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'[EE]:: Fire prevention by partial deoxygenation of'
2007\03\18@220816 by Russell McMahon

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Fire prevention by partial deoxygenation of air.

This is for data centres but should have applications elsewhere.

Nitrogen flooding during a fire may be practical - replace fire
consumed O2 with N2 to redcue influx of new air and keep O2 at people
safe but fire starving levels.



       Russell

______________________

They say:

Wood stops burning when the oxygen content falls to 17% and plastic
cables between 16 to 17%

Wagner makes electric compressors that use a special membrane to
remove some of the oxygen from the outside air, a system the company
calls OxyReduct. The excess oxygen is exhausted, and the remaining
nitrogen-rich air is pumped inside the data centre.

At 15% oxygen, it's safe for humans to enter. The lower oxygen content
of the air is similar to being at an altitude of about 6,000 feet,
Eickhorn says. He demonstrates with a lighter inside a sealed atrium
Wagner has on display at Cebit. It won't light.

2007\03\18@222553 by David VanHorn

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>
> Wood stops burning when the oxygen content falls to 17% and plastic
> cables between 16 to 17%
>
> At 15% oxygen, it's safe for humans to enter.



So the idea is to hold the oxygen content within that 1% band?
Hmm.

2007\03\18@225123 by Jinx

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> > At 15% oxygen, it's safe for humans to enter.

www.computerworld.com/action/article.do?command=viewArticleBasic&arti
cleId=9013439&source=rss_news10

Remember when oxygen booths were all the rage ? Would you
have to literally take a "breather" every now and then ? On the
other hand

http://en.wikipedia.org/wiki/Altitude_training

Perfect excuse for an athlete to use haemoglobin enhancers. Get a
part-time job in a data centre and "accidentally" take a little more
than necessary to compensate

2007\03\18@230309 by Russell McMahon

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>> Wood stops burning when the oxygen content falls to 17% and plastic
>> cables between 16 to 17%

>> At 15% oxygen, it's safe for humans to enter.

> So the idea is to hold the oxygen content within that 1% band?
> Hmm.

They really mean "A level of 15% is acceptable for fire prevention, so
that's what we use, and it is safe for people."

In fact, levels BELOW 15% are also safe for people.
Atmospheric pressure and, consequently, Oxygen partial pressures,
halve every 14,000 feet or so.
So a reduction to about 11% O2 at sea level is equivalent to an
altitude of 14,000 feet. Most people would certainly notice the
difference by that level, but its still livable and breathable by
most. Only people with medical problems couldn't handle it. Even
Everest base camp at 20,000+ feet is acceptable for all with normal
abilities, albeit with noticeable affects. It's the starting point for
acclimatisation for low Oxygen regimes.

If their claims are correct then it would sound like a wood fire is
not achievable above about 6000 feet. Sounds wrong.

Quick check.  Someone living above or preferably well above 6000 feet
please tell us if you can use matches successfully :-)




       Russell.



2007\03\18@232444 by Richard Prosser

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On 19/03/07, Russell McMahon <spam_OUTapptechTakeThisOuTspamparadise.net.nz> wrote:
{Quote hidden}

Russell,

So does that mean that the air is ~85% Nitrogen at 6000 feet? I
thought that the percentages would stay pretty much the same, just the
overall pressure dropped with altitude.

RP
> http://mailman.mit.edu/mailman/listinfo/piclist
>

2007\03\18@233131 by Jinx

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> If their claims are correct then it would sound like a wood fire
> is not achievable above about 6000 feet. Sounds wrong.

Mexico City is over 7,000ft elevation, and inhabitated places
above that. Where it's cold. And you need a fire

2007\03\19@003412 by Russell McMahon

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Content-type: text/plain; format­owed; charset 2007\03\19@022446 by Russell McMahon
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>> Atmospheric pressure and, consequently, Oxygen partial pressures,
>> halve every 14,000 feet or so.

> So does that mean that the air is ~85% Nitrogen at 6000 feet? I
> thought that the percentages would stay pretty much the same, just
> the
> overall pressure dropped with altitude.

No.
Yes indeed.

I'm assuming, quite possibly incorrectly, that it's the absolute
oxygen levels available (eg O2 partial pressure) that's important. It
could be that the relative percentage is in fact important as well as
the absolute PP. I'm basing my assumptions on things I've read on the
effect of increased O2 levels on burning, and I may have it wrong.

Burning a candle or gas flame or wood or paper in a sealed container
may provide some guide to this, although increased CO2 percentage is
going to confuse things. A burning object on a floating platform in a
'bell jar' inverted over water would give a rough indication of how
long combustion would continue.


       Russell


2007\03\19@022920 by Jinx

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> Burning a candle or gas flame or wood or paper in a sealed
> container may provide some guide to this

You'd be aware of how charcoal is/was made, and how oxygen-
starved fires smoulder, and erupt causing flashbacks when a door
or window is opened

2007\03\19@040000 by Russell McMahon

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>> Burning a candle or gas flame or wood or paper in a sealed
>> container may provide some guide to this

> You'd be aware of how charcoal is/was made, and how oxygen-
> starved fires smoulder, and erupt causing flashbacks when a door
> or window is opened

Indeed.
I'd imagine that a wad of paper with easy air access over all surfaces
would burn freely at first and then at a lesser rate as oxygen
availability decreased. Whether there was a reasonably sudden
extinction of free flame would be of interest.

AFAIK formal charcoal making relies on thermal decomposition as much
as or even without combustion per se.


       Russell

2007\03\19@152339 by peter green

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> Nitrogen flooding during a fire may be practical - replace fire
> consumed O2 with N2 to redcue influx of new air and keep O2 at people
> safe but fire starving levels.
why not just hold the 02 at fire starving levels all the time? stop the fires before they start rather than after they've been burning long enough to set off a smoke detector.


2007\03\19@164449 by Gerhard Fiedler

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peter green wrote:

>> Nitrogen flooding during a fire may be practical - replace fire
>> consumed O2 with N2 to redcue influx of new air and keep O2 at people
>> safe but fire starving levels.

> why not just hold the 02 at fire starving levels all the time? stop the
> fires before they start rather than after they've been burning long
> enough to set off a smoke detector.

Maybe because even for alpinists trained in high altitudes (low oxygen
levels) the brain doesn't work as well in that condition as it works with
normal oxygen supply? Or are you implying that with the admins they usually
hire this doesn't matter that much? :)

Gerhard

2007\03\19@165812 by peter green

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> Maybe because even for alpinists trained in high altitudes (low oxygen
> levels) the brain doesn't work as well in that condition as it works with
> normal oxygen supply? Or are you implying that with the admins
> they usually
> hire this doesn't matter that much? :)
i thought generally it was best practice to have people in there only when absolutely nessacery. It can't be a nice work environment with all that fan and aircon noise anyway.



2007\03\19@181209 by Gerhard Fiedler

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peter green wrote:

>> Maybe because even for alpinists trained in high altitudes (low oxygen
>> levels) the brain doesn't work as well in that condition as it works
>> with normal oxygen supply? Or are you implying that with the admins
>> they usually hire this doesn't matter that much? :)

> i thought generally it was best practice to have people in there only
> when absolutely nessacery. It can't be a nice work environment with all
> that fan and aircon noise anyway.

You're probably right, but still... they might want their brains working
fully in there as long as it doesn't burn. AFAIK, oxygen starved brains can
do strange things, which seems to be one of the major challenges for
activities in high altitudes.

Gerhard

2007\03\19@225306 by Russell McMahon

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>> Nitrogen flooding during a fire may be practical - replace fire
>> consumed O2 with N2 to redcue influx of new air and keep O2 at
>> people
>> safe but fire starving levels.

> why not just hold the 02 at fire starving levels all the time? stop
> the fires before they start rather than after they've been burning
> long enough to set off a smoke detector.

Permanent O2 deprivation is in fact what is described in the original
article.

I suggested Nitrogen flooding as a possible way to deal with fires.
Maintaining permanently depressed Oxygen levels requires specialist
equipment and good sealing and makes the environment less suited to
day to day human occupation. Nitrogen flooding on demand requires a
finite source of readily deployed Nitrogen gas. It may be that
dispersal systems that pipe liquid nitrogen to evaporators may be
better than using a sprinkler system. And may not.

Nitrogen flooding during a fire may be able to stop flames drawing in
new Oxygen while providing a flame adverse environment and still
allowing people to breathe. IF it worked it would be vastly superior
to most alternatives. It's conceivable that a 'fire engine' carrying
large volumes of  liquid (so cryogenic) Nitrogen (don't crash!) may be
able to deal with fires as well as by using water or foam or CO2 or
... . Much cheaper than Halon flooding, less 'toxic' than CO2
flooding. May also need to carry a fuel supply to power burners to
evaporate it rapidly enough - maybe not.

Quite possibly not viable, but ... .

How well this works can be most easily tried by adding a controlled
percentage of Nitrogen to an air sample. The end result would be
almost indistinguishable from a sample with some Nitrogen removed. The
trace gas percentages would be higher in the de-Nitrogenated sample,
but this is not liable to be very significant. These mixtures would
allow testing of the eg paper combustion claims. Nitrogen is readily
and cheaply available.


Say 1% trace gases, 21% O2, 78% N2.
1% is high.

To 100 units of air add 33 units of N2.
O2 = 21/133 = 15.8%
N2 = 108/133 = 81%
Trace = 1/133 = 0.75%
N/O = 5.14:1

Now, from 100 units of air remove 6 units of O2
O2 = 15/94 = 16%
N2 = 78/94 = 83%
Trace = 1/94 = 1.06%
N/O = 5.2:1

Arguably similar enough.
Add N2 as required for target O2 concentrations.


       Russell



2007\03\20@143315 by Herbert Graf

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On Mon, 2007-03-19 at 20:56 +0000, peter green wrote:
> > Maybe because even for alpinists trained in high altitudes (low oxygen
> > levels) the brain doesn't work as well in that condition as it works with
> > normal oxygen supply? Or are you implying that with the admins
> > they usually
> > hire this doesn't matter that much? :)
> i thought generally it was best practice to have people in there only when absolutely nessacery. It can't be a nice work environment with all that fan and aircon noise anyway.

That depends who you are. Personally I loved when I had to spend the day
in the server rooms, the AC was wonderful, and the noise is certainly
better then hearing your cube mate chatting on the phone...

TTYL

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