Hatrack River Writers Workshop: Air question

This is topic Air question in forum Open Discussions About Writing at Hatrack River Writers Workshop.

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Posted by Silver3 (Member # 2174) on :

Suppose we have two people sealed off in a very narrow area (after a collapse in a mine, for the record). How long, approximately, until they start suffocating? (actually, until they can feel the lack of air)

Narrow= they almost can't move

[This message has been edited by Silver3 (edited October 19, 2004).]

Posted by Magic Beans (Member # 2183) on :

A quick Internet search (which you could have done

) revealed the material quoted below:

quote:

The issue of suffocating in an enclosed space is not one of running
out of oxygen; it's one of being poisoned by carbon dioxide -- CO2.
CO2 becomes toxic at a concentration of 1%. (Normal atmospheric
concentration is 0.036 percent (360 ppmv).) A concentration of 10% can
cause respiratory paralysis and death within a few minutes.
How fast the CO2 level builds depends on how fast you produce it. This
would be related to how fast you are breathing. At rest you would
exhale much less than if you were exercising.
Given that a moderately active or stressed person produces about 1.7
cubic feet of CO2 per hour and assuming a concentration of 3% CO2 is
the highest safe limit, here is an equation you can use to calculate
how long a given number of people can stay in a given space before
toxic levels of CO2 build up ---
T = Number of hours of air in a sealed room

(Volume of air inside the room in cubic feet) x (3% or 0.03)
T = ---------------------------------------------------------
(Number of people) x (one person's hourly production of CO2)

Scroll down this page for explanation of that equation
FOR YOUR SAFETY - Sealed Room Atmosphere
http://yahweh.com/News/07_2002/NL7-02.html

So….using the Google calculator –
Your room of 10x10x2 meters would be –
200 (cubic meters) = 7 062.93334 cubic feet.
Let's call that 7000 cubic feet.
T = (7000 x .03) / (1 x 1.7) = 210/1.7 = 123.5 hours.

------------
From a Science Fiction author ---
"As it turns out, a 10 X 10 X 10 foot space, or 1,000 cubic feet, will
be filled with a lethal concentration of CO2 by one resting human
sized individual in just 24 hours. (The CO2 level reaches about 1% in
that time). Moderate activity will cut this time to 12 hours, and
strenuous activity to 6 hours."
Suffocation, CO2 poisoning
http://www.frontiernet.net/~jamesstarlight/Suffocation.html
Let's check that with our equation ----
(1000 x .01) / 1.7 = 17 hours. Close.
----------------
This website addresses oxygen depletion, but ignores CO2
concentrations, which makes their answer to the question, "How long
can we survive in an enclosed space?" entirely wrong.
I include it because I suppose these equations would be useful if you
were using up air in the room, but exhaling out through a tube or if
you employed air scrubbers to remove the CO2.
Question: How long can 10 healthy adult people survive in a sealed
room of dimensions 3m x 4m x 2.5m before they run out of oxygen (i.e.
the oxygen concentration drops to 12%)? An adult of average weight
consumes about 3.33 10-6 m3 s-1 of oxygen while at rest. The typical
volume of an adult is 0.1 m3.
Answer: The equation for rate of change of oxygen concentration in an
enclosure without oxygen replacement (neglecting the buildup of carbon
dioxide) is:
(total oxygen consumption rate) = (volume of oxygen consumed) / (total
time lapsed)
or : nC = {Vr - nVp}{Li - Lf}/t
[see explanations here]
How long can we survive in a sealed enclosure?
http://www-das.uwyo.edu/~geerts/cwx/notes/chap01/ox_exer.html
---------------------
A hypothetical question to a Biosphere scientist --
"[an adult] would need about 350 litres of oxygen per day (the amount
of oxygen in 1.7 cubic metres of air)."

Biosphere
http://www.newscientist.com/lastword/article.jsp?id=lw564
-----------------
Safety Information for Cavers (Spelunkers) – this is a good table that
shows the stages of Co2 poisoning at different concentrations [scroll
down]
CARBON DIOXIDE, CAVES AND YOU
Table 2. Generally accepted physiological effects of CO2 at various
concentrations by volume
http://wasg.iinet.net.au/Co2paper.html

The URL is: http://answers.google.com/answers/threadview?id=258239

Good luck!

Posted by Silver3 (Member # 2174) on :

Thanks. I'll do the maths. (Sigh)

Posted by Beth (Member # 2192) on :

Wow, that was all really interesting. Thanks for posting it!

Posted by Survivor (Member # 213) on :

Really, the variables in a situation like you describe are far too great to yield to simple calculations. Particularly underground, where other gases can be seeping into the air from the soil/rock/whatever.

If it is narrow enough that they can't move, then it could still be that they have air circulation. On the other hand, it could be that all breathable air has been removed by the collapse or that toxic gases have been introduced (possibly from a "gas pocket", a common and real danger in mines).

So depending on various circumstances, the time before they start "running out of air" could be anything from zero to infinity after a serious cave-in. Make up a number, establish a cause, and that's your answer.

Posted by bladeofwords (Member # 2132) on :

That was very interesting. I always thought it was just running out of air. Anybody know off the top of their head what the effects of the poisoning look like?

Jon

Posted by dspellweaver (Member # 2133) on :

Magic Beans, what search words did you use to bring up these results?

Posted by Magic Beans (Member # 2183) on :

http://www.google.com/search?q=oxygen+consumption+in+enclosed+space

Posted by dspellweaver (Member # 2133) on :

Thank you

Posted by Survivor (Member # 213) on :

The effects of toxic gases in an enclosed area will vary depending on the type of gas, naturally. But it is pretty common for CO2 to collect in underground areas for a variety of reasons. That would have about the same effect as "running out of air". Many other gasses would have similar effects, in low concentrations.

If the concentrations are high, then usually you just start coughing and keel over after a few seconds. But you don't always get a chance to cough first.