Prediction of the consequences of a CO2 pipeline release on building occupants

Carbon Capture and Storage (CCS) is recognised as one of a suite of solutions required to reduce carbon dioxide (CO2) emissions into the atmosphere and prevent catastrophic global climate change. In CCS schemes, CO2 is captured from large scale industrial emitters and transported to geological sites, such as depleted oil or gas fields or saline aquifers, where it is injected into the rock formation for storage. Pipelines are acknowledged as one of the safest, most efficient and cost-effective methods for transporting large volumes of fluid over long distances and therefore most of the proposed schemes for CCS involve onshore and/or offshore high pressure pipelines transporting CO2.In order to manage the risk in the unlikely event of the failure of a CO2 pipeline, it is necessary to define the separation distance between pipelines and habitable dwellings in order to ensure a consistent level of safety. For natural gas pipelines, existing and accepted QRA (Quantitative Risk Assessment) techniques can be implemented to define safety zones based on thermal hazards. However for high pressure CO2 pipelines, for which the hazard is toxic, the consequences of failure need to be considered differently, which will impact on the QRA assessment and the definition of safety distances.The requirement to develop a robust QRA methodology for high pressure CO2 pipelines has been recognised by National Grid as being critical to the implementation of CCS. Consequently, as part of the COOLTRANS (CO2 Liquid pipeline TRANSportation) research programme, failure frequency and consequence models are being developed that are appropriate for high pressure CO2 pipelines. One of the key components in the consequence modelling of a release from a CO2 pipeline is an infiltration model for CO2 into buildings to describe the impact on people inside buildings, and outside seeking shelter, during a release event.This paper describes the development of an infiltration model to predict how the concentration of CO2 within a building will change based on both wind driven and buoyancy driven ventilation of an external CO2 cloud into the building. The model considers the effects of either a constant or changing external concentration of CO2 during a release and allows the density effects of the dense cloud to be taken into account to enable the toxic effects on people within the building to be predicted. The paper then demonstrates how the ventilation model can be coupled to the results of a dispersion analysis from a pipeline release under different environmental conditions to develop the consequence data required for input into the QRA. These effects are illustrated through a case study example