Flame Geometry and Temperature Distribution of Jet Fires in Pits

Underground pipelines of different burial depths are extensively utilized in the transportation industry for the conveyance of combustible gases. Failure of these pipelines could result in a jet fire in a pit (JFP), potentially endangering nearby pipes, structures, and individuals. The objective of this study is to analyze the flame geometry and temperature distribution of a JFP. A facility, comprising a jet fire apparatus and a rectangular pit, was constructed to experimentally simulate JFPs across three distinct burial depths and nineteen nozzle exit velocities. The JFP can manifest as an impinging jet flame (IJF), a transitional jet flame (TJF) or a jet flame ejected from the pit top (JFEPT), depending on the burial depth and nozzle exit velocity. An increase in burial depth reduces the critical velocities that differentiate these three flame patterns. Empirical correlations for the flame length and width of JFPs are developed, considering different burial depths, exit velocities, and pit dimensions. Additionally, two correlations available in the literature are validated for predicting the temperature distribution of TJF and JFEPT, respectively. These findings can inform the safety design of pipeline burial depths, considering the behavior of JFPs.