The Maximum Temperature under Ceiling in Fires of a Longitudinally Ventilated Tunnel

To provide adequate protection on tunnel structure in the case of a fire, the maximum smoke temperature exposure to the construction under tunnel ceiling should be estimated. Theoretical analysis of smoke temperature under the ceiling based on the plume theory is given. The heat release rate and longitudinal ventilation velocity are both taken into account. And small-scale experimental tests were also carried out to investigate the maximum temperature under the ceiling in tunnel fires. Results of analysis and experiments both show that the maximum temperature rise under the ceiling can be divided into two regions- when the dimensionless parameter u/w* is larger than 0.12 the maximum temperature under tunnel ceiling linearly increases with the heat release rate and linearly decreases with the longitudinal ventilation velocity. And when the dimensionless parameter u/w* is smaller than 0.12, and the maximum temperature under the ceiling varies as two-third power of the dimensionless heat release rate, independent of the longitudinal ventilation velocity.