# Firebomb?



## cuttwice (Jan 18, 2011)

Hello all -

Time for my dumb noob question off the week!

I was having a discussion with a friend this morning, and it raised a question I would like the benefit of your opinions and expertise with. I am finishing an exterior project, using a commercial product from Cabot called Australian Wood Oil (which is a combination of linseed oil, tung oil, and alkyds, seasoned with some iron oxides for UV resistance, apparently, as well as some other mystery ingredients).

I had finished applying oil to one part of the piece, and had to wait to do so for the next part. My friend suggested taking the oil-soaked terry rag I applied it with and putting it into the can of oil (a gallon can with about a pint of oil left in it - enough to cover most, but not all of the rag). He said to just put the top back on the can and tap it closed. His reasoning was that I was going to use the rag and the oil again in a few hours, and didn't want to waste either oil or rags.

My first reaction was that this was a bad idea, but when I told him that I had always been told not do leave oil and rags in proximity to one another, he said that combustion requires oxygen, and with the can closed tight, the rags couldn't get any. That's consistent with what little I know about fire, but it still sounds like a bad idea to me - years of various elders and most paint cans (including this one) warning me not to leave rags near paints, and to dispose of them "properly", I guess.

I didn't do it, but now I'm wondering… So, which is right? Is putting rags in a closed can of oil a dangerous practice, or is it safe? Is oxygen necessary to start a fire, or not, and if so, is there enough in a sealed can to get a fire started?

While we're at it, how do you all dispose of rags when you're done with them, and how long are you willing to wait between applications using the same rag? I've used this stuff before, and while this can says to leave the rags in a sealed container filled with water, that sounds like it will make a toxic stew I can never throw out at all, so I didn't do it. Instead, I left the rags spread out outside (NOT in a pile), and threw them out after they were dry. That seemed OK to me, but was even that risky?

As usual, I (and my insurance agent) thank you in advance for your wisdom…

- John


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## CharlieM1958 (Nov 7, 2006)

Like you, I leave rags spread out outdoors until dry.

I do not believe there is anything dangerous about oil and rags together, per se. My understanding is that the drying process creates heat, and the heat can cause combustion of the oily rag. Theoretically, this reaction requires oxygen.

While your friend's idea is probably safe, I would be concerned that if part of the rag was exposed from the liquid, there might be enough oxygen in the sealed can for the reaction to take place.

I'll be interested to see if someone who really knows what they are talking about will chime in here.


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## Grandpa (Jan 28, 2011)

The rags should be left spread out to dry then disposed of properly…Throw them away. The danger is leaving them in a pile then they can cause heat. These can cause spontaneous combustion and a fire is started. In a can of like solvent (your finish) there is no more danger of a fire than there would be with no rag in it. Rags and oils are not dangerous unless they are left in a pile to generate heat. 
While in the USAF we used rags to wipe up oil spills or drips. these were placed in one of those triangular shaped cans with a lid on it. Supposedly if the fire begins in the can the lid will keep it contained. Every evening were were to take the rags out and put them in a plastic bag then we were able to roll the bag up and place it in a dumpster with a mountain of paper….how safe does that sound. We never had a fire even in the Arizona desert.


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## premieretreeservices (Feb 9, 2012)

Like your friend said, the combustion reaction does need the rag to go through oxidization. If it were possible for the rag to erupt in the can, the can would be combusting all the time. That being said, I've heard plenty of horror stories about rag-oil fires and I'd prefer safe over sorry.


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## bondogaposis (Dec 18, 2011)

I would think that there would be plenty of oxygen in the can. If you only have a pint in the bottom of a gallon can then you have 7 pints of air. I think it is a bad idea. Spread them out to dry and dispose of them. Rags are cheap, don't be stupid.


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## DS (Oct 10, 2011)

I keep an old oil changing catch pan just outside my shop side door. I keep some water in it and place my old rags in it for a few days. Water prevents the rags from heating above the boiling point. (212 deg. F)

Any solvents in the rags evaporate fairly quickly, even though the rags are water wet. After a few days, I remove the rags from the water pan and let them air dry on a concrete slab, then I toss them out.

Care needs to be taken such that solvents are not allowed to get into the soil as this can cause other problems. I never pour out the contents of the pan, I just let it dry out. Any dried solids are bagged and tossed in the trash periodically.


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## Danpaddles (Jan 26, 2012)

I forget what finish I had a while back, they told me to make a little ball of old T-shirt material, like an inch in diameter, and just keep it in the can, dig out out of the can between uses. Was that Gen. Finished maybe? can't remember.

Yes, a pile of rags can combust, but it takes a small pile at least. I'm with the other guys that just spread them out. Sometimes I don't even both to set them outside, I just lay then on the floor, not poled or folded. I figure, if they burn there, they won't start anything else anyway.


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## renners (Apr 9, 2010)

If you are going to reuse rags within a few hours then there's no problem keeping them in the oil can as long as the lid is closed tightly. The rags won't spontaneously combust in a sealed container.

One of my all time favourite labour saving tips is to wrap up paint brushes and rollers in cling film between coats with cling film, same principle - keep the air out - and stop them from drying until the next use (within reason).


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## cjwillie (Sep 6, 2011)

Why take any chances? I'd rather get rid of the rag and be safe than to take the chance of losing my shop just to answer that question.


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## cuttwice (Jan 18, 2011)

Thanks all for your replies.

Charlie, I too am concerned about whether there's enough oxygen to start a fire, which is why I didn't do as my friend suggested. I confess, though, that I'm tired of wasting both rags and oil (to say nothing of whatever impact throwing that stuff out has on my local landfill, which can't be good, and probably shouldn't be repeated any more than necessary).

There seems to be a a mix of opinion about whether leaving the single soaked rag in the sealed can is safe, though many of the answers advising against it seem to mirror my own "why take chances?" reaction, rather than being definitive about it being dangerous. I may try it sometime soon, but I think I'll wait for spring, and leave the can outside if I do try it. (I'm very aware that piles of solvent-soaked rags left to dry are a serious fire hazard, and am not considering this at all!)

Renners, when I used to paint houses for a living, we sometimes used to do as you describe between coats with oil-based paints. Brushes covered with latex paints can just be left sitting in the can with bristles fully submerged for short drying periods (the paint in the can won't dry out anywhere near as fast as the layer just applied), and latex cleanup is so easy that for anything longer, we'd just clean 'em.

Thanks again all!

Best,
- John


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## Tootles (Jul 21, 2011)

You can safely place you rag in the can, put on the lid and come back later.

Firstly, the concentration of solvents insde the can is most likely to be above the subtsances Upper Explosive Limit (UEL) so it cannot combust. Secondly, you have no source of ignition. You know this because your oil cans do not normally spontaneously erupt, and adding a rag does nothing to change that. Thirdly, if by any freak chance you did get some sort of spontaneous combustion inside the can, it would soon extinguish through lack of oxygen.

For any fire to occur, you need three things. Fuel, oxygen and an ignition source. With solvents / gasoline / oil / etc the fuel that ignites is the vapour, not the liquid. So your most dangerous time is when the rags are drying which occurs by the process of evaporation of the solvent. They are not dangerous when they are wet, nor are they more dangerous than a normal rag when properly dry.

The Chemical Safety Board has investigated a number of accidents involving welding around tanks containing flammable vapours. Inevitably, the vapour concentration is checked in the morning when the ambient temperature is low, but the accident happens later in the day when the temperature has warmed and the liquids in the tanks start to give off vapours. It is the same principle at play with the rags.

The reason you have a potential problem is not so much related to the fact that vapours are being emitted - that's not in itself such a dangerous thing as there is seldom a sufficient amount to produce a meaningful fire. But when you do get auto ignition from vapours from a rag, the rag, and other stuff in the bin or drawer around it provides an additional source of fuel to sustain and intensify the fire. Plus the additional heat from the burning rags could cause further or more raapid evaporation from those same rags, making it worse.

Oh, Charlie M, I think I'm the person you were hoping would answer. I spent many years dealing with coniderations such as these with respect to electrical equipment in hazardous areas.


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## MoPower (Feb 6, 2009)

Rags in a can of oil with a lid are not that much of a danger compared to OILY RAGS in a pile. The weight of the oily rags on top of each other causes compression which in turn generates heat, which of course can self combust. 
There has to be three things present for a fire to start, fuel, oxygen and heat or ignition scource. A single rag in a can of oil with a lid only provides fuel with limited oxygen ( low risk).

A can of oily rags with no lid can present all sides of the fire triangle very fast Even with a lid this is dangerous, Heat can build up and the next time the lid is opened it can flash very violently.

And of course chemical reactions from mixing rags with incompatible chemicals on them can produce the same result. This type of fire is a lot more common in homes and workshops than a lot of people realise.


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## Pimzedd (Jan 22, 2007)

If oily rags are stored in a sealed can, it should not be a problem.

Go to Justrite Mfg. page on oily waste cans. You can see that the goal is to eliminate oxygen. A rag in any sealed can should be safe.

I worked around such cans for over 27 years. Any rag that had been used with oil or flammable solvents went in the cans. Never a problem.


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## Sliverfingers (Jul 1, 2011)

The proof is in the pudding, or rather, in the melted goo of a once good garbage container. I came to work this morning and found the charred remains from where one of my employees had discarded the oily stain rags. The can had the perfect combination of sawdust and wet oily rags with an empty spray paint can for good measure. It was also parked right under the table saw. Somehow, it must have only smoldered and not burst into flame. There was little damage, other that some soot on the table. Time for a safety meeting.


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