Critical review and analysis of hydrogen safety data collection tools

The wider adoption of hydrogen in multiple sectors of the economy requires that safety and risk issues be rigorously investigated. Quantitative Risk Assessment (QRA) is an important tool for enabling safe deployment of hydrogen fueling stations and is increasingly embedded in the permitting process. QRA requires reliability data, and currently hydrogen QRA is limited by the lack of hydrogen specific reliability data, thereby hindering the development of necessary safety codes and standards [1]. Four tools have been identified that collect hydrogen system safety data: H2Tools Lessons Learned, Hydrogen Incidents and Accidents Database (HIAD), National Renewable Energy Lab's (NREL) Composite Data Products (CDPs), and the Center for Hydrogen Safety (CHS) Equipment and Component Failure Rate Data Submission Form. This work critically reviews and analyzes these tools for their quality and usability in QRA. It is determined that these tools lay a good foundation, however, the data collected by these tools needs improvement for use in QRA. Areas in which these tools can be improved are highlighted, and can be used to develop a path towards adequate reliability data collection for hydrogen systems.     

Opportunities and data requirements for data-driven prognostics and health management in liquid hydrogen storage systems

During the past decade, Prognostics and Health Management (PHM) has become an important set of tools in various areas of industry and academic reliability engineering. PHM consists of a variety of mathematical and computational methods used to support data-driven decision-making to increase the safety, availability, and reliability of complex engineering systems. In particular, PHM can provide crucial insight into reliability and safety design improvements for developing technologies where historical performance and failure data are limited. This is the case of hydrogen fueling and storage technologies. This work presents a high-level approach for designing data-driven PHM applications for bulk liquid hydrogen (LH₂) storage systems for hydrogen fueling stations. This paper addresses core aspects of the design, development, and implementation of data-driven PHM applications that can improve the reliability assessment of hydrogen components. The analysis focuses on the relationship between data availability and diagnostic/prognostic capabilities; potential challenges; and integration schemes for current risk mitigation measures. We identify potential condition-monitoring data sources for key components in an LH₂ storage system, including storage tanks, piping, and pumps. We determine that the short-term goals for the implementation of data-driven models in PHM frameworks in hydrogen systems should focus on developing adequate data collection and analysis strategies, as well as exploring the effect on reliability, safety, and regulations for hydrogen systems.     

Development of Korean hydrogen fueling station codes through risk analysis

When hydrogen fueling stations were constructed first time in Korea in 2006, there were no standards for hydrogen fueling stations. Hence the CNG (Compressed Natural Gas) station codes were temporarily adopted. In last three years, from 2006 to 2009, the studies for the development of hydrogen fueling station standards were carried out, with the support of the Korean government. In this study, three research groups cooperated to develop optimized hydrogen fueling station codes through risk analysis of hydrogen production and filling systems. Its results were integrated to develop the codes. In the first step to develop the codes, the standards for CNG stations and hydrogen fueling station were compared with each other and analyzed. By referring to foreign hydrogen fueling station standards, we investigated the potential problems in developing hydrogen fueling station codes based on the CNG station standards. In the second, the results of the high-pressure hydrogen leakage experiment were analyzed, and a numerical analysis was performed to establish the safety distance from the main facilities of a hydrogen fueling station to the protection facilities. In the third, HAZOP (Hazard and Operability) and FTA (Fault Tree Analysis) safety assessments were carried out for the on-site and off-site hydrogen fueling stations—currently being operated in Korea— to analyze the risks in existing hydrogen fueling stations. Based on the study results of the above three groups, we developed one codes for off-site type hydrogen fueling stations and another codes for on-site type hydrogen fueling stations. These were applied from September 2010.     

Liquid pump-enabled hydrogen refueling system for medium and heavy duty fuel cell vehicles: Station design and technoeconomic assessment

Recent progress in submerged liquid hydrogen (LH₂) cryopump technology development offers improved hydrogen fueling performance at a reduced cost in medium- and heavy-duty (MDV and HDV) fuel cell vehicle refueling applications at 35 MPa pressure, compared to fueling via gas compression. In this paper, we evaluate the fueling cost associated with cryopump-based refueling stations for different MDV and HDV hydrogen demand profiles. We adapt the Heavy Duty Refueling Station Analysis Model (HDRSAM) tool to analyze the submerged cryopump case, and compare the estimated fuel dispensing costs of stations supplied with LH₂ for fueling Class 4 delivery van (MDV), public transit bus (HDV), and Class 8 truck (HDV) fleets using cryopumps relative to station designs. A sensitivity analysis around upstream costs illustrates the trade-offs associated with H₂ production from onsite electrolysis versus central LH₂ production and delivery. Our results indicate that LH₂ cryopump-based stations become more economically attractive as the total station capacity (kg dispensed per day) and hourly demand (vehicles per hour) increase. Depending on the use case, savings relative to next best options range from about 5% up to 44% in dispensed costs, with more favorable economics at larger stations with high utilization.     

Empirical profiling of cold hydrogen plumes formed from venting of LH2 storage vessels

Liquid hydrogen (LH₂) storage is viewed as a viable approach to assure sufficient hydrogen capacity at commercial fuelling stations. Presently, LH₂ is produced at remote facilities and then transported to the end-use site by road vehicles (i.e., LH₂ tanker trucks). Venting of hydrogen to depressurize the transport storage tank is a routine part of the LH₂ delivery and site transfer process. The behavior of cold hydrogen plumes has not been well characterized because of the sparsity of empirical field data, which can lead to overly conservative safety requirements. Committee members of the National Fire Protection Association (NFPA) Standard 2 [1] formed the Hydrogen Storage Safety Task Group, which consists of hydrogen producers, safety experts, and computational fluid dynamics modellers, has identified the lack of understanding of hydrogen dispersion during LH₂ venting of storage vessels as a critical gap for establishing safety distances at LH₂ facilities, especially commercial hydrogen fuelling stations. To address this need, the National Renewable Energy Laboratory Sensor Laboratory, in collaboration with the NFPA Hydrogen Storage Task Group, developed a prototype Cold Hydrogen Plume Analyzer to empirically characterize the hydrogen plume formed during LH₂ storage tank venting. The prototype analyzer was field deployed during an actual LH₂ venting process. Critical findings included:

• •Hydrogen above the lower flammable limit (LFL) was detected as much as 2 m lower than the release point, which is not predicted by existing models.
• •Personal monitors detected hydrogen at ground level, although at levels below the LFL.
• •A small but inconsistent correlation was found between oxygen depletion and the hydrogen concentration.
• •A negligible to non-existent correlation was found between in-situ temperature measurements and the hydrogen concentration.

The prototype analyzer is being upgraded for enhanced metrological capabilities, including improved real-time spatial and temporal profiling of hydrogen plumes and tracking of prevailing weather conditions. Additional deployments are planned to monitor plume behavior under different wind, humidity, and temperature conditions. The data will be shared with the Hydrogen Storage Task Group and ultimately will be used support theoretical models and code requirements prescribed in NFPA 2.     

Liquid hydrogen storage system for heavy duty trucks: Configuration,performance, cost,and safety

We investigate the potential of liquid hydrogen storage (LH₂) on-board Class-8 heavy duty trucks to resolve many of the range, weight, volume, refueling time and cost issues associated with 350 or 700-bar compressed H₂ storage in Type-3 or Type-4 composite tanks. We present and discuss conceptual storage system configurations capable of supplying H₂ to fuel cells at 5-bar with or without on-board LH₂ pumps. Structural aspects of storing LH₂ in double walled, vacuum insulated, and low-pressure Type-1 tanks are investigated. Structural materials and insulation methods are discussed for service at cryogenic temperatures and mitigation of heat leak to prevent LH₂ boil-off. Failure modes of the liner and shell are identified and analyzed using the regulatory codes and detailed finite element (FE) methods. The conceptual systems are subjected to a failure modes and effects analysis (FMEA) and a safety, codes, and standards (SCS) review to rank failures and identify safety gaps. The results indicate that the conceptual systems can reach 19.6% useable gravimetric capacity, 40.9 g-H₂/L useable volumetric capacity and $174–183/kg-H₂ cost (2016 USD) when manufactured 100,000 systems annually.     

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.     

High-density automotive hydrogen storage with cryogenic capable pressure vessels

LLNL is developing cryogenic capable pressure vessels with thermal endurance 5–10 times greater than conventional liquid hydrogen (LH₂) tanks that can eliminate evaporative losses in routine usage of (L)H₂ automobiles. In a joint effort BMW is working on a proof of concept for a first automotive cryo-compressed hydrogen storage system that can fulfill automotive requirements on system performance, life cycle, safety and cost. Cryogenic pressure vessels can be fueled with ambient temperature compressed gaseous hydrogen (CGH₂), LH₂ or cryogenic hydrogen at elevated supercritical pressure (cryo-compressed hydrogen, CcH₂). When filled with LH₂ or CcH₂, these vessels contain 2–3 times more fuel than conventional ambient temperature compressed H₂ vessels. LLNL has demonstrated fueling with LH₂ onboard two vehicles. The generation 2 vessel, installed onboard an H₂-powered Toyota Prius and fueled with LH₂ demonstrated the longest unrefueled driving distance and the longest cryogenic H₂ hold time without evaporative losses. A third generation vessel will be installed, reducing weight and volume by minimizing insulation thickness while still providing acceptable thermal endurance. Based on its long experience with cryogenic hydrogen storage, BMW has developed its cryo-compressed hydrogen storage concept, which is now undergoing a thorough system and component validation to prove compliance with automotive requirements before it can be demonstrated in a BMW test vehicle.     

Simulation of hydrogen leak and explosion for the safety design of hydrogen fueling station in Korea

Hydrogen has been used as chemicals and fuels in industries for last decades. Recently, it has become attractive as one of promising green energy candidates in the era of facing with two critical energy issues such as accelerating deterioration of global environment (e.g. carbon dioxide emissions) as well as concerns on the depletion of limited fossil sources. A number of hydrogen fueling stations are under construction to fuel hydrogen-driven vehicles. It would be indispensable to ensure the safety of hydrogen station equipment and operating procedure in order to prevent any leak and explosions of hydrogen: safe design of facilities at hydrogen fueling stations e.g. pressurized hydrogen leak from storage tanks. Several researches have centered on the behaviors of hydrogen ejecting out of a set of holes of pressurized storage tanks or pipes. This work focuses on the 3D simulation of hydrogen leak scenario cases at a hydrogen fueling station, given conditions of a set of pressures, 100, 200, 300, 400 bar and a set of hydrogen ejecting hole sizes, 0.5, 0.7, 1.0 mm, using a commercial computational fluid dynamics (CFD) tool, FLACS. The simulation is based on real 3D geometrical configuration of a hydrogen fueling station that is being commercially operated in Korea. The simulation results are validated with hydrogen jet experimental data to examine the diffusion behavior of leak hydrogen jet stream. Finally, a set of marginal safe configurations of fueling facility system are presented, together with an analysis of distribution characteristics of blast pressure, directionality of explosion. This work can contribute to marginal hydrogen safety design for hydrogen fueling stations and a foundation on establishing a safety distance standard required to protect from hydrogen explosion in Korea being in the absence of such an official requirement.     

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.     

Operation scenario-based design methodology for large-scale storage systems of liquid hydrogen import terminal

This paper presents an operation scenario-based design methodology to determine the design pressure of the storage system of liquid hydrogen (LH₂) import terminals. The methodology includes operation scenario establishment, thermodynamic analysis, and structural analysis. In a case study conducted, the terminal has a storage capacity of 75,000 m³, imports cargo from a 50,000 m³ LH₂ tanker, and supplies hydrogen in vapor and liquid forms without any loss of boil-off hydrogen (BOH) as a reference case. In the deviation from the reference case, 4.7% of the entire imported LH₂ needs proper treatment as BOH under the application of a non-pressurized storage system. In addition, the vapor pressure of the imported LH₂ is the most influential in determining the design pressure. From the obtained design pressure, the structural analysis is performed in compliance with the Boiler & Pressure Vessel Code of American Society of Mechanical Engineers.     

Flexible sector coupling with hydrogen: A climate-friendly fuel supply for road transport

The substantial expansion of renewable energy sources is creating the foundation to successfully transform the German energy sector (the so-called ‘Energiewende’). A by-product of this development is the corresponding capacity demand for the transportation, distribution and storage of energy. Hydrogen produced by electrolysis offers a promising solution to these challenges, although the willingness to invest in hydrogen technologies requires the identification of competitive and climate-friendly pathways in the long run. Therefore, this paper employs a pathway analysis to investigate the use of renewable hydrogen in the German passenger car transportation sector in terms of varying market penetration scenarios for fuel cell-electric vehicles (FCEVs). The investigation focuses on how an H₂ infrastructure can be designed on a national scale with various supply chain networks to establish robust pathways and important technologies, which has not yet been done. Therefore, the study includes all related aspects, from hydrogen production to fueling stations, for a given FCEV market penetration scenario, as well as the CO₂ reduction potential that can be achieved for the transport sector. A total of four scenarios are considered, estimating an FCEV market share of 1–75% by the year 2050. This corresponds to an annual production of 0.02–2.88 million tons of hydrogen. The findings show that the most cost-efficient H₂ supply (well-to-tank: 6.7–7.5 €/kg_H2) can be achieved in high demand scenarios (FCEV market shares of 30% and 75%) through a combination of cavern storage and pipeline transport. For low-demand scenarios, however, technology pathways involving LH₂ and LOHC truck transport represent the most cost-efficient options (well-to-tank: 8.2–11.4 €/kg_H2).     

Thermodynamic parametric analysis of refueling heavy-duty hydrogen fuel-cell electric vehicles

Reliable design and safe operation of heavy-duty hydrogen refueling stations are essential for the successful deployment of heavy-duty fuel cell electric vehicles (FCEVs). Fueling heavy-duty FCEVs is different from light-duty vehicles in terms of the dispensed hydrogen quantities and fueling rates, requiring tailored fueling station design for each vehicle class. In particular, the selection and design of the onboard hydrogen storage tank system and the fueling performance requirements influence the safe design of hydrogen fueling stations. A thermodynamic modeling and analysis are performed to evaluate the impact of various fueling parameters and boundary conditions on the fueling performance of heavy-duty FCEVs. We studied the effect of dispenser pressure ramp rate and precooling temperature, initial tank temperature and pressure, ambient temperature, and onboard storage design parameters, such as onboard storage pipe diameter and length, on the fueling rate and final vehicle state-of-charge, while observing prescribed tank pressure and temperature safety limits. An important finding was the sensitivity of the temporal fueling rate profile and the final tank state of charge to the design factors impacting pressure drop between the dispenser and vehicle tank, including onboard storage pipe diameter selection, and flow coefficients of nozzle, valves, and fittings. The fueling rate profile impacts the design and cost of the hydrogen precooling unit upstream of the dispenser.     

Systematic planning to optimize investments in hydrogen infrastructure deployment

The introduction of hydrogen infrastructure and fuel cell vehicles (FCVs) to gradually replace gasoline internal combustion engine vehicles can provide environment and energy security benefits. The deployment of hydrogen fueling infrastructure to support the demonstration and commercialization of FCVs remains a critical barrier to transitioning to hydrogen as a transportation fuel. This study utilizes an engineering methodology referred to as the Spatially and Temporally Resolved Energy and Environment Tool (STREET) to demonstrate how systematic planning can optimize early investments in hydrogen infrastructure in a way that supports and encourages growth in the deployment of FCVs while ensuring that the associated environment and energy security benefits are fully realized. Specifically, a case study is performed for the City of Irvine, California – a target area for FCV deployment – to determine the optimized number and location of hydrogen fueling stations required to provide a bridge to FCV commercialization, the preferred rollout strategy for those stations, and the environmental impact associated with three near-term scenarios for hydrogen production and distribution associated with local and regional sources of hydrogen available to the City. Furthermore, because the State of California has adopted legislation imposing environmental standards for hydrogen production, results of the environmental impact assessment for hydrogen production and distribution scenarios are measured against the California standards. The results show that significantly fewer hydrogen fueling stations are required to provide comparable service to the existing gasoline infrastructure, and that key community statistics are needed to inform the preferred rollout strategy for the stations. Well-to-wheel (WTW) greenhouse gas (GHG) emissions, urban criteria pollutants, energy use, and water use associated with hydrogen and FCVs can be significantly reduced in comparison to the average parc of gasoline vehicles regardless of whether hydrogen is produced and distributed with an emphasis on conventional resources (e.g., natural gas), or on local, renewable resources. An emphasis on local renewable resources to produce hydrogen further reduces emissions, energy use, and water use associated with hydrogen and FCVs compared to an emphasis on conventional resources. All three hydrogen production and distribution scenarios considered in the study meet California's standards for well-to-wheel GHG emissions, and well-to-tank emissions of urban ROG and NO_X. Two of the three scenarios also meet California's standard that 33% of hydrogen must be produced from renewable feedstocks. Overall, systematic planning optimizes both the economic and environmental impact associated with the deployment of hydrogen infrastructure and FCVs.     

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.     

Liquid hydrogen fuel system design and demonstration in a small long endurance air vehicle

Autonomous systems have advanced substantially, yet on-board energy capacity still constrains endurance. Liquid hydrogen (LH₂) fuel storage coupled with a high efficiency fuel cell may offer greater endurance. An LH₂ storage system has been developed, featuring a lightweight dewar with active pressure control. The dewar has 20.46 L internal volume, yielding ≤7.6 kWh kg⁻¹ specific energy and ≤1.2 Wh L⁻¹ energy density (LHV basis) depending on fuel withdrawal rate and ambient conditions. It demonstrated 48 h continuous flight in the Naval Research Laboratory's Ion Tiger unmanned air vehicle, which is ∼85% longer than prior gaseous hydrogen (GH₂) fueled flights, with the same dry mass as the GH₂ system. Design considerations included matching the LH₂ evaporation rate and variable consumption rate, and satisfying constraints imposed by the existing aircraft. Heat transfer models were used to design for low dewar heat leak, which is necessary to balance evaporation and consumption. The heat leak depends on ambient temperature, with evaporation ranging from 16 g h⁻¹ at 240 K to 29 g h⁻¹ at 300 K, at 275 kPa storage pressure. The LH₂/GH₂/dewar system takes ≥4 h to reach thermodynamic equilibrium after fueling. LH₂ can extend the endurance of small autonomous systems, but at the expense of greater design effort and reduced operational flexibility.     

Projecting full build-out environmental impacts and roll-out strategies associated with viable hydrogen fueling infrastructure strategies

A transition from gasoline internal combustion engine vehicles to hydrogen fuel cell electric vehicles (FCEVs) is likely to emerge as a major component of the strategy to meet future greenhouse gas reduction, air quality, fuel independence, and energy security goals. Advanced infrastructure planning can minimize the cost of hydrogen infrastructure while assuring that energy and environment benefits are achieved. This study presents a comprehensive advanced planning methodology for the deployment of hydrogen infrastructure, and applies the methodology to delineate fully built-out infrastructure strategies, assess the associated energy and environment impacts, facilitate the identification of an optimal infrastructure roll-out strategy, and identify the potential for renewable hydrogen feedstocks. The South Coast Air Basin of California, targeted by automobile manufacturers for the first regional commercial deployment of FCEVs, is the focus for the study. The following insights result from the application of the methodology:

•

Compared to current gasoline stations, only 11%-14% of the number of hydrogen fueling stations can provide comparable accessibility to drivers in a targeted region.

•

To meet reasonable capacity demand for hydrogen fueling, approximately 30% the number of hydrogen stations are required compared to current gasoline stations.

•

Replacing gasoline vehicles with hydrogen FCEVs has the potential to (1) reduce the emission of greenhouse gases by more than 80%, reduce energy requirements by 42%, and virtually eliminate petroleum consumption from the passenger vehicle sector, and (2) significantly reduce urban concentrations of ozone and PM2.5.

•

Existing sources of biomethane in the California South Coast Air Basin can provide up to 30% of the hydrogen fueling demand for a fully built-out hydrogen FCEV scenario.

•

A step-wise transition of judiciously located existing gasoline stations to dispense and accommodate the increasing demand for hydrogen addresses proactively key infrastructure deployment challenges including a viable business model, zoning, permitting, and public acceptance.

     

Risk-informed process and tools for permitting hydrogen fueling stations

The permitting process for hydrogen fueling stations requires demonstration that the proposed facility meets certain safety requirements. Currently, many permitting authorities rely on compliance with well-known codes and standards as evidence of a safe design. To ensure that a hydrogen facility is indeed safe, the code and standard requirements should be identified using a risk-informed process that utilizes an acceptable level of risk.     

Recommended pre-operation cleanup procedures for hydrogen fueling station

The stainless steel (SS) tubing and in-line filters are found to be sources of particulates in hydrogen fuel from new hydrogen stations. The internal coating of fueling nozzle can be delaminated during fueling as another particulate source. Organic residues, acetone, heptanes, and C₄Cl₄F₆ isomers are found in new SS tubing, which also emits hydrogen sulfide and carbonyl sulfide. Nitrogen contained in new storage tanks, if not properly removed, can elevate the nitrogen concentration in hydrogen fuel. We find that high pressure hydrogen flow can remove particulates, sulfur compounds and residual organic compounds from SS tubing. However, in-line filters should be cleaned by sonication and nitrogen contained in new storage tank pumped away. It is recommended that internal coating of fueling nozzle or SS tubing should not contain oxygen in chemical composition.