Assessing the Influence of Real Releases on Explosions (AIRRE)

The primary aim of the project 'Assessing the Influence of Real Releases on Explosions' (AIRRE) was to perform a series of large-scale explosion experiments, suitable for assessing the influence of pre-ignition turbulence on gas explosions in congested geometries. The project included model validation for the CFD tool FLACS, as well as development of a robust methodology for risk assessment. The project started in 2017, and GL Industrial Services UK Ltd. (DNV GL) hosted the kick-off meeting at the Spadeadam test site on 12-13 October. During the project, a total of 16 large-scale experiments were performed providing a unique set of data, in terms of spatial scale and flow configuration, which were used for the validation of FLACS. The risk assessment methodology applied in industry has been assessed considering the influence of pre-ignition turbulence. The results of this analysis show that the current standard methodology, which does not account for the pre-ignition turbulence level, is suitable for most accidental scenarios. However, for some accidental scenarios, characterized by specific combination of ignition locations, flow and obstruction levels, pre-ignition turbulence affects significantly the resulting risk level.

The experiments conducted during the project confirmed that the presence of pre-ignition turbulence and flow can enhance significantly the overpressure developing during the explosion event, in specific scenarios, also in large-scale setups. This result is particularly relevant for quantitative risk assessment studies, in which it is common practice to replace the realistic simulated cloud with an equivalent cloud having the same reactivity level and quiescent (non-turbulent) near-stoichiometric conditions, assuming that the latter represents the "worst case scenario". A new equivalent cloud paradigm, enhanced with initial turbulence, was tested in the CFD solver FLACS. When the initial conditions are approximated correctly, such enhanced equivalent cloud mimics the explosion overpressure results obtained from the realistic cloud scenario in the FLACS simulations. These outcomes are expected to have long-lasting impact on the design of safety measures in the petroleum industry.