# GoZone: A Numerical Model for Travelling Fires Based on Cellular Automata Concept
## 9 Conclusions  
A numerical model was presented to predict the fire development in compartments. While being based on simplifying assumptions, it proved to have the capability to predict several of the important features of the development of a fire in a compartment from ignition to flashover such as fire propagation and temperature development, in fuel control as well as air control regime. Having the capability to represent several features of the compartment (real shape of the plan view of the floor, real position and surface of any opening) and of the fire load characteristics (density, rate of heat release density, time constant for fire propagation, elevation above ground level, all possibly varying across the compartment, plus any position possible for the fire origin), whereas the run time of current problems on a laptop is in the order of a minute, this model has the ambition to occupy an empty niche between the geometry constrained analytical models presented thus far for travelling fires and the more sophisticated CFD analyses. The basic idea is to combine an existing two zone model with a discretisation of the floor by a mesh of triangular or quadrilateral cells of finite size, with each cell possibly having its own characteristics with regard to fire load and its own status with regard to combustion. Fire propagation is driven by radiation from burning cells as well as from the hot smoke layer. Different sub models required particular attention for the development of this tool. The point source model was adopted to represent the fire source and to compute the radiation that it will generate to the zones of the compartment where combustion has not yet started. Discretisation of the floor and the associated fire load into cells of finite size led to the development of a non-local model concept for computing the flame length in the burning cells. It can be applied to a burning zone of any shape, which is an essential requirement for a model that has the ambition to not be geometrically constrained. This model was tested against an experimental campaign and CFD analyses, which showed good agreement compared with the Heskestad equation in terms of flame length at the centre line of the fire (for shapes of the fire where this equation applies) and it appeared to be almost mesh insensitive for a range of practical mesh sizes. Radiation from the hot smoke to the fire load was obtained by the discretisation of the lower plane of the hot smoke that was mirrored by the discretisation of the floor and  
Figure 25: Gas temperature comparison: (**a**) TG2; (**b**) TG3. computation of the view factors from all cells of the hot smoke to all cells on the floor (with due consideration of possible obstruction in the case of the ground floor with a concave shape or in the case of obstacles present in the compartment such as internal walls). An ignition strategy was developed based on the concepts of critical energy of ignition and critical heat flux. This strategy has shown reasonably good prediction capabilities including for transient heat flux exposures. Air control regime is triggered by the total oxygen content in the compartment, and the combustion or not of the different cells is then determined by their proximity to individual openings that deliver air in the compartment. The model was implemented in the existing OZone model and thus benefits from all capabilities of this model such as the possibility of openings that appear at predefined times or according to defined temperature criteria, the presence of vertical as well as horizontal openings eventually with forced ventilation, and heat loss through the boundaries of the compartment were explicitly considered. It also had the same inherent limitations such as a horizontal floor and ceiling and a ratio between the characteristic horizontal dimension of the compartment and a floor to ceiling distance that was not excessive. The new code in which these developments were implemented was given the name of GoZone.