What is the last warning sign before flashover?

The last warning sign before flashover is typically rollover. Rollover occurs when the gases and smoke that have accumulated in the upper layer of a room ignite, often leading to flames spreading across the ceiling. This phenomenon indicates that the hot gases are nearing their ignition temperature, signaling firefighters to take immediate action to prevent a full flashover, which is the rapid spread of fire throughout an entire room or building due to high temperatures and combustible materials being present.

Understanding rollover is crucial for firefighters, as it serves as a critical indicator of the imminent danger of flashover. Recognizing this stage allows for proactive measures, such as adjusting tactics or evacuating to ensure safety. The phenomenon illustrates the transition from a localized fire to a more rapidly spreading one, enabling firefighters to identify and mitigate the risks effectively.