Is WD40 Flammable? Yes and No…

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Spend enough time in a workshop and sooner or later, someone’s going to hand you a can of WD-40. It’s the trademark name of spray-on lubricant, moisture displacer, and rust preventing agents. But is WD-40 a fire hazard and should we be spraying it on things with abandon or with large amounts of caution? Let’s find out.

WD-40 is very flammable, but mostly just because of the aerosol propellant that allows it to be sprayed (usually butane). It is not very flammable once the lubricant is out of the can.

Despite this, WD-40 can be very dangerous around fire and caution needs to be exercised. Let’s take a closer look at why that is.

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Also read: What Makes Something Flammable?

What Is WD40?

WD-40 is a complicated product, not least because it’s not entirely certain who invented it (there are several different people who claim to have done so and while someone with “Larsen” or maybe, “Lawson” in their name is probably the right person, there are several people that this might apply to). 

What is known is that it was invented in 1953 as a product of the Rocket Chemical Company. WD-40 would be the company’s most successful product ever and by the end of the century, it had been renamed as the WD-40 company. 

It was invented for use in the rocket propulsion industry, and it was meant to stop the Atlas missile’s outer layer from corroding or rusting while in storage.

By 1958, it was understood that the product was useful for much more than just rocket protection and it was first sold to consumers in 1958 from a store in San Diego. 

It was aerosolized in the 1960s and had become an industrial standard use product by 1965. Its success made the WD-40 company much bigger than it had ever been and it floated on the stock exchange in 1973. 

The company is still hugely successful today and still uses the same “secret formula” for WD-40 which now accounts for nearly $400 million of annual sales. 

Is WD40 Flammable? Will It Catch Fire?

WD-40 is flammable as an aerosol and though technically, the ingredients in the WD-40 are combustible, not flammable. But in aerosol form, when propelled by the butane or other flammable aerosol, (also due to the change in surface area to volume ratio) it is highly flammable. 

If you spray WD-40 near a naked flame or spark, the odds are very good that you will get a fire and that fire may be drawn back into the can and cause an explosion.

It’s important, therefore, to work in a well-ventilated space with WD-40 which is absent flames, sparks, and other sources of ignition. 

WD-40 itself will not catch fire very well.

It does burn, but it doesn’t burn with any real energy, and when lit, it produces very little smoke and tends to burn with a low-temperature flame that does no real damage – though the WD-40 is removed from the surface and will need reapplying if you want further rust protection. 

Also read: Is Butane Flammable?

Is It Flammable When Dry? 

WD40 is combustible when dry, rather than flammable, and it burns with little smoke or heat. The main components of WD40 are petrochemical distillates, so this should come as no surprise. 

Is It Explosive?

WD-40 when sprayed can form an explosive mix with air. If there is more than 0.6% WD-40 to air and less than 8.2% WD-40 to air it will be an explosive mix.

That means that the aerosol will ignite and then propagate a self-sustaining reaction at a very high speed that results in an explosion. 

Will WD40 Spontaneously Combust?

No. WD-40 does not spontaneously combust. 

What Should You Not Use WD40 On?

WD-40 is an excellent lubricant but there are some uses that it’s not recommended for:

  • Bike chains – it traps dust and dirt in the chain and can result in accidents
  • Door hinges – it traps dirt in the hinge
  • Electronic apparatus – it can dissolve the plastics involved
  • Locks – it causes the locking mechanism to degrade
  • Paintball guns – it can destroy the seals inside the gun

Will WD40 Evaporate?

WD-40 won’t evaporate though about 20% of the chemicals in WD-40 do evaporate after application  (they’re there to help the lubricant penetrate properly in the first place). 

Is WD40 Toxic?

Yes. WD-40 when inhaled, in common with many aerosols, can cause nasal and respiratory inflammation, it may also cause headaches, nausea, and dizziness. 

Unfortunately, there is abuse potential with aerosols due to a mild high associated with inhalation but it’s worth noting that this is likely to lead to serious harm and even death, sniffing WD-40 is a very bad idea.

It’s also toxic on the skin, though it’s only going to produce a mild irritation. 

Is It A Hazardous Chemical? 

Yes, because inhaling WD-40 is dangerous and because it is flammable and explosion risk in aerosol form. 

Is It Harmful To Plants?

Yes, WD-40 is toxic to plants and it’s best to keep WD-40 away from vegetation when you’re working. 

Is It Toxic To Fish?

WD-40’s website actually addresses this. 

WD-40 does not attract fish and it’s not good for them. 

You can use WD-40 to protect fishing equipment from becoming rusted or corroded, but that’s all. 

Why Is WD40 Illegal In California?

WD-40 is now illegal in California because it contains too many “volatile organic chemicals” (VOCs) for the state to certify its use.

VOCs are meant to have a negative impact on human health though some industry experts dispute this. 


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