Class 3, Flammable Liquids, are one of the most commonly used classes of dangerous goods.  Flammable liquids have various different uses and are found in many workplaces from hair salons to industrial manufacturing plants. 

If you work with flammable liquids It is vital for you to understand the risks they pose and important to understand the differences between their properties. Improperly using, transporting, or storing flammable materials is easy to do and the consequences can be fatal.


The Difference Between Flammable and Combustible

flammable and combustible


The terms ‘flammable’ and ‘combustible’ are sometimes taken to mean the same thing.  However, this is not true, especially when considering the classification of dangerous materials.  Flammable materials are much more dangerous to work with as opposed to combustible materials. 

Flammable and combustible are terms used to describe how easily a liquid ignites.  While we usually use the term to describe liquids, it is not the liquid that burns – it’s the vapour given off by the liquid.

So, what is the difference between flammable and combustible?  Flammables will ignite at lower temperatures than combustibles when exposed to an ignition source. This specific temperature, also known as a flash point, is what separates flammables and combustibles.

A flash point is the temperature at which a material’s vapours will ignite and keep burning.  The lower a material’s flash point is, the greater the risk of a fire involving the material. Flammable liquids burn at normal working temperatures and have a flashpoint below 100°F (37.8°C).  Combustible liquids usually burn above working temperatures, need heat before they ignite, and have a flashpoint above 100°F.

The flash point allows materials to be classified according to the fire hazard they present in normal use.  People who use and transport hazardous materials use the flash point to measure the risk of an explosive, or ignitable, mixture forming when a liquid escapes from its container or packaging.  Under dangerous goods regulations, a liquid with a flash point below 140°F (60-65°C) is classified as Class 3, FLAMMABLE LIQUIDS.


Important Physical Properties of Flammable and Combustible Liquids

Flammable and combustible liquids vary in complexity but there are some crucial similarities between the two types of liquid.  Here are three defining physical characteristics to keep in mind when handling flammables and combustibles.

The flashpoint is the main physical property that defines flammable and combustible liquids. It is the minimum temperature at which the vapours given off by a liquid will ignite when mixed with air – near the surface of the liquid – and keep burning.

Boiling Point
The boiling point is the temperature that the liquid boils. It occurs when the vapor pressure of the liquid equals the atmospheric pressure.  Boiling liquids produce a lot of vapours and the harder they boil, the more vapours they release.

Flammable/Explosive Range
The flammable range of a liquid is a measure of the vapour concentration in the air where an explosion can occur, based on normal atmospheric and temperature variables.  If the vapour concentration is ‘too lean’, there is not enough fuel for ignition – If the vapour concentration is ‘too rich’, there is not enough oxygen for ignition. This flammable range is the danger zone for fires.

Most vapors from flammable liquids are heavier than air and can flow downward.


Where to Find the Info

The Safety Data Sheet: Chemical suppliers provide a Safety Data Sheet (SDS) with each product they deliver.  It contains all of the chemical, physical and safety information for the product – including its flammability and flash point. These physical properties appear in Section 9 of any SDS.  Section 7 describes the safe handling and storage requirements for each chemical.


Flash point examples

Flammable liquids with a flash point below 0° need to be treated with extreme care. These goods can ignite at any temperature.  

  • PETROL: Petrol has a flash point of -43°C, a great deal of care must be taken when storing.
  • ACETONE: Acetone has a very low flash point at -20°C. Above this temperature, it can take just 2.5% of acetone in the air to cause an explosion. 
  • BENZENE: Benzene’s flash point sits at a chilly -12°C, so it’s regarded as a highly flammable liquid. Inhalation of benzene fumes has been linked to blood disorders such as anaemia and leukemia and prolonged exposure can result in chronic health issues. 
  • METHANOL: Methanol has a flash point that sits between 11 and 12°C.
  • ETHANOL: The flash point of ethanol is 16.6°C, which is likely to be just below room temperature. 
  • KEROSENE: Kerosene’s flash point sits right on the boundary for flammable fuels at 38°C. 
  • DIESEL: Ranging from 52° to 96°, diesel’s flash point is considered high enough to be non-flammable in most environments (hence its use in compression-ignition engines). 
  • BIODIESEL: Biodiesel’s flash point of 130°C makes it a relatively stable flammable liquid. 
  • LUBE OIL: The flash point of lube oil is around the 187°C mark, rendering it relatively non-flammable. 


This article should not be used in substitute for checking the exact requirements in the applicable modal regulations.


How can hibiscus help?

Are you meeting your flammable liquid labelling requirements?

It is the responsibility of manufacturers, importers and suppliers to correctly label hazardous chemicals and once they reach your workplace, if they are transferred out of their original container, you are also responsible for the labelling of the new container.

All of the flammable liquid package labels and transport placards manufactured by Hibiscus Plc comply with GHS/ADR/IMDG/UN requirements, and are made from materials that meet the strict BS5609 standard.  BS5609 is a specification for labels that are intended for marine use, whereby both the ink and the substrate must be able to withstand 3 months continuous immersion in sea water and still be legible and have good adhesion.

For bespoke labelling, contact us on 0113 203 1942