In which stage of the burning process does rollover occur?

Rollover occurs during the explosive growth stage of the burning process. This stage is characterized by a rapid increase in fire intensity and temperature, often resulting in the ignition of gases that have accumulated in the upper layers of the fire environment.

During explosive growth, fire has transitioned from initial combustion to a state where heat and volatile gases are released. As these gases rise and flow toward areas with oxygen, they can ignite in a sudden, dramatic fashion, resulting in rollover. This phenomenon is typically observed as flames spread out along the ceiling or upper portions of a room, manifesting due to the combustion of the unburnt gases that have accumulated.

In contrast, the ignition (incipient) stage is where the fire is just beginning; the initial growth stage represents a period of slow development and heat accumulation rather than explosive action. The ventilation-limited stage signifies that the fire is limited by the amount of oxygen available, which can prevent rollover from becoming pronounced. Each of these other stages deals with fire behavior that does not involve the rapid ignition of gases in the same manner as seen in the explosive growth stage.