What fire stage occurs as the fuel is consumed and oxygen concentration falls?

• A. Incipient
• B. Growth
• C. Fully Developed
• D. Decay

Answer: (D)

Fire stages shift as the fuel and oxygen available for the fire change. The decay stage happens when the fuel has been largely consumed and the remaining oxygen is depleted, so the heat release rate drops and the flames fade. Even with high temperatures and lingering embers, the overall fire activity declines because the two main ingredients of combustion—fuel and oxygen—are in short supply. This stage follows the peak intensity of the fully developed phase, and it’s common to see smoldering, dense smoke, and hotspots as the fire winds down. If ventilation changes bring in more air, there can be risks like sudden rekindling or backdraft, but the defining trait is the diminishing flames due to exhausted fuel and reduced oxygen.