Oily Paint Rags Can Spontaneously Combust
When the first nice day of spring came to the Boston suburb of Natick, Massachusetts, Jeffrey Cullen and his pal Dave got out the wood stain, brushes, and rags to stain the front porch of Dave’s house. The can of oil-based stain they used had a warning that rags soaked with the stain may spontaneously catch fire if improperly discarded. “We laughed at the warning. How often does spontaneous combustion happen?” says Jeffrey. And then a bit later, when the stained wood was drying, and nobody was nearby, a small fire started near the porch.
Because they were hungry and had errands to run, Jeffrey, a senior video producer at Consumer Reports, and Dave, put off cleaning up. Two hours had gone by since they tossed the soaked rags in a pile next to the paint tray. When Dave pulled into the driveway, he discovered the fire. He and Jeffrey extinguished it with a bucket of water and a garden hose. “We felt really lucky that we hadn’t burned the house down,” says Jeffrey. “The fire may have burned a good 10 to 15 minutes without our noticing.”
What Went Wrong
We asked Bob Benedetti, Principal Flammable Liquids Engineer at the National Fire Protection Association, to explain just what had happened, and asked for tips for preventing fires and putting them out.
“Some oil-based wood finishes (stains, polishes, varnishes) have a tendency to spontaneously heat as they dry and cure. If rags or cloths wet with these finishes are mishandled, the spontaneous heating can accelerate and might lead to ignition and a fire,” he said.
The sunlight was irrelevant in this situation, he added, explaining that the oxidation reaction, the spontaneous heating, proceeds with or without the presence of light. How fast the overheating proceeds depends on a number of factors, including ambient temperature, how tightly packed the rags are, the nature of the oil, and other factors.
The Right Way to Dispose of Paint Rags
Do not pile or ball rags soaked with oil paint into a tight mass or toss them in the regular trash while they’re still wet.
Do allow the rags to dry thoroughly before disposal. Spread the rags outdoors, on the ground or on a metal rack, until completely dry and somewhat hard. Two full days is usually enough time, but it might take longer.
Once the rags are completely dry, they should be safe for disposal. Put them in the trash on collection day. This method allows the oil to fully cure without overheating.
If paint rags catch fire outside, extinguish the fire by dousing with water or covering with sand or dirt. Don’t disturb them until you’re sure the fire is out.
If paint rags catch fire indoors, call the fire department, get everyone outside, then (and only then) try to put the fire out with an extinguisher. If you cannot put out the fire, get out of the house and wait for the fire department.
Don’t try to put out the fire with an extinguisher unless you know how to operate it.
An Alternative to Oil-Based Paint
Consumer Reports buys and tests water-based wood stains which you’ll see in our wood stain Ratings. Bob Benedetti didn’t know of any water-based stains that pose a spontaneous heating issue, but he’s learned over the years that there’s always an oddball somewhere so read the small print on the can and follow manufacturer's instructions. For more information, check our wood stain buying guide.
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