Boiled Linseed Oil is Combustible

I have always taken this lightly because thank God it has never happened to me. After watching this news report on it, I won’t be taking it so lightly anymore.

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9 thoughts on “Boiled Linseed Oil is Combustible

  1. You are right, of course.
    Like many things in a woodworking shop, linseed oil should be handled with due respect.

    However, (and I know that’s not what you are saying, but sometimes the internet takes things out of perspective) – linseed oil doesn’t burn very well. It is hard to light a soaked rag. Which, ironically, makes it harder to disperse of. It would be easier to just burn the rags.

    Putting on linseed oil, your hand won’t suddenly burst into flames.

    But leaving a rag soaked and crumbled in a pile of shavings or dust is folly. Boiled linseed oil is worse, because the dries accelerate the process – increasing the heat produced when the oil polymerizes.

    So soak the rag in water once done. Problem solved. Keep rags and rolls used eg. for French polish in a close fitting metal or glass tin, with a tight fitting lid.

    You can also hang your rags out to dry on an outdoor clothesline (like oilskins).

    All in all, it takes s fairly specific set of conditions to enable spontaneous combustion. It is potentially dangerous, but it never happens out of the blue. Just like filling a mower with gas, there are inherent risks, but they can always be avoided.

    Kind regards

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    1. Thanks Henrik for your insight. I always soak or spray from the bottle water onto the rags before throwing them in the bin which are full of shavings. Thank God nothing has happened yet, but am I doing it right. Could something still happen even though the rags and paper towels which I use mostly are wet.

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      1. Hi Salko,

        I am no expert (but I did finish first in class in fire theory at firefighter school many years ago)

        Per your question, your method sounds reasonably fine. However, you might risk a situation where the water in the rag is absorbed by the shavings, then they and the rag dry out leaving the oil to begin polymerization in the vicinity of dry shavings.

        I prefer to put rags in a plastic bag, fill some water in and tie the bag up, then in the garbage can. Then it will stay wet and deprived of oxygen until burned in the big incinerator).

        But excellent that you bring this to everyone’s attention.

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  2. Yeah, scary stuff. But every can of linseed oil I’ve ever bought has the warnings on the back, so these folks should have been more careful. I have a bucket that I fill with water and throw rags and stuff in that, and keep it on the back patio well away from the house for a couple days. Better safe than homeless!

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  3. Salko, I’d be reluctant to throw a rag with uncured oil in a bin whether its been sprayed or not. It’s the polymerization process that produces heat.

    I don’t know enough to say whether spraying stops polymerization or not, hence the caution.

    I usually unfold the rag flat and either lay it on an uncombustible surface or hang it like a towel on an uncombustible bar. Crumpling the rags prevents the heat of polymerization from dissipating so the temp continues to rise. Spreading out the rags allows them to cool as they cure.

    I don’t toss anything in the bin until it’s fully cured.

    My father used to freak out about oily rags in the trash when I was a kid and I thought he was overdoing it. We lost a local church interior due to oily rags. Now I know.

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  4. If you spray an oily rag with water, then throw it in a bucket with shavings, it’s almost as bad as throwing the oily rag in there without spraying with water first. Water will evaporate, leaving the oily rag and shavings behind. Steve D. had it right with heat not building up when the rag is not bunched up – no heat from the curing process can build up if the rag is laid flat or hung from a line. It’s only when the rags are crumpled up that heat can’t get out, causing a dangerous situation.

    A townhouse in my complex burned about 12 years ago because of oily rags. Gotta be knowledgeable and gotta be vigilant.

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  5. I worry that a water filled bag is going to eventually burst, (or the can get crushed) lose the moisture and allow the oil to polymerize. My garbage sits in a bin behind my building, is compacted into a truck, then a large municipal depot where it’s crushed under bulldozers and packed into trucks for a 4+ hour drive to a landfill site. I’d hate to be the cause of a fire in any of those scenarios. I hang them to dry.

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