A man cleaning his oily hands with a rag


Spontaneous Combustion Hazards

Oily rags, paints, and solvents can easily ignite


There’s simple science behind the spontaneous combustion, and once you understand what causes the ignition of common household solvents and oils, you can use these safe-handling tips to avoid hazardous conditions and make sure your home isn’t damaged by one of the 1,700 annual house fires caused by spontaneous combustion.

Drying oily rags

The National Fire Protection Agency (NFPA) explains that spontaneous combustion is a by-product of spontaneous heating, which happens when some types of oils dry. The drying oil mixes with oxygen and generates heat that can build up to the ignition point of the material it’s on (e.g., a cotton rag). That means that rags soaked in oils, oil-based paints, solvents, varnishes, and paint thinners are a perfect medium for starting fires – especially when they’re tossed in an open trash can while still wet.

Important tip: About 33% of house fires are caused by third parties. If you have contractors working on your home, make very sure that they and any subcontractors have liability insurance. Your home insurance may provide some coverage for damage caused by an accidental fire, but you may not be covered if the fire is related to poor workmanship or defective materials.

What to do: Dry rags outside away from any buildings for about 48 hours; spread them apart out of direct sunlight on a nonflammable surface such as pavement, and make sure they cannot blow away. Once they have dried, place them in an airtight metal container. The NFPA also recommends filling the container with a mixture of water and detergent to break up the oils. Once the rags are safely stored, check with your local authorities for instructions on how to dispose of them.

Vapors from flammable liquids

Gasoline: You may want to pay close attention to the task the next time you put gas in your car – a single gallon has the explosive force of 14 sticks of dynamite. While gasoline in liquid form is highly flammable, its vapors are even more dangerous. They are exceptionally volatile and can ignite from being near hot tools, a working furnace, a spark, or even static electricity. • Never use gasoline as a cleaning solvent, either to clean a piece of equipment or to take grease off your hands.

  • Quickly remove any clothing on which you have spilled gasoline and take it outside. Let it dry for a few days on a nonflammable surface away from any structures. Be very careful to ensure that the gasoline has evaporated entirely from the clothes before washing and drying them. Gas can stay on clothing through the wash cycle and then ignite inside the dryer.
  • Don’t store gasoline in your house or garage or in a structure attached to either one.
  • Store gasoline only in an approved safety can that has features that help prevent leaks and explosions.
  • Never use gasoline to start a fire or on charcoal grills.
  • Before filling the tank, always turn off gasoline-powered equipment such as lawn mowers or snow blowers, and make sure the engine is cold

Other flammable liquids: Some liquids ignite at comparatively low temperatures. Paint thinner, for example, has a flash point of only 104° Fahrenheit. Once it ignites, the flames then feed on materials that would normally not have caught fire at that temperature.

The vapor from flammable liquids is also highly explosive and can ignite well away from the area the liquid is used on. That’s because the vapor is heavier than air and tends to settle close to the ground, forming currents that travel long distances from the source of the vapor. When the vapor encounters a heat source, spark, or open flame, explosions can flash back to the origin point.

  • Keep containers of flammable liquids away from heat sources, especially open flames, and keep them tightly sealed.
  • Store liquids in a cool, dry area away from sunlight.
  • Always keeps flammable liquids in the original container.

Fire extinguishers

If you frequently use oils and other flammable liquids or gases, consider purchasing a Class B fire extinguisher. These extinguishers use dry chemicals rather than water. Burning oil and grease are hotter than the boiling point of water. If you attempt to put out an oil or grease fire (including a grease-based kitchen fire) with water, the water turns to steam, which expands rapidly enough to spatter the burning matter and spread the fire.

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