The Fire Classification System in the UK

All fires can be separated into 5 different categories, depending on the type of fuel that is burning.

Categorising fires in this way makes it easier to choose the most appropriate method of fighting the fire, for example some fire extinguishers are more suited for use on certain types of fires than others.

In the UK fires are classed using the European Standard Classification of Fires, which is recognised across the EU.

Class A – Ordinary combustible fires

These are probably the most common type of fire. They occur when materials become heated to their ignition temperature and will continue to burn as long as there is heat, oxygen and fuel to burn. Materials involved in these types of fires include paper, wood, textiles, rubber, some plastics and other organic carbon based compounds.

Class A fires are probably the easiest to extinguish as spraying them with water will cool the fire, removing the heat supply which is essential for the fire to burn. Water based or foam fire extinguishers are most appropriate for putting out ordinary combustible fires.

Class B – Flammable liquids

Flammable liquids are those that have an ignition temperature of less than 100°C. These liquids also have a low flashpoint, which means that they burn easily. The flashpoint is the temperature at which a substance gives off enough vapour to be ignited. These liquids can however burn at any temperature if a source of ignition, such as a spark or naked flame is supplied.

Examples of liquids that are flammable include petrol, kerosene, alcohol, solvents and paints. Fires involving these give off a lot of heat and tend to spread very quickly. They also produce thick, black toxic smoke, which can make these fires difficult to fight.

The best approach for extinguishing a Class B fire is to use a foam fire extinguisher to smother the flames, as using water causes the fuel to scatter therefore spreading out the fire.

Class C – Flammable gases

Flammable gases such as butane, propane and petroleum gases have the potential to create an explosion, if triggered by a single spark. For this reason flammable gases have to be stored securely in sealed containers. The LEL (lower explosive limit) states the lowest concentration of flammable gas that will burn in air. This is usually around 5%, which shows just how big the danger is of potential explosions.

Fires involving flammable gases are one of the most dangerous types of fire to fight. Before attempting to put the fire out, you should make sure that the gas supply is isolated first. Most fire extinguishers are ineffective on Class C fires, the only type being suitable for use being dry power extinguishers.

Class D – Metal fires

Certain metals and powdered metals can burn if ignited, although it requires a lot of heat to ignite most metals, as they are good conductors and transfer heat away quickly to their surroundings. Powdered metals and metal shavings are easier to ignite than solid lumps of metal, so pose a higher fire risk.

Alkali metals such as potassium, magnesium, aluminium and sodium can burn when in contact with air and water. Therefore putting water or foam onto metal fires will increase the intensity of the flames and result in potentially explosive reactions that will send pieces of burning metal in all directions.

In many cases with industrial fires where there are large amounts of burning metal, the safest approach is usually to let the fire burn itself out. As Class D fires tend to produce a lot of ash, this builds up and eventually starves the fire’s Oxygen supply. If a metal fire is spotted early on, specialist type D powder fire extinguishers can be effective, although it should be ensured that they are the specific dry powder type, suitable for use on metal fires.

Electrical Fires

Short circuits, overloaded switchboards, faulty equipment and damaged wiring can all cause electrical fires. Electrical fires are not strictly a fire class of their own, as electricity is a source of ignition as opposed to a fuel. They are still important to mention however as they have their own special fire safety requirements.

Before dealing with an electrical fire, the supply of electricity must be isolated as quickly as possible. As water and foam has the power to conduct electricity, even once the electricity source has been cut off, you should not attempt to put out the fire by putting water on the flames or by using foam and water based extinguishers. Carbon dioxide and dry powder fire extinguishers are the only types of fire extinguishers recommended for safely tackling electrical fires.

Class F – Cooking oil fires

Fires involving cooking oil and fats are common both in homes, businesses and professional kitchens. They pose a very difficult challenge to extinguish, due to the high temperatures involved. Simply trying to cool the fire with water will not work; in fact using water on a burning pan is likely to cause a rapid spreading out of the flames, making the fire worse and potentially injuring anyone in its vicinity.

For this reason special fire extinguishers have been developed to address Class F fires. Wet chemical extinguishers contain a formula which cools the fire and then emulsifies to seal the surface and prevent re-ignition.

If you need advice on which fire extinguishers would be most appropriate for your business premises then get in touch with Euro Fire Protection. Our trained specialists are BAFE approved and can help you ensure your business is best protected against fire.

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