Study On Influencing Factors Of Fire Characteristics In Cable Cabin Of The Utility Tunnel

The utility tunnel is to build an underground tunnel space in the city.It centralizes the engineering pipelines for power,communication,heating,gas,water supply and drainage in the same space,and has special overhaul and hoisting ports.It monitors the tunnel space to ensure unified planning,design,construction and management is an important infrastructure guarantee for urban life.The construction of urban utility tunnel can avoid the frequent excavation of roads caused by maintenance and laying underground engineering pipelines,inconvenience and impact on residents’ life and travel,effectively utilize urban underground space,increase the service life of various engineering pipelines,and reduce the cost of repairing pavement and maintenance pipelines.As a long and narrow space tunnel,the ventilation is limited to a certain extent.Once a fire occurs,firefighters are difficult to extinguish it.If it is allowed to develop,it will cause incalculable economic losses and bring inconvenience to residents’ lives and work.Fire in the utility tunnel is mostly caused by cable fires,which are the most common factor of utility tunnel fire.By using PyroSim fire simulation software,this paper establishes a actual experimental model of a cable cabin and conducts simulation experiments on the cabin after fire.the effects of the closing time of the vents,the location of the fire source and the smoke exhaust speed on the fire are discussed.The changes of smoke diffusion,roof temperature,smoke density and visibility within 700 s after the fire are observed.Seven experimental conditions are established and simulated respectively.The analysis shows that after the fire occurs,when the exhaust speed is very small and the vents are closed in time or delayed,the oxygen content in the cable cabin is large,which provides sufficient support for the cable combustion,aggravates the cable combustion,and the extinguishing time of the fire source is late.When the vents are delayed closure and the exhaust speed is high,the oxygen content in the utility tunnel is less than that of the discharged one.After the vents are closed,the oxygen content is smaller,the oxygen consumption is faster,and the extinguishing time of the fire source is earlier.When the fire source is close to the air supply port,the heat released by the cable combustion is small,the amount of combustible gas produced is small,and the consumption of oxygen is slow,which prolongs the extinguishing time of the fire source.When the distance is far from the vents,the heat released by the fire source is larger,more flammable gases are produced,oxygen consumption is faster,the heat release rate decreases rapidly,and the combustion duration is shorter.When it is close to the exhaust vent,the oxygen content in the cable cabin is larger,and the amount of combustible gas produced by combustion is not much different from that produced by fire source far from the vent.Oxygen consumption is relatively slower and the combustion duration is longer.The results show that in a certain period of time,the later the time of closing the vents,the higher the exhaust speed and the farther the fire source is from the vents,the more favorable it is to extinguish the fire source.