Influence of Ground on Jet Fire Extension

A common accident in the industrial process industry is the puncturing of storage tanks or rupture of process pipelines containing gases. In these scenarios, the gas will escape the piece of equipment producing a single-phase gas jet. If the fluid is flammable, an ignition source is most probably encountered during the accidental scenario and a jet-fire can follow the leak. Free jets of hazardous gases and free jet-fires have been extensively analyzed in the past literature to assess their shape and extension for safety purposes. Similar analyses have been conducted to observe the effect on shape/extension of neutral jets if obstacles were present. Also, the effect of the ground proximity to the jet source has been studied. In general, the presence of obstacles and the proximity to the ground lead to enlarged hazardous areas, mainly because of the Coandă effect. In this work, flammable jets igniting and forming a jet-fire were considered. The effect of the ground proximity was analyzed, to observe the extension of the flame. Two opposed phenomena were supposed to act on the fire, differently from non-ignited jets: the Coandă effect having an attractive nature towards the ground and the buoyancy effect on the opposite direction. The relevant methane jet-fires case study was considered carrying out computational fluid dynamics (CFD) simulations using the Fire Dynamics Simulator software. The study considered both the jet source height from the ground and the gas relief flowrate effects. CFD results were summarized basing on simple dimensionless parameters to determine the eventual variation of jet-fire extension for preliminary safety analyses.