Flash fire is one of the main potential hazards of oil & gas operations. The development of the flammable cloud is directly correlated to the explosion risk. Gas cloud evolution strongly depends on the source term definition. Commercial models, specifically developed and tuned for industrial plants risk assessment often simplify the phenomena affecting the source term, introducing errors and non-conservative assumptions. Excessive simplifications become particularly critical in case of accidents in non obstructed areas, where an accurate evaluation of the extension of flammable (and explosive) clouds is fundamental to assess the risks for assets, personnel or population.

In this paper various phenomena characterizing the source term are analyzed in some typical discharge configurations, in order to introduce a robust methodology based on realistic assumptions. Diversity of scenarios has been investigated to examine the factors that can affect the gas dispersion.

The loss of integrity of a high pressure pipeline was studied in order to understand how the high momentum jet influences the atmospheric dispersion of the gas: computational fluid dynamics (CFD) simulations were compared with commercial models and ad hoc approaches.

The evolution of a thermodynamically dense gas cloud from zero momentum sources was analyzed in a benchmarking activity with literature data, CFD approach and commercial models.

The flammable gas dispersion from subsea ruptures was also investigated. Even for this kind of event the dispersion of the flammable gas is highly influenced by the source term, which is strongly uncertain. A dense/light gas released by a subsea rupture usually generates a bubbling area at sea surface. The surface gas source is characterized by an immediate dilution with air.

The main purpose of this study is the reduction of the errors associated with inaccuracies of the source term definition and gas dispersion in the consequence analysis studies.

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