Accident Analysis Modeling and Case Study of Hydrogen Refueling Station Using Root Cause Analysis (RCA)
Daniel Frey
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsRewrite Abstract with more clarity.
In Introduction: Research gap should be delivered on more clear way with directed necessity for the
conducted research work.
Examine adherence to hydrogen safety standards (e.g., ISO 19880-1, NFPA 2, SAE J2601) and regulatory frameworks.
Modify the objective of’ the study precisely and write the novelty statement based on the past research carried out.
Evaluate the implementation of safety systems, such as leak detection sensors, emergency shut-off valves, and explosion-proof designs.
Evaluate common failure modes, including leaks, pressure buildup, and mechanical failures, using methodologies like Fault Tree Analysis (FTA).
Check the Language and Grammar for the whole document.
Include economic analysis of using hydrogen fuel in the discussion section.
Authors are suggested to discuss more technical findings to strengthen the discussion section.
Include future scope in separate sections.
Author Response
Comment 1: Rewrite Abstract with more clarity.
Response 1: Thank you for your valuable feedback and suggestion. We revised the abstract to more clarity.
“As the global transition to carbon neutrality accelerates, hydrogen energy has emerged as a key alternative to fossil fuels due to its potential to reduce carbon emissions. Many countries, including Korea, are constructing hydrogen refueling stations; however, safety concerns persist due to accidents caused by equipment failures and human errors. While various accident analysis models exist, the application of Root Cause Analysis (RCA) to hydrogen refueling station accidents remains largely unexplored. This study develops an RCA model specifically for hydrogen refueling stations to identify direct, indirect, and root causes of accidents. The RCA model developed in this study uses data from accident investigation reports over the past five years, which includes information on the organizational structure and operational status of hydrogen refueling stations, as well as the RCA handbook. The primary defect sources identified were equipment defects, personal defects, and other defects. Equipment defects included design issues, installation problems, reliability issues, and misuse. Personal defects involved company and contract employee issues, while other defects included sabotage, natural phenomena, and miscellaneous causes. Compared to existing accident reports, which identified only three primary causes, the RCA model revealed nine distinct causes, demonstrating its superior analytical capability. In conclusion, the RCA model developed in this study provides a more systematic and comprehensive approach to investigating accidents at hydrogen refueling stations, which could significantly improve safety practices and assist in identifying root causes more efficiently in future incidents.”
Comment 2: In Introduction: Research gap should be delivered on more clear way with directed necessity for the conducted research work.
Response 2: Thank you for your valuable feedback and suggestion. We've added this to the introduction.
“However, there are few studies applying the RCA technique as an accident analysis model for accidents occurring at hydrogen refueling stations”
Comment 3: Examine adherence to hydrogen safety standards (e.g., ISO 19880-1, NFPA 2, SAE J2601) and regulatory frameworks.
Response 3: hydrogen refueling station in Korea are based on the domestic legal standard of hydrogen made by referring to overseas standards such as ISO. The hydrogen refueling station was designed and constructed in accordance with the “facility/technical/inspection code for use of hydrogen gases (KGS FU671,2024)” and has completed legal inspection accordingly.
Comment 4: Modify the objective of’ the study precisely and write the novelty statement based on the past research carried out.
Response 4: Thank you for your valuable feedback and suggestion.
The following content has been added:
" However, few studies have applied the RCA technique as an accident analysis model for accidents at hydrogen refueling stations, and investigations into the causes of gas accidents in Korea primarily focus on identifying immediate causes rather than root causes." The research objective has been revised to: "Therefore, this study aimed to develop an accident cause analysis model for automotive hydrogen refueling stations using the RCA technique, as one of the methods that could derive not only direct and indirect causes but also root causes of accidents when they occurred, compare the causes identified in existing accident investigation reports of actual accident cases with the causes derived using the RCA technique, and propose it for identifying root causes of accidents at hydrogen refueling stations in the future by applying it to actual accident cases."
Comment 5: Evaluate the implementation of safety systems, such as leak detection sensors, emergency shut-off valves, and explosion-proof designs.
Response 5: Thank you for your valuable feedback and suggestion.
The purpose of the RCA (Root Cause Analysis) technique is to investigate the root causes of an incident after it has occurred, focusing on identifying the underlying factors that led to the event. Since RCA is primarily concerned with understanding the fundamental reasons behind accidents or failures, evaluating the effectiveness of safety systems, such as leak detection sensors, emergency shut-off valves, and explosion-proof designs, is not within the scope of the RCA process.
Comment 6: Evaluate common failure modes, including leaks, pressure buildup, and mechanical failures, using methodologies like Fault Tree Analysis (FTA).
Response 6: Thank you for your valuable feedback and suggestion.
The following content has been added to the discussion.
"Still, this study had certain limitations in identifying root causes, as we could not directly participate in accident investigations and relied solely on accident investigation reports. Additionally, common failure modes such as pressure rise and mechanical failure were not analyzed. Future research should integrate various accident cause analysis tools applicable to domestic gas facilities and systematically assess potential failure mechanisms to enhance the safety analysis of hydrogen refueling stations."
Comment 7: Check the Language and Grammar for the whole document.
Response 7: We received proofreading services provided by the college and have made revisions throughout the document.
Comment 8: Include economic analysis of using hydrogen fuel in the discussion section.
Response 8: Thank you for the suggestion.
The socio-economic aspects of hydrogen have been added to the discussion.
“In addition to improving safety management, revitalizing the hydrogen economy requires technological advancements and policy support to enhance commercialization potential and ensure economic viability [19-20]. Optimizing the hydrogen supply chain requires an integrated consideration of production, storage, and transportation technologies, as these technologies encompass diverse characteristics and cost factors. In this context, both government and industry must not only invest in technology development and infrastructure but also conduct economic analyses and provide policy support to establish an optimal hydrogen supply chain”
Comment 9: Authors are suggested to discuss more technical findings to strengthen the discussion section.
Response 9: Thank you for your valuable feedback and suggestion.
This content has been added to the discussion section.
"The accident cause investigation results identified in the existing accident investigation report only included legal aspects, but the RCA modeling map analyzed all three aspects—equipment, personnel, and others—identifying not only legal factors but also management aspects as root causes. After comparing these results, we concluded that when analyzing accident causes at the time of occurrence, the RCA methodology was a more systematic and effective approach to identify the root causes of accidents."
Comment 10: Include future scope in separate sections.
Response 10: Thank you for your valuable feedback and suggestion.
I divided the discussion and conclusion sections. And, we included a future scope in discussion sections.
Author Response File: 
Author Response.docx
Reviewer 2 Report
Comments and Suggestions for AuthorsThe manuscript, “Accident analysis modeling and case study of hydrogen refuelling station using root cause analysis (RCA)”is quite well drafted. Kindly address the following comments
1-Graphical abstract/Highlight would be appreciated.
2-In the abstract, kindly try to incorporate the following a) A brief introduction to the topic that you're investigating. b) Explanation of why research on the topic is significant. c) Statement about the gap in the research and formulate the research question d) Your research methods and the uniqueness of your research approach.
3-The authors need to provide a schema for the process flow/methodology proposed
4- The authors can classify the types of high-pressure hydrogen vessels. Apart from H2 safety, it plays its role in socio-economic aspects. Kindly refer
Jayakumar, A., Madheswaran, D.K., Kannan, A.M., Sureshvaran, U. and Sathish, J., 2022. Can hydrogen be the sustainable fuel for mobility in India in the global context?. International Journal of Hydrogen Energy, 47(79), pp.33571-33596.
Kindly add more recent references from peer-reviewed journals, at least 25.
5-In the conclusion, restate your research gap, summarize the key contributions, state its significance and results, finally conclude your thoughts within a single paragraph.
6-The standard of English is very poor as well as the quality of the figures.
7-A comprehensive proofreading is a mandate. Check the spelling of “Pressure”, Check the Units, eg “oC” follow SI guidelines
Comments on the Quality of English LanguageThe English could be improved to express the research more clearly and subsequent value addition.
Author Response
Comment 1: Graphical abstract/Highlight would be appreciated.
Response 1: Thank you for your valuable feedback and suggestion.
However, The Safety journal does not require graphical abstracts or highlights, so it seems that this would not align with the journal's format
Comment 2: In the abstract, kindly try to incorporate the following a) A brief introduction to the topic that you're investigating. b) Explanation of why research on the topic is significant. c) Statement about the gap in the research and formulate the research question d) Your research methods and the uniqueness of your research approach.
Response 2: Thank you for your valuable feedback and suggestion.
Changed the abstract to reflect this:
“As the global transition to carbon neutrality accelerates, hydrogen energy has emerged as a key alternative to fossil fuels due to its potential to reduce carbon emissions. Many countries, including Korea, are constructing hydrogen refueling stations; however, safety concerns persist due to accidents caused by equipment failures and human errors. While various accident analysis models exist, the application of Root Cause Analysis (RCA) to hydrogen refueling station accidents remains largely unexplored. This study develops an RCA model specifically for hydrogen refueling stations to identify direct, indirect, and root causes of accidents. The RCA model developed in this study uses data from accident investigation reports over the past five years, which includes information on the organizational structure and operational status of hydrogen refueling stations, as well as the RCA handbook. The primary defect sources identified were equipment defects, personal defects, and other defects. Equipment defects included design issues, installation problems, reliability issues, and misuse. Personal defects involved company and contract employee issues, while other defects included sabotage, natural phenomena, and miscellaneous causes. Compared to existing accident reports, which identified only three primary causes, the RCA model revealed nine distinct causes, demonstrating its superior analytical capability. In conclusion, the RCA model developed in this study provides a more systematic and comprehensive approach to investigating accidents at hydrogen refueling stations, which could significantly improve safety practices and assist in identifying root causes more efficiently in future incidents.”
Comment 3: The authors need to provide a schema for the process flow/methodology proposed
Response 3: Thank you for your valuable feedback and suggestion.
We added process flow chart and some description in the method section.
"This study first developed an RCA modeling map for hydrogen refueling stations, and then applied actual hydrogen refueling station accident cases to the map to validate the root cause model and identify the root causes. Subsequently, a comparative analysis was conducted between the main causes identified in existing accident investigation reports and the causes derived from the RCA modeling map." This content has been added to the Method section, and a process flow diagram has also been included in the Method section.
Comment 4: The authors can classify the types of high-pressure hydrogen vessels. Apart from H2 safety, it plays its role in socio-economic aspects. Kindly refer
Jayakumar, A., Madheswaran, D.K., Kannan, A.M., Sureshvaran, U. and Sathish, J., 2022. Can hydrogen be the sustainable fuel for mobility in India in the global context?. International Journal of Hydrogen Energy, 47(79), pp.33571-33596.
Kindly add more recent references from peer-reviewed journals, at least 25.
Response 4: Thank you for your valuable feedback and suggestion.
"Hydrogen vessels of type 1, 2, 3, and 4 are used in Korea, and most of the hydrogen vessels used in hydrogen tube trailers in Korea are predominantly type 1" has been added to the Method section.
The socio-economic aspects of hydrogen have been added to the discussion, and the number of references has been increased.
“In addition to improving safety management, revitalizing the hydrogen economy requires technological advancements and policy support to enhance commercialization potential and ensure economic viability [19-20]. Optimizing the hydrogen supply chain requires an integrated consideration of production, storage, and transportation technologies, as these technologies encompass diverse characteristics and cost factors. In this context, both government and industry must not only invest in technology development and infrastructure but also conduct economic analyses and provide policy support to establish an optimal hydrogen supply chain.”
Comment 5: In the conclusion, restate your research gap, summarize the key contributions, state its significance and results, finally conclude your thoughts within a single paragraph.
Response 5: Thank you for your valuable feedback and suggestion.
This content has been added to the Conclusion section.
"In this study, an analysis was conducted using the RCA modeling map, which has never been applied to accidents occurring at hydrogen refueling stations. The analysis demonstrated that the RCA modeling map is effective in identifying the root causes of accidents. This finding provides valuable insights for safety management at hydrogen refueling stations and can be used as foundational data to prevent similar accidents in the future."
Comment 6: The standard of English is very poor as well as the quality of the figures.
Response 6: Thank you for your valuable feedback and suggestion.
We received proofreading services provided by the school and have made revisions throughout the document.
Comment 7: A comprehensive proofreading is a mandate. Check the spelling of “Pressure”, Check the Units, eg “oC” follow SI guidelines
Response 7: Thank you for your valuable feedback and suggestion.
The term 'pressire' in Figure 1 has been changed to 'pressure,' and all units of bar have been converted to MPa.
Author Response File: Author Response.docx
Reviewer 3 Report
Comments and Suggestions for AuthorsThe study deals with developing an accident cause analysis model concerning hydrogen refuelling stations using the Root Cause Analysis (RCA) technique. The study aims to develop a hydrogen refuelling station RCA modelling map using data from accident investigation reports over the past 5 years. Based on that, the authors validated the model by applying real data concerning a gas leak accident at a hydrogen refuelling station in Korea on January 28, 2022.
The manuscript is well-structured and explains the differences between the various accident analysis models, identifying the rationale for choosing the specific technique. The present work is highly recommended for publication after implementing minor changes:
- Figure 6 and Table 1 should be simplified to be more concise for the reader. The authors could consider adding the casual factors in a second column in Table 1 and removing figure 6.
Author Response
Comment 1: Figure 6 and Table 1 should be simplified to be more concise for the reader. The authors could consider adding the casual factors in a second column in Table 1 and removing figure 6.
Response 1: Thank you for your valuable feedback and suggestion.
Added shapes and elements to Table 1.
Author Response File: Author Response.docx
Reviewer 4 Report
Comments and Suggestions for AuthorsThis paper presented a study of several past accidents involving hydrogen refueling stations. The resulting model was based on publicly available investigative reports and employed the root cause analysis (RCA) technique. RCA was able to identify nine causes and the accident investigation reports had noted just three causes. The paper concludes therefore that RCA is "a more systematic and effective approach".
The contribution of the paper is that it presents a clear and well documented example of RCA for a particular, industrially important class of system. It provides some evidence for the effectiveness of the method, but it cannot reliably characterize the effectiveness of the approach which must require replicated uses of the method across different use-cases. I would also add that claims about effectiveness should preferably be based on sets of models implemented by different teams because an effective method should provide consistently good results when adequately qualified people are organized even if there is some variability in skill-level and experience.
I have a few more specific comments as listed below:
The introduction lists the United States as among 137 countries that have "declared carbon neutrality." I wonder if this characterization is still accurate.
On page 2, the paper describes hydrogen as an "energy source". I'd argue that hydrogen, as a practical matter, serves as an energy carrier but cannot serve as an energy source for humans living on earth.
In Figure 2, I suggest that a graphical model of RCA should include feedback paths rather than giving the impression that the method is strictly a linear algorithm -- comprised of only a single pass through each step.
On page 7, the paper states that "The accident nut fractured ..." That phrasing seems odd to me, as if an "accident nut" is a particular type of fastener.
On page 12, the paper describes the limitations of the study. I would suggest that replicability of RCA should be explicitly mentioned. I don't think this study was designed in such a way that replicability can be assessed.
Author Response
Comment 1: The introduction lists the United States as among 137 countries that have "declared carbon neutrality." I wonder if this characterization is still accurate.
Response 1: Thank you for your valuable feedback and suggestion.
Although the United States is one of the 137 countries that have declared carbon neutrality, it is, in fact, the most passive country in achieving carbon neutrality. Therefore, the sentence has been revised as follows.
“Globally, approximately 137 countries have pledged carbon neutrality by 2050, and major countries including the Korea, Japan, and China, as well as the European Union, which announced the Green Deal containing carbon emission neutrality goals, have declared carbon neutrality [1].”
Comment 2: On page 2, the paper describes hydrogen as an "energy source". I'd argue that hydrogen, as a practical matter, serves as an energy carrier but cannot serve as an energy source for humans living on earth.
Response 2:Thank you for your valuable feedback and suggestion.
We included a clear statement of the study's objective to ensure it is explicitly outlined in the paper.
“This study aims to analyze accidents at hydrogen refueling stations to prevent such incidents, in the context of the active implementation of hydrogen refueling stations and hydrogen fuel cell power plants in South Korea. To achieve this, the study uses traditional analysis methods such as Root Cause Analysis (RCA) to analyze accidents at hydrogen refueling stations and compares the causes identified in existing accident investigation reports with those derived from RCA, aiming to enhance the accuracy of accident cause analysis.”
Comment 3: In Figure 2, I suggest that a graphical model of RCA should include feedback paths rather than giving the impression that the method is strictly a linear algorithm -- comprised of only a single pass through each step.
Response 3: Thank you for your valuable feedback and suggestion.
As you know, the RCA method is a structure without a feedback path, and if the feedback path is considered as suggested by the reviewer, it can be said to be the development of a new analytic method, and the RCA method used in the current study is an application of an existing general model.
Comment 4: On page 7, the paper states that "The accident nut fractured ..." That phrasing seems odd to me, as if an "accident nut" is a particular type of fastener.
Response 4: Thank you for your valuable feedback and suggestion.
I have changed the term 'accident nut' to 'connection pipe’.
Comment 5: On page 12, the paper describes the limitations of the study. I would suggest that replicability of RCA should be explicitly mentioned. I don't think this study was designed in such a way that replicability can be assessed
Response 5: Thank you for your valuable feedback and suggestion.
This issue is not limited to RCA but is a common characteristic of all accident investigation methods. The replicability of accident analysis can vary depending on the individual interpretations of the analysts, making it important to establish clear criteria for assessing it. Future research could involve comparing the results of different analysts and conducting studies specifically focused on replicability.
Additionally, the following content has been added to the discussion:
'Further research focusing on the replicability of accident analysis methods is necessary to establish clearer standards for assessing consistency across different analysts.
Author Response File: Author Response.docx
Round 2
Reviewer 2 Report
Comments and Suggestions for AuthorsWith most changes made, I still advice the authors to incorporate small amendments specified below;
1-The organization of the work is not as per the standard template.Write "Pa" for Pascal not "pa"
2-All the figures must be redrawn for more clarity.
3-English must be improved considerably
Comments on the Quality of English Language
English must be improved considerably
Author Response
Comment 1: The organization of the work is not as per the standard template. Write "Pa" for Pascal not "pa".
Response 1: Thank you for your valuable feedback and suggestion. We revised the abstract to more clarity.
- Revised the headings, table titles, and figure captions to comply with the journal’s formatting guidelines.
- Revised the reference formatting to align with the journal’s standard template.
- The unit in Fig 1 has been corrected to MPa.
- Change the content of the method on page 4.
(Before) For the hydrogen storage equipment, the tube trailer cartridge serves as the primary storage facility with a maximum charging pressure of approximately 20Mpa; subsequently, the hydrogen gas compressed to 50-87 MPa through the hydrogen compressor is stored in medium pressure (Mid Bank, Type 1) and high-pressure vessels (High Bank, Type 1).’
(After) For the hydrogen storage equipment, the tube trailer cartridge serves as the primary storage facility with a maximum charging pressure of approximately 20MPa; subsequently, the hydrogen gas compressed to 50-87 MPa through the hydrogen compressor is stored in medium pressure (Mid Bank, Type 1) and high-pressure vessels (High Bank, Type 1).
Comment 2. All the figures must be redrawn for more clarity.
Response 2: Thank you for your valuable feedback and suggestion.
Figures that were unclear have been redrawn to improve visibility. (Fig 1, Fig 4, Fig 5)
Author Response File: Author Response.docx
Reviewer 3 Report
Comments and Suggestions for AuthorsThe authors have adequately revised the manuscript in accordance with the comments. I recommend acceptance for publication.
Author Response
Comment 1: The authors have adequately revised the manuscript in accordance with the comments. I recommend acceptance for publication.
Response 1: Thank you for the reviewer's positive feedback
Author Response File: Author Response.docx
Reviewer 4 Report
Comments and Suggestions for AuthorsThe authors have adequately addressed the concerns expressed by reviewers in the first round.
Author Response
Comment 1: The authors have adequately addressed the concerns expressed by reviewers in the first round.
Response 1: Thank you for the reviewer's positive feedback.
Author Response File: Author Response.docx
Round 3
Reviewer 2 Report
Comments and Suggestions for AuthorsWith most changes made, still, the quality of the figures and the presentation can be improved.
Kindly merge results and discussion into a single section and make a sub-section.
Do a comprehensive proofreading, and if possible use MDPI editing services.
Comments on the Quality of English LanguageThe English could be improved to more clearly express the research.
