HSE uses mathematical models to estimate risks when examining proposals develop land in the vicinity of notified high-pressure pipelines. PIPERS and MISHAP are the computer programs that embody the models, and both programs have models for studying releases of gas and flashing liquids. Two versions of MISHAP now exist. Work reported earlier, focussing on releases From natural gas pipelines, found that the version called MISHAP98 was non-conservative in some respects, and recommended that improvements be made. These have now been implemented and the present work examines the performance of the new version, called MISHAP0I that is now the routine tool for studying natural gas pipelines. PIPERS is an extension and experimental development version of MISHAP, embodying alternative ways of modelling releases from natural gas pipelines and having additional models for use in the study of risks in the vicinity of pipelines carrying flashing and non-flashing liquids. Charts how well MISHAP can reproduce the observed effects of actual pipeline accidents. More than a hundred reports describing pipeline accidents were obtained. The objectives were: to study the accident reports; for natural gas pipelines to assess the relevance of the reports to PIPERS; to draw conclusions on the MISHAP0I modelling; to identify inadequacies in the PIPERS modelling, where possible within the scope of the contract to make changes to improve the PIPERS models and to recommend any further changes required. Confirms, over an enlarged database that the fireball model generally produces a conservative result. Recommends that the risk from ignited releases from ruptured pipelines containing liquids should not be assessed using PIPERS, but using a new methodology, not yet developed, that takes account of topography.
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