On 2012-09-14, Jon Elson wrote:
J. Clarke wrote:


Nice story. Both porcelain and asbestos are fully oxidized--they will
not burn in oxygen--neither will glass--all are silicon dioxide.
Right, I agree with you. But, there must have been other materials in small
quantities in these items that were still able to be oxidized.

Perhaps it was the glass-epoxy printed circuit boards
(fiberglass bound with epoxy) which burned so spectacularly when we lost
a couple of astronauts on the launch pad. Over time, people could
forget the "-epoxy" of "glass-epoxy" and claim that it was the glass
which burned. :-)

Or, perhaps as you say, the original account got muddied a bit over
time. Still, I wanted to caution the OP that low pressure pure
O2 is still VERY dangerous stuff, and needs to be treated with utmost
caution. And that this partial pressure business is completely wrong.
compressed air where the O2 partial pressure equals atmospheric pressure
is not the same as pure O2 at atmospheric pressure.

IIRC, that capsule (one of the Gemini series, since there were
two astronauts in it?) was being run at the partial pressure of oxygen
from the atmosphere (e.g. about 20% of the full atmospheric pressure) to
minimize the problems with seals and leaks, to supply enough oxygen to
keep the astronauts alive for one of the longer flights. If it was
truly just the partial pressure, it would have been below atmospheric
pressure, and any leaks while sitting on the pad would have been coming
in instead of going out.

I am not enough of
a physicist to know why, but I am quite sure this is true. There is a
bunch of lube oil that has settled in the bottom of my air compressor tank,
and at 100 PSI, the O2 partial pressure is roughly the same as pure O2 at
atmospheric pressure. No problems, and everybody does this. But, put
pure O2 in that tank at one atmosphere, and I am fairly sure something very
bad could happen.

I think that the presence of the nitrogen (and to a much lesser
degree, the other things in our air) diluted the effect of nothing but
oxygen molecules bouncing off everything.

Yes -- even at 20% of atmosphere pressure (partial pressure of
oxygen), the puddle of oil would be bad news with the pure oxygen --
even without the extra pressure you are talking about pumping in there.
Add that, and you would be about 20 PSIG (PSI above atmospheric
pressure, as equal to the partial pressure of oxygen in a 100 PSI tank
of air.)

Be careful,
DoN.

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