Due to the intense R&D activity in the field of water mist fire suppression during the past decade, the qualitative and quantitative understanding on the performance of water mist has increased significantly. This development has led to a point in which quantitative theoretical models describing large-scale water mist fire suppression systems begin to emerge. This paper describes the composition and validation of one such model, designed for total flooding water mist applications, especially against flammable liquid hazards in enclosures. The basic construction of the model is first described, followed by an example on the validation of the model using full-scale experimental data. The model is then used to investigate the limitations to the maximum possible mist concentration in the protected space. The potential of the model as an engineering tool is illustrated by making predictions on the scaling laws associated with water mist systems in the framework of IMO MSC/Circ.668/728 as the enclosure volumes and ventilation conditions are varied. The predictions are found to be in agreement with what is indicated by the recent US Coast Guard test series in very large machinery spaces.