DOI: 10.3303/CET2290052 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Paper Received: 22 November 2021; Revised: 10 March 2022; Accepted: 3 May 2022 
Please cite this article as: Suzuki T., Shiota K., Nakayama J., Izato Y., Miyake A., 2022, Overview of the risk assessments for hydrogen refuelling 
stations in Japan, Chemical Engineering Transactions, 90, 307-312  DOI:10.3303/CET2290052 
  

 CHEMICAL ENGINEERING TRANSACTIONS  
 

VOL. 90, 2022 

A publication of 

 
The Italian Association 

of Chemical Engineering 
Online at www.cetjournal.it 

Guest Editors: Aleš Bernatík, Bruno Fabiano 
Copyright © 2022, AIDIC Servizi S.r.l. 
ISBN 978-88-95608-88-4; ISSN 2283-9216 

Overview of the Risk Assessments for Hydrogen Refuelling 
Stations in Japan 

Tomoya Suzukia, Kento Shiotab, Jo Nakayamab, Yu-ichiro Izatoab, Atsumi Miyakea* 
a Graduate School/Fuculty of Environment and Information Sciences, Yokohama National University, 79–7 Tokiwadai, 
Hodogaya–ku, Yokohama, Kanagawa 240–8501, Japan 
b Institute of Advanced Sciences, Yokohama National University, 79–5 Tokiwadai, Hodogaya–ku, Yokohama, Kanagawa 
240–8501, Japan 
miyake-atsumi-wp@ynu.ac.jp 

Hydrogen refuelling stations (HRSs) have attracted widespread attention in Japan. The Ministry of Economy, 
Trade, and Industry in Japan set a goal for the construction of HRSs in a strategic roadmap. Owing to the 
explosive and fire hazards associated with HRSs, a considerable amount of safety studies for HRSs has been 
conducted for several years; however, the safety studies conducted in Japan are yet to be reviewed. This study 
aimed to comprehensively review the safety studies conducted in Japan, particularly the risk assessment (RA) 
of HRSs, and to provide useful insights on the direction of future studies on the safety of HRSs. To this end, a 
comprehensive review of international and Japanese safety studies for HRSs was presented by adopting a 
bibliometric analysis approach and an overview of Japanese safety studies for HRSs was presented based on 
the type of HRSs. The results revealed that it is essential to conduct the RA of HRSs, particularly for HRSs yet 
to be assessed, to contribute to the decision-making process for the social implementation of HRSs in the future. 

1. Introduction 
In Japan, hydrogen is considered as a required secondary energy for reducing carbon emissions and to achieve 
carbon neutrality in 2050. Accordingly, the Ministry of Economy, Trade, and Industry, Japan designed and 
revised a strategic roadmap to achieve a ‘Hydrogen society’ (METI, 2019). Currently, hydrogen refuelling 
stations (HRSs) have attracted widespread attention in Japan, and some numerical targets of the roadmap 
include the construction of 320 and 900 HRSs by 2025 and 2030, respectively. However, owing to hydrogen 
hazards, such as hydrogen embrittlement, explosiveness, and flammability, HRSs are susceptible to accidents, 
which have been reported in accident databases (Galassi et al., 2012). Therefore, to achieve the ‘Hydrogen 
society’ goal, it is essential to guarantee the safety of the hydrogen infrastructure, including HRS. Accordingly, 
a considerable amount of safety studies for HRSs have been conducted for several years; however, compared 
to those of other countries, there has been no review on the safety studies conducted in Japan. Therefore, this 
study aimed to comprehensively review the safety studies conducted in Japan, particularly, risk assessment 
(RA) studies, and to provide useful insights on the required direction of future studies on the safety of HRSs. 
First, international and Japanese safety studies for HRSs were comprehensively reviewed using a bibliometric 
analysis approach to reveal the institutions that have mainly participated in the safety studies and to clarify the 
research domains of Japan. Next, an overview of the RAs that has been conducted in Japan was presented 
based on the type of HRSs. Lastly, the strength of Japan and the required direction of future studies on the 
safety of HRSs for the implementation of HRSs were discussed. 

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2. Bibliometric review of safety studies on HRSs
2.1 International safety studies

A comprehensive review of international safety studies for HRSs was presented to determine the institutions 
that have mainly participated in the safety studies in recent years. In this study, the VOSviewer, which is a freely 
available computer program developed for constructing and viewing bibliometric maps (van Eck and Waltman, 
2010), was employed to visualize the bibliometric data and to analyse the relationships among authors, 
institutions, and countries of publications related to the safety studies of HRSs. The data used in this study were 
retrieved from the Web of Science Core Collection, which is a comprehensive database of articles and includes 
detailed bibliographic information, on November 14, 2021. The publications were collected through the research 
topic using ‘hydrogen AND station AND safety’ or ‘hydrogen AND station AND risk’ as the search topics, 
indicating that this term was identified in the Title, Abstract, and Keywords of the publications. The final datasets 
consisted of 189 publications by 200 authors from 36 countries, and these publications were published in some 
Journals, namely, International Journal of Hydrogen Energy, Journal of Loss Prevention in the Process 
Industries, Energies, Sustainability, Energy Policy, Process Safety and Environmental Protection, and Journal 
of Cleaner Production (except for publications on nuclear energy).A total of 189 publications related to the safety 
studies of HRSs were observed in the database. Bibliographic data can be used to construct networks, such as 
co-authorship, co-occurrence, citation, bibliographic coupling, or co-citation links. To further understand the 
institutional distribution of the publications and the relationships of the safety studies among the institutions, the 
distribution of each publication was presented in a bibliographic coupling network, as shown in Figure 1. The 
circle areas in the Figure 1 represents the number of publications, the colour of the circles represents the year 
of publication, and the bibliographic coupling link represents the link between two institutions that cite the same 
document. In descending order of their number of publications, the institutions that have mainly published 
articles relating to the safety studies of HRSs include Yokohama National University (YNU), Japan; Tongji 
University, China; University of Pisa, Italy; Sandia National Laboratories, United States of America; the National 
Institute of Advanced Industrial Science and Technology (AIST), Japan; and other institutions (Figure 1). Early 
bibliometric studies around 2012 were mainly published by the University of Pisa, and studies between 2013 
and 2014 were mainly published by Tongji University. In addition, studies around 2016 were mainly conducted 
by Sandia National Laboratories and AIST. Recent studies (after 2018) on the safety of HRS were mainly 
conducted by YNU. Furthermore, China University of Petroleum, China; Air Liquide, France; and Hiroshima 
University, Japan, have conducted very recent studies on the safety of HRSs. In addition, the safety studies 
conducted by most of the institutions have similar research background owing to the relationship between these 
institutions. These results indicate that Japan has actively conducted safety studies for HRSs and achieved 
results, as the papers were published recently and the ranks of the number of published references of institutions 
in Japan were first and fifth. 

Figure 1 Bibliographic coupling network of the institutions of the publications on the safety studies of hydrogen 
refuelling station using VOSviewer 

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2.2 Japanese safety studies 

A comprehensive review of the safety studies on HRSs that have been conducted in Japan was presented to 
clarify the research domains of Japan. For this review, KH Coder (Ver. 3) was utilized to identify the keywords 
associated with the safety studies on HRSs conducted in Japan. The KH Coder is a freely available computer 
software developed for quantitative content analysis or text mining (Higuchi, 2021), and it can analyse text data 
in Catalan, Chinese (simplified), Dutch, English, French, German, Italian, Japanese, Korean, Portuguese, 
Russian, Slovenian, and Spanish. The data used in the present study were retrieved from the abstracts of 
research published from New Energy and industrial technology Development Organization (NEDO), which is 
the main funding source for research on the hydrogen policy of Japan for over 20 years. The publications were 
collected through the research topic using ‘hydrogen AND safety’ as the search topics, indicating that this term 
was identified in the Title and Abstract of the publications. 
A total of 97 publications related to HRS safety were observed in the database. Subsequently, a co-occurrence 
analysis was conducted to identify the intellectual structure of the 97 publications. To further understand the 
research domain of the safety studies for HRSs, the number of times a research term appeared in the 
publications and the relationships between these terms are presented in the network in Figure 2. The circled 
area in the image represents the number of times a term appeared in the publications, the colour of the circles 
represents the subgraph of the terms, and the network link represents the link between two terms that exhibit a 
strong relationship. As shown in Figure 2, the yellow cluster (02), which is the core of this network, was mainly 
comprised of terms, such as ‘hydrogen’, ‘development’, and ‘pressure’. Further, some communities were 
comprised of relatively high-frequency nodes of certain keywords. For example, the green cluster (01) was 
mainly comprised of terms, such as ‘material’, ‘storage’, and ‘temperature’; the red cluster (04) was mainly 
comprised of terms, such as ‘gas’ and ‘test’; the blue cluster (05) was mainly comprised of ‘catalyst’ and 
‘membrane’; and the orange cluster (06) was mainly comprised of ‘project’. In addition, the purple cluster (03) 
exhibited relatively high-frequency nodes of some key words, such as ‘safety’, ‘station’, ‘vehicle’, and ‘standard’. 
These results indicate that the safety studies for HRSs in Japan focused on studies relating to the standard of 
HRSs. 

3. An overview of risk assessments for HRSs in Japan
As previously mentioned, a considerable amount of safety studies on HRSs have been conducted in Japan. An 
overview analysis of peer-reviewed articles written by Japanese organizations was conducted. The research 
and development work of the World energy network (WE-NET) project, which is administrated by NEDO, started 
in 1993 (Hijikata, 2002). WE-NET aims to establish technologies to construct a renewable energy-based 
hydrogen energy network. This project has two objectives related to the safety measures and assessment for 
hydrogen technology: ‘Study on the safety design standards’ and ‘Establishment of safety evaluation method’. 

Figure 2 Network visualization of keywords observed in the abstract of research published from NEDO on the 
safety studies of hydrogen refuelling station using KH-Coder 

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Although the term ‘RA’ was not used in the project, it has emerged as a keyword in safety studies in recent 
years. In the rest of this paper, an overview of the safety studies on HRSs that have been conducted in Japan 
was presented based on the type of HRSs. 

3.1 Off-site HRSs 

There are two types of off-site HRSs: compressed and liquefied HRSs. Kikukawa et al. (2009) identified the 
hazards or accidental scenarios of liquefied HRSs using Hazard and Operability study (HAZOP) and Failure 
Mode and Effects Analysis (FMEA), and qualitatively evaluated the risks of the scenarios using risk matrices. 
However, no other RA studies for liquefied HRS have been reported.  
Kikukawa et al. (2008) identified the accidental scenarios of compressed HRSs using HAZOP and FMEA and 
qualitatively evaluated the risks of the scenarios using risk matrices. In addition, Kikukawa (2008) conducted 
quantitative consequence analysis and safety verification for minor hydrogen leakage. The results were utilised 
to establish current safety codes and technical standards related to Japanese HRSs. However, although the 
consequences of a part of the scenarios were quantitatively estimated and evaluated, the qualitative evaluation 
of the risks were performed using simple process configurations. To address this, after approximately 10 years, 
Suzuki et al. (2021a) conducted a quantitative risk assessment (QRA) using the most current information on 
HRS technology and updated the RA results prior to the widespread increase in the number of stations. 
Other studies related to the RA of compressed HRSs were conducted during the 10 years. For example, some 
studies attempted to improve the methodology related to the frequency analysis of hydrogen-based technology, 
such as HRSs. Kodoth et al. (2018) estimated the uncertainty and accident rate in HRSs, which is fundamental 
to the challenge of the lack of hydrogen failure data in HRSs, using a time correlation model. In addition, Kodoth 
et al. (2019) identified some appropriate failure estimators and life parameters for HRS, which are crucial for 
reducing uncertainties associated with risk and reliability quantification. Additionally, Kodoth et al. (2020) 
proposed a leak rate estimation using three approaches (non-parametric, leak-hole-size, and time-based 
evaluation methods). Further, some studies on RA and safety distance estimation have focused on hydrogen 
dispensers. For example, Hirayama et al. (2018) qualitatively evaluated the risks involved in the installation of 
hydrogen dispensers in public areas using risk matrices and concluded that the risks can be considered 
acceptable. In addition, Hirayama et al. (2019) proposed a specialized scheme that can be used to evaluate 
safety distances for hydrogen dispensers using an open access software and a widely-used calculation 
application. Suzuki et al. (2021b) estimated the quantitative risk derived from a hydrogen dispenser unit using 
multi-physics system-level modelling and in-depth simulation. Moreover, as an example of studies on safety 
measures, Sakamoto et al. (2018) evaluated the significance of safety measures in the event of simultaneous 
multiple safety measures failures, determined the combinations of safety measures failures that could lead to 
accidents, and suggested a measure for preventing and mitigating the accidental scenario by combining the 
physical model with a statistical method. 
In addition to studies on the explosion or fire risk of HRSs, there are studies related to the public acceptance of 
HRSs and comprehensive RA. For example, Ono et al. (2017) characterized the risk perception of HRSs and 
analysed the acceptance of HRS by classifying people according to attributes, such as knowledge of hydrogen 
and risk perception characteristics. In addition, Ono et al. (2017) analysed changes in the perceived acceptability 
of HRSs in response to the provision of relevant risk and safety information, and the effects of these changes 
on the general risk perception of HRSs. Hienuki et al. (2021) conducted a questionnaire survey to analyse the 
public acceptance for the implementation of hydrogen self-refuelling stations. In addition, Hienuki et al. (2020) 
established a method to identify the comprehensive risks of hydrogen energy systems, such as the social 
(economic and policy) impact of hydrogen production, individual quality of life, and the well-being of the society. 

3.2 On-site HRSs 

Organic hydride HRSs, which utilise methylcyclohexane, have attracted attention owing to their advantages, 
such as maintaining a liquid phase at ordinary temperature and pressure. Accordingly, some studies have 
attempted to identify accidental scenarios and qualitatively analyse the risks of these HRSs. For example, 
Nakayama et al. (2016) identified a large number of accidental scenarios triggered by various external factors 
using a Hazard Identification study and conducted qualitative RAs using risk matrices. Further, Suzuki et al. 
(2021c) identified accident scenarios caused by internal factors, such as deviations of the processing 
parameters from normal operation and human factors during start-up and shutdown operation procedures. In 
addition, Nakayama et al. (2019) qualitatively analysed security risks, such as terrorist attacks or managing 
disgruntled employees using the American Petroleum Institute Standard 780. Other studies have conducted 
quantitative consequence analysis and RA. For example, Tsunemi et al. (2018) conducted a quantitative 
screening-level RA. Furthermore, Tsunemi et al. (2019) identified the accidental scenarios that are required to 
conduct a detailed RA, and estimated the risk for certain scenarios, such as hydrogen leak from some 
components of the accumulator and dispenser units in an HRS. In addition, Tsunemi et al. (2017) estimated the 

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consequences and damage that could result from the explosion and heat caused by the release of 
methylcyclohexane or toluene. Further, Nakayama et al. (2017) observed a domino effect scenario caused by 
the rupturing of hydrogen cylinders heated by the radiation heat flux from a methylcyclohexane pool fire, and 
quantitatively analysed the consequences of the scenario using simulations, after which they proposed safety 
measures for the prevention and mitigation of this scenario. 
For HRSs that utilise electrolytic hydrogen generation system, there are no studies on the direct assessment of 
the risk of the HRSs; however, Kasai et al. (2016) conducted a qualitative RA for an electrolytic hydrogen 
generation system. For other type of HRSs, such as steam reforming or ammonia HRSs, there are no published 
studies on their RAs. 

3.3 Other types of HRSs 

As Japan has limited space, multiple-energy refuelling stations, which can supply a few types of energy, such 
as gasoline, CNG, and hydrogen, can ensure the efficient utilization of space. These stations may exhibit some 
kind of scenarios that are not present in off-site and on-site stations. For example, Sakamoto et al. (2016) and 
Kuroki et al. (2018) focused on a domino effect scenario that a massive gasoline pool fire forms at a gasoline 
dispenser, and the damage of a cold evaporator by thermal radiation. Although there may be similar scenarios 
to the domino effect scenarios, they are yet to be assessed. 

4. Conclusions
This study aimed to comprehensively review the safety studies conducted in Japan, particularly, the RAs, and 
to provide useful insights on the direction of future studies on the safety of HRSs. As indicated in Sections 2 and 
3, the results of the comprehensive review revealed that Japan has actively participated in the safety studies for 
HRSs and has achieved results. For example, for compressed HRSs, not only qualitative and quantitative RAs 
but also other studies related to public acceptance have been conducted, indicating that the safety studies for 
compressed HRSs are adequate for the social implementation of the widespread use of compressed HRSs. 
Additionally, RAs of organic hydride HRSs have been extensively conducted, and the accumulation of the 
knowledge is one of the strengths of Japan. In contrast, there are few studies on the RAs of liquefied HRSs and 
on-site HRSs except the organic hydride HRSs. Therefore, it is essential to conduct the RA for these HRSs and 
to mutually evaluate the results, including those of compressed and organic hydride HRSs, to contribute to the 
decision-making of the social implementation of HRSs in the future. 

Acknowledgments 

Part of this work was supported by JSPS KAKENHI Grant Number JP 18KT0012. 

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	Overview of the Risk Assessments for Hydrogen Refuelling Stations in Japan