Fire can be very dangerous and destructive. While all fires might look very similar, they are actually categorized into different classes. The different classes of fire are very important when it comes to safely extinguishing the fire.
Firefighters and other emergency responders learn about the classes of fire to help them identify risks at the scene of an emergency, and to establish how to tackle the fire. But what are the different classes of fire?
If you want to know about the different classes of fire and how to extinguish them then you are in the right place.
We have put together this useful guide with all of the information that you need to know. Keep reading to find out more.
What Is Fire?
Before we delve into the different types of fire, it is important that you understand the basic idea of what fire actually is.
Fire is an exothermic reaction made up of three components - heat, fuel, and oxygen. All three of these things must be present in order for there to be fire.
Heat is needed to start the fire and it also helps to maintain the fire. The fuel is the combustible or flammable material that burns. Once a fire runs out of fuel, it will stop.
The flames of the fire need oxygen - if a fire has no oxygen it will go out. In order to extinguish a fire you need to remove one or all of these elements.
The Classes Of Fire
Fire is categorized from A to E based on the materials involved in the fire. It is important to know what class of fire you are dealing with before you attempt to extinguish it.
Different classes of fire pose different risks and need to be put out in different ways.
Class A fires are fires that involve solid materials, also called ordinary combustible materials. These include wood, textiles and paper.
A lot of household fires will be class A fires, though it does depend on how the fire was started. Wooden furniture, clothing, and curtains all fall under this category.
Class B fires involve flammable liquids and gasses. This could be gas, diesel, alcohol, oil based paints, butane, methane and ethylene.
You are probably familiar with the flammable liquids, but you might wonder where you will come across flammable gasses.
You would be surprised at how common they are! Butane is found in most cigarette lighters and is also used in the cooling systems of refrigerators.
Methane is one of the elements that makes up the natural gas used to fuel your home and your gas appliances. Ethylene is a bit more uncommon as it tends to be used mainly for agricultural purposes.
Class C is electrical fires. This is any fire that involves an outlet/wiring or electrical appliance of any kind and a lot of house fires fall under this category.
The most common causes of electrical fires in homes are portable heaters, clothes dryers, poor wiring, and overloaded sockets.
Portable heaters cause issues when they are placed too close to other items, as the heat can set fire to flammable materials.
Clothes dryers can become an issue if the filter is not emptied and the lint builds up and can easily warm up and catch fire.
If electrical wiring is poorly installed, an electrical cable is damaged, or too many appliances are being run through one plug socket, then an electrical fire can easily start.
Once the electrical source has been removed, the fire can then be moved into a different class depending on what kind of fuels are still burning.
Fires involving combustible metals are categorized under class D. Metal tends to need to reach a very high temperature before it will set fire, but certain metals are combustible like sodium and lithium.
Metal shavings are particularly hazardous as they have a greater surface area to volume ratio, with more access to oxygen. A lot of industrial fires fall into this category, and it is unlikely that a house fire will be class D.
Class E, also known as Class K, is for cooking fires with oil or fat involved. This is different than a cooking fire which was caused specifically by a gas appliance or electrical appliance.
For a fire to fall under class E/K, the oil or fat itself must have caught fire or have played a large part in the spread of the fire.
Vegetable oil, canola oil, coconut oil, butter, olive oil, and cooking grease would all fall under this category. Some home fires and many restaurant fires are Class E/K fires.
How To Extinguish A Fire Based On Class
The various classes of fire have different methods for extinguishing the flames in a safe and effective way. That is why it is important to understand what type of fire you are dealing with before you attempt to put it out.
Putting Out A Class A Fire
Class A fires are one of the easiest to extinguish. You can use almost any kind of fire suppression technique without exacerbating the fire - dry chemical extinguishers, water, heavy materials or fire blankets, foam extinguishers, wet chemical extinguishers or carbon dioxide would all work.
Putting Out A Class B Fire
There are a few ways to put out a Class B fire. You could use a dry chemical extinguisher, a foam extinguisher, carbon dioxide, or halon (although halon is not commonly used as a fire extinguisher since it was discovered to have an adverse effect on the ozone layer).
Do not use water to put out a Class B fire. This is because the water can easily disperse the flammable gas or liquid, causing the fire to spread.
Some flammable liquids can float on water, which means that they will continue to burn on the surface of the water.
Putting Out A Class C Fire
The best way to put out an electrical fire is with a dry chemical extinguisher, or with carbon dioxide. Do not use water, as water conducts electricity. This could cause the fire to spread or cause you to be electrocuted.
If you can remove the source of electricity entirely then you can use a different method to extinguish the fire based on what materials are still burning.
Putting Out A Class D Fire
The safest way to put out a Class D fire is with a dry chemical extinguisher, but not your regular household kind.
A normal domestic fire extinguisher will exacerbate the fire due to the chemicals used inside it. You will need to use an industrial dry chemical extinguisher with different chemicals in order to put out the fire.
Industrial buildings tend to have these on hand. It is unlikely that you will come across a Class D fire unless you work in an industrial setting.
Putting Out A Class E/K Fire
There are special fire extinguishers called wet chemical fire extinguishers which are perfect for putting out kitchen fires that involve oils or grease.
Most commercial kitchens will be fitted with these extinguishers, but you may not have one in your home. Some homes have a foam extinguisher in the kitchen and these can work very well.
A fire blanket is another good option as this will starve the fire of oxygen. It is usually not a good idea to use water on a Class E/K fire, but sometimes a water mist can be good to tame the flames.
Different Types Of Fire Extinguishers
There are different types of fire extinguishers that you can get to put out certain types of fires. These are:
- Water Fire Extinguishers - water fire extinguishers are cost effective and are perfect for fighting class A fires. You can get a water jet, a water spray, a water mist, or water with added fire suppression chemicals.
- Foam Extinguishers - Foam extinguishers are perfect for use on Class A fires or fires involving flammable liquids, but they are not so good for flammable gasses. The foam seals the liquid and prevents the flammable vapor from reaching the flames, starving the fire of fuel.
- Chemical Extinguishers - You can get wet or dry chemical extinguishers, and domestic or industrial chemical extinguishers. They all have different purposes, so make sure you are using the right one for the job.
- Carbon Dioxide Extinguishers - Carbon dioxide extinguishers are perfect for using on electrical fires or fires involving flammable liquids. They don’t leave behind any residue which makes them more convenient than foam extinguishers.
- Fire Blankets - Fire blankets work by smothering the fire and starving it of oxygen. They are ideal for kitchen fires, but can also be used to help a person whose clothes are on fire.
It is important to understand the different classes of fires so that you know what kind of fire you are dealing with. This will ensure that you use the safest method to extinguish the fire.