Alistair Langsford [email removed] asks:
> Imagine you are in a sealed room. How long does it take a person to die
> because the air gets bad
It depends on the volume of the room and how many folks are trying to
breathe. Of course, I don't know *how* it depends (i.e. minutes per
liter of air per person). It also depends on the pressure and percentage
of oxygen. The greater the pressure and/or oxygen concentration (and
the fewer the people) the longer you can survive.
> - and why? Is it lack of Oxygen, or the
> presence of impurities?
It's lack of oxygen, unless impurities are also being introduced. The
human waste product, carbon dioxide, isn't harmful.
> 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.
The explosive hazard is a product of oxygen concentration not pressure.
The higher the concentration, at any pressure, the greater the risk.
The confusion comes from the fact that higher concentrations permit the
air to be `breatheable' at lower pressures. Thus, early US spacecraft
used all-oxygen atmospheres at lower pressure (some chemistry folks or
divers can probably explain the partial-pressure thing) because the
craft pressure vessel didn't need to be as strong if the internal pressure
was lower. The capsule fire in Apollo I on the launch pad changed all
that. Since then, US spacecraft have taken the weight hit and used
stronger crew pressure vessels in order to keep the oxygen concentration
closer to what it is in `normal' atmosphere.
> - - how long before a typical human unfortunate dies from bad air in this
> scenario.
A 100% concentration of oxygen at the same pressure as `air' (~20% oxygen)
would permit you to breathe about five times longer but you would probably
only use a 100% oxygen environment at lower pressure (in order to gain the
stength/weight savings of the early US spacecraft). At 20% of atmospheric
pressure (or thereabouts) you wouldn't live any longer in a 100% oxygen
environment than you would in a 20% oxygen atmosphere at standard pressure.
Below 20% of atmospheric pressure you'd having trouble breathing even in
a 100% oxygen environment.
There isn't really a simple answer to your question. Me, I'd just wing
it. Either they get out in time, or they don't. :-)
Happy Travelling,
David Johnson
Houston, Texas, USA
P.S. Note the `Misc' subject indicator in my subject line.