Is petrol flammable?
Apr 19, 2018

Is petrol flammable?

Walter Ingles Walter Ingles

Petrol, which is also known as gasoline in the United States, is a mixture of hydrocarbons obtained from the fractional distillation of crude oil. The hydrocarbon molecules that make up petrol are quite small having between 4-12 carbon atoms per molecule. Petrol has a relatively low flashpoint of -43 degrees °C and therefore it will readily burn at room temperature. According to the Australian Dangerous Goods Code (ADGC), petrol is classified as a Class 3 Flammable Liquid. The ADGC classifies all substances with a flashpoint below 60 degrees celsius as Class 3 Flammable Liquids.

What makes petrol so flammable?

At room temperature petrol remains in a liquid state. When petrol burns, it isn’t the liquid that burns, but the flammable vapours that are dispersed from the flammable liquid. Therefore the more easily an organic compound vaporizes, the more volatile or flammable it will be.

As outlined earlier, the organic molecules within petrol are relatively small with around 4-12 carbon atoms per molecule. The smaller the mass of the molecules the weaker the intermolecular forces of attraction are between the molecules. The intermolecular forces of attraction are the forces that keep the molecules together as a liquid and keep them from dispersing as a gas.  As the intermolecular forces between petrol molecules are relatively weak, it means that very little heat energy is required to break these bonds and cause the petrol molecules to disperse as gases. In fact, the intermolecular forces between the molecules in petrol are so weak that the molecules will gain enough heat energy to escape as a gas to form a flammable mixture with air at temperatures as low as -43 °C. This flammable mixture will ignite in the presence of an ignition source.

The molecules that make up diesel fuels are much larger than those that make up petrol fuels. Diesel fuels have around 12-20 carbon atoms per molecule. As their molecules are larger they have stronger intermolecular forces between their molecules which require more heat energy to break. Most diesel fuels will not release enough flammable vapours to ignite in the presence of an ignition source at temperatures below 60 degrees celsius. Therefore most diesel fuels are not classified as flammable liquids while petrol fuels are.

How to safely store petrol

As petrol fuels are very flammable, their presence may pose many risks upon people, property and the environment. To ensure that people, property and the environment are adequately protected, petrol fuels must be stored in a safe and compliant manner. As petrol is classified as a flammable liquid, all storage facilities used to store petrol must comply with the Australian Standard AS 1940-2017 - The storage and handling of flammable and combustible liquids. This standard outlines the requirements for the design, construction and operation of stores used for the storage of flammable liquids. It covers factors such as:


All these features ensure that the petrol fuels pose the least amount of risk upon the people, property and the environment.

The ventilation ensures that the flammable vapours coming from the flammable liquids are kept at a safe concentration. A low concentration of flammable vapours reduces the risk of the vapours igniting in the presence of an ignition source.

The spill containment provisions ensure that any petrol spills that may occur inside the flammable liquids store are contained. Containing petrol spills allows you to reuse the fuel and protects the environment from becoming polluted.

Petrol and other flammable liquids are incompatible with a number of other dangerous substances. To avoid violent chemical reactions, flammable liquids must be segregated from incompatible substances by certain distances determined by the dangerous goods segregation chart.

Download a FREE Dangerous Goods Segregation Chart

As large quantities of flammable liquids have the potential to cause severe fires, they must be separated from public and protected places by certain distances to avoid harm to people in the event of a fire. A petrol fire will be triggered by an ignition source and therefore all petrol storage facilities must be isolated from ignition sources.  

A public place is any place other than private property, open to the public, which the public has a right to use and which includes a public road. Parking areas for commercial buildings are not considered to be public places.

A protected place is a factory, workshop, office, store, warehouse, shop, or building where persons are employed, that is outside the property boundary of the installation.

To warn workers and visitors of the potential risks associated with the flammable liquids that are stored on a premises, clear dangerous goods signage must be displayed on all flammable liquids storage facilities.

Also to ensure the least amount of risk to those using flammable liquids, AS1940-2017 outlines certain operational requirements for those handling flammable liquids.

Different types of petrol storage facilities

To enhance the safety of those that have to store and handle flammable liquids, AS1940-2017 outlines different requirements for indoor storage and outdoor storage. Flammable liquids can be safely stored indoors using a flammable storage cabinet. For outdoor storage, flammable liquids can be stored safely using a chemical storage container that has been manufactured in full conformance to AS1940-2017. An example of a chemical storage container that has been manufactured in full conformance to AS1940 is shown below:

Petrol chemical storage container

More advanced and safer methods can be used to store, handle and dispense flammable liquids by utilising outdoor dispensing stations. Outdoor dispensing stations don’t only reduce the risk associated with petrol, but they also increase the efficiencies in storing and dispensing. Outdoor petrol dispensing stations can be manufactured to meet specific storage and dispensing requirements of those that use flammable liquids on a regular basis.

Next steps

As petrol is classified as a flammable liquid, it is very important that you store and handle the substances in a way that reduces the risks that they may have upon the people, property and environment of your organisation. This can be done by adhering to the requirements outlined in AS1940. If you would like more information on how to reduce the risks associated with flammable liquids, download our FREE eBook by clicking on the image below.

How to reduce the risk of flammable liquids in the workplace

Walter is STOREMASTA’s Dangerous Goods Adviser. He loves helping business reduce the risk that Dangerous Goods pose upon their employees, property and the environment through safe and compliant dangerous goods storage solutions.

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