A flashover occurs at the stage of a fire at which all surfaces and objects within a space have been heated to their ignition temperature, and flame breaks out almost at once over the surface of all objects in the space. Thetemperature is between 932 to 1,112 degrees Fahrenheit, although flashover temperatures can peak at about 2,000 degrees Fahrenheit.
The first phase of flashover results from the ignition of flammable gases produced by combustion (primarily carbon monoxide) that have accumulated in the upper parts of the fire area. As this is happening, the radiant heat of the original fire is heating nearby combustibles--the walls, furniture, anything in the room--and these also begin giving off flammable gases. This is called "pyrolysis." In this phase, smoke banks down quickly, reducing visibility dramatically.
The next phase of flashover is the rollover or flaming of these gases near the ceiling. This may appear as small flashes of flame in the dense smoke, or as rollover, a flame front rolling out across the ceiling. The fire has now changed from a steady-state fire to an aggressive, fast moving fire.
The rapid fire development is complete as conditions move into final phase: thermal collapse. Intense radiant heat pours down from all around. You can no longer get under the thermal balance (the stratified layer of heat and smoke). Like a building collapse, intense heat drops to floor level.

All Firefighters were ok after this flashover. There is still one at top of ladder and one on the ladder! The Firefighter on the ground was knocked off the ladder.
This picture is courtesy of Aaron Burns of
Local 2551.