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A hydrogen under-expanded jet released from a high-pressure vessel or equipment into the atmosphere through a 0.53 mm diameter orifice results in a sustained lifted flame for pressures above 4 MPa and flame blow-out at pressures below 3 MPa. Knowledge of whether the leaked hydrogen creates a sustained flame or is extinguished is an important issue for safety engineering. This study aims to clarify, in detail, a mechanism of flame stabilisation and blow-out depending on the spouting pressure. The model of flame stabilisation is derived using measurements and observations at the flame base location by means of high-speed schlieren images, laser diagnostics, and electrostatic probe techniques. The sustained stable flame originating from the 0.53 mm orifice is characterised by the existence of the spherical flame structures with a diameter of about 5 to 7 mm that appear one after another at the flame base and outside the streamlines of the hydrogen jet. As the spouting pressure reduces to 3.5 MPa, the sustained lifted flame becomes quasi-steady with higher fluctuations in amplitude of the flame base (lift-off height). In addition to that, flame structures are moving further from the hydrogen jet outlet, with a further decrease of spouting pressure leading to blow-out. The existence of spherical flame formations plays an important role in flame stabilisation. Based on the measurements of OH radicals using the PLIF method and ion currents, multiple flame surfaces were found to be folded in the flame structures. The hydrogen jet generates the vortex-like flow near its outer edge, creating flamelets upon ignition, ultimately forming the observed in the experiments spherical flame structures. [ABSTRACT FROM AUTHOR]

Vented inhomogeneous hydrogen deflagrations are conducted in a 7 m3 chamber. The effects of ignition position and inhomogeneous concentration are studied. The results show that a coupling flame structure of jet fire and flame bubble is first observed. In the case of top ignition, a M-shaped flame structure forms for average hydrogen concentration C ¯ H 2 ≤ 10.14 vol%. In the cases of center ignition and bottom ignition, the flame bubble rapidly expands towards the walls and the horizontal propagation speed of upper part of flame bubble is obviously higher than that of lower part of flame bubble for C ¯ H 2 ≥ 11.27 vol%. Moreover, the speed of horizontal flame front quickly decreases as the flame front moves away from the centerline of hydrogen jet. Three overpressure peaks appear in all scenarios, namely P open , P hel and P vib , which results from the vent failure, Helmholtz-type oscillations and thermo-acoustic oscillations respectively. The maximum overpressure dominated by P open is nearly insensitive to C ¯ H 2 for top ignition. However, the maximum overpressure induced by center ignition or bottom ignition significantly increases when C ¯ H 2 ≥ 10.14 vol%. For a given C ¯ H 2 , P vib induced by bottom ignition is always the largest. [ABSTRACT FROM AUTHOR]

As a subdivision of the hydrogen energy application field, ship-borne hydrogen fuel cell systems have certain differences from vehicle or other application scenarios in terms of their structural type, safety, environmental adaptability, and test verification. The connection method of the ship-borne hydrogen storage cylinder (SHSC) is very important for the hydrogen fuel cell ship, and the structural parameters of the SHSC are particularly important in the hydrogen refueling process. To ensure the safe and reliable operation of the hydrogen-powered ship, research on the filling of the SHSC under different connection modes was carried out during refueling. In our study, a thermal flow physical model of the SHSC was established to research the hydrogen refueling process of the series and parallel SHSCs. The influence of series and parallel modes of the SHSCs on the hydrogen refueling process was explored, and the evolution law of the internal flow field, pressure, and temperature of series and parallel SHSCs under different filling parameters was analyzed by numerical simulation. Our results confirmed the superiority of the parallel modular approach in terms of thermal safety during refueling. The results can supply a technical basis for the future development of hydrogen refueling stations and ship-board hydrogenation control algorithms. [ABSTRACT FROM AUTHOR]

This paper aims at the development and validation of a computational fluid dynamic (CFD) model for simulations of the refuelling process through the entire equipment of the hydrogen refuelling station (HRS). The absence of such models hinders the design of inherently safer refuelling protocols for an arbitrary combination of HRS equipment, hydrogen storage parameters, and environmental conditions. The CFD model is validated against the complete process of refuelling lasting 195s in Test No.1 performed by the National Renewable Energy Laboratory (NREL). The test equipment includes high-pressure tanks of HRS, pressure control valve (PCV), valves, pipes, breakaway, hose, and nozzle all the way up to three onboard tanks. The model accurately reproduced hydrogen temperature and pressure through the entire line of HRS equipment. A standout feature of the CFD model, distinguishing it from simplified models, is the capability to predict temperature non-uniformity in onboard tanks, a crucial factor with significant safety implications. • CFD model of refuelling through the entire HRS equipment reproduced NREL Test No.1. • Complete hydrogen refuelling process of 195 s simulated in 2 days on 32-core CPU. • The model can be used to design fuelling protocols for HRS with any equipment. [ABSTRACT FROM AUTHOR]

This article presents a comprehensive description of the safety system of a real installation that comprises PV panels, lithium-ion batteries, an electrolyzer, H 2 storage, a fuel cell, and a barium chloride/ammonia thermochemical prototype for heat recovery and cooling production. Such a system allows for the increase of the overall efficiency of the H 2 chain by exploiting the waste heat and transforming it into a cooling effect, particularly useful in tropical regions like French Polynesia. The study provides a great deal of detail regarding practical aspects of the system implementation and a consistent reference to the relevant standards and regulations applicable to the subject matter. More specifically, the study covers the ATEX classification of the site, the safety features of each component, the electrical power distribution, the main safety instrumented system, fire safety and the force ventilation system. The study also includes safety assessment and a section on lessons learned that could serve as guidance for future installations. In addition, an extensive amount of technical data is readily available to the reader in repository (P&ID, electrical diagrams, etc.). • Comprehensive description of the safety system of a real installation. • Great deal of detail regarding practical aspects of the system implementation. • Consistent referencing to the relevant standards applicable to the subject matter. • Layout of lessons learned and guidance for future installations. • Extensive technical data available in repository (P&ID, electrical diagrams, etc.). [ABSTRACT FROM AUTHOR]

Numerical simulations were conducted to investigate the hydrogen dispersion and deflagration in an underground garage, considering potential leaks from hydrogen fuel cell vehicles. This study constructed a geometric model based on vehicles equipped with 70 MPa hydrogen tanks and considered various accident scenarios by adjusting the orifice diameter and ignition time. The results indicated that the peak overpressure was influenced by the equivalence ratio, hydrogen distribution and ignition time. Specifically, increasing orifice diameter led to greater overpressure when ignition occurred 0.1 s after release, while the opposite trend was observed for ignition at 1 s or 10 s. Temperature and overpressure were measured to evaluate the hazard distances, revealing inconsistencies between distances determined by pressure and temperature, with the latter yielding larger results. This research contributes to determining affected areas and safety distances in hydrogen accidents, provides references for the design of parking intervals and the development of emergency plans. • Modeled hydrogen dispersion and deflagrations in an underground garage. • Examined the effects of orifice diameters and ignition times on hydrogen explosion. • Investigated the factors influencing peak overpressure. • Pressure and temperature distribution determine different Explosion-affected areas. [ABSTRACT FROM AUTHOR]

With increasing world energy demands, hydrogen is being widely deployed around the world as a potential alternative fuel as well as an energy carrier for future energy industry. However, due to the inherent properties of hydrogen, the safety during its production, transportation, storage and utilization is an important issue. Furthermore, the safety and reliability of hydrogen energy are necessary enabling condition for public acceptance. In this work, the concept of hydrogen energy safety and the influence factor of hydrogen safety on hydrogen economy are presented, the safety during hydrogen production, transmission and use is reviewed and several typical hydrogen accident cases are analyzed. The development of the latest technology in hydrogen energy safety is discussed, and recommendations are made to help providing a basis for future risk and reliability analysis to support safe and reliable hydrogen operation. • The hydrogen safety concept and its influence on hydrogen economy are discussed. • The hydrogen safety during its production, transmission and use are reviewed. • Typical hydrogen accidents are analyzed and lessons learned from them are discussed. • The development of the cutting-edge technologies for hydrogen safety is discussed. • The importance of reliable sensors for hydrogen leak detection is discussed. [ABSTRACT FROM AUTHOR]

Hydrogen technologies are expected to play a key role in the decarbonization of several sectors including energy storage and transportation. Rigorous investigation and quantification of the risk and reliability issues associated with hydrogen technologies will be critical to ensuring both their wider adoption and safe, economical operations. Quantitative risk assessment (QRA) is an important tool that has been used to enable the safe deployment of many engineering systems, including hydrogen fueling stations and hydrogen storage systems. However, QRA studies require reliability data which is currently lacking for expanding applications of hydrogen systems. To address this gap, we present a new structure for a hydrogen component reliability database (HyCReD) that can be used to generate reliability data to be used in QRA, reliability, safety studies, maintenance planning, and more. Building on our previous work examining four major hydrogen safety data collection tools (West et al., 2022) [1], our approach in this work was to consult scientific literature on reliability data collection as well as a number of existing reliability engineering databases in the oil & gas, chemical processing, and nuclear power plant sectors. The evaluation of these databases led to identifying best practices to be implemented in a data collection framework for a hydrogen component reliability database. Based on these best practices, a set of 24 requirements for the proposed database are presented, covering its characteristics and the types of data to be collected. We define the structure of the HyCReD database and 25 data elements to be collected, spanning system description, failure, shutdown, or near-miss events, and maintenance events. The data elements are then defined according to international standards used in the safety and reliability practice and potential choice lists are provided for each field. Since this database is being piloted for hydrogen fueling stations, a generic station component hierarchy developed by West (2021) [2] is used to standardize system data. Finally, we demonstrate populating the database with information extracted from five narrative reports on hydrogen fueling station incidents. • Developed requirements for hydrogen component reliability databases. • Developed HyCReD database structure for system, incident, and maintenance data. • Created definitions for data elements and failure modes. • Built generic component hierarchy for H2 fueling stations from public designs. • Demonstrated HyCReD database usability by extracting data from event narratives. [ABSTRACT FROM AUTHOR]

In recent years, sustainable development has become a challenge for many societies due to natural or other disruptive events, which have disrupted economic, environmental, and energy infrastructure growth. Developing hydrogen energy infrastructure is crucial for sustainable development because of its numerous benefits over conventional energy sources. However, the complexity of hydrogen energy infrastructure, including production, utilization, and storage stages, requires accounting for potential vulnerabilities. Therefore, resilience needs to be considered along with sustainable development. This paper proposes a decision-making framework to evaluate the resilience of hydrogen energy infrastructure by integrating resilience indicators and sustainability contributing factors. A holistic taxonomy of resilience performance is first developed, followed by a qualitative resilience assessment framework using a novel Intuitionistic fuzzy Weighted Influence Nonlinear Gauge System (IFWINGS). The results highlighted that Regulation and legislation, Government preparation, and Crisis response budget are the most critical resilience indicators in the understudy hydrogen energy infrastructure. A comparative case study demonstrates the practicality, capability, and effectiveness of the proposed approach. The results suggest that the proposed model can be used for resilience assessment in other areas. • A Holistic taxonomy of resilience is proposed for hydrogen infrastructure. • A Novel IFWINGS is proposed for advanced qualitative resilience assessment. • Importance of regulation, government preparation, and crisis response budget are discussed. • A Practical and effective application on a real hybrid wind-hydrogen power plant is presented. • Framework provides a tool for promoting sustainable development. [ABSTRACT FROM AUTHOR]

Hydrogen will likely be stored and transported at high densities to have sufficient hydrogen on-site for efficient distribution. Cryogenic compressed hydrogen (CcH 2) is a high-density hydrogen storage method combining cryogenic temperatures and high pressures. Hydrogen releases from such high-density sources will result in high-momentum jets and jet flames if the jets ignite. This study modelled CcH 2 jet flames for stagnation pressures of 2∼5 bar and stagnation temperatures of 55∼150 K. The numerical models were validated by experimental data from the literature. The results show that the flame length increases with increasing pressure but decreases with increasing temperature. The CcH 2 jet flames are longer than their room-temperature counterparts with the same mass flow rate. Then, the CcH 2 jet flame lengths were correlated with the mass flow rate and stagnation temperature. Correlations were also developed for predicting trajectory temperatures and the radial temperature distributions in the CcH 2 jet flames. The present study provides a scientific basis for developing cryogenic hydrogen safety codes and standards and quantitative risk assessment models. • Cryogenic compressed hydrogen (CcH 2) jet flames were modelled. • The CcH 2 jet flame lengths were correlated with the mass flow rate and stagnation temperature. • The trajectory and radial temperature distributions were analyzed and correlated. [ABSTRACT FROM AUTHOR]

Radiation and flame scale characteristics of ceiling jet are important key elements, which are related to the safety of hydrogen energy transport. In this study, the flame radiation characteristics caused by hydrogen-blended natural gas (mixed gas) pipeline leakage fire were investigated experimentally. The effects of heat release rate, hydrogen addition ratio, nozzle diameter and source-ceiling height are considered. The flame shape of the ceiling jet fire is modeled by a cylinder cone and a cylindrical model. The WSGGM model is applied to calculate the flame emissivity. The flame emissivity is quantized by the equivalent diameter and gas type. The flame emissivity, downward received radiative heat flux and radiative heat flux under ceiling increase with the increase of hydrogen addition ratio. The view factor is calculated by the solid flame model. Moreover, the calculated flame radiative heat flux is in a favorable agreement with experimental results. The research results may provide reference for risk assessment of hydrogen mixing. • Effect of H 2 on flame radiation of CH 4 jet fire is studied experimentally. • Fame shape of ceiling jet was modeled by the cylinder cone and a cylindrical model. • A mathematical model for the flame emissivity estimation is proposed. • A prediction model of the flame radiation the gas mixture is reported. [ABSTRACT FROM AUTHOR]

The aim of this paper is to investigate the effects of ignition position and equivalent volume concentration C ‾ H 2 on dynamic responses for vented inhomogeneous hydrogen deflagrations in a 7 m3 chamber. The results indicate that the narrow-band and wide-band processes of overpressure signals are formed during Helmholtz-type and thermo-acoustic oscillations, respectively. The displacement response depending on C ‾ H 2 is characterized by the weak vibration or a sharp increase. The acceleration impulsive response is dominated by the forced vibration component with the high-frequency and high-amplitude, while the acceleration dynamic response is dominated by the free vibration component with the low frequency and low amplitude. The high-frequency component and frequency overlapping in structural responses become more significant with the increase of C ‾ H 2 . Structural responses generated by bottom ignition are the largest due to the most violent thermo-acoustic oscillation induced by a coupled flame structure of deflagration flame and jet fire. • Inhomogeneous hydrogen deflagrations in a 7 m3 chamber with a vent were conducted. • The effect of ignition position on dynamic responses was investigated. • A coupled flame structure of the deflagration flame and jet fire was observed. • The mechanisms of dynamic responses at different stages were revealed. • The formation mechanisms of overpressure peaks were revealed. [ABSTRACT FROM AUTHOR]

This paper presents a computational fluid dynamics (CFD) model for simulating high-pressure hydrogen leakage and diffusion. The model incorporates heat exchange during hydrogen leakage diffusion and the real gas equation of state in high-pressure conditions. The CFD model can provide superior predictions of pressure, temperature, hydrogen density, and mass flow rate within the hydrogen storage cylinder changes during high-pressure hydrogen leakage compared to existing models. Moreover, the model validated by experimental data enables simulation of the spatiotemporal evolution law of hydrogen concentration and the change of the combustible region in space following a high-pressure hydrogen storage cylinder leak in various spatial scenarios. It can also determine the safe distance after the hydrogen leakage and simulate the impact of the hydrogen leakage on the surrounding environment in terms of temperature, pressure and other physical factors. Furthermore, the model is applicable for simulating the leakage and diffusion behavior of high-pressure hydrogen in various leakage conditions. This capability helps researchers understand the characteristics of high-pressure hydrogen leakage and diffusion, and further study the phenomenological evolution law of hydrogen safety accidents, so as to formulate emergency response strategies. [Display omitted] • A realistic CFD model of high-pressure hydrogen leakage diffusion is proposed. • Real gas equation of state was used and the effect of heat exchange is considered. • The changes in each parameter during high-pressure hydrogen leak are calculated. • High-pressure hydrogen leakage and diffusion in different spaces are simulated. [ABSTRACT FROM AUTHOR]

In this paper, the flame evolution and pressure dynamics of hydrogen-nitrogen-air explosions with nitrogen addition ratio (χ) ranging from 0 to 40 %, ignited at three different positions ("central", "back" or "front" with respect to the vent) in a vented cylindrical vessel, were experimentally studied. Experimental results reveal that the coupling effects of χ and ignition position significantly affect the pressure curves and flame behavior within and outside the vessel. The higher the χ, the smoother the internal flame captured by a high-speed schlieren system. When χ<30 %, the maximum reduced overpressure (P max) at different ignitions decreases with increasing χ, and the central explosion yields the best suppression of P max : when χ is increased from 0 to 30 %, P max monotonically decreases from 232 kPa to 38 kPa. However, the differences in P max among the three ignition positions become negligible when χ ≥ 30 %. The structure of the pressure peaks and the types of oscillations measured near the vent depend on the combinations of ignition location and χ. The formation of a shock wave generated by the external explosion and its effect on the internal pressure-time histories are described. In general, for a given ignition, the maximum external overpressure (P e-max) decreases with χ is increased. The most pronounced decreasing trend of P e-max is consistently observed in back explosions when χ ranging from 0 to 40 %. Furthermore, compared to other ignition positions, the highest P max is always attained in central-ignition with χ<30 %; while the highest P e-max is always attained in back-ignition with χ ≤ 30 %; as χ ≥ 10 %, both P max and P e-max recorded at front-ignitions are almost insensitive to χ. • Effects of ignition position and N 2 dilution on hydrogen explosion were studied. • Flame evolution and types of pressure peaks and oscillations were analyzed. • As χ was increased from 0 to 30 %, P max decreased by 22.4 %, 33.9 %, and 73.0 %. • External explosion appeared depending on both χ and ignition position. • Most pronounced decreasing trend of P e-max was found in back-ignition explosions. [ABSTRACT FROM AUTHOR]

Reliability is critical to enable the safe production of hydrogen as fuel. Efficient hydrogen production depends on the reliability of electrolytic cells termed an electrolyzer. The polymer electrolyte membrane (PEM) electrolyzer is one of the most promising hydrogen production technologies. However, hydrogen solubility, diffusivity, and partial pressure differences between the flow channels could affect the reliability and safety of the PEM. The operating conditions could also introduce safety issues inside the PEM electrolyzer due to membrane degradation or thinning. A degraded membrane will initiate the hydrogen produced at the cathode, tends to cross over to the anode and may cause an internal explosion should the mixture of hydrogen-oxygen get minimum ignition energy. Therefore, investigating hydrogen gas cross-over is - imperative to ensure the reliability and safety of the PEM electrolyzers. This paper presents a novel reliability model of PEM electrolyzers, considering readily observable variables relevant to the issue. The Bayesian structural equation defines the causal relationships to variables representing failure scenarios: membrane drying and hot spot formation. The study identifies that the current density and the quantity of water at PEM's anode are two critical variables responsible for the reliability of the PEM electrolyzers. Monitoring and managing these variables will help ensuring PEM's operational safety and reliability. • Investigation of hydrogen gas cross-over to ensure the reliability and safety of the PEM electrolyzers. • Identifying operating conditions of PEM electrolyzer could degrade membrane. • Permeation of hydrogen to oxygen side of PEM cell pose high fire risk. • Prediction of membrane degradation based on the operating conditions of PEM electrolyzer. [ABSTRACT FROM AUTHOR]

Hydrogen safety is the foundation of hydrogen energy industry, but there is presently a shortage of high-efficiency safety protection technologies for hydrogen. Through a combination of experiment and simulation methods, this paper reveals the effective performance of ethylene in suppressing the hydrogen explosion behaviors in a 14 L closed spherical vessel at normal temperature and pressure. The experimental and simulation results show that a small amount of ethylene can increase the hydrogen generation path in the lean hydrogen chain reaction, thus enhancing the concentration of active free radicals and causing flame instability, which ultimately leads to an increase in explosion overpressure and laminar burning velocity. But on the whole, with the increase in ethylene volume fraction, the explosion parameters show a monotonically decreasing trend. This is because the addition of ethylene makes the hydrogen-oxygen chain reaction gradually transition to the inactive free radical chain reaction, resulting in the conversion of the active free radical to the inactive free radical, and the chain reaction rate is weakened. Finally, the explosion cannot occur. This result provides a novel idea for the research of new and efficient hydrogen explosion suppression materials. [Display omitted] • Effects of C 2 H 4 on flame and pressure of hydrogen were observed. • Hydrogen explosions can be effectively suppressed by C 2 H 4. • C 2 H 4 can change hydrogen-oxygen chain reaction pathways. [ABSTRACT FROM AUTHOR]

Accidental release of high-pressure hydrogen can induce the self-ignition, and the spontaneously combusting flame can eventually induce a non-premixed jet flame or even explosion. In this study, the explosion overpressure characteristic of hydrogen jet flame outside the pipeline was investigated. Experiments were conducted on high-pressure hydrogen release pipelines with a diameter of 10 mm and pipeline lengths of 750, 1450 and 2200 mm, respectively, under different hydrogen release pressure. The impact of different initial conditions on the peak value of high-pressure hydrogen jet explosion was systematically investigated. The external pressure signals and flame images were completely collected. The results show that the external explosion overpressure decreased with the increase of axial distance away from the nozzle. When the length of the pipeline increased, the peak value of the overpressure was also gradually decreased. Meanwhile, as the high-pressure hydrogen burst pressure increased, the overpressure rose first and then decreased. With the increase of release pressure, when the hydrogen pressure exceeded 8 MPa, the hydrogen flow in the tube formed a blocked flow, so the increase of external explosion overpressure became slow. This topic can provide a reference for the safety development of the high-pressure hydrogen storage system. • External explosion overpressure of hydrogen jet flame were studied experimentally. • When the critical pressure (8 MPa) of hydrogen gas exceeded, the increase of explosion overpressure decreased. • As the length of the tube increased, the external explosion overpressure decreased. [ABSTRACT FROM AUTHOR]

Deterministic risk assessment for hydrogen installations offers an integrated solution for H 2 risk assessment, incorporating a hydrogen release model, a site-specific 3D geometry model, a Computational Fluid Dynamics (CFD) tool, and a consequence analysis methodology. Empirical engineering models expedite the preparation of source terms and harm evaluations, while CFD generates 3D contours of radiation and overpressure loads. A case study is provided by investigating a gaseous hydrogen leak of a truck in a refueling station with a large roof. The effects of leak diameters, roof configurations, and ignition locations on hydrogen dispersion, combustion, and hazard analysis are examined. Results indicate that the majority of the burnable cloud accumulates in a half-meter layer under the ceiling, diminishing within a minute. The impact of thermal radiation on individuals is insignificant, but overpressures increase the likelihood of structure failures, indirectly affecting human fatality. These findings inform the optimization of refueling station design and safety management. • CFD-based Deterministic Risk Assessment approach to assess the safety of hydrogen installations. • Addressing potential hydrogen explosions due to the current ceiling design. • Minimal injury likelihood from hydrogen flame contact or thermal radiation. • Revealing insights for optimizing ceiling design and hydrogen risk mitigation strategies. [ABSTRACT FROM AUTHOR]

Hydrogen energy is a sustainable and renewable green energy source, and its efficient application and promotion is the trend to achieve national dual-carbon goals. However, due to the unique physical and chemical properties of hydrogen, it is prone to leakage during production, storage, transportation and use, which can cause combustion or explosion accidents. Therefore, hydrogen safety issues limit the widespread application and promotion of hydrogen energy. This article briefly introduces the basic characteristics of hydrogen, hydrogen embrittlement and its leakage hazards. It then summarises the working conditions of the leakage site in the diffusion process of high-pressure hydrogen leaks, including geometric shape, leak location, initial pressure, ventilation conditions, leak size, and the influence of obstacles, as well as the influence of the external atmospheric environment and the leakage space on hydrogen diffusion and transport. The article also summarises the existing risk identification methods for hydrogen leaks and concludes on the deficiencies and shortcomings of current research on high-pressure hydrogen leak diffusion, while providing prospects for future research on high-pressure hydrogen leak diffusion and efficient utilisation. [Display omitted] • Introduces the basic properties and hydrogen embrittlement of hydrogen. • Summarise the diffusion characteristics of hydrogen leakage under different operating conditions. • Explains the effect of leakage space on hydrogen diffusion. • Summarised the risk identification methods for hydrogen leakage. • Summarised the shortcomings of current research on high pressure hydrogen leakage. [ABSTRACT FROM AUTHOR]

This paper describes the performance of explosion free in fire self-venting (TPRD-less) composite tanks in fires of realistic specific heat release rate (HRR/A), i.e., total fire HRR over the source area, A, of HRR/A = 1 MW/m2, during fire intervention. This breakthrough safety technology does not require thermally activated pressure relief devices (TPRD). It provides microleaks-no-burst (μLNB) performance of hydrogen storage tanks in fire. The study investigated two fire intervention strategies, i.e., removal of vehicle with μLNB tank from the fire, and extinction of fire by water. One carbon-carbon and one carbon-basalt double-composite wall tanks were assessed in the removal from fire scenario. Four carbon-basalt prototypes were studied in fire extinction scenarios. All six prototypes of 7.5 L and nominal working pressure of 70 MPa have demonstrated safe release of hydrogen through microchannels of the wall after the liner melting. The μLNB technology allows to apply standard intervention strategies and tactics. • Performance of self-venting (TPRD-less) tanks during fire intervention is studied. • Examined fire intervention scenarios: removal from fire, fire extinction by water. • Microleaks-no-burst carbon-carbon and carbon-basalt tanks tested in fire. • Self-venting tanks allow standard fire intervention strategies and tactics. [ABSTRACT FROM AUTHOR]

The determination of the deflagration-to-detonation transition (DDT) run-up distance L DDT is crucial in both the design of pulse detonation engines (PDEs) and safety protection. In this paper, the L DDT of stoichiometric hydrogen–oxygen premixed mixtures in millimeter-scale spiral channels were studied experimentally and high-speed photography was employed to capture the flame propagation process. The mixtures in three different rectangular cross-sectional channel widths and various initial pressures were tested. The present results show that the L DDT decreases with increasing the initial pressure, and with increasing the channel width, the larger L DDT is observed. When fitted with the L DDT ∝ P 0 −m relationship, the values of m obtained in this study ranged from 0.997 to 4.222. The critical value of 0.1 for the equivalent area divergence induced by the boundary layer ξ is proposed to distinguish the behaviors between micro and macro channels, regardless of the type of mixture and channel configuration. Additionally, an empirical formula considering the influence of the boundary layer is obtained, which allows for the quantitative prediction of L DDT. Because of the influence of curvature effect, the smaller the channel width, the greater the prediction deviation. Due to the boundary layer effect, the momentum and heat dissipation are more pronounced in smaller tubes, resulting in a loss of velocity for the detonation wave. It is suggested that the detonation wave velocity increases as the channel width and initial pressure increase. Fay's model was employed to estimate the theoretical velocity deficit, and the experimental results were in good agreement with the theoretical predictions. The current findings are valuable for the field of micro PDE and may help the assessment of the potential risk of hydrogen detonation in micro systems. • DDT run-up distance for 2H 2 -O 2 mixtures in millimeter and sub-millimeter spiral channels are investigated. • The critical value of 0.1 for the area divergence ξ is proposed. • An empirical formula for predicting the L DDT is obtained. • Detonation velocity deficits in micro spiral channels are estimated theoretically. [ABSTRACT FROM AUTHOR]

Hydrogen's unique physicochemical and combustion properties make it stand out among fuels as new hydrogen production technologies, means of transportation, and consumers emerge. The future viability of these technological solutions will depend on numerous factors, including safety, environmental, regulatory, and economic considerations. Safe deployment of these technologies requires additional research and development activities. These range from an improved quantitative understanding of hydrogen leaks, material limitations due to embrittlement, very large-volume liquefied hydrogen storage and transport, to equipment- and usage-specific considerations as is the case for gas turbines and electrolyzers.

CFD modelling of compressed hydrogen fuelling provides information on the hydrogen and tank structure temperature dynamics required for onboard storage tank design and fuelling protocol development. This study compares five turbulence models to develop a strategy for cost-effective CFD simulations of hydrogen fuelling while maintaining a simulation accuracy acceptable for engineering analysis: RANS models k-ε and RSM; hybrid models SAS and DES; and LES model. Simulations were validated against the fuelling experiment of a Type IV 29 L tank available in the literature. For RANS with wall functions and blended models with near-wall treatment, the simulated average hydrogen temperatures deviated from the experiment by 1–3% with CFL ≈ 1–3 and dimensionless wall distance y+ ≈ 50–500 in the tank. To provide a similar simulation accuracy, the LES modelling approach with near-wall treatment requires mesh with wall distance y+ ≈ 2–10 and demonstrates the best-resolved flow field with larger velocity and temperature gradients. LES simulation on this mesh, however, implies a ca. 60 times longer CPU time compared to the RANS modelling approach and 9 times longer compared to the hybrid models due to the time step limit enforced by the CFL ≈ 1.0 criteria. In all cases, the simulated pressure histories and inlet mass flow rates have a difference within 1% while the average heat fluxes and maximum hydrogen temperature show a difference within 10%. Compared to LES, the k-ε model tends to underestimate and DES tends to overestimate the temperature gradient inside the tank. The results of RSM and SAS are close to those of LES albeit of 8–9 times faster simulations.

Passive auto-catalytic recombiners (PARs) are widely used to mitigate a hydrogen hazard. The first step to evaluate the hydrogen safety by PARs is to obtain qualified test data of the PARs for validation of their analytical model. SPARC PAR tests SP8 and SP9 were conducted to evaluate the hydrogen recombination characteristics of a honeycomb-shaped catalyst PAR. To obtain the hydrogen recombination rate from the PAR test data, two methods, Method-1 and Method-2, introduced by the THAI project, were applied. Since a large gradient of hydrogen concentration developed during hydrogen injection can cause a large error in the hydrogen mass obtained by integrating the measured hydrogen concentrations, a gate was installed at the PAR inlet to homogenize hydrogen in the test vessel before the PAR operation in the tests. A computational fluid dynamics (CFD) code with a PAR model was also applied to evaluate the characteristics of the PAR recombination according to the PAR inlet conditions, and the results were compared with those from Method-1 and Method-2. It was confirmed that the recombination rates from Method-1 require a correction factor to be compatible with results from Method-2 and the CFD simulation in the case of the SPARC-PAR tests.

A computational study of the nitrogen purging of a solid oxide fuel cell stack enclosed in a hot box is presented. The stack operates on ammonia as a fuel, and in the case of a hydrogen leakage, the entire compartment is immediately purged with nitrogen to ensure that there are no regions with high oxygen concentrations. In addition to this, the speed at which a hydrogen leak can be detected is determined. The results are then compared to a case with a relocated nitrogen inlet. A computational fluid dynamics (CFD) model is developed using the Reynolds-averaged Navier–Stokes equations for compressible flow in combination with conservation of energy and species equations in OpenFOAM. The results suggest that for the maximum concentration of oxygen to be below 5%, the hot box should be purged for 35 s, corresponding to 1.1 kg of nitrogen, if the hot box was already heated. If the hot box was at T = 300 K, it should be purged for 95 s, corresponding to 3.0 kg of nitrogen. The purge of the heated hot box results in a heat loss of 18 kW on average. A leak could be detected in 3.2 s during open circuit voltage tests. Changing the location of the outlet does not affect the cold purge, but results in a minimum purge period of 48 s during the hot purge, and the leak could be detected in 2 s. This paper demonstrates how CFD methods can be employed in order to address questions related to hydrogen safety.

A reduction in greenhouse gases has become an inescapable requirement. An effective scenario for achieving carbon neutrality is to develop a hydrogen economy. Its success, however, requires strict control of the different processes involved in planned hydrogen chains. The energy chain considered in this paper is a stationary application which involves the production of hydrogen by electrolysis (a power-to gas process) and its combustion in gas turbine combined cycles to generate electricity (a gas-to-power process). In such applications, the need is twofold: (i) to control the risk of explosive atmospheres by performing safe gas detection in the presence of hydrogen and (ii) to secure the reliability of all chain processes using hydrogen-rich gases by achieving reliable analyses of these gases. This paper is dedicated to the development of hydrogen energy to decarbonize the thermal production of electricity. We will first describe the hydrogen chain that would best suit the power generation sector. Then, we will highlight the properties of hydrogen that are critical for its reliable operation. Finally, we will review the sensing technologies suitable for hydrogen-containing fuels. This review paper was published as part of a Joint Industrial Project (JIP) aimed at enabling the safe and reliable deployment of hydrogen energy.

Hydrogen energy storage is an important support for promoting global green low-carbon transformation and realizing “carbon neutrality” goal. After the “double carbon” goal was put forward, hydrogen energy storage has become a hot topic of social concern. The safety of hydrogen energy storage is one of the problems that must be focused on and solved first. Safety problems in four stages of hydrogen production, hydrogen storage, hydrogen transport and hydrogen use were summarized and analyzed, including hydrogen leakage and diffusion, hydrogen combustion and explosion, compatibility of hydrogen with metals. At the same time, the current status and development of hydrogen leakage detection sensor technologies were analyzed, and the urgent problems and future development directions of hydrogen leakage detection technologies were pointed out.

Renewable hydrogen plays a critical role in the current energy transition, and can facilitate the decarbonization and de-fossilization of hard-to-abate sectors, such as the industrial, power, transportation and buildings sectors. High pressure hydrogen valve（HPHV）is an important energy storage element for the hydrogen fueling station. Given the problems of large internal pressure fluctuation and long adjustment time of the HPHV during the operation of the current hydrogen fueling system, it is necessary to study the thermal effects of the HPHV. In the study，the pressure、temperature and velocity changes of the HPHV are studied from the aspect of numerical calculation. The hydrogen pressure and temperature changes of the model were simulated and analyzed at the different filling parameters. The accuracy of the simulation model was demonstrated by practice. The influence of the internal taper of the spool on the temperature change of 40°, 50°, 60° and 70° was studied. The influence of outlet pressure of 5 MPa, 10 MPa, 15 MPa, 20 MPa, 25 MPa on the temperature of high-pressure hydrogen valve and the influence of mass flow rate of 0.1 g/s, 0.3 g/s, 0.5 g/s, 0.8 g/s on the velocity field of hydrogen high-pressure valve. The study shows that when the taper was 60°, the optimal decompression performance, small temperature rise, and the performance was stable. The highest speed and the lowest temperature appear near the gap outlet, up to 2500 m/s and 85 K, respectively. The temperature and speed change trends were basically opposite, and the temperature change range of the outlet was 280 K–370 K. The results of this study provide great support for the research and application of ultra-high pressure hydrogen storage and hydrogen refueling, which also provide a theoretical basis for the subsequent development of the hydrogen energy industry and the wide application of hydrogen fuel cell vehicles, and provide ideas for realizing the goal of “dual carbon''.

Hydrogen can serve as an abundant, green, low-carbon, and widely applicable secondary energy source, holding significant importance in building a clean, low-carbon, secure, and efficient energy system and achieving carbon peak and carbon neutrality goals. In the research of hydrogen fuel cells, thermal management, particularly cooling methods, plays a crucial role in the operation of the battery units. This paper primarily focuses on cooling methods in thermal management, using factors such as arrangement, cooling medium, and environmental temperature as variables to establish a simulation model for the thermal behavior of cylindrical hydrogen fuel cells and conduct a parametric study. The research findings indicate that enveloping the battery with a cooling medium can enhance heat dissipation by 19 %. Arranging the hydrogen fuel cell units in a symmetrical rectangular pattern yields excellent heat dissipation results. The battery's maximum temperature increases with the rise in environmental temperature, with every 5 K increase in environmental temperature resulting in a 1.01 % rise in the battery's maximum temperature.

The urgency to mitigate greenhouse gas emissions from maritime vessels has intensified due to the increasingly stringent directives set forth by the International Maritime Organization (IMO). These directives specifically address energy efficiency enhancements and emissions reduction within the shipping industry. In this context, hydrogen is the much sought after fuel for all the global economies and its applications, for transportation and propulsion in particular, is crucial for cutting down carbon emissions. Nevertheless, the realization of hydrogen-powered vessels is confronted by substantial technical hurdles that necessitate thorough examination. This study undertakes a comprehensive analysis encompassing diverse facets, including distinct variations of hydrogen fuel cells, hydrogen internal combustion engines, safety protocols associated with energy storage, as well as the array of policies and commercialization endeavors undertaken globally for the advancement of hydrogen-propelled ships. By amalgamating insights from these multifaceted dimensions, this paper adeptly encapsulates the myriad challenges intrinsic to the evolution of hydrogen-fueled maritime vessels, while concurrently casting a forward-looking gaze on their prospective trajectory.

High-pressure hydrogen jet fire from a storage tank impinging another tank located nearby is a worst-case incident scenario. This could result in storage vessel rupture with catastrophic consequences implying life and property loss. The concept of microleaks-no-burst (μLNB) performance of hydrogen storage tanks of Type IV is explained. In this study, the breakthrough safety technology of explosion free in fire self-venting (TPRD-less) tank with nominal working pressure (NWP) of 70 MPa is validated again st the most extreme fire conditions of an impinging hydrogen jet from 70 MPa tank. The results of the successful performance of self-venting tank in momentum-dominated hydrogen impinging jet fire are analysed. This work expands further the experimental validation domain of the explosion free in fire self-venting tanks to scenario of impinging fire of the highest applied intensity of HRR/A = 19.5 MW/m2. • The concept of explosion free in fire self-venting (TPRD-less) tank is discussed. • Self-venting operation of 70 MPa tank is demonstrated in extreme jet fire conditions. • Tank did not rupture but leaked under realistic impinging hydrogen jet fire (70 MPa). • Jet fire of largest known specific heat release rate of HRR/A = 19.5 MW/m2 was applied. • The technology has the potential to exclude tank rupture in fires onboard of trains, ships, etc. [ABSTRACT FROM AUTHOR]

CFD modelling of compressed hydrogen fuelling provides information on the hydrogen and tank structure temperature dynamics required for onboard storage tank design and fuelling protocol development. This study compares five turbulence models to develop a strategy for cost-effective CFD simulations of hydrogen fuelling while maintaining a simulation accuracy acceptable for engineering analysis: RANS models k-ε and RSM; hybrid models SAS and DES; and LES model. Simulations were validated against the fuelling experiment of a Type IV 29 L tank available in the literature. For RANS with wall functions and blended models with near-wall treatment, the simulated average hydrogen temperatures deviated from the experiment by 1–3% with CFL ≈ 1–3 and dimensionless wall distance y+ ≈ 50–500 in the tank. To provide a similar simulation accuracy, the LES modelling approach with near-wall treatment requires mesh with wall distance y+ ≈ 2–10 and demonstrates the best-resolved flow field with larger velocity and temperature gradients. LES simulation on this mesh, however, implies a ca. 60 times longer CPU time compared to the RANS modelling approach and 9 times longer compared to the hybrid models due to the time step limit enforced by the CFL ≈ 1.0 criteria. In all cases, the simulated pressure histories and inlet mass flow rates have a difference within 1% while the average heat fluxes and maximum hydrogen temperature show a difference within 10%. Compared to LES, the k-ε model tends to underestimate and DES tends to overestimate the temperature gradient inside the tank. The results of RSM and SAS are close to those of LES albeit of 8–9 times faster simulations. [ABSTRACT FROM AUTHOR]

A computational study of the nitrogen purging of a solid oxide fuel cell stack enclosed in a hot box is presented. The stack operates on ammonia as a fuel, and in the case of a hydrogen leakage, the entire compartment is immediately purged with nitrogen to ensure that there are no regions with high oxygen concentrations. In addition to this, the speed at which a hydrogen leak can be detected is determined. The results are then compared to a case with a relocated nitrogen inlet. A computational fluid dynamics (CFD) model is developed using the Reynolds-averaged Navier–Stokes equations for compressible flow in combination with conservation of energy and species equations in OpenFOAM. The results suggest that for the maximum concentration of oxygen to be below 5%, the hot box should be purged for 35 s, corresponding to 1.1 kg of nitrogen, if the hot box was already heated. If the hot box was at T = 300 K, it should be purged for 95 s, corresponding to 3.0 kg of nitrogen. The purge of the heated hot box results in a heat loss of 18 kW on average. A leak could be detected in 3.2 s during open circuit voltage tests. Changing the location of the outlet does not affect the cold purge, but results in a minimum purge period of 48 s during the hot purge, and the leak could be detected in 2 s. This paper demonstrates how CFD methods can be employed in order to address questions related to hydrogen safety. [ABSTRACT FROM AUTHOR]

This paper presents a survey assessing factors contributing to the public acceptance of hydrogen as a fuel for vehicles in Malaysia. For the survey, a set of questionnaires was prepared in Google Forms and distributed to respondents through social media (WhatsApp, Facebook, Messenger, and Telegram). The survey was conducted during the movement order control in Malaysia due to the global pandemic, and the responses were collected from November to December 2021. One hundred seventy-six local respondents voluntarily participated in the survey. The responses were analysed using non-parametric statistical tests in the Statistical Package for the Social Sciences (SPSS). The highest number of respondents from the 18–25 age group is 101 (57.39 per cent), followed by 26–35 (26.7 per cent) and 36–45 (7.95 per cent). The statistical analysis of the survey shows that socio-demographics is a factor influencing public acceptance. The Spearman correlation test shows a positive correlation between Malaysia's environmental awareness and the potential to use a hydrogen-powered car; hence, there is a good chance of Malaysian acceptance of using hydrogen as fuel. Safety and public perception of hydrogen-powered cars also indicate a positive correlation, where the R- values for all questions are more than 0.5, indicating that safety is a factor that shapes public acceptance. Although the number of samples does not represent the population, it provides a reasonable basis to examine the influencing factors of public acceptance of hydrogen as a fuel for vehicles. [ABSTRACT FROM AUTHOR]

As renewable energy with no pollution but wide sources and high calorific value， hydrogen becomes increasingly important in the context of energy shortage and dual carbon goals. The safety of liquid hydrogen is an important factor impeding its application. In this regard， the research results of worldwide liquid hydrogen safety in recent years are summarized. The hazards of liquid hydrogen are discussed in view of its low temperature， leakage， and combustion. The research results of the liquid hydrogen leakage and dispersion law from experimental and numerical simulations are introduced. The latest research progress of liquid hydrogen safety protection measures is outlined. Overall， the hazards of liquid hydrogen have now been fully understood， but liquid hydrogen leakage and dispersion laws must be further studied. There are few experimental data on liquid hydrogen leakage and dispersion， and the related numerical simulations still face many difficulties. No comprehensive standards， laws， and regulations are yet formulated for the safety requirements of liquid hydrogen storage， transportation and application.

Liquid hydrogen storage is an important way of hydrogen storage and transportation, which greatly improves the storage and transportation efficiency due to the high energy density but at the same time brings new safety hazards. In this study, the liquid hydrogen leakage in the storage area of a hydrogen production station is numerically simulated. The effects of ambient wind direction, wind speed, leakage mass flow rate, and the mass fraction of gas phase at the leakage port on the diffusion behavior of the liquid hydrogen leakage were investigated. The results show that the ambient wind direction directly determines the direction of liquid hydrogen leakage diffusion. The wind speed significantly affects the diffusion distance. When the wind speed is 6 m/s, the diffusion distance of the flammable hydrogen cloud reaches 40.08 m, which is 2.63 times that under windless conditions. The liquid hydrogen leakage mass flow rate and the mass fraction of the gas phase have a greater effect on the volume of the flammable hydrogen cloud. As the leakage mass flow rate increased from 5.15 kg/s to 10 kg/s, the flammable hydrogen cloud volume increased from 5734.31 m3 to 10,305.5 m3. The installation of a barrier wall in front of the leakage port can limit the horizontal diffusion of the flammable hydrogen cloud, elevate the diffusion height, and effectively reduce the volume of the flammable hydrogen cloud. This study can provide theoretical support for the construction and operation of hydrogen production stations.

The paper is devoted to the comparative analysis of different CFD techniques used to solve the problem of high-pressure hydrogen release into the air. Three variations of a contemporary low-dissipation numerical technique (CABARET) are compared with each other and a conventional first-order numerical scheme. It is shown that low dissipation of the numerical scheme defines better resolution of the contact surface between released hydrogen and ambient air. As a result, the spatial structures of the jet and the reaction wave that arise during self-ignition are better resolved, which is useful for predicting the local effects of high-pressure hydrogen release. At the same time, the dissipation has little effect on the induction delay, so critical conditions of self-ignition can be reliably reproduced even via conventional numerical schemes. The test problem setups formulated in the paper can be used as benchmarks for compressible CFD solvers.

Risk assessment of hydrogen energy technologies is a necessary condition for the arrival of a hydrogen energy economy society. Currently, most methods for detecting hydrogen leaks use a single concentration or pressure sensor. Structural visualization and parametric diagnosis of complex flow fields cannot be solved simultaneously by a single detection method. The main objective of this work is to propose an advanced optical detection method to simultaneously monitor the outlet pressure and density field distribution during hydrogen leakage. For the detection of the density field distribution, we use double propagation of the laser beam in the hydrogen jet to improve the phase sensitivity and relay imaging of the object between each pass to maintain spatial resolution. Error analysis shows that the error of our proposed method is 2.47 %, which is within the error tolerance. The sensitivity analysis shows that our detection sensitivity is twice that of the conventional Mach-Zehnder interferometer. For the detection of outlet pressure, we propose a mathematical model in which the half-length axis of the laser spot is linearly related to the outlet pressure and use the deformation of the laser beam in the hydrogen jet to detect the outlet pressure. The results show that the hydrogen jet can be regarded as a gas-phase lens when detecting the outlet pressure, and the deformation of the laser beam profile in the horizontal direction increases linearly with the increase of the jet pressure. The results of the study can provide a reference for the detection of accidental hydrogen leakage and the improvement of hydrogen safety regulations. [ABSTRACT FROM AUTHOR]

Hydrogen leakage concentration rapid measurement is the key issue for hydrogen application as hydrogen leakage is easy to cause hydrogen safety issues such as hydrogen explosions. Non-invasive visual measurement method such as the schlieren measurement technique is the prospective solution. However, the specific relationship between the hydrogen leakage concentration and schlieren image gray remains unclear, which leads that the schlieren technique procedure is developed for visualization and acquiring qualitative information only. This paper aims to decouple the hydrogen leakage concentration from the complicated schlieren image information, and find the mapping relationship between the hydrogen leakage concentration and schlieren image gray, hence realizing a quantitative hydrogen leakage concentration analysis. Therefore, a hydrogen leakage visualization experimental bench is established to simulate and measure hydrogen leakage by a series of experiments under different leakage concentrations. The mapping relationship between the hydrogen leakage concentration and schlieren image gray is obtained by the experiments using the schlieren technique. Then, a new calibration schlieren technique with the function of visually measuring hydrogen leakage concentration is developed and verified under 80% hydrogen leakage concentration. Results of the trials demonstrated the ability of the proposed technique successfully measure concentration distributions with satisfactory accuracy. • The relationship between hydrogen concentration and schlieren image gray is decoupled. • A new calibration schlieren method is proposed to measure the hydrogen concentration. • A hydrogen visualization experimental bench is established for results verification. • A series of visualization experiments are studied to summarize the distribution rules. [ABSTRACT FROM AUTHOR]

As the applications of hydrogen as a replacement for fossil fuels and energy storage increase, more concerns have been raised regarding its safe usage. Hydrogen's extreme physical properties—its lower flammability limit (LFL), for instance—represent a challenge to simulating hydrogen leakage and, hence, mitigating accidents that occur due to such leakage. In this work, the OpenFOAM-based CFD simulation package containmentFOAM was validated by different experimental results. As in its original use, to simulate nuclear safety issues, the containmentFOAM package is capable of capturing different phenomena, like buoyant gas clouds and diffusion between gases and air. Despite being widely validated in nuclear safety, this CFD package was assessed with benchmark experiments used to validate hydrogen leakage scenarios. The validation cases were selected to cover different phenomena that occur during the hydrogen leakage—high-speed jet leakage, for example. These validation cases were the hallway with vent, FLAME, and GAMELAN experiments. From the comparison of the experimental and simulation results, we concluded that the containmentFOAM package showed good consistency with the experimental results and, hence, that it can be used to simulate actual leakage cases. [ABSTRACT FROM AUTHOR]

Although green hydrogen is an appropriate clean energy alternative, hydrogen leakage and dispersion are the challenges to establishing safe and reliable hydrogen infrastructure. Released hydrogen in confined or semi-confined space may build up flammable gas clouds, which can have severe consequences for the safety of human life and property. Proper ventilation systems will help in reducing hydrogen gas accumulation. This study presents a comprehensive study to analyse hydrogen dispersion behaviour and the influence of ventilation variations on hydrogen volumetric concentration and stratification. A computational model is developed for the leakage diffusion of hydrogen in an enclosed cuboid space with roof and door ventilation. A detailed analysis is conducted to shed light on the impact of door and roof ventilation positions on forming the flammable cloud. It is observed that the displacement flow and multi-layer stratification are established in the absence of wind or imperceptible air circulation. Single-vent configurations were ineffective, when installed at the top of the leakage point, but multiple-vent arrangements incorporating door and roof vents were found to be more efficient in extracting hydrogen. However, it should be noted that not all multiple-vent arrangements may meet safety requirements. The result indicated that the optimal arrangement for minimizing the size of a flammable cloud involves placing the door vent close to the ceiling while situating the roof vent near the source of leakage. These findings will aid in devising strategies for minimizing the occurrence of flammable cloud formation and preventing hydrogen fire and explosion incidents within partially enclosed facilities. [ABSTRACT FROM AUTHOR]

This paper summarises the first results from the joint industry project (JIP) 'Risk-reduction for hydrogen installations by partial suppression of explosions' (HyRISE). The main objective of the project is to develop fundamental knowledge that can support the development of practical solutions for mitigating hydrogen explosions in congested and confined environments by means of active systems for chemical inhibition. The aim is not to extinguish the incipient flame, but rather to lower the reactivity of the fuel-air mixture prior to ignition, and thereby reduce the consequences of an accidental explosion to a tolerable level. The paper consists of three parts: a review of previous work on chemical inhibition of premixed hydrogen-air flames, simulations with the chemical kinetics software Cantera, and experiments conducted in a 20-litre explosion vessel. The results demonstrate that chemical inhibition can be effective for hydrogen-air mixtures. However, it remains to develop efficient inhibitors and practical systems that can be implemented in industrial facilities, with satisfactory performance over a wide range of hydrogen concentrations. [ABSTRACT FROM AUTHOR]

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In the context of reducing carbon dioxide (C O 2 ) emissions, hydrogen is gaining momentum as a possible fuel for Internal Combustion Engines (ICEs). In-cylinder direct injections allow for a higher specific power density while enabling different levels of charge stratification. The high-pressure injection leads to the onset of under-expanded jets, characterized by complex patterns of shock waves and expansion fans. In ICEs simulations, such physics needs to be correctly solved to obtain a reliable assessment of the mixture formation. In this paper, the main features of hydrogen under-expanded jets are examined under the conditions typically found in turbocharged engines. Improved correlations are provided for the assessment of the Mach disk height and diameter, up to a Nozzle Pressure Ratio (NPR) equal to 60. The dependency of the hydrogen-air mixing on the cylinder temperature has been analyzed, and the unsteady jet dynamics has been examined by continuously varying the combustion chamber pressure. To the authors' knowledge, no studies of this kind can be found in the literature for the specific case of hydrogen. Lastly, a preliminary investigation of the jet-jet interaction (a Coanda-like effect) is reported. This phenomenon is observable when multi-hole injectors are employed, and it may have a great impact on the mixture formation. [ABSTRACT FROM AUTHOR]

Helium is getting more and more difficult to obtain, and it does not look like that will change anytime soon. The only alternative carrier gas to helium that Agilent recommends for gas chromatography mass spectrometry is hydrogen. Converting a gas chromatograph mass spectrometer (GCMS) to use hydrogen presents additional safety concerns and may not be possible for some systems. Helium conservation, having the GCMS system use nitrogen as a carrier gas when idle, may be a viable alternative when conversion to hydrogen is not possible. [ABSTRACT FROM AUTHOR]

Hydrogen energy has become a pivotal actor in achieving carbon neutrality by 2050 in the era of the climate crisis. Regardless of its importance, three consecutive hydrogen safety accidents and their aftermath in South Korea have aggravated the public's acceptance of hydrogen. Hydrogen-induced risks have always existed in our society regardless of technical improvement. Here, the task of the government is to manage the hydrogen risk to prevent hydrogen disasters. This study included three steps in its research design; 1) selecting experts through snowball sampling, 2) conducting a qualitative email survey, and 3) analyzing the qualitative answer sheet by applying semantic network analysis. We found that experts' evaluations of the Korean hydrogen PR policy were positive regarding responsiveness but negative regarding openness, guidelines, and control tower. Therefore, we suggest practical policy recommendations; the central government should play an important role in cultivating professional crisis management PR personnel and others. [Display omitted] • Experts positively evaluate the responsiveness of hydrogen PR policies in Korea. • Yet, experts negatively evaluate policy openness, guidelines, and control tower. • The government should improve communication about hydrogen technology. • The government needs to cultivate professional crisis management PR personnel. [ABSTRACT FROM AUTHOR]

Hydrogen has the potential to produce energy with no emissions, and therefore offers a strategic opportunity for rapid development of renewable energy storage. However, jet flames caused by the leakage of high-pressure hydrogen may cause casualties and damage equipment, so the safety issues associated with hydrogen incidents are a key issue restricting its development. Barrier walls can be an important mitigative action to reduce the hazard of hydrogen jet flames. Previous studies have evaluated the protective effect of different vertical or inclined arrangements of a single barrier wall in the vertical direction. However, in the vertical direction, a single barrier wall is not sufficient to reduce the hazards associated with high-pressure hydrogen jet flames. In this paper, a two-dimensional CFD model of high-pressure hydrogen jet flames are established. A simplified form of the hydrogen real gas equation of state is used to describe the complex behavior of high-pressure hydrogen. This CFD study employs the standard k-ε turbulence model, the eddy dissipation concept (EDC) model, and the discrete ordinate (DO) radiation model. The results display good agreement with the experimentally obtained flame shape and thermal radiation values, which confirms the applicability of the model. Based on this model, the characteristics of high-pressure jet flames are systematically studied under different forms of barrier walls and different pressures of hydrogen storage. Compared with the vertical barrier wall, barrier walls with complex structures can block the flames in front of the wall more effectively. This is proven through a remarkable decline in the vertical flame length and a reduction in the high temperature area. Comparing the five barrier wall patterns for their combined flame shape and flame temperature, it is more preferred to choose 60° Plate. The results of this study will help to better analyze the consequences of hydrogen jet flames and provide guidance for better design of barrier walls for mitigation. [ABSTRACT FROM AUTHOR]

As a carbon-free fuel, hydrogen has received significant attention recently since it can help enable low-carbon-economy. Hydrogen has very broad flammability range and very low minimum ignition energy, and thereby there are severe safety concerns for hydrogen transportation and utilization. Cryo-compressed hydrogen is popularly used in practice. Therefore, it is necessary to investigate the combustion properties of hydrogen at extremely low or cryogenic temperatures. This study aims to assess and interpret the effects of cryogenic temperature on premixed hydrogen/air flame propagation and acceleration in a thin closed channel. Different initial temperatures ranging from normal temperature (T 0 = 300 K) to cryogenic temperature (T 0 = 100 K) are considered. Both one- and two-dimensional hydrogen/air flames are investigated through transient simulations considering detailed chemistry and transport. It is found that when the initial temperature decreases from T 0 = 300 K to T 0 = 100 K, the expansion ratio and equilibrium pressure both increase substantially while the laminar flame speeds relative to unburned and burned gasses decrease moderately. The one-dimensional flame propagation is determined by laminar flame speed and thereby the combustion duration increases as the initial temperature decreases. However, the opposite trend is found to happen to two-dimensional flame propagation, which is mainly controlled by the flame surface area increase due to the no-slip side wall constraint and flame instability. Based on the change in flame surface area, three stages including the initial acceleration, steady burning and rapid acceleration are identified and investigated. It is demonstrated that the large expansion ratio and high pressure rise at cryogenic temperatures can significantly increase the flame surface area in early stage and promote both Darrieus-Landau instability (hydrodynamic instability) and Rayleigh-Taylor instability in later stage. These two instabilities can substantially increase the flame surface area and thereby accelerate flame propagation in hydrogen/air mixtures at cryogenic temperatures. The present study provides useful insights into the fundamental physics of hydrogen flames at extremely low temperatures, and is closely related to hydrogen safety. [ABSTRACT FROM AUTHOR]