With Spring bringing warmer temperatures, you may be looking at doing a few projects you had been putting off the past few months because it was too cold outside. For argument's sake, let's say one of those is refinishing a piece of wood furniture. A table, a chair, a bench, something like that. Let's also say for argument's sake, you've decided you want to refinish that piece of furniture with furniture oil or stain instead of paint because you really love that natural wood look. So, you go to the hardware store, you buy your oil or stain and a box of rags to apply it with. Once you've finished, you put the lid back on the oil, take all those oil-soaked rags you used, toss them in the trash, and grab a celebratory beer for a job well done. Hours later, you smell smoke. You follow the scent which leads you to the trash can you threw those rags into which now on fire.

How did we get from point A to point B? A little thing science calls, "spontaneous combustion."

I first heard about this after a friend shared a link on Facebook about this exact thing happening to people. Since I am pretty skeptical about nearly everything on social media, I decided to do a little digging to see if it was a real thing we should be mindful of when using oils for any project. So, I sent an e-mail to Mike Gain, Chief Fire Marshall for the Evansville Fire Department to ask the following questions:

  • Is this possible?
  • How does it happen?
  • What can we do to prevent it?
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Here's what he said:

Is it possible?

Short answer, yes.

How does it happen?

Linseed oil, which is a popular choice for finishing furniture, dries through a process you may have heard of called, oxidation. According to Fire Marshall Gain, this process causes certain materials, like linseed oil, to "self-heat to a temperature high enough" for "spontaneous combustion or spontaneous ignition to occur due to chemical, biological, or physical processes." In the case of the rags, the oil generates chemical heat on its own without the need for another heat source like a flame as it chemically reacts with oxygen in the air. This essentially turns the rag into a wick. Multiple rags lumped on top of each other in a trash can means more chemical reaction which means more heat, and more opportunity for a fire to start.

What can we do to prevent it?

According to Gain, nipping this in the bud before something terrible happens is as easy as "following a few simple and proven tips:"

  • Store piles of hay, compost, mulch, manure, and leaves away from buildings, in case a fire occurs, and keep the piles small to allow for the circulation of air and the dissipation of heat.

  • Workgroups or businesses using large quantities of oily rags should dispose of those rags in an OSHA-approved container to await pickup by an industrial cleaning company.

  • If you're working on a project at home, spread the soiled rags in a single layer on concrete to prevent the buildup of heat and allow the rags to become hard and brittle. Place the rags out of direct sunlight and secure the corners to prevent movement by wind.

With all that said, what's the likelihood this could happen to you? According to the National Fire Protection Association (NFPA), "an estimated 14,070 fires occur annually from spontaneous combustion." I don't know about you, but that number is high enough for me to make sure I follow the steps above to dispose of those rags.

[Sources: EFD Chief Fire Marshall Mike Gain via e-mail / National Fire Protection Association]

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