O2: How Much Do We REALLY Need?

[Arctic Fox]

How much oxygen is absolutely required for the human body to survive?

If it depends on time, how about for 6 months, until the original O2 levels are back.

Earth is at, what, 23%? Could we survive on 8% for six months?

 

[Phobos]

http://www.osha.gov/SLTC/smallbusiness/sec12.html

The normal atmosphere is composed approximately of 20.9% oxygen and 78.1% nitrogen, and 1% argon with small amounts of various other gases.

...

Oxygen deprivation is one form of asphyxiation. While it is desirable to maintain the atmospheric oxygen level at 21% by volume, the body can tolerate deviation from this ideal. When the oxygen level falls to 17%, the first sign of hypoxia is a deterioration to night vision which is not noticeable until a normal oxygen concentration is restored. Physiologic effects are increased breathing volume and accelerated heartbeat. Between 14-16% physiologic effects are increased breathing volume, accelerated heartbeat, very poor muscular coordination, rapid fatigue, and intermittent respiration. Between 6-10% the effects are nausea, vomiting, inability to perform, and unconsciousness. Less than 6%, spasmatic breathing, convulsive movements, and death in minutes.

 

[Arctic Fox]

Wow! I never would've thought...
And that's an excellent link, too. Thanks.

My next question: How much O2 is too much? I found this in your link;

the use of oxygen in place of fresh (normal) air for ventilation will expand the limits of flammability and increase the hazards of fire and explosion.

Is that the only problem? Is there a threshold on the amount of oxygen before it becomes a safety/flammability issue?

Could we have O2 at 50%? Would there be any benefits to breathing at increased O2 levels (memory, extended work times, concentration)?

 

[matthyaouw]

There is such a thing as oxygen poisoning; too much oxygen can be quite harmful to the brain. Back when I did biology in college, my teacher mentioned this, and told us how breathing too deep and fast could make one feel rather giddy and unwell (which two members of my class proceeded to do, and then felt a little dizzy and ill. Don't try it.) I'm not sure exactly how this works. Perhaps this would be adressed better in the biology section.

 

[Grogs]

Hyperventilation (lit. too much breathing) blows off the carbon dioxide in the blood stream too fast, increasing the pH in the bloodstream (respiratory alkalosis.) Breathing in and out of a bag increases the amount of carbon dioxide inhaled and helps return the body chemistry to normal.

Above a certain partial pressure, oxygen becomes poisonous. I can't remember what that value is, but I believe it's 1 or 2 atm. Hyperbarric chambers (which increase the total atmospheric pressure and thus the partial pressure of the oxygen) are used on severe burn victims (and if rumor is true, Michael Jackson sleeps in one. )