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Danger, Thermite and dust explosions

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9.9K views 17 replies 12 participants last post by  Plant welder  
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#1 ·
I was just reading about this on another site and figured it might pay to discuss the subject here. The thread itself is worth reading as there are a number of comments on the subject too numerous to copy and paste directly here. Here is the link to the original thread.

http://www.iforgeiron.com/topic/46297-warning-warning-warning-thermite/

Here's part of Wayne Coe's original post on the topic.

"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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Discussion starter · #4 ·
Gamble note that when you plasma cut you are oxidizing the material. So you don't have alum dust, you have alum oxide. Alum oxide has already reacted to the O2 in the cutting stream. In fact O2 in the plasma stream helps the cuts by increasing temps from what I understand.

I'm sure like many things conditions have to be "just right", but dust explosions are a very regular event. Coal dust and grain dust frequently cause explosions, and just about any dust that can burn, sawdust, steel or alum dust can explode if you get the air/ fuel ratio correct and have some sort of ignition source. Simply a pile of dust on the floor won't explode. Blow it all around with a blow gun and you can demolish a building.


You've probably been lucky enough that either you haven't had a good ignition source, or that the air/dust particle ratio wasn't right if you had something hot enough to cause this.
 
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Discussion starter · #7 ·
Louie I think the point is if you grind steel frequently and don't clean regularly ( who does), natural moisture in the air will quickly turn steel grindings to rust naturally. That solves the iron oxide issue, I know if you use water as a coolant in a saw a pile of rusty saw dust is almost a give if the pan dries out. Cut alum and steel back and forth and you make up an alum/rust mixture pretty easily.

As far as heat, if you get enough surface area exposed to O2, it's easy to burn steel. Steel wool and a battery can easily prove this. Take some steel dust and blow it over an open flame and watch the sparks.


Yes this isn't something that is going to happen every day. However it can be a potential danger in the shop you need to be aware of. How many of us take a blow gun to things to dust them off? Running a space heater in the garage because it's winter and it's cold out? Is someone else cutting with the OA torch? The comment on IFI in the link about the steel plate that had been OA cut and the bearing dust shows that it can happen when you least expect it. We frequently make dust in what we do, we work with 2 materials that when mixed can be very destructive, and we work with open flames/high temps very frequently. All the pieces are there, Just like the LOTTO, you can have any 3 numbers and not have picked the right 3 to get the prize. In this case the prize could be deadly if all the number fall into place.
 
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