Impact of sub-atmospheric pressure on fire hazard and flow field characteristics in arced channel fires: ceiling temperature, flame extension and prediction models

Underground confined energy facilities, such as storage systems and transport channels, face increased fire risk due to sub-atmospheric conditions at high altitudes. This research investigated the fire risk parameters of arced channel fires under varying sub-atmospheric pressures, heat release rates, and ceiling distances, systematically examining temperature distribution features, flow field patterns, and flame extension scale. The temperature distribution beneath the arced ceiling was analyzed by downscaled experiments and numerical simulations, and it is found that the ceiling maximum temperature declines and the temperature decay slows down as pressure diminishes. Quantitative analysis reveals an exponent of 0.46 for the power relationship between dimensionless ceiling maximum temperature of ceiling and normalized atmospheric pressure. Both the transverse and longitudinal flame extension lengths increase with decreasing pressure, with the longitudinal direction showing greater sensitivity. The flow field was visualized by numerical simulation and vortexes were found at the flame edge, which intensify under sub-atmospheric pressures. Incorporating the ceiling restriction, buoyancy effect and air entrainment coefficient, the predictive models of flame extension scale and extension area under various ambient pressures were finally developed. These findings can provide important insights into the development and control of energy fires in sub-atmospheric environments.