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A flashover is the simultaneous ignition of all flammable material in an enclosed area.
Flashover occurs when the majority of surfaces in a space are heated to the point at which they give off flammable gases that are hot enough to ignite themselves (i.e. they do not need to be touched by flame to start burning). Prior to flashover, flammable gases may be given off but are not hot enough to ignite without contact with direct flame.
The classic example of flashover is where a piece of furniture is set alight in a domestic room. The fire on the furniture produces a layer of hot smoke across the ceiling in the room. The radiated heat from this layer heats the other surfaces in the room, causing them to give off combustible gases. When the surface temperatures become high enough, these gases ignite and, in the space of a few seconds, every surface in the room may be on fire.
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