Let Burning Metals Lie

There’s not much you can do to put out a magnesium fire. Douse it with water or spray it with a fire extinguisher, and the results can even be explosive

By Theodore Gray Posted 06.11.2008 at 11:22 am 7 Comments

If you ever see a large industrial metal fire (yes, they happen) on the news, you may be surprised at what the firefighters do to extinguish it: nothing. Several metals, including lithium, sodium and magnesium, can burn easily, and from time to time large amounts catch fire in factories. But even heaps of burning metal need not cause immediate panic. They don’t blow up; instead they tend to build up ash that chokes off their oxygen supply, so they slowly burn out.

Up in Smoke: Magnesium burns slowly in air, but blowing a CO2 fire extinguisher at this pile of shavings set our equipment on fire. Mike Walker

But if you try to do something about a metal fire, you’ll probably only make it worse. For example, magnesium burns brighter immersed in carbon dioxide than it does in air. Blow a CO2 fire extinguisher at gently burning magnesium shavings, and the pile will suddenly burn much hotter and faster. (We actually set the photographer’s lights on fire when we took the top-left photo below—when we turned the fire extinguisher on the pile of shavings, it sent flaming magnesium blowing in all directions.)

In fact, magnesium reacts so well with CO2 that it will burn inside –109°F dry ice (the solid form of carbon dioxide). This jack-o’-lantern was made by lighting a handful of magnesium shavings stuffed into a hole carved in the back of a block of dry ice. It burned crazy bright for about a minute.
Water and foam are even worse on metal fires. If the metal is molten, the resulting steam explosion tends to fling it everywhere. What’s more, some hot metals can split water into oxygen and hydrogen, creating the likelihood of a major hydrogen gas explosion.

Cold Stare: The author carves a face on “Icebob Squarehead,” a jack-o’-lantern made of pure dry ice (solid carbon dioxide). Mike Walker

Even dry sand or salt, standard materials for putting out metal fires, can wreak havoc. In 1993, an industrial plant in Massachusetts had a sodium fire, which the local fire department tried to put out using salt stored for that purpose. Unfortunately, the salt turned out to be damp, and numerous firefighters were severely burned in the resulting hydrogen blast.

Next time there’s a sodium fire, the firefighters plan to do one simple thing: walk away. Metal fires are just too hot to handle.

ACHTUNG! Don’t try this at home. Burning metals are dangerous and unpredictable. Ordinary fire extinguishers can spread the fire or cause explosions.

Like what you see? For more Gray Matter, head topopsci.com/graymatter. And for Theodore Gray's one-of-a-kind periodic table poster, check out periodictable.com/posters

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7 Comments

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MadMechEng

06/11/08 at 7:45 pm

I am definitely doing that for next halloween. Pumpkins are boring unless they are being fired from cannons so dry ice and magnesium and much more fun.

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ajhalls

from Mesa, AZ

06/11/08 at 9:57 pm

Reminds me of what happened when I called to tell the fire department I had 300 lbs of sodium in my garage :) They were nice, but naturally concerned and limited me to 125 lbs. Best to have a Class D fire extinguisher on hand if you are at risk for a metal fire, you might be able to catch it when it is small enough to put out before you loose the building.

www.unrestrictedchemicals.com

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sponge7

06/11/08 at 11:45 pm

what happens when they dont know the cause of the fire and they just rush in thinking they can save it, or put it out? has some one made fume testers to see what exactly is all burning in the house?
this article is very cool

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sponge7

06/11/08 at 11:45 pm

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STRANGELoVeDr

from breckenridger, co

06/13/08 at 2:10 am

Why are Hummvee chassis's made of magnesium? Ya its light but man that stuff burns FAST!

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meyaht

07/16/09 at 1:55 pm

i hate to post on a dead topic, but its mainly only magnesium shavings and dust that are a threat. i don't know why, but i do know from practical experience involving actual magnesium wheels. someone was grinding something for a different size valve stem, opening up a hole, and somehow there was ignition, only the dust caught, the wheel did not.

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romaniamac1

10/21/09 at 4:34 am

Thank you , that helped me a lot

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