Quantitative risk assessment using a Japanese hydrogen refueling station model

Although hydrogen refueling stations (HRSs) are becoming widespread across Japan and are essential for the operation of fuel cell vehicles, they present potential hazards. A large number of accidents such as explosions or fires have been reported, rendering it necessary to conduct a number of qualitative and quantitative risk assessments for HRSs. Current safety codes and technical standards related to Japanese HRSs have been established based on the results of a qualitative risk assessment and quantitative effectiveness validation of safety measures over ten years ago. In the last decade, there has been much development in the technologies of the components or facilities used in domestic HRSs and much operational experience as well as knowledge to use hydrogen in HRSs safely have been gained through years of commercial operation. The purpose of the present study is to conduct a quantitative risk assessment (QRA) of the latest HRS model representing Japanese HRSs with the most current information and to identify the most significant scenarios that pose the greatest risks to the physical surroundings in the HRS model. The results of the QRA show that the risk contours of 10^?3 and 10^?4 per year were confined within the HRS boundaries, whereas the risk contours of 10^?5 and 10^?6 per year are still present outside the HRS. Comparing the breakdown of the individual risks (IRs) at the risk ranking points, we conclude that the risk of jet fire demonstrates the highest contribution to the risks at all of the risk ranking points and outside the station. To reduce these risks and confine the risk contour of 10^?6 per year within the HRS boundaries, it is necessary to consider risk mitigation measures for jet fires.     

Quantitative risk assessment of an urban hydrogen refueling station

Hydrogen is one of important energy source in the next generation of renewable energy. It has powerful strength such as no emission from CO2 for fuel, Nevertheless, many countries have difficulties to expand hydrogen infra due to high risky from hydrogen. Especially, the hydrogen refueling station which is located in urban area has congested structure and high population around, it has higher risk than conventional refueling station. This paper presents a quantitative risk assessment (QRA) of a high pressure hydrogen refueling station in an urban area with a large population and high congestion between the instruments and equipment. The results show that leaks from the tube-trailer and dispenser as well as potential explosion of the tube-trailer are the main risks. For the safety of the station operator, customers and people surrounding the refueling station, additional mitigation plans such as adding additional safety barrier system have to be implemented on the compressor and dispenser in order to prevent continuous release of hydrogen from an accident.     

Trade-off study between risk and benefit in safety devices for hydrogen refueling stations using a dynamic physical model

As hydrogen refueling stations become increasingly common, it is clear that a high level of economic efficiency and safety is crucial to promoting their use. One way to reduce costs is to use a simple orifice instead of an excess flow valve, which Japanese safety regulations have identified as a safety device. However, there is concern about its effect on refueling time and on risk due to hydrogen leakage. To clarify the effect, we did a study of model-based refueling time evaluation and quantitative risk assessment for a typical refueling station. This study showed that an orifice is an effective alternative safety device. The increase in refueling time was less than 10%, based on simulations using a dynamic physical model of the station. Neither was there a significant difference in the risk between a configuration with excess flow valves and one with an orifice.     

Quantitative risk assessment on 2010 Expo hydrogen station

This paper presents a QRA study on a gaseous hydrogen refueling station of 2010 World Expo. Risks to station personnel, to refueling customers and to third parties are evaluated respectively. Uncertainties that intervene in the risk analysis are also discussed. The results show that the leaks from compressors and dispensers are the main risk contributors to first party and second party risks of the Expo station, indicating that risk mitigation measures should in the first place be implemented on compressors and dispensers. For the sake of the safety of station personnel, customers, and people outside the Expo station, additional safety barrier systems must be implemented on compressors and dispensers to prevent continuous release of hydrogen from happening. With appropriate mitigation measures on compressors and dispensers, risks to all three parties of the Expo station can be reduced to the value lower than the risk acceptance criteria.     

Quantitative risk assessment of a hydrogen refueling station by using a dynamic physical model based on multi-physics system-level modeling

Numerous accidents in HRSs have been reported worldwide in accident databases; therefore, many researchers have performed quantitative risk assessments (QRAs) of HRSs to enable risk-informed decision making in determining the safety distances or risk mitigation measures. The HRSs, located in urban areas such as Tokyo in Japan, are situated in congested areas with tall buildings and high population density; thus, they have relatively narrow station areas. However, the QRAs are generally suitable for large plants such as nuclear power plants or chemical plants; therefore, relatively small plants or installations, such as HRSs, have not yet been considered as QRA objects. Hence, it is necessary to conduct detailed QRAs with risk analyses and reduce the applied uncertainties for relatively small plants or installations. We applied a model-based approach of risk assessment to model the HRS process using multi-physics system-level modeling and simulated a target system using Modelica—an equation-based, object-oriented modeling language that allows acausal modeling of complex cyber-physical systems The primary aim of this study was to conduct a QRA of an HRS based on multi-physics system-level modeling. First, we modeled the HRS components and physical relationships between the components using basic physical equations. Then, we elucidate a QRA based on the constructed model. The difference in the leakage rates due to the leak positions and dynamic behavior of the model parameters were calculated using the constructed model. Finally, we estimated the individual risks of all the scenarios and compared the resulting risk contours based on the constructed model that includes the hydrogen-fuel dynamic behavior with those based on the traditional model. These results indicate that it is possible to assess whether the risks around the station boundary are acceptable based on the scenario information obtained by evaluating the risks near the station.     

Quantitative risk assessment on a gaseous hydrogen refueling station in Shanghai

The potential risk exposure of people for hydrogen refueling stations is often a critical factor to gain authority approval and public acceptance. Quantitative risk assessment (QRA) is often used to quantify the risk around hydrogen facilities and support the communication with authorities during the permitting process. This paper shows a case study on a gaseous hydrogen refueling station using QRA methodology. Risks to station personnel, to refueling customers and to third parties are evaluated respectively. Both individual risk measure and societal risk measure are used in risk assessment. Results show that the compressor leak is the main contributor to risks of all three parties. Elevating compressors can be considered as an effective mitigation measure to reduce occupational risks while setting enclosure around compressors cannot. Both measures are effective to reduce risks to customers. As for third parties, societal risks can be reduced to ALARP region by either elevating compressors or setting enclosure around compressors. External safety distance of compressors cannot be considerably reduced by elevation of compressors, but can significantly be reduced by setting compressor enclosure. However, safety distances of the station are not very sensitive to both mitigation measures.     

Quantitative risk assessment of the interior of a hydrogen refueling station considering safety barrier systems

A quantitative risk assessment of human life during the operation of a hydrogen refueling station (HRS) is conducted. We calculate the risks for three accident scenarios: a hydrogen leak from the external piping surrounding a dispenser, a hydrogen leak from an accumulator connection piping and a hydrogen leak from a compressor/connection piping in the HRS. We first calculate the probability of accident by multiplying the estimated leak frequency with the incident occurrence probability considering the ignition probability and failure probability of the safety barrier systems obtained through event tree analysis for each scenario. We next simulate the blast and flame effects of the ignition of concentration fields formed by hydrogen leakage. We then use existing probit functions to estimate the consequences of eardrum rupture, fatalities due to displacement by the blast wave, fatalities due to head injuries, first-degree burns, second-degree burns, and fatal burn injuries by accident scenario, leak size, and incident event, and we estimate the risk distribution in 1-m cells. We finally assess the risk reduction effects of barrier placement and the distance to the dispenser and quantify the risk level that HRSs can achieve under existing law. Quantitative risk assessment reveals that the risk for a leak near the dispenser is less than 10⁻⁶ per year outside a distance of 6 m to the dispenser. The risk for a leak near the accumulators and compressors exceeds 10⁻⁴ per year within a distance of 10 m from the ignition point. A separation of 6 m to the dispenser and a barrier height of 3 m keep the fatal risk from burns to the workers, consumers and residents and passersby below the acceptable level of risk. Our results therefore show that current laws sufficiently mitigate the risks posed by HRSs and open up the possibility for a regulatory review.     

Improved safety by crossanalyzing quantitative risk assessment of hydrogen refueling stations

With the goal of building 310 hydrogen refueling stations (HRSs) in Korea by 2022, restrictions, such as location restrictions and separation distances, are being eased, so developing ways to improve technology and safety. As HRSs contain major facilities such as compressors, storage tanks, dispenser, and priority control panels, and a leakage could result in a large fire or explosion caused by an ignition source. To perform quantitative risk assessment, programs, namely, Hy-KoRAM and Phast/Safeti were used in this study. It could determine the damage range and effect on radiant heat and flame length, as well as personal and societal risks, using these programs. The crossanalysis of the two programs also improves the facility's safety and the reliability of the results.     

Energetic evaluation of hydrogen refueling stations with liquid or gaseous stored hydrogen

The future success of fuel cell electric vehicles requires a corresponding infrastructure. In this study, two different refueling station concepts for fuel cell passenger cars with 70 MPa technology were evaluated energetically. In the first option, the input of the refueling station is gaseous hydrogen which is compressed to final pressure, remaining in gaseous state. In the second option, the input is liquid hydrogen which is cryo-compressed directly from the liquid phase to the target pressure. In the first case, the target temperature of −33 °C to −40 °C [1] is achieved by cooling down. In the second option, gaseous deep-cold hydrogen coming from the pump is heated up to target temperature. A dynamic simulation model considering real gas behavior to evaluate both types of fueling stations from an energetic perspective was created. The dynamic model allows the simulation of boil-off losses (liquid stations) and standby energy losses caused by the precooling system (gaseous station) dependent on fueling profiles. The functionality of the model was demonstrated with a sequence of three refueling processes within a short time period (high station utilization). The liquid station consumed 0.37 kWh/kg compared to 2.43 kWh/kg of the gaseous station. Rough estimations indicated that the energy consumption of the entire pathway is higher for liquid hydrogen. The analysis showed the high influence of the high-pressure storage system design on the energy consumption of the station. For future research work the refueling station model can be applied to analyze the energy consumption dependent on factors like utilization, component sizing and ambient temperature.     

Harm effect distances evaluation of severe accidents for gaseous hydrogen refueling station

With the development of large-scale fell cell vehicle demonstration project worldwide, the global number of hydrogen refueling stations has increased rapidly in recent years. The external safety of hydrogen refueling stations has always been a public concern for its further development. This paper examines the harm effect distances of severe accidents for a gaseous hydrogen refueling station. First, different accident scenarios are assumed and their subsequent consequences are calculated, including physical explosion, jet fire, flash fire and confined vapor cloud explosion. Results show that physical explosion and worst case of confined vapor cloud explosion produce the longest harm effect distances for instantaneous release and continuous release, respectively. This indicates that they may be used as decisive consequences to the determination of safe distances. Second, the influences of different factors on harm effect distances are investigated, including those of release inventory, release pressure, release height, release angle, release diameter and wind velocity. Then, based on these results, several potential hazard mitigation measures are proposed such as elevating hydrogen equipment, using smaller vessel and adopting smaller pipe work, if reasonably practicable.     

A quantitative risk assessment of hydrogen fuel cell forklifts

With the increasing deployment of hydrogen fuel cell forklifts, it is essential to understand the risks of incidents involving these systems. A quantitative risk assessment (QRA) study was conducted to determine the potential hydrogen release scenarios, probabilities, and consequences in fuel cell forklift operations. QRA modeling tools, such as fault tree analysis (FTA) and event sequence diagrams (ESD), were used together with hydrogen systems data. This work provides insights into the fatality risk from a hydrogen fuel cell forklift and the reliability of its design and components. The analysis shows that the expected fatal accident rate of a hydrogen forklift is considerably higher than current fatal injury rates observed by the Bureau of Labor Statistics for industrial truck operators and material handling occupations. Nevertheless, the average individual risk posed to forklift drivers was found to be likely tolerable based on current risks accepted by industrial truck operators. Jet fires are found to dominate the system's risk, however, the risk of explosions is also considerable. An importance measures analysis shows that these risks could be mitigated by improving the design and reliability of pressure relief devices, as well as other components prone to leak such as filters and check valves. We also identify sources of uncertainty and conservatisms in the QRA process that can guide future research in hydrogen systems. These results provide powerful insight into improvements in the design of fuel cell forklifts to reduce risk and enable the safe deployment of this key technology for a decarbonized future.     

An advanced framework for leakage risk assessment of hydrogen refueling stations using interval-valued spherical fuzzy sets (IV-SFS)

The extensive population growth calls for substantial studies on sustainable development in urban areas. Thus, it is vital for cities to be resilient to new situations and adequately manage the changes. Investing in renewable and green energy, including high-tech hydrogen infrastructure, is crucial for sustainable economic progress and for preserving environmental quality. However, implementing new technology needs an effective and efficient risk assessment investigation to minimize the risk to an acceptable level or ALARP (As low as reasonably practicable). The present study proposes an advanced decision-making framework to manage the risk of hydrogen refueling station leakage by adopting the Bow-tie analysis and Interval-Value Spherical Fuzzy Sets to properly deal with the subjectivity of the risk assessment process. The outcomes of the case study illustrate the causality of hydrogen refueling stations' undesired events and enhance the decision-maker's thoughts about risk management under uncertainty. According to the findings, jet fire is a more likely accident in the case of liquid hydrogen leakage. Furthermore, equipment failure has been recognized as the most likely cause of hydrogen leakage. Thus, in order to maintain the reliability of liquid hydrogen refueling stations, it is crucial that decision-makers develop a trustworthy safety management system that integrates a variety of risk mitigation measures including asset management strategies.     

Risk analysis on mobile hydrogen refueling stations in Shanghai

To better understand the hazards and risks associated with the mobile hydrogen refueling stations, a risk analysis was preformed to improve the safety of the operation. The risks to the station personnel and to the public were discussed separately. Results show that the stationary risks of the mobile stations to the personnel and refueling customers are lower than the risk acceptance criteria over an order of magnitude, so the occupational risks and the risks to customers are completely acceptable. The third party risks can be acceptable as long as the appropriate mitigation measures, especially well designed parking area and operation time, are implemented. Leak from booster compressors is the main risk contributor to the stationary risks due to the highest failure rates according to the generic data and the worst harm effects based on the consequence evaluations. However, the failure of the tube storages will result in the largest financial loss, though the likelihood of this scenario is much less than that of failure from booster compressors. As for the road risks of the mobile stations, they can be acceptable as long as the appropriate mitigation measures, especially well-planned itinerary and transport time, are implemented.     

Current standards and configurations for the permitting and operation of hydrogen refueling stations

The literature lacks a systematic analysis of HRS equipment and operating standards. Researchers, policymakers, and HRS operators could find this information relevant for planning the network's future expansion. This study is intended to address this information need by providing a comprehensive strategic overview of the regulations currently in place for the construction and maintenance of hydrogen fueling stations.A quick introduction to fundamental hydrogen precautions and hydrogen design is offered. The paper, therefore, provides a quick overview of hydrogen's safety to emphasize HRS standards, rules, and regulations. Both gaseous and liquid safety issues are detailed, including possible threats and installation and operating expertise.After the safety evaluation, layouts, equipment, and operating strategies for HRSs are presented, followed by a review of in-force regulations: internationally, by presenting ISO, IEC, and SAE standards, and Europeanly, by reviewing the CEN/CENELEC standards. A brief and concise analysis of Italy's HRS regulations is conducted, with the goal of identifying potential insights for strategic development and more convenient technology deployment.     

Risk-informed separation distances for hydrogen refueling stations

As part of the US Department of Energy Hydrogen, Fuel Cells & Infrastructure Technologies Program, Sandia National Laboratories is developing the technical basis for assessing the safety of hydrogen-based systems for use in the development/modification of relevant codes and standards. This work includes quantitative risk assessments (QRA) of hydrogen facilities. The QRAs are used to identify and quantify scenarios for the unintended release of hydrogen and thus help identify the code requirements that would reduce the risk at hydrogen facilities to acceptable levels.     

Optimal siting and sizing of hydrogen refueling stations considering distributed hydrogen production and cost reduction for regional consumers

Hydrogen fuel cell vehicles are currently facing two difficulties in achieving their general use: the lack of hydrogen refueling stations and high hydrogen prices. Hydrogen refueling stations are the middle stage for delivering hydrogen from its sources to consumers, and their location could be affected by the distributed locations of hydrogen sources and consumers. The reasonable siting and sizing of hydrogen refueling stations could both improve the hydrogen infrastructure and reduce regional consumers' cost of using hydrogen. By considering the hydrogen life cycle cost and using a commercial volume forecasting model, this paper creates a relatively thorough and comprehensive model for hydrogen station siting and sizing with the objective of achieving the optimal costs for consumers using hydrogen. The cost‐based model includes the selection of the hydrogen sources, transportation methods, and storage methods, and thus, the hydrogen supply chain can also be optimized. A numerical example is established in Section 4 with the solution algorithm and results.     

Dynamic planning and energy management strategy of integrated charging and hydrogen refueling at highway energy supply stations considering on-site green hydrogen production

The layout of electric vehicles charging stations and hydrogen refueling stations (HRSs) is more and more necessary with the development of electric vehicles (EVs) and progress in hydrogen energy storage technology. Due to the high costs of HRSs and the low demand for hydrogen, it is difficult for independent HRSs to make a profit. This study focuses on the dynamic planning of energy supply stations on highways in the medium and long term, considering the growth of EV charging demand and the change in the proportion of hydrogen fuel cell vehicles (HFCVs). Based on the perspective of renewable energy generators (REGs), this study seeks the dynamic optimal configuration and comprehensive benefits of adding HRS and battery to existing EVCS considering the travel rules of new energy vehicles (NEVs). The results show that (1) It is profitable for REGs to invest in HRSs; (2) The economy of investment in batteries by REGs depends on the source-load matching. It is feasible only when the output of renewable energy is difficult to meet the demand. (3) The business model of REGs producing hydrogen on-site and supplying both electricity and hydrogen is feasible.