Is WD 40 Flammable? What Firefighters Want You to Know

WD 40 is one of those products that ends up in every toolbox, junk drawer, and garage in the country. People use it on squeaky hinges, rusted bolts, and stuck zippers, and they use it near engines, grills, and power tools without a second thought.

Yes, WD 40 is flammable, and the aerosol version is the one to worry about. The classic spray can is pressurized with a flammable propellant, and the product itself is a blend of petroleum based oils and solvents with a flash point of around 122°F (50°C). Sprayed as a fine mist, it will ignite from an open flame or a spark.

What's Actually in the Can

The company keeps the exact formula private, but the safety data sheet tells you what matters. WD 40 is mostly a light petroleum oil (the part that lubricates) and a hydrocarbon solvent (the part that penetrates rust and evaporates). In the aerosol can, that mixture is pushed out by carbon dioxide in newer cans and by propane or butane in older formulations and some regional versions.

The solvent portion is what gives WD 40 its flash point. The propellant, when it is a hydrocarbon gas, is flammable on its own. Either way, the mist coming out of the nozzle is a cloud of fine fuel droplets, which is the easiest form of fuel to ignite.

The Label Says It Plainly

The WD 40 can carries the words "Flammable" and "Contents under pressure" for a reason. The company's own safety instructions tell you to keep it away from heat, sparks, open flames, and hot surfaces, and to not smoke while using it. That is standard aerosol language, and it applies.

Three Ways WD 40 Starts Fires

• Spraying near flame. The mist ignites and flashes back toward the can. This is the most common WD 40 burn injury, and it usually happens at a grill, a gas stove, or a running engine.
• Spraying on hot surfaces. Lubricating a hot exhaust bolt or a hot piece of equipment can push the liquid past its flash point immediately.
• Heating the can. Aerosol cans are rated to about 120°F. A can left on a dashboard in summer or near a heater can rupture, and a rupturing can of flammable contents near any ignition source is a fireball.

Once It Dries, the Risk Drops

The solvent in WD 40 evaporates within minutes, leaving behind a thin film of light oil. That residual oil has a much higher flash point and is not a meaningful fire hazard on a door hinge or a bike chain. The danger is in the spraying, not in the parts you sprayed yesterday.

One exception: saturated rags or paper towels. Like any petroleum product, a pile of WD 40 soaked rags can hold heat and, in rare cases, contribute to a smoldering fire. Let them dry flat or toss them in a sealed metal container.

NonAerosol WD 40

WD 40 sells the same product in a nonaerosol trigger bottle and in bulk cans. Those contain the same oils and solvents but no propellant, and they don't produce a fine mist. They still have a flash point of about 122°F and should be kept away from heat, but they are considerably less likely to flash than the spray can.

Using It Safely

• Never spray near an open flame, a pilot light, a lit cigarette, or a running engine.
• Let hot parts cool before lubricating them.
• Don't store cans in a vehicle or near a heat source.
• Don't puncture or burn empty cans. They still contain propellant.
• Work in a ventilated area. The vapor is not just flammable, it is also not good to breathe.

WD 40 is a useful product and it is safe when used the way the label describes. The mistakes we see almost always involve an open flame within a few feet of the nozzle. Keep those apart and you'll be fine. For related reading, see whether motor oil is flammable and whether aerosol deodorant is flammable.