Safety

Historically it has been a challenge to simulate the experimentally observed cellular structures and marginal behavior of multidimensional hydrogen-oxygen detonations in the presence of losses even with detailed chemistry models. Very recently a quasi-two-dimensional inviscid approach was pursued where losses due to viscous boundary layers were modeled by the inclusion of an equivalent mass divergence in the lateral direction using Fay’s source term formulation with Mirels’ compressible boundary layer solutions. The same approach was used for this study along with the inclusion of thermally perfect detailed chemistry in order to capture the correct ignition sensitivity of the gas to dynamic changes in the thermodynamic state behind the detonation front. In addition the strength of transverse waves and their impact on the detonation front was investigated. Here the detailed San Diego mechanism was applied and it has been found that the detonation cell sizes can be accurately predicted without the need to prescribe specific parameters for the combustion model. For marginal cases where the detonation waves approach their failure limit quasi-stable mode behavior was observed where the number of transverse waves monotonically decreased to a single strong wave over a long enough distance. The strong transverse waves were also found to be slightly weaker than the detonation front indicating that they are not overdriven in agreement with recent studies.

The PRHYDE project (PRotocol for heavy duty HYDrogEn refueling) funded by the Clean Hydrogen partnership aims at developing recommendations for heavy-duty refueling protocols used for future standardization activities for trucks and other heavy duty transport systems applying hydrogen technologies. Development of a protocol requires a validated approach. Due to the limited time and budget the experimental data cannot cover the whole possible ranges of protocol parameters such as initial vehicle pressure and temperature ambient and precooling temperatures pressure ramp refueling time hardware specifications etc. Hence a validated numerical tool is essential for a safe and efficient protocol development. For this purpose engineering tools are used. They give good results in a very reasonable computation time of several seconds or minutes. These tools provide the heat parameters estimation in the gas (volume average temperature) and 1D temperature distribution in the tank wall. The following models were used SOFIL (Air Liquide tool) HyFill (by ENGIE) and H2Fills (open access code by NREL). The comparison of modelling results and experimental data demonstrated a good capability of codes to predict the evolution of average gas temperature in function of time. Some recommendations on model validation for the future protocol development are given.

Methanol as a liquid phase hydrogen storage carrier has broad prospects. Although the on-board methanol reforming hydrogen fuel cell system (MRFC) has long been proposed to replace the traditional hydrogen fuel cell vehicle the inherent safety of the system itself has rarely been studied. This paper adopted the improved method of Inherently Safer Process Piping (ISPP) to evaluate the pipeline inherent safety of MRFC. The process data such as temperature pressure viscosity and density were obtained by simulating the MRFC in ASPEN HYSYS. The Process Stream Characteristic Index (PSCI) and risk assessment of jet fire and vapor cloud explosion was carried out for the key streams with those simulated data. The results showed the risk ranks of different pipelines in the MRFC and the countermeasures were given according to different risk ranks. Through the in-depth study of the evaluation results this paper demonstrates the risk degree of the system in more detail and reduces the fuzziness of risk rating. By applying ISPP to the small integrated system of MRFC this paper realizes the leap of inherent safety assessment method in the object and provides a reference for the inherent safety assessment of relevant objects in the future.

Hydrogen an advanced energy source is growing quickly in its infrastructure and technological development. Urban areas are constructing convergence-type hydrogen refilling stations utilizing existing gas stations to ensure economic viability. However it is essential to conduct a risk analysis as hydrogen has a broad range for combustion and possesses significant explosive capabilities potentially leading to a domino explosion in the most severe circumstances. This study employed quantitative risk assessment to evaluate the range of damage effects of single and domino explosions. The PHAST program was utilized to generate quantitative data on the impacts of fires and explosions in the event of a single explosion with notable effects from explosions. Monte Carlo simulations were utilized to forecast a domino explosion aiming to predict uncertain events by reflecting the outcome of a single explosion. Monte Carlo simulations indicate a 69% chance of a domino explosion happening at a hydrogen refueling station if multi-layer safety devices fail resulting in damage estimated to be three times greater than a single explosion

Safety and reliability have long been recognized as key issues for the development commercialization and implementation of new technologies and infrastructure and hydrogen systems are no exception to this rule. Reliability engineering quantitative risk assessment (QRA) and knowledge exchange each play a key role in proactive addressing safety – before problems happen – and help us learn from problems if they happen. Many international research activities are focusing on both reliability and risk assessment for hydrogen systems. However the element of knowledge exchange is sometimes less visible. To support international collaboration and knowledge exchange the International Energy Agency (IEA) convened a new Technology Collaboration Program “Task 43: Safety and Regulatory Aspects of Emerging Large Scale Hydrogen Energy Applications” started in June 2022. Within Task 43 Subtask E focuses on Hydrogen Systems Safety. This paper discusses the structure of the Hydrogen Systems Safety subtask and the aligned activities and introduces opportunities for future work.

Updates to the separation distances between different exposures and bulk liquid hydrogen systems are included in the 2023 version of NFPA 2: Hydrogen Technologies Code. This work details the models and calculations leading to those distances. The specific models used including the flow of liquid hydrogen through an orifice within the Hydrogen Plus Other Alternative Fuels Risk Assessment Models (HyRAM+) toolkit are described and discussed to emphasize challenges specific to liquid hydrogen systems. Potential hazards and harm affecting individual exposures (e.g. ignition sources air intakes) for different unignited concentrations overpressures and heat flux levels were considered and exposures were grouped into three bins. For each group the distances to a specific hazard criteria (e.g. heat flux level) for a characteristic leak size informed by a risk-analysis led to a hazard distance. The maximum hazard distance within each group was selected to determine a table of separation distances based on internal pressure and pipe size rather than storage volume similar to the bulk gaseous separation distance tables in NFPA 2. The new separation distances are compared to the previous distances and some implications of the updated distances are given.

Shock-flame interactions (SFI) occur in a variety of combustion scenarios of scientific and engineering interest which can distort the flame extend the flame surface area and subsequently enhance heat release. This process is dominated by Richtmyer-Meshkov instability (RMI) that features the perturbation growth of a density-difference interface (flame) after the shock passage. The main mechanism of RMI is the vorticity deposition results from a misalignment between pressure and density gradients. This paper focuses on the multi-dimensional interactions between shock wave and flame in a hydrogen-air mixture. The simulations of this work were conducted by solving three-dimensional fully-compressible reactive Navier-Stokes equations using a high-order numerical method on a dynamically adapting mesh. The effect of wall friction on the SFI was examined by varying wall boundary condition (free-slip/no-slip) on sidewall. The results show that the global flame perturbation grows faster with the effect of wall friction in the no-slip case than that in the free-slip case in the process of SFI. Two effects of wall friction on SFI were found: (1) flame stretching close to the no-slip wall and (2) damping of local flame perturbation at the no-slip wall. The flame stretch effect leads to a significantly higher growth rate in the global flame perturbation. By contrast the damping effect locally moderates the flame perturbation induced by RMI in close proximity to the no-slip wall because less vorticity is deposited on this part of flame during SFI.

The capabilities of an OpenFOAM solver to reproduce the transition of stoichiometric H2-air mixtures to detonation in obstructed 2-D channels were tested. The process is challenging numerically as it involves the ignition of a flame kernel its subsequent propagation and acceleration interaction with obstacles formation of shock waves ahead and detonation onset (DO). Two different obstacle configurations were considered in 10-mm high × 1-m long channels: (i) wavy walls (WW) that mimic the behavior of fencetype obstacles but prevent abrupt area changes. In this case flame acceleration (FA) is strongly affected by shock-flame interactions and DO often results from the compression of the gas present between the accelerating flame front and a converging section of the channel. (ii) Fence-type (FT) obstacles. In this case FA is driven by the increase in flame surface area as a result of the interaction of the flame front with the unburned gas flow field ahead particularly downstream of obstacles; shock-flame interactions play a role at the later stages of FA and DO takes place upon reflection of precursor shocks from obstacles. The effect of initial pressure p0 = 25 50 and 100 kPa at constant blockage ratio (BR = 0.6) was investigated and compared for both configurations. Results show that for the same initial pressure (p0 = 50 kPa) the obstacle configurations could lead to different final propagation regimes: a quasi-detonation for WW and a choked-flame for FT due to the increased losses for the latter. At p0 = 25 kPa however while both configurations result in choked flames WW seem to exhibit larger velocity deficits than FT due to longer flame-precursor shock distances during quasi-steady propagation and to the increased presence of unburnt mixture downstream of the tip of the flame that homogeneously explodes providing additional support to the propagation of the flame.

This paper mainly introduces the main pain point of China's civil hydrogen energy supply chain - the problem of storage and transportation and analyzes the safety economy and scale effect and other issues of the existing hydrogen energy storage and transportation compares with other storage and transportation technology solutions and comprehensively screens out the storage and transportation technology solution mainly based on liquid hydrogen technology. The liquid hydrogen technology solution has significant advantages over the existing compressed hydrogen system in terms of safety economy and scale effect especially for future large-scale hydrogen energy application scenarios. In addition the future hydrogen energy storage and transportation system based on liquid hydrogen technology can help improve the overall utilization efficiency of country’s renewable energy promote the country's energy transition promote the electrification of the country's transportation sector and help achieve China's carbon emission reduction 2030/2060 target.

The introduction of hydrogen in natural gas pipeline systems introduces integrity challenges due to the nature of interactions between hydrogen and line pipe steel materials. However not every natural gas pipeline is equal in regards to the challenges potentially posed by the repurposing to hydrogen. Existing codes and practices penalise high-grade materials on the basis of a perceived higher susceptibility to hydrogen embrittlement in regards to their increased strength. This philosophy challenges the realisation of a hydrogen economy because it puts at economical and technical risk the conversion of almost half of the natural gas transmission systems in western countries.

The paper addresses the question whether pipe grade is actually a good proxy to strength and predictor to assess the performance of steel line pipes in hydrogen. Drivers that could affect the suitability of pipeline conversion in hydrogen from an integrity management perspective and industry experience of other hydrogen-charging applications are reviewed. In doing so the paper challenges the basis of the assumption that low-grade steels (up to X52 / L360) are automatically safer for hydrogen repurposing while at the other end of the spectrum higher-grade materials (>X52 / L360) are inevitably less suitable for hydrogen service.

Ultimately the paper discusses that materials sampling and testing of representative line pipes populations should be placed at the core of hydrogen repurposing strategies in order to safely address conversion and to maximize the hydrogen chain value. The paper addresses alternatives to make the sampling smart and cost-effective.

In a context of the decarbonization of the power sector the gas turbine manufacturers are expected tohandle and burn hydrogen or hydrogen/natural gas mixtures. This evolution is conceptually simple in order to displace CO2 emissions by H2O in the combustion exhaust but raises potential engineering andsafety related questions. Concerning the safety aspect the flammability domain is wider and the laminar flame speed is higher for hydrogen than for natural gas. As a result handling fuels with increased hydrogen concentration should a priori lead to an increased the risk of flammable cloud formation with air and also increase the potential explosion violence.<br/>A central topic for the gas turbine manufacturer is the quantification of the hydrogen fuel content from which the explosion risk increases significantly when compared with the use of natural gas. This work will be focused on a risk study of the fuel supply piping of a gas turbine in a scenario where mixing between fuel and air would occur. The pipes are a few dozens of meters long and show singularities: elbows connections with other lines … They are operated at high temperature and atmospheric or high pressure.<br/>The paper will first highlight through CFD modelling the impact of increasing hydrogen content in the fuel on the explosion risk based on a geometry representative of a realistic system. Second the quantification of the explosion effects will be addressed. Some elements of the bibliography relative to flame propagation in pipes will be recalled and put in sight of the characteristics of the industrial case. Finally a CFD model proposed recently for accounting for methane or hydrogen flames propagating in long open steel tubes was used to assess a hydrogen fuel content from which the flame can strongly accelerate and generate significative pressure effects for a flammable mixture initially at atmospheric conditions.

Hydrogen refuelling stations are an important part of the infrastructure for promoting the hydrogen economy. Since hydrogen is a flammable and explosive gas hydrogen released from high-pressure hydrogen storage equipment in hydrogen refuelling stations will likely cause combustion or explosion accidents. Studying high-pressure hydrogen leakage in hydrogen refuelling stations is a prerequisite for promoting hydrogen fuel cell vehicles and hydrogen refuelling stations. In this work an actual-size hydrogen refuelling station model was established on the ANSYS FLUENT software platform. The computational fluid dynamics (CFD) models for hydrogen leakage simulation were validated by comparing the simulation results with experimental data in the literature. The effects of ambient wind speed wind direction leakage rate and leakage direction on the diffusion behaviors of the released hydrogen were investigated. The spreading distances of the flammable hydrogen cloud were predicted using an artificial neural network for horizontal leakage. The results show that the leak direction strongly affected the flammable cloud flow. The ambient wind speed has complicated effects on spreading the flammable cloud. The wind makes the flammable cloud move in certain directions and the higher wind speed accelerates the diffusion of the flammable gas in the air. The results of the study can be used as a reference for the study of high-pressure hydrogen leakage in hydrogen refuelling stations.

This paper intends to give an impression of new technologies and processes that are in development for application to achieve decarbonization and about which less or no experience on associated hazards exists in the process industry. More or less an exception is hydrogen technology because its hazards are relatively known and there is industry experience in handling it safely but problems will arise when it is produced stored and distributed on a large scale. So when its use spreads to communities and it becomes as common as natural gas now measures to control the risks will be needed. And even with hydrogen surprise findings have been shown lately e.g. its BLEVE behavior when in a liquified form stored in a vessel heated externally. Substitutes for hydrogen are not without hazard concern either. The paper will further consider the hazards of energy storage in batteries and the problems to get those hazards under control. Relatively much attention will be paid to the electrification of the process industry. Many new processes are being researched which given green energy will be beneficial to reduce greenhouse gases and enhance sustainability but of which hazards are rather unknown. Therefore as last chapter the developments with respect to the concept of hazard identification and scenario definition will be considered in quite detail. Improvements in that respect are also being possible due to the digitization of the industry and the availability of data and considering the entire life cycle all facilitated by the data model standard ISO 15926 with the scope of integration of life-cycle data for process plants including oil and gas production facilities. Conclusion is that the new technologies and processes entail new process and personal hazards and that much effort is going into renewal but safety analyses are scarce. Right in a period of process renewal attention should be focused on possibilities to implement inherently safer design.

Hydrogen is an environmentally friendly fuel that can facilitate the upcoming energy transition. The development of an extensive infrastructure for hydrogen transport and storage is crucial. However the mechanical properties of structural materials are significantly degraded in H2 environments leading to early component failures. Pipelines are designed following defect-tolerant principles and are subjected to periodic pressure fluctuations. Hence these systems are potentially prone to fatigue degradation often accelerated in pressurized hydrogen gas. Inspection and maintenance activities are crucial to guarantee the integrity and fitness for service of this infrastructure. This study predicts the severity of hydrogen-enhanced fatigue in low-alloy steels commonly employed for H2 transport and storage equipment. Three machine-learning algorithms i.e. Linear Model Deep Neural Network and Random Forest are used to categorize the severity of the fatigue degradation. The models are critically compared and the best-performing algorithm are trained to predict the Fatigue Acceleration Factor. This approach shows good prediction capability and can estimate the fatigue crack propagation in lowalloy steels. These results allow for estimating the probability of failure of hydrogen pipelines thus facilitating the inspection and maintenance planning.

The main purpose of this work is to investigate the influence of methane addition in methane-hydrogen-air mixture (φ = 0.8 – 1.6) on the critical conditions for transition to detonation in a 90-deg wedge corner. Similar to hydrogen-air mixtures investigated previously [1] methane-hydrogen-air mixtures results showed three ignition modes weak ignition followed by deflagration with ignition delay time higher than 1 μs strong ignition with instantaneous transition to detonation and third with deflagrative ignition and delayed transition to detonation. Methane addition caused an increase in the range of 3.25 – 5.03% in the critical shock wave velocity necessary for transition to detonation for all mixtures considered. For example in stoichiometric mixture with 5% methane in fuel (95% hydrogen in fuel) in air the transition to detonation velocity was approx. 752 m/s (an increase of 37 m/s from hydrogen-air) corresponding to M = 1.89 (an increase of 0.14 from hydrogen-air) and 75.7% (an increase of 4.7% from hydrogen-air) of speed of sound in products. Also similar to hydrogen-air mixture the transition to detonation velocity increased for leaner and richer mixture. Moreover it was observed that methane addition in general increased the pressure limit at the corner necessary for transition to detonation.

The transition to a sustainable future with hydrogen as a key energy carrier necessitates a comprehensive understanding of the safety aspects of hydrogen including liquid hydrogen (LH₂). Hence this study presents a detailed computational fluid mechanics analysis to explore accidental LH₂ leakage and dispersion in a hydrogen refuelling station under varied conditions which is essential to prevent fire and explosion. The correlated impact of influential parameters including wind direction wind velocity leak direction and leak rate were analysed. The study shows that hydrogen dispersion is significantly impacted by the combined effect of wind direction and surrounding structures. Additionally the leak rate and leak direction have a significant effect on the development of the flammable cloud volume (FCV) which is critical for estimating the explosion hazards. Increasing wind velocity from 2 to 4 m/s at a constant leak rate of 0.06 kg/s results in an 82% reduction in FCV. The minimum FCV occurs when leak and wind directions oppose at 4 m/s. The most critical situation concerning FCV arises when the leak and wind directions are perpendicular with a leak rate of 0.06 kg/s and a wind velocity of 2 m/s. These findings can aid in the development of optimised sensing and monitoring systems and operational strategies to reduce the risk of catastrophic fire and explosion consequences.

The safety engineering design of hydrogen systems and infrastructure worker education and training regulatory compliance and engagement with other stakeholders are significant to the viability and public acceptance of hydrogen farms. The only way to ensure these are accomplished is for the field of hydrogen safety engineering (HSE) to grow and mature. HSE is described as the application of engineering and scientific principles to protect the environment property and human life from the harmful effects of hydrogen-related mishaps and accidents. This paper describes a whole hydrogen farm that produces hydrogen from seawater by alkaline and proton exchange membrane electrolysers then details how the hydrogen gas will be used: some will be stored for use in a combined-cycle gas turbine some will be transferred to a liquefaction plant and the rest will be exported. Moreover this paper describes the design framework and overview for ensuring hydrogen safety through these processes (production transport storage and utilisation) which include legal requirements for hydrogen safety safety management systems and equipment for hydrogen safety. Hydrogen farms are large-scale facilities used to create store and distribute hydrogen which is usually produced by electrolysis using renewable energy sources like wind or solar power. Since hydrogen is a vital energy carrier for industries transportation and power generation these farms are crucial in assisting the global shift to clean energy. A versatile fuel with zero emissions at the point of use hydrogen is essential for reaching climate objectives and decarbonising industries that are difficult to electrify. Safety is essential in hydrogen farms because hydrogen is extremely flammable odourless invisible and also has a small molecular size meaning it is prone to leaks which if not handled appropriately might cause fires or explosions. To ensure the safe and dependable functioning of hydrogen production and storage systems stringent safety procedures are required to safeguard employees infrastructure and the surrounding environment from any mishaps.

Hydrogen is the most abundant element on earth being a low polluting and high efficiency fuel that can be used for various applications such as power generation heating or transportation. As a reaction to climate change authorities are working for determining the most promising applications for hydrogen one of the best examples of crossborder initiative being the IPCEI (Important Project of Common European Interest) on Hydrogen under development at EU level. Given the large interest for future uses of hydrogen special safety measures have to be implemented for avoiding potential accidents. If hydrogen is stored and used under pressure accidental leaks from pressure vessels may result in fires or explosions. Worldwide researchers are investigating possible accidents generated by hydrogen leaks. Special attention is granted to the atmospheric dispersion after the release so that to avoid fires or explosions. The use of consequence modelling software within safety and risk studies has shown its’ utility worldwide. In this paper there are modelled the consequences of the accidental release and atmospheric dispersion of hydrogen from a pressure tank using state-of-the-art QRA software. The simulation methodology used in this paper uses the “leak” model for carrying out discharge calculations. This model calculates the release rate and state of the gas after its expansion to atmospheric pressure. Accidental release of hydrogen is modelled by taking into account the process and meteorological conditions and the properties of the release point. Simulation results can be used further for land use planning or may be used for establishing proper protection measures for surrounding facilities. In this work we analysed two possible accident scenarios which may occur at an imaginary hydrogen refuelling station accidents caused by the leaks of the pressure vessel with diameters of 10 and 20 mm for a pressure tank filled with hydrogen at 35 MPa / 70 MPa. Process Hazard Analysis Software Tool 8.4 has been used for assessing the effects of the scenarios and for evaluating the hazardous extent around the analysed installation. Accident simulation results have shown that the leak size has an important effect on the flammable/explosive ranges. Also the jet fire’s influence distance is strongly influenced by the pressure and actual size of the accidental release.

Hydrogen recombination catalyst is useful tool for reducing hydrogen in closed area. The catalyst is known to be poisoned under wet condition in long time use. The study is focused on the behavior of pre-oxidized Pd nanoparticle as the hard-used catalyst in high humidity environment by comparison of alumina and titanium oxide supports using in situ X-ray absorption spectroscopy technique. The reduction of surface oxide layer of Pd/TiO2 was promoted by water during hydrogen recombination although the reduction reaction of Pd/Al2O3 was inhibited by water.

The large deployment of hydrogen technologies for new applications such as heat power mobility and other emerging industrial utilizations is essential to meet targets for CO2 reduction. This will lead to an increase in the number of hydrogen installations nearby local populations that will handle hydrogen technologies. Local regulations differ and provide different safety and/or separation distances in different geographies. The purpose of this work is to give an insight on different methodologies and recommendations developed for hydrogen (mainly) risk management and consequences assessment of accidental scenarios. The first objective is to review available methodologies and to identify the divergent points on the methodology. For this purpose a survey has been launched to obtain the needed inputs from the subtask participants. The current work presents the outcomes of this survey highlighting the gaps and suggesting the prioritization of the actions to take to bridge these gaps.

The MultHyFuel project notably aims to produce the data missing for usable risk analysis and mitigation activity for Hydrogen Refuelling Stations (HRS) in a multi-fuel context. In this framework realistic releases of hydrogen that could occur in representative multi-fuel forecourts were studied. These releases can occur inside or outside fuel dispensers and they can interact with a complex environment notably made of parked cars and trucks. This paper is focused on the most critical scenarios that were addressed by a sub-group through the use of Computational Fluid Dynamics (CFD) modelling. Once the corresponding source terms for hydrogen releases were known two stages are followed:<br/>♦ Model Validation – to evaluate the CFD models selected by the task partners and to evaluate their performance through comparison to experimental data.<br/>♦ Realistic Release Modelling – to perform demonstration simulations of a range of critical scenarios.<br/>The CFD models selected for the Model Validation have been tested against measured data for a set of experiments involving hydrogen releases. Each experiment accounts for physical features that are encountered in the realistic cases. The selected experiments include an under-expanded hydrogen jet discharging into the open atmosphere with no obstacles or through an array of obstacles. Additionally a very different set-up was studied with buoyancy-driven releases inside a naturally ventilated enclosure. The results of the Model Validation exercise show that the models produce acceptable solutions when compared to measured data and give confidence in the ability of the models and the modellers to capture the behaviour of the realistic releases adequately. The Realistic Release Modelling phase will provide estimation of the flammable gas cloud volume for a set of critical scenarios and will be described at the second stage.

A field test series where a composite pressure vessel for hydrogen is exploded by fire 1) to provide the facts and the data for the safety distance based on overpressure; 2) to validate the current status of mitigation barrier per KGS FP216 and further designs for developments of the codes and standards relating to hydrogen refueling stations. A pair of barriers to be tested are installed approximately 4 m apart standing face to face. The explosion source is a type-4 composite vessel of 175 L filled with compressed hydrogen up to 70 MPa. The vessel is in the middle of the barriers and the body part is heated with an LPG burner until it blows out. The incident overpressures from the blast are measured with 40 high-speed pressure sensors which are respectively installed 2 to 32 m away from the explosion. In the tests with the barrier constructed per the current status of KGS FP216 the explosion of the vessel resulted in partial destruction of the reinforced concrete barrier and made the steel plate barrier dissociated from the foundation then flew away approximately 25 m. The peak overpressure was 14.65 kPa at 32 m. The test data will be further analyzed to select the barriers for the subsequent tests and to develop the codes and standards for hydrogen refueling stations.

This work is part of the MULTHYFUEL E.U. research program [1] aiming at enabling the implementation of hydrogen dispersers in refuelling stations. One important challenge is the severity of accidents due to a leakage of hydrogen from a dispenser in the forecourt. The work presented in this paper deals with the quantification of the leakage scenarios in terms of frequencies and severities. The risk analysis exercise although performed by experts showed very large discrepancies between the frequencies of leakages of the same categories and even between the consequences. A large part of the disagreement comes from the failure databases chosen as shown in the paper. The mismatch between the components on which the databases have been settled and the actual hydrogen components may be responsible for this situation. However as it stands limited confidence can be laid on the outcome of the risk analysis.<br/>A new method is being developed to calculate the frequencies of the leakage and the flowrate based on an accurate description of each component and of each hazardous situation. For instance the possibility for a fitting to become untight due to pressure cycling is modelled based on the contact mechanics. Human errors can also be introduced by describing the tasks. In addition of the description of the method the application to a disperser is proposed with some comparison to experiments. One of the outcomes is that leakage cross sections can be much larger than expected.

Hydrogen is promoted as an alternative energy given the global energy shortage and environmental pollution. A scientific basiscan be provided for the safe use and emergency treatment of hydrogen based on hydrogen leakage and combustion behavior.This study examined the stagnation parameters of dynamic hydrogen leakage and flame propagation in turbulent jets undernormal temperatures and high pressure. Based on van der Waals’ equation of state for gas a theoretical model for completelypredicting stagnation parameters outlet gas velocity and flow rate changes in the process of high-pressure hydrogen leakagecould be proposed and the calculation result of this model was compared with the experimental result with an error within±10%. The progression and propagation of the flame in turbulent jets after ignition were recorded using the background-oriented schlieren image technology and the propagation speed of flame from the ignition position downward and upwardwas calculated. Moreover the influence of initial pressure nozzle diameter and ignition position on the flame propagationprocess and propagation speed was analyzed.

Quantitative Risk Assessments (QRA) is an important tool for enabling safe deployment of hydrogen technologies and is increasingly embedded in the permitting process. Following the framework developed in our companion paper we conducted a detailed QRA on the uncontrolled releases from a high-capacity hydrogen fueling station with liquid hydrogen (LH2) storage. We characterized gaseous and liquid hydrogen releases determined the causal pathways that led to them and the frequency of the potential hazardous outcomes. These hazardous scenarios were modeled to estimate their potential harm on station users. The analysis results reveal that the total frequency for a major hydrogen release is 1.48 × 10− 2 times per station-year. However considering the control barriers in the station the expected frequency of ignition events is reduced to 1.35 × 10− 5 ignition per stationyear. The expected fatality risk is within the tolerable limit for hydrogen fueling stations but still remains higher than that of conventional gasoline stations. The most severe scenario identified involves a high-pressure GH2 release leading to a jet fire with jet flames reaching up to 15 m in length. The most probable sources of GH2 releases are from the gaseous hydrogen filters while for LH2 releases cryogenic pumps are the primary contributors. To improve the accuracy of QRAs for LH2 systems we identified critical gaps including the need for improved reliability data that must be addressed.

The development of hydrogen production technologies and new uses represents an opportunity to accelerate the ecological transition and create a new industrial sector. However the risks associated with the use of hydrogen must be considered. Mitigation of a hydrogen explosion in an enclosure is partly based on prevention strategies such as detection and ventilation and protection strategies such as explosion venting. Even if applications involving hydrogen probably are most interesting for vented explosions in weak structures the extreme reactivity of hydrogen-air mixtures often excludes the use of regular venting devices such as in highly constrained urban environments. Thus having alternative mitigation solutions can make the effects of the explosion acceptable by reducing the flame speed and the overpressure loading or suppressing the secondary explosion. The objective of this paper is to present experimental studies of the mitigation of hydrogen-air deflagration in a 4 m3 vented enclosure by injection of inhibiting powder (NaHCO₃). After describing the experimental set-up the main experimental results are presented for several trial configurations showing the influence of inhibiting powder in the flammable cloud on flame propagation. An interpretation of the mitigating effect of inhibiting powder on the explosion effects is proposed based on the work of Proust et al.

A wireless near-field hydrogen gas sensor is proposed which detects the leaking hydrogen near its source to achieve fast response and high reliability. The proposed sensor can detect leaking hydrogen in 100ms with nearly no delay due to hydrogen diffusion in space. The overall response time is shortened by orders of magnitude compared to conventional sensors according to simulation results. Over 1 year of maintenance interval is empowered by wireless design based on Bluetooth low energy protocol.

In confined spaces hydrogen released with low momentum tends to accumulate in a layer below the ceiling; the concentration in this layer rises and can rapidly enter the flammability range. In this context ventilation is a key safety equipment to prevent the formation of such flammable volumes. To ensure its well-sizing to each specific industrial context it is necessary to dispose of reliable engineering models. Currently the existing engineering models dealing with the buoyancy-driven H2 dispersion in a ventilated enclosure mainly focus on the natural-ventilation phenomenon. However forced ventilation is in some situations more adapted to the industrial context as the wind direction and intensity remains constant and under control. Therefore two existing wind-assisted ventilation models elaborated by Hunt and Linden [1] and Lowesmith et al. [2] were tested on forced ventilation applications. The main assumption consists in assuming a blowing ventilation system rather than a suction system as the composition and velocity of the entering air are known. The fresh air enters the down opening and airhydrogen mixture escapes through the upper one. The adapted models are then validated with experimental data releasing helium rather than hydrogen. Experiments are conducted on a 1-m3 ventilated box controlling the release and ventilation rates. The agreement between both analytical and experimental results is discussed from the different comparisons performed.

Following a desktop study undertaken in 2021 to identify hazard scenarios associated with the use of liquid and compressed hydrogen on commercial shipping Shell has started a programme of large-scale experiments on the consequences of a release of liquid hydrogen. This work will compliment on-going research Shell has sponsored within several joint industry projects but will also address immediate concerns that the maritime industry has for the transportation of liquid hydrogen (LH2). This paper will describe the first phase of experiments involving the release of LH2 onto various substrates as well as dispersion across an instrumented test pad. These results will be used to address the following uncertainties in risk assessments within the hydrogen economy such as (1) Quantify the impact of low wind speed and high humidity on the buoyancy of both a passive and momentum jet dispersion cloud (2) Gather additional data on liquid hydrogen jet fires (3) Understand the likelihood for the formation of a sustained pool of hydrogen (4) Characterise materials especially passive fire protective coatings that are exposed to LH2. Not only will these experiments generate validation data to provide confidence in the Shell consequence tool FRED but they will also be used by Shell to support updates and new regulations developed by the International Maritime Organisation as it seeks to reduce CO2 intensity in the maritime industry.

Hydrogen is one of a handful of new low carbon solutions that will be critical for the transition to net zero. The upscaling of production and applications entails that hydrogen is likely to be stored in liquid phase (LH2) at cryogenic conditions to increase its energy density. Widespread LH2 use as an alternative fuel will require significant infrastructure upgrades to accommodate increased bulk transport storage and delivery. However current LH2 bulk storage separation distances are based on subjective expert recommendations rather than experimental observations or physical models. Experimental studies of large-scale LH2 release are challenging and costly. The existing large-scale tests are scarce and numerical studies are a viable option to investigate the existing knowledge gaps. Controlled or accidental releases of LH2 for hydrogen refueling infrastructure would result in high momentum two-phase jets or formation of liquid pools depending on release conditions. Both release scenarios lead to a flammable/explosive cloud posing a safety issue to the public.<br/>The manuscript reports exploratory study to numerically determine the safety zone resulting from cryogenic hydrogen releases related to LH2 storage and refueling using the in-house HyFOAM solver further modified for gaseous hydrogen releases at cryogenic conditions and the subsequent atmospheric dispersion and ignition within the platform of OpenFOAM V8.0. The current version of the solver neglects the flashing process by assuming that the temperature of the stored LH2 is equal to the boiling point at the atmospheric condition. Numerical simulations of dispersion and subsequent ignition of LH2 release scenarios with respect to different release orientations release rates release temperatures and weather conditions were performed. Both hydrogen concentration and temperature fields were predicted and the boundary of zones within the flammability limit was also defined. The study also considered the sensitivities of the consequences to the release orientation wind speed ambient temperature and release content etc. The effect of different barrier walls on the deflagration were also evaluated by changing the height and location.

With the advancement of Fuel Cell Vehicles (FCVs) detecting hydrogen leaks is critically important in facilities such as hydrogen refilling stations. Despite its significance the dynamic response performance of hydrogen sensors in confined spaces particularly under ceilings has not been comprehensively assessed. This study utilizes a catalytic combustion hydrogen sensor to monitor hydrogen leaks in a confined area. It examines the effects of leak size and placement height on the distribution of hydrogen concentrations beneath the ceiling. Results indicate that hydrogen concentration rapidly decreases within a 0.5–1.0 m range below the ceiling and declines more gradually from 1.0 to 2.0 m. The study further explores the attenuation pattern of hydrogen concentration radially from the hydrogen jet under the ceiling. By normalizing the radius and concentration it was determined that the distribution conforms to a Gaussian model akin to that observed in open space jet flows. Utilizing this Gaussian assumption the model is refined by incorporating an impact reflux term thereby enhancing the accuracy of the predictive formula.

Lead–acid batteries are widely used in modern battery-powered ships. During the charging process of lead–acid batteries hydrogen gas is released which poses a potential hazard to ship safety. To address this this paper first establishes a turbulent flow model for hydrogen deflagration. Then using FDS6.7.9 software simulations of hydrogen deflagration are conducted and a simulation model of the ship’s cabin is constructed. The changes in temperature and pressure during the hydrogen deflagration process in the ship’s cabin are analyzed and the evolution process of hydrogen deflagration in the ship’s cabin is derived. Hydrogen deflagration poses a significant threat to the fire safety of battery-powered ships. Additionally a comparative analysis of hydrogen deflagration under different hydrogen concentrations is performed. It is concluded that battery-powered ships using lead–acid batteries should pay attention to controlling the hydrogen concentration below 4%.

As a clean and renewable energy carrier hydrogen is one of the most promising alternative fuels. Cryogenic compressed hydrogen can achieve high storage density without liquefying hydrogen which has good application prospects. Investigation of the safety problems of cryogenic compressed hydrogen is necessary before massive commercialization. The present study modeled the instantaneous flow field using the Large Eddy Simulation (LES) for cryogenic (50 and 100 K) underexpanded hydrogen jets released from a round nozzle of 1.5 mm diameter at pressures of 0.5-5.0 MPa. The simulation results were compared with the experimental data for validation. The axial and radial concentration and velocity distributions were normalized to show the self-similar characteristics of underexpanded cryogenic jets. The shock structures near the nozzle were quantified to correlate the shock structure sizes to the source pressure and nozzle diameter. The present study on the concentration and velocity distributions of underexpanded cryogenic hydrogen jets is useful for developing safety codes and standards.

Cryogenic liquid hydrogen offers a promising solution for achieving high-density hydrogen storage and efficient on-site distribution. However the potential hazards associated with hydrogen leakages necessitate thorough investigations. This research aims to model cryogenic hydrogen release from circular and high aspect ratio (HAR) nozzles tested by Sandia. The test conditions cover reservoir pressures and temperatures corresponding to cryogenic hydrogen storage. The study conducts computational simulations using OpenFOAM to examine hydrogen concentration temperature fields mass fraction and temperature distributions achieving good agreement with the experimental data. To further explore the study of velocity variations shows a consistent decay rate with room-temperature jets. The numerical data reveals comparable inverse centreline hydrogen mass fractions (0.254 for HAR and 0.26 for circular) and normalised centreline temperature decay rates (0.031 for HAR and 0.032 for circular). The present computational model holds the potential for further analysis of cryogenic hydrogen in large-scale facilities.

As a paradigm of clean energy hydrogen is gradually attracting global attention. However its unique characteristics of leakage and autoignition pose significant challenges to the development of high-pressure hydrogen storage technologies. In recent years numerous scholars have made significant progress in the field of high-pressure hydrogen leakage autoignition. This paper based on diffusion ignition theory thoroughly explores the mechanism of high-pressure hydrogen leakage autoignition. It reviews the effects of various factors such as gas properties burst disc rupture conditions tube geometric structure obstacles etc. on shock wave growth patterns and autoignition characteristics. Additionally the development of internal flames and propagation characteristics of external flames after ignition kernels generation are summarized. Finally to promote future development in the field of high-pressure hydrogen energy storage and transportation this paper identifies deficiencies in the current research and proposes key directions for future research.

As the global transition to carbon neutrality accelerates hydrogen energy has emerged as a key alternative to fossil fuels due to its potential to reduce carbon emissions. Many countries including Korea are constructing hydrogen refueling stations; however safety concerns persist due to accidents caused by equipment failures and human errors. While various accident analysis models exist the application of the root cause analysis (RCA) technique to hydrogen refueling station accidents remains largely unexplored. This study develops an RCA modeling map specifically for hydrogen refueling stations to identify not only direct and indirect causes of accidents but also root causes and applies it to actual accident cases to provide basic data for identifying the root causes of future hydrogen refueling station accidents. The RCA modeling map developed in this study uses accident cause investigation data from accident investigation reports over the past five years which include information on the organizational structure and operational status of hydrogen refueling stations as well as the RCA handbook. The primary defect sources identified were equipment defect personal defect and other defects. The problem categories which were the substructures of the primary defect source “equipment defect” consisted of four categories: the equipment design problem the equipment installation/fabrication problem the equipment reliability program problem and the equipment misuse problem. Additionally the problem categories which were the substructures of the primary defect source “personal defect” consisted of two categories: the company employee problem and the contract employee problem. The problem categories which were the substructures of the primary defect source “other defects” consisted of three categories: sabotage/horseplay natural phenomena and other. Compared to existing accident investigation reports which identified only three primary causes the RCA modeling map revealed nine distinct causes demonstrating its superior analytical capability. In conclusion the proposed RCA modeling map provides a more systematic and comprehensive approach for investigating accident causes at hydrogen refueling stations which could significantly improve safety practices and assist in quickly identifying root causes more efficiently in future incidents.

Currently there are many gaps in the research on the safety of hydrogen-powered trains and the hazardous points vary across different scenarios. It is necessary to conduct safety analysis for various scenarios in order to develop effective accident response strategies. Considering the implementation of hydrogen power in the rail transport sector this paper reviews the development status of hydrogen-powered trains and the hydrogen leak hazard chain. Based on the literature and industry data a thorough analysis is conducted on the challenges faced by hydrogen-powered trains in the scenario of electrified railways tunnels train stations hydrogen refueling stations and garages. Existing railway facilities are not ready to deal with accidental hydrogen leakage and the promotion of hydrogen-powered trains needs to be cautious.

As a clean energy carrier hydrogen is essential for global low-carbon energy transitions due to its unique combination of safe transport properties and energy density. This investigation employs computational fluid dynamics (ANSYS Fluent) to systematically characterize hydrogen dispersion through soil media from buried pipelines. The research reveals three fundamental insights: First leakage orifices smaller than 2 mm demonstrate restricted hydrogen migration regardless of directional orientation. Second dispersion patterns remain stable under both low-pressure conditions (below 1 MPa) and minimal thermal gradients with pipeline temperature variations limited to 63 K and soil fluctuations under 40 K. Third dispersion intensity increases proportionally with higher leakage pressures (exceeding 1 MPa) greater soil porosity and larger particle sizes while inversely correlating with burial depth. The study develops a predictive model through Sequential Quadratic Programming (SQP) optimization demonstrating exceptional accuracy (mean absolute error below 10%) for modeling continuous hydrogen flow through moderateporosity soils under medium-to-high pressure conditions with weak inertial effects. These findings provide critical scientific foundations for designing safer hydrogen transmission infrastructure establishing robust risk quantification frameworks and developing effective early-warning systems thereby facilitating the practical implementation of hydrogen energy systems.

Hydrogen fuel cell vessels represent a vital direction for green shipping but the risk of large-scale hydrogen leakage and diffusion in their enclosed compartments is particularly prominent. To enhance safety a simplified three-dimensional model of the deck-level cabins of the “Water-Go-Round” passenger ship was established using SolidWorks (2023) software. Based on a hydrogen leakage and diffusion model the effects of leakage location leakage aperture and initial ambient temperature on the diffusion patterns and distribution of hydrogen within the cabins were investigated using FLUENT software. The results show that leak location significantly affects diffusion direction with hydrogen leaking from the compartment ceiling diffusing horizontally much faster than from the floor. When leakage occurs at the compartment ceiling hydrogen can reach a maximum horizontal diffusion distance of up to 5.04 m within 540 s; the larger the leak aperture the faster the diffusion with a 10 mm aperture exhibiting a 40% larger diffusion range than a 6 mm aperture at 720 s. The study provides a theoretical basis for the safety design and risk prevention of hydrogen fuel cell vessels.

Achieving global net-zero emissions by 2050 demands integrated and scalable strategies that unite decarbonization technologies across sectors. This review provides a forwardlooking synthesis of carbon capture and storage and hydrogen systems emphasizing their integration through artificial intelligence to enhance operational efficiency reduce system costs and accelerate large-scale deployment. While CCS can mitigate up to 95% of industrial CO2 emissions and hydrogen particularly blue hydrogen offers a versatile low-carbon energy carrier their co-deployment unlocks synergies in infrastructure storage and operational management. Artificial intelligence plays a transformative role in this integration enabling predictive modeling anomaly detection and intelligent control across capture transport and storage networks. Drawing on global case studies (e.g. Petra Nova Northern Lights Fukushima FH2R and H21 North of England) and emerging policy frameworks this study identifies key benefits technical and regulatory challenges and innovation trends. A novel contribution of this review lies in its AI-focused roadmap for integrating CCS and hydrogen systems supported by a detailed analysis of implementation barriers and policy-enabling strategies. By reimagining energy systems through digital optimization and infrastructure synergy this review outlines a resilient blueprint for the transition to a sustainable low-carbon future.

A simulation study was conducted on the hydrogen leakage diffusion process and influencing factors of fuel cell vehicles in enclosed spaces. The results indicate that when hydrogen leakage flows towards the rear of the vehicle it mainly flows along the rear wall of the space and diffuses to the surrounding areas. Setting ventilation openings of different areas on the top of the carriage did not significantly improve the spatial diffusion speed of the leaked hydrogen and the impact on the concentration of leaked hydrogen was limited to the vicinity of the ventilation openings. The ventilation opening at the rear can accelerate the diffusion of hydrogen gas to the external environment significantly reducing the concentration of hydrogen and rate of gas rise. When the leaked hydrogen gas flows towards the front of the vehicle and above the space the concentration of hydrogen mainly increases along the height direction of the space. The research results have significant safety implications for the use of fuel cell semi-trailer trucks.

As one of the most promising renewable green energies hydrogen power is a popularly accepted option to drive automobiles. Commercial application of fuel cell vehicles has been started since 2015. More and more hydrogen safety concerns have been considered for years. Tunnels are an important part of traffic infrastructure with a mostly confined feature. A hydrogen leak followed possibly by a hydrogen fire is a potential accident scenario which can be triggered trivially by a car accident while hydrogen-powered vehicles operate in a tunnel. Water spray is recommended traditionally as a mitigation measure against tunnel fires. The interaction between water spray and hydrogen fire is studied by way of numerical simulations. By using the computer program of Fire Dynamics Simulator (FDS) tunnel fires of released hydrogen in different scales are simulated coupled with water droplet injections featured in different droplet sizes or varying mass flow rates. The cooling effect of spray on hot gases of hydrogen fires is apparently observed in the simulations. However in some circumstances the turbulence intensified by the water injection can prompt hydrogen combustion which is a negative side effect of the spray.

In this study a liquid hydrogen (LH2) safety valve evaluation device was developed to enable safe and stable performance testing of pressure safety valves (PSVs) under realistic cryogenic and high-pressure conditions. The device was designed for flexible use by mounting all components on a mobile frame equipped with wheels and the pressurization rate inside the vessel was controlled through a boil-off gas (BOG) generator. Two experiments were conducted to investigate the effect of LH2 production rate on PSV operation. When the production of LH2 increased by about 2.4 times the number of PSV operations rose from 15 to 20 and the operating pressure range shifted slightly upward from 10.68~12.53 bar to 10.68~13.2 bar while remaining within the instrument’s error margin. These results indicate that repeated valve cycling and increased hydrogen production contribute to gradual changes in PSV operating characteristics. Additionally the minimum temperature experienced by the PSV decreased with repeated operations reaching approximately 77.9 K. The developed evaluation system provides an effective platform for analyzing PSV performance under realistic LH2 production and storage conditions.

This study explores the safety problems of hydrogen leakage and explosion in hydrogen fuel cell buses through Computational Fluid Dynamics simulations. The research investigates the diffusion behavior of hydrogen in the passenger cabin depending on the leakage position and flow rates identifying a stratified constant-concentration layer formed at the top of the cabin. Leakage near the rear wall of the vehicle provided the highest hydrogen concentration while at higher flow rates the diffusive process accelerated the spreading of flammable hydrogen concentrations. Hydrogen ignition simulations showed a fast internal pressure increase and secondary explosions outside the vehicle. Thermal hazards in the cases were higher than overpressure. The research’s additional analysis of ignition timing and source location shows that overpressure peaked initially with delayed ignition but declined afterward while rear-ignited flames exhibited the farthest high-temperature hazard range at 10.88 m. These findings are fundamental for giving insight into hydrogen behavior in confined spaces and thus guiding risk assessment and emergency response planning for the development of safety protocols in hydrogen fuel cell buses contributing to the safer implementation of hydrogen energy in public transportation.