Quick question about oxygen!

[Ragitsu]

Will a normal human suffer any lasting internal damage/die if they have to take in pure O2 (as composed to the mixture we have on Earth) to survive in a spaceship emergency?

[Markdoc]

Re: Quick question about oxygen!

 

Depends how long it is. In the short term, the effects are dizziness, fatigue, fluid in the lungs, difficulty in focusing your eyes. If air pressure is less than normal, you can actually tolerate these effects better - and still get the oxygen you need to survive. Longer term, you will suffer neural damage and start to get physical damage to your lungs, due to subsurface bleeding, and muscle spasms, from fluid leakage and abnormal neuronal firing.

 

So at about 1/3 of normal air pressure, you can breathe 100% oxygen for several weeks without apparent harm - longer than that, in animal studies, led to changes in brain chemistry and seizures. At 100% normal pressure you get oxygen toxicity in about an hour - so the severe effects listed above. You can recover from that, but more than a couple of hours (guessing here, because we have no data) would probably lead to severe permanent brain damage - and you'd almost certainly be blind and nonfunctional by then.

 

cheers, Mark

[Tasha]

Re: Quick question about oxygen!

 

NASA used a fairly pure O2 mixture in the early space program. The problem with it is that ANY spark will cause a fire that the Pure O2 will cause to spread so fast that it's not funny. Heck in Pure O2 things we consider non-combustable (like iron and steel) will generate a flame.

[Ragitsu]

Re: Quick question about oxygen!

 

Thank you, Markdoc. Thank you, Tasha.

 

Looks like someone's not dying after all.

[Markdoc]

Re: Quick question about oxygen!

 

NASA used a fairly pure O2 mixture in the early space program. The problem with it is that ANY spark will cause a fire that the Pure O2 will cause to spread so fast that it's not funny. Heck in Pure O2 things we consider non-combustable (like iron and steel) will generate a flame.

 

100% oxygen in fact - at 5psi (normal air is 14.7). That's how I know about the long term effects of breathing pure oxygen

There were two reason for that. First off, it reduced weight if you only carried oxygen: that was the main reason. The second reason for that is that nitrogen is easily dissolved in blood (oxygen isn't) - if you suffer a pressure drop, you ran a good risk of getting the bends, and in space that could easily be fatal. Also since space suits are not pressurized to the same level as the cabin (for a long time they also used low pressure oxygen) if you did a spacewalk, you'd need to decompress for 2-5 hours before you could come back inside - meaning your spacecraft also needed a decompression lock, adding more weight.

 

But yeah, the tradeoff was fire risk. It wasn't quite as extreme as you suggest, otherwise they would never had made it off the ground, but in the end, it was still enough to total one Apollo Mission and end the reliance of low pressure oxygen.

 

cheers, Mark

[The Weapon]

Re: Quick question about oxygen!

 

NASA used a fairly pure O2 mixture in the early space program. The problem with it is that ANY spark will cause a fire that the Pure O2 will cause to spread so fast that it's not funny. Heck in Pure O2 things we consider non-combustable (like iron and steel) will generate a flame.

 

Russia tried it too, but each side had an accident on earth with a fire, both fatal. It's a really bad idea. If the partial pressure is the same as earth's (1/5 atmosphere) then it shouldn't be a problem, but then you have a problem transferring to somewhere that has normal pressure.

[Cancer]

Re: Quick question about oxygen!

 

Yes, you need a buffer gas for a long-term human-breatheable atmosphere. On Earth that's N2. CO2 most definitely does not work. Hmmm. Reading a bit about Ne and Ar in a diving context, I'm not sure those could be acceptable permanent buffer gases.

[Tasha]

Re: Quick question about oxygen!

 

Yes' date=' you need a buffer gas for a long-term human-breatheable atmosphere. On Earth that's N2. CO2 most definitely does not work. Hmmm. Reading a bit about Ne and Ar in a diving context, I'm not sure those could be acceptable permanent buffer gases.[/quote']

 

Heinlein wrote about using He as a buffer gas in "Have Space Suit will travel". In the book the only side effect was talking funny. I don't know how realistic it would be to use He, but NASA seems to have the gas mixture thing licked.

[Cancer]

Re: Quick question about oxygen!

 

Divers use helium and it seems to be free of most adverse effects. The other inert gases have some narcotic effects (bad for just about everything), and take longer to flush out of the system (which is bad for diving, maybe not so for constant-pressure situations like space). They're also more expensive than helium to buy, it seems, but I think that's because a major helium industry already exists while there's little demand for neon or argon (in particular, argon should be really cheap once you had the facilities built).

[Markdoc]

Re: Quick question about oxygen!

 

Divers use helium and it seems to be free of most adverse effects. The other inert gases have some narcotic effects (bad for just about everything)' date=' and take longer to flush out of the system (which is bad for diving, maybe not so for constant-pressure situations like space). They're also more expensive than helium to buy, it seems, but I think that's because a major helium industry already exists while there's little demand for neon or argon (in particular, argon should be really cheap once you had the facilities built).[/quote']

 

Yeah, but the helium/oxygen mix (called Heliox) suffers the same tissue penetration issues as nitrogen, only the effect is faster. That means any pressure changes run the same risk as nitrogen of giving you the bends, and decompression needs to be even slower - after prolonged dives on Heliox (which is the only time, it's used, really) decompression can take up to 48 hours - meaning two days in the tank for each working shift. Neon or argon, I have no real data to work from (no surprise there ), but at this point a simple nitrox mixture - just like we are breathing now - seems as good an answer as any.

 

cheers, Mark

[Old Man]

Re: Quick question about oxygen!

 

I recommend using nitrous oxide as the buffer gas.

[amanojaku]

Re: Quick question about oxygen!

 

Don't you need some level of CO2 to maintain some sort of breathing reflex? I seem to have read once that someone tried a pure O2 mix but it needed some CO2 to maintain the breathing reflex. Could be wrong but I swear I remember that. I read so much sometimes I'll recall a passage but not the book.

[Lawnmower Boy]

Re: Quick question about oxygen!

 

That factoid appears as part of the premise of Larry Niven's short story, "The Flight of the Horse," subsequently the fixup Rainbow Mars. A quick search turns up Hypercapnia, the state of having an excess of carbon dioxide in the blood. Per Wikipedia, "[h]ypercapnia normally triggers a reflex which increases breathing and access to oxygen, such as arousal and turning the head during sleep. A failure of this reflex can be fatal, as in sudden infant death syndrome." A decline in blood oxygen content is more weakly associated with similar reflexes.

 

So it looks as though sleep apnea would be more dangerous in an atmosphere without carbon dioxide, but hardly critically so.

[Drhoz]

Re: Quick question about oxygen!

 

Don't you need some level of CO2 to maintain some sort of breathing reflex? I seem to have read once that someone tried a pure O2 mix but it needed some CO2 to maintain the breathing reflex. Could be wrong but I swear I remember that. I read so much sometimes I'll recall a passage but not the book.

 

Dr Karl on Triple J's Morning Show brings up that very matter a few times every year. Including the time he nearly killed himself in live TV because he'd hyperventilated with helium, and without enough CO2 left in his bloodstream to trigger the breathing reflex. He noticed the tunnel vision first. Eventually he realised he was dying and forced himself to start breathing again.

[Markdoc]

Re: Quick question about oxygen!

 

Dr Karl on Triple J's Morning Show brings up that very matter a few times every year. Including the time he nearly killed himself in live TV because he'd hyperventilated with helium' date=' and without enough CO2 left in his bloodstream to trigger the breathing reflex. He noticed the tunnel vision first. Eventually he realised he was dying and forced himself to start breathing again.[/quote']

 

But the problem is not the presence (or absence) of CO2 in the atmosphere: it's only 0.04% in air. In contrast it's about 5.3% in the air in your lungs - your body produces CO2 as a waste product when you breathe in oxygen, so the amount in the air is irrelevant. The problem with passing out is hyperventilating or what's called "gas-flushing", where you flush CO2 out of your blood and build up concentrations of gases other than CO2 in your blood to the point where the locally-produced CO2 cannot dissolve efficiently. That messes with your body's monitoring system.

 

Long story short: your body monitors CO2 in your blood to control the breathing process, but it's not C02 intake that's relevant - it's your body's CO2 output that matters.

 

So even in an atmosphere of 100% oxygen, you would not experience breathing problems (at least, not due to lack of CO2). In fact, the problem is the exact opposite: even in such an environment, you need CO2 scrubbers to remove excess CO2 from the atmosphere or you'd soon asphyxiate in the CO2 your own body was producing. This is actually a big problem in space, because while you can use materials like zeolite to adsorb CO2 (and then just jettison it) that means you are also jettisoning oxygen - that's why the international space station needs regular top-ups with oxygen - a lot of it is bound into waste products and dumped. But if it wasn't dumped, the internal environment would soon be too toxic to survive.

 

Edit: to put it in perspective - 3% CO2 in the atmosphere will cause headaches, dizziness, weakness, blurred vision and after an hour or so, theres a risk of unconsciousness and death

10% C02 will put you under in less than a minute, with death following in 3-4 minutes. In an biggish-sized space ship room (let's say 4 metres by 4 metres by 2 metres - your average human will produce enough C02 to gas themselves to death in less than a day - long before they run out of oxygen).

 

This is generally true. I think people tend to underestimate the waste problem - but it's actually the most difficult part of prolonged survival in space: how do you survive your own waste production? (CO2, nitrites, heat, etc.)

 

cheers, Mark

[Michael Hopcroft]

Re: Quick question about oxygen!

 

NASA used a fairly pure O2 mixture in the early space program. The problem with it is that ANY spark will cause a fire that the Pure O2 will cause to spread so fast that it's not funny. Heck in Pure O2 things we consider non-combustable (like iron and steel) will generate a flame.

 

Which is what happened to the Apollo 1 mission. A trial run of testing the environment resulted in a fire that ripped through the capsule and killed the crew, including veteran astronaut Gus Grissom. The accident delayed the Apollo program for almost a year and marked the first astronaut casualties in the American space program.