Anyone interested in fire safety at some point has probably wondered what different kinds of fires there are. The type of fire changes depending on the type of fuel that is burning. And as we covered in our Fire Triangle blog post in May, fuel is one of the vital three components of any fire. Different kinds of fires require different kinds of fire extinguishing methods and tools. So, understanding the difference between them could help save lives and a lot of money in damages – especially if a fire is in the workplace. All UK fires are classed according to the European Standard Classification of Fires, which is used across the European Union. This blog post will look at the different classes of fire and how you can prevent/fight them.
Ordinary Combustible Fires (Class A)
This is the most common kind of fire and the materials involved in an ordinary fire are what you might expect: paper, rubber, wood, textiles, etc. Ordinary combustible fires occur when fuel is heated and ignited; they’ll continue to burn if there is a supply of oxygen and ample fuel. This type of fire is the most common, but it’s also the easiest to fight, as they can be extinguished with water, which cools the fire down until it cannot stay alight. It’s best to use either water- or foam-based extinguishers to put out a class A fire.
Flammable Liquid Fires (Class B)
If a liquid has an ignition temperature lower than 100°C, then it can be considered a flammable liquid. Flammable liquids also have a low flashpoint – which is the temperature at they give off gas/vapour. Flammable liquids will burn if they get too hot or if any source of ignition is applied. Petrol, alcohol, paints, solvents, and kerosene are all examples of common flammable liquids. Flammable-liquid fires are extremely hot and they spread very quickly. They also produce toxic black smoke that makes them particularly deadly and very hard to fight. Foam fire extinguishers are the best option for flammable liquid fires as they suffocate the flames. Do not use water to fight this kind of fire as it splashes and scatters the liquid fuel, spreading the fire further.
Flammable Gas Fires (Class C)
Flammable gases can cause an explosion if just one spark ignites them. Because of their highly dangerous nature, they are stored in sealed containers that protect them from outside heat and ignition sources. Common flammable gases are propane, butane, and different petroleum gases. The lower explosive limit (LEL) is the minimum concentration of flammable gas in the air that might explode if ignited. For most flammable gases, the LEL is just 5%, making them incredibly dangerous if mismanaged. For flammable gas fires, it is always best to ensure that the gas supply has been cut off before you even attempt to fight the flames. Otherwise, you could be walking into a large explosion. Whilst most fire extinguishers are ineffective at extinguishing flammable gas fires, dry powder extinguishers can be effective. In fact, dry powder extinguishers are effective against class A, B, C, D, and E fires, so they are easily the most versatile fire extinguishers available.
Metal Fires (Class D)
Some metals burn ferociously when ignited. Some metals can burn when they are fully solid, although it usually requires a significant amount of heat to ignite metals because they are very good conductors and transfer heat away very quickly and efficiently. However, metal powder or metal shavings are much easier to ignite as they do not conduct heat as well. As such, any metal that is broken up into tiny pieces poses a much higher risk of fire. Some metals (such as sodium, aluminium, magnesium, and potassium) actually burn when they come into contact with water and air, so water and foam fire extinguishers are out of the question and may cause a violent explosive reaction – and given that this explosion will send pieces of burning metal in all directions, it is best to not take the chance. If there is a large amount of burning metal, it is probably best to let it burn out naturally as metal fires produce a lot of ash that usually starves the fire of oxygen after a while. However, if you spot a metal fire early enough, then a powder fire extinguisher will work, but only if it is the dry power variety – the other variety will make matters worse. Metal fires are very dangerous and it is best to talk to an expert in your local fire authority if you are worried that your premises is at risk of a metal fire.
With all kinds of fire, oxygen and fuel are necessary for them to spread. This is why our fire shutters and fire curtains work so effectively: they prevent the fire spreading into the next room, finding more fuel and a fresh oxygen source. That’s all we have time for part 1, but please come back to read What Different Kinds of Fire Are There? (Part 2).