Recent advances in software for modelling the risks associated with gas explosions in congested spaces using the Multi Energy Method

When calculating risks from explosions, accurate prediction of the effects of congestion on overpressure has a significant impact. In addition, the protection offered by buildings is also an important factor. The TNO Multi Energy (ME) Method, integrated with source term discharge and dispersion models to assess the extent of flammable clouds, is often used for predicting overpressures (Van Den Berg, 1985). Developed as a more accurate alternative to the TNT-equivalence model, it could initially only be applied in a general manner using conservative assumptions. However, since then, a number of initiatives have been undertaken to improve its usability. The GAME project in 1995 provided correlations to help select appropriate curves based on parameters such as volume blockage ratio, equipment diameter, flame length and laminar burning velocity. This was extended by the GAMES project in 1998 which gave guidance on combining multiple explosion sources and validated the model against CFD predictions. Further research published in 2002 (RIGOS) provided guidance on when equipment separated by finite distance should be treated as single obstructed regions. This paper describes the recent implementation of the ME method in a software model for Process QRA (see for example Cavanagh et al, 2009) which can be used to predict the risks to people from VCEs and takes account of the guidance from the GAME, GAMES and RIGOS projects. The software allows graphical definition of a plant and selects the most appropriate ME curve based on a number of user defined parameters. It enables the definition of explosion sources, areas of congestion, population distributions, buildings and appropriate vulnerability levels on a GIS map. The paper also presents a simple case study for a typical installation with a number of buildings, each offering different levels of protection to their occupants, and describes the risks calculated using the built in guidance described above. Results are presented as traditional F/N curves to illustrate the effects of vulnerability modelling on the resulting risks.