Studies On Ceiling Jet Characteristics Of Passage Fire In Various Sealing Conditions

In building fires,passages are the most trusted safe ways for people to escape,but at the same time they are also "death traps" which are filled with smoke.In recent years,there have been numerous cases of building fires and there have also been many cases of passage tires.The space formed by the passage is restricted horizontally and has no restrictions in the longitudinal direction.This will aggravate the spread of the fire.Flame and dense smoke will block the safety exit and escape passage of the building,which can easily cause casualties or even mass casualties.The entrances on both sides of the passage inside a building are usually in different sealing conditions due to the structural design of the building and the opening or closing of the fire door.It can be fully open,half open,or completely closed.The sealing condition will have an impact on the development of the passage fire.Previous studies on passage fire seldom take into account the effect of sealing on fire development.The researches of the maximum temperature beneath a confined ceiling are mainly for smoke plume impinging the ceiling.The studies of the flame extension behavior are also mostly about the case where the ceiling is unconfined by the side wall or the ceiling is confined but the heat release rate of the fire is small.In this paper,the characteristics of ceiling jet behavior for passage fire in various sealing conditions are studied by numerical simulation.The temperature distribution beneath the ceiling of ceiling jet driven by strong plume is studied.We also study the flame extension behavior when persistent flame impinges the ceiling.And the influence of different sealing conditions on the temperature distribution beneath the ceiling is studied.These studies include following three parts:Study on temperature distribution and maximum temperature beneath the ceiling with ceiling jet driven by strong plumes in passages.The results show that the temperature beneath the ceiling increases with the heat release rate and decreases with the source-ceiling height in the zone near the flame impingement,however,decreases with the heat release rate and increases with the source-ceiling height in the zone away from the fire source.Besides,the maximum temperature rise beneath the ceiling in each scenario was analyzed and then an empirical correlation for the maximum temperature beneath the ceiling was proposed was proposed based on the fitting of the data.And the maximum temperature decreases with the heat release rate and increases with the source-ceiling height.The flame extension length for an impinging flame beneath the confined ceiling in a passage is investigated.Based on the analysis of the temperature distribution beneath the ceiling,the position of the flame edge was determined by using 500? as the temperature of flame edge.Thus the flame extension length beneath the ceiling was obtained.The results show that the flame length increases with the heat release rate and decreases with the source-ceiling heights and the burner size.Meanwhile,the calculation model of the extension length beneath the ceiling was obtained.Study on temperature distribution and height of smoke layer in passage fires under various sealing conditions.It is found that when the passage is not completely closed,the "passage air supplement effect" will appear.And the greater the opening size,the greater the heat release rate,the stronger the "passage air supplement effect".When the heat release rate is the same,the ceiling temperature are relatively high when the sealing condition are "closed-closed,half-half,half-open,open-open" and relatively low when the sealing condition are "closed-half,closed-open".When the heat release rate is low,the smoke layer is the highest with sealing condition of "open-open" and lowest with sealing condition of "closed-closed".When the heat release rate is high,the smoke layer is the highest in open side of the passage with sealing condition of "closed-open",relatively high with sealing condition of "open-open" and lowest with sealing condition of "closed-closed".At the same time,the distribution of temperature and height of smoke layer under different sealing conditions is given.The research results in this paper will provide important references for fire fighting and evacuation in actual building passage fires.