Abstract: This paper experimentally studied the influence of the longitudinal ventilation on the smoke exhaust performance of the vertical shaft and the ceiling temperature distribution. HRR and longitudinal ventilation velocity were considered during the fire tests. The results show that ventilation velocity has an impact on HRRs of heptane. For small square pool fires (≤11 cm) , HRRs keep approximately constant regardless of the ventilation velocities while for relatively large square pool fires (≥14 cm), HRRs decrease initially and then keep approximately unchanged with the increase of the ventilation velocities. Besides, when the ventilation velocities in the tunnel are low, the smoke is exhausted from the shaft by adhering the shaft sidewalls, and the smoke temperature on the downstream side of the shaft is low, indicating a good exhaust performance. When the ventilation velocity in the tunnel is high, the boundary separation in the shaft occurs and the smoke temperature downstream the shaft is high, and the smoke moves further, indicating a low smoke exhaust efficiency of the shaft. Therefore, it is suggested that in a naturally ventilated tunnel fire, low velocity can be employed, but the high ventilation velocity should be avoided.

Key words: tunnel fire, vertical shafts, longitudinal ventilation, temperature distribution, smoke spread