Experimental study of flame extension behavior under different curved ceilings in underground spaces

As a common form of underground spaces, the geometry and spatial structure of curved ceilings significantly affect flame extension behavior. This paper comprehensively examines the effects of various fire heat release rates and burner ceiling distances, experimentally investigating the evolution of flame extension length and spread area under different curved ceiling conditions. The results indicate that the transverse flame extension length of ceiling jet increases with the ceiling radius; while, the longitudinal flame extension length decreases. These phenomena were elucidated through an analysis of the influence by curved ceiling structure and the buoyancy component on the unburned fuel flow beneath the ceiling. A model of normalized transverse flame extension length for both horizontal and curved ceilings was established by incorporating a ceiling radius influencing factor \(\ell\) $\ell$ of arced structures. Additionally, the ceiling radius had a minimal effect on the normalized flame extension area, then the dimensionless longitudinal flame extension length prediction model was proposed, demonstrating strong agreement between experimental and predicted values. This study offers theoretical support for the fire safety design of curved ceiling buildings.