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Understanding the Fire Classes in the UK

The fire classification in the UK is based on the type of fuel source of the fire. This standard is in line with the European Standard Classification of Fires and it is recognised across the EU. There are five fire classes, signified by the letters A to F (note that the letter E is replaced by an electric spark symbol but more on that later) and the different types of fire extinguishers are designed to battle each one of them more effectively. 

If you are looking to buy a fire extinguisher, you would probably need to know what the classes of fire in the UK are, what causes each one of them and what is the best type of fire extinguisher to put them out.

Class A Fires

Class A fires are the most common. They are usually fuelled by common organic materials, such as paper, wood or fabrics. Luckily, they are also the easiest to extinguish by removing the second of the three elements of the fire triangle – heat. Cooling the fire down is achieved by spraying it with water or the appropriate fire extinguisher.

Foam and water fire extinguishers are most suitable to fight a Class A fire. However, dry powder and wet chemical fire extinguishers can also be used on ordinary combustible fires.

Class B Fires

Class B fires are caused by flammable liquids, such as alcohol, paint, petrol, solvents or kerosine. The ignition temperature for such fires is relatively low (under 100°C) and they burn easily at any temperature if a naked flame or another source of ignition is applied. 

What makes Class B fires exceptionally hazardous is that they spread fast and they produce thick smoke, which is difficult to navigate through and which can be extremely toxic when inhaled. This makes them very challenging to fight. 

The best fire extinguishers to use on Class B fires are CO2 and dry powder

Class C Fires

Class C fires are caused by flammable gases and they are one of the most dangerous, as just a single spark is enough to cause an explosion. According to the OH & S (occupational health and safety) standards for working with flammable gases such as methane, propane, petroleum gases and butane, those must be stored in special containers. The lowest concentration of these gases in the air required for a fire to occur is approximately 5%, which is a dangerously low LEL (lower explosive limit).

The only type of fire extinguisher that can be used to put out a class C fire is a dry powder extinguisher. All other types of extinguishers will be completely ineffective in this situation. Therefore, it is of utmost importance to ensure that you have the correct extinguisher if your business involves storing or handling flammable gasses. 

Class D Fires

Class D fires are fueled by the ignition of certain metals (especially powdered metals or metal shavings). Most metals require a high amount of heat to combust but once they catch on fire, metals are excellent conductors as they transfer heat to the surrounding fire and spread the fire at an alarming rate. This makes metal fires potentially devastating. 

Choosing the right fire extinguisher is even more important when it comes to metal fires. Only specific dry powder extinguishers, namely the L2 and the M28, can be used to fight those. You should never use a water or foam-based fire extinguisher on a class D fire because some metals, including magnesium, aluminium, potassium and sodium, burn faster when exposed to water and air. Using the wrong fire extinguisher can not only intensify the blaze but it can even cause an explosion, which could pose a serious threat to anyone standing nearby, especially the fire extinguisher user. 

Electrical Fires

Electrical fires are the only fires that are not referred to with a class letter. Even though Class E would be a logical choice of a name, electrical fires are marked with a special electric spark symbol instead (it resembles a flash of lightning). The reason for that is that electricity causes ignition but it’s not a source of fuel for the fire.

However, electrical fires have their own class because there are special steps that need to be taken when dealing with them, as opposed to any other type of fire. The first step is to isolate the electricity supply which caused the fire before attempting to extinguish it.

Then, you can only use CO2 or dry powder extinguishers on electrical fires because water is an electrical conductor, hence water or foam extinguishers can amplify the fire, rather than stop it. 

Class F Fires

Class F fires involve grease, fat and cooking oils, so they are very common in house fires and fires in the restaurant and hospitality industry. Whether a class F fire occurs in a domestic or a professional kitchen, the high temperatures involved make it very difficult to control. Also, a common mistake that people do in these kinds of situations is to throw water at the fire to try to put it out. This will have the complete opposite effect and will likely spread the fire even more.

Class F fires require their own category of fire extinguishers – wet chemical extinguishers. They are designed to simultaneously cool down the fire and to prevent reignition. 

We hope that our comprehensive guide on the fire classes in the UK has helped you learn and increase your fire safety awareness. Read our blog for more! 

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