Effect of the Opening Area of Compartment on the Backdraft Time

: When a fire occurs in a ventilation confined compartment, the fire gradually weakened and finally self-extinguishes due to the oxygen concentration in the compartment will decrease and eventually below the flammable limit. Meanwhile, a large amount of high-temperature combustible substance is generated in the compartment during this period by pyrolysis or evaporation of fuel. When the compartment ventilation is improved, such as the window is broken, fresh air flows into the compartment and mix with high-temperature combustible substances and lead to the fire occurs again. This special phenomenon during the development of a compartment fire is called backdraft. In addition, a large amount of high-temperature combustible substances is accumulated in the compartment before the backdraft occurs. Therefore, once a backdraft occurs, it always leads to a flashover, which means a fire has reached fully development stage and is out of control. Hence, a backdraft will lead to substantial finical loss and heavy casualties. To investigate the influence of compartment opening area on backdraft time, we conducted fire experiments of solid fuel in a reduced-scale compartment. The temperature and the gas concentration in the compartment were measured by thermocouples and gas analyzer, respectively. Results show that the backdraft time of solid fuel would become shorter as the opening area of the compartment increases. The results of this research could improve the understanding of the backdraft mechanism of solid fuel and provide a strategy to delay or even restrain the backdraft occurrence for firefighters.