Is oil flammable?

Aug 27, 2018 Posted by Walter Ingles

Oils such as engine and motor oil are viscousious petrochemicals that have been derived from the fractional distillation of crude oil. Oils are immiscible with water, which means that the two liquids won’t mix. Crude oil is formed deep underground from the decomposition of organic organisms such as zooplankton and algae. After millions of years of geological heat and pressure, the organic matter transforms into oil and gas.

Engine oils are made up of heavier hydrocarbons that have around 18-34 carbon atoms per molecule. Oils made from larger molecules normally have a higher flash-point because of the strong intermolecular forces between the molecules. Engine oils normally have a flashpoint greater than 150 °C. Substances that have a flashpoint above 150 °C are classified as C2 combustibles. As these substances have a flashpoint above 150 °C, they are not classified as flammable liquids. For a substances to be classified as a class 3 flammable liquid, it must have a flashpoint below 60 °C.   

Why are oils less volatile than flammable liquids

Oils are not classified as flammable liquids because they don’t give off enough flammable vapours to ignite in the presence of an ignition source at temperatures below 60 °C. When flammable liquids burn, it is not the liquid that burns, but the flammable vapour that is dispersed from the flammable liquid. The more easily a liquid gives of flammable vapours, the more easily it will ignite in the presence of an ignition source.

Flammable liquids that give off a lot of flammable vapours are those that are made up of relatively small molecules. Smaller molecules have weaker intermolecular forces of attraction between the molecules. Molecules with weak intermolecular forces of attraction require less heat energy to break the bonds between the liquid molecules and cause them to escape as a vapour.

Engine oils are made up of large molecules which have between 18-34 carbon atoms per molecule. The intermolecular forces of attraction between the molecules are a lot stronger than the forces of attraction that would exist between the small molecules that make up petrol. As the intermolecular forces of attraction are stronger, substances like engine oil will not burn at room temperatures. A substance such as engine oil would have to be subject to temperatures greater than 150 °C, for it to produce enough flammable vapours to ignite in the presence of an ignition source.

Because engine oils have a flashpoint above 150 °C, they are classified as C2 combustibles and not Class 3 Flammable liquids.

How to safely store oils

Even though engine oils are not classified as class 3 flammable liquids, they must be stored in a safe and compliant manner. If engine oils were subject to higher temperatures, there is a possibility that they would produce enough flammable vapours to ignite in the presence of an ignition source.

The Australian Standard that outlines the requirements for the storage and handling of combustible liquids is AS1940 - The storage and handling of flammable and combustible liquids. This standard outlines the design requirements for indoor and outdoor combustible liquid storage facilities as well as the segregation and separation requirements for the positioning of combustible liquids stores. The design requirements for outdoor combustible liquids stores includes factors such as:


AS1940 also outlines other requirements for the storage of combustible liquids including:

  • How combustible liquids must be segregated from other incompatible chemicals.
  • How combustible liquids stores must be separated from ignition sources and in a protected place.  

Design requirements for outdoor combustible liquids stores

Ventilation

To keep the concentration of combustible vapours within the store below the workplace exposure standard, combustible liquids storage facilities must have sufficient ventilation. A ventilation system can be a mechanical ventilation system or a natural ventilation system. Mechanical ventilation systems installed on combustible liquids storage facilities must be intrinsically safe and therefore natural ventilation systems are more practical and the preferred option. A compliant natural ventilation system can be achieved by having two walls of a combustible liquids store open to the outside atmosphere. These openings on the store can be cladded with a wall of fixed louvers.

Spill containment

To ensure that any potential spills within the combustible liquids storage container are contained in a safe and compliant manner, all combustible liquids storage facilities must have a spill containment sump in the base of the storage facility. The capacity of the spill containment sump depends on the quantity of oils being stored within the unit. The required spill containment capacities according to AS1940 are shown below:

Facilities storing less than 10,000L

Spill containment capacity = 100% of the largest package within the store + 25% of the aggregate capacity of the store.

Facilities storing between 10,000L - 100,000L

Spill containment capacity = 100% or the largest package within the store + 25% of the aggregate capacity of the store + 10% of storage capacity between 10,000L and 100,000L.

Facilities storing more than 100,000L  

Spill containment capacity = 100% of the largest package within the store + 25% of the aggregate capacity of the store + 10% of storage capacity between 10,000L and 100,000L + 5% of the storage capacity exceeding 100,000L

Segregation requirements for combustible liquids storage facilities

Flammable and combustible liquids are incompatible with a number of other classes of dangerous goods. If incompatible classes of dangerous goods mix it can result in violent chemical reactions that could harm people and property. To reduce the risk of violent chemical reactions, flammable and combustible liquids must be segregated from other incompatible classes of dangerous goods. The compatibility of flammable/combustible liquids with other classes of dangerous goods is shown on the chart below.

 

Class 3 - Flammable/Combustible Liquids

Class 2.1 - Flammable Gas

Segregate

Class 2.2 - Non-flammable, Non-toxic Gas

Keep Apart

Class 3 - Flammable/Combustible Liquids

Compatible

Class 4.1 - Flammable Solids

Keep Apart

Class 4.2 - Spontaneously Combustibles

Segregate

Class 4.3 - Dangerous When Wet

Segregate

Class 5.1 - Oxidising Agents

Segregate

Class 5.2 - Organic Peroxides

Isolate

Class 6 - Toxic Substances

Keep Apart

Class 8 - Corrosive Substances

Keep Apart

 

Key:

Keep Apart: Dangerous goods of these Classes should be kept apart by at least 3m. Consult the SDS or supplier

Segregate: These combinations of dangerous goods should be segregated by at least 5m and kept in separate compounds or building compartments.

Isolate: This requirement applies to organic peroxides, for which dedicated stores or storage cabinets are recommended. Adequate separation from other buildings and boundaries is required.

Compatible: Dangerous goods of the same Class should be compatible; consult SDS or suppliers about requirements for individual substances.

Separation from ignition sources and protected places

To reduce the risk of harm to people and property, flammable and combustible liquids such as oils must be separated from ignition sources and protected places. Combustible liquids storage facilities must be separated from all ignition sources by a distance of at least 3 metres. Stores of combustible liquids must also be separated from onsite protected places by a distance of least 3 metres. AS1940 defines an onsite protected place as:

A building where people are employed within the property boundary, including offices, warehouses, manufacturing or processing areas, amenities and other dangerous goods stores where quantities exceed minor storage.

Indoor storage of oils

AS1940 outlines different storage requirements for the indoor storage and the outdoor storage of combustible liquids. Combustible liquids can be safely stored indoors using a safety cabinet that has been manufactured in full conformance to AS1940. A cabinet that has been manufactured in full conformance to AS1940 must have:

  • The walls, floor, doors and roof of the flammable cabinet must be constructed from a double walled sheet steel construction. The gap between these walls must be no less than 40mm and can be left empty or filled with a fire resistant insulation.
  • The gaps around the doors and the walls of the flammable storage cabinet shall be sealed to prevent heat radiation and the spread of flames in the event of a fire.
  • The base of the cabinet shall form a liquid tight sump of at least 150mm deep. This sump must be designed in such a way that packages are prevented from being stored in the sump. This sump will contain any spills that may occur inside the cabinet.
  • The shelves inside the cabinet must be perforated to allow for free air movement inside the cabinet. The shelves should also be sturdy and capable of carrying the maximum possible load.
  • The inside of the cabinet including the shelves shall be designed in such a way that any spills are directed into the sump in the base of the cabinet.
  • The doors of the cabinet shall be self-closing, close-fitting and held shut automatically by catches at two or more points.
  • If the doors are equipped with a device to hold the doors permanently open when the cabinet is being loaded, the doors must automatically close when the temperature exceeds 80 degrees celsius.
  • Materials that are critical to the structural integrity of the cabinet must not melt at temperatures below 850 degrees celsius. Seals and gaskets are an exemption to this requirement

Next steps

Oils are not classified as class 3 flammable liquids because they do not give off enough flammable vapours to ignite in the presence of an ignition source at temperatures below 60 °C. Even though oils are not classified as flammable liquids, they must be stored in full conformance to AS1940. AS1940 is the standard that outlines the requirements for the storage and handling of flammable and combustible liquids such as oils. Safe storage of oils can be achieved by following the guidelines outlined above, and adhering to the requirements of AS1940. If you would like more information on how to reduce the risk of flammable and combustible liquids in your workplace, download our free ebook by clicking on the image below.

How to reduce the risk of flammable liquids in the workplace

Walter Ingles

Walter Ingles Compliance Specialist

Walter is STOREMASTA’s Dangerous Goods Adviser. He loves helping businesses 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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