[Detailed] Is Diesel flammable or explosive: Does It Catch Fire?

Diesel Fuel is a very popular engine fuel used in many places worldwide, especially in Europe and Asia Continents. As a widely used Common fuel, as much as it gains fame, it also raises questions about potential health, environmental, and fire safety.

Is Diesel Flammable? Well, according to the reports of OSHA Diesel Fuel is classified as a Flammable element, which means Diesel can ignite/catch fire. The flashpoint of Diesel Fuel is approximately 125-204 Degrees Fahrenheit or about 52-82 Degrees Celsius. It means that in the normal ambient pressure & temperature it won’t burn.

Thus, we’ll take a look at the dissimilarities between flammable and combustible fuel liquids. So, you can acknowledge yourself about why, when, or Diesel Fuel inflames.

Is Diesel flammable

Is Diesel Flammable or Combustible?

Although Flammable and Combustible are quite a bit identical, they don’t mean to be the same.

Many people say that “Flammable refers it’ll catch on flames and Combustible refers to it’ll burst when in fire contact.” Which isn’t correct.

OSHA aka Occupational Safety & Health Administration has set up some precise criteria of 29 CFR 1980 standards for Flammable and Combustible Liquids.

OSHA Regulation Determines Them Like:

1. Flammable Liquids:

Any fuel liquids with less than 100 degrees Fahrenheit (37.8 °C) Flashpoint.

2. Combustible Liquids:

Any liquid component with more than 100 degrees Fahrenheit (37.8 °C) Flashpoint.

But the old definition is modified.

Now, OSHA states that any liquid substances that have Flashpoints below 93 degrees Celsius (199.4 °F) are considered Flammable Liquid.

3. Flashpoint:

The minimum temperature and air pressure in which an element will emit fumes adequately to ignite in contact with fire.

Note: Solid and Water matters don’t fire the way there. These substances effuse flammable fumes, that can burst into flames in the specific temperature with the ideal concentration.

Thus, we know that flammable liquids are very risky and can easily ignite the exposure of flames even at the lowest temperature, unlike other liquid substances. But, flammable/combustible and non-flammable liquids, are usually fire hazard elements. The only distinction is at what temperature they start to inflame.

Is Diesel a C1 Or C2?

There are two individual classes of fuel liquids, that define whether the diesel fuel is flammable or combustible.

Well, you already know that the fire–point and flashpoint of any combustible fuels are below their boiling point. On the other hand, flammable liquids flashpoint and fire point are above their optimum boiling point. 

According to the OSHA, Fuel Standard Regulations classifies flammable and combustible liquids as C1 and C2.

  • Class C1: Flammable liquid substances with closed cup flashpoint above 60 degrees Celsius and below 93 degrees Celsius.
  • Class C2: Combustible liquid substances with Flashpoint above 93 degrees Celsius.

So, according to the fuel’s flashpoint and fire point you’ll be able to identify whether a type of Diesel fuel liquid is C1 or C2. This explains that with the lower flashpoint, Diesel fuel is highly a C1 (Class1) substance. On their hand higher flashpoint is the combustible diesel (depends on the Diesel type).

Does Diesel Catch Fire Easily?

Usually, Diesel Fuel is quite harmless while it is in the liquid state in the ambient temperatures. However, when it starts to give off vapors in the exposure of accelerants like temperature/flame/air pressure, it gets very dangerous. Thereby, a bit of fire can make the Diesel Fuel explode and spread around rapidly in that case.

Thereby, diesel will start to emit vapor and that can mix up with the air over a wide area in the flashpoint. If the temperature is way greater than 100 °F and keeps on rising vapor starts to mix with a wide range too.

Here are some OSHA details about Diesel–

  • The explosive limit of Diesel is 1-10%, which means that this fuel can start vaporizing and ignite with only 1% of diesel vapor mixed in the air.
  • OSHA standard 1910.252 has strictly prohibited operating any welding/cutting arc near the presence of Diesel vapors (Explosive Vapor).

At What Temperature Is Diesel Flammable?

At What Temperature Is Diesel Flammable

From the definition of Flammable Liquids, we know that the flashpoint range of Diesel is 100–180 degrees Fahrenheit (37-82 ° C). The range refers to the different flashpoints of different kinds of Diesel Fuel (C1, C2, C3, C4). Therefore, Diesel Fuel’s classified as Flammable when its flashpoint is more than140 degrees Fahrenheit.

So, at what temperature is Diesel Fuel Flammable?

This depends on the individual Flashpoint of the Diesel Fuels. But in general, at any temperature above 100 (or precisely 125-206) degrees Fahrenheit, a Diesel Fuel starts to emit flammable vapor, then Diesel becomes flammable. But, at any temperature below 100 degrees, this liquid is combustible.

Can You Pour Diesel on a Fire?

Pouring Flammable liquids on fire is considered very hazardous. Flammable liquids like Gasoline or some Diesel types with lower flashpoints and explosive vapor pressure tend to ignite and explode around a lot quicker. As flammable liquids mix vapor with air very fast, the fuel can ignite while it’s still in the air.

Therefore, you still can experiment with pouring diesel on an open fire by following these safety measures –

  • Be sure to keep as distant as possible from the fire source while pouring fuel.
  • Be sure to pour the diesel out of the container as fast as you can (it can catch fire while still in the air).
  • The container of the Diesel must be top cut off.
  • Keep easy access to a fire extinguisher in case things go north.

It is comparably safer to pour combustible Diesel Fuel on a Fire than Gasoline. But, although you can pour Diesel on fire, as it’s a fire hazard liquid, you better not.

Read also: Is Crude Oil Flammable? Does Crude Oil Burn Easily? Why?

Is Kerosene More Flammable Than Diesel?

Kerosene is classified as one of the flammable substances, and it’s in a similar class (class PGIII, class II) to Diesel Fuel. But Diesel is not as Flammable as Kerosene, in short Kerosene is more flammable than Diesel Fuel.

Thereby, Kerosene has lower flashpoint than flammable diesel (which is less than 100 °F). Also, the preignition temperature of 428 degrees Fahrenheit.

Regarding that, Kerosene is less combustible than Diesel. As combustible Diesel consists of 126°F flashpoint and 493°F of preignition temperature.

So, with lower auto-ignition temperature and flashpoint Kerosene is a bit more flammable than Diesel.

What Class Flammable Liquid Is Diesel?

As Diesel fuel can be both flammable and combustible, you could say that it’s categorized into more than one class.  

From the classifications of OSHA flammable liquids, Diesel is a Class II combustible liquid. As it avails a flashpoint of more than 100°F and less than 140°F.

Thus, diesel is precisely a Class II combustible liquid with ≥ 37.8 degrees Celsius ≤ 60 degrees Celsius. Whereas, Gasoline, kerosene, and other lower flashpoint liquids are Class 1 Flammable liquids.

Is Diesel Fuel a Class 3 Flammable Liquid?

No, Diesel Fuel is not ranked/classified as the class 3 (class III) Flammable Liquid.

According to the National Fire Coding Classification, flammable and combustible liquids are Gasoline, Diesel, Heating Oil, etc.

Therefore, the Class 3 flammable liquids (Class IIIB) are not Diesel, Gasoline, or Heating Oil. Rather than that these fuel liquids belong to Class 1 and Class 2 flammable/combustible liquids.

It’s because only the liquids that consist of above 200 degrees Fahrenheit (93 °C) flashpoint are Class IIIB liquids. So, any flammable or combustible fuel liquids less than 200 °F flashpoints are not Class 3B liquids.

Can Static Electricity Ignite Diesel?

If there’s a small presence of static electricity inflammable/combustible liquid, it will easily be able to ignite with a bit of accelerant. Thereby, the accelerants could be the increase of temperature, hot surface, sparks, arc welding, and so on.

Furthermore, several other things can make Static Electricity Ignite Diesel–

  • Turbulence in The Container tank– The Diesel container being filled to the brim makes the fuel accumulate Static Electricity. It can become hazardous and ignite in the fuel transfer process.
  • Diesel Liquids Flowing Through– When Diesel flows through the hoses/pipes due to leakage, the friction stores up a high amount of static electricity. In this case, a significant increase in the velocity/temperature of diesel flow can catch fire.
  • Solid Components Inside Fuel– The Semi-solid specks of dust, residue, rust, and sludge inside old Diesel Fuel store up static power. Too much increase of these particles will make the fuel explosive.
  • Water Particle in Diesel– Water droplets can easily build up electric static energy from speed, heat, and pressure. In many reports, water particles, and water foam with static electricity in diesel have initiated fire ignition.
  • High-speed Liquid Discharge– Excessive speedy Diesel fill/discharge from jet nozzles tend to charge up with static energy. High flow Diesel spraying in the container tank without any protection measures will lead the Diesel to inflame.
  • Collision of Solids– Applying Sandblasting in a Diesel tank can put an impact on the solid component in the tank’s body. Although sandblasting clears oxidation, the process is enough to produce static electricity and ignite.

Read also: Is Petroleum Oil Flammable Or Combustible?

Final Words

To appropriately tell if Diesel is Flammable or not, both fuel liquids are Fire Hazard, the Gasoline is the typical Flammable liquid. But, on the other hand, Diesel fuel is graded as a combustible liquid.

However, not to create a mistake, the Diesel Fuel will burn or ignite. It is capable to burn as fuel as well in certain conditions, it will act like a flammable liquid, and will be very hazardous.