Semenov Diagrams, Flashover and Instabilities

Fixed fire area, representative of a fully involved fuel package, e.g. chair, crib, pool 

Ignition of a second item, representing an initial fire (e.g. chair, liquid spill) and the prospect of ignition of an adjoining item. 

Opposed flow flame spread, representing spread on a horizontal surface, e.g. floor, large chair, mattress, etc. 

Here Af. will be taken to represent the projected external fuel surface area that would experience the direct heating of the compartment. From Equation (11.21), accounting approximately for the effects of oxygen and temperature, and distribution effects in the compartment, the fuel mass flux might be represented for qualitative considerations as 

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