Flashover
A flashover is the near-simultaneous ignition of most of the directly exposed combustible material in an enclosed area. When certain organic materials are heated, they undergo thermal decomposition and release flammable gases. Flashover occurs when the majority of the exposed surfaces in a space are heated to their autoignition temperature and emit flammable gases (see also flash point). A small flame can reach flashover in 3-5 minutes. Flashover normally occurs at between 500 °C (932 °F) and 600 °C (1,112 °F) for ordinary combustibles and an incident heat flux at floor level of 20 kilowatts per square metre (2.5 hp/sq ft).
Flashover typically occurs between the growth stage and fully developed stage of a fire. This phenomenon is caused by various heat transfer mechanisms such as radiation, convection, and conduction, which lead to a sudden increase of temperature within the compartment.
An example of flashover is the ignition of a piece of furniture in a domestic room. The fire involving the initial piece of furniture can produce a layer of hot smoke, which spreads across the ceiling in the room. The hot buoyant smoke layer grows in depth, as it is bounded by the walls of the room. The radiated heat from this layer heats the surfaces of the directly exposed combustible materials in the room, causing them to give off flammable gases, via pyrolysis. When the temperatures of the evolved gases become high enough, these gases will ignite throughout their extent.
In October 2013, the Fire department of Oak Ridge, Tennessee filmed a controlled demonstration of a flashover fire and uploaded it to the video-sharing platform YouTube for educational purposes. The description of the video emphasizes the importance of a "Home Escape Plan" in saving lives.
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