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[vivisdf9304]

Excluding the supply of food and water, what about the oxigen? How far and how deep should you be till lack of ventilation becomes a problem?

I'm sure real miners know about this.

[Khan Boyzitbig]

If there are plants capable of producing oxygen down there too the limiting factor would be proximity to the upper mantle rather than O2. Otherwise it depends more on how much oxygen you start such an endeavour with. It was an issue for people escaping POW camps in WWII because they couldn't get much air down there via the entry hole.

[Arx]

It's very much possible, you just need pumps to keep the air moving (which was one of the breakthroughs for escaping POWs, as well - getting working pumps going). The deeper you go, the better the pumps need to be and of course it's an issue if the pumps break down, but it can be done.

[ChairmanPoo]

If there are plants capable of producing oxygen down there too the limiting factor would be proximity to the upper mantle rather than O2.

the limiting factor would be sunlight. how often have you seen plants in caves?

[Khan Boyzitbig]

Bioluminescent fungi live in caves. Several plants do not need sunlight in order to produce oxygen or grow.

[scriver]

I was thinking about real miners need to worry about pockets of gas when they break new space. Are we envisioning an underground dwelling that stays the same size, like a Fallout Vault, or one that constantly undergoes expansion, like a Dwarf Fortress or other mining-economy dwelling?

I'm also not sure if gas leaks can happen (or rather how common it would be that they do) by themselves just from cracks forming to already mined shafts. Might need some kind of air tight insulation at the edges of the livable spaces to prevent that if it's a problem.

[misko27]

It's a small note, but if you lived most-or-all of your life underground you'd probably need vitamin-D supplements, probably through food enriched for that purpose. I know I take supplements for that specific purpose, and I'm not even a shut-in or something; if you lived underground it would have the potential to be an issue.

[ChairmanPoo]

  Several plants do not need sunlight in order to produce oxygen or grow.

Plants produce oxygen via photosyntesis. There are non photosyntetic plants but they don't produce oxygen.

Bioluminescent fungi live in caves.

But no plants rely on that, or can realistically rely on that tiny amount of light. And chemosyntesis doesn't produce oxygen either

[wierd]

If you have access to geothermal energy in sufficiently reliable and abundant quantities, then the use of sulfur lamps solves the light problem pretty neatly. Not a 'perfect' match for sunlight, but pretty damn close.

https://en.wikipedia.org/wiki/Sulfur_lamp

Spoiler: spectral distribution of sulfur lamp vs sunlight (click to show/hide)

You can see that sulfur lamp has a nice continuous emission spectral gradient, which is far superior what is typically found in CFLs or LEDs, which have very efficient, and very strong peaks of emission in narrow bands of the spectrum. Sulfur lamp is more of a black body emitter by nature, so it emits a nice full spectrum. However, you can also see that it favors photons that are more "greenish" in terms of human perception, which is the frequency range REJECTED by photosynthetic plant life. Adding the lithium, sodium, or potassium bromide/iodide salts to alter its emission spectra is highly encouraged, as it will bump the photon populations to favor orange/yellow light emission, which is what photosynthetic plants really want to eat.

For vitamin D synthesis, one can supplement the sulfur lamps with normal mercury vapor CFLs, with a bit less rare earth oxide powder on the inside. (so that you get more of the 'not so nice UV light' the excited mercury vapor produces.) That would "flavor" the sulfur lamp light a bit, and allow vitamin D synthesis "the natural way."

One could also conceivably just install a huge array of high intensity UV LEDs in light strips, and issue orange goggles to everyone to avoid premature blindness.

A potentially useful side effect of using geothermal energy, is that you need to diffuse the heat collected from the power generators. (You are injecting water into heated rock strata, which then turns into steam that turns turbines. You need to cool the steam off again to recycle the water. That means you need to dispose of the heat.) If you use the upper levels of the underground structure as a giant passive heatsink, you can use the thermal difference gradient to drive convection in the structure's atmosphere, and use the heat of the power plant to "stir" the air for you. One could conceivably get this for free, and without costly (and maintenance nightmare inducing) pumps/fans.  (See for instance, how a 'heat pipe' diffuser works. You would be using the whole complex as the heat pipe, the slightly humid air of the complex as the phase transitioning working fluid, the hot and cold parts of the complex as the two surfaces, and gravity to return the cooled fluid back to the hot side.)

[Karnewarrior]

-[snip]-

Neat. I suppose one could find an underground river to provide water? Or maybe get it from an aquifer?


AFAIK, OP, I think one of the major issues with living underground is also the expense of plotting and digging out all the rooms. It's simply far cheaper to build up than to build down.