[Beowulf] HVAC and room cooling...

Jim Lux james.p.lux at jpl.nasa.gov
Sat Jan 31 18:38:36 EST 2004


----- Original Message -----
From: "Per Lindstrom" <klamman.gard at telia.com>
To: "Daniel Pfenniger" <daniel.pfenniger at obs.unige.ch>
Cc: "John Hearns" <john.hearns at clustervision.com>;
<rossini at u.washington.edu>; <beowulf at beowulf.org>
Sent: Saturday, January 31, 2004 11:54 AM
Subject: Re: [Beowulf] HVAC and room cooling...


> ATTENTION!
>
> Liquid Nitrogen is deadly dangerous as it will shut off the breathing
> function of the human body when the Oxygen content falls below 19.5 %
> and thereby causing suffocation.
>
That high?  I'm not so sure.. Consider for instance that conscious ness has
mostly to do with partial pressure of oxygen in the gas being breathed,
which then transfers to the PO2 in your blood.  As a rule of thumb, the
pressure drops by half with every 18,000 feet of elevation change (5500 m).
Most people can tolerate a sudden pressure drop to an equivalent altitude of
5000 ft without losing consciousness, and, for instance, the Federal
Aviation Administration, uses 10,000 ft as a cutoff.

19.5% oxygen, compared to the usual 21%, is a partial O2 pressure change of
about 2000 ft or so (600m).

I would go for 9.5% (it's well established that suddenly taking someone to
5000 meters will cause unconsciousness, although not that quickly... you
have to go to something like 15,000 m/40,000 ft to get rapid
unconsciousness).

They do this sort of training in altitude chambers for pilots to impress on
them the need to "keep that mask fastened tightly, even if you think you're
getting sick"

We're sort of off topic here, but think in terms of those little oxygen
masks that drop "in case of a sudden cabin depressurization"... Not only
will there be nosebleeds and broken eardrums a plenty if this happens, but I
think you'd better move pretty fast to get that mask on.

By the way, if you know the loss of oxygen is coming, you can hold your
breath (or just not breathe) and be conscious for quite a while (30 seconds
to minute would be fairly easy..). The problem with the nitrogen purge is
that you don't realize it, and you keep on breathing, flushing the oxygen
from your lungs, until it's too late.

My math may be all wrong here, but that's the general idea.
> This is not an unusual accident type in the Oil- & Gas- as well as in
> the Shipping industry. For the sake of your safety I'm recommending the
> use of an Industrial Safe Working Practice as a guideline before any
> work commence.
>
> A reference:
**http://www.medicine.uiowa.edu/biochemstores/Pages/ln2msds.htm
>
> Best regards
> Per Lindstrom
>
>
> Daniel Pfenniger wrote:
>
> > John Hearns wrote:
> >
> >> On Fri, 30 Jan 2004, A.J. Rossini wrote:
> >
> >
> >>> to people that it isn't possible, but someone brought up "portable
> >>> liquid nitrogen" -- for the room, NOT for overclocking -- I'm trying
> >>> to get stable systems, not instability :-).
> >>>
> >>
> >> Daft idea.
> >> What happens when the liquid nitrogen vapourises? It turns to
> >> nitrogen gas. And if you are unlucky anyone in the room chokes...
> >> I was reminded of this in the lift of a chemistry department where
> >> we have an opteron cluster - a large sign reminding that LNO2 and
> >> dangerous chemicals are not allowed in passenger lifts.
> >
> >
> > When liquid N2 vaporizes in a closed room the natural fraction of N2
> > in air, already 78% by volume, just increases. N2 is thus not toxic,
> > the only risk by increasing N2 volume is to reach a too low O2
> > concentration
> > for mammals beings breathing in the room.
> >
> > Dan
> > _______________________________________________
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>
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