Is Fuel Oil Flammable or Combustible? 

This article will answer the question, “is fuel oil flammable or combustible”? It also covers several topics about flammability and combustibility, fuel oil properties, also the precautions for safely handling fuel oil.

Is Fuel Oil Flammable or Combustible?

Fuel oil is combustible and quickly ignited when exposed to heat, spark, open flame, or another ignition source. Carbon and hydrocarbon chains in fuel oil are easily combined with oxygen to generate CO2 and H2O as well as heat energy, making it flammable.

What Is the Definition of Fuel Oil?

Fuel oil is a byproduct of the refining of crude oil. The first phase of extracting crude oil from the earth’s depths, a refinery processes produce various oil products, including gasoline.

It’s possible to extract fuel from natural gas and oil resources. Examples of strategic nonrenewable natural resources include petroleum and natural gas.

Oil and natural gas are vital commodities that affect many people. For an economy function, it relies heavily on petroleum and natural gas.

When hydrocarbons are heated to extremely high temperatures and pressures, they generate petroleum, a natural product of these conditions.

However, it does not include coal or other deposits of hydrocarbons in a solid form that are not obtained through the activities of the oil and gas industry.

Gaseous hydrocarbons are formed due to a natural process when hydrocarbons are exposed to air pressure and temperature.

The most common forms of fuel oils are distillate and residual. 

What Are the Differences Between Flammability and Combustibility?

For liquids that pose a potential fire threat, there are flammable and combustible liquid classifications:

  • A flammable liquid is any liquid with a flash point less than 37.8°C (100 F) at a pressure of 40 psi that can ignite under certain conditions (276 kPa)
  • A combustible liquid has a flash point of 37.8°C or 100 F or higher

What is Flammability?

Flammability is the ability of a substance to ignite. We can use combustible materials safely if we know what they are made of. Gasoline is common examples of flammable materials.

Extremely Flammable and Highly Flammable are two classifications of combustible materials. Extremely Flammable materials have a flash point of 0°C and a boiling point of 35°C. 

These substances are typically kept as gaseous mixtures at room temperature in a vacuum-sealed hermetic container under high pressure. 

R12 is the R-number for highly combustible materials. The boiling point of materials classified as Highly Flammable is infinity, and the flash point is 21 degrees Celsius. 

What is Combustibility?

Combustible materials, however, must be at a temperature before they can ignite. 

To produce and maintain a flame, to be ‘combustible,’ it must first reach a specific temperature which depends on its composition.

If a material has a flash point over the maximum expected ambient temperature in a geographic location, it can be considered ‘combustible.’

What Are the Properties of Fuel Oil?

Oils used in motor vehicles contain modest concentrations of sulfur, nitrogen, and oxygen components in complex and variable mixes of aliphatic (alkanes, alkenes, and cycloalkanes) and aromatic hydrocarbons. 

Various factors, such as the refinery where the oil was refined, the inclusion of additives or modifiers, and more, influence the exact chemical makeup of different types of fuel oils. 

When working with flammables and combustibles, keep these three features in mind:

Flash Point

Flash Point is the lowest temperature of a material that emits steam/gas and will ignite and burn instantly when exposed to a heat source or pilot flame. The lower the flash point, the more explosive the material is.

Speed of Evaporation

A fuel oil’s evaporation speed is determined by whether or not it is easy to evaporate under particular conditions, such as sufficient oxygen content around the fuel oil and an adequate temperature. 

Octane Number

An octane number is used to represent the likelihood that fuel oil may explode, and the number in fuel oil is an integer that includes several percent of iso-octane and heptane. 

The heptane number is reduced to zero, and the octane is given the value of 100. Eighty-six percent iso-octane and 24 percent heptane are found in fuel oil with an octane value of 86. A fuel oil’s detonation risk decreases with increasing octane rating.

Tendency to Detonate

Denotation is the combustion process in the engine that causes heat as a result of combustion, causing the fuel oil mixture that has not been exposed to sparks from the spark plug to experience discharge. A solid inclination to detonate can harm the motor.

What Are the Precautions For the Safe Handling of Fuel Oil?

  • An operator’s education and training must be adequate.
  • There needs to be adequate airflow.
  • Avoiding harm is possible by using proper personal protective equipment (PPE).
  • You should not come into contact with any ignition source, including heat, hot surfaces, flammable materials, and open flames.
  • It is illegal to smoke within 100 feet of a fuel oil source.
  • Pets and children should be kept out of reach of any sharp objects.
  • Avoid letting the storage face the sun directly.
  • The container must be kept at a constant temperature and be adequately ventilated to maintain its tight seal.
  • Keep your skin, eyes, and clothes free of any contact with the substance.
  • It is not suggested to inhale vapor or aerosol.
  • Extra care can be taken to avoid static discharges.

More information about this.


Fuel oil is flammable and combustible. Some storage management can keep fuel oil from igniting. 

Frequently Asked Question (FAQs): Is Fuel Oil Flammable or Combustible?

What are the different classifications of fuel oil?

Distillate and residual fuel oils are the two most common types of fuel oils. There are no high-boiling ingredients in distillate fuel oils because they are vaporized and condensed during the distillation process.

Is used fuel oil a hazardous waste material?

For recycling purposes, containers or tanks carrying spent oil should be labeled “Used Oil.” As hazardous waste, “Waste Oil” must be handled with care.


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