Gas Temperatures

Gas temperature is of great importance for the assessment of heat exposure to tunnel users and tunnel structures, estimation of fire detection time and possibility of fire spread and to design ventilation systems. In this chapter, the theory of fire plumes in ventilated flows is presented with a focus on the maximum ceiling gas temperature and its position in tunnel fires. The maximum ceiling excess gas temperature can be classified into two regions, depending on the ventilation velocity. Each can be divided into two subregions. The first subregion exhibits a linear increase which transits into a constant period, depending on the fire size, ventilation and effective tunnel height. The position of the maximum ceiling gas temperature is directly related to a dimensionless ventilation velocity. A theoretical analysis of the upper smoke layer is presented, and correlations for the distribution of ceiling gas temperature along the tunnel are given to support this analysis. Finally, a one-dimensional model of average gas temperatures in tunnel fires with longitudinal ventilation is presented.