Ground influence on high-pressure methane jets: Different concentration clouds scenarios

Because of their relevant consequences (in particular, associated with domino effect), accidental highpressure flammable gas releases are one of the major hazards in the industrial safety framework. It is likely that the accidental loss of containment can involve obstacles that, as a matter of fact, are present in any process facility. As obstacle, flat surfaces (e.g., walls, ground, etc.), equipment (e.g., tanks, pipes, etc.) or structures can be counted. Focusing on the scenario of an accidental high-pressure unignited methane jet interacting with an obstacle, this work investigates how the proximity to the ground influences the jet cloud extent when considering different concentrations of methane in air. Varying the height above the ground of the source term, the effect of the ground was systematically studied through an extensive Computational Fluid Dynamics analysis. Thanks to the sensitivity analysis performed, the main achievement is the demonstration that methane releases observed at different concentrations in air, from sources at different pressures and outflowing from accidental holes of different sizes are similarly influenced by the ground presence. The conclusion of the present work is that, the assessment of the hazardous area extent of the flammable release at any concentration of interest can be evaluated exploit an analytical model specifically derived, providing a useful alternative of practical precision to more expensive CFD computations. This way, for this specific accidental scenario, delineating the area involved within the flammability limits become easier and faster.