Cloth rags used for staining were the cause of a recent house fire in the Okanagan Valley. Chief Wayne Williams of the Penticton Fire Rescue said that it’s believed that the rags spontaneously combusted in the container which was left outside the building near the garage. Once ignited, the fire jumped to the building and eventually engulfed the structure in flames.
Certain animal and vegetable oils will break down under the correct circumstances. This breakdown causes an exothermic reaction (it releases heat). As more heat is released, the breakdown process is speeded up and even more heat is released. If there is adequate fuel, insulation, and ventilation, this process can break into open flaming combustion.
This process is called spontaneous combustion. The process is not really spontaneous; rather it is a process that follows normal laws of chemistry. Terms like ‘auto-ignition’ or ‘self-heating’ are more appropriate.
Spontaneous combustion only works with animal and vegetable oils. Mineral oils (like motor oil) don’t break down and build up heat the way animal and vegetable oils do. However, if stain rags are thrown in with motor oil soaked rags, the stain rag can cause ignition and the motor oil can accelerate the fire.
Many woodworking stains are made with vegetable oils (like linseed oil). These stains are great products. The user just needs to remember the hazard when applying these products. A cotton rag used to apply stain has the perfect surface area-to-mass ratio to run this exothermic reaction clear to ignition. A small amount of stain can catch fire quickly given the right circumstances. In some cases, stain rags have set for days before igniting.
Stain manufacturers are aware of this hazard. That’s why these products have consumer warning labels on how to dispose of stain rags properly. Chief Williams recommends disposing of the rags in an airtight container so that no oxygen can fuel the fire. Soak the rags in water and seal them in an airtight container. Remove containers as soon as possible by bringing them to the landfill site for safe disposal.
Chief Williams states that these types of fires are not unusual. He recommends taking proper precautions to avoid fires caused by staining rags.