Comparison of EPA and Gaussian Plume approaches for modelling ammonia dispersion: A case study at Immingham Green Energy Terminal

Large-scale ammonia (NH 3 ) storage is central to the transition to hydrogen-based energy systems, but its accidental release poses significant toxic hazards. This study develops and validates an accessible dispersion modelling framework to address limitations in existing regulatory tools for Quantitative Risk Assessment (QRA). A Gaussian Plume (GP) dispersion model was implemented in MATLAB and validated against 13 large-scale ammonia release test data achieving performance metrics of fractional bias = −0.012, root mean square error = 20.4 % and Pearson correlation coefficient = 0.957 for distances >100 m. The validated model was applied to simulate worst-case and alternative release scenarios at the planned Immingham Green Energy Terminal (IGET) in the UK, following U.S. EPA Risk Management Program guidance. Results showed a toxic endpoint distance (TED) of 51.5 km for the worst-case tank release, exceeding the EPA reference distance of 40.2 km by 28.1 %. Sensitivity analysis of pipeline failure scenarios (5–300 mm) demonstrated substantially reduced TEDs (0.1–16.1 km). A GIS-based population exposure analysis estimated up to 1.29 million potentially affected individuals in the worst cases, demonstrating the value of credible release modelling for emergency planning. The methodology bridges the gap between simple EPA reference curves and complex CFD tools, enabling rapid, defensible consequence modelling for early QRAs. • The Gaussian Plume model was validated for ammonia dispersion beyond 100 m. • The worst-case discharge predicted a hazardous endpoint distance of 51.5 km. • The EPA's reference distances may underestimate large-scale NH 3 release. • Site-specific weather data enhanced the accuracy of alternate scenarios. • A GIS study identified approximately 1.29 million persons as potentially vulnerable.