Humans can really breath Mars air?

[inconceivable]

I was shocked to see that in the Mars 500 project they are breathing an Argon/O2 mixture to simulate Martian air.  For 10 days volunteers breathed the mixture with success.

Is this for real?   We can really breathe Martian air?

 http://www.universetoday.com/14200/learning-to-breathe-mars-air-video/

[DataCable]

We can really breathe Martian air?

No, because the Martian atmosphere contains only traces of oxygen, never mind the fact that it averages roughly one half of one percent the pressure of Earth's at sea level.

[cjameshuff]

My only guess is that they were simulating the mix you'd get by pressurizing Martian atmosphere and removing the CO2. I'm not sure why they thought argon in place of nitrogen would make any difference...atmospheric nitrogen is biologically inert as far as humans are concerned, and argon is a noble gas. Helium and neon have been used in diving as a replacement for nitrogen, and astronauts have used pure low-pressure oxygen. And in fact, an argon-oxygen mix has been experimented with as a decompression gas for astronauts. (And enough experimentation has been done for diving purposes to find that it's about 2.3 times as narcotic as nitrogen under the high pressures encountered in diving.)

So...no, we can't breathe Mars air. Yes, we can breathe mixes with argon in place of nitrogen. No, this isn't news to anyone, except apparently the Mars 500 folks.

[Trebor]

Not for very long...

[ka9q]

I was going to mention the increased narcotic property of argon vs nitrogen, but it's not significant as long as you keep the total pressure low. It would seem to be a problem only in diving, not space flight.

If the speed of sound is significantly different from air then speech will be affected.

What's the definitive word on long-term human tolerance of pure O₂ atmospheres? I know that elevating ppO₂ above that in sea level air is eventually toxic, and the fire hazard is greater even when the ppO₂ is no higher, so that alone is good reason to have a diluent gas.

[cjameshuff]

I haven't heard of low pressure O2 is an issue apart from comfort and fire safety. (Water evaporates more readily, lower heat capacity, etc.)

The Apollo missions involved breathing pure oxygen at 5 psi for an extended period of time, without apparent harm. Interestingly, a major issue was risk of the bends with the rapid decompression to 5 psi, which was solved by having the astronauts breathe pure oxygen for a while before launching...I would have guessed that oxygen would be similarly prone to causing the bends (it is in fact a fair bit more soluble in water than nitrogen). It appears this isn't the case.

So there are some safety benefits to low pressure oxygen, provided you can control the fire safety issues. In the case of a decompression accident, not only is there a lower pressure differential and slower loss of gas, there's less risk of the bends. From the diving experiments, it looks like argon wouldn't be an improvement over nitrogen...it apparently makes decompression sickness worse. Neon, maybe, but that's hard to find. Helium works, if you can tolerate the side effects...

Another thing that makes this experiment a rather strange one...it's not hard to separate argon from nitrogen if it turns out to be needed. You don't even need to do something like fractional distillation...argon, like oxygen, is considerably more soluble in water than nitrogen.

[ka9q]

I would have guessed that oxygen would be similarly prone to causing the bends (it is in fact a fair bit more soluble in water than nitrogen). It appears this isn't the case.

Actually, I think it is. But you can adapt a little more quickly because you can use up the dissolved O₂, unlike dissolved N₂ that you have to breathe back out.

As you probably know, one of the changes made after the Apollo 1 fire was the use of a 60% O₂ + 40% N₂ mix in the cabin during prelaunch and ascent. The astronauts still breathed 100% O₂; presumably the risk of a fire occurring within a suit was considered acceptable. Over the first few days of the mission the cabin was slowly vented to allow the remaining N₂ to escape and be replaced by pure O₂ from the life support system.

Apparently this mix, though substantially enriched in O₂ over sea level air, reduced the fire hazard enough to be worthwhile.

The 60-40 mix has the property that at 5 psi (nominal cabin pressure in flight) the ppO₂ is the same as in sea level air, meaning the astronauts could breathe it immediately after reaching orbit. But it occurred to me that it would have been possible to launch with ordinary air in the cabin if, instead of bleeding the cabin down to 5 psi during ascent and holding it there, it had been bled down to vacuum and then refilled with 100% O₂. The crew would be in their suits and breathing 100% O₂ anyway.

But I can see two problems with my idea, and they're probably why it wasn't used. First, bleeding the cabin to vacuum would mean pressurizing the suits and making it more difficult to move and operate controls at a critical time. Second, such a sudden drop from 15+ psi to 3.75 psi (the nominal suit pressure) might have caused the bends even when breathing pure O₂. Only dropping to 5+ psi was probably safer.

[ka9q]

I took a look at the Wikipedia article on the Martian atmosphere. The figures will probably be updated with Curiosity data, but the current numbers (as mole fractions) are:

CO₂: 95.32%
N₂: 2.7%
Ar: 1.6%
O₂: 0.13%
CO: 0.07%
H₂O: 0.03%
NO: 0.013%
Traces of Ne, Kr, CH₂O (formaldehyde), Xe, O₃, CH₄.

So I guess the idea is to extract the Ar and N₂ and use them as diluent gases with O₂, presumably produced from local resources.

Note that several of the trace constituents are highly toxic and would have to be removed, particularly the 0.07% (700 ppm) of carbon monoxide which by itself would be quite fatal. The formaldehyde, ozone and nitric oxide are also problems. (If you just removed the CO₂, the percentages of these poisons in the remainder would be considerably higher.)

I'm not sure what separation process would be used, but the easiest thing to do is to first remove the CO₂ and then pull all the chemically inert gases apart from the chemically active ones. This would keep the trace noble gases, which would be okay. We already breathe them here.

Removing all but the Ar and N₂ from Martian air (and ignoring the trace of O₂) would result in a mixture of 62.8%  N₂ and 37.2% Ar. If this were used as 79% of manufactured breathing air, the overall mixture would be 21% O₂, 29.4% Ar and 49.6% N₂. The air we breathe on earth is 21% O₂, 78% N₂ and 1% Ar, with traces of many other gases, so it ought to be just fine.

[Glom]

But what's the partial pressures? That's more relevant to the human.

[smartcooky]

Note that several of the trace constituents are highly toxic and would have to be removed, particularly the 0.07% (700 ppm) of carbon monoxide which by itself would be quite fatal. The formaldehyde, ozone and nitric oxide are also problems. (If you just removed the CO₂, the percentages of these poisons in the remainder would be considerably higher.)

I'll say they are, especially the CO. If only the CO₂ were extracted, the CO would make up 1.5% of the remainder.

Add AR or N₂ to make up 79% of the dilution gas with 21% oxygen and the CO content ends up at about 900 ppm!

Doses over 100 ppm are hazardous to health; 800 ppm will cause nausea and convulsions in less than an hour, and unconsciousness within 2 hours.

[ka9q]

But what's the partial pressures? That's more relevant to the human.

Not really, because the Martian atmosphere is so thin (< 1% of earth's surface level pressure), and toxic CO₂ is so much of it, that whatever useful gases there are (Ar, N₂) will have to be compressed a lot to form part of a human-breathable atmosphere. So percentages are what's important.

[ka9q]

I'll say they are, especially the CO. If only the CO₂ were extracted, the CO would make up 1.5% of the remainder.

Add AR or N₂ to make up 79% of the dilution gas with 21% oxygen and the CO content ends up at about 900 ppm!

I think you mean 9,000 ppm -- which is even worse. Fatal almost in seconds.

[smartcooky]

I'll say they are, especially the CO. If only the CO₂ were extracted, the CO would make up 1.5% of the remainder.

Add AR or N₂ to make up 79% of the dilution gas with 21% oxygen and the CO content ends up at about 900 ppm!

I think you mean 9,000 ppm -- which is even worse. Fatal almost in seconds.

No, that would only be true if you simply removed the CO₂ and used the remainder as dilution gases then added the requisite amount of oxygen to give the 4:1 ratio.

100 L of Martian atmosphere contains 95 L of CO₂ and 90ml of CO

Removing the 95 L of CO₂ leaves 90ml of CO in 5L of the remaining gases... 1.8%

If you try to make a breathable air by simply adding oxygen to that, then you would add 1.25L of oxygen (80/20 ratio) and that means you are left with 90ml in 6.25L of air....1.47% or 14,700 ppm. That will lead to unconsciousness after 2–3 breaths and death in less than three minutes.

However, you simply would not try that. You would at least add enough Argon or Nitrogen to make up to 79 L of dilution gas, and then add 21 L oxygen, and you would be back to 90ml CO in 1 L,of air... 0.09% or 900 ppm.

Of course, this is will not be enough. The CO will have to be removed too. While scrubbing CO₂ is well understood and usually involves the use of either Lithium Hydroxide (as per Apollo) or Sodium Hydroxide, scrubbing CO is not so easy, and it has to be got down to a very low level. Even as little as 35 ppm will cause dizziness and headaches after six hours of continual exposure. Its going to have to come down to 5 - 10 ppm at least.

[ka9q]

No, that would only be true if you simply removed the CO₂ and used the remainder as dilution gases then added the requisite amount of oxygen to give the 4:1 ratio.

I don't understand. Wasn't that the plan? I thought the idea is to manufacture O₂ from Martian rocks and soil (which, like the crust of the earth, consists almost entirely of various oxygen-containing compounds like carbonates, silicates, titanates, sulfates and oxides) and then use the inert components of the Martian atmosphere (N₂, Ar) as diluent gases to make a breathable mixture similar to that of the earth's atmosphere, only with more argon and less nitrogen.

I suppose it might also be possible to extract the O₂ from atmospheric CO₂, but that is a very stable molecule and I'm not sure it would be as easy as getting it from certain minerals. Ilmenite (iron titanate, FeTiO₃) seems to be a favorite in proposals to make O₂ on the moon.

[ka9q]

scrubbing CO is not so easy, and it has to be got down to a very low level.

I agree it has to be taken to a very low level, but why is that hard? CO and CH₂O (formaldehyde) are both reducing agents -- i.e., they burn -- so just add pure O₂ and use a catalyst or heat to oxidize them to H₂O and CO₂.

The other harmful gases are O₃ and NO. Both are unstable molecules (positive enthalpies of formation) so they can be catalytically decomposed to O₂ and N₂.

Note also that you don't really need to process much of this stuff, as diluent gases can remain in the habitat atmosphere indefinitely -- just add O₂ as it is consumed and extract H₂O, CO₂ and other, uh, miscellaneous gases as necessary. Additional diluent will be needed only to compensate for leaks, new construction, etc.