# Risk Assessment of Hydrogen Cyanide for Available Safe Egress Time in Fire Simulation
## 2 Description of Fire Simulation  
### Computational Domain and Fire Source for Fire Simulation  
The fire model applied for the fire simulation is the representative field model Fire Dynamics Simulator (FDS, ver. 6.7.9) [20]. The subgrid turbulence model of FDS, which employs the large eddy simulation (LES) technique, utilizes the Deardorff model, and the combustion model uses the mixing-controlled fast chemistry (MCFC) approach. Additionally, efficient prediction of the mixture fraction is achieved through lumped species. Figure 1 shows the computational domain for the fire simulation. Among the various spatial types applicable to performance-based design (PBD), a residential building was selected [21]. All spaces except the fire room are assumed to be closed off by fire doors. Additionally, the floors, ceilings, and walls of the building were uniformly assumed to be concrete [19]. Typically, the configuration of apartment buildings is more complex, with various structures that may exist. However, since the purpose of the fire simulation is to evaluate the potential hazards of HCN during a residential building fire, a simplified layout was considered to minimize the impact of spatial geometry, as referenced from similar previous studies [20]. The doorway of the fire room was fully open (dimensions: 1.0 m (x) \(\times\) 2.0 m (z)). Additionally, an evacuation exit (1.0 m (x) \(\times\) 2.0 m (z)) was opened to allow the heat and smoke generated in the fire room to be vented. The fire source was set to have an area of 1 m\({}^{2}\) in the center of the floor of the fire room. To assess the risk of HCN in the fire simulation, physical quantities considered in life safety codes were selected for comparison. Specifically, these quantities were predicted at a height of 1.8 m, corresponding to the breathing zone, measured from the center of the floor of the evacuation exit. The predicted physical quantities included gas temperature, visibility, and concentrations of O\({}_{2}\), CO, CO\({}_{2}\), and HCN. Figure 1: Computational domain for residential building. To determine the impact of HCN on fire hazard assessment, the specific fire scenario selected may yield limited results compared to the general outcomes. In other words, the selected space type, types of combustibles, and heat release rate (HRR) for fire simulation may not encompass all fire conditions. Therefore, to derive generalized conclusions, it is necessary to conduct fire simulations for a multitude of fire scenarios. However, realistically, performing fire simulations for an extensive range of conditions can be challenging. Thus, this study confined the space type to residential buildings and evaluated the hazard posed by HCN based on variations in combustible types, changes in HRR, and sensitivity analysis of HCN yield. The time-dependent HRR set for the fire simulation is illustrated in Figure 2. To select the HRR, recent reports from the Republic of Korea over a five-year period for PBD were statistically analyzed. Typically, for conducting fire simulations for PBD, HRR is simplified using information provided by the design fire curve, which is derived from measurements in fire experiments. The design fire curve quantitatively provides key factors such as the fire growth rate (FGR, \(\alpha\)) and peak HRR (\(\dot{Q}_{peak}\)), enabling a statistical approach. For residential buildings, approximately 70% of FGR was found to be 'Medium (\(\alpha\) = 0.01172 kW/s\({}^{2}\))'. Additionally, with \(\dot{Q}_{peak}\) averaging around 1700 kW [22], a statistical fire growth curve for residential buildings can be established. To assess the fire hazards posed by HCN in residential building configurations, four types of combustibles were selected. The HRR was set identically regardless of the combustible type chosen. In reality, different combustibles exhibit varying burning rates and release different amounts of thermal energy. Consequently, this could result in different HRR values.