Classes of Fires & Fire Extinguishers
Superficially, fires look the same. They’re hot, and they burn with flames. However, the underlying chemistry can be radically different, changing the type of extinguisher you should use to put them out. Some fire types are significantly more hazardous than others and require special extinguishers. Others will intensify if you use the wrong extinguisher on them.
In this post, we look at the different classes of fires and the fire extinguishers you should use to combat them.
Class A - Solid Fuel
Class A fires, also called “ordinary fires,” burn using solid fuel. Examples include cardboard or paper fires in offices or wood fires in a timber yard.
Class A fires are common for two reasons:
- Solid fuels are abundant – you can find them present in most buildings
- Solid fuels are hard to eliminate – the majority of organizations rely on combustible materials to operate
Firefighters and first responders can use several fire extinguishers on Class A fires. Water, foam, wet chemical, and ABC dry powder are all effective.
Class B - Flammable Liquids
Class B fires burn using flammable liquids as fuel. Examples include hydrocarbon fuels, petrochemicals, inks, solvents, paint, and cleaning fluids.
Class B fires are responsible for 2 percent of uncontrolled fires but for one-fifth of all fire-related fatalities. Fire spreads quickly and uncontrollably, often leading to explosions.
Organizations follow international hazardous substance labelling standards to reduce the risk of dangerous Class B fires. These inform operatives how they should use and store substances in their possession.
If a class B fire starts, you can use the following extinguisher types:
- ABC dry powder
- CO2 gas
Do not use water on a liquid fire as it won’t be effective and may make it worse.
Class C - Flammable Gases
Class C fires use flammable gases, such as butane or methane, as fuel sources. Gas fires, like liquid fires, can be explosive. Therefore, organizations should only ever use qualified professionals to work on gas-based systems.
The best method for dealing with gas fires is to shut off the gas supply. Once you deprive them of fuel, they will go out rapidly.
If that isn’t possible, you can use a fire extinguisher. However, you should only use ABC dry powder on gas fires, not other methods.
Class D - Flammable Metals
Class D fires burn using flammable metals, such as potassium, magnesium, and lithium, as their fuel source. While most metals aren’t combustible, some are. Furthermore, when in their pure form, they may react violently if they come into contact with water, making the fire worse.
If you have a metal fire, the best way to extinguish it is by using special dry powder fire extinguishers. The dry powder creates a barrier between the combustible material and the surrounding air, denying flames access to oxygen. Once smothered, flames disappear, and the fire can no longer spread as easily.
Class D fires were once rare. However, they are becoming more common, thanks to the increasing prevalence of electric vehicles on the road. As batteries find more applications in society, Class D fires will continue to increase unless there are significant changes in dominant battery chemistries.
Class F - Fats And Oils
Class F fires use fats and oils as fuel sources. Strictly speaking, they are liquid-based fires but have their category. They commonly occur in kitchens, though they can happen on container ships and transport vehicles.
Class F fires usually result from leaving cooking equipment unattended. To extinguish this type of fire, only use wet chemical extinguishers. Do not use any other type of extinguisher as they may not be suitable for extremely high-temperature fires.
Electrical fires do not have their classification anymore. That’s because electricity is not a type of fuel but rather a way that a specific kind of energy propagates.
However, fires involving electrical equipment are common, so many extinguishers still advertise their ability to combat this type of fire.
To eliminate an electrical fire, you should use either of the following fire extinguishers:
- Dry powder
Conductive extinguishing substances, such as water, may make the fire worse and lead to additional hazards. Dry powder is best in low-voltage situations, while CO2 is superior when there is a stronger current.
As with gas fires, shutting off the electricity supply can reduce the intensity of the fire and make it easier to bring it under control.