A couple of days ago I finally got round to using some teak oil on my patio dining table. Well, it looks a whole lot better now, thanks for asking, but my attention was drawn to the small print on the side of the oil can which said “Warning: rags used to apply oil may spontaneously ignite… dry flat or rinse well with warm soapy water.”
So how does that work? Is there some kind of weird chemical reaction going on? I tried washing out the rag (actually it was an old pair of underpants - I’m all for recycling) but the oil didn’t really come out and it just made the sink all brown and oily. So, I wadded up the rag, still wet, and threw it in the rubbish.
I have two questions…
What is the mechanism by which the oil can generate enough heat to ignite cotton?
Are my oily pants about to set fire to my dustbin and the wooden shed it is sitting next to (it is hot, in the 90s today). Filling in the insurance paperwork would be rather embarrassing. (I would take them out only I’m at work, 40 miles away.)
Three questions actually…
3) Is a rag no longer spontaneously-combustible once it’s dried out, in other words is it just the drying out stage that’s dangerous?
Some oils like linseed oxidise quite readily; if you soak them into a rag, this provides not only a lot of surface area (think of the individual fibres of the rag being coated with a thin film of oil), but crumpling the rag into a ball provides a situation where heat cannot easily escape - and as heat builds up, the rate of oxidation increases until… FOOM!
Reminds me of that SNL bit with Dan Akroyd where he’s the manufacturer of Halloween costumes, and Jane Curtain is interviewing him about the safety of the costumes. “The costume is just a bag of oily rags!”
Don’t take the situation lightly. Last summer a house nearby mine burnt down. They had workers in doing some painting who left some oily rags laying around. Even though there was someone at home at the time, by the time the fire was under control the house was a goner.
Linseed oil is particularly dangerous. Make sure that all rags with oily residue are laid out flat so that heat cannot build up. Casual mishandling of oily rags can lead to a catastrophy.
It should be noted that only drying oils, those which oxidize as they cure, are liable to self-combust. Linseed oil, as mentioned, is a candidate, probably the leading candidate. Tung oil is also a candidate, though a lot of what’s sold as tung oil actually isn’t, or has been chemically altered into varnish. Walnut oil, possibly, though it doesn’t dry very quickly, and is unlikely to build up the requisite heat. But motor oil, canola oil, sewing machine oil, none of these oils cure, and none will spontaneously combust (though they can certainly blaze up from an external heat source).
I once nearly burnt my parents’ house down with spontaneously combusting oily rags. I had just started applying “Danish oil” (a commercial product consisting of linseed oil plus some coloring) to a set of unfinished pine shelves. My family was going out to a concert that evening, so I stopped, leaving a small pile of oil-soaked rags (about a foot in diameter and four inches high) in a plastic garbage can in the garage.
My parents left the concert early. When they opened the garage door to park the car, smoke started billowing out, and they discovered that the garbage can had melted from the heat. Thankfully, there was no actual flames — just smoldering; it could have been much worse. For the rest of the project, I was damn well sure to hang all of the rags out to dry before throwing them away, and I didn’t have any further problems.
We recycle kitchen grease at work. The grease comes into the plant in drums covered with old coffe sacks. The sacks (soaked in grease) go into a dumpster which goes up in flames a few times a year. No external heat source other than the sun and grease has a fairly high flash point. Not sure of the thermodynamics but it happens and I get called out of bed to go fix it.
The fire dept I belonged to was called one night to a smell of smoke in a 100 year old farmhouse. We found a similar situation. The rags had ignited, the plastic trash can had ignited and the wood that was being refinished had ignited. At which point, the flames just died out! There were not quite enough btu’s being produced to get the exposed wood beyond the smouldering stage. Most amazing thing I’ve seen. 30 or 40 boards with their surface lightly charred and then just stopped!
So Colophon , let us know if you set your neighborhood on fire or not!
In the museum in which I work, I have to take all of the rags which I’ve used to clean artifacts outside at the end of the evening. We have those cement barriers out back which are designed to keep a truck from crashing into the place (which, honestly, I’ve never understood because I can’t imagine that a museum in Podunk, BFE would be a terrorism target. But I digress . . .) Those barriers make a great “laundry line”, and since no one sees back there, it’s a great place to lay out all the rags. After a while, it starts looking like Tibetan prayer flags.
I learned to do this one winter’s afternoon, when my curator gasped in horror seeing the laundry bin where I had stuffed all of my greasy, oily rags, which was positioned right next to the heater. He explained, in no uncertain terms, why this was a certified Bad Idea.
Linseed oil-soaked rags nearly burned down the school where I work - someone had left a pile of them wadded up in a corner, and in the middle of the night, there was a small fire. Luckily the smoke alarm went off and no major damage was done. So - yeah, take it seriously.
The One Meridian Plaza fire of February 1991 which claimed the lives of three Philadelphia firefighters started with oily rags improperly handled by a contractor.
My standard is to place rags in an empty paint can and seal it. No supply of oxygen-no problem.
If you don’t have a proper sealed container, as suggested by danceswithcats, I suggest retrieving that oily rag from the trash bin and hanging it outside on the clothes line. The risk of spontaneaous combustion will be greatly reduced. And if it does self-combust, you house won’t go up with it.
But your neighbors might suspect your cusine at home if you tell them your underwear goes up in flames on its own every so often.