Flashover

The flashover ( dt shoot-through, nor flashover, flashover, F / O) is a phase within a fire event and refers to the sudden transition of a damage fire (eg room fire ) from the development phase to full fire phase. This process occurs most rapidly over the entire fire area.

Definition

The definition of the International Organization for Standardization for the flashover is: ". The rapid transition of all surfaces of combustible materials of a sphere towards a fire "

Fire Protection Engineering from the flashover is described as the boundary between the development phase (pre- flashover ) and the fully developed fire ( post-flashover ) of a room fire. General criterion for flashover is the rise in room temperature to 500-600 ° C, a heat flux density ( the flames and the smoke ) of 15 to 20 kW / m² or beating out flames from the chamber openings.

The time to flashover is strongly dependent on the factors of the fire room size, ventilation and fire load.

Formation

In the development phase initially burn furnishings ( such as a sofa, table, furniture ) and form combustion gases and pyrolysis gases. Can not be dissipated through space openings, the resulting smoke, there is an accumulation of heat on the ceiling. The strongly heated smoke layer is now shining on the entire furnishing an ever increasing heat radiation. At the same time the temperature rises throughout the fire area. The surfaces of the combustible, but not yet burning objects pyrolyze and then ignite at 15 to 20 kW / m² heat flux (see solar constant ) or a flue gas temperature of 500 to 600 ° C abruptly without pilot flame. The horizontal flame propagation speed in the room ( other material through an ignition burning objects ) is then about 10 m / min. The result is a full fire of space and temperatures of about 1000 ° C. Further information on the burning rate, heat release, temperature development before and after the flashover and time to onset of flashover can be found in the research reports No. 130 and 142 of the Research Centre for Fire Engineering at the University of Karlsruhe (TH).

Pre- and post-flashover

As a pre- flashover fire is defined as the development phase prior to flashover. At the time of survival for people lying on the ground and the approach of a respirator squad is still possible. As a post-flashover or full fire is called the state after flashover. It prevailing temperatures are partially above 1000 ° C. Due to the large amounts of energy released in this phase survival is short possible. Even modern protective clothing of a firefighter can protect at this moment only for a few seconds before severe burns.

Confusion

On the Internet and in some cases also in the training of fire brigades, the term flashover is erroneously equated ( backdraft german) with the concept of flue gas ignition (English rollover ), or the smoke gas explosion. When the smoke gas ignition, it is merely the burning of pyrolysis of a smoke layer, the flashover to the phenomenon described above. In fire protection engineering, there is the clear definition above.