Simulation Study Of The Fire Smoke Value On A Underground Pipe Gallery

With the development of the society as well as the gradual deepening of the urbanization process,the city's utilized land area is becoming less and less.Thus,the area on the ground hasn't fulfilled people's requirement for the production and living and the underground structural development gets more and more attention.Among these,the application of underground pipe gallery not only utilizes the underground space,but also saves the land resources.And the underground pipe gallery will route all kinds of municipal integrated pipelines intensively like the drainage,communications,heating power,fuel gas and so on,forming the public tunnel space.Moreover,special access holes,ventilation smoke outlets,lifting outlets and the fire fighting systems are set up,which are a modern type and the important municipal infrastructure.And the infrastructure is scientifically and effectively managed.As the pipe gallery is buried underground,there is a risk of fire hazard.Fire hazards do not only do harm to the personal safety of the people who work inside the pipe racks but also cause great economic damage.Therefore,in the new times of vigorously carrying out the pipe gallery to the great degree,during the times of research on the fire disasters on the pipe gallery,the regulations of the fire spread as well as after-calamity ventilation and smoke discharge are of great significance to the improvement of fire fighting design standards and elimination of the fire risks of the utility tunnel.In the text,the cable compartment of a certain pipe gallery in Dianjiang County,Chongqing City is chosen as the research objective.And the models are set up,the relative parameters are set.Moreover,the ventilation openings and the fireproof doors are closed and simulated after the fire disasters happen in the pipe racks,analyzing the development of the fire disasters,heat releasing rates,regulations and characteristics of fire spread.And also the contents stated above are made as the reference data,combining with the regulations,based on different ventilation types,different ventilation working conditions are designed.Meanwhile,the post-quake smoke exhaust effects are studied to provide the feasible suggestions for the post-quake smoke exhaust.In Scenario one,the closing of ventilation outlets and the fire resisting doors,regulations of the development of the fire disasters,and the smoke spread as well as temperature,content of CO,distribution characteristics of the content of CO₂ are studied.When T equals to 207s,the power of fire sources comes to 2MW and when T equals to490s,the heat releasing rate has come to 18MW.When T reaches up from 533s to 610s,the heat releasing rate starts to decrease rapidly.When T equals to 650s,the flames start to go out because of lack of the oxygen,so the heat releasing rates gradually decrease until0.Under the airtight status,the smoke gas,temperature,CO content,CO₂ content all show symmetric distribution.While the temperature at the center of the fire source is higher than the one which is at both sides of the fire source.So the closer it moves to the fire source,the higher the temperature will be.At the place where it is 1.6m around the eyes of people,the utmost temperature of point A at the center of the fire source can reach up to 200?,while point B and D which are 50m away from the center of the fire source,point C and E which are 100m away can all reach up to 80?.While the contents of CO and CO₂ tend to be stable after a quick rising in the earlier period,and the peak value of CO content can reach up to around 2000ppm.And the peak value of the volume of CO₂ can reach up to around 6%.In Scenario 2,the way of mechanic ventilation and mechanic exhaust is done in the way that the smoke spread is firstly done,making the inlet wind speed as the variable,designing the four working conditions respectively with the outlet wind speed as the ration.While the inlet wind speeds from Scenario 2 to Scenario 5 are respectively 0.2m/s?0.5m/s?0.8m/s and1m/s,which is evenly set up as 2m/s.Of all the four working conditions,only in Scenario 3 was the most of the smoke gas exhausted after the simulation was finished.On the pipe racks,you could see the things which were above 15.However,in Scenarios 2,4and 5,there was part of the smoke gas which were not exhausted.And the temperature all decreased to the initial temperature in the environment.While the contents of CO and CO₂ in scenario 2 did not decrease within the safety evaluation index after the simulation was finished,and the ones in Scenario 3,4 and 5 all decreased within the safety evaluation index.When the mechanical inlet ventilation and mechanical exhaust were applied,even though the inlet wind speed was larger,still the smoke exhaust was not done so perfectly.In Scenario 3,the natural ventilation was applied at the inlet part,while the mechanical exhaust was still used at the air outlets to implement the smoke exhaust where three working conditions were designed.The inlets were all set as open in Scenario 6,7 and 8while the wind rates at the outlet are respectively set as 2m/s?3m/sand 4m/s.When the simulation was finished in Scenario 6,the rest of the great smoke gas on the left side of the fire source was not exhausted.The overall visibility of the pipe racks was lower than 10m while the contents of CO and CO₂ did not go within the safety value;However,only the smoke exhaust effects in Scenario 7 and 8 are the best of all with an overall visibility of more than 20m.And the temperature,contents of CO and CO₂ all decreased within the safety value.The mechanical inlet was applied at the air inlet in scenario 4 while the natural ventilation was applied at the outlet to exhaust the smoke after the disaster with 3 working conditions.And the inlet wind speeds of scenario 9,10 and 11 are respectively 2m/s,3m/s and 4m/s.In addition,the outlets were all set up as open.While the three working conditions in Scenario 4,the smoke gas can be exhausted fast in the pipe racks at an earlier period.However,as the time went by,due to the long fire areas in the pipe racks and far distance of the inlet and outlet,in case of no installation of jet ventilation,the wind pressure could not press out the smoke gas at a high temperature which accumulated at the outlet.Because of this,the cooled air entering from the inlet was heated by the high temperature smoke gas,forming to a great deal of heated air,making the temperature inside the pipe racks gradually increase to above 70?.While in the three working conditions of Scenario 4,only the contents of CO and CO₂ in Scenario 11 decreased below the safety value.Therefore,in the actual post-quake fire exhausts,this way should not be used as for the fire exhausting.The mechanical ventilation and mechanical exhaust air were suggested to be used for the post-quake smoke exhaust or the natural wind was applied at the wind inlet.While mechanical ventilation was used to exhaust the smoke.From the economical view,natural ventilation and mechanical exhaust were more suggested to carry out the smoke exhaust after the disaster.