Which model includes heat, fuel, oxygen, and chemical reaction?

• A. Fire tetrahedron
• B. Fire triangle
• C. Growth stage of fire
• D. Decay stage of fire

Answer: (A)

The model tested is the fire tetrahedron. It builds on the fire triangle by adding the chemical chain reaction as a fourth element. Heat, fuel, and oxygen are the three materials needed to start and sustain combustion, but the flame also depends on the ongoing chemical reactions that release energy. When that chemical reaction is present, the flame continues; remove any one element, and the fire can’t sustain itself. The fire triangle covers only heat, fuel, and oxygen, while growth and decay stages describe how a fire develops over time, not what sustains it.