Fire Safety Science Digital Archive

The prediction of the heat release rate in compartment fires is still a challenging question due to the feedback of the environmental variables on the burning rate. A set of large-scale, mechanically-ventilated pool fire experiments supports the present analysis. Most of these tests yielded a quasi steady-state with limited pyrolysis compared to well-ventilated conditions. From a well-stirred reactor approach, the effect of vitiation on the steady-state pyrolysis rate is discussed. The Global Equivalence Ratio concept, expressed as 0 2 " / f c O ? = A m ?H q Y ?H ? ? ?? , is introduced to classify the experiments. It also appears to be the main factor in determining the under-ventilated pyrolysis rate whenever the airflow inlet is situated high in the fire room. Whenever the inlet position is low, however, the oxygen concentrations tend to be stratified and the well-stirred reactor approach fails to predict the pyrolysis rate. In both cases, a zone modelling approach including the dependency of pyrolysis on the oxygen content near the flame provides a better estimation of the fuel mass loss rate and hence of the heat release rate.