In sci.space.tech Kent Paul Dolan wrote:
"harmoneverett" wrote:

wrote:

You want an environment with enough pressure that
construction workers can promptly ditch their
space suits, or at least reduce them. That's
going to require ~3psi of air pressure (pure
oxygen).

why pure oxygen? The eventual goal is to be able
to breathe in it, but for the moment, an air tank
doesn't weigh anything.

Because if you're going to be sending gases up to
achieve ~3 psi of blood oxygen tension, the minimum
IIUC to sustain human life for extended periods, you
are money ahead to send oxygen, which is breathable,

I'd argue slightly about the 3PSI, you can go a fair bit lower if your goal
is "won't die in 5 minutes without exertion".

At the lung wall at 37C is 47 torr (780 torr = 1 atmosphere = 14.7 PSI) of
water vapour.
This can't be reduced, and is a hard limit (barring hypothermia).
About 15 torr of CO2, at normal metabolic rates.


People (nutters) have climbed everest without supplemental oxygen.
At the top, you're looking at 276 torr, of which about 1/5 is O2.

So, at the lung wall, we have 276-62 torr = 214 torr of atmosphere, or
43 torr of oxygen.
So, for pure O2, 43+62 = 125 torr
or 2.35 PSI will get you the same oxygen saturation as on the top of
everest.
About 1.2PSI or so is the pressure at which you're about as well off
as you are holding your breath in normal atmosphere.

Below this, you get rapid de-oxygenation of the blood as it passes through
the lungs.

snip
I think you're missing the point that if you put 3
psi of oxygen _inside_ the human body, you have to
put 3 psi _outside_ the human body as well, or the
person just explodes.

Err, no.

If you try to hold your breath, your lungs rupture.
If you don't, you'r fine until you die from
lack of oxygen (about a minute until you need more
than CPR).