Study On Fire Safety Of Cable Compartment In A Utility Tunnel

China's technology of utility tunnels is on the initial stage of research and construction.And the most dangerous area as to fire risks on the stage of operation is the cable compartment.This paper analyzes the hidden dangers,fire causes and firing characteristics in the cable cable compartment based on a real construction work.The thermal parameters of the cable sheath materials are determined,also,the law of fire development and smoke spreading under different fire condition had been researched using the method of combining experiment with FDS numerical simulation.The repartition of fire and fire protection facilities were also studied Through performance-based fire protection design.First,the combustion test of the cable sheath material in the combustion furnace was carried out.The changes of temperature and the concentration of CO and C02 in the combustion furnace were monitored.A model was established in FDS based on the actual size of the combustion furnace and the location of detectors.Through the comparison of different size grids,the choice of wall plane and the setting of fire source parameters,the numerical results are compared with the experimental results.They showed great coherence and the error of peak value is less than 20%.Thus it can provide a reference to the setting of fire thermal parameters in the cable compartment of utility tunnels.Then,based on a real cable compartment of utility tunnel,the method of wall selectionis established by comparing the results of numerical calculation.Meanwhile,according to the principle of "trusted and most unfavorable",the law of the development of fire and smoke spreading were studied,by setting up six different fire conditions,with consideration of whether the fire proof door is open,natural ventilation and smoke exhaustion,mechanical negative pressure exhaustion,full ventilation and smoke exhaustion.And the maximum fire scale was determined.At the same time,the maximum temperature rising formula of the fire in the cable compartment is determined with Reference to Kurioka model and empirical formula for maximum temperature rise in tunnel fires.The maximum temperature distribution inside the utility tunnel under the same smoke exhaustion mode in cable compartment was compared and analyzed in addition to the comparison with the longitudinal temperature distribution characteristics of tunnel fire.The quantitative relationship between smoking temperature and the concentration of smoke in cable compartment was also determined according to the relationship between the variety of temperature on smoke exhaustion and the mass flow rate of air inflow.Finally,combined with the results of the analysis above of different fire scenarios,taking the safety of personnel in the event of fire into account,the most unfavorable fire scenario was selected.The methods of determining the fire zones and fire fighting facilities with different lengths were studied based on the concept of performance-based fire protection design.It is suggested that the high pressure water mist fire extinguishing system should be adopted when the length of the fire zone is more than 250m.The automatic fire extinguishing system of superfine dry powder is recommended when the length of the fire zone is less than 250m.In case of fire,the fire can be controlled around the fire initiating point,and the risk of fire will be reduced to the minimum.