Is Brake Fluid Flammable?

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Although it is not a volatile liquid, brake fluid is inflammable. All modern brake fluids are based on polyalkylene glycols and experiments have found that polyalkylene glycols spontaneously ignite on surfaces that are heated to 734 to 752 degrees Fahrenheit  (390 to 400 degrees Celsius).

Therefore, if a collision occurs and modern brake fluid splashes on an exhaust system that is 734 degrees Fahrenheit or over, it will ignite immediately.

The ferocity that brake fluid can burn when it comes into contact with a manifold or exhaust system can be so intense that it can spread to other plastics such as air filters and cable covers.

This is unless it is quickly extinguished. Otherwise, a whole vehicle can become engulfed in minutes. The integrity of the brake fluid reservoir tends to determine if there will be a fireball or not.

To find out more about brake fluid and its flammable properties, read on as we discuss what brake fluid is and what the safety precautions are to prevent any catastrophic fires from occurring.

What is brake fluid?

Brake fluid is a hydraulic fluid that moves certain particles within your vehicle’s braking system. Without brake fluid, you will not be able to stop your vehicle when you want.

Brake fluid is needed in cars, buses, trucks, motorbikes, and even in certain bicycles. To ensure the brakes of a vehicle are in working order, they need to be maintained, including the brake fluid.

Brake fluid should be inspected by a professional to make sure your brakes are working sufficiently. If you have the knowledge to do this yourself, then this is also acceptable.

But, you must always be extra cautious about checking your brake fluid and the non-flammable condition of your brakes.

The types of brake fluids 

There are three varieties of brake fluid currently available on the market. These are:

  • DOT 3
  • DOT 4
  • DOT 5

DOT stands for the US Department of Transportation and there is also a DOT 5.1 which is glycol-based but with similar standards to the DOT 5. It also has the properties of silicon-based hydraulic fluids.

Both DOT 3 and DOT 4 come with glycol-based fluids while DOT 5 is based on silicon.

DOT 3 and DOT 4 can absorb water but DOT 5 can not. This is crucial when we consider the billing point of brake fluid. Hydraulic systems depend on compressed fluids to produce power and force. The liquids then become condensed while gases are compressible.

If the brake fluid becomes a gas or boils, it will not be able to transmit enough force to power the hydraulic system.

Therefore, when it comes to brakes, they can become entirely disabled. This is why you must ensure you have the right brake fluids with the correct properties for vehicles.

So is Brake fluid Flammable? 

Brake fluid is indeed flammable but it burns slowly. The three major variations of brake fluids (DOT3, DOT4, and DOT5) all burn but, compared to gasoline, they do not burn as quickly or as explosively. 

Brake fluid tends to burn in slow motion, much like vegetable oil but a little faster than your average candle wax will burn. 

To understand why and how brake fluid is flammable, we need to consider its components and properties.

Ethyl-glycol-based fluids are flammable and can burn quite well. It has been found that silicone-based brake fluids also support burning despite some brands stating that they are non-flammable.

As we stated, their flammability is not as explosive as gasoline or other volatile liquids. Instead, it burns in a similar way to vegetable oil with a small flicker of flame.

You can also come across some mineral oil-based brake fluids which are also quite flammable, burning similarly to candle wax or baby oil. 

So, the question remains – can brake fluid cause a fire? Well, while it is flammable, it actually has a low ignition capability when being the primary cause of a fire.

To understand its flammability, we need to explore its flashpoint. This is the temperature where a flammable substance transforms into vapor and burns.

A brake fluid’s flashpoint is very high at 210-375 degrees Fahrenheit (98.8 – 190 degrees Celsius) but this depends on the type.

Under regular temperatures, brake fluid will not ignite because it has a high auto-ignition temperature of 540 – 675 degrees Fahrenheit (282 – 357 degrees Celsius).

If brake fluid burns on an exhaust manifold during an accident, it will cause a fire which can spread to other components of the vehicle. Therefore, you must be very careful when handling brake fluid near fire sources.

Furthermore, brake fluid is also pretty corrosive and toxic. This means it can eat through metal parts very easily if under the right conditions.

The glycol variety of such hydraulic fluids alone can peel off car paint if it comes into contact with it.

So, what about DOT 4 brake fluid? As a polyglycol ether-based hydraulic fluid, DOT 4 can burn at high temperatures. Its flashpoint is on the lower end of the 210-375 degrees Fahrenheit limit.

This means it will easily burn compared to silicon-based fluids. If it is exposed to temperatures of 540-675 degrees Fahrenheit, it can even self-ignite.

DOT 3 brake fluid is also flammable due to it being a glycol-based liquid. It has a boiling point of 483 degrees Fahrenheit (250 degrees Celsius) so is classified as moderately flammable with a rating of just 1.

Its flashpoint is relatively low at 230 degrees Fahrenheit (110 degrees Celsius) meaning it can easily ignite, especially when you compare it to other brake fluid varieties.

In Summary 

Brake fluid is one of the most important components of a vehicle’s clutch and braking system. It plays a vital role in the transfer of power throughout a vehicle’s performance.

However, it can also burn when under high enough temperatures resulting in dangerous situations.

As it is an ethyl-glycol derivative, you must be careful when handling brake fluid. If there is an open fire source or a heated element nearby, it could catch fire. It is also toxic and can corrode your vehicle’s paint.

This is why you must know the different types of brake fluids so you ensure you choose the right one for your vehicle.

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