Fire hazards with oil finishes

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Han wrote:

You can't make a thermite reaction using alumium and mere rust -- it's the wrong iron oxide. You certainly can do it with grinding wheels, although the usual reaction is merely some unusually bright sparks.
(Yes, alumium. I'm a Humphry Davy fanboy)
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True. An explosion is unlikely. I have made thermite from rusty nails and aluminum scrapings though. It burns about as bright as magnesium.
An unexpected source of fire that I experienced was using a grinding wheel on a grinder that also had a cloth buffing wheel attached. Fibers would fly off the buffing wheel and gather in the dust collector port. Then a spark from the grinding wheel would ignite it. Once the fire gets pulled into the dust collector then you've got a full blown inferno in your cyclone.
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<...snipped...>
At least the metal particles keep the static charge from building up and causing an explosion... :)
--
No dumb questions, just dumb answers.

Larry Wasserman - Baltimore, Maryland - snipped-for-privacy@charm.net
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There's a TV series, "Brainiac", in which they regularly apply thermite to various objects.
Stuff will burn through just about anything.
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Sat, Oct 21, 2006, 1:17pm snipped-for-privacy@none.com (GregD.) doth come in and mumbles: <snip> I would like to make a test with rags soaked with oil and see how long it would take before it catches fire. I'm wondering which oil is generating the most heat (tung oil, linseed oil, danish, etc.) and how long it takes, based on your experience (if you had any), to get the smoke or an actual flame. <snip>
OK, so go ahead and do it.
This stuff has been beat to death, here and elsewhere. All you have to do is check.
As for asking here, my rule is, in this order: 1. Check every where I can. 2. Ask my mother. 3. Ask here. Always worked so far.
JOAT It's not hard, if you get your mind right. - Granny Weatherwax
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As for asking here, my rule is, in this order: 1. Check every where I can. 2. Ask my mother. 3. Ask here. Always worked so far.
Great idea, but I don't have your mother's phone number.
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Mon, Oct 23, 2006, 2:14am (EDT+4) snipped-for-privacy@snet.net (EdwinPawlowski) doth sayeth: Great idea, but I don't have your mother's phone number.
Just as well, she gives lousy advice.
JOAT If it can't kill you, it ain't a sport.
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I've tried it a few times with boiled linseed oil and once with tung oil but I've never managed to even get smoke. All my attempts have been used with rags cut from old cotton T-shirts that have been used to apply a finish. I've left them crumpled in plastic cups both inside (under observation) and out in the sun on a hot day for up to about 6 hours. I suspect my rags were just too small but until I can manage to get a reaction it's just a guess. I'd be interested in hearing the conditions that are required to get an actual fire going.
Ken Muldrew snipped-for-privacy@ucalgazry.ca (remove all letters after y in the alphabet)
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Tue, Oct 24, 2006, 6:16pm (EDT+4) snipped-for-privacy@ucalgazry.ca (KenMuldrew) doth sayeth: <snip> I've left them crumpled in plastic cups both inside (under observation) and out in the sun on a hot day for up to about 6 hours. <snip>
I haven't checked, but I'd suspect it might take longer than six hours. In any event, I wouldn't want to take chances on it not happening.
JOAT If it can't kill you, it ain't a sport.
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J T wrote:

One of the local tv stations or maybe it was 60-60 or 20 minutes ran a story on the spontaneous combustion of linseed oil soaked rags. They put theirs insider of a corrugated cardboard box to help it retain heat wihout cutting off oxygen and put it in the sun. It took several hours but caught fire the same day, IIFC.
But I think the time to ignition is going to vary wuite a lot on conditions, the type of and concentration of driers in the oil, the age of the oil and so on.
One person posted in here that he hung a linseed oil soaked rag on a closeline in the sun and it caught fire within a couple of hours. I find that hard to believe.
'Overnight' has been long enough to burn a few buildings down.
--

FF


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snipped-for-privacy@webtv.net (J T) wrote:

That was 6 hours in the sun. The cups were left on concrete blocks forming the rim of a firepit so I just left them there until the rags became stiff.

Full agreement; I'm always very careful. I would still like to be able to reproduce the phenomenon, though.
Ken Muldrew snipped-for-privacy@ucalgazry.ca (remove all letters after y in the alphabet)
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(KenMuldrew)

Sheesh! One would suppose the participants would have taken the advice given earlier to the OP and LOOKED IT UP!
http://irc.nrc-cnrc.gc.ca/pubs/cbd/cbd189_e.html
We may presume that the same conditions obtain south of the border.
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(remove all letters after y in the alphabet)
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Oh, thought the cross-section and temperature pretty much described it all.
The plural of anecdote is not data.
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My former neighbor treated a half dozen flag staffs with boiled linseed oil prior to a holiday parade, than tossed the rag in the garage trash can. The fire department was called two hours later when he began to see a haze of smoke throughout the attached house, then his wife came across the street to ask for help. I found the garage full of smoke and four foot flames in the melting trash can. My extinguisher had the flames out about three minutes before the fire dept arrived to knock down the drywall in the garage and ventilate the house. There was no structural damage, but smoke damage required complete interior and exterior repainting, and destroyed many personal goods.

which has never been shown to cause a dust collector fire in the typical woodworking workshop. If you find evidence to the contrary, please post it here. If you do not, please post that as well, so that we do not waste our time re-hashing unsupported hearsay (again). Hopefully, we will await the results of your investigations before continuing with this topic of discussion.

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For some reason I woke up this morning thinking about this discussion (mind works in mysterious ways). I realize it's a bit late but here goes.
Most people seek to avoid spontaneous combustion so I think you'll find little real experience with it among woodworkers, and certainly none at the level that you're looking for--most of us who have had one experience with it consider that enough for a lifetime and don't continue to make the same mistakes of storage that would let us gather enough anecdotal data to be able to compare different finishes.
That said, I'm not sure your question really has an answer. The time to combust depends on too many variables. To take a couple of extremes, hang an oil-soaked rag on a clothesline and toss a bunch of wadded up rags into a barrel of oil. Neither will combust no matter how long you leave them. The rag on the clothseline has plenty of oxygen, but it also has a lot of surface exposed to free convection--that keeps it cool enough to not combust, or even get perceptibly warmer than an adjacent dry rag. The rags in the oil barrel aren't exposed to oxygen at all, so they don't heat.
To get spontaneous combustion you need a lot of oily surface exposed to air, but also need to have that air trapped so that it acts as an insulator and you need enough thickness of insulation to hold in the heat. How soon it happens depends on how oily the rags are and in what quanntity and how tightly wadded--too oily and it won't happen, not oily enough and it won't happen, too tightly wadded it won't happen, not tightly enough it won't happen, not _enough_ of it wadded up and it won't happen and in the range in which it will happen there's a range from "barely goes" to "goes right quick".
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wrote: Very well said...

.. especially that part. LOL but you make an excellent point.

I think "confined" might be a better word than "trapped" -- after all, if the rags are in an *airtight* container (where the air is certainly "trapped") there won't be any combustion, because there is not enough available oxygen. Unless the container is large enough in comparison to the volume of oily rags... which of course is yet *another* variable to consider...

--
Regards,
Doug Miller (alphageek at milmac dot com)
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