What is the difference between Class A, B, and C fires in the context of ARFF?

What is the difference between Class A, B, and C fires in the context of ARFF?

• A. Class A are ordinary combustibles; Class B are flammable liquids (fuel); Class C are energized electrical fires.
• B. Class A are electrical; Class B are wood; Class C are plastics.
• C. Class A are metals; Class B are plastics; Class C are gases.
• D. Class A are liquids; Class B are solids; Class C are gases.

Answer: (A)

In ARFF, fires are categorized by the type of fuel involved and whether electricity is part of the equation, which guides the suppression approach. Class A fires involve ordinary combustibles such as wood, paper, cloth, or rubber. They burn with heat that can be cooled and saturated, so water or water-based agents are effective to lower the temperature and prevent reignition. Class B fires involve flammable liquids like fuels, oils, or solvents. The vapors can spread and float, so the goal is to suppress vapors and prevent the fuel from spreading. Foam or dry chemical agents are used because they smother the flame and separate the fuel from the air; water alone is usually avoided because it can spread the liquid. Class C fires involve energized electrical equipment. The priority is to de-energize the equipment if it’s safe to do so, and to use nonconductive extinguishing agents to avoid electrical shock or further arcing. Water is generally avoided on live electrical fires; once power is off, techniques similar to non–electrical fires may be used as appropriate. So the difference lies in the material fueling the fire and whether electrical energy is involved, which determines the most effective extinguishing method.

In ARFF, fires are categorized by the type of fuel involved and whether electricity is part of the equation, which guides the suppression approach.

Class A fires involve ordinary combustibles such as wood, paper, cloth, or rubber. They burn with heat that can be cooled and saturated, so water or water-based agents are effective to lower the temperature and prevent reignition.

Class B fires involve flammable liquids like fuels, oils, or solvents. The vapors can spread and float, so the goal is to suppress vapors and prevent the fuel from spreading. Foam or dry chemical agents are used because they smother the flame and separate the fuel from the air; water alone is usually avoided because it can spread the liquid.

Class C fires involve energized electrical equipment. The priority is to de-energize the equipment if it’s safe to do so, and to use nonconductive extinguishing agents to avoid electrical shock or further arcing. Water is generally avoided on live electrical fires; once power is off, techniques similar to non–electrical fires may be used as appropriate.

So the difference lies in the material fueling the fire and whether electrical energy is involved, which determines the most effective extinguishing method.