An investigation was conducted into minimising effective dose to members of the public in the unlikely event of an accident by optimising design parameters and site locations of future fusion power plants. This is part of our defence in depth approach for tritium safety that also includes significant work on the prevention of accidents. Calculations were performed using Atmospheric Dispersion Modelling System (ADMS5), a validated software package that models plume dispersion with editable inputs including multiple buildings, stack height, terrain topography and meteorological data. To decrease the effective dose to on-site workers and the public, stack height, release duration and site boundary should be maximised. The minimum recommended stack height and site boundary distance are 60 m and 250 m, respectively. It was also found that very unstable weather conditions that cause enhanced vertical mixing, Pasquill-Gifford Stability Class A, minimise effective dose to members of the public. The impact of these changes on effective doses are demonstrated quantitatively. Analysis of tritium dispersion and dose rates provides upper bounds on releasable tritium inventories that can be stored on site. It is envisaged that future fusion power plants such as DEMO can use this information when designing and choosing a location for their site.