Back to basics: Is diesel fuel flammable or combustible? (2024)

We hear the terms ‘flammable’ and ‘combustible’ thrown around every day, and often used interchangeably. However, there are key differences between the two, and understanding them can be of great benefit.

What do we mean by flammable?

Diesel fuel, according to some definitions, isn’t flammable at all. There are four grades of flammability, where a liquid has to have a “flash point” of different degrees celsius or below. A flash point is the lowest temperature that will cause a liquid to evaporate to the point of ignition. The grades start between 23 and 35 degrees Celsius and go up to grade four, being between 60 and 93 degrees Celsius

When something is referred to as flammable, what we usually mean is that it’s easily ignitable. Highly flammable materials include paper, cooking oil, some paint thinners and methylated spirits.

A license isn’t required to store flammable material it’s important to store it correctly. A room with diesel fuel that isn’t stored securely could be full of flammable vapours.

Not only is diesel considered a grade 4 flammable, it’s also a combustible.

The basics of combustibility

Combustibility is a way of describing the likelihood of something bursting into flame, either through contact with fire or being put through the process of combustion.

To be combustible, a liquid has to have a flash point of between 60 degrees celsius and boiling point. This is the range that diesel fuel finds itself in, which is why we refer to the motors found in diesel vehicles as internal combustion engines.

Our guide to flammable and combustible liquids

We’ve explored the details of the grades of flammability, in addition to safety compliance measures and regulatory standards for the safe storage, distribution and usage of diesel fuels, in our comprehensive guide to flammable and combustible liquids.

The guide has recently been updated to incorporate the latest standards for 2019 and is essential reading for anyone who wants to know more about how to handle diesel fuel correctly.