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 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.     

Comparative risk assessment of liquefied and gaseous hydrogen refueling stations

Several countries are incentivizing the use of hydrogen (H₂) fuel cell vehicles, thereby increasing the number of H₂ refueling stations (HRSs), particularly in urban areas with high population density and heavy traffic. Therefore, it is necessary to assess the risks of gaseous H₂ refueling stations (GHRSs) and liquefied H₂ refueling stations (LHRSs). This study aimed to perform a quantitative risk assessment (QRA) of GHRSs and LHRSs. A comparative study is performed to enhance the decision-making of engineers in setting safety goals and defining design options. A systematic QRA approach is proposed to estimate the likelihood and consequences of hazardous events occurring at HRSs. Consequence analysis results indicate that catastrophic ruptures of tube trailer and liquid hydrogen storage tanks are the worst accidents, as they cause fires and explosions. An assessment of individual and societal risks indicates that LHRSs present a lower hazard risk than GHRSs. However, both station types require additional safety barrier devices for risk reduction, such as detachable couplings, hydrogen detection sensors, and automatic and manual emergency shutdown systems, which are required for risk acceptance.     

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.     

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.     

加氢站定量风险分析研究

结合定量风险分析理论和加氢站的特点,从加氢站的事故场景、事故频率、事故后果、死亡概率和个人风险与社会风险5个方面进行了研究,提出了加氢站定量风险分析模型,并结合某加氢站进行了实例计算分析,计算出该加氢站量化的个人风险和社会风险,再与国内外认可的可接受风险标准进行比较,得出其风险水平是否可接受的分析结论。其量化的风险分析结论将对加氢站建设的审批和公众安全认可具有重要指导意义。     

A comparative techno-economic and quantitative risk analysis of hydrogen delivery infrastructure options

The comparative techno-economic analysis and quantitative risk analysis (QRA) of the hydrogen delivery infrastructure covering the national hydrogen demands are presented to obtain a comprehensive understanding of the infrastructure of commercial hydrogen delivery. The cost calculation model, which was based on the hydrogen delivery scenario analysis model (HDSAM), was employed to estimate the costs of hydrogen fuel delivery in Seoul, Korea, whose area is small enough to not require intermediate delivery stations. The QRA methodology was modified to be suitable for the comparative analysis of the whole hydrogen infrastructure. The capacities of a hydrogen refueling station and the hydrogen market penetration were employed as the main variables and the two scenarios, viz. the gaseous and liquid hydrogen delivery options, were considered. The analysis results indicate that the delivery system of gaseous hydrogen was superior in terms of cost and that of liquid hydrogen was superior in terms of safety. Both delivery options were affected by the capacity of the station and the market penetration, and the cost and risk drastically changed, especially when the two variables were small. Thus, according to the results, the economic and safety issues of the hydrogen delivery infrastructure are critical to achieving a hydrogen energy society.     

Hydrogen refuelling stations in the Netherlands: An intercomparison of quantitative risk assessments used for permitting

As of 2003, 15 hydrogen refuelling stations (HRSs) have been deployed in the Netherlands. To become established, the HRS has to go through a permitting procedure. An important document of the permitting dossier is the quantitative risk assessment (QRA) as it assesses the risks of the HRS associated to people and buildings in the vicinity of the HRS. In the Netherlands, a generic prescribed approach exists on how to perform a QRA, however specific guidelines for HRSs do not exist. An intercomparison among the QRAs of permitted HRSs has revealed significant inconsistencies on various aspects of the QRA: namely the inclusion of HRS sub-systems and components, the HRS sub-system and component considerations as predefined components, the application of failure scenarios, the determination of failure frequencies, the application of input parameters, the consideration of preventive and mitigation measures as well as information provided regarding the HRS surroundings and the societal risk. It is therefore recommended to develop specific QRA guidelines for HRSs.     

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.     

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.     

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.     

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.     

Data requirements for improving the Quantitative Risk Assessment of liquid hydrogen storage systems

Quantitative Risk Assessment (QRA) supports the development of risk-informed safety codes and standards which are employed to enable the safe deployment of hydrogen technologies essential to decarbonize the transportation sector. System reliability data is a necessary input for rigorous QRA. The lack of reliability data for bulk liquid hydrogen (LH₂) storage systems located on site at fueling stations limits the use of QRAs. In turn, this hinders the ability to develop the necessary safety codes and standards that enable worldwide deployment of these stations. Through a QRA-based analysis of a LH₂ storage system, this work focuses on identifying relevant scenario and probability data currently available and ascertaining future data collection requirements regarding risks specific to liquid hydrogen releases. The work developed consists of the analysis of a general bulk LH₂ storage system design located at a hydrogen fueling station. Failure Mode and Effect Analysis (FMEA) and traditional QRA modeling tools such as Event Sequence Diagrams (ESD) and Fault Tree Analysis (FTA) are employed to identify, rank, and model risk scenarios related to the release of LH₂. Based on this analysis, scenario and reliability data needs to add LH₂-related components to QRA are identified with the purpose of improving the future safety and risk assessment of these systems.     

Quantitative risk assessment of a mobile hydrogen refueling station in Korea

Hydrogen infrastructure is expanding. Mobile hydrogen refueling stations are advantageous because they can be moved between locations to provide refueling. However, there are serious concerns over the risk of various accident scenarios as the refueling stations are transported. In this study, we conduct a quantitative risk assessment of a mobile hydrogen refueling station. Risks that may occur at two refueling locations and the transport path between them are analyzed. Our evaluation reveals that risks are mostly in an acceptable zone and to a lesser degree in a conditionally acceptable zone. The greatest single risk factor is an accident resulting from the rupture of the tube trailer at the refueling site. At sites with no tube trailer and during the transport, the risk is greatest from large leaks from the dispenser or compressed gas facility. The mobile hydrogen refueling station can be safely built within acceptable risk levels.     

Improving hydrogen refueling stations to achieve minimum refueling costs for small bus fleets

Fuel cell vehicles using green hydrogen as fuel can contribute to the mitigation of climate change. The increasing utilization of those vehicles creates the need for cost efficient hydrogen refueling stations. This study investigates how to build the most cost efficient refueling stations to fuel small fleet sizes of 2, 4, 8, 16 and 32 fuel cell busses. A detailed physical model of a hydrogen refueling station was built to determine the necessary hydrogen storage size as well as energy demand for compression and precooling of hydrogen. These results are used to determine the refueling costs for different station configurations that vary the number of storage banks, their volume and compressor capacity.It was found that increasing the number of storage banks will decrease the necessary total station storage volume as well as energy demand for compression and precooling. However, the benefit of adding storage banks decreases with each additional bank. Hence the cost for piping and instrumentation to add banks starts to outweigh the benefits when too many banks are used. Investigating the influence of the compressor mass flow found that when fueling fleets of 2 or 4 busses the lowest cost can be reached by using a compressor with the minimal mass flow necessary to refill all storage banks within 24 h. For fleets of 8, 16 and 32 busses, using the compressor with the maximum investigated mass flow of 54 kg/h leads to the lowest costs.     

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.     

Risk assessment by means of Bayesian networks: A comparative study of compressed and liquefied H2 transportation and tank station risks

Rational decision making in land use planning and licensing of H₂ infrastructure surrounded by other industrial activities and by population should take account of individual and societal risks. QRA software packages produce a risk matrix of potential consequences versus event probabilities without indicating uncertainty, and results are therefore shrouded in ambiguity. Due to the ‘black-box’ effect of a package, the calculations also lack transparency. Bayesian Belief Network (BBN) software modeling cause-consequence chains allow easy inspection of intermediate results and sensitivity tracking, and it can take account of data distributions instead of point values. For support of decision making, risk analysts should in addition determine the utilities of decision alternatives. Utilities describe desirability of benefits on a single scale. Rationally weighing risks versus benefits results in more transparent and defendable decisions. Example risk analyses of two types of refueling stations and three hydrogen supply transportation types applying BBNs are worked out.     

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.     

A non-destructive fault diagnosis method for a diaphragm compressor in the hydrogen refueling station

Costly and time-consuming maintenance of the hydrogen compressors due to their frequent breakdown severely hinders the deployment and promotion of hydrogen refueling station (HRS), and effective condition monitoring and fault diagnosis is the key to reduce the unscheduled downtime of the compressor. This paper proposes a non-destructive method for fault diagnosis of diaphragm compressors for HRSs based on the acoustic emission (AE) signal. The AE signals in the time domain are segmented into angle-domain signals correspond to a working cycle. The feature events of the moving components are determined through the measured AE signal in both angle-domain and angle-frequency domain based on short-term Fourier transform (STFT). Those feature events signals are innovatively applied to identify the typical abnormal conditions of excessively high oil pressure, slightly inadequate oil pressure and seriously inadequate oil pressure, replacing the traditional and destructive pressure measuring method. The results show that this method can be used to effectively diagnose abnormal working conditions and indicate that this method can be utilized as a powerful tool in the non-destructive condition monitoring and fault diagnosis of the diaphragm compressors.