The purpose of fire classification is to help identify the type of fire and therefore choose the best extinguishing method. Fire classification is most often based upon the type of material and fuel for combustion.

There are five main classes of fires. Although the naming of them may differ around the world, the characteristics are similar. The following naming conventions (Class A, B, C, D, K) are used in the United States.

Class A: Ordinary Combustibles

A class A fire is a fire that is fueled by combustible materials, such as wood, paper, or fabric. Class A fires are the most common type of fire and are often started by careless accidents, such as smoking in bed or leaving a candle unattended. Class A fires have relatively low ignition temperatures, and once the fuel or oxygen has been depleted, the fire will burn out. Generally speaking, if the fire leaves ash behind, it’s likely a Class A Fire. Class A fires can be very destructive, but they can be easily extinguished with water.

Class B Fires: Liquids & Gases

Class B fires are fueled by liquids or gases. They are often started by gasoline, oil, paint, or alcohol, or by gases such as methane or propane. Class B fires can be very dangerous because they can spread quickly and are difficult to extinguish. They also have a low flashpoint, which means they burn easily at any temperature if exposed to a fire source. Class B fires also spread rapidly and produce a thick black smoke as they burn.

A solid stream of water should never be used to extinguish this type of fire because it can cause the fuel to scatter, spreading the flames. The most effective way to extinguish a liquid fire is by inhibiting the chemical chain reaction of the fire, which is done by dry chemical extinguishing agents, although smothering with CO2 or, for liquids, foam is also effective.

Class C Fires: Electrical Fires

Electrical fires involve potentially energized electrical equipment. This type of fire may be caused by short-circuiting machinery or overloaded electrical cables or electric tools, appliances, motors, and transformers. Electrical fires can be a severe hazard to firefighters using water or other conductive agents since electricity can be conducted from the fire, through water, to the firefighter’s body and can cause death.

Hence, it is important to use the proper extinguishing agent, such as CO2 or a dry chemical extinguisher.

Class D Fires: Metallic Fires

Class D fires are often started by flammable metals, such as magnesium, titanium, or potassium. Class D fires can be very dangerous because they can spread quickly and are difficult to extinguish. Water is not effective against Class D fires, so it is important to use the proper extinguishing agent, such as a dry chemical extinguisher.

Class K Fires: Grease Fires or Cooking Fires

A class K fire is a fire that is fueled by cooking oils or grease. Class K fires are often started by kitchen accidents, such as leaving a pan of oil unattended on the stove. Class K fires are technically a type of liquid fire, but they are separated out as their own class because of their unique setting. Class K fires are most common in the food service and restaurant industry but can occur in any kitchen. Class K fires can be very dangerous because they can spread quickly and are difficult to extinguish. Water is not effective against Class K fires, so it is important to use the proper extinguishing agent, such as a wet chemical extinguisher.

Conclusion

Every class of fire presents a real level of danger. However, fires that are likely to spread quickly or cause explosions can be the most dangerous. That’s why understanding the different fire classifications can help to suppress or extinguish them as effectively and safely as possible.

Fire Classifications
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