Publications

The work was done with respect to hydrogen safety of ITER vacuum vessel in cases of loss of cooling and loss of vacuum accidents. Experiments were conducted at sub-atmospheric pressures from 1 bar to 200 mbar and elevated temperatures up to 300 oC. Hydrogen concentration was changed from lower to upper flammability limits in all the range of pressures and temperatures. The experiments were performed in a spherical explosion bomb equipped with two quartz windows. The flame propagation velocity was measured using pressure method and high speed shadow cinematography. The theoretical flame velocities were calculated by Cantera code using Lutz and Mueller mechanisms. The influence of the initial temperature and pressure conditions on the laminar flame speed SL overall reaction order n and Markstein length LM are presented in this work and compared with the results of a theoretical model.

The present paper illustrates an innovative steel processing route developed by employing hydrogen direct reduced pellets and an open slag bath furnace. The paper illustrates the direct reduction reactor employing hydrogen as reductant on an industrial scale. The solution allows for the production of steel from blast furnace pellets transformed in the direct reduction reactor. The reduced pellets are then melted in open slag bath furnaces allowing carburization for further refining. The proposed solution is clean for the decarbonization of the steel industry. The kinetic chemical and thermodynamic issues are detailed with particular attention paid to the slag conditions. The proposed solution is also supported by the economic evaluation compared to traditional routes.

In 2003 the US Department of Energy (DOE) initiated a project to coordinate the development of a national template of hydrogen codes and standards for both vehicular and stationary applications. The process consisted of an initial evaluation to determine where there were gaps in the existing hydrogen codes and standards and the codes and standards required to fill these gaps. These codes and standards were to be developed by several Standards Development Organizations (SDOs). This effort to develop codes and standards has progressed from a position in 2003 when there were relatively few codes and standards that directly addressed hydrogen technology applications to the position at the end of 2008 where requirements to permit hydrogen technologies have been implemented in primary adopted codes- building and fire codes in hydrogen specific codes such as National Fire Protection Association (NFPA) 52 NFPA 55 and NFPA 853 and in many of the hydrogen specific component standards that are referenced primarily in the NFPA codes and standards. This paper describes the three levels of codes and standards that address hydrogen technologies for the built environment:<br/>Level 1. Primary adopted building and fire codes<br/>Level 2. Hydrogen specific codes and standards references in primary adopted code<br/>Level 3. Hydrogen specific component standards referenced in hydrogen specific codes<br/>This paper also describes the progress to date in populating these three levels with the required hydrogen codes and standards. The first two levels are essentially complete and are undergoing refinement and routine revision. Level 3 the hydrogen specific component standards is the furthest from having first edition documents that address requirements for a hydrogen system component.<br/>The DOE is focusing much of their codes and standards development efforts on these hydrogen specific component standards with the expectation that a first edition of most of these standards will be issued by 2010.

Liquid hydrogen carriers are considered to be attractive hydrogen storage options because of their ease of integration into existing chemical transportation infrastructures when compared with liquid or compressed hydrogen. The development of such carriers forms part of the work of the International Energy Agency Task 32: Hydrogen-Based Energy Storage. Here we report the state-of-the-art for ammonia-based and liquid organic hydrogen carriers with a particular focus on the challenge of ensuring easily regenerable high-density hydrogen storage.

The flame propagation regimes for the stoichiometric hydrogen-air mixtures in an obstructed semiconfined flat layer have been numerically investigated in this paper. Conditions defining fast or sonic propagation regime were established as a function of the main dimensions characterizing the system and the layout of the obstacles. It was found that the major dependencies were the following: the thickness of the layer of H2-air mixture the blockage ratio and the distance between obstacles and the obstacle size. A parametric study was performed to determine the combination of the above variables prone to produce strong combustions. Finally a criterion that separates experiments resulting in slow subsonic from fast sonic propagations regimes was proposed.

In this podcast David Ledesma talks to Martin Lambert Head of OIES Hydrogen Research about the key messages from the recent European Hydrogen Conference and how they fit with the ongoing research in OIES.   In particular they cover the heightened energy security concerns following the Russian invasion of Ukraine and hydrogen ambitions in the REPowerEU document published by the European Commission in early March 2002.   They then go on to talk about the growing realism about where hydrogen is more likely to play a role and some of the key challenges to be overcome. Addressing the challenges of creating business cases for use of hydrogen in specific sectors and for transporting it to customers the conversation also addresses the importance of hydrogen storage and the recognition that this area needs more focus both technically and commercially.   Finally they talk about the geopolitics of hydrogen and how energy security concerns may influence future development pathways.

The podcast can be found on their website

The development of a hydrogen-based economy is the perfect nexus between the need of discontinuing the use of fossil fuels (trying to mitigate climate change) the development of a system based on renewable energy (with the use of hydrogen allowing us to buffer the discontinuities produced in this generation) and the achievement of a local-based robust energy supply system. However extending the use of hydrogen as an energy vector must still overcome challenging issues with the key issues being related to its storage. Cryogenic or pressurized storage is relatively expensive technically complex and presents important safety concerns. As a promising alternative the use of organic hydrogen carriers has been suggested in recent years. The ideal carrier will be an organic compound with a low melting point and low viscosity with a significant number of unsaturated carbon–carbon bonds in addition to being easy to hydrogenate and dehydrogenate. These properties allow us to store and transport hydrogen in infrastructures designed for liquid fuels thus facilitating the replacement of fossil fuels by hydrogen

The absorption of CO2 is of importance in carbon capture utilization and storage technology for greenhouse gas control. In the present work we clarified the mechanism of how metal-based ionic liquids (MBILs) Bmim[XCln]m (X is the metal atom) enhance the CO2 absorption capacity of ILs via performing molecular dynamics simulations. The sparse hydrogen bond interaction network constructed by CO2 and MBILs was identified through the radial distribution function and interaction energy of CO2-ion pairs which increase the absorption capacity of CO2 in MBILs. Then the dynamical properties including residence time and self-diffusion coefficient confirmed that MBILs could also promote the diffusion process of CO2 in ILs. That's to say the MBILs can enhance the CO2 absorption capacity and the diffusive ability simultaneously. Based on the analysis of structural energetic and dynamical properties the CO2 absorption capacity of MBILs increases in the order Cl− → [ZnCl4]2-→ [CuCl4]2-→ [CrCl4]- → [FeCl4]- revealing the fact that the short metal–Cl bond length and small anion volume could facilitate the performance of CO2 absorbing process. These findings show that the metal–Cl bond length and effective volume of the anion can be the effective factors to regulate the CO2 absorption process which can also shed light on the rational molecular design of MBILs for CO2 capture and other key chemical engineering processes such as IL-based gas sensors nano-electrical devices and so on.

GASFLOW is a finite-volume computer code that solves the time-dependent two-phase homogeneous equilibrium model compressible Navier–Stokes equations for multiple gas species with turbulence. The fluid-dynamics algorithm is coupled with conjugate heat and mass transfer models to represent walls floors ceilings and other internal structures to describe complex geometries such as those found in nuclear containments and facilities. Recent applications involve simulations of cryogenic hydrogen tanks at elevated pressures. These applications which often have thermodynamic conditions near the critical point require more accurate real-gas Equations-of-State (EoS) and transport properties than the standard ideal gas EoS and classical kinetic-theory transport properties. This paper describes the rigorous implementation of the generalized real-gas EoS into the GASFLOW CFD code as well as the specific implementation of respective real-gas models (Leachman's NIST hydrogen EoS a modified van der Waals EoS and a modified Nobel-Abel EoS); it also includes a logical testing procedure based upon a numerically exact benchmark problem. An example of GASFLOW simulations is presented for an ideal cryo-compressed hydrogen tank of the type utilized in fuel cell vehicles.

This discussion session concerned experimental and theoretical investigations of the atomistic properties underlying the energetics and kinetics of hydrogen trapping and diffusion in metallic systems.

This article is a transcription of the recorded discussion of ‘Hydrogen transport and trapping: from quantum effects to alloy design.‘ at the Royal Society Scientific Discussion Meeting Challenges of Hydrogen and Metals 16–18 January 2017. The text is approved by the contributors. Y.-S.C. transcribed the session. H.L. assisted in the preparation of the manuscript.

Link to document download on Royal Society Website 

The Joint Research Centre (JRC) of the European Commission together with the European Association of Research and Technology Organisations (EARTO) the European Standards Organisations (ESO) CEN and CENELEC and the European Commission Directorate-General Enterprise and Industry (ENTR) have launched an initiative within the context of the European Forum on Science and Industry to bring the scientific and standardization communities closer together. The second and very successful workshop in a series entitled “Putting Science into Standards" was held in at the Institute for Energy and Transport of the JRC in Petten on 21-22 October 2014.<br/>The workshop focused on Power to Hydrogen (P2H) and Hydrogen Compressed Natural Gas (HCNG) which represent a promising and major contribution to the challenging management of increased integration of renewable energy sources in the overall energy system. The workshop offered a platform to exchange ideas on technologies policy and standardization issues. The participation of major stakeholders from both industry and research to this event proved fruitful in moving towards consensus on the relevant technical issues involved and at identifying a common way forward to increase the maturity and market visibility of P2H components and systems. Other outcomes include a clarification of expectations of industry of where and how policy and standardization can contribute to a competitive development of P2H and related issues. The workshop results will be used to devise a roadmap on "Opportunities for Power to Hydrogen and HCNG" by CEN/CENELEC outlining the next steps of standardization activities.

The integration of a hydrogen gas storage arrangement in vehicles has not been without its challenges. Gaseous state of hydrogen at ambient temperature combined with the fact that hydrogen is highly flammable results in the requirement of more robust high pressure storage systems that can meet modern safety standards. To develop these new safety standards and to properly predict the phenomena of hydrogen dispersion a better understanding of the resulting flow structures and flammable region from controlled and uncontrolled releases of hydrogen gas must be achieved. With the upper and lower explosive limits of hydrogen known the flammable envelope surrounding the site of a uncontrolled hydrogen release can be found from the concentration field. In this study the subsonic release of hydrogen was emulated using helium as a substitute working fluid. A sharp orifice round turbulent jet is used to emulate releases in which leak geometry is circular. Effects of buoyancy and crossflow were studied over a wide range of Froude numbers. The velocity fields of turbulent jets were characterized using particle image velocimetry (PIV). The mean and fluctuation velocity components were well quantified to show the effect of buoyancy due to the density difference between helium and the surrounding air. In the range of Froude numbers investigated (Fr = 1000 750 500 250 and 50) the increasing effects of buoyancy were seen to be proportional to the reduction of the Fr number. While buoyancy is experienced to have a negligible effect on centerline velocity fluctuations acceleration due to buoyancy in the other hand resulted in a slower decay of time-averaged axial velocity component along the centerline. The obtained results will serve as control reference values for further concentration measurement study and for computational fluid dynamics (CFD) validation.

In this study we conducted hydrogen gas filling and discharging cycling tests to examine the thermal behaviour in hydrogen storage tanks under actual use conditions. As a result it was confirmed that the gas temperature in the tank varied depending on the initial test conditions such as the ambient temperature of the tank and the filling gas temperature and that the gas temperature tended to stabilize after several gas filling and discharging cycles.

In case fires break out on the lower deck of a car carrier ship or a ferry the fuel cell vehicles (FCVs) parked on the upper deck may be exposed to radiant heat from the lower deck. Assuming that the thermal pressure relief device (TPRD) of an FCV hydrogen cylinder is activated by the radiant heat without the presence of flames hydrogen gas will be released by TPRD to form combustible air-fuel mixtures in the vicinity. To investigate the possibility of this accident scenario the present study investigated the relationship between radiant heat and TPRD activation time and evaluated the possibility of radiant heat causing hydrogen releases by TPRD activation under the condition of deck temperature reaching the spontaneous ignition level of the tires and other automotive parts. It was found: a) the tires as well as polypropylene and other plastic parts underwent spontaneous ignition before TPRD was activated by radiant heat and b) when finally TPRD was activated the hydrogen releases were rapidly burned by the flames of the tires and plastic parts on fire. Consequently it was concluded that the explosion of air-fuel mixtures assumed in the accident scenario does not occur in the real world.

In order to simulate an accidental hydrogen release from the high pressure pipe system of a hydrogen facility a systematic study on the nature of transient hydrogen jets into air and their combustion behavior was performed at the KIT hydrogen test site HYKA. Horizontal unsteady hydrogen jets from a reservoir of 0.37 dm3 with initial pressures of up to 200 bar have been investigated. The hydrogen jets released via round nozzles 3 4 and 10 mm were ignited with different ignition times and positions. The experiments provide new experimental data on pressure loads and heat releases resulting from the deflagration of hydrogen–air clouds formed by unsteady turbulent hydrogen jets released into a free environment. It is shown that the maximum pressure loads occur for ignition in a narrow position and time window. The possible hazard potential arising from an ignited free transient hydrogen jet is described.

This study investigated the influence of segregations on hydrogen environment embrittlement (HEE) of AISI 304L type austenitic stainless steels. The microstructure of tensile specimens that were fabricated from commercially available AISI 304L steels and tested by means of small strain-rate tensile tests in air as well as hydrogen gas at room temperature was investigated by means of combined EDS and EBSD measurements. It was shown that two different austenitic stainless steels having the same nominal alloy composition can exhibit different susceptibilities to HEE due to segregation effects resulting from different production routes (continuous casting/electroslag remelting). Local segregation-related variations of the austenite stability were evaluated by thermodynamic and empirical calculations. The alloying element Ni exhibits pronounced segregation bands parallel to the rolling direction of the material which strongly influences the local austenite stability. The latter was revealed by generating and evaluating two-dimensional distribution maps for the austenite stability. The formation of deformation-induced martensite was shown to be restricted to segregation bands with a low Ni content. Furthermore it was shown that the formation of hydrogen induced surface cracks is strongly coupled with the existence of surface regions of low Ni content and accordingly low austenite stability. In addition the growth behavior of hydrogen-induced cracks was linked to the segregation-related local austenite stability.

The thermal degradation of two epoxy resin/carbon fiber composites which differ by their volume fractions in carbon fiber (56 and 59 vol%.) was investigated in cone calorimeter under air atmosphere with a piloted ignition. The external heat flux of cone calorimeter was varied up to 75 kW.m-2 to study the influence of the carbon fiber amount on the thermal decomposition of those composites. Thus main parameters of the thermal decomposition of two different composites were determined such as: mass loss mass loss rate ignition time thermal response parameter ignition temperature critical heat flux thermal inertia and heat of gasification. As a result all the parameters that characterize the thermal resistance of composites are decreased when the carbon fiber volume fraction is increased.

The development of a set of safety codes and standards for hydrogen facilities is necessary to ensure they are designed and operated safely. To help ensure that a hydrogen facility meets an acceptable level of risk code and standard development organizations (SDOs) are utilizing risk-informed concepts in developing hydrogen codes and standards. Two SDOs the National Fire Protection Association (NFPA) and the International Organization for Standardization (ISO) through its Technical Committee (TC) 197 on hydrogen technologies have been developing standards for gaseous hydrogen facilities that specify the facilities have certain safety features use equipment made of material suitable for a hydrogen environment and have specified separation distances. Under Department of Energy funding Sandia National Laboratories (SNL) has been supporting efforts by both of these SDOs to develop the separation distances included in their respective standards. Important goals in these efforts are to use a defensible science-based approach to establish these requirements and to the extent possible harmonize the requirements. International harmonization of regulations codes and standards is critical for enabling global market penetration of hydrogen and fuel cell technologies.

One of the focus areas in the heavy-duty transport industry globally is de-carbonization of trucks dozers shovels semi-trucks buses etc. Hydrogen fuel cells (FCs) technology is one considered solution for the industry due to its zero-emissions its MW scalability and capacity to store large amounts of energy for long duration continuous power operation. Underground deep mines is another option for deployment and operation of hydrogen FCs. Benefits include lower emissions improved health comfort and safety as well as reduced operating costs. Underground mining trucks loaders and other machines have power ratings up to 750 kW which proves difficult for battery and tethered electric energy. Hydrogen FCs have the ability to overcome these power and energy storage limitations. The risks and technologies associated with delivering storing and using hydrogen underground first need to be investigated and proven safe. This work presents the design construction and operation of a mining ventilation test facility (VTF) at the North-West University in South Africa that aims to quantify the risk of hydrogen in confined ventilated environments. Initial work has been conducted on measuring concentrations of hydrogen released in the temporary ventilation site and is discussed.

CFD simulations investigating the effect of ventilation airflow on hydrogen release behaviour in an underground mining tunnel were performed using FLACS hydrogen. Both dispersion and combustion scenarios of a hydrogen release coming from a severed distribution pipeline were investigated. Effects on the hydrogen dispersion such as ventilation strength and the mechanism of air flow supply (a pull or push fan) and mine opening surface roughness surface cavities and obstructions were explored. Results showing the effect of changing the position of the leak adding a cavity on the ceiling of the tunnel and changing the roughness of the walls are given. Overpressure sensitivity to the ignition delay was also considered. From the results for the varied ventilation regimes and spatial scenarios it is difficult to identify the optimal ventilation strategy giving the safest conditions for hydrogen distribution and refuelling in an underground mine.

The design of ventilation system has implications for the safety of life and property and the development of regulations and standards in the space with the hydrogen storage equipment. The impact of both the position and the area of a single vent on the dispersion of hydrogen in a cuboid space (with dimensions L x W x H ¼ 2.90 0.74 1.22 m) is investigated with Computational Fluid Dynamics (CFD) in this study. Nine positions of the vent were compared for the leakage taking place at the floor to understand the gas dispersion. It was shown a cloud of 1% mole fraction has been formed near the ceiling of the space in less than 40 s for different positions of the vent which can activate hydrogen sensors. The models show that the hydrogen is removed more effectively when the vent is closer to the leakage position in the horizontal direction. The study demonstrates that the vent height of 1.00 m is safer for the particular scenario considered. The area of the vent has little effect on the hydrogen concentration for all vent positions when the area of the vent is less than 0.045 m2 and the height of the vent is less than 0.61 m.

During the World Expo Shanghai there were one hundred fuel-cell sight-seeing cars in operation at the Expo Site. The sight-seeing cars were not allowed to drive out of the Expo Site and the stationary hydrogen refuelling station was not permitted to build at the Expo Site for the sake of safety. A flexible solution to refuel the cars was the application of mobile hydrogen refuelling stations. To better understand the hazards and risks associated with the mobile hydrogen refueling stations a risk analysis was preformed to improve the safety of the operations. The risks to the station personnel and to the public were discussed separately. Results show that the stationary risks of the mobile stations to the personnel and refueling customers are lower than the risk acceptance criteria over an order of magnitude so occupational risks and risks to customers are completely acceptable. The third party risks can be acceptable as long as the appropriate mitigation measures are implemented especially well designed parking area and operation time. Leak from boosters is the main risk contributor to the stationary risks because of its highest failure rates according to the generic data and its worst harm effects based on the consequence evaluations. As for the road risks of the mobile stations they can be acceptable as long as the appropriate mitigation measures are implemented especially well-designed moving path and transportation time.

The Isle of Grain (IoG) presents a technically feasible commercially viable strategic location to build and operate a hydrogen production facility which would be a key enabler to the UK meeting the Net Zero 2050 target.

As highlighted in the ‘Net Zero – The UK’s contribution to stopping global warming’ report published by The Committee on Climate Change in May 2019 hydrogen is set to have a major part to play in reducing UK carbon dioxide emissions. Carbon Capture and Storage (CCS) is also seen as essential to support those supplies.

The report further recognises that this will involve increased investments and that CCS and hydrogen will require both capital funding and revenue support.

For hydrogen to have a part to play in the decarbonisation of London and the south east of England a large-scale hydrogen production facility will be required which will provide a multi vector solution through the decarbonisation of the gas grid.

This report and any attachment is freely available on the ENA Smarter Networks Portal here. IGEM Members can download the report and any attachment directly by clicking on the pdf icon above.

The different CFD tools used by the NoE HySafe partners are applied to a series of integral complex Standard Benchmark Exercise Problems (SBEPs). All benchmarks cover complementarily physical phenomena addressing application relevant scenarios and refer to associated experiments with an explicit usage of hydrogen. After the blind benchmark SBEPV1 and SBEPV3 with subsonic vertical release in a large vessel and in a garage like facility SBEPV4 with a horizontal under-expanded jet release through a small nozzle SBEPV5 covers the scenario of a subsonic horizontal jet release in a multi-compartment room.<br/>As the associated dispersion experiments conducted by GEXCON Norsk Hydro and STATOIL were disclosed to the participants the whole benchmark was conducted openly. For the purpose of validation only the low momentum test D27 had to be simulated.<br/>The experimental rig consists of a 1.20 m x 0.20 m x 0.90 m (Z vertical) vessel divided into 12 compartments partially even physically by four baffle plates. In each compartment a hydrogen concentration sensor is mounted. There is one vent opening at the wall opposite the release location centrally located about 1 cm above floor with dimensions 0.10 m (Y) times 0.20 m (Z). The first upper baffle plate close to the release point is on a sensitive location as it lies nearly perfectly in the centre of the buoyant jet and thus separates the flow into the two compartments. The actual release was a nominally constant flow of 1.15 norm liters for 60 seconds. With a 12mm nozzle diameter this corresponds to an average exit velocity of 10.17 m/s.<br/>6 CFD packages have been applied by 7 HySafe partners to simulate this experiment: ADREAHF by NCSRD FLACS by GexCon and DNV KFX by DNV FLUENT by UPM and UU CFX by HSE/HSL and GASFLOW by FZK. The results of the different participants are compared against the experimental data. Sensitivity studies were conducted by FZK using GASFLOW and by DNV applying KFX.<br/>Conclusions based on the comparisons and the sensitivity studies related to the performance of the applied turbulence models and discretisation schemes in the release and diffusion phase are proposed. These are compared to the findings of the previous benchmark exercises.

In Europe electrification is considered a key option to obtain a cleaner production of steel at the same time as the electricity system production portfolio is expected to consist of an increasing share of varying renewable electricity (VRE) generation mainly in the form of solar PV and wind power. We investigate cost-efficient designs of hydrogen-based steelmaking in electricity systems dominated by VRE. We develop and apply a linear cost-minimization model with an hourly time resolution which determines cost-optimal operation and sizing of the units in hydrogen-based steelmaking including an electrolyser direct reduction shaft electric arc furnace as well as storage for hydrogen and hot-briquetted iron pellets. We show that the electricity price following steelmaking leads to savings in running costs but to increased capital cost due to investments in the overcapacity of steel production units and storage units for hydrogen and hot-briquetted iron pellets. For two VRE-dominated regions we show that the electricity price following steel production reduces the total steel production cost by 23% and 17% respectively as compared to continuous steel production at a constant level. We also show that the cost-optimal design of the steelmaking process is dependent upon the electricity system mix.

Report presents the preliminary experimental results on hydrogen subsonic leakage in a closed vessel under the well-controlled boundary/initial conditions. Formation of hydrogen-air gas mixture cloud was studied for a transient (10 min) upward hydrogen leakage which was followed by subsequent evolution (15 min) of explosive cloud. Low-intensity ( 0.46⋅10−3 m3/sec) hydrogen release was performed via circular (diameter 0.014 m) orifice located in the bottom part of a horizontal cylindrical vessel ( ≈4 m3). A spatially distributed net of the 24 hydrogen sensors and 24 temperature sensors was used to permanently track the time dependence of the hydrogen concentration and temperature fields in vessel. Analysis of the simultaneous experimental records for the different spatial points permits to delineate the basic flow patterns and stages of hydrogen subsonic release in closed vessel in contrast to hydrogen jet release in open environment. The quantitative data were obtained for the averaged speeds of explosive cloud envelop (50% fraction of the Lower Flammability Limit (LFL)) propagation in the vertical and horizontal directions. The obtained data will be used as an experimental basis for development of the guidelines for an indoors allocation of the hydrogen sensors. Data can be also used as a new benchmark case for the reactive Computational Fluid Dynamics codes validation.

Virtually all major automotive companies are currently developing hydrogen-powered vehicles. The vast majority of them employ compressed hydrogen tanks and components as a means of storing the fuel onboard. Compressed hydrogen vehicle fuel systems are designed in the same way as compressed natural gas vehicles (NGV) i.e. the high pressure (up to 70 MPa) fuel is always contained within the system under all conditions with the exception of vehicular fire. In the event of a vehicle fire the fuel system is protected using a non-reclosing thermally activated pressure relief device (PRD) which safely vents the contents. Hydrogen fuel system PRDs are presently qualified to the performance requirements specified in draft hydrogen standards such ANSI/CSA HPRD 1 and EIHP Rev. 12b. They are also qualified with individual fuel tank designs in accordance with the engulfing bonfire requirements in various published/draft tank standards such as CSA B51 Part 2 JARI S001 SAE TIR J2579 ANSI/CSA HGV 2 ISO DIS 15869.2 and EIHP Rev. 12b. Since 2000 there have been over 20 documented NGV tank failures in service 11 of which have been attributed to vehicle fires. This paper will examine whether currently proposed hydrogen performance standards and installation requirements offer suitable fuel system protection in the event of vehicular fires. A number of alternative fire protection strategies will be discussed including:

• The requirement of an engulfing and/or localized fire test for individual tanks fuel systems and complete vehicles;
• The advantages/disadvantages of point source- surface area- and/or fuse-based PRDs
• The use of thermal insulating coatings/blankets for fire protection resulting in the NONventing of the fuel
• The specification of appropriate fuel system installation requirements to mitigate the effect of vehicular fires.

We analytically investigated the influence of light hydrocarbons on turbulent premixed H2/air atmospheric flames under lean conditions in view of safe handling of H2 systems applications in H2 powered IC engines and gas turbines and also with an orientation towards modelling of H2 combustion. For this purpose an algebraic flame surface wrinkling model included with pressure and fuel type effects is used. The model predictions of turbulent premixed flames are compared with the set of corresponding experimental data of Kido et al. (Kido Nakahara et al. 2002). These expanding spherical flame data include H2–air mixtures doped with CH4 and C3H8 while the overall equivalence ratio of all the fuel/air mixtures is fixed at 0.8 for constant unstretched laminar flame speed of 25 cm/s by varying N2 composition. The model predictions show that there is little variation in turbulent flame speed ST for C3H8 additions up to 20-vol%. However for 50 vol% doping flame speed decreases by as much as 30 % from 250 cm/s that of pure H2–air mixtures for turbulence intensity of 200 cm/s. With respect to CH4 for 50 vol% doping ST reduces by only 6 % cf. pure H2/air mixture. In the first instance the substantial decrease of ST with C3H8 addition may be attributed to the increase in the Lewis number of the dual-fuel mixture and proportional restriction of molecular mobility of H2. That is this decrease in flame speed can be explained using the concept of leading edges of the turbulent flame brush (Lipatnikov and Chomiak 2005). As these leading edges have mostly positive curvature (convex to the unburned side) preferential-diffusive-thermal instabilities cause recognizable impact on flame speed at higher levels of turbulence with the effect being very strong for lean H2 mixtures. The lighter hydrocarbon substitutions tend to suppress the leading flame edges and possibly transition to detonation in confined structures and promote flame front stability of lean turbulent premixed flames. Thus there is a necessity to develop a predictive reaction model to quantitatively show the strong influence of molecular transport coefficients on ST.

The study of steels which guarantee safety and reliability throughout their service life in hydrogen-rich environments has increased considerably in recent years. Their mechanical behavior in terms of hydrogen embrittlement is of utmost importance. This work aims to assess the effects of hydrogen on the tensile properties of quenched and tempered 42CrMo4 steels. Tensile tests were performed on smooth and notched specimens under different conditions: pre-charged in high pressure hydrogen gas electrochemically pre-charged and in-situ hydrogen charged in an acid aqueous medium. The influence of the charging methodology on the corresponding embrittlement indexes was assessed. The role of other test variables such as the applied current density the electrolyte composition and the displacement rate was also studied. An important reduction of the strength was detected when notched specimens were subjected to in-situ charging. When the same tests were performed on smooth tensile specimens the deformation results were reduced. This behavior is related to significant changes in the operative failure micromechanisms from ductile (microvoids coalescence) in absence of hydrogen or under low hydrogen contents to brittle (decohesion of martensite lath interfaces) under the most stringent conditions.

The present document is part of a larger literature survey of this WP aiming to establish the current status of gas utilisation technologies in order to determine the impact of hydrogen (H₂) admixture on natural gas (NG) appliances. This part focuses on the non-combustion related aspects of injecting hydrogen in the gas distribution networks within buildings including hydrogen embrittlement of metallic materials chemical compatibility and leakage issues. In the particular conditions of adding natural gas and hydrogen (NG / H2) mixture into a gas distribution network hydrogen is likely to reduce the mechanical properties of metallic components. This is known as hydrogen embrittlement (HE) (Birnbaum 1979). This type of damage takes place once a critical level of stress / strain and hydrogen content coexist in a susceptible microstructure. Currently four mechanisms were identified and will be discussed in detail. The way those mechanisms act independently or together is strongly dependent on the material the hydrogen charging procedure and the mechanical loading type. The main metallic materials used in gas appliances and gas distribution networks are: carbon steels stainless steels copper brass and aluminium alloys (Thibaut 2020). The presented results showed that low alloy steels are the most susceptible materials to hydrogen embrittlement followed by stainless steels aluminium copper and brass alloys. However the relative pressures of the operating conditions of gas distribution network in buildings are low i.e. between 30 to 50 mbar. At those low hydrogen partial pressures it is assumed that a gas mixture composed of NG and up to 50% H2 should not be problematic in terms of HE for any of the metallic materials used in gas distribution network unless high mechanical stress / strain and high stress concentrations are applied. The chemical compatibility of hydrogen with other materials and specifically polyethylene (PE) which is a reference material for the gas industry is also discussed. PE was found to have no corrosion issues and no deterioration or ageing was observed after long term testing in hydrogen gas. The last non-combustion concern related to the introduction of hydrogen in natural gas distribution network is the propensity of hydrogen toward leakage. Indeed the physical properties of hydrogen are different from other gases such as methane or propane and it was observed that hydrogen leaks 2.5 times quicker than methane. This bibliographical report on material deterioration chemical compatibility and leakage concerns coming with the introduction of NG / H₂ mixture in the gas distribution network sets the basis for the upcoming experimental work where the tightness of gas distribution network components will be investigated (Task 3.2.3 WP3). In addition tightness of typical components that connect end-user appliances to the local distribution line shall be evaluated as well.

The objective of this work was to enable the safe design of hydrogen pressure vessels by measuring the fatigue crack growth rates of ASME code-qualified steels in high-pressure hydrogen gas. While a design framework has recently been established for high-pressure hydrogen vessels a material property database does not exist to support the design calculations. This study addresses such voids in the database by measuring the fatigue crack growth rates of three different heats of ASME SA-372 Grade J steel in 100 MPa hydrogen gas. Results showed that the fatigue crack growth rates were similar for all three steel heats although the highest-strength steel appeared to exhibit the highest growth rates. Hydrogen accelerated the fatigue crack growth rates of the steels by as much as two orders of magnitude relative to anticipated crack growth rates in inert environments. Despite such dramatic effects of hydrogen on the fatigue crack growth rates measurement of these properties enables reliable definition of the design life of steel hydrogen containment vessels.

The EC funded Naturalhy project is investigating the possibility of promoting the swift introduction of hydrogen as a fuel by mixing hydrogen with natural gas and transporting this mixture by means of the existing natural gas pipeline system to end-users. Hydrogen may then be extracted for use in hydrogen fuel cell applications or the mixture may be used directly in conventional gas-fired equipment. This means that domestic customers would receive a natural gas (methane)/hydrogen mixture delivered to the home. As the characteristics of hydrogen are different from natural gas there may be an increased risk to end-users in the event of an accidental release of gas from internal pipe work or appliances. Consequently part of the Naturalhy project is aimed at assessing the potential implications on the safety of the public which includes end-users in their homes. In order to understand the nature of any gas accumulation which may form and identify the controlling parameters a series of large scale experiments have been performed to study gas accumulations within a 3 m by 3 m by 2.3 m ventilated enclosure representing a domestic room. Gas was released vertically upwards at a pressure typical of that experienced in a domestic environment from hole sizes representative of leaks and breaks in pipe work. The released gas composition was varied and included methane and a range of methane/hydrogen mixtures containing up to 50% hydrogen. During the experiments gas concentrations throughout the enclosure and the external wind conditions were monitored with time. The experimental data is presented. Analysis of the data and predictions using a model developed to interpret the experimental data show that both buoyancy and wind driven ventilation are important.

The study of hydrogen as an alternative fuel clean and “environment friendly” has been in the last years and continues to be object of many studies international projects and standard development. Hydrogen is a fundamental energy carrier to be developed together with other renewable resources for the transition to a sustainable energy system.<br/>But experience has shown how often the introduction and establishment of a new technology does not necessarily pass through radical changes but can be stimulated by slight modifications to the “present situation”.<br/>So the worldwide experience with natural gas as industrial automotive and domestic fuel has been the incentive to the present interest towards hydrogen–methane mixtures. The possible use of existing pipeline networks for mixtures of natural gas and hydrogen offers a unique and cost-effective opportunity to initiate the progressive introduction of hydrogen as part of the development of a full hydrogen system.<br/>The aim of the work presented in this paper is the investigation of the dispersion and stratification properties of hydrogen and methane mixtures. Experimental activities have been carried out in a large scale closed apparatus characterized by a volume of about 25 m3 both with and without natural ventilation. Mixtures of 10%vol. hydrogen – 90%vol. methane and 30%vol. hydrogen – 70%vol. methane have been studied with the help of oxygen sensors and gas chromatography.

"This paper summarises the modelling and experimental programme in the EC FP6 project HYPER. A number of key results are presented and the relevance of these findings to installation permitting guidelines (IPG) for small stationary hydrogen and fuel cell systems is discussed. A key aim of the activities was to generate new scientific data and knowledge in the field of hydrogen safety and where possible use this data as a basis to support the recommendations in the IPG. The structure of the paper mirrors that of the work programme within HYPER in that the work is described in terms of a number of relevant scenarios as follows: 1. high pressure releases 2. small foreseeable releases 3. catastrophic releases and 4. the effects of walls and barriers. Within each scenario the key objectives activities and results are discussed.<br/>The work on high pressure releases sought to provide information for informing safety distances for high-pressure components and associated fuel storage activities on both ignited and unignited jets are reported. A study on small foreseeable releases which could potentially be controlled through forced or natural ventilation is described. The aim of the study was to determine the ventilation requirements in enclosures containing fuel cells such that in the event of a foreseeable leak the concentration of hydrogen in air for zone 2 ATEX is not exceeded. The hazard potential of a possibly catastrophic hydrogen leakage inside a fuel cell cabinet was investigated using a generic fuel cell enclosure model. The rupture of the hydrogen feed line inside the enclosure was considered and both dispersion and combustion of the resulting hydrogen air mixture were examined for a range of leak rates and blockage ratios. Key findings of this study are presented. Finally the scenario on walls and barriers is discussed; a mitigation strategy to potentially reduce the exposure to jet flames is to incorporate barriers around hydrogen storage equipment. Conclusions of experimental and modelling work which aim to provide guidance on configuration and placement of these walls to minimise overall hazards is presented. "

Hydrogen dispersion in an enclosure is numerically studied using simple analytical solutions and a large-eddy-simulation based CFD code. In simple calculations the interface height and temperature rise of the upper layer are obtained based on mass and energy conservation and the centreline hydrogen volume fraction is derived from similarity solutions of buoyant jets. The calculated centreline hydrogen volume fraction using the two methods agree with each other; however discrepancies are found for the calculated total flammable volume as a result of the inability of simple calculations in taking into account local mixing and diffusion. The CFD model in contrast is found to be capable of correctly reproducing the diffusion and stratification phenomena during the mixing stage.

A total of 12 ventilation experiments with various combinations of hydrogen release rates and ventilation speeds were performed in order to study how ventilation speed and release rate effect the hydrogen concentration in a closed system. The experiential facility was constructed out of steel plates and beams in the shape of a rectangular enclosure. The volume of the test facility was about 60m3. The front face of the enclosure was covered by a plastic film in order to allow visible and infrared cameras to capture images of the flame. The inlet and outlet vents were located on the lower front face and the upper backside panel respectively. Hydrogen gas was released toward the ceiling from the center of the floor. The hydrogen gas was released at constant rate in each test. The hydrogen release rate ranged from 0.002 m3/s to 0.02 m3/s. Ventilation speeds were 0.1 0.2 and 0.4 m3/s respectively. Ignition was attempted at the end of the hydrogen release by using multiple continuous spark ignition modules on the ceiling and next to the release point. Time evolution of hydrogen concentration was measured using evacuated sample bottles. Overpressure and impulse inside and outside the facility were also measured. The mixture was ignited by a spark ignition module mounted on the ceiling in eight of eleven tests. In the other three tests the mixture was ignited by spark ignition modules mounted next to the nozzle. Overpressures generated by the hydrogen deflagration in most of these tests were low and represented a small risk to people or property. The primary risk associated with the hydrogen deflagrations studied in these tests was from the fire. The maximum concentration is proportional to the ratio of the hydrogen release rate to the ventilation speed within the range of parameters tested. Therefore a required ventilation speed can be estimated from the assumed hydrogen leak rate within the experimental conditions described in this paper.

In the problem of the protection by the consequences of an explosion is actual for many industrial application involving storage of gas like methane or hydrogen refuelling stations and so on. A simple and economic way to reduce the peak pressure associated to a deflagration is to supply to the confined environment an opportune surface substantially less resistant then the protected structure typically in stoichiometric conditions the peak pressure reduction is around the 8 bars for a generic hydrocarbon combustion in an adiabatic system lacking of whichever mitigation system. In general the problem is the forecast of the peak pressure value (PMAX) of the explosion. This problem is faced using CFD codes modelling the structure in which the explosion is located and setting the main parameters like concentration of the gas in the mixture the volume available the size of vent area and obstacles (if included) and so on. In this work the idea is to start from empirical data to train a Neural Network (NN) in order to find the correlation among the parameters regulating the phenomenon. Associated to this prediction a fuzzy model will provide to quantify the uncertainty of the predicted value.

In this paper a case of hydrogen release in a typical research laboratory for the characterisation of hydrogen solid-state storage materials has been considered. The laboratory is equipped with various testing equipments for the assessment of hydrogen capacity in materials typically in the 1 to 200 bar pressure range and temperatures up to 500°C. Hydrogen is delivered at 200 bar by a 50 l gas bottle and a compressor located outside the laboratory. The safety measures directly related to hydrogen hazard consist in a distributed ventilation of the laboratory and air extraction fume hoods located on top of each instrument. Goal of this work is the modelling of hydrogen accidental release in a real laboratory case in order to provide a more fundamental basis for the laboratory safety design and assist the decision on the number and position of the safety sensors. The computational fluid dynamics code (CFD) ANSYS-CFX has been selected in order to perform the numerical investigations. Two basic accidental release scenarios have been assumed both at 200 bar:  a major leak corresponding to a guillotine breaking of the hydrogen distribution line and a smaller leak typical for a not properly tight junction.

Correct selection and application of materials is essential to ensure safety and economy in production transportation and storage of hydrogen. There are several sources of materials challenges related to hydrogen. Established component producers may have limited experience in this specific field. Process developments may involve new process conditions with new demands on the materials. Further new materials will be added to the engineering toolbox to be used. The behaviour of these materials for hydrogen service may need additional documentation. Finally focus on hydrogen susceptibility and hydrogen damages alone may take away awareness of other subjects as trace elements by-products and change in raw materials which may be of as high importance for safety and quality. This overview of challenges and recommendations is made with emphasis on water electrolysis.

Experiments were performed to investigate the radiative heat emission of small scale hydrogen/air explosions also impurified by minor amounts of inert particles and organic fuels. A volume of 1.5 dm3 hydrogen was injected into ambient air as free-jet and ignited. In further experiments simultaneously inert Aerosil and combustible fuels were injected into the blasting hydrogen/air gas cloud. Fuels were a spray of a solvent (Dipropyleneglycol-methylether) and dispersed particles (milk powder). The combustion was observed with a DV camcorder an IR camera and two different fast scanning spectrometers in NIR and IR range using a sampling rate of 100 spectra/s. The intensity calibrated spectra were analyzed using ICT-BaM code to evaluate emission temperature and intensity of H2O CO2 CO NO and soot emission. Using the same code combined with the experimental results total heat emission of such explosions was estimated.

The development of an infrastructure for the future hydrogen economy will require the simultaneous development of a set of codes and standards. As part of the U.S. Department of Energy Hydrogen Fuel Cells & Infrastructure Technologies Program Sandia National Laboratories is developing the technical basis for assessing the safety of hydrogen-based systems for use in the development/modification of relevant codes and standards. This work includes experimentation and modelling to understand the fluid mechanics and dispersion of hydrogen for different release scenarios including investigations of hydrogen combustion and subsequent heat transfer from hydrogen flames. The resulting technical information is incorporated into engineering models that are used for assessment of different hydrogen release scenarios and for input into quantitative risk assessments (QRA) of hydrogen facilities. The QRAs are used to identify and quantify scenarios for the unintended release of hydrogen and to identify the significant risk contributors at different types of hydrogen facilities. The results of the QRAs are one input into a risk-informed codes and standards development process that can also include other considerations by the code and standard developers. This paper describes an application of QRA methods to help establish one key code requirement: the minimum separation distances between a hydrogen refuelling station and other facilities and the public at large. An example application of the risk-informed approach has been performed to illustrate its utility and to identify key parameters that can influence the resulting selection of separation distances. Important parameters that were identified include the selected consequence measures and risk criteria facility operating parameters (e.g. pressure and volume) and the availability of mitigation features (e.g. automatic leak detection and isolation). The results also indicate the sensitivity of the results to key modelling assumptions and the component leakage rates used in the QRA models.

This paper is concerned with predicting the impact on the probability of failure of adding hydrogen to the natural gas distribution network. Hydrogen has been demonstrated to change the behaviour of crack like defects which may affect the safety of pipeline or make it more expensive to operate. A tool has been developed based on a stochastic approach to assess the failure probability of the gas pipeline due to the existence of crack-lie defects including the operational aspects of the pipeline such as inspection and repair procedures. With various parameters such as crack sizes material properties internal pressure modelled as uncertainties a reliability analysis based on failure assessment diagram is performed through direct Monte Carlo simulation. Inspection and repair procedures are included in the simulation to enable realistic pipeline maintenance scenarios to be simulated. In the data preparation process the accuracy of the probabilistic definition of the uncertainties is crucial as the results are very sensitive to certain variables such as the crack depth length and crack growth rate. The failure probabilities of each defect and the whole pipeline system can be obtained during simulation. Different inspection and repair criteria are available in the Monte Carlo simulation whereby an optimal maintenance strategy can be obtained by comparing different combinations of inspection and repair procedures. The simulation provides not only data on the probability of failure but also the predicted number of repairs required over the pipeline life thus providing data suitable for economic models of the pipeline management. This tool can be also used to satisfy certain target reliability requirement. An example is presented comparing a natural gas pipeline with a pipeline containing hydrogen.

This article presents a power to SNG (synthetic natural gas) system that converts hydrogen into SNG via a methanation process. In our analysis detailed models for all the elements of the system are built. We assume a direct connection between a wind farm and a hydrogen generator. For the purposes of our calculations we also assume that the hydrogen generator is powered by the renewable source over a nine-hour period per day (between 21:00 and 06:00) and this corresponds to the off-peak period in energy demand. In addition a hydrogen tank was introduced to maximize the operating time of the methanation reactor. The cooperation between the main components of the system were simulated using Matlab software. The primary aim of this paper is to assess the influence of various parameters on the operation of the proposed system and to optimize its yearly operation via a consideration of the most important constraints. The analyses also examine different nominal power values of renewables from 8 to 12 MW and hydrogen generators from 3 to 6 MW. Implementing the proposed configuration taking into account the direct connection of the hydrogen generator and the methanation reactor showed that it had a positive effect on the dynamics and the operating times of the individual subsystems within the tested configuration

This work dedicated to a mathematical description of energy transition scenarios consists of three main parts. The first part describes modern trends and problems of the energy sector. A large number of charts reflecting the latest updates in energy are provided. The COVID-2019 pandemic’s impacts on the energy sector are also included. The second part of the paper is dedicated to the analysis of energy consumption and the structure of the world fuel and energy balance. Furthermore a detailed description of energy-efficient technologies is given. Being important and low-carbon hydrogen is discussed including its advantages and disadvantages. The last part of the work describes the mathematical tool developed by the authors. The high availability of statistical data made it possible to identify parameters used in the algorithm with the least squares method and verify the tool. Performing several not complicated steps of the algorithm the tool allows calculating the deviation of the average global temperature of the surface atmosphere from preindustrial levels in the 21st century under different scenarios. Using the suggested mathematical description the optimal scenario that makes it possible to keep global warming at a level below 1.7 ◦C was found.

Underground or partial underground tunnels form a very important part of modern road transportation systems. As the development of hydrogen cars advancing into the markets it is unavoidable in the near future that hydrogen cars would become the users of ordinary road tunnels. This paper discusses potential fire scenarios and fire hazards of hydrogen cars in road tunnels and implications on the fire safety measures and ventilation systems in existing tunnels. The information needed for carry out risk assessment of hydrogen cars in road tunnels are discussed. hydrogen has a low ignition energy and wide flammable range suggesting that leaks have a high probability of ignition and result hydrogen flame. CFD simulations of hydrogen fires in a full scale 5m by 5m square cross-section tunnel were carried out. The effect of the ventilation on controlling the back-layering and the downstream flame are discussed.

For the sake of the increasing demand of hydrogen fuel cell vehicles there are more concerns on the safety of hydrogen refueling stations. As one of the key pieces of equipment the hydrogen dispenser has drawn attention on this aspect since it involves massive manual operations and may be bothered by a high probability of failure. In this paper a numerical study is conducted to simulate the possible leakage events of the hydrogen dispenser based on a prototype in China whose working pressure is 70 MPa. The leakage accident is analyzed with respect to leakage sizes leak directions and the time to stop the leakage. It is found that due to the large mass flow rate under such high pressure the leak direction and the layout of the components inside the dispenser become insignificant and the ignitable clouds will form inside the dispenser in less than 1 s if there is a leakage of 1% size of the main tube. The ignitable clouds will form near the vent holes outside the dispenser which may dissipate quickly if the leakage is stopped. On the other hand the gas inside the dispenser will remain ignitable for a long time which asks for a design with no possible ignition source inside. The results can be useful in optimizing the design of the dispenser regarding the reaction time and sensitivity requirements of the leakage detector the size and amount of vent holes etc.

This paper provides a critical study of current Australian and leading international policies aimed at supporting electrical energy storage for stationary power applications with a focus on battery and hydrogen storage technologies. It demonstrates that global leaders such as Germany and the U.S. are actively taking steps to support energy storage technologies through policy and regulatory change. This is principally to integrate increasing amounts of intermittent renewable energy (wind and solar) that will be required to meet high renewable energy targets. The relevance of this to the Australian energy market is that whilst it is unique it does have aspects in common with the energy markets of these global leaders. This includes regions of high concentrations of intermittent renewable energy (Texas and California) and high penetration rates of residential solar photovoltaics (PV) (Germany). Therefore Australian policy makers have a good opportunity to observe what is working in an international context to support energy storage. These learnings can then be used to help shape future policy directions and guide Australia along the path to a sustainable energy future.

The scenario of detonative ignition in shocked mixture is significant because it is a contributor to deflagration to detonation transition for example following shock reflections. However even in one dimension simulation of ignition between a contact surface or a flame and a shock moving into a combustible mixture is difficult because of the singular nature of the initial conditions. Initially as the shock starts moving into reactive mixture the region filled with reactive mixture has zero thickness. On a fixed grid the number of grid points between the shock and the contact surface increases as the shock moves away from the latter. Due to initial lack of resolution in the region of interest staircasing may occur whereby the resulting plots consist of jumps between few values a few grid points and these numerical artifacts are amplified by the chemistry which is very sensitive to temperature leading to unreliable results. The formulation is transformed replacing time and space by time and space over time as the independent variables. This frame of reference corresponds to the self-similar formulation in which the non-reactive problem remains stationary and the initial conditions are well-resolved. Additionally a solution obtained from short time perturbation is used as initial condition at a time still short enough for the perturbation to be very accurate but long enough so that there is sufficient resolution. The numerical solution to the transformed problem is obtained using an essentially non-oscillatory algorithm which is adequate not only for the early part of the process but also for the latter part when chemistry leads to appearance of a shock and eventually a detonation wave is formed. A validation study was performed and the results were compared with the literature for single step Arrhenius chemistry. The method and its implementation were found to be effective. Results are presented for values of activation energy ranging from mild to stiff.

When a hydrogen supply station is to be installed in Japan three fundamental laws must be taken into consideration: the High Pressure Gas Safety Law the Building Standards Law and the Fire Service Law. The High Pressure Gas Safety Law in particular regulates procedures for safety concerning hydrogen supply stations. This law came under review accompanying consideration of the potential utilization of fuel cell vehicles and hydrogen stations. At that time the Japan Petroleum Energy Center (JPEC) investigated safety technology for hydrogen supply stations and prepared a draft of the law. Since then a new combined gasoline/hydrogen supply station compliant with the revised law was established on December 2006. There are a large number of safety precautions incorporated into this station model which conform to the law. As a result of these modifications it was possible to reduce the safe setback distance. In this paper we present an overview of the new hydrogen supply station model the safety precautions and the regulations the station is based on.

The effect of surfaces on the extent of high pressure vertical and horizontal unignited jets is studied using CFD numerical simulations performed with FLACS Hydrogen and Phoenics. For a constant flow rate release of hydrogen from a 284 bar storage unit through a 8.5 mm orifice located 1 meter from the ground the maximum extent of the flammable cloud is determined as a function of time and compared to a free vertical hydrogen jet under identical release conditions. The results are compared to methane numerical simulations and to the predictions of the Birch correlations for the size of the flammable cloud. We find that the maximum extent of the flammable clouds of free jets obtained using CFD numerical simulations for both hydrogen and methane are in agreement with the Birch predictions. For hydrogen horizontal free jets there is strong buoyancy effect observed towards the end of the flammable cloud thus noticeably reducing its centreline extent. For methane horizontal free jets this effect is not observed. For methane the presence of the ground results in a pronounced increase in the extent of the flammable cloud compared to a free jet. The effects of a surface on vertical jets are also studied.