How would the human body be affected if oxygen levels increased by a lot?

Our air is 78% nitrogen and 21% oxygen. If it increased to 30% oxygen, what would the effects be and how long would it take for the effects to affect us.

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    $\begingroup$ This might be a question for biology.stackexchange. There's some real-world experience with astronauts and divers breathing an atmosphere with a high oxygen content. From what I can find, it doesn't make much of a difference when you're acclimatized to it. $\endgroup$ – Abulafia Nov 25 '14 at 12:36
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    $\begingroup$ You become more flammable is the main danger. en.wikipedia.org/wiki/Apollo_1 $\endgroup$ – John Meacham Nov 26 '14 at 0:53
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    $\begingroup$ "Fire" was my first thought as well. Note that there were times where the oxygen levels were that high: giant bugs came out of that. $\endgroup$ – JDługosz Dec 21 '14 at 23:59
  • $\begingroup$ Cancer risk rises. Hemoglobin, well, RBCs will reduce over time. Slightly higher risk of free radical production. Essentially, look at the high altitude effects and invert them or study hyperbaric effects. $\endgroup$ – The Nate Feb 26 '16 at 10:08

30% Oxygen levels are not a huge deal as far as respiration goes. You would perform better in endurance events as it is easier to get more oxygen into your system but your body would adapt.

100% Oxygen can be dangerous or even toxic but a relatively modest increase to 30% is unlikely to have many side effects on humans.

There is going to be one large side effects though - fire.

At 30% oxygen levels fires burn faster, hotter and more easily. Even wet vegetation will burn and wildfires could easily sweep through any areas with available fuel.

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    $\begingroup$ It's worth noting that these effects are also dependent on air pressure. In a space suit, for example, astronauts breathe close to 100% oxygen, which is non-toxic because they are in an extremely low pressure environment. Likewise, 30% oxygen would be toxic to a diver operating at 200m underwater. Oxygen toxicity is dependent on the partial pressure of the oxygen, rather than on the percentage of oxygen in the atmosphere. $\endgroup$ – ckersch Nov 25 '14 at 17:03
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    $\begingroup$ As a diver I can confirm that a partial pressure of about 1.4atmospheres is considered to be the point at which oxygen becomes toxic. This is a safety point and not the actual limit (which I believe is around 1.6). That means that with 30% oxygen you'd be looking at about 5 times the air pressure before worrying about toxicity. And at 100% oxygen you'd still be needing 1.5 atmospheres of pressure before you were worrying. I should note that this assumes no other illnesses that could be exagerated by this (ie this info is for people fit enough to be diving). $\endgroup$ – Chris Nov 25 '14 at 17:18
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    $\begingroup$ Note that the diver limit of 1.4/1.6 is acute poisoning, around 75% you will run into problems over the long term. $\endgroup$ – Thijser Nov 25 '14 at 18:57
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    $\begingroup$ @Chris That's a simplification. In reality there's a time vs pressure tradeoff--you can tolerate more oxygen if you are exposed to it for less time. $\endgroup$ – Loren Pechtel Nov 26 '14 at 2:03
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    $\begingroup$ @JasonC: I considered that myself but the fire hazard isn't really an effect on the human body... $\endgroup$ – Chris Nov 26 '14 at 9:10

In short: No benefits, no short-term damages. But quite possibly adverse long-term effects.

A normal person breathes about 7 1/2 to 8 liters per minute in rest and under normal conditions, containing 1.6 to 1,7 liters of oxygen. Only about 0.3 liters make it into the blood.

Patients with hypoxia are often supplied with oxygen. The "standard" amount is 2 liters per minute, which effectively means doubling the normal amount of oxygen. In Emergency care, 5-6 liters per minute are not uncommon, albeit only for a short time.
None of these doses are usually sustained for months or years, so it is hard to tell what long-term effects they may have (well, 5-6 liters will certainly lead to lung damage over a longer period of time, but you might quite possibly support 2 liters for years).

Saturation in healthy people in normal atmosphere under normal pressure is slightly below 100% (around 95-98%) unless you have a really bad hangover or a condition like COPD (then you may have around 91-92% or so).

Doubling, tripling, or quadrupling the amount of oxygen (without elevated pressure so oxygen goes into watery solution) thus cannot have any measurable positive effect, since saturation cannot possibly go above 100%, and it is already there anyway.

On the other hand, oxygen is a radical and apart from being directly neurotoxic at very high doses and directly damaging lung tissue at very high doses, moderately elevated oxygen exposure will eventually increase cell aging and the risk of cancer (especially in "exposed" tissue such as the lungs).

Higher not-immediately-toxic levels of oxygen may also have effects on equipment and environment that may not be neglegible and that may affect humans indirectly:

  • higher levels of ozone
  • increased tendency for metals to rust
  • increased tendency for some organic materials to age and decay, and bleach out
  • fire accelerant, flashing sparks
  • accelerated growth of aerob or opportunistically aerob microorganisms (some fungi, most yeasts, and some bacteria)
  • $\begingroup$ Best answer here. You were robbed. Robbed, I say! $\endgroup$ – The Nate Feb 26 '16 at 15:58
  • $\begingroup$ (But seriously, there would be short term advantages, just not, as you point out, unalloyed ones.) $\endgroup$ – The Nate Feb 26 '16 at 16:20

Arthropodes would evolve to become larger. In the paleozoic era, when the oxygen levels were higher than today, giant insects roamed the Earth surface.

Most of the other animals and plants would evolve in response of this. Some of these evolutions would be problematic, others won't. The humans are no exception, and a race of giants may evolve. In some areas it will be normal to find a lot of people with more than 2 meters of height.

Fires will burn much more. As explained by @TimB.

People will be stronger and more suitable for hard work. As explained by @ArtOfCode.

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    $\begingroup$ But you probably don't want to deal with 60cm+ mosquitoes... $\endgroup$ – Brian Drummond Nov 25 '14 at 18:12
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    $\begingroup$ @BrianDrummond I didn't said that this would be a good thing. $\endgroup$ – Victor Stafusa Nov 25 '14 at 18:19

Current atmospheric O2 levels are about 21%, though the Oxygen compensation point dictated by C3 plants who produce our O2 limits it to about 23% at current CO2 levels. Higher CO2 levels permits increased photosynthesis rates and a correspondingly higher atmospheric O2% level.

220 ppm CO2 has a upper O2 limit of 23%O2. 350 ppm CO2 has a upper O2 limit of 27%O2. 700 ppm CO2 has a upper O2 limit of 35%O2.

These limits are "theoretical max" which you'll never reach due to O2 consumption from both organic metabolism, and from inorganic O2 fixation (I.e. rust and other metal oxidation). Once you hit the O2 compensation point, plants stop growing... they reach a point where the O2 levels provide a compensating force on enzymes that halt production of Rubisco.

Whats this mean in modern terms? well... we have increased volcanic activity, massive forest burning in Thialand and Brazil which has driven up CO2 levels since 1800. The increase CO2 raises the maximum O2 concentration and hense the plant-based biolevels possible (ie. more crops, faster growth of plants/food).

global O2 levels move VERY slowly, though its worth noting that past CO2 levels around 1500 ppm correlated to about 35%O2, so even at high compensation points (max levels) they never reached very high.

Humans can supposedly breath 50%O2 all day long without issues, and Scuba Divers like myself can get Nitrox-certifications to use 40% Nitrox (40% O2 with 60% N2) for shallow dives (the higher O2%, reduces the %N2 in the mix to slow nitrogen gas uptake in the blood... basically we use it to do longer dives without having to decompress).

Your question about 30% is interesting. 1) it would give endurance athletes a higher "effective" VO2 Max and would theoretically allow marathon runners to run at slightly higher speeds/effort while staying in the aerobic-exercise zone. This doesn't mean they could go farther, total energy is based on calories available... only that they could burn the same energy faster. ;)

2) Sprinters and other anaerobic activities would be unaffected... except for recovery rates! Hockey players, basketball, soccer, etc where stop and go windsprints are common could see reduced recovery times (i.e. hockey players could go back on the ice after shorter breaks without lactic acid building up). Even in todays pro sports you see this on football sidelines and hockey benches where winded all-stars will dawn a O2 mask to reduce lactic acid. So you could sprint more often, but not necessarily any faster.

3) Insects wouldn't be bigger. The giant insects in eras past were originally thought to be from O2 absorption, but studies in hyperbaric chambers have shown that O2 absorption rates are not limiting factors. Most scientists attribute ancient giant inserts to a lack of predators in that era, and an abundance of food. They simply lived long and ate well (in addition to theories about indeterminate growth and genetic differences in ancestors).

4) Fire hazards may be an issue, though an increased oxygenation rate of metals and spoiling of foods would be the most common issue for sure.

5) Lastly, its worth noting that CO2 levels in your blood are what trigger your brain to breath. The peripheral chemoreceptors in you carotid arteries will trigger breaths when CO2 concentration rises to 40mmHg. The CO2 levels in your blood vary between breaths from 35 to about 45mmHg are generated by metabolic means. So will increasing atmospheric CO2 levels affect your ability to breath? Nope. 40mmHg which is found in your blood and lungs alveolar space is 53000 ppm... which is why it diffuses out of your blood and into the lung space (since air is only ~400ppm). Increased CO2 and O2 levels shouldn't affect your ability to trigger breathing unconsciously. ;)

  • $\begingroup$ Hmm. Just try to breath under a cover and you will see how much air CO2 concentration affects your breath rate. $\endgroup$ – Anixx Dec 21 '14 at 22:06

It would be brilliant. 30% oxygen atmosphere would mean that our human bodies have more available oxygen and would take more in in a single breath; this means that we would be able to respire faster in times of necessity, giving us more strength etc. However, if we use this extra strength often, it is also entirely possible that we'd need more food to supply the glucose also required in respiration.

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    $\begingroup$ As a university-trained physiologist, unfortunately not so. Even 100% oxygen doesn't add much physiological performance at all. $\endgroup$ – Monty Wild Nov 25 '14 at 22:03
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    $\begingroup$ Yeah, it would be brilliant--as in fire. $\endgroup$ – Loren Pechtel Nov 26 '14 at 2:03
  • $\begingroup$ All those benefits come from having more oxygen than you are adapted for and not than we have. $\endgroup$ – The Nate Feb 26 '16 at 10:18
  • $\begingroup$ @TheNate ...which is exactly what the situation would be, if "the oxygen level suddenly increase by a lot". $\endgroup$ – ArtOfCode Feb 26 '16 at 13:00
  • $\begingroup$ Unless those "times of necessity" fall within the window of adaptation, the respiration rates would normalize. This is a matter of individual adaptation and takes weeks to months. It's the equivalent of coming down from high-altitude conditioning. $\endgroup$ – The Nate Feb 26 '16 at 15:54

As an Asthmatic who used to get hooked up to a Nebulizer a few times as a kid, I remember feeling sick and even vomiting once or twice from it.

Granted the Nebulizer also contained medication in the form of vapor, but the doctor seemed to think the increased percentage of Oxygen was likely what was creating the nausea and subsequent vomiting.

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    $\begingroup$ Was the nebulizer concentrating Oxygen? I believe all my home unit for my daughter does is compress the air and force it through the liquid albuterol to vaporize it for inhalation. $\endgroup$ – Michael Richardson Jun 7 '16 at 17:44

At 30% O2 in an atmosphere of 101.325 kPa partial pressure of oxygen would be: (I'll only use the 3 main gasses in the atmosphere to calculate it: ~1% error):

Normal: 19.14 kPa O2

$$ \left| \begin{array}{cc|ccc|c} \text{Gas}&\text{%}&\text{gr/mol}&\text{Mols}&\text{Fractal Mol}&\text{Partial Pressure (kPa)}\\ \text{N}_{2}&\text{78.08%}&28.0134&2.78&\text{80.4%}&81.5\\ \text{Ar}&\text{0.93%}&39.948&0.02&\text{0.06%}&0.68\\ \text{O}_{2}&\text{20.95%}&31.9988&0.65&\text{18.8%}&19.14\\ \text{Total}&\text{100%}&99,9602&3.46&\text{100%}&101.325 \end{array} \right| $$ Your world: 27.19 O2 $$ \left| \begin{array}{cc|ccc|c} \text{Gas}&\text{%}&\text{gr/mol}&\text{Mols}&\text{Fractal Mol}&\text{Partial Pressure (kPa)}\\ \text{N}_{2}&\text{69.18%}&28.0134&2.47&\text{72.5%}&73\\ \text{Ar}&\text{0.82%}&39.948&0.02&\text{0.06%}&0.61\\ \text{O}_{2}&\text{30%}&31.9988&0.94&\text{27.35%}&27.715\\ \text{Total}&\text{100%}&99,9602&3.43&\text{100%}&101.325 \end{array} \right| $$ For life it wouldn't be too much difference, I mean, animals would be faster, stronger and have a higher metabolic rate, also insect would be bigger, but our actual life could survival in this world without die. Oxygen toxicity is when O2 is above 50 kPa so it wouldn't be a problem. Also animals would have lesser lifespan, (oxidative stress), basically some species of reactive oxygen are found in the air and damage our bodies (even damage the DNA of our cells) and this contribute to the animal aging.

Remeber that fire will burn heater and easy, fire forest will be more common, hotter and dangerous.

If you want to know more you can check other of my answers like this (+ explanation of bigger insects!) and this (explanation of some gasses and more about O2 levels).

  • $\begingroup$ From the second table, 71.08% + 0.84% + 30% = 101.92%. $\endgroup$ – Victor Stafusa Apr 30 '18 at 22:47
  • $\begingroup$ @VictorStafusa I've just edit the post. Now the numbers are a bit more precise. Sadly it isn't still perfect :(, I can't find a proper formula to calculate the decrease of N2 and Ar when the O2 increase. $\endgroup$ – Ender Look May 1 '18 at 3:50

I should also guess that it would severely shorten our lifespan, as oxygen is the main reason for the cell walls to decay and age. This is called oxidation, and is the direct cause to why antioxidants are said to be beneficial to your age expectancy.


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