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From: (Steve Harris
Newsgroups: sci.chem,
Subject: Re: Nitrogen KILLS
Date: 7 Oct 2004 11:00:48 -0700
Message-ID: <>

"hanson" <> wrote in message

> However, there seems to be something still elusive and not
> mentioned yet for that stated "quick death" quality ascribed to N2.
> For instance sudden cabin pressure loss at 30'000+ ft results
> in unconsciousness so fast that the pilots can't even relay what
> happened.
> OTOH mountaineers like the Austrians Messner & Habeler have
> climbed the ~ 30'000 ft Mt. Everest twice without any O2 gear.
> Maybe some posters in can shed light onto this.
> The thread started in sci.chem.
> hanson


There's nothing too strange about any of this, if you remember only
that your lungs are a wonderful gas exhanger, and they work totally
passively-- ie, they work just as well to clean oxygen OUT of the
blood, if you breathe nitrogen or "breathe" vacuum or low pressure
air.  So in neither instance do you get nearly the time you do from
holding your breath. Of course, if your cabin depressurizes, you CAN'T
hold your breath.

You have enough oxygen in your brain tissue to support consciousness
for about 5 seconds. If your blood pressure goes to zero (ie, your
head is cut off) you get that 5 seconds and about 5 more (the oxygen
in your brain capillaries) and then it's light's out.  If your merely
heart stops, you get another 5 seconds on top of this from diasolic
flow, but after 15 seconds total, it's still lights out.

If you decompress, the blood passing through your lungs is instantly
deoxygenated, and your consciousness time is the time it takes that
blood to reach your brain. Maybe 20 seconds. A bit longer if you're
not in total vacuum, but rather only in an airplane at 30,000 feet
(not vacuum but 0.3 atm).

If you breathe nitrogen, you would in theory get 20 seconds after your
lungs were pretty much deoxygenated (ie, down to 30% of normal oxygen
content). BUT it takes some breaths to do that, since your functional
residual lung capacity (what's in your lungs at the end of a normal
expiration) is 4 or 5 times your "tidal volume" (what you breathe in a
normal breath). So if you take your oxygen level down (say) 20% with
each breath, your oxygen is (0.8)^5 = .32 = 32% of normal after 5
breaths, so at 5 seconds a breath it takes 25 seconds to get you
functionally to the top of Everest or a cockpit at 28,000 ft. Add a
few more seconds for ciculation time to the head, and 40 seconds total
is a fair estimate for how long to pass out. Faster, of course, if you
huff and puff.

I've seen suggestions that nitrogen should be used in gas chambers for
a much more humane execution than happens with stinky and chokey
hydrogen cyanide. Nitrogen's odorless, and there's very little feeling
of hypoxia when you breathe it. You just pass out, which is what makes
it so dangerous. And with nitrogen you could use the old equipment,
but dispense with most of the time and effort associated with handling
cyanide gas and keeping it away from everybody but the condemed.
Unfortunately, cyanide is historically what we started with, and it's
hard to change habit.

A final thought: somebody suggested that nitrogen might have narcotic
effects that nobody notices even at normal pressures, since we've
adapted to them. But there is no evidence for this. People breathing
pure oxygen or oxy-helium don't suddenly become smarter or more hyped
up. They don't notice any difference at all.

The narcotic effects of nitrogen in diving start to become apparent at
about 4 atm absolute, or 5 times what's normally breathed at sea
level. And are mild, even then.  Many divers can still operate at 6 or
even at 7 times normal pressure, though it's not recommended. The
world record for deep scuba air diving is around 12 or 13 times normal
pressure, though it's killed many a diver trying for lower, so I think
recording of that as a record has been suspended.


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