Critical Factors Determining the Onset of Backdraft Using Solid Fuels

Abstract

Backdraft is an explosive fire phenomenon which typically occurs during fire-fighting activities, occasionally leading to fire-fighter fatalities. Real backdraft incidents involve complex fuel gas mixtures consisting of the products of underventilated burning and pyrolysis following burnout. However, most experimental research into backdraft has used methane gas or flammable liquids as fuel. Some aspects of real backdraft behavior may have been overlooked as a consequence of this simplicity. A reduced scale series of compartment fire tests have been carried out to investigate the critical factors governing the onset of backdraft, using polypropylene and high density polyethylene samples as fuel. It is established that there are critical temperatures for auto-ignition of the pyrolysis gases leading to backdraft which vary with fuel properties. For polypropylene the highest temperature in the compartment must be above 350°C for auto-ignition of the fuel gases, while mixtures in the presence of a pilot source can be ignited down to about 320°C. Backdraft cannot occur when the compartment temperature is below 320°C. For polyethylene, the corresponding temperature for auto-ignition is 320°C. In parallel with these tests, a series of pyrolysis investigations have been carried out using the fire propagation apparatus, with FTIR gas analysis. The observed critical temperatures for backdraft correlate well with the evolved pyrolysis gases. Analysis shows that higher temperatures are required for backdraft when the CO/CO 2 ratio is small, and that below the auto-ignition temperature, backdraft can only occur above a CO/CO 2 ratio of about 35%. It is concluded that the crucial factors determining whether backdraft occurs or not are the maximum temperature and the CO/CO 2 ratio in the compartment, prior to opening the door.

Experimental study on the backdraft phenomenon of solid fuel

“…According to the experimental results, they established a theoretical model and deduced the critical condition of backdraft. Wu et al [ 26 , 27 ] conducted reduced-scale experiments to study temperature conditions and critical factors of backdraft. Their results indicated that before the opening of a compartment, maximum temperature and the CO/CO2 ratio in the compartment were crucial factors that determined whether backdraft occurred or not.…”

Computational Study of Compartment Size Effects on Backdraft Intensity

“…백드래프트에 대한 실험연구는 위험성 등을 고려해서 축소규모의 구획실을 대상으로 한 연구가 많다 (2)(3)(4)9) . 이러한 연구의 하나로서 Fleishmannn 등은 축소 구획실에서 메탄 가스연료에서 발생하는 백드래프트가 발생하는 연료농도 한계값과 압력양상을 검토한 바 있다 (3) .…”