Can't watch the video now, but are you saying they are vacuums or pressurized? If they are vacuums, the highest vacuum you can have is -1 atmosphere, I.e. No air.
5-6 atmospheres would be PRESSURIZED, not vacuum.
Also, a vacuum would pull in water from the water table, you'd need pressure to keep it out.
Vacuum would be good for fire prevention, things can't burn if there's no oxygen. Pressure, on the other hand, will greatly amplify fire, if you just pressurize air. If you want to avoid that, you have to pressurize with a neutral gas like nitrogen, which would be expensive if there is any regular amount of gas leakage.
In either case, you'd have to build compartments that were pressure/vacuum proof (think a submarine or spacecraft) -- and in either case, leaving the pressure vessel would pose dire risks to occupants.
I'll try to watch the video when I'm back on WiFi.
From the transcript, this is what the "5 atmospheres" thing meant -- it was about the pressure differential, and that whether the inside is at 1 atm or 0 atm isn't a big deal if the tunnel has to be underground (in which case it already has to stand quite a bit of outside pressure!):
> Exactly. And looking at tunneling technology, it turns out that in order to make a tunnel, you have to — In order to seal against the water table, you've got to typically design a tunnel wall to be good to about five or six atmospheres. So to go to vacuum is only one atmosphere, or near-vacuum. So actually, it sort of turns out that automatically, if you build a tunnel that is good enough to resist the water table, it is automatically capable of holding vacuum.
Thank you for clarifying. I misspoke earlier slightly, but the result is the same: when you build a tunnel strong enough to withstand the water table, it can hold a near vacuum. This helps transport and energy efficiency.. but also presents interesting issues for fire safety.
Sure, but it's -1 atm gradient, which is how we commonly measure pressure. I.e., when you fill your car tires to 32 psi, that's 32 psi over atmospheric. When you're talking about pressure, it's the gradient that matters.
It was taught as psia, -g, & -d (or absolute, gauge, and differential) when I was in school, so I read your -1 atm as psid. Your car example would be 32 psi gauge assuming STP, or ~36 psi absolute.
The miners are below the surface and not at 1 atm, so any gauge measures taken there would be psid.
5-6 atmospheres would be PRESSURIZED, not vacuum.
Also, a vacuum would pull in water from the water table, you'd need pressure to keep it out.
Vacuum would be good for fire prevention, things can't burn if there's no oxygen. Pressure, on the other hand, will greatly amplify fire, if you just pressurize air. If you want to avoid that, you have to pressurize with a neutral gas like nitrogen, which would be expensive if there is any regular amount of gas leakage.
In either case, you'd have to build compartments that were pressure/vacuum proof (think a submarine or spacecraft) -- and in either case, leaving the pressure vessel would pose dire risks to occupants.
I'll try to watch the video when I'm back on WiFi.