Risk assessment methodology for high-pressure CO2 pipelines incorporating topography

•Shallow layer code enables QRA of high-pressure CO2 pipeline incorporating topography.•Lagrangian particle-tracking models offer promise for CO2 dispersion modelling.•Individual and societal risk calculated and represented geographically using QuickRisk.•Topography shown to significantly impact CO2 dispersion, individual and societal risk. This paper presents a risk assessment methodology for high-pressure CO2 pipelines developed at the Health and Safety Laboratory as part of the EU FP7 project CO2Pipehaz. Traditionally, consequence modelling of dense gas releases from pipelines at major hazard impact levels is performed using integral models with limited or no consideration being given to weather bias or topographical features of the surrounding terrain. Whilst dispersion modelling of CO2 releases from pipelines using three-dimensional CFD models may provide higher levels of confidence in the predicted behaviour of the cloud, the use of such models is resource-intensive and usually impracticable. An alternative is to use more computationally efficient shallow layer or Lagrangian dispersion models that are able to account for the effects of topography whilst generating results within a reasonably short time frame. In the present work, the proposed risk assessment methodology for CO2 pipelines is demonstrated using a shallow-layer dispersion model to generate contours from a sequence of release points along the pipeline. The simulations use realistic terrain taken from UK topographical data. Individual and societal risk levels in the vicinity of the pipeline are calculated using the Health and Safety Laboratory's risk assessment tool QuickRisk. Currently, the source term for a CO2 release is not well understood because of its complex thermodynamic properties and its tendency to form solid particles under specific pressure and temperature conditions. This is a key knowledge gap and any subsequent dispersion modelling, particularly when including topography, may be affected by the accuracy of the source term.