Safety

Global warming is an accepted fact of life on Earth posing grave consequences in the form of weather patterns with life-threatening outcomes for inhabitants and their cultures especially those of island countries. These wild and unpredictable weather patterns have persuaded authorities governments and industrial leaders to adapt a range of solutions to combat the temperature rise on Earth. One such solution is to abandon fossil fuels (hydrocarbons) for energy generation and employ renewable energy sources or at least use energy sources that do not generate greenhouse gases. One such energy carrier is hydrogen which is expected to slowly replace natural gas and will soon be pumped into the energy distribution pipeline network. Since the current energy distribution network was designed for hydrocarbons its use for hydrogen may pose some threat to the safety of urban society. This is the first time an overview article has examined the replacement of hydrocarbons by hydrogen from a totally different angle by incorporating material science viewpoints. This article discusses hydrogen properties and warns about the issue of hydrogen embrittlement in the current pipeline network if hydrogen is to be pumped through the current energy distribution network i.e. pipelines. It is recommended that sufficient study and research be planned and carried out to ensure the safety of using the current energy distribution network for hydrogen distribution and to set the necessary standards and procedures for future design and construction.

Hydrogen offers the UK a unique opportunity to deliver on our Net Zero ambitions enabling deep decarbonisation of the parts of the energy system that are challenging to electrify balancing the energy system by providing large scale long duration energy storage and reducing pressure on electricity infrastructure. The UK Government in recognition of the centrality of hydrogen to the future energy system has set a 10GW hydrogen production ambition to be achieved by 2030. This ambition and its supporting policies such as the Hydrogen Business Model the Low Carbon Hydrogen Standard and the Hydrogen Transport and Storage Business Models will unlock private sector investment and kick-start the UK’s hydrogen activity. Encouragingly the UK has a positive track record of deploying low carbon technologies. The  combination of the UK’s world leading policies and incentive schemes alongside a vibrant  Research Development and Innovation (RD&I)  and engineering environment has enabled rapid  deployment of technologies such as offshore wind  and electric vehicles. Yet despite being world leaders  in deployment early opportunities for regional  supply chain growth and job creation were not fully  realised and taken advantage of from inception. The  hydrogen sector is therefore at a tipping point. To  capitalise on the economic opportunity hydrogen  offers the UK must learn from prior technology  deployments and build a strong domestic hydrogen  supply chain in parallel to championing deployment.

Hydrogen is unique amongst low carbon  technologies. It represents a significant economic  opportunity with future hydrogen markets estimated  by the Hydrogen Innovation Initiative to be worth  $8tn and hydrogen technology markets estimated to reach $1tn by 20501 but crucially it is also still a nascent market. Unlike many other low carbon technologies where supply chains are already well established hydrogen supply chains are embryonic meaning that the UK has an opportunity to anchor these supply chains here and establish itself as a global leader.

The UK is well placed to capitalise on this opportunity with favourable geography and geology  that enables us to produce and store hydrogen cost effectively coupled with a strong pipeline of hydrogen projects a stable policy environment that is attractive to investors and a wealth of transferable skills and expertise from the oil and gas industry.

We must ensure that alongside our focus on deployment we are also investing in technology and supply chains. Not only will this deliver exponential economic benefits from the projects supported by Government but it will also enable us to tackle increasing global supply chain constraints. Hydrogen UK estimated in its Economic Impact Assessment that hydrogen could deliver 30000 jobs annually and £7bn of GVA by 2030

It is important to be targeted and strategic in our investment and activities and recognise that hydrogen represents a wide range of technologies and the UK should not expect to lead in every area. Hydrogen UK with the support of the Hydrogen Delivery Council has undertaken analysis of the hydrogen value chain building on UK strengths and identifying the high value items that can deliver significant impact and benefit to the UK. We have also conducted widespread engagement with project developers to identify the barriers to utilising UK technology in projects and with technology developers to identify the challenges and barriers to investing and siting development and manufacturing in the UK.

The report can be found on Hydrogen UK's website.

Proton exchange membrane electrolyzer cell (PEMEC) will play a central role in future power-to-H2 plants. Current research focuses on the materials and operation parameters. Setting up experiments to explore operational accident scenarios about safety feasibility is not always practical. This paper focuses on building mathematical and prediction models of hydrogen and oxygen mixing scenarios of PEMEC. A mathematical model of the PEMEC device was customized in the Aspen Custom Model (ACM) software and integrated various critical Physico-chemical phenomena as the original data set for the prediction model. The results of the mathematical simulation verified the experimental results. The prediction model proposes an artificial neural network (ANN) framework to predict component distribution in the gas stream to prevent hydrogen-oxygen explosion scenarios. The presented approach by training ANN to 1000 sets of hydrogen-oxygen mixing simulation data from ACM is applicable to bypass tedious and non-smooth systems of equations for PEMEC.

For the safe and efficient utilization of hydrogen-enriched natural gas combustion in industrial gas-fired boilers the present study adopted a combination of numerical simulation and field tests to investigate its adaptability. Firstly the combustion characteristics of hydrogen-enriched natural gas with different hydrogen blending ratios and equivalence ratios were evaluated by using the Chemkin Pro platform. Secondly a field experimental study was carried out based on the WNS2- 1.25-Q gas-fired boiler to investigate the boiler’s thermal efficiency heat loss and pollutant emissions after hydrogen addition. The results show that at the same equivalence ratio with the hydrogen blending ratio increasing from 0% to 25% the laminar flame propagation speed of the fuel increases the extinction strain rate rises and the combustion limit expands. The laminar flame propagation speed of premixed methane/air gas reaches the maximum value when the equivalence ratio is 1.0 and the combustion intensity of the flame is the highest at this time. In the field tests as the hydrogen blending ratio increases from 0% to nearly 10% with the increasing excess air ratio the boiler’s thermal efficiency decreases as well as the NOx emission. This indicates that there exists a tradeoff between the boiler thermal efficiency and NOx emission in practice.

In recent years new chemical release agents based on silane are being used in the tire industry. Silane is an inorganic chemical compound consisting of a silicon backbone and hydrogen. Silanes can be thermally decomposed into high-purity silicon and hydrogen. If silane is stored and transported in Intermediate Bulk Containers (IBCs) equipped with safety valves in vented semi-confined spaces such as ISO-Containers hydrogen can be accumulated and become explosive mixture with air. A conservative CFD analysis using the GASFLOW-MPI code has been carried out to assess the hydrogen risk inside the vented containers. Two types of containers with different natural ventilation systems were investigated under various hypothetical accident scenarios. A continuous release of hydrogen due to the chemical decomposition of silane from IBCs was studied as the reference case. The effect of the safety valves on hydrogen accumulation in the container which results in small pulsed releases of hydrogen was investigated. The external effects of the sun and wind on hydrogen distribution and ventilation were also evaluated. The results can provide detailed information on hydrogen dispersion and mixing within the vented enclosures and used to evaluate the hydrogen risks such as flammability. Based on the assumptions used in this study it indicates that the geometry of ventilation openings plays a key role in the efficiency of the indoor air exchange process. In addition the use of safety valves makes it possible to reduce the concentration of hydrogen by volume in air compared to the reference case. The effect of the sun which results in a temperature difference between two container walls allows a strong mixing of hydrogen and air which helps to obtain a concentration lower than both the base case and the case of the pulsed releases. But the best results for the venting process are obtained with the wind that can drive the mixture to the downwind wall vent holes.

The NREL Hydrogen Sensor Laboratory was commissioned in 2010 as a resource for sensor developers end-users and regulatory agencies within the national and international hydrogen community. The Laboratory continues to provide as its core capability the unbiased verification of hydrogen sensor performance to assure sensor availability and their proper use. However the mission and strategy of the NREL Sensor Laboratory has evolved to meet the needs of the growing hydrogen market. The Sensor Laboratory program has expanded to support research in conventional and alternative detection methods as hydrogen use expands to large-scale markets as envisioned by the DOE National Clean Hydrogen Strategy and Roadmap. Current research encompasses advanced methods of hydrogen leak detection including stand-off and wide area monitoring approaches for large scale and distributed applications. In addition to safety applications low-level detection strategies to support the potential environmental impacts of hydrogen and hydrogen product losses along the value chain are being explored. Many of these applications utilize detection strategies that supplement and may supplant the use of traditional point sensors. The latest results of the hydrogen detection strategy research at NREL will be presented.

Gas leak detection on a production site is a major challenge for the safety and health of workers for environmental considerations and from an economic point of view. In addition flammable gas leaks are a safety risk because if ignited they can cause serious fires or explosions. For these reasons Acoem Metravib in collaboration with TotalEnergies One Tech R&D Safety has developed for the past four years a system called AGLED for the early detection localization and classification of such leaks exploiting acoustics and artificial intelligence driven by physics. Numerous tests have been conducted on a theater representative of gas production facilities created by TotalEnergies in Lacq (France) to build a robust learning database of leaks varying in flowrates exhaust diameters and also types (hole nozzle flange...). Moreover to limit the number of false alarms a relearning strategy has been implemented to handle unexpected disturbances (wildlife human activities meteorological events...). The presented paper describes the global architecture of the system from noise acquisition to the gas leak probability and coordinates. It gives a more in-depth look at the relearning algorithm and its performance in various environments. Finally thanks to a complementary collaboration with Air Liquide an example of test campaign in a real industrial environment is presented with an emphasis on the improvement obtained through relearning.

A gas turbine is usually installed inside an acoustic enclosure where the fuel gas supply system is also placed. It is common practice using CFD analysis to simulate the accidental fuel gas release inside the enclosure and the consequent dispersion. These numerical studies are used to properly design the gas detection system according to specific safety criteria which are well defined when the fuel gas is a conventional natural gas. Package design is done to prevent that any sparking items and hot surfaces higher than auto-ignition temperature could be a source of ignition in case of leak. Nevertheless it is not possible to exclude that a leakage from a theoretical point of view could be ignited and for this reason a robust design requires that the enclosure structure is able to withstand the overpressure generated by a gas cloud ignition. Moving to hydrogen as fuel gas makes this design constraint much more relevant for its known characteristics of reactiveness large range of flammability maximum burning velocity etc. In such context gas leak and dispersion analysis become even more crucial because a correct prediction of these scenarios can guide the design to a safe configuration. The present work shows a comparison of the dispersion of different leakages inside a gas turbine enclosure carried out with two different CFD tools Ansys CFX and FLACS. This verification is considered essential since dispersion analysis results are used as initial conditions for gas cloud ignition simulations strictly necessary to predict the consequence in term of overpressure without doing experimental tests.

Hydrogen energy is a cornerstone of the future climate-neutral economy. Yet as undetected leaks easily generate dangerous atmospheres sensing systems must timely detect accumulated hydrogen to prevent ignitions and explosions. Eye-readable sensors (ERSs) displaying intuitive readouts promise to guarantee safe use and universal access to hydrogen-based technology. This review highlights the impact of reversible ERSs in hydrogen moni toring to contextualize their current and potential applicability. First sensing mechanisms for gasochromic tungsten oxide films and switchable metal hydrides are critically overviewed. Then pivotal strategies targeting real-time monitorization indoors and permanent leak recording outdoors are presented along with standard hydrogen leakage scenarios elucidating opportunities for ERSs. Finally important challenges and desirable userfriendly concepts are discussed with the purpose of narrowing the gap between this class of sensors and the forthcoming hydrogen society.

MARCOGAZ has prepared this document to provide comprehensive information on the odorisation of hydrogen and natural gas (H2-NG) mixtures as well as pure hydrogen. The primary goal is to assist in determining the crucial data to be taken into account when odorising gases containing hydrogen.

The document is structured into two main sections with the initial part focusing on the theoretical interactions between hydrogen and odorants. Subsequent sections delve into the existing data related to this subject. The conclusions section offers additional considerations on the topic.

The report can be found on their website.

For the safe utilization and management of hydrogen energy within a fuel-cell room in a hydrogen-fueled house an explosion test was conducted to evaluate the potential hazards associated with hydrogen accident scenarios. The overpressure and heat radiation were measured for an explosion accident at distances of 1 2 3 5 and 10 m for hydrogen–air mixing ratios of 10% 25% 40% and 60%. When the hydrogen–air mixture ratio was 40% the greatest overpressure was 24.35 kPa at a distance of 1 m from the fuel-cell room. Additionally the thermal radiation was more than 1.5 kW/m2 which could cause burns at a distance of 5 m from the hydrogen fuel-cell room. Moreover a thermal radiation in excess of 1.5 kW/m2 was computed at a distance of 3 m from the hydrogen fuel-cell room when the hydrogen–air mixing ratio was 25% and 60%. Consequently an explosion in the hydrogen fuel-cell room did not considerably affect fatality levels but could affect the injury levels and temporary threshold shifts. Furthermore the degree of physical damage did not reach major structural damage levels causing only minor structural damage.

Hydrogen has become a key enabler for decarbonization as countries pledge to reach net zero carbon emissions by 2050. With hydrogen infrastructure expanding rapidly beyond its established applications there is a requirement for robust safety practices solutions and regulations. Since the 1980s considerable efforts have been undertaken by the nuclear community to address hydrogen safety issues because in severe accidents of water-cooled nuclear reactors a large amount of hydrogen can be produced from the oxidation of metallic components with steam. As evidenced in the Fukushima accident hydrogen combustion can cause severe damage to reactor building structures promoting the release of radioactive fission products to the environment. A number of large-scale experiments were conducted in the framework of national and international projects to understand the hydrogen dispersion and combustion behaviour under postulated accidental conditions. Empirical engineering models and numerical codes were developed and validated for safety analysis. Hydrogen recombiners known as Passive Autocatalytic Recombiner (PAR) were developed and have been widely installed in nuclear containments to mitigate hydrogen risk. Complementary actions and strategies were established as part of severe accident management guidelines to prevent or limit the consequences of hydrogen explosions. In addition hydrogen monitoring systems were developed and implemented in nuclear power plants. The experience and knowledge gained from the nuclear community on hydrogen safety is valuable and applicable for other industries involving hydrogen production transport storage and use.

In August 2022 Shell started construction of Holland Hydrogen I (HH I) a 200 MW electrolyser plant in the port of Rotterdam’s industrial zone on Maasvlakte II in the Netherlands. HH I will produce up to 60000 kg of renewable hydrogen per day. The development and demonstration of a safe layout and plant design had been challenging due to ambitious HH I project premises many technical novelties common uncertainties in hydrogen leak effect prediction a lack of large-scale water electrolyzer operating history and limited standardization in this industry sector. This paper provides an industry perspective of the major challenges in commercial electrolyzer plant HSSE risk assessment and risk mitigation work processes required to develop and demonstrate a safe design and it describes lessons learned in this area during the HH I project. Furthermore the paper lists major common gaps in relevant knowledge engineering tools standards and OEM deliverables that need closure to enable future commercial electrolyzer plant projects to develop an economically viable and plant design and layout more efficiently and cost-effectively.

In this paper we study the dispersion ignition and flame characteristics of blended jets of hydrogen and methane (as a proxy for natural gas) at near-atmospheric pressure for a fixed volumetric flow rate which mimics the scenario of a small-scale unintended leak. A reduction in flame height is observed with increasing hydrogen concentration. A laser is tightly focused to generate a spark with sufficient energy to ignite the fuel. The light-up boundary defined as the delineating location at which a spark ignites into a jet flame or extinguishes is determined as a contour. The light-up boundary increases in both width and length as the hydrogen content increases up to 75% hydrogen at which point the axial ignition boundary decreases slightly for pure hydrogen relative to 75% hydrogen. Ignition probability a key parameter regarding safety is computed at various axial locations and is also shown to be higher near the nozzle as well as non-zero at further downstream locations as the hydrogen content in the blend increases. Planar laser Raman scattering is used in separate experiments to determine the concentration of both fuel species. Mean fuel concentrations well below the lower flammability limit are both within the light-up boundary and have non-zero ignition probabilities.

HyResponder is a European Hydrogen Train the Trainer programme for responders. This paper describes the key outputs of the project and the steps taken to develop and implement a long-term sustainable train the trainer programme in hydrogen safety for responders across Europe and beyond. This FCH2 JU (now Clean Hydrogen Joint Undertaking) funded project has built on the successful outcomes of the previous HyResponse project. HyResponder has developed further and updated educational operational and virtual reality training for trainers of responders to reflect the state-of-the-art in hydrogen safety including liquid hydrogen and expand the programme across Europe and specifically within the 10 countries represented directly within the project consortium: Austria Belgium the Czech Republic France Germany Italy Norway Spain Switzerland and the United Kingdom. For the first time four levels of educational materials from fire fighter through to specialist have been developed. The digital training resources are available on the e-Platform (https://hyresponder.eu/e-platform/). The revised European Emergency Response Guide is now available to all stakeholders. The resources are intended to be used to support national training programs. They are available in 8 languages: Czech Dutch English French German Italian Norwegian and Spanish. Through the HyResponder activities trainers from across Europe have undertaken joint actions which are in turn being used to inform the delivery of regional and national training both within and beyond the project. The established pan-European network of trainers is shaping the future in the important for inherently safer deployment of hydrogen systems and infrastructure across Europe and enhancing the reach and impact of the programme.

Hydrogen Fuel Cell Electric Vehicles (HFC EVs) represent an alternative to replace current internal combustion engine vehicles. The use of these vehicles with storage of compressed gaseous hydrogen (CGH2) or cryogenic liquid hydrogen (LH2) in confined spaces such as tunnels underground car parks etc. creates new challenges to ensure the protection of people and property and to keep the risk at an acceptable level. Several studies have shown that confinement or congestion can lead to severe accidental consequences compared to accidents in an open atmosphere. It is therefore necessary to develop validated hazard and risk assessment tools for the behaviour of hydrogen in tunnels. The HYTUNNEL-CS project sponsored by the FCH-JU pursues this objective. Among the experiments carried out in support of the validation of the hydrogen safety tools the CEA conducted tests on large-scale jet fires in a full-scale tunnel geometry.<br/>The tests were performed in a decommissioned road tunnel in two campaigns. The first one with 50 liters type II tanks under a pressure of 20 MPa and the second one with 78 liters type IV tanks under 70 MPa. In both cases a flate plate was used to simulate the vehicle. Downward and upward gas discharges to simulate a rollover have been investigated with various release diameters. For the downward discharge the orientation varied from normal to the road to a 45° rearward inclination. The first campaign took place under a concrete vault while the second under a rocky vault. Additional tests with the presence of a propane fire simulating a hydrocarbon powered vehicle fire were performed to study the interaction between the two reactive zones.<br/>In the paper all the results obtained during the second campaign for the evolution of the hydrogen jet-fire size the radiated heat fluxes and the temperature of the hot gases released in the tunnel are reported. Comparisons with the classical correlations from open field tests used in engineering models are also presented and conclusions are given as to their applicability.

This paper presents a systematic investigation that encompasses the safety assessment of a fuel preparation room (FPR) intended for a hydrogen-fueled ship. The primary objective is to determine the appropriate ventilation strategy to mitigate the risks associated with potential hydrogen leakage. The study focuses on a case involving an FPR measuring 10.2 m × 5.3 m × 2.65 m which is part of a 750 DWT hydrogen-powered fishing vessel. To identify the potential events leading to hydrogen dispersion an event tree analysis is conducted. Additionally existing regulations and guidelines related to the safety assessments of hydrogen leakage in enclosed areas are summarized and analyzed. Computational fluid dynamics FLACS-CFD are utilized for the consequence analysis in order to evaluate the impact of ventilation on hydrogen dispersion and concentration within the FPR. The research findings indicate significant effects of ventilation on the hazards and safety assessments of FPRs and high-pressure fuel gas supply systems. The study highlights that hydrogen vapor tends to accumulate at the ceiling and in the corners and spaces created by the equipment. The position and size of ventilation openings greatly influence the dispersion of hydrogen leakage. Proper ventilation design including top inlet ventilation and outlet ventilation on the opposite side helps to maintain a safe FPR by facilitating the efficient dispersion of hydrogen vapor. Moreover locating inlet ventilation on the same side as the outlet ventilation is found to hinder dispersion while the cross-ventilation achieved by placing inlets and outlets on opposite sides enhances airflow and dispersion. Consequently it is recommended to prioritize the structural design of FPRs and implement enhanced safety measures. Additionally updating the relevant regulations to address these concerns is strongly advised.

The accurate determination of the potential impact radius is crucial for the design and risk assessment of hydrogen pipelines. The existing methodologies employ a single point source model to estimate radiation and the potential impact radius. However these approaches overlook the jet fire shape resulting from high-pressure leaks leading to discrepancies between the calculated values and real-world incidents. This study proposes models that account for both the mass release rate while considering the pressure drop during hydrogen pipeline leakage and the radiation while incorporating the flame shape. The analysis encompasses 60 cases that are representative of hydrogen pipeline scenarios. A simplified model for the potential impact radius is subsequently correlated and its validity is confirmed through comparison with actual cases. The proposed model for the potential impact radius of hydrogen pipelines serves as a valuable reference for the enhancement of the precision of hydrogen pipeline design and risk assessment.

This paper presents work undertaken by the HSE as part of the Hytunnel-CS project a consortium investigating safety considerations for fuel cell hydrogen (FCH) vehicles in tunnels and similar confined spaces.<br/>Hydrogen vehicles typically have a Thermally activated Pressure Release Device (TPRD) providing protection to the on-board storage of the vehicle. Upon activation the content of the vessel is released in a blowdown. The release of this hydrogen gas poses a significant hazard of ignition. The consequences of such an ignition could also be compounded by confinement or congestion.<br/>HSE undertook a series of experiments investigating the consequences of these events by releasing hydrogen into a tunnel and causing ignitions. A sub-section of these tests involved steel structures providing congestion in the tunnel. The mass of hydrogen released into the tunnel prior to ignition was varied by storage pressure (up to 59 MPa) release diameter and ignition delay. The ignition delays were set based on the expected worst-case predicted by pre-simulation models. To assess the consequences overpressure measurements were made down the tunnel walls and for the tests with congestion at the face and rear of the congestion structures. The flame arrival time was also measured using exposed-tip thermocouples resulting in an estimate for flame speed down the tunnel. The measured overpressure and flame extent results are presented and compared against overpressure levels of concern.

Hydrogen Fuel Cell Electric Vehicles (HFC EVs) represent an alternative to replace current internal combustion engine vehicles. The use of these vehicles with storage of compressed gaseous hydrogen (CGH2) in confined spaces such as tunnels underground car parks etc. creates new challenges to ensure the protection of people and property and to keep the risk at an acceptable level. The HYTUNNEL-CS project sponsored by the FCH-JU was launched to develop validated hazard and risk assessment tools for the behavior of hydrogen leaks in tunnels. Among the experiments carried out in support of the validation tools the CEA has conducted tests on gas dispersion in a full-scale tunnel geometry. In the tests carried out hydrogen is replaced by helium under a pressure of 70 MPa in a 78 liter tank. The car is simulated by a flat plate called chassis and the discharges are made either downwards under the chassis or upwards to take into account a rollover of the car during the accident. Different thermally activated pressure relief device (TPRD) diameters are examined as well as different orientations of the discharge. Finally the mixing transient of helium with air is measured for distances between -50 and +50m from the release. Performing CFD simulations of such an under-expanded jet in an environment as large as a road tunnel demands a compressible flow solver and so a large computational cost. To optimize this cost a notional nozzle approach is generally used to replace the under-expanded jet by a subsonic jet that has the same concentration dilution behavior. The physics at the injection point is then not resolved and a model of these boundary conditions has to be implemented. This article first reviews the main experimental results. Then a model of boundary conditions is proposed to have a subsonic hydrogen jet that matches the dilution characteristics of an under-expanded jet. Furthermore this model is implemented in the TRUST LES computer code and in the Neptune-CFD RANS computer code in order to simulate some helium dispersion experiments. Finally results from the CFD simulations are compared to the experimental results and the effect of the exact shape of the tunnel is also assessed by comparing simulations with idealized flat walls and real scanned walls.

This paper presents work undertaken by the HSE as part of the Hytunnel-CS project a consortium investigating safety considerations for fuel cell hydrogen (FCH) vehicles in tunnels and similar confined spaces. The test programme investigating hydrogen dispersion in tunnels involved simulating releases analogous to Thermally activated Pressure Relief Devices (TPRDs) typically found on hydrogen vehicles into the HSE Tunnel facility. The releases were scaled and based upon four scenarios: cars buses and two different train designs. The basis for this scaling was the size of the tunnel and the expected initial mass flow rates of the releases scenarios. The results of the 12 tests completed have been analysed in two ways: the initial mass flow rates of the tests were calculated based upon facility measurements and the Able-Noble equations of state for comparison to the intended initial flow rate; and observations of the hydrogen dispersion in the tunnel were made based on 15 hydrogen sensors arrayed along the tunnel. The calculated mass flow rates showed reasonable agreement with the intended initial conditions showing that the scaling methodology can be used to interpret the data based on the full-scale tunnel of interest. Observations of the hydrogen dispersion show an initial turbulent mixing followed by a movement of the mixed hydrogen/air cloud down the tunnel. No vertical stratification of the cloud was observed but this effect could be possible in longer tunnels or tunnels with larger diameters. Higher ventilation rates in the tunnel resulted in a reduction of the residence time of the hydrogen and a slight increase in the dilution.

Hydrogen as one of the most promising renewable clean energy sources holds significant strategic importance and vast application potential. However as a high-energy combustible gas hydrogen poses risks of fire and explosion in the event of a leakage. Hydrogen production plants typically feature large spatial volumes and complex obstacles which can significantly influence the diffusion pathways and localized accumulation of hydrogen during a short-term high-volume release further increasing the risk of accidents. Implementing effective hydrogen leakage monitoring measures can mitigate these risks ensuring the safety of personnel and the environment to the greatest extent possible. Therefore this paper uses CFD methods to simulate the hydrogen leakage process in a hydrogen production plant. The study examines the molar fraction distribution characteristics of hydrogen in the presence of obstacles by varying the ventilation speed of the plant and the directions of leakage. The main conclusions are as follows: enhancing ventilation can effectively prevent the rapid increase in hydrogen concentration with higher ventilation speeds yielding better suppression. After a hydrogen leak in a confined space hydrogen tends to diffuse along the walls and accumulate in corner areas indicating that hydrogen monitoring equipment should be placed in corner locations.

Hydrogen is commonly used as feedstock in industrial processes and is regarded as a potential future energy carrier. However its reactivity and low density make it difficult to handle and store safely. Indoor hydrogen dispersion can cause a fire or explosion hazard if encountering an ignition source. Safety practices often use time expensive modelling techniques to estimate risk associated with hydrogen. A neural network based surrogate model could efficiently replace Computational Fluid Dynamics (CFD) modelling in safety studies. To lower the dimensionality of this surrogate model a dimensional analysis based on Buckingham’s Pi-theorem is proposed. The dimensional analysis examines stratified filling and highlights the functional parameters involved in the process. Stratified filling occurs for buoyancy dominated releases and is characterized by layers of decreasing concentration starting at the ceiling of the enclosure and developing towards the bottom. The study involves four dimensional cases that were simulated using Computational Fluid Dynamics (CFD) to demonstrate the usefulness of the proposed dimensionless time and dimensionless volume. The setup considered in this paper consists of a parallelepiped enclosure with standard atmospheric conditions a single release source and one pressure outlet to ensure constant pressure during the release. The results of the CFD simulations show a distinct pattern in the relation of hydrogen molar fraction and dimensionless time. The pattern depends on the dimensionless height of the measurement location. A five-parameter logistic (5PL) function is proposed to fit the data from the CFD models. Overall the paper provides insights into the functional parameters involved in the evolution of hydrogen mass fractions during stratified filling. It provides a nondimensional surrogate model to compute the evolution of the local concentrations of hydrogen during the development of stratification layers.

Building safe and convenient fuelling stations is key to deploying the arrival of commercial/public-use fuel cell electric vehicles (FCEVs). As the most public-facing hydrogen applications second only to the FCEVs hydrogen stations are an efficient tool to educate the public about hydrogen safety and normalize its use to fill up our vehicles. However as an emerging technology it is the industry’s responsibility to ensure that fuelling infrastructures are designed and maintained in accordance with established safety standards and thus that the fuelling process is inherently safe for all users. On the other end it is essential that consumers have all the necessary information at reach to help them feel safe while fuelling their zero-emission vehicles.<br/>This paper will provide a snapshot of the safety systems used to help protect members of the public using hydrogen fueling stations as well as the information used to educate people using this equipment. This will cover the different processes involved in hydrogen fueling stations the dangers that are present to customers and members of the public at these sites and the engineering design choices and equipment used to mitigate these dangers or prevent them from happening. Finally this paper will discuss the crucial role of understanding the dangers of hydrogen at a public level and showing the importance of educating the public about hydrogen infrastructure so that people will feel comfortable using it in their everyday lives.

The aim of the H21 project is to undertake measurements analysis and field trials to support the safe repurposing of Great Britain’s natural gas distribution network for hydrogen. As part of this project work has been ongoing to identify aspects of existing natural gas procedures that will need to be modified for hydrogen and to support the development of new procedures. This has included a review of the scientific basis of current displacement purging practices analysis of the potential implications of switching from natural gas to hydrogen and experimental support work. The reduced density and viscosity of hydrogen means that minimum purging velocities should (in principle) be higher for hydrogen to avoid stratification and ensure adequate removal of the purged gas during pipeline purging operations. A complicating factor is the high molecular diffusivity of hydrogen (roughly three times that of natural gas) which causes hydrogen to mix over short distances more rapidly than natural gas. Current models for pipeline purging do not take into account the mixing effect related to molecular diffusion. The wider flammable limits lower ignition energy and greater potential for combustion to transition from deflagration to detonation with hydrogen means that indirect purging with nitrogen is currently being investigated for distribution pipelines. This paper reviews the ongoing analysis of hydrogen pipeline purging and discusses a potential future scientific programme of work aimed at developing a new pipeline purging model that accounts for molecular diffusion effects.