A model to evaluate tunnel fire characteristics

Abstract This paper presents a semi-empirical model for the determination of the physical characteristics of fire in tunnels. Classically, a fire is simply associated to its heat release rate. By definition, the heat release rate is given by the product of the smoke mass flow rate by the temperature rise in the smoke. However, for a given fire, the values of these two quantities remain correlated and more, the size of the fire is not independent of the released heat. This study is focused on heptane pool fires which offer the advantage of involving only one combustible in the combustion process and of linking the fire size to pool size. The purpose of this note is to develop a model able to define for a given heptane pool diameter, a set of values for heat release rate, smoke flow rate and smoke temperature. From an analysis of the combustion products, the burning rate and the air entrainment rate into the flame, a system of equations is derived. A comparison with international recommendations is made.