What distinguishes a fully developed flame from a developing flame in fire consequence analysis?

• A. Color
• B. Fully developed has maximum HRR
• C. Developing flame is extinguished
• D. They have identical HRR

Answer: (C)

Fire stages are defined by how much energy the fire is releasing over time. In the developing stage, the flame is still growing and the heat release rate is rising as more fuel begins to burn. In the fully developed stage, the fire has reached the highest rate of heat release for the space, with combustion consuming available fuel at its peak. Extinguishment is not a defining feature of the developing stage—it can happen at any point if fuel runs out or suppression occurs. Color can change with soot and airflow and isn’t a reliable marker of stage, and having the same heat release rate would imply no difference between stages, which isn’t the case.