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Knowledge Base » Health and Safety » Combustible Materials

Combustible Materials

Last updated on 21st April 2023

What are combustible materials?

Combustible materials are solids or liquids that can easily ignite and burn. If a combustible material is exposed to fire or heat, it is likely to ignite, burn or release flammable vapours.

To understand what combustible materials are, you first need to understand combustion. Combustion is a chemical reaction that produces both heat and light. It is an example of a high-temperature exothermic reaction between a fuel and an oxidant.

Combustion releases thermal energy into the atmosphere. As combustion usually happens at a high temperature, light and sound energy is often also released into the environment.

When measuring the combustibility of materials, how easily the material bursts into flame as a result of fire or combustion is considered. Combustible materials are at greater risk of catching and spreading fire.

Examples of combustible materials include:

Combustible Solids Combustible Liquids
Wood Oil
Paper Greases
Rubber Lubricants
Plastic Oil based paint
Coal Cooking gas
Charcoal Kerosene oil
Cloth Cleaning solvents
Straw Diesel fuel

Combustion can be both complete and incomplete. Complete combustion is when the combustible material leaves no residue or carbon, whereas incomplete combustion leaves a residue behind after it is burned.

Wood is a combustible material

What are non-combustible materials?

Unlike combustible materials that catch fire and burn, non-combustible materials are materials that do not ignite, burn or release any flammable vapours if they are subjected to fire or heat. If a non-combustible material is close to or in contact with a flame in the presence of oxygen, it will not catch fire.

Examples of non-combustible materials include:

  • Brick masonry.
  • Concrete.
  • Cement.
  • Steel.
  • Ceramics.
  • Stone.
  • Sand.
  • Water.
  • Glass.

How should combustible materials be stored?

The correct storage of combustible materials is paramount. Understanding the risks combustible materials pose, and understanding how to control these risks, can help to prevent fires and explosions.

As a general rule, combustible materials should never be stored near exits, or close to electrical equipment or heating equipment. Where possible, combustible materials should be stored in a separate, well-ventilated storage area. Combustible materials should always be kept away from any incompatible substances that could be potential sources of ignition.

It is also recommended to keep combustible materials in an area that has appropriate fire resistance. These areas should also not exceed the maximum storage capacity, as this can raise the fire risk. Only store as few a number of combustible materials as possible at any one time.

Combustible or flammable materials should also be stored in sealed containers that are not conductive, if possible. Keeping the doors of the storage area closed at all times can also help to reduce the risk of fire.

Combustible and flammable materials should also be kept out of direct sunlight and in a temperature-controlled area. The storage area should also be cool and dry.

If the combustible material that is being stored is a liquid or chemical, it will need to be stored in a purpose-made container or cabinet that is located in a separate area that has good ventilation and is away from ignition sources. The container or cabinet should be sealed when not in use. The container should also not be made of another combustible or flammable material, such as plastic.

It is also important to ensure that combustible materials or other hazardous substances are labelled correctly. It is legally required that all mixtures must be classified, labelled and packaged in line with the EU CLP Regulation. Visit the Health and Safety Executive (HSE) website for more information on correctly labelling combustible substances.

Diesel is a combustible material

What are flammable and combustible materials?

Although combustible materials and flammable materials are similar, there are some important distinctions that those working with these materials should be aware of. We already know that a combustible material is something that can burn, or combust, in air. A flammable material is combustible; however, it ignites at lower temperatures.

Whilst a combustible material does not ignite as easily, a flammable material usually catches fire as soon as it is exposed to fire. This makes flammable materials more dangerous.

Some examples of flammable materials include:

Flammable Solids Flammable Liquids
Flour Aerosol cans
Cotton Hand sanitiser
Linen Nail varnish
Acrylic Nail varnish remover
Polyester Acetone
Nylon Gasoline
Alkali metals Alcohol

How flammable or combustible a material is usually depends on the volatility of the materials. If material is exposed to a flame or another ignition source, it is classified as flammable or combustible based on the specific temperature that will cause it to catch fire. The lowest temperature that the material will generate vapours and ignite is known as the flashpoint.

Although flashpoints can vary in different materials, there are specific flashpoint thresholds that distinguish combustible materials from flammable materials:

Flammable Material Flashpoint:

If the flashpoint is below 37.8°C, it is considered a flammable material.

Combustible Material Flashpoint:

If the flashpoint is between 37.8°C and 93.3°C, it is considered a combustible material.

Coal mining

How do combustible materials affect building safety?

When a material or substance is being used for construction or is being stored in a building, it is important to consider the combustibility of the substance and what safety measures, or procedures, can be put into place.

All combustible materials must be prevented from coming into contact with any potential sources of ignition. Failure to do this could compromise the safety of a building and result in the materials igniting, releasing vapours, catching fire, or even creating an explosion.

As different materials have different flashpoints, some materials may be more dangerous than others. Determining the flashpoint of the material is the first step in ensuring the safety of a building.

This information can be found on the Safety Data Sheet (SDS). This describes the hazards that a hazardous substance can prevent, as well as information on how to store the substance, necessary safety procedures, and any emergency measures that should be employed. All hazardous substances should come with an SDS.

Materials with low combustibility can be used in construction so as to reduce the fire risk. This tactic may be employed for apartment buildings, office buildings and residential houses. If materials with higher combustibility are used, this can heighten the fire risk.

There are specific preventative actions, measures and procedures that can be employed to reduce the risk of combustible materials to building safety.

1. Reducing the number of combustible materials used or stored in the building.

2. Installing fire sprinklers, fire extinguishers and other safety equipment.

3. Storing combustible materials correctly.

4. Clearly labelling or specifying any materials that are more flammable or combustible.

5. Keeping fire escapes, emergency routes, doors and stairways obstruction-free.

6. Using flame-retardant materials where possible.

7. Ensuring there are no leaks when using chemicals or combustible liquids.

8. Taking extra care when demolishing a structure or undertaking any building work to ensure tank structures or other combustible materials are not disrupted and ignited.

9. Using less combustible paint or varnish on the walls or furniture.

10. Using the smallest amount of combustible or flammable liquid as possible.

11. Installing smoke detectors throughout the building.

12. Switching off or unplugging electricals when not in use.

13. Not smoking indoors.

Fire alarms

Do combustible materials require a risk assessment?

If combustible materials are present in the workplace, a risk assessment is necessary to ensure the safety of employees, the general public and the building itself. A fire risk assessment is a legal requirement to ensure a building has all the necessary precautions in place in the event of a fire. As combustible materials are a major indicator of the risk of fire, these need to be considered in the risk assessment.

A risk assessment must be recorded and accessible if a building has five or more regular occupants, or if a business has five or more employees. If you do not meet these criteria, a risk assessment is still required to ensure the safety of all those involved, although it does not need to be formally recorded.

A risk assessment can determine whether any safety measures need to be put into place. The risk assessment can be based on the information provided in the Safety Data Sheet (SDS). It is the responsibility of the business owner or building owner to conduct the risk assessment, although they can allocate another qualified person to do this instead.

The risk assessment should be reviewed annually, or if any changes are made to the materials present in the building. The risk assessment should include any risks that are identified, and any actions or recommendations based on these risks.

The risk assessment should take into account:

  • The types of materials, their flashpoints and their properties.
  • How many combustible materials are present.
  • How the materials are stored and handled.
  • The size of the area.
  • Any potential ignition sources.
  • The presence of combustible or flammable liquids.
  • Any ventilation provisions.
  • Any potential risks posed by the presence of combustible materials.
  • Procedures in the event of a fire.
  • The fire evacuation plan. For more information on how to conduct a fire safety evacuation plan, visit our knowledge base.
  • The means of escape in the event of a fire.
Fire exit.

Banning combustible materials

In 2018, the government consulted with the Royal Institute of British Architects (RIBA) regarding the banning of combustible materials in the external walls of high-rise buildings. This ban was being considered in response to the Grenfell Tower fire in 2017, where 72 people died and more than 70 others were injured.

RIBA recommended that the only possible way to ensure that these buildings were safe in the future was to enact a complete ban on the use of combustible materials. The ban was confirmed by the UK government on 1st October 2018.

High-rise residential buildings and hospitals, care homes and student accommodation higher than 18 metres tall would also be covered under the ban. Exempt from the ban are hotels and office buildings. These are viewed as a lower risk because of the evacuation strategies they have in place.

As well as banning combustible materials from being used in future builds, the government also pledged to give support to local authorities to enable them to carry out emergency work that removes or replaces any aluminium composite material (ACM) cladding that is deemed as unsafe.

Following this legislation, RIBA has made further recommendations which reduce the risk that combustible materials pose.

These recommendations include:

  • Extending the ban to also include hotels, hospitals, boarding houses, and any other buildings that would be at risk of multiple fatalities.
  • Further clarification is needed about any exempt materials, as well as information about materials that do not result in fire spreading through external walls.
  • Further research is needed into the use of structural timber within external walls.
  • Buildings higher than 11 metres tall should be included in the ban.
  • The ban should only place restrictions on plasterboard, sheathing board, insulation, outermost cladding, and other elements of the building that fit the European classifications A2-s1, d0 and A1. The ban should not apply to the primary structure, as this should have fire protection that is adequate, in line with Building Regulations.
Cooking gas is a combustible material

Difference between A1 and A2 classifications

To comply with the ban on combustible materials in external walls, materials must now meet a fire classification of A2-s1 or A1. Understanding the difference between A1 and A2 classifications is therefore vital.

Before looking at A1 and A2 classifications in more detail, let’s first look at the seven different classifications for individual products.

A1 Non-combustible
A2 Limited combustibility
B Combustible materials with very limited contribution to fire
C Combustible materials with limited contribution to fire
D Combustible materials with a medium contribution to fire
E Combustible materials with a high contribution to fire
F Combustible materials – Easily flammable

There are also three classification levels for smoke emissions:

s1 Smoke emissions are absent or very low
s2 Smoke emissions with average volume intensity
s3 Smoke emissions with high volume intensity

Although A1 and A2 classified materials are similar, there are some important distinctions to be aware of. Materials classified as A1 are completely non-combustible. This means they will not ignite or burn when exposed to expected levels of fire or heat and will have no contribution to fire. Examples of A1 materials include aluminium, natural stone, concrete, porcelain, brick masonry and cement.

Materials classified as A2 have limited combustibility. In the event of a fire, A2 materials will have a limited contribution to the fire.

Both A1 and A2 materials can be used on high-rise developments, as they are not classed as combustible. However, materials classified as A2 must also be classified as s1, with smoke emissions being absent or very low in order to meet the accepted fire classification.

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About the author

Nicole Murphy

Nicole Murphy

Nicole graduated with a First-Class Honours degree in Psychology in 2013. She works as a writer and editor and tries to combine all her passions - writing, education, and psychology. Outside of work, Nicole loves to travel, go to the beach, and drink a lot of coffee! She is currently training to climb Machu Picchu in Peru.

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