# Risk Assessment of Hydrogen Cyanide for Available Safe Egress Time in Fire Simulation
## 3 Simulation Results and Discussion of Fire Scenarios
### HCN Yield Sensitivity Analysis Results  
As part of evaluating the hazards of HCN in fires, a study was conducted to examine the impact of predicted HCN concentration results on ASET outcomes during fire simulations. The factor most directly related to the predicted HCN concentration is \(y_{HCN}\). Unlike \(y_{CO}\) and \(y_{S}\), the information on \(y_{HCN}\) is relatively limited in the field of fire engineering. Moreover, \(y_{HCN}\) can vary significantly depending on ventilation conditions, and this factor should be considered when utilizing this information. Therefore, this study aimed to assess the potential risk by evaluating the variation in the time to reach the threshold through a sensitivity analysis of the \(y_{HCN}\) values presented in Table 2, adjusted by \(\pm 50\%\). This considers the challenges and uncertainties in \(y_{HCN}\) measurements, as well as variations due to ventilation conditions, under the selected fire simulation conditions.  
Figure 8 compares the times at which each parameter reaches the threshold values based on the sensitivity analysis of \(y_{HCN}\). Due to the sensitivity analysis on \(y_{HCN}\), the results for visibility and gas temperature show minimal differences but are remarkably similar. Examining the results for HCN concentration in Figure 8a for GM21, it is evident that, as expected, increasing the input \(y_{HCN}\) in the fire simulation leads to a significant decrease in the time to exceed the threshold value. As the \(y_{HCN}\) for GM21 increased by 1.5 times, the time for HCN concentration to exceed the threshold value decreased from 373 s to 239 s. Comparatively, this represented a difference of approximately 124 s compared to the fastest time to reach the threshold value for visibility. Similarly, Figure 8b shows that as \(y_{HCN}\) increases, there is a sharp decrease in the time for HCN concentration to exceed the threshold value. Compared to the gas temperature, which exceeds the threshold value in the fastest time, the difference decreases dramatically from 112 s to 14 s according to the change in \(y_{HCN}\).  
Figure 9 shows the results of evaluating the time to reach the threshold value of each parameter as RRS, based on the variation in \(y_{HCN}\) observed in Figure 8. Since this is a sensitivity analysis on \(y_{HCN}\), only the RRS for HCN concentration changes. For GM21, when \(\Delta y_{HCN}/y_{HCN}\) = 0.5, the RRS is 47.0 points, but when \(\Delta y_{HCN}/y_{HCN}\) = 1.5, it increases to 74.4 points, indicating a rise of 27.4 points. Examining the results for PAN, RRS increases from 40.7 points to 92.7 points according to the change in \(y_{HCN}\), indicating that it could be comparable to the RRS for visibility and gas temperature. Previous studies measuring \(y_{HCN}\) have shown that \(y_{HCN}\) can increase by about 7 to 10 times depending on ventilation conditions, and thus, it can be deduced that the risk score for HCN concentration could increase significantly.  
Figure 8: Comparison of time to reach threshold values of parameters with HCN yield.  
Consequently, within the fire simulation conditions considered in this study, the RRS evaluation results for HCN concentration showed a high score of up to approximately 92 points. ASET is determined according to the parameter that first reaches the threshold value of the life safety code, and it could be determined by visibility or gas temperature, which are close to 100 points in RRS. However, HCN concentration, which can indicate relatively high risk as a direct cause of casualties in fires, was found to be significant. Furthermore, considering the uncertainty in the measurement results and the need for expanded information on the input parameters required for predicting HCN, the impact of HCN on ASET is expected to be even greater.