Abstract: The security response after gas leakage in the utility tunnel was analyzed and studied by simulation based on Fluent and verified by experiment. The results show that when gas leakage occurs in the utility tunnel and the gas detector alarms, the ventilation system is started and the pipeline pressure is reduced to 0.4 MPa. It can be repaired online after 150 s ventilation; if the concentration of alarm is lower than the cut- off concentration with the cut- off concentration set to be 45% of the lower explosive limit, the pipeline pressure will continue to be reduced to 0.08 MPa, and the pipeline pressure will be repaired on-line after 150 s of ventilation; if the concentration of the alarm is higher than the cut-off concentration, the emergency cut-off will be carried out. The pipeline will be repaired after ventilation for 310 s.

Key words: fire protection, utility tunnel, gas leakage, security response, Fluent