# Development of a Fire Risk Assessment Program for Submerged Tunnels
## 4 Validation of Submerged Tunnel Quantitative Risk Assessment Program  
### Verification of Road Tunnel Quantitative Risk Assessment Results  
To validate the Quantitative Risk Assessment Program (SFT_QRA), a comparison was made with the existing commercial program, Road QRA. The parameters used to verify the quantitative risk assessment of a general road tunnel are shown in Table 3, while Table 4 presents the comparative results of the quantitative risk assessment for a general road tunnel. The total risk calculated using SFT_QRA was found to be 27.2% lower than that of Road QRA. This difference is attributed to the fact that Road QRA applies the accident occurrence rates for each vehicle type as stipulated by the Ministry of Land, Infrastructure and Transport (2020) [10], which are based on accident rates recorded over five years (2017). According to the guidelines, when no specific technical data is available, referenced data can be cited and applied without additional constraints. However, this approach may lead to discrepancies between the applied statistical data and current accident statistics. As a result, the total risk is reduced, and consequently, the estimated fatalities per 10,000 years, the frequency of one fatality occurrence, and the return period all yield lower values compared to the results of the currently applied quantitative risk assessment. This indicates the necessity of revising the current guidelines and updating the relevant statistical data. In this regard, SFT_QRA, which allows for the application of the latest statistical data, is considered a more appropriate tool for quantitative risk assessment. The total risk for small-vehicle-only road tunnels was found to be 0.41% lower in SFT_QRA compared to Road QRA. The input parameters used in SFT_QRA and Road QRA were identical, and the resulting analysis showed a 0.41% reduction, as presented in Table 4. This difference is attributed to the fact that both SFT_QRA and Road QRA utilize FDS-based fire analysis as the fundamental approach for quantitative risk assessment. Although the time-step settings in FDS were identically subdivided in both programs,  
Figure 2: Input windows for railway tunnel evacuation analysis and FED assessment. the division of a single time-step is not uniform, leading to discrepancies in the exact timing of recorded results. As a result, minor deviations exist in the recorded timeframes. However, these deviations are not statistically significant, with a maximum difference of approximately 0.05 s. It is considered that this small timing discrepancy in fire duration affected the maximum fatality FED analysis. Therefore, the final analysis results are considered identical within a maximum error margin of 0.4%. A quantitative risk assessment was conducted for general road tunnels and small vehicle-only road tunnels using the SFT_QRA developed in this study and the existing commercial Road QRA program under identical input conditions. The results confirm that, apart from discrepancies caused by differences in the application range of accident probabilities by vehicle type in fire incident statistics, there were no significant differences between the two programs for general road tunnels. However, regarding the recommendations outlined in the current relevant guidelines, an additional feature was implemented in the developed program to allow for the differentiation of application years when applying statistical data.