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Warning! Warning! Warning!!! Thermite


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This is another thread that I started on that other Forum.  Because of the recent threads posted here recently about Poison Gases  think that this one needs to be a Sticky here, along with the ones regarding the Poison Gases.

Warning, Warning, Warning Explosive mixture

While I was at Fred Rowe's house back in May, we were discussing grinding various materials.I commented,

"NEVER, EVER GRIND STEEL AND ALUMINUM ON THE SAME MACHINE OR USE THE SAME DUST COLLECTION SYSTEM".

This also applies to wood or other handle material.

Steel filings and Aluminum filings are the two components of Thermite, and very powerful explosive.

Google Thermite and you will come up with bunches of hits.

Here we are not trying to make Thermite, we are trying NOT to make Thermite.

Several years ago I saw an article in one of my Blacksmithing Newsletters where a blacksmith had been grinding steel. Later his son came in and use his grinder to grind some aluminum. The next day the blacksmith started using his grinder again and was engulfed in a ball of flame. There were pictures of him in the article. Both hands and arms as well as his chest and face received 3rd degree burns. It is surprising how little steel filings and aluminum filings it takes to make a very violent explosion or very hot fire.

In April at the Batson Blade Symposium Dan Johnson of Steven Bader Company was talking about how they had advised a customer how to set up his dust collection system, which included directions about spark arresters, and distance from the grinder for the collection container and not to mix products. The customer took the cheap way and placed the container close to the grinder and mixed materials. The thermite exploded, leveled the concrete building and killed several workers. Wound up that it was not the cheaper way to do it.

Not only steel and aluminum should not be mixed, wood and other products also. Hot sparks from steel and wood dust can make a very mean fire and sometimes explosions.

Be careful and don't make Thermite in your shop! 

Warning, Warning, Warning Explosive mixture
 
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Steel filings and aluminum is not chemically sufficient to set up a thermite reaction. The mixture's constituents are powdered aluminum and red iron oxide (Fe2O3). Easy enough as iron powder or filings readily rust and we get Fe2O3. The reaction requires a very hot flame to get it started. Once started stand back and shield your eyes. The heat generated is 8,000 degrees F. Magnesium ribbon will start it. Put a few ounces on the hood of a car ignite it and watch it burn through the hood then the engine block and then through anything underneath it and leave a puddle of molten iron on the tarmac. Many wood workers have been familiarized with this  problem Usually the aluminum sticks to the grinding wheel and someone later  grinds rusty steel, and then whoosh.   Cheers,   SLAG.

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Thermite isn't quite that easy. However something just as dangerous is. A dust comp full of aluminum and wood dust that gets hit by steel sparks makes for a pretty serious fire. Search class D fire.

Aluminum is not only a useful structural metal but makes for much more effective rocket fuels, incendiary devices, etc. anything that burns can be made hotter with the addition of aluminum from saw dust, shavings or powder. The finer the faster just like most chemical reactions.

What's even better is how easy it is to light and how HARD it is to put out. Without enough of the right kind of extinguishers burying it in sand is at least a way to keep it from spreading. One of the really nasty things about an aluminum fire is how hot it is and how it will cause other compounds to break down often releasing enough oxy to keep it going. This is why you do NOT put water on a class D, metal, fire. They're hot enough to break water down into hydrogen and oxygen which then burn again only MORE.

Nasty things Class D fires.

Frosty The Lucky.

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I am not sure that a thermite reaction would have leveled a building, as it is highly exothermic but not particularly explosive. However, a dust explosion certainly would have (just look up thermobaric explosives). 

I once experienced a very small one while working as a gopher at a local machine shop the summer after high school. While sanding stainless steel tubes with a belt sander on a lathe, I used compressed air to blow off previously accumulated (unknown composition)  metal dust on the lathe just as I hit the power switch. The spark ignited some of the dust and left me with a little burn on my hand and arm and much improved wisdom. 

Dad was a work lead at a feed plant, and got thrown 30+ feet when the dust in a grain elevator lit off. 

Any flammable powder mixed with air can cause a devastating explosion. Coincidentally, almost anything that we grind fits in this description. Be safe, and keep a clean work area (in addition to the advice above from others). Just don't clear dust with compressed air! :blink:

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Mr. Frosty The allies, during World War Two, discovered that powdered aluminum added to the explosives, in bombs, boosted the shattering power by about 40%. (brissance is the term for that power) The aluminum effect was noticed and put to use in 1943. Today aluminum flock is added to blasting explosives to increase their effectiveness. (that includes slurry explosives such as ANFO, etc).

Any finely divided "fuel" mixed with a chemical oxidizer can explode. The mixture is called a Sprengel sxplosive. Examples include a finely divided flour and air mixture plus a spark in a grain elevator, can blow it to pieces. (several decades back there was an average of about 3 grain elevator blasts per year, in North America) Finely divided coal dust mixed with just the right amount of air has resulted in mine explosions and fires. Ethylene gas (or other liquid short chain hydrocarbon) mixed in the right proportion with air and ignited at the optimal time for such mixing will result in a fuel air explosion. (similarly, hyperbaric explosives work using the same principle).

Incidentally, aluminum fires are not only very hot but give off poisonous fumes. why they built the Bradley armored personnel carriers from aluminum intrigues me. Any R.P G. could turn the vehicle into a funeral pyre

We may be getting off topic for this blacksmithing site.    Cheers,    SLAG.

Edited by SLAG
clarification, & adding information.
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My great-grandfather operated the "Lightfoot" grist mill, on the Robinson River in Culpepper County, Virginia.

Some of my earliest memories are of playing around that mill, and I clearly recall the abundance of "no smoking" signs, warning about the dangers of dust explosions.

As a child, the idea of dust "exploding" seemed far-fetched, but the adults took it very seriously.

Flash-Forward to the late 1970's .....

A "dry" bearing, supporting the end of a large diameter shaft in a printing machine, has pounded itself into a pile of dust in the bottom of the side cover of the machine.

The side cover was about 6' square and 18" deep, fabricated from 1/4 inch steel plate.

My crew had removed the cover to replace the bearing, and the decision was made to cut a service window into the cover, to facilitate future lubrication of that "problem" bearing.

( Poorly designed, imported junk machine.  :angry: )

We hauled the cover over to the shop, and, because the cover was so heavy and clumsy to handle, we left it, standing upright on the "Towmotor" forks, and cut the "service window" with an Acetylene torch.

All went well, and before long, the flame cutting was done, leaving lots of sparks, smoldering in the pile of powdered steel bearing.

No problems, ... No hazards, ... Just another job.

Until the cover slipped, and fell, ... hollow side down, ... onto the floor.

At that point, the pile of "powdered" bearing, and smoldering sparks from the torch, combined with a sufficient amount of air, in a confined space, ... and ... K A B O O M !

That 500-600 pound cover, instantly "levitated" to about waist high.

Forever dispelling any doubts I may have had, in regard to the potential power, ... and the likelihood, ... of dust explosions.

 

Unintended consequences of that sort, are the primary reason I disapprove of dust collection systems in general, ... and particularly on grinders.

 

.

 

 

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There is much valuable information coming out here.  At first blush some of it does not apply in the blacksmith shop, but if you think about it a little you realize how it does, or by extension makes us think of other issues we need to be concerned with.  Thanks all for your contributions.

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As a child in Ohio we used Magnesium/Aluminum turnings from a local plant to burn a stump.  There are a number of things mixed with powdered aluminum which will produce a violent reactions. 

This doesn't begin to cover all the assorted dusts like flour, wood, and, in Louisiana, sugar  that have produced catastrophic explosions.   Most of the members living in the Midwest will have stories of explosions in grain elevators.

As a child I amused my self with blowing powdered iron through a Bunsen burner flame to watch the sparks.   A little alter I discovered a way to make a fuse out of #0000 steel wool. The moral of the story is: if it will burn under any conditions when finely divided it will burn faster when mixed with air.

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Slag, they use aluminum on the Bradley because it's light and it works. They can survive a hit from an RPG, depending on the type of RPG and how it strikes. It also helps that crews actually get out of the darn thing to do their jobs, unlike some other countries...if it takes a round hard enough that you have to worry about irritating fumes from an aluminum fire, or it being hot enough to actually catch the aluminum on fire, the crew has probably already been killed by shrapnel and spalling. Kinda like worrying whether or not the lubricant on the ekg pads is a skin irritant during cardiac arrest.

Not the only oxidizer either, worked at a metal plant in alabama that worked with zirconium.  They would sometimes amuse themselves at lunch by setting down the wipe rags (used to catch fines on wire being drawn down) outside at lunch in the sun on a hot day and watching them catch fire. They had a fire one day in a scrap drum, and I'm not sure they ever did fix the hole in the roof...30 feet up.

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Mr. Special.   Thanks for the fascinating information. Burning aluminum is not just irritating but it is extremely poisonous. (as is the depleted uranium in kinetic energy armor piercing anti-tank rounds. (A.P.D.S.) ) Moral of this information, is, if you experience an aluminum fire quickly extinguish an aluminum fire or get the h..l out of the smithy. Such a situation would be very unlikely. Modern shaped charge munitions can penetrate up to 22 inches of hardened steel. Explosive reactive armor has been around for 25 to 30 years, long after the Bradley was initially adopted by the U.S. armed services. It is scheduled to be replaced soon. Another factoid for the I. F. I. fraternity, is that a thermite fire is not a common occurrence. In most such cases the grinding wheels had aluminum clogged surfaces.(often caked on). Grinding wheels should be subjected to regular wheel dressing sessions . A  clogged wheel does a very poor job at grinding, & the grinding time much longer.   Cheers     SLAG.

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Hmm. That's news to me.  Aluminum burns to create  aluminum oxides.  Those are some of the most stable (unreactive) and hard compounds around. A lot of grinding abrasives and most colored gem stones are comprised of aluminum oxides.  You may be right, but I haven't ever heard of that before.  Do you have any links to that info?  I don't want to dismiss the danger if it's there, but I'd prefer not to add things to the list of dangerous fumes if they aren't truly dangerous.

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Aluminum and most every metal I know of we're or anybody NOT in a gvt. lab is likely to come in contact with has to be pretty finely divided to burn in open air. Even reactive metals like Titanium and niobium have to be pretty fine shavings or have the help of corrosives or electricity to oxidize.

What this thread has to do with blacksmithing is as a warning to be careful of the powders and dusts we generate. Taking a hand file to metal will divide it finely enough to made it flammable. Provided ignition temperature is high enough.

I've never seen aluminum combust, even when the shop teacher demonstrated with a cutting torch and shot of straight oxy.

I don't know about you guys but I use a garage sale cake pan to catch cuttings under my cutoff band saw. I know from experimentation as a teen that red rust makes for poor thermite where black iron oxide is DeKind. It's still hard to light but not out of reach for a kid. The only way thermite CAN "explode" is improperly prepared, any explosion is from steam, not the thermite reaction. You MUST dry it in an oven @ 230f to remove hygroscopic moisture. After which it burns unspectacularly at least till it hits residual oil in the V8 engine's crank case and shoots jets of flaming oil. About 6oz. will go through the hood, and engine IF you can keep it in a close stream.

Mess with home brew thermite as kid, ME?

Accidental thermite is unlikely in a shop but a class D fire is a whole different matter and can be a hazard on lots of fronts from: burning the shop to the ground to poisonous byproducts, gasses, smoke and "ash". I believe the real warning that applies here is, "Don't get so involved worrying (thermite!!!) you ignore the trash barrel of oily lathe cuttings in the corner.

Frosty The Lucky.

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You aren't the only one Frosty.  I still make my own exploding targets and aluminum powder is a component.  I had never heard that the fumes from burning aluminum are poisonous and didn't know if I was misinformed and lucky or if information regarding the toxicity of burning aluminum had been incorrect/overstated on here.

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I've never heard of aluminum oxide being toxic but I try to stay out of smoke anyway. Including aluminum dust in the solid rocket fuel is what made Jato rockets work and is a major component of the SRBs on the shuttle and other rockets.

Handy stuff aluminum powder.

Frosty The Lucky.

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I can clearly remember 6th or 7th grade science class where the instructor taught us about dust explosions with a 1 gallon paint can with a hose into the bottom, some flour and a small candle. he'd blow into the hose to aerosolize the flour and the flame from the candle in the can would ignite it. We thought it was great in class as the explosion in the can with the lid on it made a great bang. He continued to do the demo with greater amounts of flour until he blew the lid clear up to the 8' over head lights and took out the bulbs. At that point we moved on to something else. LOL.

 

His was the same class where we made thermite as a class experiment. If I remember correctly the topic had to do with how many atoms of FeO3 you needed to react with Al so you ended up with Fe and Al2O3 after the experiment.  For the demo he had a steel plate suspended over 2 bricks and burned a hole thru the plate. Probably a REALLY good idea I didn't read this thread at that time or I'd have set fire to all sorts of things with a ready supply of powdered alum.

Could you see the mess something like this would cause in todays class rooms? He'd have the whole county locked down and probably end up on national TV in cuffs.

 

 

I've never really thought of thermite as "explosive", though I knew what it did and that the military used it for material demolition. I also never really thought about the dangers of grinding two dissimilar metals on the same machine. I do remember a buddy of mine burning up his delta bench sander when he used it to grind down and reshape the edges on a new magnesium trowel and then touched up the ends on some steel pins. he was lucky to get that out of the shop before he set fire to the whole place. At the time I was thinking it was more the fact that magnesium burns even in a solid state than the fact it was a dust reaction. I knew you could set fire to steel if the surface area to O2 was high enough and you added heat, like when you use a battery to set fire to steel wool.

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It's not the aluminum oxide that is that toxic. Other compounds created by the shaped charge are deadly. The contents and liquids in the tank (or A.P.C.) react with the molten aluminum and copper, this melange creates the toxic mess. I would not inhale any aluminum compounds nor fine dust, no matter how they are generated. Some aluminum comounds have been implicated (but not definitively proved) in neurodegenerative diseases.  (such as Alzheimers disease), etc.   I do not know of any blacksmith that forges in a Bradley. So let us all relax.   Cheers.    SLAG.

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While the concept of aluminum dust and rusted steel dust mixing in a dust collector is real the ignition thereof is unlikely at best. The addition of magnesium ribbon, sparklers WM etc as an ignition source is thankfully not common. That said the very purchase of powdered aluminum and ammonium nitrate will usually get you put on some form of watchlist.if you add that to the discussions about the pros/cons of fighting vehicle armor no matter how vauge they may be ?

Just a thought !

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The connection between aluminum and Alzheimer's was shown to be a mistake made in the testing. For years the labs doing the research used a test standard dye containing aluminum to stain brain and nerve tissues. Alzheimer's effected tissues retained the dye which then tested positive for high levels of aluminum. The connection is no longer in effect since they changed dye.

Frosty The Lucky.

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I would so forge in a Bradley.....wasn't for those pesky first sergeants. Ain't shape charges that have been killing them, mostly EFPs and oversized HME bombs....although saw a lot of aluminum oxide used to give em a boost. First sergeants also frown on Leyden jars, and electroplating in the trailers and swa huts...don't ask.  (did NOT get the joke of making a Baghdad battery in Baghdad.)

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