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Thread: : Fire prevention by partial deoxygenation of air
www.piclist.com/techref/index.htm?key=fire+prevention
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face BY : Russell McMahon email (remove spam text)



>> 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



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