Difference Between Flammable and Combustible Materials

Once it’s started, a fire can rip through a building in minutes, destroying stock, damaging the premises beyond repair and taking lives. To stay safe, business owners must be aware of the properties of all the materials or liquids on their premises that could start or accelerate a fire.

Some materials are more easily ignitable than others. This makes them more hazardous to work with. It also presents challenges to storing them safely. Developing effective fire safety procedures means knowing the difference between flammable and combustible materials and liquids.

The consequences of not being vigilant about fire safety laws can be devastating for a business. A fire can race through a building in minutes, destroying everything in its wake. It only takes one mistake to wreck a business totally. Staying safe means always being aware of the enormously destructive potential of fire.

The Health and Safety Executive (HSE) recently investigated an explosion caused by the improper handling of flammable liquid at John Winters & Company Limited of Halifax. In April 2021, an enormous fire erupted at the dental supply company that caused massive amounts of damage.

A worker incorrectly poured heptane from a metal drum into a plastic bulk container. The spill from this simple act caused a static charge that sparked an explosion. It was made worse by the incorrect storage of cardboard boxes that added fuel to the fire. The premises were quickly engulfed in flames. More than 60 firefighters fought to extinguish the blaze. Luckily, no one was hurt or killed in this incident.

The company was found guilty of breaching the Health and Safety at Work etc. Act 1974 and fined £30,000 and ordered to pay an additional £8,030.94 in costs. HSE inspector Andrea Jones said: “Implementing appropriate control measures when handling flammable liquids is essential.”

The definition of flammable and combustible materials is determined by their ignition temperature. To be categorised as flammable, a substance will ignite at a lower temperature than a substance categorised as combustible.

Flammable materials are more likely to catch fire and are more hazardous than combustible materials. The temperature at which flammable and combustible materials ignite and keep burning is known as the flash point.

The lower the flash point, the more flammable the material is.

To be considered combustible, a material or liquid must have a flash point greater than 37.8°C and below 93.3°C. Most workplaces aren’t at a temperature exceeding the lowest combustible flash point of 37.8°C. So, combustible materials aren’t likely to form vapours that can be ignited by a spark and turn into a blaze.

Common combustible materials include:

• Wood
• Paper
• Coal
• Plastic
• Straw
• Cloth

Some common combustible liquids and their flash points are:

• Diesel: 52 to 82°C
• Lube oil: 187°C
• Paint thinner: 40°C
• Vegetable oil: 315°C
• Olive oil: 210°C
• Formaldehyde: 64°C

Although they don’t have a high flash point, combustible liquids should still be kept in special storage facilities. All combustible materials need to be held in an orderly fashion, as build-ups can present a considerable fire risk. Think about a pile of cardboard boxes left in a corner or a stack of tins of cooking oil. Both of these seem innocuous enough. But if a fire occurs, that stack of combustible materials and liquids will give the blaze the fuel to rage out of control and consume a building.

Flammable materials and liquids are more hazardous than combustible materials and liquids. To be considered flammable, a material or liquid must have a flash point below 37.8°C. Flammable materials can easily form vapours that can start a fire as they have a lower flash point.

Common flammable materials include:

• Polyester
• Cotton
• Flour
• Nylon
• Acrylic
• Linen

Some common flammable liquids and their flash points are:

• Petrol: -43°C
• Acetone: -20°C
• Benzene: -11°C
• Methanol: 12°C
• Kerosene: 38°C
• Ethanol: 16.6°C

So, if you keep any flammable liquid with a flash point of 20°C, you must store it in an environment that’s lower than this temperature. Some liquids have flash points beneath – 0°C. So, extra precautions must be taken.

Petrol gasoline, for instance, has a flashpoint of around -43°C. Diesel fuel has a flash point of between 52 and 82°C. You can easily see that more care needs to be taken when storing petrol gasoline than diesel fuel.

Always be on guard and aware of the high risks of using and storing flammable materials.

Depending on their characteristics, flammable and combustible materials are typically grouped into classes, such as Class A, B, C and D.

The grouping of flammable and combustible materials into classes is commonly based on different systems, such as the NFPA (National Fire Protection Association) system or the DOT (Department of Transportation) system. These systems use other classification schemes to categorize hazardous materials based on their properties.

In the NFPA system, materials are classified into different classes:

• Class A: These are ordinary combustible materials, such as wood, paper, cloth and plastics. They are typically organic in nature and leave ash after burning
• Class B: These are flammable liquids and gases including gasoline, oil, propane and alcohol. They have a lower flash point and can ignite easily when exposed to an ignition source
• Class C: This class refers to energized electrical equipment or circuits. The primary hazard associated with Class C materials is electrical shock, but they can also cause a fire if an electrical fault occurs
• Class D includes combustible metals such as magnesium, titanium, sodium and potassium. These metals can ignite and burn at high temperatures. Special extinguishing agents are required to control fires involving them

It’s important to note that different classification systems may be used in different contexts and industries. Still, the above classification is commonly used for general fire safety discussions.

Flammable and combustible liquids and materials should never be exposed to ignition sources or kept in environments that are equal to or above their flash points. Any substance categorised as especially hazardous should come with an attached safety data sheet (SDS) provided by the manufacturer. The SDS should contain relevant information on the flash point of the substance and guidelines on how to use and store it correctly.

Some general rules to follow regarding flammable or combustible materials are:

• Do not store them near exits
• Do not store them near electrical equipment or heat sources
• Keep flammable or combustible materials away from incompatible substances
• Keep them in labelled, sealed containers – preferably those supplied by the manufacturer
• Keep flammable or combustible materials in temperature-controlled areas out of direct sunlight
• Only store the minimum amount of flammable or combustible materials required
• If possible, replace flammable or combustible materials with other substances
• Use personal protective equipment (PPE) when using flammable or combustible materials
• Develop safe work procedures and ensure they’re followed by everyone
• Regularly perform risk assessments
• Provide employees with adequate fire safety training

Overall, the presence of flammable and combustible materials in a building necessitates careful consideration and adherence to fire safety measures. Understanding their properties, implementing appropriate precautions, and complying with relevant regulations are essential for maintaining building safety and minimizing the risk of a fire-related incident.

Fire safety training ensures you meet UK health and safety legislation obligations.

Industries and authorities across the UK recognise our Fire Awareness Training course. It teaches people about the correct safety measures to control or eliminate risks. Your team must have a solid knowledge of fire safety and remain vigilant to avoid accidents, reduce your fire risks and stay safe at work.