At what stage of fire development does the fire's heat release rate become primarily limited by the amount of available fuel and oxygen, rather than the fire's own growth?

The fire's heat release rate, which is the rate at which thermal energy is generated by combustion, becomes primarily limited by the amount of available fuel and oxygen, rather than the fire's own growth, during the fully developed stage.

During the preceding growth stage, the fire's heat release rate increases significantly as the fire expands, involving more combustible materials. This stage often culminates in flashover, a rapid transition where all exposed combustible surfaces within a compartment ignite almost simultaneously due to radiant heat feedback, marking the end of the growth-driven heat release rate increase and the onset of the fully developed stage.

Once the fire is in the fully developed stage, its heat release rate reaches its maximum potential and is no longer primarily driven by the fire's own spread or increasing involvement of new materials. Instead, the heat release rate becomes constrained by the total amount of available fuel or the total amount of available oxygen. If there is an abundance of fuel but restricted openings for air, the fire becomes ventilation-limited, meaning the heat release rate is controlled by the incoming oxygen supply. Conversely, if there is ample oxygen but the combustible materials are scarce or are being rapidly consumed, the fire becomes fuel-limited, meaning the heat release rate is controlled by the available fuel.