Sciencemadness Discussion Board

Magnesium Alloy Fire extinguishing

Reefer - 25-2-2005 at 09:26

Hi All,

Does anyone know which type of fire extinguisher is suitable for using on a Magnesium Alloy fire.

Cheers,
Reefer.

[Edited on 26-2-2005 by chemoleo]

chemoleo - 25-2-2005 at 09:28

Sand.
Don't use chlorinated dry extinguishers, or water.

uber luminal - 25-2-2005 at 11:51

any non-flamable, non-decomposing particulate(for those temps).

Lime works.

so does liquid nitrogen. that puts out just about anything.

neutrino - 25-2-2005 at 13:50

You can't use carbon dioxide extinguishers, as magnesium reduces that energetically. Nitrogen would have the same problem. I’m not sure if the liquid part matters, as magnesium will burn quite happily in dry ice and liquid nitrogen isn’t that much colder (compared to burning magnesium, that is).

chemoleo - 25-2-2005 at 14:24

Ah, but you forget that liquid N2 has an enormous capacity to carry away heat (meaning that the magnesium nitride reaction wouldn't last long), simply because it goes via the liquid-gas transition..... water, with burning coal, for instance, is very effective in extinguishing it, because of the above and because it can seep into the finest cracks, reducing flame temperature.
Anyway... I wouldn't use N2 nonetheless...when sand is infinitely cheaper and safer.

[Edited on 25-2-2005 by chemoleo]

Eclectic - 25-2-2005 at 20:36

Alumina might be the most effective inexpensive material. Magnesium will strip oxygen from silica, CaCO3, and Ca(OH)2.
CaO, and MgO would work, as would MgCl2.

Mr. Wizard - 25-2-2005 at 20:37

The recommended agent is dry salt, NaCl, or graphite to cover the burning metal. Often it does not cool the metal, but just slows the rate of burning until the material can cool, be moved, or separated from any exposures. Emphasis on dry! Small grains slow the air to the molten metal surface, and can actually put out smaller fires.

JohnWW - 25-2-2005 at 20:44

Magnesium burns in nitrogen to form the nitride, Mg3N2.

Eclectic - 25-2-2005 at 21:01

Sodium vapors might be given off if using salt on a hot burning magnesium fire. It would probably go out, but I wouldn't want to be anywhere near it!
:o

uber luminal - 26-2-2005 at 00:34

the point of liquid nitrogen is not to add Nitrogen. The point is to add something that is really cold. cold enough to transfer enough heat to prevent the reaction from continuing. this works very well. its not practical though, i mean who keeps liquid nitro around for the chance of fires.

I work at a US DOE facility. guess what you see in every room, and ever 600 or so feet, in the hallways... a big red barrel of Ca(OH)2. I would say that the govt. would probably have chosen the cheapest and most effective material, but given that we know the US govt. never does anything cheap...

but you get the idea that at least its a good chemical for putting out fires.

unionised - 3-3-2005 at 12:33

Is it just me who wonders about
Ca(OH)2 --> CaO + H2O
and
Mg+ H2O __> H2 + MgO
?
On a good day I might worry about it picking up CO2 from the air too.

Twospoons - 3-3-2005 at 14:30

Liquid nitrogen is useless for this sort of cooling. Non-contact boiling puts a nice insulating layer of gaseous N2 between the heat source and the liquid. It insulates so well you can stick your finger in liquid N2 for a couple of seconds, with only slight cooling ( I've done it myself), and you finger is only at 30C!

neutrino - 3-3-2005 at 15:32

I’ve heard that you can also keep it on your tongue for a while (I think this works because the tongue is one of the warmest parts of the body).

Anyway, how much would the fact that the MgO on the burning Mg is a powder affect this?

Eclectic - 3-3-2005 at 16:03

It depends on the density of the powder, dense granular MgO would smother the fire, light fluffy MgO probably wouldn't work so well. Also it will pick up water and CO2 from the air. I'd keep a bucket of fine granular alumina/corundum sand/grit around if I was worried about a Mg fire. It should be available from sandblaster suppliers at a reasonable price. SiC would also work, but at a higher price.

uber luminal - 3-3-2005 at 21:49

Quote:

Liquid nitrogen is useless for this sort of cooling. Non-contact boiling puts a nice insulating layer of gaseous N2 between the heat source and the liquid. It insulates so well you can stick your finger in liquid N2 for a couple of seconds, with only slight cooling ( I've done it myself), and you finger is only at 30C!


Have you ever tried to put out a fire this way? You seem to be confused about your finger, and a mulch of 1200C(at the surface) metal/metal oxide. One of the two has more energy associated with it. the other is your finger.

On a dumb side note, my old school had a science teacher that would swig liquid nitr. in his mouth and spit it out in a loud foom! I later heard he was having major problems with all of his teeth.

unionised, your totally right about the ca(oh)2. I looked at your post and felt puzzled. so I went and checked our red barrels today, and they say not to use on Mg fires... (but for other metals its ok? that doesnt make sense. We work with other metals that are just as reactive...) The list says to use the tan buckets, which have what looks like good ole' SiO2.

The thing is, like Mr.Wizard was saying, the fire keeps burning under whatever you smother it with. The only thing I have seen take it out completely is the liquid nitrogen. (assuming enough is added to stop the rxn, as well as take away the remaining heat as fast as the solid Mg will alow it.)

[Edited on 4-3-2005 by uber luminal]

Magpie - 10-1-2006 at 21:38

Here's a fun video showing why you can't use a CO2 fire extinguisher on a magnesium fire. It takes some time (10-15 minutes for me) to watch but I thought worth it. ;)

http://cgi.ebay.com/Magnesium-Ribbon-Shreds-Turnings_W0QQite...


Edit: It ran much faster the 2nd & 3rd time I watched it. It's great to watch mad scientists in action!

Note: You have to give the video a few seconds to load below the eBay listing.

[Edited on 11-1-2006 by Magpie]

[Edited on 11-1-2006 by Magpie]

Doesn't that look like a father-son team? It warms my heart to see this family quality time. :D

[Edited on 11-1-2006 by Magpie]

Fleaker - 11-1-2006 at 16:06

LOL! <Magpie...


As far as sand goes, magnesium will burn in that too, I melt it on the 10lb quantity pretty frequently and I can say that you will need a lot of sand...plus as it reacts with moisture in the air, the magnesium silicide yields silane gas which spontaneously combusts. We already discussed the fact that it burns in N2 gas and CO2 gas/solid/liquid, but if I had some burning and needed to put it out immediately, I'd go with some sort of heavier-than-air noble gas.

gm137 - 29-4-2007 at 04:46

In the case of small quantities of magnesium, covering the metal with sand generally works well; for larger amounts, I have a graphite-based dry chemical extinguisher. There are normally really expensive, but army / navy surplus stores often carry this type quite cheaply (they're used to fight fires involving magnuesium alloy aircraft parts). Only worth getting if you do a lot of work with reactive metals.