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What Are The 5 Different Classes Of Fire?

What Are The 5 Different Classes Of Fire?

Fires can be categorized into 5 classes primarily based on the fuel source that the fire burns from. Not every fire is the same, with different classes of fires requiring different extinguishing agents for effective extinguishment.

Applying the wrong extinguishing agent to a fire can be very dangerous, and may even cause the fire to burn with increased intensity. To help understand the different types of fires and the proper method for extinguishing each type of fire, we explore the 5 different classes of fire.

Class A – Ordinary Combustibles

Class A fires are generally the most common types of fires out of the different classes of fires. These fires occur when ordinary combustible materials such as wood, cloth, paper, rubber, and plastics ignite.

The commonly found ordinary combustible materials that Class A fires use as fuel enables these types of fires to spread and intensify rapidly.

Class A fires can be extinguished by cooling the combustible fuel to a temperature that is below ignition temperature. The most effective extinguishing agents to use on Class A fires include water (such as water mist systems) and gaseous fire suppression systems, as well as foam, dry chemical powder, and wet chemicals.

Class B – Flammable Liquids & Gases

Class B fires use flammable liquids and gases as a fuel source. These fires typically use petroleum greases, gasoline, tars, oils, oil-based paints, solvents, lacquers, alcohols, and flammable gases as a fuel base.

Class B fires represent high-risk fire hazards in industries such as power generation facilities, mining sites, and oil & gas worksites. Water is ineffective in extinguishing Class B fires as it causes the fuel to scatter, spreading the flames further.

These types of fires can be extinguished by smothering or removing the oxygen supply from a fire. The extinguishing agents used for Class B fires include foam, dry chemical powder, and gaseous fire suppression systems.

Class C – Electrical Fires

Class C fires are electrical fires caused by electrical components and energized electrical equipment such as wiring, controls, motors, machinery, and appliances. These types of fires are common in industries that make use of heavy electrical equipment such as data centres and industrial manufacturing facilities.

Electrical fires can be caused by short-circuiting machinery, overloaded electrical cables, or faulty wiring. Using water as an extinguishing agent is very dangerous as water conducts electricity and can cause serious harm to nearby individuals. Additionally, the use of water as an extinguishing agent often causes further costly damage to electrical equipment and other critical assets.

Class C fires require electrically non-conductive extinguishing agents to safely extinguish a fire, such as dry chemical powder and gaseous fire suppression systems. The most effective gaseous fire suppression systems for Class C fires include HFC227ea, FK-5-1-12, and inert gas fire suppression systems.

Class D – Combustible Metals

Class D fires use combustible metallic substances as a fuel source. These types of fires involve combustible metals such as magnesium, titanium, zirconium, sodium, lithium, and potassium.

Class D fires usually occur in the laboratory, industrial and manufacturing environments that use manufacturing processes to cut, drill, or mill combustible metals. Most metal fires occur when the metal dust, flakes, and shavings generated during the manufacturing process ignite and spread.

Common extinguishing agents such as water are ineffective against Class D fires, and may even enhance the burning of these fires. Special dry powder agents are used to extinguish Class D fires through heat absorption and smothering (eliminating the oxygen element from a fire).

Class K – Grease/Cooking Fires

Class K fires use combustible cooking oils, fats, and grease as a fuel source. Spillages of cooking oils near the many heat sources found in commercial kitchens often result in Class K fires.

Cooking fires spread rapidly and can be very difficult to manage. Wet chemical agents are the most effective extinguishing agent to use on Class K fires. Fire blankets can also be used to smother cooking fires.

Summary

The 5 classes of fires all behave differently, burn from different fuel sources, and require different extinguishing agents to put the fire out effectively. 

Classes Of Fire Infographic
This table summarizes the differences between the 5 classes of fire.

FST Fire Suppression Systems

For sufficient protection against fire hazards, each class of fire must be addressed with the right extinguishing agent.

FST supplies a wide range of fire suppression systems, including gaseous fire suppression systems and low pressure water mist systems. Contact Us to find the right fire protection solution suited to your unique environment.

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