I worked with a guy once that set fire to his garage by leaving a pile of rags soaked with linseed oil in the garage. He was lucky a neighbor noticed smoke coming out of the garage and called the fire dept. or I'm sure the guy would have lost his house.

 

In spontaneous combustion, as linseed oil is a natural product, a pile of rags soaked in linseed oil will start to compost, decay, and that will lead to increased temperature until the flash point of linseed oil is reached. Back in the day most if not all paints were made as a combination of linseed oil, mineral spirits, and white lead paste. My wife's grandfather was a house painter and according to his son, he never bought a gallon of ready-made paints. Grandpa always stored his oily rags in a steel container with a lid.

 

Paint formulas from "The Home Mechanic's Handbook" 1945:

 

That is a cool book, J. Amazon has it for 12$, think I will get me a copy.
I betcha practically no one paints the underside of porch flooring anymore.

 

That is a cool book, J. Amazon has it for 12$, think I will get me a copy.
I betcha practically no one paints the underside of porch flooring anymore.
I read books quite often and develop in this direction, I have been doing this for a long time and write various stories. Although I read a lot, sometimes I have problems with it and I use EduBirdie to help. This is a great resource where everything is done quickly and efficiently.

Great book, thanks for the gift! I liked her too.

 

Here's a link to the video. He tests a variety of scenarios to see which (if any) actually combust, and there were several surprises.

 

This brings up a question...if a rag is dried (i.e., lay it out on the floor), and then gets wet again (e.g., placed in water), is it once again able to spontaneously combust?

 

No, it cannot spontaneously combust after the oil is dried. When linseed oil dries, it reacts with oxygen in a chemical reaction called oxidation. This chemical reaction is exothermic, meaning it generates heat. Once the oil is dried, it is completely oxidized and no more reaction will occur. Wetting it makes no difference, neither is it necessary to prevent spontaneous combustion. If oily rags are dried flat and not crumpled, there is not enough heat generated to induce combustion.

 

I watched that video yesterday, really glad I did. I've thrown Rubio rags in the trash before but never will again. I considered myself very lucky after watching it, humbled myself quite a bit.

 

I've always wondered what is gained when people put oily rags in a water bucket - assuming that doesn't allow the oil to oxidize? Would there then still be a concern? These worries are why I tend toward water-based finishes 🤷‍♀️

 

I never wad up rags. I have old rags for changing the oil in my mowers. I always lay them our flat on a concrete floor or drape them over the handle of a hand truck. I also turn pens and have loads of paper towels with CA glue on them. I toss them on the concrete floor to dry and "defuse." Never in a pile. I have also put them in a can of water.

 

It's not ALL oil, it's drying oils.
Drying oils, like those in wood finishes, go through a curing process that creates heat. When laid out flat or hung on a line, tthe heat is allowed to dissipate. When wadded up in a pile, the heat generated can't dissipate and builds until it eventually combusts.

 

Fascinating, educational, and horrifying! Thanks for sharing what could be a life-saving instructional video, Johnt9431.

 

I burn my rags in a metal can with holes in the sides to draw air for better burning.

Prior to burning, I put the rags in a US GI issue metal ammunition can.

 

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another real example. Even out doors. In his case hot Sun. The rags were soaked with deck oil. The fire burned while I was away from home. A fireman toldme that if the deck haven't been Ipe, the whole house would have probably burned down as Ipe doesn't burn well

 

Thankful it was extinguished and the damage was contained.

 

The speed at which this can happen may be a surprise to some. Had a technical position with a resin manufacture. Major customers were coatings coatings mfrs.
During a delivery of bulk linseed the truck driver followed all procedures properly. After emptying the delivery hose he used a rag to wipe any drips from both the truck connection and the hose end. He the placed this balled up rag on the trailer’s fender, in the sun and went to double check that all valves had been closed properly. In less than 5 minutes when he returned to the fender area of the trailer the balled up rag was smoking profusely. This was in the Northern US and the ambient temp was approximately 50F at the time.

 

Simple Common Sense....Unless you are in such a rush...just spread the rags out until they dry. fold them back up until needed again..

Otherwise...you WILL be in a rush to call 911.

Take the time to do it right. The Dungeon Woodshop ALWAYS spreads out any oil soaked rags flat on top of the tablesaw, when I am done.

Maybe instead of spreading all this "it will BURN THE HOUSE down.." stuff..maybe post how to prevent such things...