Safety

Hydrogen embrittlement (HE) remains a pressing issue in materials science and engineering given its significant impact on the structural integrity of metals and alloys. This exhaustive review aims to thoroughly examine HE covering a range of aspects that collectively enhance our understanding of this intricate phenomenon. It proceeds to investigate the varied effects of hydrogen on metals illustrating its ability to profoundly alter mechanical properties thereby increasing vulnerability to fractures and failures. A crucial section of the review delves into how different metals and their alloys exhibit unique responses to hydrogen exposure shedding light on their distinct behaviors. This knowledge is essential for customizing materials to specific applications and ensuring structural dependability. Additionally the paper explores a diverse array of models and classifications of HE offering a structured framework for comprehending its complexities. These models play a crucial role in forecasting preventing and mitigating HE across various domains ranging from industrial settings to critical infrastructure.

Canada’s commitment to be net-zero by 2050 combined with ATCO’s own Environmental Social and Governance goals has led ATCO to pursue hydrogen blending within the existing natural gas system to reduce CO2 emissions while continuing to provide safe reliable energy service to customers. Utilization of hydrogen in the distribution system is the least-cost alternative for decarbonizing the heating loads in jurisdictions like Alberta where harsh winter climates are encountered and low-carbon hydrogen production can be abundant. ATCO’s own Fort Saskatchewan Hydrogen Blending Project began blending 5% hydrogen by volume to over 2100 customers in the Fall of 2022 and plans to increase the blend rates to 20% hydrogen in 2023. Prior to blending ATCO worked together with DNV to examine the impact of hydrogen blended natural gas to twelve Canadian appliances: range/stove oven garage heater high and medium efficiency furnaces conventional and on demand hot water heaters barbeque clothes dryer radiant heater and two gas fireplaces. The tests were performed not only within the planned blend rates of 0-20% hydrogen but also to higher percentages to determine how much hydrogen can be blended into a system before appliance retrofits would be required. The testing was designed to get insights on safety-related combustion issues such as flash-back burner overheating flame detection and other performance parameters such as emissions and burner power. The experimental results indicate that the radiant heater is the most sensitive appliance for flashback observed at 30 vol% hydrogen in natural gas. At 50% hydrogen the range and the radiant burner of the barbeque tested were found to be sensitive to flashback. All other 9 appliances were found to be robust for flashback with no other short-term issues observed. This paper will detail the findings of ATCO and DNV’s appliance testing program including results on failure mechanisms and sensitivities for each appliance.

To contribute to a more diverse and efficient energy infrastructure large quantities of hydrogen are requested for industries (e.g. mining refining fertilizers…). These applications need large scale facilities such as dozens of electrolyzer stacks from atmospheric pressure to 30 bar with a total capacity ranging from 100 up to 400 MW and associated hydrogen storage from a few to 50 tons.

Local use can be fed by electrolyzer in 20 feet container and stored in bundles with small volumes. Nevertheless industrial applications can request much bigger capacity of production which are generally located in buildings. The different technologies available for the production of hydrogen at large scale are alkaline or PEM electrolyzer with for example 100 MW capacity in a building of 20000 m3 and hydrogen stored in tube trailers or other fixed hydrogen storage solution with large volumes.

These applications led to the use of hydrogen inside large but confined spaces with the risk of fire and explosion in case of loss of containment followed by ignition. This can lead to severe consequences on asset workers and public due to the large inventories of hydrogen handled.

This article aims to provide an overview of the strategy to safely design large scale hydrogen production facilities in buildings through benchmarks based on projects and literature reviews best practices & standards regulations. It is completed by a risk assessment taking into consideration hydrogen behavior and influence of different parameters in dispersion and explosion in large buildings.

This article provides recommendations for hydrogen project stakeholders to perform informed-based decisions for designing large scale production buildings. It includes safety measures as reducing hydrogen inventories inside building allocating clearance around electrolyzer stacks implementing early detection and isolation devices and building geometry to avoid hydrogen accumulation.

We combine state-of-the-art thermo-metallurgical welding process modeling with coupled diffusion-elastic– plastic phase field fracture simulations to predict the failure states of hydrogen transport pipelines. This enables quantitatively resolving residual stress states and the role of brittle hard regions of the weld such as the heat affected zone (HAZ). Failure pressures can be efficiently quantified as a function of asset state (existing defects) materials and weld procedures adopted and hydrogen purity. Importantly simulations spanning numerous relevant conditions (defect size and orientations) are used to build Virtual Failure Assessment Diagrams (FADs) enabling a straightforward uptake of this mechanistic approach in fitness-for-service assessment. Model predictions are in very good agreement with FAD approaches from the standards but show that the latter are not conservative when resolving the heterogeneous nature of the weld microstructure. Appropriate mechanistic FAD safety factors are established that account for the role of residual stresses and hard brittle weld regions.

The publication presents methods and pre-test results of a stand for testing CHSS in terms of resistance to open fire. The basis for the conducted research is the applicable provisions contained in the UN/ECE Regulation R134. The study includes an overview of contemporary solutions for hydrogen storage systems in high-pressure tanks in means of transport. Development in this area is a response to the challenge of reducing global carbon dioxide emissions and limiting the emissions of toxic compounds. The variety of storage systems used is driven by constraints including energy demand and available space. New tank designs and conducted tests allow for an improvement in systems in terms of their functionality and safety. Today the advancement of modern technologies for producing high-pressure tanks allows for the use of working pressures up to 70 MPa. The main goal of the presented research is to present the requirements and research methodology verifying the tank structure and the security systems used in open-fire conditions. These tests are the final stage of the approval process for individual pressure vessels or complete hydrogen storage systems. Their essence is to eliminate the occurrence of an explosion in the event of a fire.

The development of liquid hydrogen storage systems is a key aspect to enable future clean air transportation. However safety analysis research for such systems is still limited and is hindered by the limited experience with liquid hydrogen storage in aviation. This paper presents the outcomes of a preliminary safety assessment applied to this new type of storage system accounting for the hazards of hydrogen. The methodology developed is based on hazard identification and frequency evaluation across all system features to identify the most critical safety concerns. Based on the safety assessment a set of safety recommendations concerning different subsystems of the liquid hydrogen storage system is proposed identifying hazard scopes and necessary mitigation actions across various system domains. The presented approach has been proven to be suitable for identifying essential liquid hydrogen hazards despite the novelty of the technology and for providing systematic design recommendations at a relatively early design stage.

Hydrogen is a promising carbon-free energy carrier for large-scale applications yet its adoption faces unique safety challenges. Microscopic physicochemical properties such as high diffusivity low ignition energy and distinct chemical pathways alter the safety of hydrogen systems. Analyzing the HIAD 2.0 incident database an occurrence-based review of past hydrogen incidents shows that 59% arise from general industrial failures common to other hydrocarbon carrier systems. Of the remaining 41% only 15% are unequivocally linked to the fuel’s unique properties. This study systematically isolates hazards driven by hydrogen’s intrinsic properties by filtering out confounding factors and provides an original clear characterization of the different failure mechanisms of hydrogen systems. These hydrogen-specific cases are often poorly described limiting their contribution to safety strategies and regulations improvement. A case study on pipeline failures illustrates how distinguishing hydrogen-specific hazards supports targeted risk mitigation. The findings highlight the need for evidence-based regulation over broadly precautionary approaches.

The increasing adoption of liquid hydrogen (LH2) as a clean energy carrier presents significant safety challenges particularly in confined underground spaces like tunnels. LH2′s unique properties including high energy density and cryogenic temperatures amplify the risks of leaks and explosions which can lead to catastrophic overpressures and extreme temperatures. This study addresses these challenges by investigating the diffusion and explosion behaviour of LH2 leaks in tunnels providing critical insights into disaster prevention and structural resilience for underground infrastructure. Using advanced numerical simulations validated through theoretical calculations and experimental analogies the study analyses hydrogen diffusion patterns overpressure dynamics and thermal impacts following an LH2 tank rupture. Results show that LH2 explosions generate overpressures exceeding 50 bar and temperatures surpassing 2500 ◦C far exceeding the hazards posed by gaseous hydrogen leaks. Mitigation measures such as suction ventilation and high humidity significantly reduce explosion impacts underscoring their value for tunnel safety. This research advances understanding of hydrogen safety in confined spaces demonstrating the importance of integrating mitigation measures into tunnel design. The findings contribute to disaster prevention strategies offer insights into optimizing safety protocols and support the development of resilient infrastructure capable of accommodating hydrogen technologies in a rapidly evolving energy landscape.

Numerical simulations reveal the combustion dynamics of hydrogen-blended natural gas (H-BNG) in semi-open spaces. In the typical semi-open space scenario increasing the hydrogen blending ratio from 0% to 60% elevates peak internal pressure by 107% (259.3 kPa → 526.0 kPa) while reducing pressure rise time by 56.5% (95.8 ms → 41.7 ms). A vent size paradox emerges: 0.5 m openings generate 574.6 kPa internal overpressure whereas 2 m openings produce 36.7 kPa external overpressure. Flame propagation exhibits stabilized velocity decay (836 m/s → 154 m/s 81.6% reduction) at hydrogen concentrations ≥30% within 2–8 m distances. In street-front restaurant scenarios 80% H-BNG leaks reach alarm concentration (0.8 m height) within 120 s with sensor response times ranging from 21.6 s (proximal) to 40.2 s (distal). Forced ventilation reduces hazard duration by 8.6% (151 s → 138 s) while door status shows negligible impact on deflagration consequences (412 kPa closed vs. 409 kPa open) maintaining consistent 20.5 m hazard radius at 20 kPa overpressure threshold. These findings provide crucial theoretical insights and practical guidance for the prevention and management of H-BNG leakage and explosion incidents.

The use of hydrogen as fuel presents many safety challenges due to its flammability and explosive nature combined with its lack of color taste and odor. The purpose of this paper is to present an electrochemical sensor that can achieve rapid and accurate detection of hydrogen leakage. This paper presents both the component elements of the sensor like sensing material sensing element and signal conditioning as well as the electronic protection and signaling module of the critical concentrations of H2. The sensing material consists of a catalyst type Vulcan XC72 40% Pt from FuelCellStore (Bryan TX USA). The sensing element is based on a membrane electrode assembly (MEA) system that includes a cathode electrode an ion-conducting membrane type Nafion 117 from FuelCellStore (Bryan TX USA). and an anode electrode mounted in a coin cell type CR2016 from Xiamen Tob New Energy Technology Co. Ltd (Xiamen City Fujian Province China). The electronic block for electrical signal conditioning which is delivered by the sensing element uses an INA111 from Burr-Brown by Texas Instruments Corporation (Dallas TX USA). instrumentation operational amplifier. The main characteristics of the electrochemical sensor for hydrogen leakage detection are operation at room temperature so it does not require a heater maximum amperometric response time of 1 s fast recovery time of maximum 1 s and extended range of hydrogen concentrations detection in a range of up to 20%.

Hydrogen is a sustainable clean source of energy and a viable alternative to carbon-based fossil fuels. To support the transport sector’s transition from fossil fuels to hydrogen a hydrogen refuelling station network is being developed to refuel hydrogen-powered vehicles. However hydrogen’s inherent properties present a significant safety challenge and there have been several hydrogen incidents noted with severe impacts to people and assets reported from operational hydrogen refuelling stations worldwide. This paper presents the outcome of an analysis of hydrogen incidents that occurred at hydrogen refuelling stations. For this purpose the HIAD 2.1 and H2tool.org databases were used for the collection of hydrogen incidents. Forty-five incidents were reviewed and analysed to determine the frequent equipment failures in the hydrogen refuelling stations and the underlying causes. This study adopted a mixed research approach for the analysis of the incidents in the hydrogen refuelling stations. The analysis reveals that storage tank failures accounted for 40% of total reported incidents hydrogen dispenser failures accounted for 33% compressors accounted for 11% valves accounted for 9% and pipeline failures accounted for 7%. To enable the safe operation of hydrogen refuelling stations hazards must be understood effective barriers implemented and learning from past incidents incorporated into safety protocols to prevent future incidents.

To mitigate explosion hazards arising from hydrogen leakage and subsequent mixing with air the injection of inert gases can substantially diminish explosion risk. However prevailing research has predominantly characterized inert gas dilution effects on explosion behavior under quiescent conditions largely neglecting the turbulence-mediated explosion enhancement inherent to dynamic mixing scenarios. A comprehensive investigation was conducted on the combustion behavior of 30% 50% and 70% H2-air mixtures subjected to jet-induced (CO2 N2 He) turbulent flow incorporating quantitative characterization of both the evolving turbulent flow field and flame front dynamics. Research has demonstrated that both an increased H2 concentration and a higher jet medium molecular weight increase the turbulence intensity: the former reduces the mixture molecular weight to accelerate diffusion whereas the latter results in more pronounced disturbances from heavier molecules. In addition when CO2 serves as the jet medium a critical flame radius threshold emerges where the flame propagation velocity decreases below this threshold because CO2 dilution effects suppress combustion whereas exceeding it leads to enhanced propagation as initial disturbances become the dominant factor. Furthermore at reduced H2 concentrations (30–50%) flow disturbances induce flame front wrinkling while preserving the spherical geometry; conversely at 70% H2 substantial flame deformation occurs because of the inverse correlation between the laminar burning velocity and flame instability governing this transition. Through systematic quantitative analysis this study elucidates the evolutionary patterns of both turbulent fields and flame fronts offering groundbreaking perspectives on H2 combustion and explosion propagation in turbulent environments.

With the global expansion of hydrogen infrastructure the safe and efficient transportation of hydrogen is becoming more important. In this study several technical factors including material degradation pressure variations and monitoring effectiveness that influence hydrogen transportation using pipelines are examined using system dynamics. The results show that hydrogen embrittlement which is the result of microstructural trapping and limited diffusion in certain steels can have a profound effect on pipeline integrity. Material incompatibility and pressure fluctuations deepen fatigue damage and leakage risk. Moreover pipeline monitoring inefficiency combined with hydrogen’s high flammability and diffusivity can raise serious safety issues. An 80% decrease in monitoring efficiency will result in a 52% reduction in the total hydrogen provided to the end users. On the other hand technical risks such as pressure fluctuations and material weakening from hydrogen embrittlement also affect overall system performance. It is essential to understand that real-time detection using hydrogen monitoring is particularly important and will lower the risk of leakage. It is crucial to know where hydrogen is lost and how it impacts transport efficiency. The model offers practical insights for developing stronger and more reliable hydrogen transport systems thereby supporting the transition to a low-carbon energy future.

The MultHyFuel project aims to develop evidence-based guidelines for the safe implementation of Hydrogen Refueling Stations (HRS) in a multi-fuel context. As a part of the generation of good practice guidelines for HRS Hazardous Area Classification (HAC) methodologies were analyzed and applied to case studies representing example configurations of HRS. It has been anticipated that Negligible Extent (NE) classifications might be applicable for sections of the HRS for instance a hydrogen generator. A NE zone requires that an ignition of a flammable cloud would result in negligible consequences. In addition depending on the pressure of the system IEC 60079-10-1:2020 establishes specific requirements in order to classify the hazardous area as being of NE. One such requirement is that a zone of NE shall not be applied for releases from flammable gas systems at pressures above 2000 kPag (20 barg) unless a specific detailed risk assessment is documented. However there is no definition within the standard as to the requirements of the specific detailed risk assessment. In this work an example for a specific detailed risk assessment for the NE classification is presented:<br/>• Firstly the requirements of cloud volume dilution and background concentration for a zone of NE classification from IEC 60079-10-1:2020 are analyzed for hydrogen releases from equipment placed in a mechanically ventilated enclosure.<br/>• Secondly the consequences arising from the ignition of the localized cloud are estimated and compared to acceptable harm criteria in order to assess if negligible consequences are obtained from the scenario.<br/>• In addition a specific qualitative risk assessment for the ignition of the cloud in the enclosure was considered incorporating the estimated consequences and analyzing the available safeguards in the example system.<br/>Recommendations for the specific detailed risk assessment are proposed for this scenario with the intention to support improved definition of the requirement in future revisions of IEC 60079-10-1.

In the present study pilot simulations of the phenomena of blast wave and fireball generated by the rupture of a high-pressure (35 MPa) hydrogen tank (volume 72 L) due to fire were carried out. The computational fluid dynamics (CFD) model includes the realizable k-ε model for turbulence and the eddy dissipation model coupled with the one-step chemical reaction mechanism for combustion. The simulation results were compared with experimental data on a stand-alone hydrogen tank rupture in a bonfire test. The simulations provided insights into the interaction between the blast wave propagation and combustion process. The simulated blast wave decay is approximately identical to the experimental data concerning pressure at various distances. Fireball is first ignited at the ground level which is considered to be due to stagnation flow conditions. Subsequently the flame propagates toward the interface between hydrogen and air.

A sudden release of compressed gases and the formation of a jet flow can occur in nature and various engineering applications. In particular high-pressure hydrogen jets can spontaneously ignite when released into an environment that contains oxygen. For some scenarios these high-pressure hydrogen jets can be released into a mixture containing hydrogen and oxygen. This scenario can possibly lead to a wide range of combustion regimes such as jet flames slow or fast deflagrations or even hazardous detonations. Each combustion regime is characterized by typical pressures and temperatures however fast transition between regimes is also possible.<br/>A common project between Tel Aviv University (TAU) Nuclear Research Center Negev (NRCN) and Commissariat à l’Energie Atomique et aux énergies alternatives (CEA) has been recently launched in order to understand these phenomena from experimental modelling and numerical points of view. The main goal is to investigate the dynamics and combustion regimes that arise once a pressurized hydrogen jet is released into a reactive environment that contains inhomogeneous concentrations of hydrogen steam and air.<br/>In this paper we present the first numerical results describing high-pressure hydrogen release obtained using a massively parallel compressible structured-grid flow solver. The experimental arrangements devoted to this phenomenon will also be described.

In the past few years CEA has been fully involved at both experimental and modeling levels in projects related to hydrogen safety in nuclear and chemical industries and has carried out a test program using the experimental bench SSEXHY (Structure Submitted to an EXplosion of HYdrogen) in order to build a database of the deformations of simple structures following an internal hydrogen explosion. Different propagation regimes of explosions were studied varying from detonations to slow deflagrations.<br/>During the experimental campaign it was found that high-speed deflagrations corresponding to relatively poor hydrogen-air mixtures resulted in higher specimen deformation compared to those related to detonations of nearly stoichiometric mixtures. This paper explains this counter-intuitive result from qualitative and quantitative points of view. It is shown that the overpressure and impulse from head-on reflections of hydrogen flames corresponding to poor mixtures of specific concentrations could have very high values at the tube end.

As a key link in the application of hydrogen energy hydrogen refueling stations are significant for their safe operation. This paper established a three-dimensional 1:1 model for a seaport hydrogen refueling station in Ningbo City. In this work the CFD software FLUENT was used to study the influence of leakage angles on the leakage of high-pressure hydrogen through a small hole. Considering the calculation accuracy and efficiency this paper adopted the pseudo-diameter model. When the obstacle was far from the leakage hole it had almost no obstructive effect on the jet's main body. Still it affected the hydrogen whose momentum in the outer layer of the jet has been significantly decayed. In this condition there would be more hydrogen in stagnation. Thus the volume of the flammable hydrogen cloud was hardly affected while there was a significant increase in the volume of the hazardous hydrogen cloud. When the obstacle was close to the leakage hole it directly affected the jet's main body. Therefore the volume of the flammable hydrogen cloud increased. However the air impeded the hydrogen jet relatively less because the hydrogen jet contacted the obstacle more quickly. The hydrogen jet blocked by the obstacle still has some momentum. Therefore there was no more hydrogen in stagnation and no significant increase in the volume of the hazardous hydrogen cloud.

The integration of hydrogen energy systems into nearly zero-emission buildings (nZEB) is emerging as a viable strategy to curtail greenhouse gas emissions associated with energy use in these buildings. However the indoor or outdoor placement of certain hydrogen system components or equipment necessitates stringent safety measures particularly in confined environments. This study aims to investigate the dynamics of hydrogen dispersion within an enclosure featuring forced ventilation analyzing the interplay between leakage flow rates and ventilation efficiency both experimentally and numerically. To simulate hydrogen's behavior helium gas which shares similar physical characteristics with hydrogen was utilized in experiments conducted at leakage flows of 4 8 and 10 L/min alongside a ventilation rate of 30 air changes per hour (ACH). The experiments revealed that irrespective of the leakage rate the oxygen concentration returned to its initial level approximately 11 min post-leakage at a ventilation rate of 30 ACH. This study also encompasses a numerical analysis to validate the experimental findings and assess the congruence between helium and hydrogen behaviors. Additionally the impact of varying ACH rates (30 45 60 75) on the concentrations of oxygen and hydrogen was quantified through numerical analysis for different hydrogen leakage rates (4 8 10 20 L/min). The insights derived from this research offer valuable guidance for building facility engineers on designing ventilation systems that ensure hydrogen and oxygen concentrations remain within safe limits in hydrogen-utilizing indoor environments.

With increasing global interest in molecular hydrogen to replace fossil fuels more attention is being paid to potential leakages of hydrogen into the atmosphere and its environmental consequences. Hydrogen is not directly a greenhouse gas but its chemical reactions change the abundances of the greenhouse gases methane ozone and stratospheric water vapor as well as aerosols. Here we use a model ensemble of five global atmospheric chemistry models to estimate the 100-year time-horizon Global Warming Potential (GWP100) of hydrogen. We estimate a hydrogen GWP100 of 11.6 ± 2.8 (one standard deviation). The uncertainty range covers soil uptake photochemical production of hydrogen the lifetimes of hydrogen and methane and the hydroxyl radical feedback on methane and hydrogen. The hydrogeninduced changes are robust across the different models. It will be important to keep hydrogen leakages at a minimum to accomplish the benefits of switching to a hydrogen economy.

In South Korea securing ground space for installing hydrogen refueling stations in urban areas is challenging due to limited ground space and high-density development. Safety concerns for hydrogen systems in enclosed urban environments also require careful consideration. To address this issue this study explored a method of undergrounding hydrogen infrastructure as a solution for urban hydrogen charging stations. This study examined the characteristics of hydrogen diffusion and concentration reduction under leakage conditions within a confined hydrogen infrastructure focusing on key safety systems including emergency shut-off valves (ESVs) and ventilation fans. We discovered that the ESV reduced hydrogen concentration by over 80%. Installing two or more ventilation fans arranged horizontally improves airflow and enhances ventilation efficiency. Moreover increasing the number of fans reduces stagnant zones within the space effectively lowering the average hydrogen concentration.

Hydrogen leakage in Proton Exchange Membrane (PEM) fuel cells poses critical safety efficiency and operational reliability risks. This study introduces an innovative infrared (IR) thermography-based methodology for detecting and quantifying hydrogen leaks towards the outside of PEM fuel cells. The proposed method leverages the catalytic properties of a membrane electrode assembly (MEA) as an active thermal tracer facilitating real-time visualisation and assessment of hydrogen leaks. Experimental tests were conducted on a single-cell PEM fuel cell equipped with intact and defective gaskets to evaluate the method’s effectiveness. Results indicate that the active tracer generates distinct thermal signatures proportional to the leakage rate overcoming the limitations of hydrogen’s low IR emissivity. Comparative analysis with passive tracers and baseline configurations highlights the active tracer-based approach’s superior positional accuracy and sensitivity. Additionally the method aligns detected thermal anomalies with defect locations validated through pressure distribution maps. This novel non-invasive technique offers precise reliable and scalable solutions for hydrogen leak detection making it suitable for dynamic operational environments and industrial applications. The findings significantly advance hydrogen’s safety diagnostics supporting the broader adoption of hydrogen-based energy systems.

Green hydrogen is a promising energy vector for industrial applications. However hydrogen leaks can occur causing greenhouse effects and posing safety risks for operators and local communities potentially leading to legal liabilities. Industry 4.0 focuses on digital industrial modernization while Industry 5.0 emphasizes collaborative humancentered and sustainable processes. This study developed and analyzed an Industry 5.0 proof of concept as an additional safety layer for hydrogen leak management. The proof of concept was implemented using Raspberry Pi microcomputers integrated computer vision and OpenAI GPT-3 for dynamic email communication. A legal liability analysis for Chile and Spain identified potential challenges in transitioning the system into a marketready product. The findings suggest the system should act as a complementary safety layer rather than a primary detection system to mitigate legal liability risks as operational deployment without full certification and validation could lead to malfunctions. This study illustrated how hydrogen detection and management can be integrated into Industry 5.0 smart systems. With growing global interest in sustainable engineering and AI regulation as reflected in Regulation (EU) 2024/1689 legal considerations over technologies like the one presented in this study are becoming increasingly relevant.

The transition from fossil fuels to the renewable energies (wind solar) is a key factor to face climate change and build a sustainable reliable and secure energy system. To balance the intermittent energy demand and supply affecting the renewable sources the surplus of electrical energy may be converted in hydrogen and then storage in geological formations. While the risks associated to the natural gas storage in the sub-surface are well known from decades those associated with hydrogen underground storage (UHS) are relatively underexplored. This paper presents an inventory of risks related to large H2-storage in depleted gas and oil fields salt caverns and aquifers. Different issues such as integrity and durability of materials H2 leakages and interaction with the reservoir H2 uncontrolled outflow from the wellhead with potential combustion of air-hydrogen mixture (fire and explosion) soil subsidence and induced seismicity are analyzed.

Following the growing use of hydrogen in the industry gas explosions have become a critical safety issue. Computational Fluid Dynamic (CFD) and in particular the Large Eddy Simulation (LES) approach have already shown their great potential to reproduce such scenarios with high fidelity. However the computational cost of this approach is an obvious limiting factor since fine grid resolutions are often required in the whole computational domain to ensure a correct numerical resolution of the deflagration front all along its propagation. In this context Adaptive Mesh Refinement (AMR) is of great interest to reduce the computational cost as it allows to dynamically refine the mesh throughout the explosion scenario only in regions where Quantities of Interest (QoI) are detected. This study aims to demonstrate the strong potential of AMR for the LES of explosions. The target scenario is a hydrogen-air explosion in the GraVent explosion channel [1]. Using the massively parallel Navier- Stokes compressible solver AVBP a reference simulation is first obtained on a uniform and static unstructured mesh. The comparison with the experiments shows a good agreement in terms of absolute flame front speed overpressure and flow visualisation. Then an AMR simulation is performed targeting the same resolution as the reference simulation only in regions where QoI are detected i.e. inside the reaction zones and vortical structures. Results show that the accuracy of the reference simulation is recovered with AMR for only 12% of its computational cost.