Experimental study of impinging ceiling flame structure and flow characteristics in a corridor fire under various sub-atmospheric pressures

Fire accidents in narrow and long spaces such as corridors occur frequently, resulting in casualties and property damage, which has attracted a lot of attention from scholars. The flame extension behavior after it impinges on a ceiling is a fundamental phenomenon of fire inside a confined space. The flame geometric boundary of ceiling thermal flow impingement determines its thermal impact to the building, which is more complex for fire in a narrow structure, i.e., a corridor. Moreover, such fire can happen in high-altitude locations with naturally sub-atmospheric environment, which also alerts the fire behavior complicatedly. This study investigated the ceiling impinging flame structure and flow characteristics in a corridor fire under various sub-atmospheric pressures, for which the evolutionary mechanism of their coupling effects (narrow confined space; sub-atmospheric pressure) has not been revealed in the past. A series of experiments is performed under various source-ceiling heights, fire heat release rates, and reduced pressures (from 55 to 100 kPa). Results show that pressure significantly affects the ceiling flame geometry, and that for a given fire heat release rate, the flame extension length is larger under lower sub-atmospheric pressures. When the fire heat release rate is relatively low in normal pressure, the flame extension length in the central of the ceiling is larger than that in the two sides, and a half-ellipse geometry is presented (which is primarily controlled by fuel supply). However, the flame in the two sides extend farther compared with that in the central of the ceiling, presenting a “U” shape as the atmospheric pressure decreases and the fire heat release rate increases (primarily affected by the side wall constraint). A new correlation was proposed to describe the dimensionless flame extension area with a proposed dimensionless fire release rate. This study helps understanding the ceiling flame extension behavior in a corridor under sub-atmospheric pressures and provides a reference for fire prevention in high-altitude areas.