## 5 Conclusions  
This study evaluates the finite element analysis of the reinforced concrete protection wall model from the KGS FP217, and composite structures were performed to investigate the behavior of the protection wall under a hydrogen gas tank explosion in a worst-case scenario through the TNT equivalent method. In addition, this study also compares the spherical free air blast between ConWep and ALE simulation with different distances between TNT and the protection wall. Following are the conclusion from this study.  
1. To decrease the displacement and cracks on the structure after an explosion, the placement of an H-beam and reinforcement technique should be used. The use of an H-beam in reinforced concrete improves blast performance by increasing the blast capacity and better controlling displacement. In comparison with the distance between reinforced concrete protective structure at 1.6 m and 3.6 m the displacement reduce from 250 mm to 109 mm at wall thickness of 0.12 m, whereas for the composite structure the displacement reduce from 245 mm to 68 mm.  
2. Blast scenario could be infinite, and with increasing the standoff distance, pressure values, damage, and displacement values decrease. When the standoff distance between the protection wall and the explosion is the same for reinforced concrete and composite structure protection wall, the deflection at the center is nearly the same, but with increasing the distance between the explosive and protection wall, the displacement and damage on the structure reduce. At a standoff distance of 1.6 m the structure collapsed, and at a distance of 3.6 m the structure had moderate damage after an explosion for worse-case scenario. When the thickness of the protection wall increased to 200 mm the structure gets low damage for both reinforced and composite structure. At the distance of 3.6 m the displacement decreases from 109 mm to 53 mm for reinforced concrete protection wall with the thickness of 0.12 m and 0.2 m, respectively.  
3. According to simulation results for the worst-case scenario, the minimum requirement of the barrier wall, as in KGS FP217, is not safe at a distance of 1.6 m after the hydrogen gas tank explosion. During the site visit to hydrogen gas storage, it was found that the distance between the protection wall and storage was 1.53 m. Moreover, the minimum distance between the protection wall and the hydrogen gas tank is not mentioned in the code book. Incident pressure obtained from the ALE simulation and ConWep during the worst-case scenario explosion of different variables may be taken as a guideline for the selection of protection structure and standoff distance between the protection wall and hydrogen gas tank storage.  
4. Use of H-beam as a composite structure during 30 kg of hydrogen gas explosion had minimum damage at a stand-off distance of 3.6 m compare with worse -case scenario.  
5. Good agreement between ConWep and ALE simulation for incident pressure at spherical free-air burst. This incident pressure can be taken as a reference to predict the blast pressure.  
Conceptualization, S.K., T.O. and C.P.; methodology, S.K., T.O. and C.P.; software, S.K., T.O. and C.P.; formal analysis, S.K., T.O. and C.P.; writing--original draft preparation, S.K., T.O., T.J. and C.P.; writing--review and editing, S.K., T.O., T.J. and C.P. All authors have read and agreed to the published version of the manuscript.  
This research was supported by \"Regional Innovation Strategy (RIS)\" through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (MOE) (2022 RIS-005) and by the Korea Institute of Energy Technology Evaluation and Planning (KETEP) and the Ministry of Trade, Industry and Energy (MOTIE) of the Republic of Korea (No. 20215810100020).  
Not applicable.  
The authors declare no conflict of interest.