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When you absoultely have to cool down a
building quickly. Liquid helium will rise
cooling as it goes, cold air will then drop
giving a double whammy of cold. Helium
manages to get into everywhere allowing
you to smother a fire from underneath and
in between floors. Pump it into an
elevator
shaft to save the internal
structure of a building.
Some interesting comparisons of different systems that are commercially available
http://www.pyrogen....ads/Pyroleaflet.pdf
[Ling, Jul 04 2005]
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//Liquid helium will rise// It will? You
mean capillary-wise through the pores
in the concrete? I don't get
it.
Plus, I suspect that rapidly
chilling a large structure by about 300
degrees will cause some problems of its
own. Steel will contract differently from
concrete, which will contract differently
from glass, which will contract
differently from office workers, etc etc. |
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Liquid helium will change form rather
quickly at STP and yes will rise. |
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Doing anything to excess will have its
problems. Is it possible you could give
me a
bit more credit here? |
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//Liquid helium will change form rather
quickly at STP and yes will rise.// OK,
so what you mean is that you pump
liquid helium in, and it will then
vapourize and rise. Fair enough.
However, what will happen is this. The
liquid helium will form a pool in the
basement, where it will cool whatever it
is in contact with. It will boil, absorbing
a large amount of heat from its
immediate surroundings (and, if present
in sufficient amounts, cracking the
concrete it's in contact with) and
producing helium gas at a very low
temperature. This gas will indeed rise
up the building. However, the heat
capacity of helium gas (or indeed any
gas) is so ludicrously low that the rising
gas will have very little cooling capacity,
even though it is initially very cold. So,
the "cold" aspect of the liquid helium is
effectively
irrelevant.
However, you do
have the asphyxiant properties of the
helium gas, which might well
extingquish fires simply by displacing
the oxygen, so it's not a completely
wrong idea.
Liquid helium costs
something like $1-2 per litre, by the
way. So, credit as an interesting
halfbaked idea, but not as a practical
solution. |
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What is the speed of rising helium, is it
slower than a helium balloon? As for
price it costs less than many of the non
water fire supression systems. Earlier
you said that it did have the capability
to cool by a great degree and now you
negate that? What if this were high
pressure low temperature gas helium? |
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From your first argument one could
argue against the usage of water under
pressure, for property damage and
damage to humans inside. |
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Impressive how one couldn't find a way
that could make it work in ones mind
but instead had to destruct it and stack
it into ways it wouldn't work first. |
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Hmmm. OK, a quick back-of-envelope
calculation suggests that you need only
a few tens of thousands of dollars'
worth of helium to displace all the air in
a smallish building. So, cost-wise, it's
on the edge. However, I suspect that
the helium gas would vent through the
roof and, once gone, would simply pull
a very strong current of rising air up
behind it, reigniting the fire in the still-
hot building. So, not completely
whacko, but I'd sooner you try it on
your building first :-) |
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Nitrogen would be much cheaper. I do not know if the point where air + more N2 disallows fire is still within people's ability to remain conscious though (and not asphyxiate). |
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Getting there, thank you Basepair. |
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Do you find it interesting that as you
are doing out more calculations, the
idea becomes less whacko? My idea,
didn't change. |
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But remember it would be bringing cold
air back with it from behind. |
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Zimmy, agreed that it would be cheaper
but with helium, it would be there and
gone much faster causing fewer
asphyxiating qualities. |
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+ I can't think why this should not be tested. |
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{Ling}, most impressive. I was looking up quite a few fire suppressants and never saw anything like that. |
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A pool of liquid nitrogen on the roof would be cheaper, faster and automatic. When the fire occurs below, the nitrogen could be released and would flow downwards, cooling all before it, turning into gas en route until it hit the fire. It would then rapidly expand into gas, choking the fire. If the fire were really bad and compromised the structural integrity of the nitrogen pool on the roof or the roof itself,the nitrogen would work the same way - the pool would go and the nitrogen would dump down into the fire. |
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I thought nitrogen was still barely lighter than air. I guess i was mistaken? |
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It's a very good conductor of heat, if that helps. |
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//What is the speed of rising helium, is
it slower than a helium balloon? //
Free helium gas should rise faster
than a balloon, though it will mix with
air and hence become less bouyant, I
imagine.
// Earlier you said
that it did have the capability to cool by
a great degree and now you negate
that? //
It is very simple: liquid
helium will have a large cooling effect,
since the latent heat of vapourization is
high (it absorbs a lot of energy in order
to boil and form helium gas). The gas
itself has negligible cooling effect: it
takes very little energy to warm up
helium gas from -269°C (the b.p. of
liquid helium) to, say, +300°C. So,
there is no inconsistency here: we are
talking about the difference between a
liquid and gas.
//What if this
were high pressure low temperature gas
helium?//If you try to fill a building with
compressed helium, the building will
simply go pop. And the helium gas
*will* be at low temperature (initially
-269°C) if it comes from the boiling of
liquid helium, but this won't really make
much difference, for the reasons noted
above.
The reason I was so
negative to your initial posting is that
you had several wrong assumptions,
including the statement that liquid
helium would rise and that the coldness
of the gas it produces would be helpful
(it won't be). The idea of using helium
gas (whether produced by pumping in a
liquid or pumping in a gas - no matter)
as a rising fire asphyxiant is OK, though
I still think it will rise too fast and leak
out of the top of the building, and
simply drive a blast of air both before
and behind it. |
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[Basepair] from what I've read today, temp seems to play a factor in combustability- I wonder if [sartep] can make a case for extinguishment prior to asphyxiation. (Your point of replacement volume of gases seem quite valid. (using liquid He in my opinion would break each an every window though). |
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I'm sure that temperature plays some
part in combustibility (if nothing else,
cooling a hot object
will reduce the production of
combustible
gases from plastics etc). But my
argument is that using a very cold *gas*
is not an efficient way to cool a building
quickly. I can comfortably hold my
hand in the vapour sitting above liquid
nitrogen in a large Dewar (-196°C)
more or less indefinitely. It's not the
temperature, it's the heat capacity. |
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Yes, but if you were to hold the cold
nitrogen and close your hand, you
would tell a different story about
cooling. |
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//Yes, but if you were to hold the cold
nitrogen and close your hand, you
would tell a different story about
cooling.//
Exactly! That is my
damned point! Liquid nitrogen will
freeze your hand quickly because of its
high latent heat of vapourization,
nitrogen vapour at the same
temperature will not, because of its low
specific heat. The same goes for
helium.
So, in your scheme,
you are relying on the cold helium *gas*
rising up the building, and my point is
that it won't cool anything worth a
damn. Fill the building with *liquid*
helium and of course it will be cooled
very quickly, but that's not really an
option. Filling an entire modest
building with *liquid* helium would
require something like 10 million litres
(for a 30 x 30 x 10 metre building) of
the stuff, which is going to cost you
something like $10million.
Stick to the asphyxiant effect
of helium - it's more plausible. |
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As the article states, I said pump it into
an elevator shaft. Or pump it into the
floor just below the fire. This depends
on the size of your building. If you
have control of the building you could
open the elevator doors to the floor
below the fire. Once again, there are
ways that this can or may work more
efficiently but you feel that you must
stack a situation in such a way that it
can only fail. You have again twisted it
to say I am filling up the whole building. |
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I'm thinking forget fires and think air-con. |
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//I'm thinking forget fires and think air-con// I read that as "fire-and-forget air-con" and thought this was some weapon of mass ventilation. |
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[Sartep] Take it easy. Half the point of
the HB is to examine ideas and find
flaws, and hence find the way forward.
If we all just say "great idea" with no
critique, then what is the reason for
posting here?
All I am saying
is that if your scheme relies on cold
helium gas (coming from liquid helium
in the elevator shaft if you like) rising
up the building, then there will be
asphyxiant effect on the fire (great
while it lasts) but no worthwhile cooling
effect (which was the main thrust of
your original post). Cool down. |
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It is kind of a cool idea. |
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Again, you are trying to say I am angry
for some benefit of your own. I see, I
lost some sort of sapient social game,
now you can tell me that I am angry in a
check mate fashion. Extra credit using
the idea (cool down) to express that. |
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I see you are doing a service but
twisting what others say is wrong, it
creates a devide between you and
another one. |
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My end statement is that the elements
are there to do the desired effect, and
the logic you used in 2 places was the
same logic that wouldn't allow water to
be used either. Often times I try to be
efficient, instead of posting 2 ideas, I
will post one idea that does two desired
effects. |
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He would only displace oxygen, and probably diffuse away before cooling the fire. Bromine containing compounds work better, because they are free radical poisons, chemically interfering with the combustion process, and are heavier than air, so pool around the fire. Think Halons. Unfortunately, they are also greenhouse gases.
The cooling aspect of He would probably be less than water, since the latent heat of evaporation of He is so low, and it would boil away before getting to the fire, so would not cool the fire directly |
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Agreed, will not work as well as halons. Further, you want to smother the fire at its base, not on top, so you ideally want a heavier gas to begin with. Try spraying with liquid nitrogen or ground dry ice. |
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Liquid N2 has been used to snuff oil well fires. |
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...and everyone would speak with silly voices... |
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