Home-made fireball

[rsser]

Thought this might be of interest; borrowed from a reputable source:

Most woodworkers know that a spark can cause an explosion in air filled with fine wood dust. Other hazards, less well-known, can exist for a number of other finely divided materials; the explosive destruction of flour mills is one example.The flammable properties of steel wool show how this works. Steel wool is like kindling. You could hold a match to a nail and never get action. But touch the match to fine steel wool and it starts burning immediately.
A recent accident suffered by a British Columbia craftsman shows a danger that may lurk in the use of sander/grinders. First, a bit of background: thermite has long been a source of intense heat for welding large items such as railway rails and bridge sections. In wartime it was the primary constituent for incendiary bombs. Thermite is composed of powdered aluminum and iron oxide.The aluminum acts as a reducing agent; when it reacts with the iron oxide, the result is molten iron, aluminum oxide and large amounts of heat.
The incident in which the craftsman was injured began when his son used his belt sander to remove the heads of some aluminum pop rivets.This loaded the sander belt with fine aluminum particles and deposited more on the surface of the grinder stand. When he then used the sander to smooth the edge of a piece of rusted angle iron, the conditions were right for existence of what was, in effect, a small amount of thermite. A brilliant two-foot diameter fireball erupted, then instantly vanished, leaving dense white smoke with little odor. The intense heat blistered his hands and arms and removed a good bit of his hair and mustache. Fortunately he was wearing eye protection, so has fully recovered.
The message here is that any time you are grinding aluminum, be sure to clean the belt or wheel thoroughly before moving on to other metals, as well as cleaning up any accumulation on or around the sander/grinder.

[ptc]

Did not know that.
Thank's Ern.

[BobL]

I find this story surprising hard to believe, or he got the 100,000000 to 1 chance reaction. To start the thermite reaction (Rust plus Aluminium) a source of intense heat such as a burning piece of Mg ribbon is required. It also needs to be applied for more than a fraction of a second than sparks would provide.

[joe greiner]

Seems to have originated here:

http://www.hanford.gov/rl/?page=542&parent=506

but apparently massaged in transit. Dunno how British Columbia got into the act, except BC is next to Washington State - location of Hanford atomic energy reservation. Story cites occurrence in Oz.

Joe

[Article99]

Mythbusters did something very similar to this ages ago, I think.

They filled a small chamber with very fine wood particles, and hit it with a few different ignition sources, but they couldn't get it to blow, I don't think.

Might be worth a look for those interested.

[BobL]

Mythbusters did something very similar to this ages ago, I think.

They filled a small chamber with very fine wood particles, and hit it with a few different ignition sources, but they couldn't get it to blow, I don't think.

Might be worth a look for those interested.

I looked up their website and couldn't see anything on this experiment. While the mythbusters are fun, their scientific/knowledge method leaves a lot to be desired and I wouldn't be trusting my life to any experiment done by these guys. The main reason they can't get stuff to blow up is that they don't consider the air to fuel ratios needed to get the reaction started the values needed to keep the reaction propagating. We should be thankful their explosion experiments don't work all that well otherwise we'd really be in trouble with every nutter around the place able to blow stuff up - and I would have to leave my shed to break wind in my shed otherwise I would continually have blackend face.

The most common industrial dust explosions are coal dust - somehwere I read there are about 1 a week aomewhere around the world. In the case of floor sanders, where dust is very prevalant, the majority of these that are injured or killed on the job are by the finishes they use, not the dust they generate. One reaction that seems a bit easiler to start than most is grain dust/flour/air which is why grain silos can be dangerous.

[Ianab]

They filled a small chamber with very fine wood particles, and hit it with a few different ignition sources, but they couldn't get it to blow, I don't think.

You can definately ignite fine wood dust if you get it fine enough and mixed into the air. It goes up in a fireball, but in an enclosed space it's an explosion. Same with flour, coal dust and photocopier toner.

A normal home workshop dust collecter isn't going to explode because there is never a high enough concentration of dust in the system and no decent ignition source. But on an industrial scale it can and does happen.

A handfull of belt sander dust thrown onto a bonfire will produce a very impressive fireball. Kids - DONT TRY THIS AT HOME

Ian

[Groggy]

I'd be interested if anyone can find an officially documented occurrence of a wood dust explosion (dusty; dust extractor) anywhere worldwide in a non-commercial environment.

We did this on another group with 30-40 participants back in the '90s and could not find a single occurrence. There were a few occurrences of dust extractors blamed for igniting paint cleaner fumes but these do not count.

[Iain]

I agree with the Mythbusters testing, not overly thorough, I recall many moons ago the US Air Force had jet aircraft exploding for no apparant reason, tests were conducted to no avail with information provided by aircrew that the cabin was 'exploding'.
After several laboratory tests were conducted using cabin furniture (seats, parachutes etc) no explosions resulted then someone introduced a new factor, a well used seat cushion complete with oil and grease stains from air and ground maintainence crew, and voila, an explosion with the introduction of oxygen and hot air in a simulated high altitude experiment.
Thus the culprit was found, which is something that the Mythbusters seem to overlook in their one hour experiments.
Having worked in a forensic field for a few years I found that there can be several unusual factors that can contribute to an otherwise unfathomable incident, often overlooked or never even considered to be a contributing factor.

[Carry Pine]

Remember Iain, 'Fireball hockey and all its derivatives are banned by the Scout Association'.

Lucky my Venturers only played Fireball soccer and AFL!

Carry Pine

[rrich]

How many rivets would need to be sanded off to produce enough aluminum?

How much rusted steel would need to be cleaned with the sander to produce enough ferrous oxide?

How could one get the spark hot enough for ignition?

A fireball???

Sorry folks, it doesn't sould plausable to me.

[Groggy]

Sorry folks, it doesn't sould plausable to me.

I don't know about the thermite argument, but when I was young and stupid (I'm much older now ) I ground some aluminium on a wheel and a grizzled old foreman told me, in no uncertain terms, that the aluminium fills the pores of the grinding wheel. When it heats up the expansion can cause the wheel to crack and self destruct at high speed. Either way results in pain and injury.

[rsser]

The point of the post was to warn about powdered aluminum and iron oxide, not the wood dust legend.

I agree the incident might be rare due to the contingencies of the combination, but motorbike accidents are (relatively) rare and I still ride with helmet and leathers.

The source was the Lee Valley website btw.

[Edited to make more sense ;-} ]

[simso]

Sounds like a crock, if your using a grinding well then yes you can load the wheel up with aluminium and create a dangerous situation, every mechanical apprenticeship will warn you of this. But a linisher/grinder belt, not likely

[la Huerta]

send it in to MYTHBUSTERS !


funny i was sanding aluminium last night...no fireball though