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I somehow thought that pure oxygen was poisonous[1], and it needed to be a nitrogen mix. I mean, I guess this stunt demonstrates that I'm clearly mistaken, or t

I somehow thought that pure oxygen was poisonous[1], and it needed to be a nitrogen mix. I mean, I guess this stunt demonstrates that I'm clearly mistaken, or that the nuance is in the pressures involed? 1: https://en.wikipedia.org/wiki/Oxygen_toxicity https://en.wikipedia.org/wiki/Oxygen_toxicity

greesil 1y ago
It's dangerous in an enclosed environment, see Apollo 1 for more details.
tjohns 1y ago
There's definitely nuance here. Pure oxygen puts oxidative stress on your cells. Your body can handle that just fine at 1 atm, but at elevated partial pressures the increased concentration will (quickly) overwhelm your cellular mechanics. Underwater, the maximum operating depth for 100% O2 is 6 meters (20 feet) - which isn't very much at all. If you dive any deeper than that, you'll be at severe risk for a seizure and unconsciousness, and likely drown. (I'm simplifying, see [1].) Which is why you don't go diving with pure O2. However, in this case the freediver wouldn't be breathing compressed O2 gas underwater. They would've been breathing it at the surface, at 1 atm. [1]: https://en.wikipedia.org/wiki/Maximum_operating_depth https://en.wikipedia.org/wiki/Maximum_operating_depth
QuinnyPig 1y ago
Yes. It’s under pressure that oxygen toxicity becomes an issue. It’s why you’ve gotta pay attention to your depth when diving with enriched air.
TylerE 1y ago
It is, kinda sorta, but at 1 atm you need to be breathing pure o2 for ~24 hrs before its meaningful (and longer than that before treatment is anything beyond "stop breathing pure o2". The dose isn't even cumulative. Just being on room air for 20-30 minutes resets the clock.
teraflop 1y ago
Yes, partial pressure is what matters. Normal air at 1 bar (1 atmosphere) contains about 0.2 bar of O2. Pure oxygen at sea level is 1 bar of O2. The article you linked has a graph showing that 0.5 bar of O2 can be tolerated pretty much indefinitely, and it takes hours for significant toxicity to show up at 1 bar. Higher partial pressures cause much faster symptoms.
deleted 1y ago
[deleted]
Retric 1y ago
It’s really several factors. Supplemental oxygen is common for people with diminished lung capacity, carbon monoxide exposure etc. However long term it’s not a good idea for healthy people. https://en.wikipedia.org/wiki/Oxygen_therapy https://en.wikipedia.org/wiki/Oxygen_therapy At low pressure pure oxygen can similarly be beneficial, mountain climbers eventually need supplemental oxygen for Mount Everest though a few have made the trip without it they can’t stay at that altitude indefinitely. It can even help on airplane flights as commercial airlines don’t set things to sea level. Where healthy people run into issues is when partial pressures get well over 100% at sea level. Part of the issue is people adjust their breathing based on carbon dioxide not oxygen levels. So at say 10 atmospheres at normal atmospheric mixtures your breathing the equivalent of 210%, but you don’t slow down enough to compensate. Thus why divers care so much about gas mixtures, however people with diminished lung capacity are going to encounter issues at different levels than normal divers.
mapt 1y ago
Oxygen weathering is a primary constraint on life on Earth, and every carbon-hydrogen based organism in the past 2.5 billion years has had to develop biochemical coping mechanisms for this toxic gas that wants to react with carbon and with hydrogen; It is harnessing this reaction ("respiration") with biologically mediated processes and modulating it to specific rates that permits us life. For humans, acute breathing gas toxicity only happens in a high pressure environment. Air approximates an 80/20 nitrogen-oxygen mix. Atmospheric pressure is 14.7psi. The 120psi air compressor in your auto body shop is equivalent to a dive only 81 meters deep. SCUBA divers and later saturation divers have probed the various limits of the human cardiopulmonary system using very specialized gas blends all the way down to 700 meters. Too much oxygen partial pressure causes all the symptoms you see listed, and higher partial pressures cause symptoms to appear faster. > The curves show typical decrement in lung vital capacity when breathing oxygen. Lambertsen concluded in 1987 that 0.5 bar (50 kPa) could be tolerated indefinitely. This means you could breath 80/20 nitrox at 2.5 bar, or 37 psi, or 25 meters depth, "indefinitely" in the sense of hours or days. PS: Chronic use of 100% oxygen at atmospheric pressure causes other types of toxicity. Some of the oxidative damage therein, accumulated over the years at a normal 20%, probably directly analogizes parts of the human aging process. Other types of oxidative damage probably work faster than proportional exposure. We only start to notice damage like this in people with impaired lung function who rely on an artificial supply of oxygen boosted to beyond an 80/20 ratio, to breath.
- thrown-0825 1y ago
  Found the SCUBA diver
  - SOLAR_FIELDS 1y ago
    Indeed, the grandparent post is a pretty good summary of the takeaways you get from taking PADI’s enriched air nitrox course (which is a requirement if you ever want to dive with enriched air). In the olden days this was tracked manually (the ratio of your depth to percentage of air and time under water) via so called “dive tables”. The purpose and output of the dive table is to determine the safe amount of time you could dive at a certain depth without risking narcosis. As this is a sliding window based on multiple variables - and you are very rarely maintaining a constant depth as you dive - it’s of course annoying and less accurate to hand calculate this. Modern dive computers just seamlessly calculate it all for you nowadays.

greesil 1y ago

It's dangerous in an enclosed environment, see Apollo 1 for more details.

tjohns 1y ago

There's definitely nuance here. Pure oxygen puts oxidative stress on your cells. Your body can handle that just fine at 1 atm, but at elevated partial pressures the increased concentration will (quickly) overwhelm your cellular mechanics. Underwater, the maximum operating depth for 100% O2 is 6 meters (20 feet) - which isn't very much at all. If you dive any deeper than that, you'll be at severe risk for a seizure and unconsciousness, and likely drown. (I'm simplifying, see [1].) Which is why you don't go diving with pure O2. However, in this case the freediver wouldn't be breathing compressed O2 gas underwater. They would've been breathing it at the surface, at 1 atm. [1]: https://en.wikipedia.org/wiki/Maximum_operating_depth https://en.wikipedia.org/wiki/Maximum_operating_depth

QuinnyPig 1y ago

Yes. It’s under pressure that oxygen toxicity becomes an issue. It’s why you’ve gotta pay attention to your depth when diving with enriched air.

TylerE 1y ago

It is, kinda sorta, but at 1 atm you need to be breathing pure o2 for ~24 hrs before its meaningful (and longer than that before treatment is anything beyond "stop breathing pure o2". The dose isn't even cumulative. Just being on room air for 20-30 minutes resets the clock.

teraflop 1y ago

Yes, partial pressure is what matters. Normal air at 1 bar (1 atmosphere) contains about 0.2 bar of O2. Pure oxygen at sea level is 1 bar of O2. The article you linked has a graph showing that 0.5 bar of O2 can be tolerated pretty much indefinitely, and it takes hours for significant toxicity to show up at 1 bar. Higher partial pressures cause much faster symptoms.

deleted 1y ago

[deleted]

Retric 1y ago

It’s really several factors. Supplemental oxygen is common for people with diminished lung capacity, carbon monoxide exposure etc. However long term it’s not a good idea for healthy people. https://en.wikipedia.org/wiki/Oxygen_therapy https://en.wikipedia.org/wiki/Oxygen_therapy At low pressure pure oxygen can similarly be beneficial, mountain climbers eventually need supplemental oxygen for Mount Everest though a few have made the trip without it they can’t stay at that altitude indefinitely. It can even help on airplane flights as commercial airlines don’t set things to sea level. Where healthy people run into issues is when partial pressures get well over 100% at sea level. Part of the issue is people adjust their breathing based on carbon dioxide not oxygen levels. So at say 10 atmospheres at normal atmospheric mixtures your breathing the equivalent of 210%, but you don’t slow down enough to compensate. Thus why divers care so much about gas mixtures, however people with diminished lung capacity are going to encounter issues at different levels than normal divers.

mapt 1y ago

Oxygen weathering is a primary constraint on life on Earth, and every carbon-hydrogen based organism in the past 2.5 billion years has had to develop biochemical coping mechanisms for this toxic gas that wants to react with carbon and with hydrogen; It is harnessing this reaction ("respiration") with biologically mediated processes and modulating it to specific rates that permits us life. For humans, acute breathing gas toxicity only happens in a high pressure environment. Air approximates an 80/20 nitrogen-oxygen mix. Atmospheric pressure is 14.7psi. The 120psi air compressor in your auto body shop is equivalent to a dive only 81 meters deep. SCUBA divers and later saturation divers have probed the various limits of the human cardiopulmonary system using very specialized gas blends all the way down to 700 meters. Too much oxygen partial pressure causes all the symptoms you see listed, and higher partial pressures cause symptoms to appear faster. > The curves show typical decrement in lung vital capacity when breathing oxygen. Lambertsen concluded in 1987 that 0.5 bar (50 kPa) could be tolerated indefinitely. This means you could breath 80/20 nitrox at 2.5 bar, or 37 psi, or 25 meters depth, "indefinitely" in the sense of hours or days. PS: Chronic use of 100% oxygen at atmospheric pressure causes other types of toxicity. Some of the oxidative damage therein, accumulated over the years at a normal 20%, probably directly analogizes parts of the human aging process. Other types of oxidative damage probably work faster than proportional exposure. We only start to notice damage like this in people with impaired lung function who rely on an artificial supply of oxygen boosted to beyond an 80/20 ratio, to breath.

thrown-0825 1y ago
Found the SCUBA diver
- SOLAR_FIELDS 1y ago
  Indeed, the grandparent post is a pretty good summary of the takeaways you get from taking PADI’s enriched air nitrox course (which is a requirement if you ever want to dive with enriched air). In the olden days this was tracked manually (the ratio of your depth to percentage of air and time under water) via so called “dive tables”. The purpose and output of the dive table is to determine the safe amount of time you could dive at a certain depth without risking narcosis. As this is a sliding window based on multiple variables - and you are very rarely maintaining a constant depth as you dive - it’s of course annoying and less accurate to hand calculate this. Modern dive computers just seamlessly calculate it all for you nowadays.