Experimental study on temperature profile in a branched tunnel fire under natural ventilation considering different fire locations

Reduced scale experiments in a branched tunnel were carried out to study the variation of the maximum gas excess temperature beneath the ceiling and temperature profile under natural ventilation considering different fire locations. Flame behaviors and ceiling temperature profile were recorded and analyzed. The results show that due to unbalanced air entrainment, the fire located at the intersection of the tunnel tilts towards the sidewall. The maximum temperature beneath the ceiling when fire locates at the intersection is slightly lower than that when fire locates at the two other locations because the accumulated high temperature smoke is less. Based on experimental data, a model predicting the maximum temperature beneath the ceiling was proposed. It correlates the experimental data well and also agrees reasonably with the temperature measured in full scale tests from other's work. Besides, dimensionless expression for longitudinal temperature decay in a branched tunnel was proposed. The predicted longitudinal ceiling temperature was close to the measured data for the main tunnel but slightly higher for the branch due to the rough surface of the joint. The influence of branch on the temperature profile in the main tunnel was also discussed. •Experiments on fire locations were conducted in a reduced-scale branched tunnel.•Flame characteristics and temperature profile were recorded and analyzed.•Fire located at the intersection tilts towards the sidewall.•Models for maximum temperature and longitudinal temperature decay were proposed.•The models obeys reasonably with the experimental results.