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View Full Version : Semi OT - A Cool Demonstration; Why Magnesium Fires are so Dangerous



Fasttrack
05-21-2013, 07:48 AM
Some time ago, there was a post on here about a machine shop accident that could have been disastrous but was turned around by a quick thinking employee. There was a lathe that had been turning magnesium with a chip tray full of turnings. Something went amiss and the magnesium turnings caught fire. Luckily, they were able to grab up the lathe with a forklift and carry it outside on a gravel pad and let it burn out with no damage to the shop. The lathe was not so fortunate... ;)

As most of us know, you cannot use water to extinguish or cool a magnesium fire because of it will actually disassociate the water as it burns, producing hydrogen gas - which is also flammable! What may be less well known is that it burns in both nitrogen and carbon dioxide atmospheres so CO2 extinguishers have no effect. The only practical way to fight a magnesium fire is to bury it in dry sand or let it run its course.

Here's a cool video I stumbled across of burning magnesium shavings in a block of dry ice. The result of the flames through the ice is pretty cool.

http://www.youtube.com/watch?v=_xCbal2YyaE

firbikrhd1
05-21-2013, 08:12 AM
Magnesium fires can be extinguished in two ways other than those you have mentioned. There is an extinguishing agent, Met-L-X, a powder that will extinguish magnesium fires. Another method uses water under about 100 PSI from a straight stream nozzle to accomplish several things. Initially it accelerates the burning causing the magnesium to form a molten puddle, second it cools the exposures and lastly it blows the molten/burning magnesium away from the remaining solid not yet involved magnesium basically removing the heat from the fuel and ultimately extinguishing the fire. As this takes place there is quite a fireworks display and it can be an exciting experience for new firefighters the first time they attempt it.
I have used this method many times on vehicles to extinguish magnesium fires in the various components of newer cars.

Fasttrack
05-21-2013, 09:09 AM
Magnesium fires can be extinguished in two ways other than those you have mentioned. There is an extinguishing agent, Met-L-X, a powder that will extinguish magnesium fires. Another method uses water under about 100 PSI from a straight stream nozzle to accomplish several things. Initially it accelerates the burning causing the magnesium to form a molten puddle, second it cools the exposures and lastly it blows the molten/burning magnesium away from the remaining solid not yet involved magnesium basically removing the heat from the fuel and ultimately extinguishing the fire. As this takes place there is quite a fireworks display and it can be an exciting experience for new firefighters the first time they attempt it.
I have used this method many times on vehicles to extinguish magnesium fires in the various components of newer cars.


I had heard of Met-L-X but didn't consider it practical for shop use because of the cost. The water technique on the other hand ... WOW! I bet that would be cool to watch. Thanks for sharing your professional knowledge. My hat goes off to the firefighters out there. I've had the pleasure of working with several as a pyrotechnician and I'm grateful for all you do!

Dr Stan
05-21-2013, 09:15 AM
Magnesium fires can be extinguished in two ways other than those you have mentioned. There is an extinguishing agent, Met-L-X, a powder that will extinguish magnesium fires. Another method uses water under about 100 PSI from a straight stream nozzle to accomplish several things. Initially it accelerates the burning causing the magnesium to form a molten puddle, second it cools the exposures and lastly it blows the molten/burning magnesium away from the remaining solid not yet involved magnesium basically removing the heat from the fuel and ultimately extinguishing the fire. As this takes place there is quite a fireworks display and it can be an exciting experience for new firefighters the first time they attempt it.
I have used this method many times on vehicles to extinguish magnesium fires in the various components of newer cars.

Glad to hear new products and techniques have been developed for class D fires. When I went to the Navy's firefighting schools (1 a year for 4 years) we were taught to never use water but isolate them and let it burn out, like what the people did with the lathe. I used this when some students accidentally added magnesium to a crucible when we were casting aluminum. It kinda gets your heart started when you look over and a large "Roman candle" is going off in your hot metals lab. :eek:

A.K. Boomer
05-21-2013, 09:18 AM
I used to burn mag two different ways - one was to fill a beer can full of it and light it at the opening - let it spread internally and then toss it in our creek out back, spectacular for sure,,,


the other was to fill a coffee can full - light the top, let it get up a good head of depth on it, about 1/4 or 1/3 ,then stand back as far as you can with a garden hose and use your thumb to create a nozzle, get it dialed to where you have a good stream going with perfect distance and all's you got's to do is move over 5 feet sideways to make your connection, it's unreal, it's spectacular even in broad daylight... at night it's Mag-nificent... but you might want to wear sunglasses, so hot you will end up with about half the steel coffee can you started with...

To tell you the truth I think if I had some kinda mag fire in a shop like FS stated id have to look at the situation,,, Actually - besides the intense heat Mag fires are pretty docile - till you add water that is, depending on the situation and the lathe design and such I could see putting on some welding leathers and helmet and just going in with a rake and slowly pulling the majority of it out of the chip pan and onto the cement floor,

if you can achieve this your pretty much home free,,, then either let it burn out there or drag the majority of that outside,,,

just like any solid form fuel the more you separate it the more it loses the ability to transfer and keep burning - small mag particles sometimes won't even survive on their own and will burn out before they consume all their usable potential,
You will however pay an initial price when stirring it up as you expose hot spots and add oxygen, hence the protective measures (esp. as it's dropping to the floor)...

flylo
05-21-2013, 09:30 AM
In high school we used burn it on purpose everytime we had a sub & when my kids were scouts we'd bring VW cases to the campouts & show the kids metal burning.

A.K. Boomer
05-21-2013, 09:39 AM
yes that's where I got mine - VW and Porsche engine cases,

the beer can method I mentioned was cool cuz it would sink 5 ft down and put on one hell of a show as it continues to burn under water, its so hot it sets up a steam vapor barrier around it...

bborr01
05-21-2013, 09:41 AM
just going in with a rake and slowly pulling the majority of it out of the chip pan and onto the cement floor,

if you can achieve this your pretty much home free,,, .

Boomer,

Don't ever burn magnesium on a cement floor either. When I was an apprentice many years ago I had some magnesium to machine. One of the journeymen told me that it would burn. Of course, I had to bring some home and try burning it. I put a little pile of it on the concrete out front of my shop and lit it. After about a minute or so, there was an explosion about like a centerfire handgun. The magnesium was gone and there was/is a crater in the concrete where it exploded. Probably thermal expansion or something like that. That was the last time I burnt magnesium.

Brian

A.K. Boomer
05-21-2013, 09:49 AM
Good point - just like you don't want to use river rocks for campfires or they could take someones head off - cement is very porous but mag is so hot and it happens so quick the steam does not have time to escape,

you can drop it one the floor and then just drag it outside in the dirt - Or - You could drop it on the floor and "git" - if it means saving your lathe I would rather fill in a pock mark in the cement and patch a hole in the ceiling :p

Fasttrack
05-21-2013, 09:50 AM
Boomer,

Don't ever burn magnesium on a cement floor either. When I was an apprentice many years ago I had some magnesium to machine. One of the journeymen told me that it would burn. Of course, I had to bring some home and try burning it. I put a little pile of it on the concrete out front of my shop and lit it. After about a minute or so, there was an explosion about like a centerfire handgun. The magnesium was gone and there was/is a crater in the concrete where it exploded. Probably thermal expansion or something like that. That was the last time I burnt magnesium.

Brian


That is also why they tell you not to torch near concrete. There is some amount of moisture trapped in the concrete and when you heat it, it turns to steam. Just welding or torching close to a concrete floor can cause this on a smaller scale. Small chips will pop off the surface where ever molten metal hits it. Apart from tearing up the floor, it also has the potential to splatter you with molten metal! I will admit to being a victim on more than one occasion :)

A.K. Boomer
05-21-2013, 10:47 AM
I think the key to working with the stuff is simple, frequent cleanings, as in never letting any substantial amount build up in the first place...

Georgineer
05-21-2013, 11:05 AM
To tell you the truth I think if I had some kinda mag fire in a shop like FS stated id have to look at the situation,,,

Remember to use a blue filter to protect your eyes...

George

EVguru
05-21-2013, 11:20 AM
A forgotten hazard is a linisher.

Nice pile of rusted steel dust + Aluminium dust + spark = flash burns.

A.K. Boomer
05-21-2013, 11:22 AM
for sure that's one of the reasons I said to grab a welding helmet - that and because it gives your face protection, an auto-darkening welding helmet would allow you to see but as the chips fell to the floor it would go off into darkening mode,,,

if you keep things clean this situation should never occur in the first place, but if you don't and it does it just depends on a bunch of other things,

Im not saying people should resort to this every time, Im just saying for me and what I know about the stuff it could very well be an option VS letting my machine and house burn down...

bobw53
05-21-2013, 11:28 AM
My Mag experiences, besides burning the mag strips in chem class.

All fires on purpose. Back in the day had to machine these stupid mag castings, going at it kind of wussy mostly with HSS, tiny chips and fines, that stuff,
in a piece of paper would spark up like nothing.

Had the same job come back around recently... several times, and since I'm older and wiser, better tools, bigger chips. Couldn't get this crap to light
for anything... Hmmm lets wash the coolant residue off and let it dry out real good. Hey it lights.... sort of... even with a torch, hit it with water...
pretty spectacular.

So the size of the chips seem to matter, surface area to volume I'd guess.

We have a 2" bar of magnesium that came from some job a while ago. Our exterminator asked if he could have a little slice... He takes a couple of
little shavings off with his pocket knife to get his camp fires going fast.

Titanium.... 2.5" x 3.5" plate/bar, sawing at a 45 degree angle on the little 7x12. The little saw lives outside because it doesn't rain here, so its on
an extension cord, which was apparently damaged. And Ti on a little saw makes nice fluffy birds nests of chips. Like steel wool but lighter and fluffier.
So I'm doing my thing in the shop, the saw is doing its thing outside one of the rollup doors and I BOOM, and a big giant puff of smoke. Go out and there
are little piles of Ti swarf burning all over the place on the ground and one big pile, and a big black hole in the extension cord.

Take that lesson for what its worth. Don't leave the extension cord under the saw.

A.K. Boomer
05-21-2013, 11:48 AM
Iv always wondered about the energy ratio involved here that has to do with FT's OP,,,

I mean this stuff burns so hot it makes water a fuel due to it making usable hydrogen,,, damn, so right there we have this one fuel source (although granted very expensive) enable to separate and ignite another that's basically free. what is the BTU ratio there when water is added? when you see the effect "go off" in front of you it looks like the water (hydrogen) is adding at least ten fold,,, and what if it was refined somehow and other cheaper materials added - just makes you wonder that's all...

Black_Moons
05-21-2013, 12:01 PM
Sadly magnesium does not 'liberate' any energy from water.
It simply seperates it due to intense heat that then recombines explosively. Heating the water will require energy, and basicly all you are doing is asorbing energy over a period of time (Heat) and turning it into violent explosions (sudden heat). You still end up with the same amount of water you started off with.

Fasttrack
05-21-2013, 12:04 PM
Sadly magnesium does not 'liberate' any energy from water.
It simply seperates it due to intense heat that then recombines explosively. Heating the water will require energy, and basicly all you are doing is asorbing energy over a period of time (Heat) and turning it into violent explosions (sudden heat). You still end up with the same amount of water you started off with.

Damn conservation of energy. :p

Jaakko Fagerlund
05-21-2013, 12:36 PM
Haven't had to put out a magnesium fire, but knowing that it likes oxygen, carbon dioxide and nitrogen...then how it reacts to argon or helium? Okay, they would be extremely expensive to use as a firefighting stuff, but those are the gases usually around in a metal shop.

A.K. Boomer
05-21-2013, 12:58 PM
Damn conservation of energy. :p


there's always a catch ya know?

vincemulhollon
05-21-2013, 01:31 PM
Helium's not going to work unless the fire is in the ceiling. Argon would work.
The intense heat means intense convection currents means its going to take a huge amount to keep the fire out until the metal cools below ignition point. Its not going to be practical. Like blowing enough argon onto the fire will mostly just spatter it everywhere making it even worse.

I would have to think if there are any organic compounds that would be non-reactive with white hot Mg and not toxic... none?

Fasttrack
05-21-2013, 01:34 PM
Haven't had to put out a magnesium fire, but knowing that it likes oxygen, carbon dioxide and nitrogen...then how it reacts to argon or helium? Okay, they would be extremely expensive to use as a firefighting stuff, but those are the gases usually around in a metal shop.

I don't know but I wonder how well even something heavy like pure argon would work. The magnesium burns so hot that I would think the draft would be quite strong. I don't think helium would stand a chance (unless, of course, you fill the entire room with one of these gases). But just streaming some gas out of your welding hose probably won't help much.

vincemulhollon
05-21-2013, 01:44 PM
gases usually around in a metal shop.

Cutting torch oxy? Yes sounds insane at first glance, but think about it. The problem isn't the Mg turnings burning or the total amount of heat being given off in the shop (well, hopefully, anyway). The problem is the heat is dumped into your precision scraped lathe ways and lathe paint. So if you blew it off the lathe somewhere harmless (hopefully the dirt in the backyard rather than your oily rag collection) then the lathe won't be hurt because nothing will be burning on it. And oxy would make it burn as fast as iron sparks off a grinder rather than hitting the ground burning. As long as you don't care if the dirt is on fire, you'd be OK.

Open question if this would be more or less dangerous. Usually you've only got enough time to run, not fool around, so its probably irrelevant.

One idea not discussed is just to burn it as its made. One chip burning is mostly harmless, you lose the plant when a whole 55 gallon drum goes up at once. So if you could find a way to continuously shovel / blow / dump into a charcoal grill you'd be fine as long as it burns continuously.... more or less. If it stops burning, even for an instant, and a pile builds up and then goes off, then you've got problems.

One thing to consider about Mg disposal is you don't get only MgO you get some Magnesium nitride and that plus water (inevitable, in your nose if not the environment) gives you ammonia. Which is going to be stinky. So if you ever wondered why Mg fire starter fires are sometimes stinky, well, now you know. So continuous disposal might have ammonia issues unless you use pure O2.

Dr Stan
05-21-2013, 02:19 PM
Nice pile of rusted steel dust + Aluminium dust + spark = flash burns.

A.K.A. thermite

A.K. Boomer
05-21-2013, 02:40 PM
Question for the rapid oxidation guru's, is there any added oxygen to a magnesium fire when water is thrown upon it? right or wrong I was told yes a long time ago...

bob_s
05-21-2013, 08:47 PM
My friend's dad was in a nazi forced labor camp machining magnesium parts for F-109's. He said that they dealt with fires by throwing heaps of iron cuttings onto the parts.

After he intentionally crashed one of the large lathes he spent the rest of the war in Auschwitz.