Experimental Research And Numerical Simulation On Ventilation Of Backdraft In Compartment Fire

Backdraft is a special phenomenon of the development process in building fire, having a strong invisibility, abruptness, destructiveness and serious threats to the staff in the fire, especially the safety of firefighters. In view of current research and based on experiment anslysis of the physico-chemical characteristics of solid combustibles, we established a small-scale and a full-scale backdraft experiment with solid combustible as fuel in connection with numerical sumulation. Through these, we analyzed the impact of ventilation to backdraft in compartment and fire hazard on backdraft, and gived firefighters some propose practical forcible fire-fighting strategies to enter the confined space.Through a series experiments of physico-chemical characteristics of paulownia, we have got burnning characteristics about it. Pore of paulownia wood mainly belonging to linear crack is developed and widely distributed by scan electronic microscope. Through element analysis test and limiting oxygen index test, we can get that paulownia wood whose C/H radio is 6 can quickly extinguished in low oxygen environment and combustion products mainly is hydrocarbons. We can know its ignition point is 308 ℃ by burning point test and SDR is about 15 by test method for density of smoke. Its pyrolysis temperature is 250 ℃ and activation energy “E” is about 76 k J/(mol?K) through the experiment of pyrolysis analysis. Beside, we can draw a conclusion that combustion kinetics first-order natural logarithm curve in high-temperature area correlation coefficient is close to 1. Paulownia wood residue presents the shape of the fish scales through radiation ignition analysis experiment Curves of mass, gas concentration and heat release rate are also got.Small-scale backdraft experiment appliance with different openings is manufactured by ourselves and be used on backdraft, including different vertical position(top-end, middle-end, bottom-end), different horizontal position(left-section, middle-section, right-section) and different opening size(window opening, door opening and fully opening). The difficulty of backdraft occuring from high to low is bottom-end >top-end> middle-end, left-section≈right-section>middle-section and window opening >door opening> whole opening. Backdraft delay time from short to long is: middle-end<top-end<bottom-end and fully opening<door opening<window opening. There is no significant difference in different horizontal positions. There are flame, radiation, smoke and cold air four different temperature areas in backdraft. Temperature change in compartment has no obvious relationship with the open position. Temperature at the opening from high to low is top-end>middle-end>bottom end. Heating rate after backdraft from high to low is middle-section>left-section≈right-section. Instantaneous pressure of vents is 5 times than atmospheric pressure. Temperature in compartment, gas concentrations vary sharply, reflecting the change before and after backdraft. Through curve fit from experiments, we can get that the nessary condition is the temperature at the top of compartment was above 100 ℃.From full-scale backdraft experiment, temperature measured in office and corridor can reflect the change trend of backdraft occurring and visibility inside can show the change of hot smoke layer and ventilation condition. Before backdraft, the peak temperature in door and corridor is respectively 400 ℃ and 73 ℃. After backdraft, indoor temperature rises sharply to 600 ℃,entering the stage of flashover after 85 s and the temperature peak value is nearly 1 200 ℃. Meanwhile, temperature in the corridor rises to 484 ℃, after 54 s rises abruptly again and the peak is near 870 ℃. Backdraft in compartment can trigger a flashback, posing a great threat to the safety.Numerical simulation results can reflect better the process of backdraft fire in compartment and temperature distribution in the flame region, but slightly lower than that measured from experiment. Temperature, O2 concentration and air pressure curve can indicate the occurring of backdraft, and are consistent with the data measured by the test, indicating that numerical simulation with high credibility and reliability of the results. Some proposals have been given to firefighters to enter seaked compartments intergating with experiments and simulation results.