And injury to it can cause spleen cells to colonize other parts of the abdomen. You could end up with extra spleens!

At first.

I was also a kid doing this, my cousins and I held ourselves underwater with the ladder rungs in a swimming pool.

At first, yeah a minute was tough. But then it rapidly increased. Unfortunately I don't remember where we topped out, but I think ~3 minutes.

We would also swim pool lengths underwater(but it was a relatively small pool at a condo building). I think I swam 9 once.

They'd let us stay out all night at that pool, it was great. Florida summers don't really get chilly.

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

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

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.

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.

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.

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

At low pressure pure oxygen can similarly be beneficial, mountain climbers can use oxygen to offset lower pressures. 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.

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.