In this paper

the FDS simulation method is used to study the variation of critical ventilation velocity for double-source tunnel fires.The influence of HRR of downstream fire and the distance between the fires on critical ventilation velocity is mainly investigated.By analyzing the process of energy conversion

the reason for this changes is also investigated.The results show that under certain HRR of upstream fire and distance between the fires

the critical ventilation velocity increases approximately linearly with increasing HRR of downstream fire.For the case where the distance between the fires is zero

the critical ventilation velocity is identical to that for single fire with summed HRR.For a certain HRR of upstream and downstream fire

the decrease is quadratic in critical ventilation velocity with increasing distance of fires.For certain HRR of upstream fire

there is always a maximum distance that the critical ventilation distance was no longer influenced by the downstream fire

and the maximum distance increases linearly with increasing HRR of downstream fire.The critical ventilation velocity in double-source tunnel fires is largely different from single fire.Hence for the design of a ventilation system for tunnels

the critical ventilation velocity should be calculated more appropriately by considering the distribution of the fires

and the plan for fire controlling and evacuation work can be conducted more efficiently.