Linseed Oil - Spontaneous Combustion is a REAL danger for homeowners!

I had my doubts about spontaneous combustion... till my readers spoke out!  Spontaneous combustion, more common in horror movies than in real life, refers to the phenomenon that occurs when an object suddenly bursts into flame without obvious cause.  No match, no sparks, no lightning, no electrical short or smoking cigarette... nothing!

What causes it?  With linseed oil and other oils used to finish wood, including some exterior deck sealers and wood stains, heat is generated during the drying process.  This is because these oils do not dry like paint (through the evaporation of a solvent or water).  Instead, they dry through the same process that generates fire... oxidation.

Despite the testimonials (read "horror stories") about spontaneous combustion at the end of this article, the fact is it's a difficult phenomenon to reproduce.  I've tried to cause it a number of times and have never been able to.  But, then again, I believe in lots of things I haven't personally seen.  I think that's known as "faith".  And trust me... spontaneous combustion is real!

Oxidation generates lots of heat... and can cause fires!

And that's the key!  Burning is rapid oxidation.  For spontaneous combustion to occur, enough heat must accumulate so fire can start.  You would never see a piece of furniture spontaneously combust because the oil oxidizes in open air so the surface never even gets warm to the touch!  But a pile of oil-soaked rags can...

A pile of oil-soaked rags can get smokin' hot...

In every case of spontaneous combustion of drying oils that I have found, the cause has been a bunch of oil soaked rags.  It seems that, as the oil oxidizes, the rags act as an insulator, allowing the oxidizing oil  to become hot enough to cause the cloth to smoke and eventually ignite.  The bigger the pile, the greater the possible heat and the greater the risk.

Room temperature is also a factor.  The warmer it is, the quicker the rags can reach ignition temperature.

Let my readers tell you their scary stories...

• "Spontaneous combustion is real!  Our house burned down on Labor Day, 2009 due to spontaneous combustion from an old bath towel with wood stain on it.  It was not a pile of rags.  My husband had used it as a drop cloth while pouring wood stain into his sprayer.  In the middle of the night it ignited in our garage.  By the time we woke up, the garage was fully engulfed in flames and our house, with a wood shake roof, went up soon after.  Thankfully everyone got out fine and our pets were all rescued by the firefighters.  We were surprised to hear how common spontaneous combustion is from wood stain and how the general public has no idea of the dangers.
• "I was just reading up on linseed oil and spontaneous combustion and just wanted to confirm that it can in fact happen.  While using a linseed oil based decking stain I tossed the soaked rags into a bucket along with other trash (paper towels, a rag previously soaked in mineral spirits, etc.)  The bucket caught fire after I left the job site.  Fortunately the bucket was in the driveway and away from the house - a good precaution!  So albeit a seemingly unlikely scenario, it was a scary lesson in chemistry."
• "Last night we left a rag we had used to linseed oil some furniture on top of some newspaper on top of the kitchen table. At one o'clock smoke came in to the bedroom and alarmed us. The rag was eventually found to be smoking, extremely hot but just short of actual flames. It had begun to oxidize the table underneath.  The smoke had spread throughout he house. The linseed oil container was right beside the rag. We were not aware of this extremely dangerous aspect of linseed oil.  I am sure that the can had proper warning unfortunately it more than ten years old and could not be read. I was curious whether the aging of the oil could have an effect but found no evidence to support that hypothesis. I hope my reporting of my experience has been helpful."
• "The combustibility of linseed oil is very real and serious. A few days ago, old cotton sweatpants used as rags to apply linseed oil to an old table self-combusted. I finished applying the linseed oil and left the rag on top of a plastic container in a shed. At some point over the next few days.... the top of the container had melted and the sweatpants rag was charred black with a central brown ring.  I think that there was not enough air to permit the whole rag to burn, as it extinguished itself. Always being so careful with solvents and paints, I almost filled my pants when I came upon this as I never knew that this could happen with linseed oil. The combustive nature of linseed oil rags may not happen outside in the middle of winter, but on a warm sunny summer day watch out! Later after talking to others, certain cloth material that has smaller fibers such as cotton actually promotes combustion due to the small fluffy fibers. Anyone, I repeat ANYONE, using LINSEED OIL Soaked Rags should either burn rags immediately following use or store in a metal container with a lid soaking in water!
• "You may not have had an incident but many others have - even losing their homes if not their lives.  Jack London whom I used to read as a child (all those wolf books) apparently lost his almost completed "Wolf House" to a hot August night and a careless craftsman who left a pile of linseed oil soaked rags in the house. Linseed oil-soaked combustibles need to be treated with a great deal of respect.  When the manufacturers tell customers to store the residues according to their instructions they really, really mean it. Back when I was a teenager I used to polish my .22 rifle stock with linseed oil but there was no warning back then about the potential problem as there is now. I was lucky.  As an aside, I have just recently demolished a cottage in which the interior pine planks had been treated with what must have been unboiled linseed oil back in the 1930s. The stuff was still not cured in places in the 1990s.  Thank God for modern chemistry!
• "Spontaneous combustion of linseed soaked rags happened to me once as a teen with first use of boiled linseed. I placed oil-soaked rags in a paper bag to throw out later and went to lunch. About an hour and a half later when I returned to check the finish, I noticed a very strong smell and found was the bag with a dark brown discoloration.  As I picked up the bag it burst into flames. I was lucky I returned when I did or the workshop may have had serious damage. I threw the bag out the door on ground and watched it burn quite fiercely with heavy black smoke ( from oil I surmise)."
• "Just a word about the combustibility of linseed oil.  We used boiled linseed oil on our woodwork and forgot the rags on our kitchen countertop and left for a hockey game.  When we got home, we smelled and saw smoke....bad enough that we were panicking and running around the house trying to find where it was coming from.  Minutes later, we found the smoldered pile of linseed oil rags on our kitchen counter.  It had burned a hole about 9" in diameter into our Formica countertop, inches from a pile of newspaper.  We were very lucky our house didn't burn down.  Scary!"
• "Just had a comment concerning the tendency of  linseed oil-soaked rags to spontaneously combust.  I was returning to Denver from Salida, CO. were I had just built a deck and treated it with boiled linseed oil.  When I finished wiping the deck of excess linseed oil, I chucked the three towels in the back of my pickup and headed for Denver.  (Note that two of the towels were from two weeks prior wipings of excess linseed oil and one from that day's final treatment).  While driving down the highway I noticed smoke coming from the back of the truck.  I quickly pulled over to see that the rags had ignited themselves.  Voila! Spontaneous combustion of linseed oil rags just like the warning label said might happen.   I was both shocked and amazed.  And really glad nothing else in my truck burned including me and my family.  Just thought you would be interested in my story since your article states you have not seen this happen.
• "I also had the rag catch fire...after laying it now in my garage and leaving for work....so my experience with boiled linseed oil has been a nightmare. It is a miracle my house didn't burn down!"

This is your brain on linseed oil...

Well, that's it.  If you ever had any doubts of the danger of spontaneous combustion with linseed oil, consider them vanquished.  Like me, none of these readers had a clue, and fortunately none of them lost their  lives.