Quantitative Backdraft Experiments

This paper focuses on 17 experiments in a 1.2 m by 1.2 m by 2.4 m compartment. A methane burner, flowing at either 70 kW or 200 kW, was ignited inside a closed compartment and burned until the initially available oxygen was consumed. After the fire self-extinguished, the burner was left on allowing the unburned fuel mass fraction in the compartment to increase. After removing a hatch, covering a 1 . 1 m wide by 0.4 m high slot opening, a gravity current entered the compartment. It traveled across the floor, mixed with the unburned fuel, and was ignited by a spark near the burner. After mixture ignition, a backdraft occurred as a deflagration ripped through the compartment culminating in a large external fireball. Histories recorded prior to backdrafl included: fuel flow rates, upper layer temperatures, lower layer temperatures, upper layer species concentrations for 0 2 , CO2, CO, and HC. Data collected to quantify the backdraft included opening gas flow velocities and compartment pressures. Results indicate that unburned fuel mass fractions >lo% are necessary for a backdrafl to occur.