In this study, we used a 1/5-scale model tunnel to investigate the temperature characteristics of backlayering thermal fumes in addition to the heat release rate and the longitudinal ventilation velocity in a tunnel fire. The ventilation flow through the model tunnel provided a sufficient turbulent flow as the Reynolds number based on ventilation velocity and tunnel height was 40,000 or more. The governing scaling parameter in this experiment was the dimensionless parameter Q* /Fr . In addition to Froude's and Reynolds' similarity laws, the similarity of the thermal characteristics in the tunnel wall was considered in making the model tunnel. We clarify the conditions under which the backlayering thermal fumes maintain a stratified layer. Empirical equations of the thermal fume height in the longitudinal ventilation are derived from the experimental data. The evacuation safety based on the height of thermal fumes is examined in detail.
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