
How much oxygen for a person to survive in an air-tight enclosure? (2004) - galfarragem
http://members.shaw.ca/tfrisen/how_much_oxygen_for_a_person.htm
======
danielvf
If you want to live in an air tight containers, you need to also be concerned
about co2 buildup.

~~~
madaxe_again
Came to say precisely this. Before you run out of o2 the co2 levels will
likely render you unconscious, and will potentially also suppress your
breathing.

I took a lungful (choked on the first breath, coughed, started really choking)
of air heavy with co2 in a pub cellar once. Only because I fainted on top of
the kegs above the co2 saturated air on the floor (leaky cylinder valve) am I
here to tell you about it. Tastes like acidic metal and black velvet rushes
in.

~~~
masklinn
An other fun danger of insufficiently aerated rooms: in wine countries, until
cellars aeration became more widespread a huge danger was CO buildup in
cellars from fermentation, to these days people regularly die during initial
fermentation, and a warning you get is "if you see somebody unconscious at the
bottom of the cellar stairs you do _not_ go down to help, you call the
firefighters, trying to help just ensures they have two bodies to retrieve".

~~~
mrfusion
What if you hold your breath to help?

~~~
giardini
That would work if you have excellent breath-holding ability. But since you're
exerting yourself by carrying an ~150-lb body, there is a risk you'll pass out
because you're holding your breath. So you probably should take multiple
trips, repeatedly moving the person partially and then returning to get good
air. You should _slowly_ exhale all the while.

DO NOT hyperventilate before holding your breath and exerting yourself! Reason
is, if you hyperventilate, then take a big breath, hold it and exert yourself
you are likely to pass out _instantly_ w/o warning! [This was something we
learned as kids - do not do this! You _will_ pass out (and you also risk
embolism/stroke).

~~~
mrfusion
Why slowly exhale? Why is hyperventilating first bad?

~~~
giardini
_" Why slowly exhale?"_ \- So you don't increase the pressure in your lungs.

 _" Why is hyperventilating first bad?"_ \- Should you hyperventilate and then
hold your breath and any pressure is put on your lungs, YOU WILL PASS OUT!
Don't do this!

Essentially hyperventilation reduces the blood's CO2 level. It becomes so low
(while hyperventilating) that the body does not detect when the CO2 level
subsequently rises to a dangerous level(while diving/holding your breath). The
body fails to urge you to breathe fresh air and so you unwittingly pass out.

See the following two links for more info:

"The Choking Game: Self-induced hypocapnia":
[https://en.wikipedia.org/wiki/Choking_game#Self-
induced_hypo...](https://en.wikipedia.org/wiki/Choking_game#Self-
induced_hypocapnia)

Deep-water divers hyperventilate and then take a big breath immediately before
they dive. Sometimes "shallow water blackout" (same as what happens to kids in
the "choking game) occurs, endangering the diver:

[https://en.wikipedia.org/wiki/Shallow_water_blackout](https://en.wikipedia.org/wiki/Shallow_water_blackout)

------
tzs
A related question that might be interesting is in a container of a given
volume that is perfectly sealed except for one hole to the outside air, and
with no fans or other systems to encourage air exchange, how big does the hole
need to be to keep oxygen levels high enough and CO2 levels low enough for
survival indefinitely?

My intuition at first says that it would need to be a big hole because there
won't be much airflow since the pressure inside and outside will be the same.
But that is looking at it wrong.

It's the individual gases that matter. If CO2 is more concentrated inside than
out, then there will be a net transfer of CO2 out. Similarly for O2 coming in.
It's a diffusion problem, not an airflow problem, and I've got no usable
intuition for that.

A interesting variant would be to make the hole intermittent. Assuming that my
house is perfectly sealed when the doors are closed, do the normal openings
for my daily comings and goings provide sufficient time for enough O2 to
diffuse in and CO2 to diffuse out to keep my inside air breathable?

~~~
jpeanuts
This is a question I've asked myself before too. Here's a back-of-envelope
calculation which seems to suggest that diffusion alone will never be enough
to keep someone alive inside a box. I'd be really interested to hear if
someone can confirm or refute this.

Let's assume CO2 transfer is entirely diffusion-limited, i.e. the worst-case
of completely still air. The diffusive flux of some gas-component (per unit
area per unit time) J is governed by concentration-gradient (dn/dx) multiplied
by a magic diffusion coefficient D, which depends on the molecular properties
of the gas. For CO2 in air D = 1.6e-5 m^2/s. Let's assume the gradient is
linear so dn/dx = (n_{inside} - n_{outside}) / length. Now n_{outside) = 0.04%
* 1 kg/m^3 = 4e-4 kg/m^3. We should decide what level of CO2 we can tolerate,
0.5% should be on the safe side, so n_{inside} = 5e-3 kg/m^3.

Length is a bit trickier. If (a) we assume completely stagnant air inside and
outside, length should be chosen as the size of the box ~1 m say. However if
(b) we assume that inside and outside are pretty well-mixed _individually_ ,
due by breathing, wind etc., then length should be about the depth of the
hole, or thickness of the box-material, say 1 cm = 0.01 m. For case (a) CO2
leaves our box at a rate of about 7e-8 kg/s/m^2, for (b) 7e-6 kg/s/m^2.

From the original article, a human breaths .84 kg of O2/day, let's estimate a
production of 1kg CO2/day (the extra carbon atom can't be all _that_
significant), or 1e-5 kg/s.

To compute the area of hole needed to maintain 0.5% CO2, we just divide 1e-5
by J, to get the area. In case (a) we need an enormous area of 135 m^2, in (b)
"only" 1.35 m^2.

This seems to suggest that "air-holes" must work (if indeed they work at all)
with air-flow. This doesn't necessary require an over- or under-pressure in
the box - a suction can be generated by wind passing over a box with holes on
both sides - this process would be far more efficient at restoring atmosphere
than diffusion. But would be less reliable.

~~~
xenadu02
Heat is another helper here. Body heat would eventually cause a chimney effect
unless the single hole is on the bottom of the box. That will create an air
current, greatly increasing the speed of diffusion.

------
foobarbecue
Your result of "0.042 day" is also known as "an hour."

~~~
SeanDav
or, when multiplied by 1000, perhaps something else...

~~~
raddad
...Life, The Universe and Everything.

~~~
raddad
What? Nobody read The Hitchhiker's Guide to the Galaxy? Heck, it was also the
first computer game I ever played.

------
mrfusion
What about the scene from pirates of the Caribbean where they walk underwater
in an upside down rowboat. Is that realistic?

~~~
meric
If you're asking about the oxygen levels, I'd say so. At a rough guess of 1m^2
of oxygen per person in the boat, for two people. That's an hour of walking
according to the article. (Assuming water takes less oxygen to walk in)

I think it'd float to the top though. It'll need some kind of weight...

A one ton metal boat shaped object would do:

[http://kwc.org/mythbusters/2007/11/episode_92_pirates_2_row_...](http://kwc.org/mythbusters/2007/11/episode_92_pirates_2_row_boat.html)

~~~
yoha
Nitpick: s/1m^2/1m^3

> I think it'd float to the top though. It'll need some kind of weight...

A simple way of thinking about it is that boats float because they contain air
(rather than water). The fact that they are upside down or the right way up
changes little.

Since the rowboat can support two people, it should definitely float to the
surface, dragging them along with it.

~~~
eric_h
> Since the rowboat can support two people, it should definitely float to the
> surface, dragging them along with it.

Only if the air bubble occupied the entire inner portion of the hull. If it
were, say, only half the volume of the hull - I suspect it would be neutrally
buoyant with the weight of two people.

~~~
robotresearcher
People are roughly* neutrally bouyant in water. Thus they don't weigh anything
when submerged. Otherwise swimming would be very hard indeed. So you would
need to weigh down the boat to sink all that air and wood.

*depending on depth and body composition, but give or take a bit, neutral.

~~~
eric_h
Agreed, but boats when not filled with air are typically negatively buoyant.
I'd wager that there's an air bubble small enough to make the whole system
negatively buoyant, but large enough to sustain the people breathing it for
some period of time.

------
mirimir
I'm reminded of _A Pail of Air_ by Fritz Leiber.

------
dragonbonheur
Twenty thousand leagues under the sea had an interesting part about the same
problem.

------
mjw_byrne
Whoa whoa. This means Sunshine wasn't scientifically accurate?!

------
jsilence
Would be nice if this calculation were in iPython notebook or Cruncher
([https://www.cruncher.io/](https://www.cruncher.io/)).

