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Comment by belovedeagle | Hacker News Reader

I wonder - did they take steps to replenish the cave's oxygen? If not, it's useless for the next person...

I guess this is kind of silly and naive, but it's what I would do.

The air in the cave will come to equilibrium with the partial pressures of gasses in the water, which itself is in equilibrium with the atmosphere. It's not as closed as system as you think, even though it probably wouldn't outgas oxygen as fast as the divers were metabolizing it.

This is a really interesting point. How big would a cave need to be in order to support the oxygen requirements of a single human? I assume surface area of the water is the important factor?

Also the level of circulation of the water connecting it to the ocean/aquifer. Diffusion is a ton slower than convection.

As it was already air-filled, it almost certainly has a natural opening to the atmosphere, and will eventually reach normal gas levels (hard to say without more information whether that's a few hours or a few days, but very unlikely to be more than a few weeks).

As an aside, the issue described is not a low level of O2, but rather a high level of CO2 (which is typical for an air-space in a wet cave). Removing CO2 from the airspace is a radically different problem from adding O2 to the airspace.

It should eventually get back to equilibrium from gas interchange with the water, but I have no idea of what the time frame would be for that.

I'm a little surprised there aren't caches of emergency supplies for situations like these.

Cave-divers are expected (and taught) to carry reserve gas supplies with them. From the description, they had reserve supplies - enough reserves to search for an hour - but failed to recover their guideline within that time.

The issue was that they lost their guide-line leading to the exit, rather than running out of gas. In such a scenario, no amount of reserve caches could really solve that problem.

Some divers carry a few odds and ends in their buttpacks for longer duration dives, but you never factor this sort of stay into a plan, and don't want to take unnecessary equipment or kit in with you. Where there's been a lot of sump diving (submerged passages between larger air-filled chambers), there are a number of kits like these in some areas, but they're usually left by the expedition and taken back out with them.

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