frogfot
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Automatic fire protection
Is there any low cost and low maintenance device(s) one could place in a chemicals locker that can be automatically activated by possible fire? Be it
electronically or chemically triggered..
The target is a wooden locker (will change to plastic soon) mainly with org solvents and org compounds. At surrounding temps of +30*C to -20*C.
Would be good to have some (maintenance free) funky baggies that release buttloads of fire retardent stuff on heating.. any idea?
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Lambda
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My chemical cabinet
I had a filtered-air inlet in the side-wall at the bottom of my chemical cabinet. A computer blower was mounted here, with speed controle. If a spill
where to occure, then the fluide (or whatever) would not run directly into the air-inlet hole, for it was mounted on the side wall at the bottom. The
filter was from a cooking sucktion ventilator, wich have fairly wide air-inlet poures, and thus give relatively little resistance to airflow. On the
top of the chemical cabinet was the air outlet, connected to a piping system to the outside world (whatever this may mean). The ventilator was mounted
on the air-inlet side, so that corrosive fumes would not pass through the ventilator itself. Air-inlet at the bottom, and air-outlet on the top seems
to me to be logicall, for warm air would allways rise, and thus assist the system in it's air cleansing turbulance. In the air-outlet pipe was a
thermo-element mounted, which would detect temperatures above a threathhold level, thus indicating a fire. In the event of a fire, a CO2 (carbon
dioxide) cylinder would flush the chemical cabinets interiour through a valve opperated system. First a large burst of CO2 would run through the
chemical cabinet, an then the valve would switch down to a long lasting small steady flow. This long lasting steady flow would hopefully prevent
further ignition, and last long enough for the accident to be discovered and neutralised.
Remark:
1.- If metall powders are to be stored, then CO2 must be avoided.
2.- By keeping certain chemicals together, extiquiching the fire may be finetuned according to the nature of the compounds.
3.- Fluids may run out of the chemical cabinet, and may be cought in a basin or tub.
4.- Chemical combinations that sustain a fire should be avoided, and sepperated from eachother (kept appart).
5.- Fluids should be kept away from anything that can explode.
6.- A thermo element as detector may be slow acting, but more reliable than IR or gas and smoke detectors. These sensitive devices may become attacked
by the fumes of corrosive chemicals and mailfunction.
7.- Filters should be checked from time to time, and replaced if necessary.
8.- If the door of the chemical cabinet is blown open, then this system is likely to fail. A different or additional sytem may be implemented or
added.
Note:
I never had an accident, and this system was NEVER TESTED !
My chemical cabinet was allso made up of independent steal compartments, with there own sepperate door. A millitary coat hanging cabinet with five
doors. Five shelves were added per compartment, totaling twenty five shelves in all, and five air inlet holes and five air outlet holes.
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Magpie
lab constructor
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Mood: Chemistry: the subtle science.
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Frogfot,
As I mentioned in a recent fume hood post I saw a CO2 deluge system piped to the fume hood duct in a greasy spoon restaurant. I would think that
these are commercially available. I suspect that it is triggered by high temperature. When I get a chance I will investigate this further by talking
to the restaurant cook.
I keep all my flammable solvents and bulk acids/bases in a 2.3m x 3.1m plastic shed that is located in my backyard 3m from my house. My sulfuric acid
is triple contained with the outer container being a 20 liter high density polyethylene bucket. For the solvents the secondary containment is a
plastic wash pan. There are 2 passive vents in my shed. It has been very hot here the last few weeks (> 100 deg F (39C)) but when I walk into the
shed there's no strong chemical smell.
[Edited on 8-8-2005 by Magpie]
The single most important condition for a successful synthesis is good mixing - Nicodem
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frogfot
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That system would most probably be above 100$.
Btw, I've never seen electrical valves that can do something in between on/off.. Lambda, where did you get it and how was it mounted on the CO2
container?
So.. temp sensing would be most reliable.
Mine cabinet is not vented since it's on the balcony, outside. It would be logical to put the temp sensor in the top part of the cabinet. Even if
doors would be wide open, the heat would rise to the top (it's protected from the wind).
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Lambda
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Just some additional idees
Frogot, there was quit a bit of electronics involved, mainly timer- and thermo-scensing circuitry. The valve was just an ordinary push-leaver, with a
full burst at a 20 - 30 degree push-in angle. In a CO2 cylinder, I think they use needle valves, which are very gas-tight and are less likely to
freeze by the cold expanding CO2 gas flow. I now have very proffesional magnetically opperated valves, but with less flow. They allso will not freeze
upon opening, for then they may not close on time.
How did it work:
In the case of a fire, the valve handle would be pushed in at a 20 - 30 degree angle. This was done by a servo-motor used in a car as a windscreen
wiper. It would stop when the valve was open, wich was detected by a micro-switch (the kind you find in the door of a microwave oven, used to switch
the system off when the door is opend during opperation). The valve would stay open for about 5 - 10 seconds, and then move back to a few degrees,
wich was allso detected by a micro-switch, and stay in that position to enable a small continuous CO2 gas flow. If a fire is again detected by the
thermo-element, then the valve would again be fully pushed in to maximum flow for about 5 - 10 seconds, and then go back to the minimal flow position.
There was allso a bit of welding and lathe work involved, but this is not allways necessary. In the case of an ordinary CO2 fire extinquicher, the
handle may be pushed in by the action of a rotating threaded shaft driven buy the same car windscreen wiper motor (they are very strong, and reliable
and have all the gearworks allready mounted inside).
Example:
When you rotate a fixated threaded shaft through a nut, and this nut is prevented from turning, it will move up or down this shaft, depending on the
rotation direction (clockwise or anti-clockwise). This nut may be hindge mounted on the CO2 cylinders valve leaver.
Where to find the stuff:
A windscreen wiper motor can be found in a car scrap yard.
Microswitches can be found in microwave ovens.
A CO2 cylinder can be found in any IRS-building, you have paid for it already (this is meant to be a joke, and not as an instignator to commit a
criminal act by theft or endagering the lives of others in the case of a fire outbreak).
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Lambda
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Maintenance free system idea
Frogot, it may also be possible to seal in a little Ether or stabilized Chloroform into a glass vail, like the ones they use together with a file and
"snap off" head. This vail may be springloaded, and when the heat of a fire would pop it, the system would collaps. This collapsing system
may then opperate a CO2 gas cylinder lever.
A springloaded piece of fishing Nylon string, may be the easyest of all. It will snap, if heated too high. Don't use springloaded Solder wire,
for this material is known to creap under stress.
The only reason I use a "bomb-full" electronical system, is because I am a "Techno-freak". Murphy is going to kick my ass oneday,
for this overcomplication mania of mine. Just keep things simple is my advice, then the least can go wrong.
The temperature you mentioned of -20 degrees celsius can be problematic for some liquid chemicals. But you allready know this.
[Edited on 9-8-2005 by Lambda]
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frogfot
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Aha, so theres a mechanism that pushes the CO2 container handle.. I'd go with your second idea with a bolt that rotates and pushes a nut to
required level..
Using a strong stepper motor one would eliminate the need of those switches you've mentioned that indicate when the handle is pushed in.. you
just tell the motor to do known amount of steps..
Hehe, would be cool to add a microcontroller to the system so it can "watch" over the chemicals cabinet.. so it can do several things.. maby
command a speaker to give off warning sound in case of fire.. mmm
But originally I had in mind something simpler that involves chemical activation.. I mean, say we're heating NaHCO3 and it gives off CO2. So
having a bag of NaHCO3 in the cabinet could retard the fire to some extent.
The only problem is, this is a slow reaction..
Maby theres a more reliable chem..
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praseodym
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What about CuCO3 instead? It is less stable than NaHCO3, i think, hence more effective.
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12AX7
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Aren't ammonium phosphate, sodium diborate (I hate "tetraborate", it doesn't make sense!), and uh something else ammonium, like
sulfate? the preferred fire retardants?
Tim
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Lambda
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The problem with all these solids is, that they give you a hard time to clean them up afterwards. A powder or foam extinquicher is the last resource I
would use, if CO2 can handle the problem. Water often gives you a lot of additional damage, risk of electrocution and flamable organic fluids drift
and burn on the surface. Water allso dissolves many salts and can cause all kinds of secondary reactions.
If CO2, Halon or N2 can be used, then this would give the least cleanup afterwards. CO2 and Halon has an additional advantage that it's cold, and
thus has the abillity to cool a flamable vapour down below it's flashpoint, appart from the oxygen displacement propperties.
Remark:
Firefighting, extinquiching and prevention is a very specialized science in it's own right.
[Edited on 10-8-2005 by Lambda]
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Lambda
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Warning about oxygen displacing compounds!
When you personly are using an oxygen displacing compound like CO2, Halon, N2 etc. in a confined aeria, then there is a substantional risc of dropping
down unconscious. This will hit you before you even notice any giddyness, so be aware !
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frogfot
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Heh, been actually reading some pages on extinguishers, and CO2 is considered to be one of the most inefficient. Its only advantage is the easy clean
up as you've said.
The most efficient and flexible are powder based extinguishers..
But that probably wouldn't apply to a fixed bag with say an unstable carbonate salt.. it'll start working only when a high enough temp is
reached.. at the time when it could be too late..
Looked up the fire retardants that 12AX7 mentioned and they seem to be used as impregnators in paper and wood. Their main fire retarding effect comes
with promoted charring.. Although they suppose to evolve ammonia (flammable gas!) that's said to choke fire.. hmm
Maybe it's just time to switch to a metallic cabinet..
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Lambda
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Make life as tough as possible for a fire, but first of all, try and prevent it from ever happening
Frogot, we have both seen film footages of even experienced personel using CO2, without success. How often have we seen kitchen oil fires, testing
suction systems go out of hand with experienced fire brigade personel ? But remember, this system was going to be used in a closed cabinet. Cloth
material is indeed often inpregnated with Ammonium oxalate etc. However, using one system dose not mean that an other system has to be excluded. I
have a few powder extiquechers and foam extiquicher as a backup, as for a bucket of sand. The intention here, is not to use one system over an other,
but to kick ass with all available assets at hand. Good planing is essential, and this depends on the situation and the chemicals involved. I allso
have a good firebrigade gas mask, fire blanket and eye washer at hand. You can allso catch on fire you know. A good high flow shower is essential in
every laboratory, but how far can we go financially ?
[Edited on 12-8-2005 by Lambda]
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Magpie
lab constructor
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restaurant hood system
As promised I talked to the cook at the greasy spoon restaurant about his fire protection system. It is a "Sentinel" model supplied by
Oxarc. It is triggered by high temperature. It uses a dry chemical rated for "B" and "C" type fires. There are 2 large nozzles
located right above the cooking area (griddle). He said all restaurants are required to have such a system.
The single most important condition for a successful synthesis is good mixing - Nicodem
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