This paper describes a package of computer models that has been developed to assess the risks from gas releases at above ground installations associated with natural gas transmission pipelines. The package can be applied to compressor stations (containing compressor enclosures and associated gas treatment equipment) and pressure reduction stations, through to single block valve installations. It has been designed for used by safety engineers in performing quantified risk and hazard analysis, as required to meet regulatory requirements, such as the COMAH Regulations or the DSEAR Regulations in the UK. It can also be used in the design stage of projects to support decisions related to site layout for example. The package contains a range of mathematical models to assess the consequences of accidental releases of gas (including outflow, dispersion, gas accumulation, fire, explosion and thermal and overpressure response), validated by data from large and full scale experiments. The individual models are linked in a logical manner constructed around a series of “knowledge bases” that provide a defined structure to allow a wide range of different scenarios to be assessed. The predictions of the consequences arising from various scenarios can be combined with estimates of the frequency of initiating events (based on industry statistics where available, or using predictive models), in risk calculation routines which sum the outcomes for the different scenarios to calculate individual and/or societal risk. To illustrate the use of the techniques, examples of their application are given. In particular, it is shown how the risks arising from releases from high pressure vessels or in confined volumes, such as compressor enclosures, can be evaluated.

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