Shop Safety

Jean-Claude · Post by **Jean-Claude** » Thu Apr 12, 2001 4:35 pm

I hope I can get this to attach, it's a rather scary incident that happened to a gentleman I know. Given the materials involved, I though it would be of interest here.

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Workshop Accident Report
by John Purdy

(The following article was originally published in the "The Safety Valve" Volumn 29, Issue 4, March/April 2001, a publication of the "Vancouver Island Model Engineers." To view the original article, go to Vancouver Island Model Engineers March/April newsletter <http://www.steammachine.com/vime/index.html>)

I'm sending you the following details of an incident that has happened to me while using a 1" belt grinder. I feel it might be applicable for publication in the newsletter as a warning for others. Although I was using a commercial model (Delta model 31- 050) I feel it is just as applicable to any type, commercial or home made.

On 25 Jan I was using the grinder to smooth the edge of a hacksaw cut on a 2" length of 1.5" angle iron. I had been grinding for about 1.5 to 2 minutes when there was a loud "THUMP" accompanied by an approximately 2-foot diameter brilliant yellow- orange fireball. The fireball lasted no more than 1/2 second and then completely extinguished itself. It completely enveloped the machine and my hands to half way up my fore arms and to the top of my stomach.

As soon as it went out it was obvious that I had suffered some serious burns to my hands, as besides large white areas on the heel of each thumb and the palm of my left hand the skin was hanging from the heel of both hands from my little finger to my wrist and from the finger joint of my left hand. Also the right cuff of my shirt was smouldering, my face felt burning, and I could hear the front of my hair sizzling. Nothing on the bench was burning. The only evidence was a few streaks of white powder on the bench top and on a few items lying on the bench. The workshop was filled with dense white smoke with very little odour.

My fingers and the ends of my thumbs escaped relatively unscathed as they were resting on the machine's table and were protected from the heat flash by it. Besides the burns to my hands, my neck, chin, cheeks, lips and the end of my nose suffered first-degree burns and have recovered after peeling as if a bad sunburn. I was wearing glasses and these protected my eyes, which appear to not have been damaged.

I also lost half my moustache, 3/ 4 of my eyebrows, and about 1" off the front of my hair. My eyelashes were curled by the heat but not singed .The burns to my face were caused solely by radiant heat, as the fireball did not come that high.

Initially I could not understand how I could have suffered such severe burns from such a brief exposure to the heat. Later that evening after some thinking and quest10ning of my son (who also uses my workshop), it became clear what had happened. A few days earlier he had ground the heads off about twelve 1/8" aluminium pop rivets. Finely divided aluminium mixed with finely divided ferrous oxide (the black powder residue from grinding steel) produce a compound called "THERMITE".

Thermite is used to fill incendiary bombs and commercially to weld large steel items i.e. railway rails into continuous lengths. It burns at approximately 3500 deg C (6300 deg F) hence the extensive burns from such a short exposure time. The end result was, excluding my fingers; I suffered deep second-degree burns to about 60% of my left hand and 50% of my right hand.

Interestingly there is no warning of this possible occurrence in the safety section of the manufacture's owner's manual. As a. result I have sent a Copy of the contents of this letter complete with pictures of my hands to Delta Machinery.

Their reply should be interesting!

In light of my experience I feel there should be a very STRONG warning passed on to the readership as to the dangers posed by grinding steel after having ground aluminium, unless the machine is thoroughly cleaned of all aluminium dust. The potential is certainly there Â£or even more serious injury. Due to the potential seriousness of this incident I have also sent a copy of this letter's contents to the editors of ME, MEW and ElM, Live Steam, Modeltec and Australian Model Engineer in order to maximize the dissemination of this information.

Dick Harrold - Retired
Indiana University
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Another good reason to avoid aluminum!
Jean-Claude

Raselsnarf · Post by **Raselsnarf** » Thu Apr 12, 2001 5:07 pm

Now that is a good bit of info that I did not know. That is good to keep in mind for any kind of grinding period. Thanks for the info Jean-Claude

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Kiernan Delaney
The Drunken Irishman

Krag · Post by **Krag** » Thu Apr 12, 2001 6:14 pm

Titanium and magnesium will do the same thing! I've never seen it blow like that, but I've seen a pile of it burn...and burn....and burn....

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Krag von Berghen
KragAxe Armoury

Member's Pics

Armourkris · Post by **Armourkris** » Thu Apr 12, 2001 9:11 pm

Yea, thermite burns hot...REALLY hot..
but it can be fun.
still, i didnt know tha could happen, i'll have to keep that in mind next time i;m on the grinder

tybolt

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What, drawn, and talk of peace! I hate the word, As I hate hell, all Montagues, and thee:

Bjorn · Post by **Bjorn** » Thu Apr 12, 2001 9:53 pm

While on sagety and the grinding of dissimiliar metals...

One must be careful about grinding aluminum on aluminum oxide grinding wheels. The problem is that the aluminum clogs the "pores" of the aluminum oxide grinding wheels
instead of wearing them away as an iron alloy would. this allows heat to buildt up in the wheel when used later and can cause the stone to fracture with what could be disasterous results.

Bjorn

ARMOURERERIC · Post by **ARMOURERERIC** » Thu Apr 12, 2001 11:09 pm

I have been told by several owners of prop making firms in Los Angeles that the fire marshall as park of the annual commercial occupancy permit inspection check to see that proper disposal of grindings after each project so that we don't burn down a whole city block having the kind of accident you describe. I had a fire marshal once tell me of a thermite fire at a theatrical armour shop in Burbank that burned right thru the 6" concrete floor slab.

Eric

Lochlainn · Post by **Lochlainn** » Fri Apr 13, 2001 8:15 am

Amazing how two common metals, when mixed and ignited, become such a powerful combustible.

I saw a demonstration with a thermite grenade; they will and do go through engine blocks without stopping. Nasty stuff.

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Lochlainn
I'm a Liberal and I'm OK!
*Insert gratuitous inflammatory remark here*

Jonathon More · Post by **Jonathon More** » Fri Apr 13, 2001 8:44 am

never thought about dissimalar metals, but then i dont let piles of dust build up. I'm a steel fabricator by trade, and we once had a small fire in the dust collector of our shot blaster. Nasty little bugger, wouldnt go out for hours. got the fd in to handle it, didnt want to be responsible for a big explosion in the cabinet. So be carefull even of steel dust,it does smolder for days and can pop off if it gets enough oxygen in the mix. I guess the moral of this story is 'keep your shop clean and your tools sharp'. Best lesson i learned from my dad when i was growing up.

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Johnathon
pax, pax, est non mi pax

Galileo · Post by **Galileo** » Sat Apr 14, 2001 1:35 am

I went to a junior college in a navy town, and the Chemistry instructor showed us a thermite reaction outside.... He said the Navy uses them to destroy important documents, while still inside the filing cabinets as it'll burn right through everything. He also mentioned there wasn't much left in the way of ash even.

Very hot stuff...
G--

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Gabriel Tullis

"I am Gabriel. I stand in the presence of God."
Luke 1:19 (KJV)