This study relates to the dispersion of dense gases within, and then downstream of, building complexes. The physical arrangement would typically comprise a group of buildings so arranged that their wake regions would interact. The release itself is taken to be continuous, and could have high or low momentum, in any horizontal direction. A review of earlier work on dispersion within and affected by building arrays was undertaken. Although this indicated that much of the previous work in this area was focussed either on elevated (passive) plumes being brought down to ground level by buildings, or on the detailed effects of street canyons on pollution line sources such as traffic exhaust fumes, it did enable the significant effects and key parameters to be identified. To enhance the understanding thus gained, computational fluid dynamics (CFD) modelling was undertaken for a typical chlorine release within varying arrays of varying geometry. The results obtained from CFD supported the original insights, qualitatively as expected, they were also analysed on some detail, and then used to inform the development of a series of flow charts which have been presented to guide the consequence analyst to the appropriate modelling choices.
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