Safety

In transport and storage of hydrogen the risks are mainly seen in its volatile nature its ability to form explosive mixtures with air and the harsh conditions (high pressure or low temperature) for efficient storage. The concept of Liquid Organic Hydrogen Carriers (LOHC) offers a technology to overcome the above mentioned threats. The present submission describes the basics of the LOHC technology. It contains a comparison of a selection of common LOHC materials with a view on physical properties. The advantages of a low viscosity at low temperatures and a high flash point are expressed. LOHCs are also discussed as a concept to import large amounts of energy/hydrogen. A closer look is taken on the environmental and safety aspects of hydrogen storage in LOHCs since here the main differences to pressurized and cryo-storage of hydrogen can be found. The aim of this paper is to provide an overview of the principles of the LOHC technology the different LOHC materials and their risks and opportunities and an impression of a large scale scenario on the basis of the LOHC technology.

A reversible solid oxide cell (rSOC) reactor can operate efficiently in both electrolysis mode and in fuel cell mode. The bidirectional operability enables rSOC reactors to play a central role as an efficient energy conversion system for energy storage and sector coupling for a renewable energy driven society. A combined system for electrolysis and fuel cell operation can result in complex system configurations that should be able to switch between the two modes as quickly as possible. This can lead to temperature profiles within the reactor that can potentially lead to the failure of the reactor and eventually the system. Hence the behavior of the reactor during the mode switch should be analyzed and optimal transition strategies should be taken into account during the process system design stage. In this paper a one dimensional transient reversible solid oxide cell model was built and experimentally validated using a commercially available reactor. A simple hydrogen based system model was built employing the validated reactor model to study reactor behavior during the mode switch. The simple design leads to a system efficiency of 49% in fuel cell operation and 87% in electrolysis operation where the electrolysis process is slightly endothermic. Three transient operation strategies were studied. It is shown that the voltage response to transient operation is very fast provided the reactant flows are changed equally fast. A possible solution to ensure a safe mode switch by controlling the reactant inlet temperatures is presented. By keeping the rate of change of reactant inlet temperatures five to ten times slower than the mode switch a safe transition can be ensured.

Clean fuel is advocated to be used for sustainability. The number of liquefied petroleum gas (LPG) and hydrogen vehicles is increasing globally. Explosion hazard is a threat. On the other hand the use of hydrogen is under consideration in Hong Kong. Explosion hazards of these clean fuel (LPG and hydrogen) vehicles were studied and are compared in this paper. The computational fluid dynamics (CFD) software Flame Acceleration Simulator (FLACS) was used. A car garage with a rolling shutter as its entrance was selected for study. Dispersion of LPG from the leakage source with ignition at a higher position was studied. The same garage was used with a typical hydrogen vehicle leaking 3.4 pounds (1.5 kg) of hydrogen in 100 s the mass flow rate being equal to 0.015 kgs−1 . The hydrogen vehicle used in the simulation has two hydrogen tanks with a combined capacity of 5 kg. The entire tank would be completely vented out in about 333 s. Two scenarios of CFD simulation were carried out. In the first scenario the rolling shutter was completely closed and the leaked LPG or hydrogen was ignited at 300 s after leakage. The second scenario was conducted with a gap height of 0.3 m under the rolling shutter. Predicted results of explosion pressure and temperature show that appropriate active fire engineering systems are required when servicing these clean fuel vehicles in garages. An appropriate vent in an enclosed space such as the garage is important in reducing explosion hazards.

Lean premixed swirl combustion is widely used in gas turbines and many other combustion Processes due to the benefits of good flame stability and blow off limits coupled with low NO_x emissions. Although flashback is not generally a problem with natural gas combustion there are some reports of flashback damage with existing gas turbines whilst hydrogen enriched fuel blends especially those derived from gasification of coal and/or biomass/industrial processes such as steel making cause concerns in this area. Thus this paper describes a practical experimental approach to study and reduce the effect of flashback in a compact design of generic swirl burner representative of many systems. A range of different fuel blends are investigated for flashback and blow off limits; these fuel mixes include methane methane/hydrogen blends pure hydrogen and coke oven gas. Swirl number effects are investigated by varying the number of inlets or the configuration of the inlets. The well known Lewis and von Elbe critical boundary velocity gradient expression is used to characterise flashback and enable comparison to be made with other available data. Two flashback phenomena are encountered here. The first one at lower swirl numbers involves flashback through the outer wall boundary layer where the crucial parameter is the critical boundary velocity gradient Gf. Values of Gf are of similar magnitude to those reported by Lewis and von Elbe for laminar flow conditions and it is recognised that under the turbulent flow conditions pertaining here actual gradients in the thin swirl flow boundary layer are much higher than occur under laminar flow conditions. At higher swirl numbers the central recirculation zone (CRZ) becomes enlarged and extends backwards over the fuel injector to the burner baseplate and causes flashback to occur earlier at higher velocities. This extension of the CRZ is complex being governed by swirl number equivalence ratio and Reynolds Number. Under these conditions flashback occurs when the cylindrical flame front surrounding the CRZ rapidly accelerates outwards to the tangential inlets and beyond especially with hydrogen containing fuel mixes. Conversely at lower swirl numbers with a modified exhaust geometry hence restricted CRZ flashback occurs through the outer thin boundary layer at much lower flow rates when the hydrogen content of the fuel mix does not exceed 30%. The work demonstrates that it is possible to run premixed swirl burners with a wide range of hydrogen fuel blends so as to substantially minimise flashback behaviour thus permitting wider used of the technology to reduce NOx emissions.

From the perspective of risk control when hydrogen fuel and fuel cells are used on ships there is a possibility of low-flash fuel leakage leading to the risk of explosion. Since the fuel cell space (cabin for fuel cell installations) is an enclosed space any small amount of leakage must be handled properly. In ship design area classification is a method of analyzing and classifying the areas where explosive gas atmospheres may occur. If the fuel cell space is regarded as a hazardous area all the electrical devices inside it must be explosion-proof type which will make the ship’s design very difficult. This paper takes a Chinese fuel cell powered ship as an example to analyze its safety. Firstly the leakage rates of fuel cell modules valves and connectors are calculated. Secondly the IEC60079-10-1 algorithm is used to calculate the risk level of the fuel cell space. Finally the ship and fuel cells are optimized and redesigned and the risk level of the fuel cell space is recalculated and compared. The result shows that the optimized fuel space risk level could be reduced to the level of the non-hazardous zone.

Numerical  simulations  have  been  conducted  for  LH2   massive  releases  and  the  subsequent atmospheric dispersion using an in-house modified version of the open source computational fluid dynamics (CFD) code OpenFOAM. A conjugate heat transfer model has been added for heat  transfer   between  the  released  LH2   and  the  ground.  Appropriate  interface  boundary conditions  are   applied  to  ensure  the continuities  of  temperature  and  heat  fluxes.  The significant temperature difference between the cryogenic hydrogen and the ground means that the released LH2 will instantly enter in a boiling state resulting in a hydrogen- air gaseous cloud  which  will   initially  behave  like  a dense  gas.  Numerical  predictions  have  been conducted  for  the   subsequent  atmospheric  dispersion  of  the  vaporized  LH2   for  a series  of release scenarios - with and without retention pits - to limit the horizontal spread of the LH2 on the ground. The considered cases included the instantaneous release of 1 10 and 50 tons of LH2   under  neutral   (D)  and  stable  (F)  weather  conditions.  More  specifically  3F  and  5D conditions were simulated with the former representing stable weather conditions under wind speed  of  3  m/s  at   10  m  above  the  ground  and  the  later  corresponding  to  neutral  weather conditions under 5 m/s wind speed (10 m above the ground). Specific numerical tests have also been conducted for selected scenarios under different ambient temperatures from 233 up to 313 K. According to the current study although the retention pit can extend the dispersion time it can significantly reduce the extent of hazards due to much smaller cloud size within both the flammability and explosion limits. While the former has negative impact on safety the  later  is  beneficial.  The   use  of  retention  pit  should  hence  be  considered  with  caution  in practical applications.

Technologies that have traditionally been used in fixed installations to detect hydrogen gas leaks such as Catalytic and Electrochemical Point Sensors have one limitation: in order for a leak to be detected the gas itself must either be in close proximity to the detector or within a pre-defined area. Unfortunately outdoor environmental conditions such as changing wind directions and quick dispersion of the gas cloud from a leaking outdoor installation often cause that traditional gas detection systems may not alert to the presence of gas simply because the gas never reaches the detector. These traditional gas detection systems need to wait for the gas to form a vapor cloud which may or may not ignite and which may or may not allow loss prevention by enabling shutting down the gas facility in time. Ultrasonic Gas Leak Detectors (UGLD) respond at the speed of sound at gas leak initiation unaffected by changing wind directions and dilution of the gas. Ultrasonic Gas Leak Detectors are based on robust microphone technology; they detect outdoor leaks by sensing the distinct high frequency ultrasound emitted by all high pressure gas leaks. With the ultrasonic sensing technology leaking gas itself does not have to reach the sensor – just the sound of the gas leaking. By adding Ultrasonic Gas Leak Detectors for Hydrogen leak detection faster response times and lower operation costs can be obtained.

High-strength aluminum alloys are widely used in industry. Hydrogen embrittlement greatly reduces the performance and service safety of aluminum alloys. The hydrogen traps in aluminum profoundly affect the hydrogen embrittlement of aluminum. Here we took a coincidence-site lattice (CSL) symmetrically tilted grain boundary (STGB) Σ5(120)[001] as an example to carry out molecular dynamics (MD) simulations of hydrogen diffusion in aluminum at different temperatures and to obtain results and rules consistent with the experiment. At 700 K three groups of MD simulations with concentrations of 0.5 2.5 and 5 atomic % hydrogen (at. % H) were carried out for STGB models at different angles. By analyzing the simulation results and the MSD curves of hydrogen atoms we found that in the low hydrogen concentration of STGB models the grain boundaries captured hydrogen atoms and hindered their movement. In high-hydrogen-concentration models the diffusion rate of hydrogen atoms was not affected by the grain boundaries. The analysis of the simulation results showed that the diffusion of hydro-gen atoms at the grain boundary is anisotropic.

The European Community requires a vehicle-level bonfire test for vehicles using plastic fuel tanks for conventional fuels (ECE R-34 Annex 5). A similar test could be applied to hydrogen-fuelled vehicles. It would test a realistic vehicle with its complete fuel and safety systems. An advantage of such a test is that the same test could be applied independent of the hydrogen storage technology (compressed gas liquid or hydride). There are currently standards for bonfire testing of a bare Compressed Natural Gas (CNG) tank and its Pressure Relief Device (PRD). This standard is FMVSS 304 in the U.S. and ISO 15869-1 in Europe. Japan has a similar standard. It requires that a bare tank and its associated PRD be subjected to a propane flame for 20 minutes. The tank must either survive or safely vent its contents. No modern composite wound tank is expected to survive for 20 minutes – so this is not a tank test but really a PRD test. The test procedure requires the PRD to be shielded from direct impingement of the flames – but the shield is not well specified. If it shields the PRD too well the PRD will not activate and the tank will burst. This paper describes the results of a CNG and a hydrogen tank burst from such tests. The mechanical energy released is enormous. It is simply unacceptable to allow the tank to burst – the PRD and venting system must work. Organizations in the U.S Europe and Japan are in the process of modifying the CNG tank bonfire test for compressed hydrogen storage. A bare tank with a single PRD is not a good simulation of a hydrogen fuel system installed in an actual vehicle. There will usually be multiple tanks plumbed together at either the tank pressure or at the intermediate pressure (after the pressure regulator). There may be more than one PRD. The tank may be shielded (from debris) or insulated to protect it from an underbody pool fire. Also the heat transfer from the simulated pool fire (propane flame) will be very different when mounted in a vehicle versus the bare tank test. A vehicle-level pool fire test will alleviate these problems. It is therefore recommended that the bare tank test be replaced by or augmented with a vehicle-level bonfire test similar to ECE R-34 Annex 5.

During the course of a severe accident in a light water nuclear reactor large amounts of hydrogen can be generated and released into the containment during reactor core degradation. Additional burnable gases [hydrogen (H2) and carbon monoxide (CO)] may be released into the containment in the corium/concrete interaction. This could subsequently raise a combustion hazard. As the Fukushima accidents revealed hydrogen combustion can cause high pressure spikes that could challenge the reactor buildings and lead to failure of the surrounding buildings. To prevent the gas explosion hazard most mitigation strategies adopted by European countries are based on the implementation of passive autocatalytic recombiners (PARs). Studies of representative accident sequences indicate that despite the installation of PARs it is difficult to prevent at all times and locations the formation of a combustible mixture that potentially leads to local flame acceleration. Complementary research and development (R&D) projects were recently launched to understand better the phenomena associated with the combustion hazard and to address the issues highlighted after the Fukushima Daiichi events such as explosion hazard in the venting system and the potential flammable mixture migration into spaces beyond the primary containment. The expected results will be used to improve the modeling tools and methodology for hydrogen risk assessment and severe accident management guidelines. The present paper aims to present the methodology adopted by Institut de Radioprotection et de Suˆ rete Nucleaire to assess hydrogen risk in nuclear power plants in particular French nuclear power plants the open issues and the ongoing R&D programs related to hydrogen distribution mitigation and combustion.

The aim of this project was to review the current purge standards for UK domestic installations in particular IGEM/UP/1B and carry out experiments to assess the validity of those standards for use in hydrogen in order to understand and recommend safe purge practices for hydrogen in a domestic environment.

This report provides the results and conclusions relating to the relative safety of purging domestic installations to hydrogen compared to Natural Gas and the implications of releasing any purged gas

into an enclosed volume representing a small room.

The two high-level findings from this work are:

• changeover to hydrogen will result in an increased risk of flammability inside the installation pipework
• changeover to hydrogen will result in a reduced risk of a build-up of flammable gas in any room where purging occurs.

This work recognises a number of important differences between hydrogen and methane. Hydrogen is more flammable than methane in air particularly at high concentrations. Hydrogen can maintain a flame at 4% but does not support general three dimensional deflagration until about 8.5%. Above about 18% given increased obstruction within the combustion zone or passage of the flame along a pipe the deflagration can transition to detonation. The flame speed suddenly increases to ~2000m/s. It is very important to avoid this situation although the inventory in a domestic pipe is low. This risk of detonation can occur at concentrations up to 59% and the risk of deflagration remains to 75 %.Methane behaves very differently to this with a range of deflagration of about 4.8 to 16% and a detonation range only marginally narrower. Initiating detonation is however much more difficult with methane.

The risks with hydrogen are associated with a wide range of flammability with methane the risks are smaller and mainly in lower concentrations of gas in air. Because of this it is particularly important to ensure hydrogen pipes are appropriately purged.

This paper presents experiments performed at Canadian Nuclear Laboratories (CNL) to examine the dispersion behaviour of helium in a polycarbonate enclosure that was representative of a residential parking garage. The purpose was to gain a better understanding of the effect of buoyancy- or winddriven natural ventilation on hydrogen dispersion behaviour. Although hydrogen dispersion studies have been reported extensively in the literature gaps still exist in predictive methods for hazard analysis. Helium a simulant for hydrogen was injected near the centre of the floor with a flow rate ranging from 5 to 75 standard litres per minute through an upward-facing nozzle resulting in an injection Richardson number ranging between 10-1 and 102. The location of the nozzle varied from the bottom of the enclosure to near the ceiling to examine the impact of the nozzle elevation on the development of a stratified layer in the upper region of the enclosure. When the injection nozzle was placed at a sufficiently low elevation the vertical helium profile always consisted of a homogenous layer at the top overlaying a stratified layer at the bottom. To simulate outdoor environmental conditions a fan was placed in front of each vent to examine the effect of opposing or assisting wind on the dispersion. The helium transients in the uniform layer predicted with analytical models were in good agreement with the measured transients for the tests with injection at lower elevations or with no wind. Model improvements are required for adequately predicting transients with significantly stratified profiles or with wind.

Underground hydrogen storage is a potential way to balance seasonal fluctuations in energy production from renewable energies. The risks of hydrogen storage in depleted gas fields include the conversion of hydrogen to CH4(g) and H2S(g) due to microbial activity gas–water–rock interactions in the reservoir and cap rock which are connected with porosity changes and the loss of aqueous hydrogen by diffusion through the cap rock brine. These risks lead to loss of hydrogen and thus to a loss of energy. A hydrogeochemical modeling approach is developed to analyze these risks and to understand the basic hydrogeochemical mechanisms of hydrogen storage over storage times at the reservoir scale. The one-dimensional diffusive mass transport model is based on equilibrium reactions for gas–water–rock interactions and kinetic reactions for sulfate reduction and methanogenesis. The modeling code is PHREEQC (pH-REdox-EQuilibrium written in the C programming language). The parameters that influence the hydrogen loss are identified. Crucial parameters are the amount of available electron acceptors the storage time and the kinetic rate constants. Hydrogen storage causes a slight decrease in porosity of the reservoir rock. Loss of aqueous hydrogen by diffusion is minimal. A wide range of conditions for optimized hydrogen storage in depleted gas fields is identified.

As an alternative to the construction of new infrastructure repurposing existing natural gas pipelines for hydrogen transportation has been identified as a low-cost strategy for substituting natural gas with hydrogen in the wake of the energy transition. In line with that a 342 km 3600 natural gas pipeline was used in this study to simulate some technical implications of delivering the same amount of energy with different blends of natural gas and hydrogen and with 100% hydrogen. Preliminary findings from the study confirmed that a three-fold increase in volumetric flow rate would be required of hydrogen to deliver an equivalent amount of energy as natural gas. The effects of flowing hydrogen at this rate in an existing natural gas pipeline on two flow parameters (the compressibility factor and the velocity gradient) which are crucial to the safety of the pipeline were investigated. The compressibility factor behaviour revealed the presence of a wide range of values as the proportions of hydrogen and natural gas in the blends changed signifying disparate flow behaviours and consequent varying flow challenges. The velocity profiles showed that hydrogen can be transported in natural gas pipelines via blending with natural gas by up to 40% of hydrogen in the blend without exceeding the erosional velocity limits of the pipeline. However when the proportion of hydrogen reached 60% the erosional velocity limit was reached at 290 km so that beyond this distance the pipeline would be subject to internal erosion. The use of compressor stations was shown to be effective in remedying this challenge. This study provides more insights into the volumetric and safety considerations of adopting existing natural gas pipelines for the transportation of hydrogen and blends of hydrogen and natural gas.

Direct Numerical Simulations (DNS) are performed to investigate the process of spontaneous ignition of hydrogen flames at laminar turbulent adiabatic and non-adiabatic conditions. Mixtures of hydrogen and vitiated air at temperatures representing gas-turbine reheat combustion are considered. Adiabatic spontaneous ignition processes are investigated first providing a quantitative characterization of stable and unstable flames. Results indicate that in hydrogen reheat combustion compressibility effects play a key role in flame stability and that unstable ignition and combustion are consistently encountered for reactant temperatures close to the mixture’s characteristic crossover temperature. Furthermore it is also found that the characterization of the adiabatic processes is also valid in the presence of non-adiabaticity due to wall heat-loss. Finally a quantitative characterization of the instantaneous fuel consumption rate within the reaction front is obtained and of its ability at auto-ignitive conditions to advance against the approaching turbulent flow of the reactants for a range of different turbulence intensities temperatures and pressure levels.

While significant increase in turbulent burning rate in lean premixed flames of hydrogen or hydrogen-containing fuel blends is well documented in various experiments and can be explained by highlighting local diffusional-thermal effects capabilities of the vast majority of available models of turbulent combustion for predicting this increase have not yet been documented in numerical simulations. To fill this knowledge gap a well-validated Turbulent Flame Closure (TFC) model of the influence of turbulence on premixed combustion which however does not address the diffusional-thermal effects is combined with the leading point concept which highlights strongly perturbed leading flame kernels whose local structure and burning rate are significantly affected by the diffusional-thermal effects. More specifically within the framework of the leading point concept local consumption velocity is computed in extremely strained laminar flames by adopting detailed combustion chemistry and subsequently the computed velocity is used as an input parameter of the TFC model. The combined model is tested in RANS simulations of highly turbulent lean syngas-air flames that were experimentally investigated at Georgia Tech. The tests are performed for four different values of the inlet rms turbulent velocities different turbulence length scales normal and elevated (up to 10 atm) pressures various H₂/CO ratios ranging from 30/70 to 90/10 and various equivalence ratios ranging from 0.40 to 0.80. All in all the performed 33 tests indicate that the studied combination of the leading point concept and the TFC model can predict well-pronounced diffusional-thermal effects in lean highly turbulent syngas-air flames with these results being obtained using the same value of a single constant of the combined model in all cases. In particular the model well predicts a significant increase in the bulk turbulent consumption velocity when increasing the H₂/CO ratio but retaining the same value of the laminar flame speed.

Free quasi-two-dimensional outward propagation of the ultra-lean hydrogen-air flames was studied in a horizontal closed flat channel in order to minimize the influences of gravity and natural convection. Experiments were carried out with a sequential change of initial hydrogen concentration in the premixed gaseous  hydrogen-air  mixtures  in  the  range  from  3  to  12  vol.  %  H2   under  normal  pressure  and temperature   conditions.   Two   types   of   critical   (in   term   of   concentration   threshold   behavior) morphological phenomena were observed - formation of a pre-flame kernel and primary bifurcation of the pre-flame kernel and the higher order (secondary tertiary etc.) bifurcations of the individual locally spherical and restricted in space flame fronts. For the given initial ambient conditions (channel thickness initial gas mixture pressure and temperature) variation of initial mixture stoichiometry results in a few substantial changes in overall flame shape. These changes were recorded at the specific concentration limits  which   delineate  three  characteristic  macroscopic  morphological  forms  (morphotypes)  of  the ultra-lean  hydrogen-air  flame's  ""trails""  -  ""ray-like""  ""dendritic""  and  ""quasi-uniform"".   Transitions between the revealed basic flame morphotypes took place in different ways. The ""pre-flame kernel-to- rays"" and ""rays-to-dendrites"" transitions were abrupt and resembled the first order transitions in physics. -to-quasi-uniform morphology"" were significantly blurred and can be regarded as analogue to the second order transitions.

During the 13th Five-Year Plan China's natural gas industry developed rapidly and a diversified supply and marketing pattern was formed including domestic conventional gas unconventional gas (shale gas tight sandstone gas coalbed methane etc.) coal-based synthetic natural gas imported LNG and imported pipeline gas. The gross calorific value of gas sources ranged from 34 MJ/m3 to 43 MJ/m3 and the maximum difference of calorific value between different gas sources exceeded 20%. On May 24th 2019 the National Development and Reform Commission and other three ministries/commissions jointly issued the Supervision Regulation on the Fair Access of Oil and Gas Pipeline Network Facilities and required that a natural gas energy measuring and pricing system shall be established within 24 months from the implementation date of this Regulation. In order to speed up the construction of China's natural gas energy measuring system this paper summarizes domestic achievements in the construction of natural gas energy measuring system from the aspects of value traceability and energy measurement standard and analyzes natural gas flowrate measurement technology calorific value determination technology value traceability localization intelligentization and application technology of key energy measurement equipment natural gas pipeline network energy balancing technology based on big data analysis multi-source quality tracking and monitoring technology and energy measurement standard system the need of new energy detection and measurement technology and put forward strategy for the development of natural gas measuring in China. And the following research results are obtained. First China's natural gas energy measuring system can basically meet the requirements of implementing natural gas energy measurement but it still falls behind the international leading level in terms of calibration and application of high-level flowmeter (such as 0.5 class) high-accuracy gas reference material level of calorific value reference equipment and measurement standard system and needs to be further improved. Second it is necessary for China to speed up the research and application of the localization and intelligentization technologies of key energy measurement equipment. Third natural gas pipeline network shall be equipped with measurement check method energy balancing system based on big data analysis and multi-source quality tracking and monitoring system so that the energy transmission loss index of natural gas pipeline network can be superior to the international leading level (0.10%). Fourth to realize the large-scale application of hydrogen energy and bio-energy and the mixed transportation of hydrogen bio-methane and natural gas it is necessary to carry out research on new technology and standardization of hydrogen/bio-methane blended natural gas detection and measurement.

The characterization of liquid hydrogen (LH2) releases has been identified as an international research priority to facilitate the safe use of hydrogen as an energy carrier. Empirical field measurements such as those afforded by Hydrogen Wide Area Monitoring can elucidate the behavior of LH2 releases which can then be used to support and validate dispersion models. Hydrogen Wide Area Monitoring can be defined as the quantitative three-dimensional spatial and temporal profiling of planned or unintentional hydrogen releases. The NREL Sensor Laboratory developed a Hydrogen Wide Area Monitor (HyWAM) based upon a distributed array of hydrogen sensors. The NREL Sensor Laboratory and the Health and Safety Executive (HSE) formally committed to collaborate on profiling GH2 and LH2 releases which allowed for the integration of the NREL HyWAM into the HSE LH2 release behavior investigation supported by the FCH JU Prenormative Research for the Safe Use of Liquid Hydrogen (PRESLHY) program. A HyWAM system was deployed consisting of 32 hydrogen measurement points and co-located temperature sensors distributed downstream of the LH2 release apparatus developed by HSE. In addition the HyWAM deployment was supported by proximal wind and weather monitors. In a separate presentation at this conference “HSE Experimental Summary for the Characterisation Dispersion and Electrostatic Hazards of LH2 for the PRESLHY Project” HSE researchers summarize the experimental apparatus and protocols utilized in the HSE LH2 releases that were performed under the auspices of PRESLHY. As a supplement to the HSE presentation this presentation will focus on the spatial and temporal behavior LH2 releases as measured by the NREL HyWAM. Correlations to ambient conditions such as wind speed and direction plume temperature and hydrogen concentrations will be discussed in addition to the design and performance of the NREL HyWAM and its potential for improving hydrogen facility safety.

The Hydrogen Incidents and Accidents Database (HIAD) is an international open communication platform collecting systematic data on hydrogen-related undesired incidents which was initially developed in the frame of HySafe an EC co-funded Network of Excellence in the 6th Frame Work Programme by the Joint Research Centre of the European Commission (EC-JRC). It was updated by JRC as HIAD 2.01 in 2016 with the support of the Fuel Cells and Hydrogen 2 Joint Undertaking (FCH 2 JU). Since the launch of the European Hydrogen Safety Panel2 (EHSP) initiative in 2017 by FCH 2 JU the EHSP has worked closely with JRC to upload additional/new incidents to HIAD 2.0 and analyze them to gather statistics lessons learnt and recommendations through Task Force 3. The first report to summarise the findings of the analysis was published by FCH 2 JU in September 2019. Since the publication of the first report the EHSP and JRC have continuously worked together to enlarge HIAD 2.0 by adding newly occurred incidents as well as quality historic incidents which were not previously uploaded to HIAD 2.0. This has facilitated the number of validated incidents in HIAD 2.0 to increase from 272 in 2018 to 593 in March 2021. This number is also dynamic and continues to increase as new incidents are being continuously added by both EHSP and JRC; and validated by JRC. The overall quality of the published incidents has also been improved whenever possible. For example additional information has been added to some existing incidents. Since mid-2020 EHSP Task Force TF3 has further analysed the 485 events which were in the database as of July 2020. For completeness of the statistics these include the events considered in our first report3 as well as the newly added/validated events since then. In this process the EHSP has also re-visited the lessons learnt in the first report to harmonise the approaches of analysis and improve the overall analysis. The analysis has comprehensively covered statistics lessons learnt and recommendations. The increased number of incidents has also made it viable to extract statistics from the available incidents at the time of the analysis including previously available incidents. It should be noted that some incidents reported is of low quality therefore it was not included in the statistical analysis.

Adding hydrogen to mains natural gas has been identified as one of the main strategies to reduce CO2 emissions in the United Kingdom. This work aims to characterise the explosion severity of 80:20 v./v. methane/hydrogen blends (‘a blend’) and methane vented deflagrations. The explosion severity of homogenous mixtures was measured in a 15 m3 cubic steel chamber in which the relief area was provided by four windows and a door covered with polypropylene sheet. The pressure increase over time was characterised using piezo-resistive pressure transducers and the flame speed was estimated using ionisation probes installed in the walls of the enclosure. The explosion severity of both mixtures was determined for different equivalence ratios from lean to rich mixtures. The pressure over time presented very similar behaviour for both mixtures comprising multiple peaks divided into three main stages: a first stage related to a spherical confined explosion until the opening of the vent a second stage generated by increased combustion during venting and an oscillatory peak generated by acoustic disturbances with the enclosure. A slight increase in the first stage overpressure was observed for the blend in comparison with methane regardless of the equivalence ratio but no general trend in pressure was observed for other stages of the propagation. The effect of the blockage ratio on explosion severity was studied by adding metallic elements representing furniture in a room.

To maximise power density practical gas turbine combustion systems have several injectors which can lead to complex interactions between flames. However our knowledge about the effect of flame-flame interactions on the flame response the essential element to predict the stability of a combustor is still limited. The present study investigates the effect of hydrogen enrichment flame-flame interaction confinement and asymmetries on the linear and non-linear acoustic response of three premixed flames in a simple can combustor. A parametric study of the linear response characterised by the flame transfer function (FTF) is performed for swirling and non-swirling flames. Flame-flame interactions were achieved by changing the injector spacing and the level of hydrogen enrichment by power from 10 to 50%. It was found that the latter had the most significant effect on the flame response. Asymmetry effects were investigated by changing one of the flames by using a different bluff-body to alter both the flame shape and flow field. The global flame response showed that the asymmetric cases can be reconstructed using a superposition of the two symmetric cases where all three bluff-bodies and flames are the same. Overall the linear response characterised by the flame transfer function (FTF) showed that the effect of increasing the level of hydrogen enrichment is more pronounced than the effect of the injector spacing. Increasing hydrogen enrichment results in more compact flames which minimises flame-flame interactions. More compact flames increase the cut-off frequency which can lead to self-excited modes at higher frequencies. Finally the non-linear response was characterised by measuring the flame describing function (FDF) at a frequency close to a self-excited mode of the combustor for different injector spacings and levels of hydrogen enrichment. It is shown that increasing the hydrogen enrichment leads to higher saturation amplitude whereas the effect of injector spacing has a comparably smaller effect.

The development of a hydrogen energy-based society is becoming the solution for more and more countries. Fuel cell electric vehicles are the best carriers for developing a hydrogen energy-based society. The current research on hydrogen leakage and the diffusion of fuel cell electric vehicles has been sufficient. However the study of hydrogen safety has not reduced the safety concerns for society and government management departments concerning the large-scale promotion of fuel cell electric vehicles. Hydrogen safety is both a technical and psychological issue. This paper aims to provide a comprehensive overview of fuel cell electric vehicles’ hydrogen dispersion and the burning behavior and introduce the relevant work of international standardization and global technical regulations. The CFD simulations in tunnels underground car parks and multistory car parks show that the hydrogen escape performance is excellent. At the same time the research verifies that the flow the direction of leakage and the vehicle itself are the most critical factors affecting hydrogen distribution. The impact of the leakage location and leakage pore size is much smaller. The relevant studies also show that the risk is still controllable even if the hydrogen leakage rate is increased ten times the limit of GTR 13 to 1000 NL/min and then ignited. Multi-vehicle combustion tests of fuel cell electric vehicles showed that adjacent vehicles were not ignited by the hydrogen. This shows that as long as the appropriate measures are taken the risk of a hydrogen leak or the combustion of fuel cell electric vehicles is controllable. The introduction of relevant standards and regulations also indirectly proves this point. This paper will provide product design guidelines for R&D personnel offer the latest knowledge and guidance to the regulatory agencies and increase the public’s acceptance of fuel cell electric vehicles.

The anticipated upscaling of hydrogen energy applications will involve the storage and transport of hydrogen at cryogenic conditions. Understanding the potential hazard arising from leaks in high-pressure cryogenic storage is needed to improve hydrogen safety. The manuscript reports a series of numerical simulations with detailed chemistry for the transient evolution of ignited high-pressure cryogenic hydrogen jets. The study aims to gain insight of the ignition processes flame structures and dynamics associated with the transient flame evolution. Numerical simulations were firstly conducted for an unignited jet released under the same cryogenic temperature of 80 K and pressure of 200 bar as the considered ignited jets. The predicted hydrogen concentrations were found to be in good agreement with the experimental measurements. The results informed the subsequent simulations of the ignited jets involving four different ignition locations. The predicted time series snapshots of temperature hydrogen mass fraction and the flame index are analyzed to study the transient evolution and structure of the flame. The results show that a diffusion combustion layer is developed along the outer boundary of the jet and a side diffusion flame is formed for the near-field ignition. For the far-field ignition an envelope flame is observed. The flame structure contains a diffusion flame on the outer edge and a premixed flame inside the jet. Due to the complex interactions between turbulence fuel-air mixing at cryogenic temperature and chemical reactions localized spontaneous ignition and transient flame extinguishment are observed. The predictions also captured the experimentally observed deflagration waves in the far-field ignited jets.

Hydrogen dispersion in stagnant environment resulting from blowdown of a vessel storing the gas at cryogenic temperature is simulated using different CFD codes and modelling strategies. The simulations are based on the DISCHA experiments that were carried out by Karlsruhe Institute of Technology (KIT) and Pro-Science (PS). The selected test for the current study involves hydrogen release from a 2.815 dm3 volume tank with an initial pressure of 200 barg and temperature 80 K. During the release the hydrogen pressure in the tank gradually decreased. A total of about 139 gr hydrogen is released through a 4 mm diameter. The temperature time series and the temperature decay rate of the minimum value predicted by the different codes are compared with each other and with the experimentally measured ones. Recommendations for future experimental setup and for modeling approaches for similar releases are provided based on the present analysis. The work is carried out within the EU-funded project PRESLHY.

Hydrogen is widely considered a clean source of energy from the viewpoint of reduction in carbon dioxide emissions as a countermeasure against global warming and air pollution. Various efforts have been made to develop hydrogen as a viable energy carrier including the implementation of fuel cell vehicles (FCVs) and hydrogen refuelling stations (HRSs). A good network of hydrogen refuelling stations is essential for operating FCVs and several hydrogen refuelling stations have been constructed and are in operation worldwide [1]. However despite the potential benefits of hydrogen its flammability creates significant safety concerns. Furthermore even though the energy density of hydrogen is lower than that of gasoline and there is no carbon present which means the amount of radiant heat flux released during combustion is relatively small hydrogen must be handled at high pressure in order to make the cruising range of a fuel cell vehicle (FCV) equal to that of gasoline-powered vehicles. Therefore it is essential to properly evaluate these safety concerns and take reasonable and effective countermeasures. Approximately 50 accidents and incidents involving HRSs have been reported globally [2]. Sakamoto et al. [2] analysed accidents and incidents at HRSs in Japan and the USA to identify the safety issues. Most types of accidents and incidents are small leakages of hydrogen but some have led to serious consequences such as fire and explosion. Recently there was a serious incident in Norway at Kjørbo where a strong explosion was observed [3] – indeed this was within a short time of two other serious incidents in the USA and South Korea showing that the frequency of such incidents may be higher as deployments increase. Use of hydrogen forklifts (and the associated refuelling infrastructure) is another challenge to consider. Hydrogen refuelling stations are often installed in urban areas facing roads and are readily accessible to everyone. Therefore a key measure to approve the hydrogen refuelling stations is safety distances between the hydrogen infrastructure and the surrounding structures such as office buildings or residential dwellings. Whilst a lot of work has been carried out on safety distances (see e.g. [4-6) the accident scenario assumptions and safety distances varied widely in those studies. As a result no consensus has yet emerged on the safety distances to be used and efforts are still needed to bridge the gap between international standards and local regulations (see e.g. [7-8]). The paper analyses this issue and provides guidance on the way forward.

The use of hydrogen is expected to increase rapidly in the future. Leakage of hydrogen pipework are the main forms of safety problems in hydrogen utilization. In this paper a numerical model of hydrogen leakage and diffusion in pipe joints was established. The Schlieren + high-speed camera is used in experiments to observe the leakage of hydrogen in the pipe joints. In addition the shape and size of the scratches in the tube were statistically analyzed. Finally the leakage characteristics of double ferrule joints with scratches are experimentally analyzed. For the two scratch sizes the critical pressure values for the vortex transition are 0.2 MPa and 0.03 MPa. Through our experimental process some practical experience and suggestions are given.

In this study the combustion of submicron-sized Al particles in air was studied numerically with a particular focus on the effect of hydrogen addition. Oxidation of the Al particles and the interaction with hydrogen-related intermediates were considered by regarding them as liquid-phase molecules initially. Zero- and One-dimensional numerical simulations were then carried out to investigate the effect of the hydrogen addition on fundamental combustion characteristics of the Al flame by calculating properties such as ignition delay time and flame speed. Our attention was paid to how the hydrogen chemistry is coupled with the Al oxidation process. Numerical results show that the hydrogen addition generally reduces the reactivity of Al such that the flame speed and temperature decrease while it  can greatly shorten ignition delay times of the Al flame depending on initial temperatures.

Hydrogen safety is an important topic for hydrogen energy application. Unintended hydrogen releases and combustions are potential accident scenarios which are of great interest for developing and updating the safety codes and standards. In this paper hydrogen releases and delayed ignitions were studied.

The effects of different mole fractions of hydrogen and carbon dioxide on the combustion characteristics of a premixed methane–air mixture are experimentally and numerically investigated. The laminar burning velocity of hydrogen-methane-carbon dioxide-air mixture was measured using the spherically expanding flame method at the initial temperature and pressure of 283 K and 0.1 MPa respectively. Additionally numerical analysis is conducted under steady 1D laminar flow conditions to investigate the adiabatic flame temperature and dominant elementary reactions. The measured velocities correspond with those estimated numerically. The results show that increasing the carbon dioxide mole fraction decreases the laminar burning velocity attributed to the carbon dioxide dilution which decreases the thermal diffusivity and flame temperature. Conversely the velocity increases with the thermal diffusivity as the hydrogen mole fraction increases. Moreover the hydrogen addition leads to chain-branching reactions that produce active H O and OH radicals via the oxidation of hydrocarbons which is the rate-determining reaction.

In the current work the combustion behavior of hydrogen-carbon monoxide-air mixtures in semiconfined geometries is investigated in a large horizontal channel facility (dimensions 9 m x 3 m x 0.6 m (L x W x H)) as a part of a joint German nuclear safety project. In the channel with evenly distributed obstacles (blockage ratio 50%) and an open to air ground face homogeneous H2-CO-air mixtures are ignited at one end. The combustion behavior of the mixture is analyzed using the signals of pressure sensors modified thermocouples and ionization probes for flame front detection that are distributed along the channel ceiling. In the experiments various fuel concentrations (cH2 + cCO = 14 to 22 Vol%) with different H2:CO ratios (75:25 50:50 and 25:75) are used and the transition regions for a significant flame acceleration to sonic speed (FA) as well as to a detonation (DDT) are investigated. The conditions for the onset of these transitions are compared with earlier experiments performed in the same facility with H2-air mixtures. The results of this work will help to allow a more realistic estimation of the pressure loads generated by the combustion of H2-CO-air mixtures in obstructed semi-confined geometries.

Building  the  international  hydrogen  supply  chain  requires  the  large-scale  liquefied   hydrogen(LH2) carrier. During shipping LH2 with LH2 Carrier the tank is pressurized by LH2 evaporation due to heat ingress from outside. Before unloading LH2 at the receiving terminal reducing the tank pressure is essential for the safe tank operation. However pressure reduction might cause flashing leading to rapid  vaporization  of liquefied  hydrogen  liquid  leakage.   Moreover  it  was  considered  that  pressure recovery phenomenon which was not preferred in terms of tank pressure management occurred at the beginning  of  pressure  reduction.  Hence  the   purpose  of  our  research  is  to  clarify  the phenomenon inside  the  cargo  tank  during   pressure  reduction.  The  CFD  analysis  of  the  pressure  reduction phenomenon was conducted with the   VOF based in-house CFD code utilizing the C-CUP scheme combined  with  the  hybrid   Level  Set  and  MARS  method.  In  our  previous  research  the  pressure reduction  experiments   with  the  30  m³  LH2  tank  were  simulated  and  the  results  showed  that  the pressure   recovery  was  caused  by  the  boiling  delay  and  the  tank  pressure  followed  the   saturation pressure  after  the  liquid  was  fully  stirred.  In  this  paper  the  results  were re-evaluated  in  terms  of temperature.  While  pressure  reduction  was  dominant  the  temperature  of  vapor-liquid  interface decreased.  Once  the  boiling  bubble  stirred  the  interface  its  temperature  reached  the  saturation temperature  after  pressure  recovery  occurred.  Moreover  it  was  found  that  the  liquid  temperature during  pressure  reduction  could  not  be  measured  because  of  the  boiling  from  the  wall  of  the thermometer. The CFD analysis on pressure reduction of 1250 m³ tank for the LH2 Carrier was also very could occur in the case of the 1250 m³ tank in a certain condition. These results provide new insight into the development of the LH2 carrier.

Hydrogen has the physical and chemical characteristics of being flammable explosive and prone to leakage and its safety is the main issue faced by the promotion of hydrogen as an energy source. The most common scene in vehicle application is the longitudinal wind generated by driving and the original position of hydrogen concentration sensors (HCSs) did not consider the influence of longitudinal wind on the hydrogen leakage trajectory. In this paper the computational fluid dynamics (CFD) software STAR CCM 2021.1 is used to simulate the hydrogen leakage and diffusion trajectories of fuel cell vehicles (FCVs) at five different leakage locations the longitudinal wind speeds of 0 km/h 37.18 km/h and 114 km/h and it is concluded that longitudinal wind prolongs the diffusion time of hydrogen to the headspace and reduces the coverage area of hydrogen in the headspace with a decrease of 81.35%. In order to achieve a good detection effect of fuel cell vehicles within the longitudinal wind scene based on the simulated hydrogen concentration–time matrix the scene clustering method based on vector similarity evaluation was used to reduce the leakage scene set by 33%. Then the layout position of HCSs was optimized according to the proposed multi-scene full coverage response time minimization model and the response time was reduced from 5 s to 1 s.

The development of safe dispensing equipment for the fueling of heavy duty (HD) vehicles is critical to the expansion of this newly and quickly expanding market. This paper discusses the development of a HD dispenser and nozzles assembly (nozzle hose breakaway) for these new larger vehicles where flow rates are more than double compared to light duty (LD) vehicles. This equipment must operate at nominal pressures of 700 bar -40o C gas temperature and average flow rate of 5-10 kg/min at a high throughput commercial hydrogen fueling station without leaking hydrogen. The project surveyed HD vehicle manufacturers station developers and component suppliers to determine the basic specifications of the dispensing equipment and nozzle assembly. The team also examined existing codes and standards to determine necessary changes to accommodate HD components. From this information the team developed a set of specifications which will be used to design the dispensing equipment. In order to meet these goals the team performed computational fluid dynamic pressure modelling and temperature analysis in order to determine the necessary parameters to meet existing safety standards modified for HD fueling. The team also considered user operational and maintenance requirements such as freeze lock which has been an issue which prevents the removal of the nozzle from LD vehicles. The team also performed a failure mode and effects analysis (FMEA) to identify the possible failures in the design. The dispenser and nozzle assembly will be tested separately and then installed on an innovative HD fueling station which will use a HD vehicle simulator to test the entire system.

This paper presents an experimental study of a hydrogen fusible link developed for use in the detection of hydrogen and in the activation of passive ventilation or other safety systems. Fusible links are commonly used to passively close fire dampers in the event of a fire; they generally consist of two pieces of metal joined together by a low temperature alloy to form a single device. When exposed to fire the link will heat up and eventually melt the alloy causing the metal pieces to separate. The same principle has been adopted for the hydrogen fusible link in which hydrogen recombiner catalyst was coated onto small rectangular brass plates. These plates were then soldered together to create prototypes of the hydrogen fusible link. When the resulting link is exposed to a hydrogen-air mixture an exothermic reaction occurs on the catalyst surface that will heat up the link and melt the solder separating the two sections of the hydrogen fusible link. A series of experiments was performed to characterize the thermal response of the hydrogen fusible links to various hydrogen-air mixtures. The effect of both hydrogen concentration and its rate of accumulation on the increase of catalyst temperature was examined. This study demonstrated the applicability of the hydrogen fusible link for managing hydrogen risk.

Hydrogen has the potential as an energy solution to contribute to decarbonisation targets as it has the capability to deliver low-carbon energy at the scale required. For this to be realised the suitability of the existing natural gas pipeline networks for transporting hydrogen must be established. The current paper describes a feasibility study that was undertaken to assess the potential for repurposing the UK’s Local Transmission System (LTS) natural gas pipelines for hydrogen service. The analysis focused on SGN’s network which includes 3000 km of LTS pipelines in Scotland and the south of England. The characteristics of the LTS pipelines in terms of materials of construction and operation were first evaluated. This analysis showed that a significant percentage of SGN’s LTS network consists of lower strength grades of steel pipeline that operate at low stresses which are factors conducive to a pipeline’s suitability for hydrogen service. An assessment was also made of where existing approaches in pipeline operation may require modifications for hydrogen. The effects of changes in mechanical properties of steel pipelines on integrity and lifetime as a result of potential hydrogen degradation were demonstrated using fitness-for-purpose analysis. A review of pipeline risk assessment and Land-Use Planning (LUP) zone calculations for hydrogen was undertaken to identify any required changes. Case studies on selected sections of the LTS pipeline were then carried out to illustrate the potential changes to LUP zones. The work concluded with a summary of identified gaps that require addressing to ensure safe pipeline repurposing for hydrogen which cover materials performance inspection risk assessment land use planning and procedures.

Hydrogen fuel cell vehicle (HFCV) technology poses great promise as an alternative to significantly reduce the environmental impact of the transport sector’s emissions. However hydrogen fuel cell technology is relatively new therefore confirmation of the reliability and safety analysis is still required particularly for fire scenarios within confined spaces such as tunnels. This study applied the computational fluid dynamics (CFD) simulations in conjunction with probabilistic calculation methods to determine the associated thermal risk of a hydrogen jet fire in a tunnel and its dependency on scenarios with different tunnel slopes longitudinal and transverse ventilation velocities and fire positions. A large-scale model of 102 m in which the effects of outlined parameter variations on the severity of the fire incident were analysed. It is found that both tunnel ventilation techniques and slope were critical for the effective ejection of accumulated heat. With ventilation playing a primary role in the ejection of heat and gas and slope ensuring the stability of the ejected heat probabilities of thermal burns were found to be reduced by up to approximately 35% with a strong suggestion of critical combinations to further reduce the dangers of hydrogen tunnel fires.

In the case of a severe nuclear power plant accident hydrogen gas formation may occur from the core degradation and cooling water evaporation and subsequent oxidation of zircaloy. These phenomena increase the risk of hazardous combustion events in the reactor especially when combined with an ignition source. If not handled carefully these types of accidents can cause severe damage to the reactor building with potential radioactive effects on the environment. Although hydrogen-air combustion has been investigated before hydrogen-air-steam mixtures remain unstudied under reactor-like conditions. Thus this study investigated such mixtures’ combustion regimes. A closed tube of 318 liters (7.65m tall and 0.23m inner diameter) measures the flame speed flame propagation and shock wave behaviors for 11-15 %vol hydrogen mixtures combined with 0 20 or 30 %vol steam and air. Thus both the effect of steam and hydrogen content was investigated and compared. The experimental setup combined photomultiplier tubes pressure sensors and shock detectors to give a full view of the different combustion regimes. A number of obstacles changed the in-chamber turbulence during flame propagation to provide further reactor-like environments. This changed turbulence affected the combustion regimes and enhanced the flame speed for some cases. The results showed varying combustion behaviors depending on the water vapor concentration where a higher concentration meant a lower flame speed reduced pressure load and sometimes combustion extinction. At 0 %vol steam dilution the flame speed remained supersonic for all H2 concentrations while at 30 %vol steam dilution the flame speed remained subsonic for all H2 concentrations. Thus with high levels of steam dilution the risk for shock waves leading to potential reactor building destruction decreases."

Hydrogen is an environmentally friendly source of renewable energy. Energy generation from hydrogen has not yet been widely commercialized due to issues related to risk management in its storage and transportation. In this paper the authors propose a hybrid multiple-criteria decision-making (MCDM)-based method to manage the risks involved in the storage and transportation of hydrogen (RSTH). First we identified the key points of the RSTH by examining the relevant literature and soliciting the opinions of experts and used this to build a prototype of its decision structure. Second we developed a hybrid MCDM approach called the D-ANP that combined the decision-making trial and evaluation laboratory (DEMENTEL) with the analytic network process (ANP) to obtain the weight of each point of risk. Third we used fuzzy evaluation to assess the level of the RSTH for Beijing China where energy generation using hydrogen is rapidly advancing. The results showed that the skills of the personnel constituted the most important risk-related factor and environmental volatility and the effectiveness of feedback were root factors. These three factors had an important impact on other factors influencing the risk of energy generation from hydrogen. Training and technical assistance can be used to mitigate the risks arising due to differences in the skills of personnel. An appropriate logistics network and segmented transportation for energy derived from hydrogen should be implemented to reduce environmental volatility and integrated supply chain management can help make the relevant feedback more effective.

Throughout the history of the mining petroleum process and nuclear industries continuous efforts have been made to develop and improve measures to prevent and mitigate accidental explosions. Over the coming decades energy systems are expected to undergo a transition towards sustainable use of conventional hydrocarbons and an increasing share of renewable energy sources in the global energy mix. The variable and intermittent supply of energy from solar and wind points to energy systems based on hydrogen or hydrogen-based fuels as the primary energy carriers. However the safety-related properties of hydrogen imply that it is not straightforward to achieve and document the same level of safety for hydrogen systems compared to similar systems based on established fuels such as petrol diesel and natural gas. Compared to the conventional fuels hydrogen-air mixtures have lower ignition energy higher combustion reactivity and a propensity to undergo deflagration-to-detonation-transition (DDT) under certain conditions. To achieve an acceptable level of safety it is essential to develop effective measures for mitigating the consequences of hydrogen explosions in systems with certain degree of congestion and confinement. Extensive research over the last decade have demonstrated that chemical inhibition or partial suppression can be used for mitigating the consequences of vapour cloud explosions (VCEs) in congested process plants. Total and cooperation partners have demonstrated that solid flame inhibitors injected into flammable hydrocarbon-air clouds represent an effective means of mitigating the consequences of VCEs involving hydrocarbons. For hydrogen-air explosions these same chemicals inhibitors have not proved effective. It is however well-known that hydrocarbons can affect the burning velocity of hydrogen-air mixtures greatly. This paper gives an overview over previous work on chemical inhibitors. In addition experiments in a 20-litre vessel have been performed to investigate the effect of combinations of hydrocarbons and alkali salts on hydrogen/air mixtures.

The minimum distances between exposures and bulk liquid hydrogen listed in the National Fire Protection Agency’s Hydrogen Technology Code NFPA 2 are based on historical consensus without a documented scientific analysis. This work follows a similar analysis as the scientific justification provided in NFPA 2 for exposure distances from bulk gaseous hydrogen storage systems but for liquid hydrogen. Validated physical models from Sandia’s HyRAM software are used to calculate distances to a flammable concentration for an unignited release the distance to critical heat flux values and the visible flame length for an ignited release and the overpressure that would occur for a delayed ignition of a liquid hydrogen leak. Revised exposure distances for bulk liquid hydrogen systems are calculated. These distances are related to the maximum allowable working pressure of the tank and the line size as compared to the current exposure distances which are based on system volume. For most systems the exposure distances calculated are smaller than the current distances for Group 1 they are similar for Group 2 while they increase for some Group 3 exposures. These distances could enable smaller footprints for infrastructure that includes bulk liquid hydrogen storage tanks especially when using firewalls to mitigate Group 3 hazards and exposure distances. This analysis is being refined as additional information on leak frequencies is incorporated and changes have been proposed to the 2023 edition of NFPA 2.

In the framework of the HYTUNNEL-CS European project sponsored by FCH-JU a set of preliminary tests were conducted in a real tunnel in France. These tests are devoted to safety of hydrogen-fueled vehicles having a compressed gas storage and Temperature Pressure Release Device (TPRD). The goal of the study is to develop recommendations for Regulations Codes and Standards (RCS) for inherently safer use of hydrogen vehicles in enclosed transportation systems. Two scenarios were investigated (a) jet fire evolution following the activation of TPRD due to conventional fuel car fire and (b) explosion of compressed hydrogen tank. The obtained experimental data are systematically compared to existing engineering correlations. The results will be used for benchmarking studies using CFD codes. The hydrogen pressure range in these preliminary tests has been lowered down to 20MPa in order to verify the capability of various large-scale measurement techniques before scaling up to 70 MPa the subject of the second experimental campaign.

Several manufacturers are developing heavy duty (HD) hydrogen stations and vehicles as zeroemissions alternatives to diesel and gasoline. In order to meet customer demands the new technology must be comparable to conventional approaches including safety reliability fueling times and final fill levels. For a large HD vehicle with a storage rated to 70 MPa nominal working pressure the goal to meet liquid fuel parity means providing 100 kg of hydrogen in 10 minutes. This paper summarizes the results to date of the PRHYDE project efforts to define the concepts of HD fueling which thereby lays the groundwork for the development of the safe and effective approach to filling these large vehicles. The project starts by evaluating the impact of several different assumptions such as the availability of static vehicle data (e.g. vehicle tank type and volume) and station data (e.g. expected station precooling capability) but also considers using real time dynamic data (e.g. vehicle tank gas temperature and pressure station gas temperature etc.) for optimisation to achieve safety and efficiency improvements. With this information the vehicle or station can develop multiple maps of fill time versus the hydrogen delivery temperature which are used to determine the speed of fueling. This will also allow the station or vehicle to adjust the rate of fueling as the station pre-cooling levels and other conditions change. The project also examines different steps for future protocol development such as communication of data between the vehicle and station and if the vehicle or station is controlling the fueling.

In this work experiments on horizontal hydrogen jet releases from a 2.815 dm³ volume tank to the ambience are described. For the main experimental series tank valve and release line were cooled down to a temperature of approx. 80 K in a bath of liquid nitrogen. As a reference similar experiments were also performed with the uncooled tank at ambient temperature. The releases were carried out through four nozzles with different circular orifice diameters from 0.5 to 4 mm and started from initial tank pressures from 0.5 to 20 MPa (rel.). During the releases pressures and temperatures inside the vessel as well as inside the release line were measured. Outside the nozzle further temperature and hydrogen concentration measurements were performed along and besides the jet axis. The electrostatic field builtup in the jet was monitored using two field meters in different distances from the release nozzle and optical observation via photo and video-cameras was performed for the visualization of the H2-jet via the BOS-method. The experiments were performed in the frame of the EU-funded project PRESHLY in which several tests of this program were selected for a comparative computational study the results of which will also be presented at this conference. So on the one hand the paper gives a comprehensive description of the facility on the other hands it also describes the experimental procedure and the main findings.

Hydrogen which has a high energy density and does not emit pollutants is considered an alternative energy source to replace fossil fuels. Herein we report an experimental study on hydrogen leaks and ventilation methods for preventing damage caused by leaks from hydrogen fuel cell rooms in homes among various uses of hydrogen. This experiment was conducted in a temporary space with a volume of 11.484 m3 . The supplied pressure leak-hole size and leakage amount were adjusted as the experimental conditions. The resulting hydrogen concentrations which changed according to the operation of the ventilation openings ventilation fan and supplied shutoff valve were measured. The experimental results showed that the reductions in the hydrogen concentration due to the shutoff valve were the most significant. The maximum hydrogen concentration could be reduced by 80% or more if it is 100 times that of the leakage volume or higher. The shutoff valve ventilation fan and ventilation openings were required to reduce the concentrations of the fuel cell room hydrogen in a spatially uniform manner. Although the hydrogen concentration in a small hydrogen fuel cell room for home use can rapidly increase a rapid reduction in the concentration of hydrogen with an appropriate ventilation system has been experimentally proven.

Hydrogen (H2 ) is attracting attention as a renewable energy source in various fields. However H2 has a potential danger that it can easily cause a backfire or explosion owing to minor external factors. Therefore H2 gas monitoring is significant particularly near the lower explosive limit. Herein tin dioxide (SnO2 ) thin films were annealed at different times. The as-obtained thin films were used as sensing materials for H2 gas. Here the performance of the SnO2 thin film sensor was studied to understand the effect of annealing and operating temperature conditions of gas sensors to further improve their performance. The gas sensing properties exhibited by the 3-h annealed SnO2 thin film showed the highest response compared to the unannealed SnO2 thin film by approximately 1.5 times. The as-deposited SnO2 thin film showed a high response and fast response time to 5% H2 gas at 300 ◦C of 257.34% and 3 s respectively.

The  understanding  of  physical  phenomena  occurring  during  the  refueling  of  H2  tanks  used for hydrogen mobility applications is the key point towards the most optimal refueling protocol. A lot of experimental investigations on tank refueling were performed in the previous years for different types and sizes of tank. Several operating conditions were tested through these experiments. For instance the HyTransfer project gave one of the major outputs on the understanding of the physical phenomena occurring during a tank refueling. From a numerical perspective the availability of accurate numerical tools is another key point. Such tools could be used instead of the experimental set-ups to test various operating conditions or new designs of tanks and injectors. The use of these tools can reduce the cost of the refueling protocol development in the future. However they first need to be validated versus experimental data. This work is dedicated to CFD (Computational Fluid Dynamics) modeling of the hydrogen refueling of a long horizontal 530L type IV tank. As of now the number of available CFD simulations for  such  a large  tank  is  low  as  the  computational  cost  is  significant  which  is  often considered as a bottleneck for this approach. The simulated operating conditions correspond to one of the  experimental  campaigns  performed  in  the  framework  of  the  HyTransfer  project. The  3D  CFD model is presented. In a first validation step the CFD results are compared with experimental data. Then  a  deeper  insight  into  the  physics  predicted  by  the  CFD  is  provided.   Finally  two  other methodologies  with  the  aim  to  reduce  the  computational  cost  have   been  tested.

The Hy4Heat Safety Assessment has focused on assessing the safe use of hydrogen gas in certain types of domestic properties and buildings. The summary reports (the Precis and the Safety Assessment Conclusions Report) bring together all the findings of the work and should be looked to for context by all readers. The technical reports should be read in conjunction with the summary reports. While the summary reports are made as accessible as possible for general readers the technical reports may be most accessible for readers with a degree of technical subject matter understanding. All of the safety assessment reports have now been reviewed by the HSE<br/>Annex prepared to support Site Specific Safety Cases for hydrogen gas community demonstrations based on work undertaken by the Hy4Heat programme. It covers a collection of recommended risk reduction measures for application downstream of the Emergency Control Valve (ECV)

Transformers are generally considered to be the costliest assets in a power network. The lifetime of a transformer is mainly attributable to the condition of its solid insulation which in turn is measured and described according to the degree of polymerization (DP) of the cellulose. Since the determination of the DP index is complex and time-consuming and requires the transformer to be taken out of service utilities prefer indirect and non-invasive methods of determining the DP based on the byproduct of cellulose aging. This paper analyzes solid insulation degradation by measuring the furan concentration recently introduced methanol and dissolved gases like carbon oxides and hydrogen in the insulating oil. A group of service-aged distribution transformers were selected for practical investigation based on oil samples and different kinds of tests. Based on the maintenance and planning strategy of the power utility and a weighted combination of measured chemical indicators a neural network was also developed to categorize the state of the transformer in certain classes. The method proved to be able to improve the diagnostic capability of chemical indicators thus providing power utilities with more reliable maintenance tools and avoiding catastrophic failure of transformers.

Liquid hydrogen (LH2) compared to compressed gaseous hydrogen offers advantages for large-scale transport and storage of hydrogen with higher densities. Although the gas industry has good experience with LH2 only little experience is available for the new applications of LH2 as an energy carrier. Therefore the European FCH JU funded project PRESLHY conducted pre-normative research for the safe use of cryogenic LH2 in non-industrial settings. The central research consisted of a broad experimental program combined with analytical work modelling and simulations belonging to the three key phenomena of the accident chain: release and mixing ignition and combustion. The presented results improve the general understanding of the behavior of LH2 in accidents and provide some design guidelines and engineering tools for safer use of LH2. Recommendations for improvement of current international standards are derived.