This project has made an important contribution to the understanding of flow and dispersion in process plants. This has led to improved methods of inventorising and monitoring VOC emissions which contribute to ground level ozone formation and global warming. Furthermore, fugitive emissions can constitute an annual product loss up to the value of 2m US dollars for a typical refinery. Better targeting of controls thus leads to improved environmental and financial performance. The main research method used was wind tunnel modelling, allowing physical simulation of dispersion around small scale plant models under a controlled environment. The principle geometric feature of process units which differentiates them from “conventional” buildings is their porous nature, establishing internal ventilation flows. By varying model parameters describing porosity, measurements were made to characterise the corresponding wake flow & dispersion behaviour. A comprehensive, practical description of wake dispersion dynamics has been developed for three dimensional porous obstacles. Results clearly show that wake dispersion is strongly sensitive to plant porosity since ventilation flows cause major changes in wake behaviour. As a result, commercial solid building dispersion models cannot be applied to porous process units. Using the wind tunnel data set generated, a new wake dispersion model has been developed for porous structures. Research results have been put into practice by making recommendations for full scale measurement strategies, guiding the interpretation of full scale measurements, planning modifications to Shell’s existing dispersion modelling system (HYMNS), thereby significantly improving the accuracy of flux predictions, and preparing practical guidelines for process plant emissions control & dispersion modelling.