitrox comes with the risk of oxygen toxicity if your dive exceeds the allowable limit (because of the increased ppO2 under pressure) and as I avoid doing more than a couple of dives at a time or running up against the deco limit I don’t generally bother with it. Stranger ---
**Author:** ![k9bfriender](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/k9bfriender/32/3283_2.png) [@k9bfriender](https://boards.straightdope.com/u/k9bfriender)\ **Post date:** [February 16, 2021, 8:37pm UTC](https://boards.straightdope.com/t/what-are-the-necessary-components-of-air-to-sustain-human-or-mammalian-life/933009/28 "2021-02-16T20:37:33Z")
> [@Chronos](#): > > This is not true. If you take a liter of oxygen at STP and a liter of nitrogen at STP, and put all of both into a balloon, then the volume will be a little less than 2 L, because the skin of the balloon itself does exert some pressure, but only a little less, because most balloon materials exert only a very small amount of pressure (rather, they mostly stretch to increase their volume, until the pressure inside is very close to the pressure outside). > [@Machine\_Elf](#): > > This is not possible. The density of nitrogen at STP is 1 gram per cc, and the density of oxygen at STP is 1.429 grams per cc. If what you say is true, then the density of air at STP would be 2.429 grams per cc, but it’s not; it’s 1.225 grams per cc. My mistake, I had to go back and see where I saw that at, as I said, gasses are weird, and it’s about concentrations, not pressure. If you have a box with 100% nitrogen, with a membrane that keeps nitrogen from diffusing, but allowing oxygen, then the pressure in that box will increase as it equalized the percentage of oxygen in the box and outside. That’s the part that doesn’t care about pressure. Not sure why I mixed that up, as the actual [demonstration is to fill a latex balloon with Sulfur hexafluoride](https://aapt.scitation.org/doi/abs/10.1119/1.2343044?journalCode=pte), and if you leave it alone for a time, it will slowly inflate further. ---
**Author:** ![Ponderoid](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ponderoid/32/19221_2.png) [@Ponderoid](https://boards.straightdope.com/u/Ponderoid)\ **Post date:** [February 17, 2021, 6:45am UTC](https://boards.straightdope.com/t/what-are-the-necessary-components-of-air-to-sustain-human-or-mammalian-life/933009/29 "2021-02-17T06:45:09Z")
Thanks for all the responses, everybody. Especially for setting me straight about needing a tiny bit of CO2 for the breathing reflex. I read that in some popular science book or magazine article ages ago. I’m still unclear on whether it’s okay for people to stay in a pure O2 environment within the right pressure range long term, or do health effects start to crop up if it’s not diluted with nitrogen or a noble gas? ---
**Author:** ![DesertDog](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/desertdog/32/11503_2.png) [@DesertDog](https://boards.straightdope.com/u/DesertDog)\ **Post date:** [February 17, 2021, 8:10am UTC](https://boards.straightdope.com/t/what-are-the-necessary-components-of-air-to-sustain-human-or-mammalian-life/933009/30 "2021-02-17T08:10:23Z")
> [@Stranger\_On\_A\_Train](#): > > The [NASA Technical Reports Server](https://ntrs.nasa.gov) has a wealth of papers on the topic although most are from the 'Sixties in support of the Mercury/Gemini/Apollo spaceflight programs. Spaceflight programs since then have used combined oxygen/nitrogen atmospheres because of the flammability hazard of pure oxygen, although pure oxygen is used in prebreathing in preparation for extravehicular activities because pressure suits operate at a significantly reduced internal pressure. Apollo 1 had low-pressure O2 cabin atmosphere and it was one of the big factors in the astronauts’ deaths. Materials – specifically the nylon netting used for stowage – reacted badly and generated a lot more heat than expected. During the big pause before the project was restarted was redesigning the cabin for regular old air and only a bit less than sea level to get the partial pressure up. ---
**Author:** ![eburacum\_45](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/eburacum_45/32/3385_2.png) [@eburacum\_45](https://boards.straightdope.com/u/eburacum_45)\ **Post date:** [February 17, 2021, 9:47am UTC](https://boards.straightdope.com/t/what-are-the-necessary-components-of-air-to-sustain-human-or-mammalian-life/933009/31 "2021-02-17T09:47:18Z")
> [@Ponderoid](#): > > I’m still unclear on whether it’s okay for people to stay in a pure O2 environment within the right pressure range long term, or do health effects start to crop up if it’s not diluted with nitrogen or a noble gas? This is something I’ve been wondering about for a long time. Most of my recent reading seems to suggest that you would be fine in an oxygen atmosphere at about 1/5 Earth pressure if no other gases were present. This would make it considerably easier to create a liveable environment on Mars, or in a pressurised habitat somewhere else, because you would only have to find oxygen (an element that is common in many of the rocks of the Solar System) whereas nitrogen is much more difficult to source. There are differences between a low pressure O2 atmosphere and a full pressure N2/O2 atmosphere that might cause problems; flames and ignition behave slightly different in low pressure O2, but I really don’t know if this behaviour is significant enough to be dangerous. You can get O2 trapped in your clothing in a low pressure O2 environment, which could be dangerous when you go back to a full pressure N2/O2 environment; at least one death has happened in this way. But that seems a fairly unusual set of circumstances. ---
**Author:** ![eburacum\_45](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/eburacum_45/32/3385_2.png) [@eburacum\_45](https://boards.straightdope.com/u/eburacum_45)\ **Post date:** [February 17, 2021, 9:51am UTC](https://boards.straightdope.com/t/what-are-the-necessary-components-of-air-to-sustain-human-or-mammalian-life/933009/32 "2021-02-17T09:51:19Z")
Note, however, that growing crops in a nitrogen-free environment would require the use of nitrate fertiliser, and you couldn’t rely on nitrogen-fixing crops like legumes to revitalise the soil. ---
**Author:** ![Pardel-Lux](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/pardel-lux/32/20182_2.png) [@Pardel-Lux](https://boards.straightdope.com/u/Pardel-Lux)\ **Post date:** [February 17, 2021, 10:33am UTC](https://boards.straightdope.com/t/what-are-the-necessary-components-of-air-to-sustain-human-or-mammalian-life/933009/33 "2021-02-17T10:33:05Z")
N² in the air is not metabolizable by plants, it behaves to all intents and purposes like an inert gas. The double bond N=N is very strong, only some bacteria can break it. When these bacteria live symbiotically in the roots of some plants, they “fix” nitrogen, i.e.: they make it bioavailable in the form of easier to break up compounds (for instance ammonia) that plant take up through the roots, usually with the help of mycorrhizal fungi, but never through the leaves. For those interested in this stuff the book [Cesar’s last breath](https://www.amazon.de/Caesars-Last-Breath-Sextillions-Molecules/dp/0316381659) by Sam Kean would be an interesting read, though he does not mention the space programm. ---
**Author:** ![Broomstick](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/broomstick/32/246_2.png) [@Broomstick](https://boards.straightdope.com/u/Broomstick)\ **Post date:** [February 17, 2021, 10:45am UTC](https://boards.straightdope.com/t/what-are-the-necessary-components-of-air-to-sustain-human-or-mammalian-life/933009/34 "2021-02-17T10:45:44Z")
> [@carnivorousplant](#): > > Don’t NASA astronauts breathe pure oxygen at low pressure? Only in very limited and specific circumstances has that ever happened, and not anymore. Most space habitats where people live/work for any extended time, like Mir, the space shuttle or the international space station maintain air pressure pretty close to sea level with a similar mix of gasses. It is, after all, what humans are adapted to. The old Skylab had only about 1/3 of sea level pressure, and on board the air was about 74% oxygen and 25% nitrogen. Spacesuits these days are also pressurized to a similar standard (actually, just a bit less) and presumably the astronauts on spacewalks are breathing a similar air mixture. In the very, very early days of space flight pure oxygen was used because that allowed the lowest air pressure possible, but that was only for a few hours or days, and there were a couple of spectacular demonstrations of the hazards of using pure oxygen (see Apollo One) and it’s urge to chemically combine with other stuff rapidly i.e. fire. NASA astronauts do not, so far as I know, breathe 100% pure oxygen at any time in the present. Or, for that matter, any other astronauts/cosmonauts/space travelers. ---
**Author:** ![Broomstick](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/broomstick/32/246_2.png) [@Broomstick](https://boards.straightdope.com/u/Broomstick)\ **Post date:** [February 17, 2021, 10:53am UTC](https://boards.straightdope.com/t/what-are-the-necessary-components-of-air-to-sustain-human-or-mammalian-life/933009/35 "2021-02-17T10:53:27Z")
Missed edited window: “Except for pre-breathing for extra-vehicular activities” as noted by others. ---
**Author:** ![eburacum\_45](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/eburacum_45/32/3385_2.png) [@eburacum\_45](https://boards.straightdope.com/u/eburacum_45)\ **Post date:** [February 17, 2021, 11:09am UTC](https://boards.straightdope.com/t/what-are-the-necessary-components-of-air-to-sustain-human-or-mammalian-life/933009/36 "2021-02-17T11:09:30Z")
> [@Pardel-Lux](#): > > N² in the air is not metabolizable by plants, it behaves to all intents and purposes like an inert gas. Absolutely. If the crops grown in space do not have access to nitrogen-fixing bacteria via the routes you mention, all the necessary nitrogen would need to be supplied as nitrate fertiliser. Nitrogen is uncommon on Mars, the Moon, and Mercury, but abundant on Earth, Venus and Titan, as well as many objects further out such as Triton and Pluto. If we ever build space habitats outside Earth orbit one problem they will face will be sourcing nitrogen for food. ---
**Author:** ![Broomstick](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/broomstick/32/246_2.png) [@Broomstick](https://boards.straightdope.com/u/Broomstick)\ **Post date:** [February 17, 2021, 11:13am UTC](https://boards.straightdope.com/t/what-are-the-necessary-components-of-air-to-sustain-human-or-mammalian-life/933009/37 "2021-02-17T11:13:14Z")
> [@Chronos](#): > > Is concentration of oxygen actually a problem, or is it partial pressure of oxygen? I can’t see how diluting it (without displacing it) would make any difference to fires or metabolic processes. They’re both important. But while I have some understanding of it I’m not sure I can explain it clearly. The “partial pressure” of oxygen is important because your body requires a certain number of oxygen molecules to sustain life. At low overall pressures that means that oxygen needs to be a higher percentage of the air to provide sufficient oxygen molecules until finally you get so low pressure that 100% of the air you breathe needs to be oxygen to keep you alive. 100% oxygen at something like 2 psi might be the absolute minimum to sustain life (that’s a wild guess, I didn’t look up the exact pressure). But 100% oxygen at sea level pressure can actually be toxic - in the early days of baby incubators preemies were given very high levels of oxygen, like 100%, and it destroyed their retinas leaving them permanently blind (this is why Stevie Wonder can’t see). It’s not too healthy in adults, either. [Here’s the wiki on oxygen toxicity.](https://en.wikipedia.org/wiki/Oxygen_toxicity) > [@k9bfriender](#): > > Adding water vapor to a gas doesn’t increase or decrease its density Yes, actually it does - you’re example of the balloon does not apply to Earth’s atmosphere. Pilots have to take humidity and it’s effect on air density into account when making calculations for flight, such as for take-offs. It’s not the only factor that has to be considered, but high/low humidity does affect aircraft performance, just as high/low temperatures do. I know this from actual real-life experience. > [@Little\_Nemo](#): > > Andy Weir’s novel _Artemis_ is set in a lunar colony. In the course of the book, he mentions that the colony has a pure oxygen atmosphere with only twenty percent normal air pressure; basically, Earth’s atmosphere with all of the non-oxygen removed. > > Weir’s usually pretty good with the hard science but I’ve always questioned whether this would be workable. Well… in the sense you could breathe such air without immediately dying, sure… but not sure it would be healthy or safe (there would still be a fire risk) long term. > [@Little\_Nemo](#): > > A morbid trivia note I’ve heard is that when people are confined in a sealed environment it isn’t a lack of oxygen that kills them. They die from an overdose of carbon dioxide while there is still a breathable amount of oxygen. This is true. It was a problem on the Apollo 13. We can only tolerate a small amount of CO2 in the air. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [February 17, 2021, 11:48am UTC](https://boards.straightdope.com/t/what-are-the-necessary-components-of-air-to-sustain-human-or-mammalian-life/933009/38 "2021-02-17T11:48:34Z")
> [@Broomstick](#): > > But 100% oxygen at sea level pressure can actually be toxic - in the early days of baby incubators preemies were given very high levels of oxygen, like 100%, and it destroyed their retinas leaving them permanently blind (this is why Stevie Wonder can’t see). It’s not too healthy in adults, either. [Here’s the wiki on oxygen toxicity.](https://en.wikipedia.org/wiki/Oxygen_toxicity) Yes, that would be an example of a very high partial pressure of oxygen. I (and everyone else) already know that’s bad. ---
**Author:** ![Napier](https://avatars.discourse-cdn.com/v4/letter/n/ce73a5/32.png) [@Napier](https://boards.straightdope.com/u/Napier)\ **Post date:** [February 17, 2021, 1:15pm UTC](https://boards.straightdope.com/t/what-are-the-necessary-components-of-air-to-sustain-human-or-mammalian-life/933009/39 "2021-02-17T13:15:46Z")
> [@Chronos](#): > > The question you always have to ask when working with gases is, what are you keeping constant? The answer to that question is usually not obvious, so it always needs to be specified. If you add water vapor to air while keeping the volume and number of particles of other gases constant, you’ll increase its density (and also its pressure). […] The OP didn’t stipulate that we’d constrain the pressure and temperature of the air at what was most appropriate for breathing, but I had supposed we would. OP, did you mean to throw open these other considerations? ---
**Author:** ![Little\_Nemo](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/little_nemo/32/3120_2.png) [@Little\_Nemo](https://boards.straightdope.com/u/Little_Nemo)\ **Post date:** [February 17, 2021, 4:14pm UTC](https://boards.straightdope.com/t/what-are-the-necessary-components-of-air-to-sustain-human-or-mammalian-life/933009/40 "2021-02-17T16:14:56Z")
> [@Broomstick](#): > > > [@Little\_Nemo](#): > > > > Andy Weir’s novel _Artemis_ is set in a lunar colony. In the course of the book, he mentions that the colony has a pure oxygen atmosphere with only twenty percent normal air pressure; basically, Earth’s atmosphere with all of the non-oxygen removed. > > > > Weir’s usually pretty good with the hard science but I’ve always questioned whether this would be workable. > > Well… in the sense you could breathe such air without immediately dying, sure… but not sure it would be healthy or safe (there would still be a fire risk) long term. Weir presented this as an environment that a large group of people were living in for years at a time. As I said, I questioned whether this would be possible and wondered about the health issues to the people and the dangers to equipment presented by pure oxygen. I also wondered about the long term effects of breathing air at only twenty percent pressure. Would your lungs atrophy and lose the capacity to function at normal air pressure? [Previous page](https://boards.straightdope.com/t/what-are-the-necessary-components-of-air-to-sustain-human-or-mammalian-life/933009.md?page=1) [Next page](https://boards.straightdope.com/t/what-are-the-necessary-components-of-air-to-sustain-human-or-mammalian-life/933009.md?page=3)