# Computational Fluid Dynamics of Compartent Fires: A Review of Methods and Applications
## 1 Introduction  
A compartment fire is defined as a fire which occurs in a closed space or a room in which the fire behavior is mainly dependent on natural physical processes such as combustion, heat transfer, and fluid dynamics. The way they interact with the environment differs from open fires in terms of oxygen restriction, smoke containment, and energy release [1, 2]. Computational Fluid Mechanics (CFD) modeling for a compartment fire is defined by the numerical simulation of fire behavior, smoke, heat, and gases within a confined space, such as a room or building. This type of modeling is essential in fire safety engineering for understanding fire dynamics, the real fire scenario, temporal evolution of temperature and other properties in the compartment, evaluating safety measures, and for designing effective fire protection systems [3]. It provides valuable insights into fire behavior and helps to improve fire safety design, which can result in decreasing risks in buildings. For example, from fire protection point of view, predicting the concentration of soot particles using CFD can provide visibility estimation for a person who is trapped in an enclosed space fire and is looking for an exit sign [4]. CFD has been conducted in fire safety science since 1980s [5]. Besides that, there have been always constant attempts to review and improve the CFD methods in fire modeling, starting with [PERSON] in 1997 [6], who reviewed the fire dynamics study tools using the time-averaged approach for the random turbulent fluctuations caused by fluid flow [5], to [PERSON] et al. [7] in 2024, who investigated the challenges in compartment fire modeling. From a traditional point of view, a compartment fire in its natural mode (i.e., without suppression or control) includes five stages from the first point to the last: ignition, pre-development, flashover, fully developed, and decay [8; 9]. However, according to the newer studies [10; 11], when the total fuel and burning materials are consumed and HRR drops to zero (i.e., end of the decay phase), an additional stage called the cooling phase starts in which the compartment structure and product gases begin to cool down. This is particularly important when coupling CFD models with structural analysis, fire resistance design, and post-fire assessments. The cooling phase is not considered in fire dynamics as there is no fire, but its heat transfer mechanism, arising from residual heat stored in the compartment structure and product gases, should be accounted for. A schematic diagram for the temporal evolution of heat release rate in different stages of a compartment fire is illustrated in Figure 1.  
In order to exploit CFD methods in fire modeling, a variety of computer tools have been developed. Among them, FDS (Fire Dynamics Simulator) (developed by the National Institute of Standards and Technology--NIST) [12] based on the Fortan, OpenFOAM (Open Field Operation And Manipulation) (developed by OpenFOAM Foundation) based on the C++, and ISIS (CALIF ISIS-developed by IRSN (Institut de Radioprotection et de S\(\acute{\rm e}\)rete Nucl\(\acute{\rm e}\)aire: Institute for Radiological Protection and Nuclear Safety)) [13] are the tools which are widely used in the numerical simulation of compartment fires. In addition, a specific fire model based on code developed by FM Global [14], called FireFOAM, is used to tackle fire dynamics and combustion modeling. CFD tools provide an environment to simulate fluid flow and related physical processes (e.g., heat transfer, combustion, etc.) through virtual models, allowing for detailed analysis and predictions without the need for physical experiments. Aside from the required level of expertise to use them, these tools are like machines that need fuel to operate. The initial inputs prepared by the user are considered the fuel. Inputs may include the dimensions, ignition and fire source, fuel type, thermomechanical properties of the materials and boundaries such as compartment walls, duration of the simulation in question, etc.