What Are the Key Differences Between Flammable and Combustible Materials?

January 28, 2019
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If your workplace handles certain hazardous materials, such as flammable chemicals, it’s vital for you to understand the risks they pose. In particular, you must recognise the difference between flammables and combustibles. The level of risk that a material poses and how easily it can cause a fire is often affected by whether it’s flammable or combustible.

This article will clearly define what separates flammable and combustible materials. Knowing this will enable you to better understand their properties so you can handle and store them safely in your workplace.

What is the Difference Between Flammable and Combustible?

Flammable and combustible materials differ based on the temperatures they must be exposed to in order to catch fire. Specifically, 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.

Flammable and combustible materials in a warehouse

The flash point is the lowest temperature at which hazardous materials will generate vapours and ignite if exposed to an ignition source.

These temperatures vary from material to material, but there are certain flash point thresholds that separate flammables from combustibles.

What are the Flash Points of Flammables and Combustibles?

Flammable materials Combustible materials
A material is considered flammable if it has a flash point of any temperature below 37.8 ºC. A material is considered combustible if it has a flash point higher than 37.8 ºC and below 93.3 ºC.

Flammable and combustible materials will generate vapours when exposed to a temperature at, or above, its flash point, which can easily ignite when exposed to an ignition source. Therefore, the lower the flash point of a material, the higher the risk is. This is because the temperature of most workplaces will not be above the lowest combustible flash point (37.8 ºC), which means that combustibles won’t start to form vapours in a normal working environment. Oppositely, flammables are more likely to form vapours in normal work environments, because their flash points are lower.

This is why it’s so crucial to know exactly what flammable or combustible materials you have in your workplace, so you can control the risks accordingly. For example, if you have a flammable material with a flash point of 25 ºC, storing it under 25 ºC will prevent it from generating vapours that could ignite. If they have a lower flash point however, such as -20 ºC, then you will need to implement further control measures to prevent existing vapours from igniting.

You can find examples of flammable and combustible materials, as well as their flash points, in the table below.

Flammables Flash point Combustibles Flash point
Petrol gasoline* -43 ºC Diesel fuel* 52 ºC to 82 ºC
Ethanol 16.6 ºC Phenol 79 ºC
Acetone -20 ºC Kerosene* 38 ºC -72 ºC
Methanol 12 ºC Formaldehyde 64 ºC
Propylene oxide -37 ºC Hydrazine 52 ºC
Ethyl chloride -50 ºC Paint thinner* 40 ºC
Benzene -11 ºC Naphthalene 78.89 ºC

*Note: this may vary depending on the specific composition.

Flammable bucket of blue paint

If your workplace stores or uses any of these, or any other flammable or combustible materials, it’s vital for you to understand how to control their risks. Otherwise, you will leave your workplace susceptible to a fire or even an explosion.

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How Flammable and Combustible Materials Affect Building Safety

It’s essential that you prevent flammables and combustibles from coming into contact with sources of ignition, particularly if the materials can create vapours or an explosive atmosphere. Otherwise, the fire safety of your building could be compromised.

Certain materials will require stricter controls than others to minimise these fire risks, especially depending on their flash point. Therefore, the first step you should take is to check material safety data sheets (MSDS or SDS) of every hazardous substance you store on site.

The law requires all hazardous materials to come with material safety data sheets. These provide information that helps you to decide what safety procedures are necessary for a certain hazardous material.

The information that MSDSs should contain include:

  • Associated hazards.
  • Composition.
  • First aid measures.
  • Firefighting measures.
  • Accidental release measures.
  • Handling and storage requirements.
  • Exposure controls and PPE requirements.
  • Physical and chemical properties.
  • Stability and reactivity, including incompatible materials.
  • Toxicological and ecological information.
  • Disposal considerations.

In particular, EU guidance on the compilation of safety data sheets states that safety data sheets should have comprehensive information about the material, and that employers and workers should use this as a source of information about hazards and safety precautions. Furthermore, it says that the sheets should give the flash point of volatile liquids that are classified as flammable.

Sign for the location of material safety data sheets

With the information provided by MSDS, you can determine what specific safety measures to put in place for the materials in your workplace.

For example, an MSDS may help you determine that you need to:

Substitute materials for less volatile alternatives.

Substitution is one of the first steps in the hierarchy of control. Therefore, wherever possible, you should swap high risk materials for ones that have a lower risk of causing a fire.

Check that there is suitable ventilation.

Wherever your workplace stores hazardous chemicals, ventilation is crucial for removing any vapours from the building. This minimises the chance of them setting on fire.

Ensure the storage area is appropriate.

Make sure you keep hazardous materials in a location with suitable fire resistance and never exceed maximum capacities. It’s crucial to store flammables and combustibles in non-conductive, sealed containers (such as glass or plastic). If this is not possible, containers must be appropriately grounded to prevent static charge. Furthermore, you must keep any potential sources of ignition away from the storage area and ensure the doors of storage rooms and cabinets are kept closed.

Store all hazardous materials with compatible substances.

Never store incompatible substances together as it can worsen the fallout in the event of a fire.

Control the temperature of the storage facilities.

If you control the temperature of the area to limit vapours, make sure you monitor this closely. You should also store all containers out of direct sunlight.

Ensure staff know how to decant correctly.

Staff must follow their workplace’s decanting process to ensure they don’t cause spills. More specifically, they must always decant into properly labelled, suitable containers and never reuse containers for different materials. This can cause a volatile reaction.

Reduce the quantity of materials that your workplace holds.

Your workplace should only ever hold the minimum necessary to keep the business running. Do not overstock, as this can worsen the fallout of an accident.

Improve the fabric of the building.

In some cases, the materials of your building could pose a significant fire risk. A notable example can be seen in the Grenfell Tower tragedy, which was made significantly worse by the unsafe aluminium composite material (ACM) cladding. As of 2018, the government have banned this combustible material, as it poses a major fire risk. If yours has this type of cladding, the building owner must replace it.

As long as you recognise the different safety requirements of flammable and combustible materials, you can easily minimise fire safety risks in your workplace. Always pay attention to the MSDS and follow any training provided to you regarding hazardous materials.

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