Compartment fires fully developed

For a fully developed fire, conduction commonly overshadows convection and radiation therefore, a limiting approximation is that h hk, which implies Tw T. This result applies to structural and boundary elements that are insulated, or even to concrete structural elements. This boundary condition is conservative in that it gives the maximum possible compartment temperature. 

One aspect of fully developed fires that will not be addressed here is their production of combustion products. When compartment fires become ventilation-limited, they bum incompletely, and can spread incomplete products such as CO, soot and other hydrocarbons throughout the building. It is well established that the yield of these incomplete products goes up as the equivalence ratio approaches and exceeds 1. More information on this issue can be found in the literature [1],... 

Thomas, P.H. and Heselden, A.J.M., Fully-developed fires in single compartment, a co-operative research programme of the Conseil International du Batiment, Fire Research Note 923, Joint Fire Research Organization, Borehamwood, UK, 1972. 

When heat fluxes to the lower part of the compartment are high enough to ignite common combustible materials, a rapid transition occurs to a fully developed fire. This transition usually takes less than a minute and is referred to as flashover. When flashover occurs, it is no longer possible to survive in the fire compartment. All exposed combustible materials become involved in the fire (note burning rug and table top in Figure 14.1d). Commonly used criteria for the onset of flashover are a hot smoke layer temperature of 600°C and an incident heat flux at floor level of 20kW/m2. 

Flashover leads to the fully developed stage of a fire in which all exposed combustibles in the compartment are involved. The temperatures and heat fluxes in the compartment and the types of combustible materials that are present control the generation rate of fuel volatiles. Typical... 

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