Is Brake Fluid Flammable?

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If you’ve got a vehicle, then there’s a good chance that you’ve got some brake fluid. It is, of course, used in braking systems and it acts as a particular type of hydraulic fluid that transfers power effectively from the wheels to quickly reduce speeds (or bring a vehicle to a stop). But the big question that many car owners have is whether or not that brake fluid represents a fire hazard.

Yes, brake fluid is flammable. Though brake fluid is not classified as a volatile liquid, brake fluid is moderately flammable, and if it were to leak out of the brakes and spray over the manifold or exhaust? It would definitely catch fire.

So, here’s what you really need to know about brake fluid. 

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Also read: What Makes Something Flammable?

What Is Brake Fluid?

Brake fluid is a class of hydraulic fluid that is designed to work in the braking systems and clutch of many different automobiles, motorcycles and it can be used for light trucks and even bicycles too. 

It works by changing force into pressure which helps to amplify the force that can be placed on the brake and that, in turn, accelerates the process of slowing down or stopping. 

As with most hydraulic fluids, it is not particularly compressible when heated, so it doesn’t change volume as it affects the transfer of force. 

In order for a substance to be classified as brake fluid, it will need to satisfy local regulations regarding such fluids. 

In the United States, there are many standards from the Department of Transport and the Federal Motor Vehicle Safety Standards and the brake fluid must conform to the specific standards for the exact application it is being used for. 

Oddly, one of the standards requires that all brake fluids be colorless or amber in color if the vehicle is to run on the streets. However, there is another standard that says a fluid of DOT Grade 5 must be purple!

To work properly brake fluids must retain their level of viscosity (a measure of how easy the fluid flows) under a wide range of temperatures, it has to have a very high boiling point so that it does not become gas while under pressure and heat, it cannot corrode the machines it is used in and it must have a very low level of compressibility. 

Also read: Is Transmission Fluid Flammable? Yes and No…

So, What Color Is Brake Fluid?

Sorry, if we got you confused with the standards. The kind of brake fluid you use in a car should be a sort of yellow/amber color.

If it changes, it means your brake fluid needs replacing. 

Is Brake Fluid Flammable?

Yes. This is in stark contrast to the majority of hydraulic oils which are, generally, combustible rather than flammable (though water-based hydraulic oils are neither). 

Brake fluid is not a single formula, however, and some forms of brake fluid are more flammable than others. 

If you need to know the flashpoint of the brake fluid that you are using for safety reasons, you must consult the manufacturer or read the supplied Material Safety Data Sheet for that fluid.

It is impossible for us to give you a meaningful “average” for the flammability of brake fluid because of the variations in the formula for it.

You can see in this video how flammable it is:

Also read: Is Power Steering Fluid Flammable?

Is Brake Fluid More Flammable Than Petrol?

No. Petrol (gasoline) has a flashpoint of 40 degrees Fahrenheit. This means it is highly flammable and the gasoline vapors are known to be incredibly easy to catch fire in the presence of a flame or spark.

However, while we cannot give you an exact flashpoint for any given brake fluid, we’d expect that in many cases it would be between 210- and 375-degrees Fahrenheit. 

That’s quite a bit higher than the flashpoint of petrol and as such, you don’t need to treat brake fluid as you would petrol. Though both should be kept carefully if they are available in large quantities in the location you are in. 

Also read: How Long Is Spilled Gasoline Flammable For?

Can Brake Fluid Combust?

Yes. While brake fluid may not be highly flammable, it is certainly combustible and you would expect that it would catch fire if exposed to a naked flame between 210- and 375-degrees Fahrenheit in temperature. At higher temperatures, there is a potential for auto-ignition that is spontaneous combustion.

It’s important to note that again, the exact point at which any given brake fluid will auto-ignite (if it does at all) will be defined by the manufacturer. As a rule of thumb, it becomes likelier at temperatures above 500 degrees Fahrenheit, but this is not a good number to base any safety precautions you have to take on.

Also read: Is Hydraulic Fluid Flammable? Yes and No…

Can Brake Fluid Explode?

Yes and no. The brake fluid itself is not an explosive like, say, dynamite. 

However, if brake fluid were to auto-ignite within a container (because it became so hot) it would release a lot of heat. This heat would cause the brake fluid to expand and potentially if this happened enough… the pressure inside the container could tear it apart and it would explode. 

What Happens If You Spilled Brake Fluid?

It’s best not to spill brake fluid as the formulation used most widely in personal vehicles is an aggressive solvent and it can dissolve paint and other surface compounds very quickly, indeed.

It is vital that if you do spill brake fluid you start to clean it up immediately to prevent as much damage as you can. 

Soak up any excess fluid using a paper towel – don’t wipe it as that just means spreading the fluid around. 

Once you’ve soaked it up, wash the surface with soapy water. Dry it for safety too. 

What Happens If You Mix Chlorine With Brake Fluid?

OK, we said that brake fluid wasn’t explosive in the same way that dynamite is explosive. But you can make it explode in the same way.

And you do that by adding chlorine to it. Now, you probably don’t keep chlorine gas laying around your garage or carport but you may well have some pool cleaner.

Pool cleaner contains calcium hypochlorite, a substance that is excellent at releasing chlorine when in touch with the water in your pool, it’s also good at releasing chlorine when it comes in touch with brake fluid.

It is essential, therefore, to store your pool cleaner as far from your brake fluid as you can and never pour either of them into the same vessel. 

This video goes into the science of this reaction with some good demonstrations:

Also read: Is Chlorine Flammable?

Is Brake Fluid Toxic?

Yes, the active ingredient in the most commonly used brake fluids is diethylene glycol (DEG) it’s sometimes used as an anti-freeze too.

As you probably already know, drinking anti-freeze is a very, very bad idea and diethylene glycol is slightly sweet, smells of nothing, and is colorless, but if you drink it, unless you get to the hospital very quickly, you are likely to be seriously injured or it could cause you to die. 

We would also recommend that you avoid getting it in your eyes or on your skin, if you do, wash it off immediately with water and if there is any irritation – seek medical assistance. 

How Much Brake Fluid Is Lethal?

Just 100 ml of brake fluid is estimated to be enough to kill a person.

It will destroy your brain, heart, kidneys, and lungs and the poisoning is almost impossible to reverse once it has taken place.

Does Brake Fluid Take Off Paint?

Yes. Brake fluid will easily dissolve the paint.

It’s a powerful solvent. 

Also read: Is Paint Flammable/Combustible?

Will Brake Fluid Eat Through Plastic?

Yes. Pretty much as with paint, if you are foolish enough to put brake fluid in a plastic container, or worst of all, a plastic bag, it won’t stay there for long. It will dissolve the plastic. 

If you spill brake fluid onto plastic or painted plastic, you need to immediately soak it up using paper towels. Then wash the area with soapy water and dry it.

You may find that it then helps to wipe the surface with isopropyl alcohol which will remove any brake fluid that you haven’t detected.

If it etches the clearcoat layer then you should be able to polish it out with aluminum polish. 

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