Well, my message appears to have been eaten by the TML mailer
daemon.
> Imagine you are in a sealed room. How long does it take a person to die
> because the air gets bad - and why? Is it lack of Oxygen, or the
> presence of impurities?
The time depends on the size of the room, who is breathing, and
whether they are conserving their air. Normally about 4% of
the air is converted from oxygen (O2) to carbon dioxide (CO2)
per lungful, but this may change as the ratio changes.
Normally there is 20-21% O2 in the air, humans need at least
half that to survive.
CO2 is poisonous, however. I heard once that CO2 poisoning
would kill you before O2 deprivation would in this situation.
This may have only been under pressure, however.
There are easy ways to neutralize the CO2, however. Divers
that use recycled air do this (supplementing with additional
O2). There are also ways to convert it back to O2 (I think
submarines do this now).
> If the room is filled not with air, but with Oxygen only:
> - - what atmospheric pressure should it be at to be safe? I believe that if
> the pressure is too high the atmosphere promotes any sort of minor
> spark into a serious fire/explosive hazard.
Any room filled with O2 is a fire hazard. The O2 doesn't
actually explode, but it promotes burning of anything else
in the room. As the pressure increases, this effect will
increase, so that more and more becomes vulnerable, but...
The real hazard is that pure O2 is deadly at ANY kind of
pressure above 1 atmosphere. Pure O2 will allow you to
breathe at a LOWER pressure, however.
> - - how long before a typical human unfortunate dies from bad air in this
> scenario.
I don't think the CO2 poisoning effect would be diminished
(it might actually be worse, since there will be more O2 to
convert). Therefore, no longer than before.
It's a bit complicated to determine exactly how long the
unfortunate has. Partial pressures determine if the air
is breatheable and/or poisonous. 5% CO2 at 2 atmospheres
is as poisonous as 10% CO2 at 1. Less O2 is also needed
at higher pressures, and even 20% O2 can become poisonous
if the pressure gets high enough.
As a rough rule of thumb, you could divide the volume of
air in the room by the volume of a lungful of air. This
is how many lungfuls would convert 4% of the air from O2
to CO2 (alter this 4% number drastically based on activity
level--perhaps 1-10%?). At one atmosphere, the air will
be unbreatheable when the O2 drops to 10% or the CO2 rises
to its toxicity level (whatever that is).
Increasing pressure would help prevent O2 deprivation
(assuming the O2 partial pressure doesn't reach toxic
levels), but it would not reduce the CO2 poisoning effect.
,-----------------.
|Gerald S Williams|
|[email removed]|
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AT&T DSP tools development