Be Careful! Spontaneous Combustion Is Real.

Spring Cleaning and Oily Rag Fires

Now that Spring is starting to make an appearance, many folks will be getting ready to refinish weathered outdoor decks, wood trim and furniture to look beautiful again. Be careful! You need to know about some very real fire risks when with working oil finishes.

A while back we had a fire break out on one of our jobs in the middle of the night. Fortunately, it was confined to an exterior area where it could not affect the main property. Even so, it destroyed some tools and a wood fence and brought out the fire department. We were very lucky. If it had happened adjacent to the main structure, or if it had occurred during the dry summer months, things could have been much, much worse.

We were shocked and disturbed that such a thing could happen on one of our jobsites. We are meticulous about keeping safe working areas. Everyone on the crew is safety conscious and we have regular safety meetings. We clean-up at the end of every day.

How does this happen?

My project manager and the fire department explained to me what happened. A painting station had been set up on the grounds outside in order to pre-finish a large quantity of IPE deck material. We had been using the station to hand apply a widely used material called IPE Oil to all sides of the deck boards. We would clean and coat the boards in the station, then transfer them to racks for drying.

Before transferring the treated boards to the drying rack, we would wipe off any excess oil with clean cotton rags. Our safety protocol was to place all used rags into a water-filled five-gallon bucket at the end of the day and seal the top before leaving. Although protocol had been followed that day, one rag apparently got left out. Turns out the questionable rag had only been used once and our employee thought it looked clean enough for continued use the next day. Wrong!

The rag was left on a bench next to the plastic paint station and sometime during the night it had caught fire. Once the rag was in flames it quickly spread to the plastic and that in turn caught the fence and tool box on fire. What a mess.

Spontaneous fires

The most common type of Spontaneous Combustion Fires are caused by improperly disposed of oil and stain soaked rags. As we have learned, the rags do not have to be “soaked”.

The products to be careful with are any oil-based paints, stains, teak and especially linseed oils. Varnishes, polyurethane and paint thinners are also problematic.

As I have learned the hard way, spontaneous combustion is not some interesting but freaky theory like ancient aliens. It is a real and predictable phenomenon. It WILL happen very predictably when cloth with any of the above oils on it is slowly heated to its ignition point through oxidation. This occurs over the course of only 3-6 hours.

Oxidation and heat

Oils and stains are designed to “oxidize” (interact with the oxygen in air) in order to dry properly. Apparently, any substance will begin to release heat as it oxidizes. When the material is spread out thinly on a board, the heat build-up is miniscule and not a problem. But, if this heat has no way to escape, as happens inside a wadded or piled-up stack of rags, the temperature will raise high enough to ignite the oil and the cloth. Once a fire actually catches, look out. It can spread quickly to any other combustibles in the area and as you might imagine cause great damage to your home or property.

Prevention of spontaneous combustion fires begins with education about the risk. You and your employees need to understand how this works and take it seriously. Next, you must require really good housekeeping around the work area and strictly follow an oily rag protocol. A clean work area can prevent a fire from spreading and getting bigger by not allowing the fire fuel to burn.

Fully understanding the potential risk is the key step in eliminating these preventable fires.

Oily Rag Disposal Protocol

According to our local Los Altos Hills Fire Department you must take the following steps:

• Use a container with a tight-fitting lid. A metal can is preferable, but a plastic can or even a zip lock bag can work if nothing else is available.
• Place soiled and used rags inside and then fill the rest the way with water, seal the top and do not open it. This will prevent the oils from oxidizing, and thus keep the rags from heating up and igniting.
• Contact your local garbage disposal company for their policy on disposal of both the can/bag etc., and its contents. Some companies will actually permit disposal in the regular household trash, but you need to check first.

I would emphatically also add to the list above, that if you are working with any of these volatile oil materials, only do so in areas free of combustibles, that would be safe even if a fire happened to develop.

Thinking “fail-safe” will let you sleep better at night.