possible cause of shop fire

H

Hmathews

Joined
Feb 22, 2005
Messages
1,004
I read a thread on another forum (that became a sticky) about grinding aluminum and steel on the same grinder and causing an accidental thermite fire because of the accumulation of aluminum dust being hit with hot steel sparks. It evidently starts a fire that is extremely hot and almost impossible to put out. Water just provides oxygen and hydrogen and makes it that much worse. I've never done it or personally known of anyone that has, but if it is even remotely possible, it would sure be worth avoiding. Maybe someone that is more familiar with the process of creating this type of disaster and what caused it will chime in. Its been too many years since my chemestry classes...

I don't know if this has been mentioned on the makers forum before or not but I've not seen it if it has and thought it was worth bringing up.

We have a new rule at Twin Blades... No grinding Aluminum at all!
 
Metal fires are Class D fires and need special extinguishers...but it is cheap to get a refill in a standard 5 or 10 pound ABC extinguisher with D powder
 
The chemical reaction is between Iron Oxide (usually rust,Fe2O3 if I remember correctly) and Aluminum. It requires an incredibly hot ignition source though, usually in the form of a strip of Magnesium. I'm not sure whether the sparks from a grinder are really hot enough for that, and I don't mean that as I don't think they are, I literally mean I don't know.

Water provides the electrical connection for the rusting of the iron to occur readily, so that would certainly increase the amount of rust that you have. I'm fairly certain that water wouldn't speed up the reaction any further since the water would evaporate and remain H20 as opposed to splitting into hydrogen and oxygen.

It's a pretty cool reaction to watch, although I doubt you really want to watch it in your shop.
 
Metal fires use salt [NaCl ] which melts and excludes oxygen or sand which also excludes oxygen.We used to have at home a red painted bucket with a rounded bottom filled with sand .This from the WWII days and was there to put out incindiery bombs which were magnesium.
Make sure you clean your work areas often !
 
Destraal said:
The chemical reaction is between Iron Oxide (usually rust,Fe2O3 if I remember correctly) and Aluminum. It requires an incredibly hot ignition source though, usually in the form of a strip of Magnesium. I'm not sure whether the sparks from a grinder are really hot enough for that, and I don't mean that as I don't think they are, I literally mean I don't know.

Water provides the electrical connection for the rusting of the iron to occur readily, so that would certainly increase the amount of rust that you have. I'm fairly certain that water wouldn't speed up the reaction any further since the water would evaporate and remain H20 as opposed to splitting into hydrogen and oxygen.

It's a pretty cool reaction to watch, although I doubt you really want to watch it in your shop.
Click to expand...

this is correct...thermite is a mix of Iron oxide (rust) and aluminum...

and it burns so hot that if you were to pour water in it, it would immediately vaporize, separating the oxygen an hydrogen in the process, and make things a whole heck of alot worse.


also, pure aluminum in and of itself is highly explosive, so that is what would have caused that dept. of energy thing that artmichalek posted a link to.

also, many things when in powder form (specifically while in the air), are extremely flammable/explosive.

Thermite v. Ice
 
stealthchaser13 said:
and it burns so hot that if you were to pour water in it, it would immediately vaporize, separating the oxygen an hydrogen in the process, and make things a whole heck of alot worse.
Click to expand...
While it is possible to thermally separate Oxygen and Hydrogen, it's much more likely that it will vaporize before reaching the necessary temperatures. Now this would still make an explosion of sorts, but not because of exploding Hydrogen (which would take it straight back to water again anyways, for the most part). When going from liquid to gas there's a drastic increase in volume, which is what causes the explosion. So the expanding gas throws the thermite all over the place making it look like a fiery explosion, when in reality it's burning stuff being thrown by a separate explosion. Think putting a dry ice bomb in a camp fire, obviously the CO2 isn't burning, but fire still goes everywhere.

Regardless as to whether there's splitting of the water molecules (molecules, not atoms), the water would vaporize first, which causes the observed effect. Water turns from liquid to gas at 212 F, at 4000 F about 3% of all the water molecules would've dissociated.

http://en.wikipedia.org/wiki/Water_splitting
http://en.wikipedia.org/wiki/Steam_explosion
 
Last edited:
I am by no means an expert by my understanding is as follows:

Aluminum powder was a revolution in Rocketry, they add it to solid fuels and see a SIGNIFICANT increase in the energy of the reaction, probably something similar here, even without the thermite connection.

I also remember a bit of an issue with one of our (USA's) troop transports that sported aluminum armor plate, and would have really big problems if hit with any kind of warhead (very nasty fumes and fires i think).

Basic point is that Aluminum can be nasty when you're talking about fire.

-- Adam
 
Iron Oxide + Aluminum = Thermite.
I've seen sparks from the grinder land in the iron dust heap under the wheel and ignite it with an ember that spread throug the powder as if it was wood shavings (it was PURE iron powder).
Iron dust is (was) used as tinder to light a fire with flint and steel.
I use it mixed with wood shavings and charred paper in this way to start my forge (yes, I like to start my coal forge with flint and steel! :D).
Add some titanium and you've got auto-igniting thermite.
Nasty.

And, correct, you NEVER try to extinguish a fire with melting metal in it (or a thermite fire) using water. The water separates into hydrogen and oxygen and
1) H and O recombine in H-O combustion. Scary.
2) steel starts to BURN. SCARIER! :eek:
True, most water just turn into vapor, but it doesn't require ALL water to turn into H and O. It just requires SOME water to do it.
You have to use oxygen depriving stuff to extinguish such a fire.
 
You guys share a lot of useful information i can tell you this flash powder is made form very fine alumimum dust and an oxidizer one is potasium perchlorate.It burns fast and hot and bright white. If contained it explodes depending on the amount as little as 2 grams can leave you without a hand.J<D>
 
I'm no chemist but it's worth noting that all sorts of fun things in a typical shop can burn very quickly and when you least expect it. In addition to "powdered" metals and woods, let's not forget that oil rags can combust hours after use. Linseed oil is known for this.

IIRC the safest way to store oily rags is in a sealed metal can filled with water. This prevents them getting the air they need to oxidize, heat up and go "poof".
 
it's not about the heat separating the hydrogen from the oxygen, it's about the aluminum being more attractive to the oxygen than the hydrogen at that moment

-Page
 
I spent time this weekend at a rally [www.rallynewyork.com] with a team of race fire-rescue guys. While most rallys depend on local fire-rescue groups these fellows go to many SCCA events .Their pickup truck had eight fire extinguishers , jaws of life , sawz-all .They are trained in rescue and one was also medical trained .
The fire extinguishers I was not familiar with .They were made by www.firefreeze.com .They swore by these and said they never needed more than one to put out a car fire .A water based system that would put out fires with various things --including metal such as magnesium and aluminum !!! Hydrocarbons like oil included. This might be a good solution for knifemakers.
 
Ha! It happened to me and I have posted it several times on the forum. I cleaned up some aluminum signs for my wife and was grinding a blade a few days later when this unbelievable white flash started up in my water trough (that had no water in it at the time... oops) It burned straight through the bottom of a stainless steel trough and damaged my concrete floor. It lasted less than a minute. After a few minutes on the interwebz, I realized I had made thermite. Funny thing is, I have tried to reproduce it with no luck. You must need exact ratios or something.

Be careful.... it is real.

Also...

Make sure you have access to all the nooks-n-crannies around your forging area. I have catapulted hot steel 10ft away from the anvil and behind the tool bench against the wall. I had to pour a bucket of water behind it because the plywood backing of the bench when to the ground. I cut a 6" clearance from the floor and keep it free of clutter, now.

Rick
 
You must log in or register to reply here.
Back
Top