This paper presents a case study, which is currently being carried out on a high-pressure sub-sea gas export pipeline. The main objective of the case study is to determine if the risk mitigation measures that are already in place are sufficient considering the level of risk for different sections of the pipeline. The methodology utilizes a Geographical Information System and the Computer Assisted Shipping Traffic (COAST) database to determine the level of risk caused by vessels traveling over the pipeline. The factors considered are damaged due to anchor drop and drag, vessel foundering and grounding over the pipeline. Live vessel tracks obtained from nearby radar stations are used to determine the annual traffic volume, size, type and speed of vessels as well as vessel headings. This information is then fed into the COAST database and presented graphically. The pipeline is then divided into equal area cells and the probability of anchor dropping and dragging and vessel foundering and grounding are calculated based on the type, size and speed of the vessels identified to have passed over the pipeline. The results of the frequency of occurrences and fatalities are presented and then evaluated against the set As Low As Reasonable Practicable (ALARP) level. The "hot spots" of the pipeline are identified and a base case study is carried out for the risk reduction measures that are in place (if any) for each of the "hot spots" identified. Alternative risk reduction measures are considered and a cost benefit analysis is carried out to determine the most feasible option. The risk levels are then recalculated with the risk reduction measures in place to see if this has reduced the risk to ALARP. The COAST database is thought to be very useful as it can be updated to reflect the current navigational practices of vessels and hence, it would be easy to update analyses as and when required.
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