Which stage is characterized by a declining heat release rate as the fuel is consumed?

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

Answer: (A)

In fire development, the stage where heat release rate declines as the remaining fuel is consumed is the decay stage. Once most of the fuel is burned, there’s less material available to combust, so the energy output drops even if flames linger. This contrasts with the growth stage, where heat release rate rises as the fire grows and more fuel catches fire. Ignition is the initial start of combustion, usually followed by increasing heat release as the fire develops. The fire tetrahedron is a model of the elements needed for combustion (fuel, heat, oxygen, and chemical reactions); it isn’t a phase describing how heat release changes over time.