Which of the following correctly defines the stage of flashover?

Flashover is the stage in a fire where there is a rapid and widespread spread of flames throughout a room or area. It occurs when the heat from the combustion gases and the adjacent surfaces raise the temperature to the ignition point of most, if not all, combustible materials within that space, causing them to ignite almost simultaneously. This phenomenon drastically increases the heat and produces a significant amount of smoke, making it one of the most dangerous phases of a fire event for both victims and firefighters.

In contrast, the other definitions do not accurately describe flashover. Containment within a limited area refers to a situation where the fire is still manageable, but it does not encompass the widespread nature of flashover. Complete cooling of all objects suggests that there is no active fire or heat present, which is the opposite of what occurs during flashover. Instantaneous extinguishing of flames implies that the fire has been suppressed or extinguished, which is not representative of the flashover stage, where flames are expanding rapidly.