| In recent years,with the rapid development of economy and urbanization,utility tunnel develops rapidly.On the one hand,it can centrally control the risks of underground pipelines,on the other hand,it can effectively use underground space.But there are also many risks in the utility tunnel,among which the cabin cabin is one of the places with greater safety risks,mainly because the fire caused by cables will cause large-scale fire,resulting in huge economic losses.Therefore,the study of cable fire mechanism and control methods is the current research hotspot at home and abroad.Firstly,this paper analyses the causes and characteristics of cable fire in cable cabin of utility tunnel.Aiming at the danger of cable cabin fire,taking a utility tunnel project as a prototype,a fire calculation model is established.Three different boundary conditions(enclosed space,nonenclosed space and ventilation)were simulated to study the fire smoke spread,temperature change,visibility change,toxic and harmful gas concentration change in cabin.The research shows that cable fire has gone through three stages: initial growth stage,maximum power combustion stage and combustion attenuation stage.Under closed conditions,in the first six minutes of the initial growth stage of the fire,due to the flame retardant effect of cable surface materials,the fire burning increased slowly,the changes of fire temperature and toxic gas concentration met the evacuation of maintenance personnel,and the fire burning reached the maximum power state in about 13 minutes.The fire was extinguished 30 minutes later,and the length of the ignited cable was about30 m.In the non-closed condition,the fire extinguishes after 60 minutes because of the small amount of air supply in the vent,although the combustion time is prolonged.The length of the ignited cable is about 40 m.It shows that the burning range of cables in the whole ignition zone is relatively small,and the effect of suffocation extinguishing by closing fire doors is obvious.In the absence of wind,smoke can be well distributed at the top of the cabin in the early stage of fire,with obvious stratification with air.The distribution of temperature and visibility is axially symmetrical with the center of the fire source.With longitudinal wind speed,it can effectively restrain the spread of fire smoke to the upper wind side of the fire source,but the stratified structure of the smoke is destroyed and the visibility of the lower wind side of the fire source decreases.In order to study the smoke ventilation measures in cable cabin fire,the smoke exhaust effects of four different ventilation and smoke exhaust schemes(air supply at one side and exhaust at the other side,Induced fan exhaust smoke,air supply on both sides and exhaust in the middle,air exhaust on both sides and air supply in the middle)are calculated and analyzed.By comparing the smoke exhaust effect,visibility change,toxic and harmful gas concentration change.The results show that the smoke exhaust effect of scheme 2,with the help of the induction fan,is better than that of scheme 1,but the smoke exhaust time of scheme 2 is still long.Under the centralized smoke exhaust mode of scheme 4,the suction effect is produced under the smoke exhaust outlet,and the overall smoke exhaust effect is reduced.The third scheme distributes the smoke exhaust outlet,which weakens the suction effect at the smoke exhaust outlet and increases the smoke exhaust effect.By comparison,the smoke exhaust effect of scheme 3 is better than that of scheme 4.Finally,according to the characteristics of cable cabin fire,water mist fire extinguishing system is used as fire extinguishing facility of cable cabin,and the fire growth process under the condition of fine water mist is analyzed.The results show that the heat release rate of the fire will decrease rapidly after a short rise when the water mist fire extinguishing system is started,which can effectively prevent the spread of cabin fire.This paper has 116 figures,3 tables and 64 references. |
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