[AR] Re: breathing nitrogen
- From: Henry Spencer <hspencer@xxxxxxxxxxxxx>
- To: Arocket List <arocket@xxxxxxxxxxxxx>
- Date: Wed, 20 Apr 2016 14:23:46 -0400 (EDT)
On Wed, 20 Apr 2016, John Dom wrote:
You're not going to suffocate by taking a sniff of nitrogen...
Not because of a whiff of N2 no. I do not know how many times one can
breathe pure nitrogen. My guess is 5-7 times before you pass out.
Anybody knows better?
Maybe a couple of breaths to flush most of the oxygen out of your lungs,
and then 10-15 seconds for deoxygenated blood to reach your brain. At
which point, clunk, you're unconscious, without warning. (And within a
minute you're probably dying -- the orthodox "three minutes" without
breath assumes there is still oxygen in your lungs.)
When using nitrogen, this needs care even if you're not deliberately
breathing it. Plenty of ventilation is the best defence. Bear in mind
that nitrogen boiled from liquid, or nitrogen that has been used to
pressurize LOX, will be cold and hence heavier than air, so it will have
some tendency to flow downward and pool in low spots.
(For that matter, oxygen boiloff from LOX has the same behavior, and is
hazardous for a different reason: it greatly increases fire hazards.
Automobile engines have been known to catch fire spontaneously in oxygen
clouds. Don't stand in a boiloff plume, however pleasantly cool it might
be on a hot day; oxygen-saturated clothing is very dangerous and must be
taken off at once, no matter how embarrassing this is.)
I read of people stepping down a few steps down a ladder inside a tank,
unaware it had been nitrogen purged. ... Such happened on
several occasions in chemical industry, even some who went down for help
without an air blanket perished.
Many occasions, involving various gases. The industrial-safety buzzword
for such hazards is "first entry". The first guy down into the tank
really needs to be wearing a harness with a safety line, so he can be
pulled out, quickly, without rescuers having to enter the tank themselves.
First entry was a bit of a concern on first arrival of new space-station
modules (which generally started out with air in them, of course, but
might have been sitting sealed for quite a while...).
Henry
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