Safety

In the prospect of a safe use of hydrogen in our society one important task is to evaluate under which conditions the storage of hydrogen systems can reach a sufficient level of safety. One of the most important issues is the use of such system in closed area for example a private garage or an industrial facility. In the scope of this paper we are mainly interested in the following scenario: a relatively slow release of hydrogen (around 5Nl/min) in a closed and almost cubic box representing either a fuel cell at normal scale or a private garage at a smaller scale. For practical reasons helium was used instead of hydrogen in the experiments on which are based our comparisons. This kind of situation leads to the fundamental problem of the dispersion of hydrogen due to a simple vertical source in an enclosure. Many numerical and experimental studies have already been conducted on this problem showing the formation of either a stably stratified distribution of concentration or the formation of a homogeneous layer due to high enough convective flows at the top of the enclosure. Nevertheless most of them consider the cases of accidental situation in which the flow rate is relatively important (higher than 10Nl/min). Numerical simulations carried out with the CEA code Cast3M and a LES turbulence model confirm the differences of results already observed in experimental helium concentration measurements for a same injection flow rate and two different injection nozzle diameters contradicting simple physical models used in safety calculations.

Sandia National Laboratories has worked with stakeholders and original equipment manufacturers (OEMs) to develop scientific data that can be used to create risk-informed hydrogen codes and standards for the safe operation of indoor hydrogen fuel-cell forklifts. An important issue is the possibility of an accident inside a warehouse or other enclosed space where a release of hydrogen from the high-pressure gaseous storage tank could occur. For such scenarios computational fluid dynamics (CFD) simulations have been used to model the release and dispersion of gaseous hydrogen from the vehicle and to study the behavior of the ignitable hydrogen cloud inside the warehouse or enclosure. The overpressure arising as a result of ignition and subsequent deflagration of the hydrogen cloud within the warehouse has been studied for different ignition delay times and ignition locations. Both ventilated and unventilated warehouses have been considered in the analysis. Experiments have been performed in a scaled warehouse test facility and compared with simulations to validate the results of the computational analysis.

A prospective global market share of Electric vehicle (EV) Hybrid electric vehicle (HEV) and Hydrogen Fuel Cell Vehicle (HFCV) is expected to grow due to stringent emission regulation and oil depletion. However it is essential to secure protection against high-pressure hydrogen gas and high-voltage in fuel cell vehicles and thus needs to develop a technique for safety assessment of HFCV. In this experiment 8 research institutes including the Korea Automobile Testing and Research Institute Hyundai Motor Company took part in. This project was supported by the Ministry of Land Transportation and Maritime Affairs of the Republic of Korea.

Compressed natural gas (CNG) is being increasingly used as a clean transportation fuel. However for further reduction in emissions particularly NOx H-CNG mixture with ~ 20 % hydrogen is recommended. Presently most of the H-CNG mixture is produced by blending hydrogen with CNG. For hydrogen production Steam Methane Reforming (SMR) is a major process accounting for more than 90% of hydrogen production by various industries. In this process natural gas is first reformed to syn gas under severe operating conditions (Pressure 20-30 bar temperature 850-950 deg C) followed by conversion of CO to hydrogen in the shift reactor. Other method of hydrogen production such as electrolysis of water is more expensive. Further there are issues of safety with handling of hydrogen its storage and transportation for blending. In order to overcome these problems a single step compact process for the production of H-CNG gaseous mixture through low severity steam methane reforming of natural gas has been developed. It employs a catalyst containing nickel nickel oxide magnesium oxide and silica and has the capability of producing H-CNG mixture in the desired proportion containing 15-20 vol % hydrogen with nil CO production. The process is flexible and rugged allowing H-CNG production as per the demand. The gaseous H-CNG product mixture can directly be used as automobile fuel after compression. The process can help as important step in safe transition towards hydrogen economy. A demonstration unit is being set up at IOC R&D Centre.

We present an experimental investigation of the different concentration build-up regimes encountered during a release of helium/air mixture in an empty enclosure without ventilation. The release is a vertical jet issuing from a nozzle located near the floor. The nozzle diameter the flow rate and the composition of the injected mixture have been varied such that the injection Richardson number ranges from 6 × 10−6 to 190. The volume Richardson number which gives the ability of the release to mix the enclosure content ranges from 2 × 10−3 to 2 × 104. This wide range allowed reaching three distinct regimes: stratified stratified with a homogeneous upper layer and homogenous.

The project “Towards a Hydrogen Refuelling Infrastructure for Vehicles” (THRIVE) aimed at the determination of conditions to stimulate the building of a sustainable infrastructure for hydrogen as a car fuel in The Netherlands. Economic scenarios were constructed for the development of such an infrastructure for the next one to four decades. The eventual horizon will require the erection of a few hundred to more than a thousand hydrogen refuelling stations (HRS) in The Netherlands. The risk acceptability policy in The Netherlands implemented in the External Safety Establishments decree requires the assessment and management of safety risks imposed on the public by car fuelling stations. In the past a risk-informed policy has been developed for the large scale introduction of liquefied petroleum gas (LPG) as a car fuel and a similar policy will also be required if hydrogen is introduced in the public domain. A risk assessment methodology dedicated to cope with accident scenarios relevant for hydrogen applications is to be developed. Within the THRIVE project a demo risk assessment was conducted for the possible implementation of an HRS within an existing station for conventional fuels. The studied station is located in an urban area occupied with housing and commercial activities. The HRS is based on delivery and on-site storage of liquid hydrogen and dispensing of high pressure gaseous hydrogen into vehicles. The main challenges in the risk assessment were in the modelling of release and dispersion of liquid hydrogen. Definition of initial conditions for computational fluid dynamics (CFD) modelling to evaluate dispersion of a cold hydrogen air mixture appears rather complex and is not always fully understood. The modelling assumptions in the initial conditions determine to a large extent the likelihood and severity of potential explosion effects. The paper shows the results of the investigation and the sensitivity to the basic assumptions in the model input.

High-order perturbation solutions have been obtained for the simple physical model describing the LH2 spreading with a continuous spill and are shown to improve over the first-order perturbation solutions. The non-dimensional governing equations for the model are derived to obtain more general solutions. Non-dimensional parameters are sought as the governing parameters for the non-dimensional equations and the non-dimensional evaporation rate is used as the perturbation parameter. The results show that the second-order solutions exhibit an improvement over the first-order solutions with respect to the pool volume; however there is still a difference between numerical solutions and second-order solutions in the late stage of spread. Finally it is revealed that the third-order solutions almost agree with numerical solutions.

This paper is devoted to a benchmarking exercise of the EUROPLEXUS code against several large scale deflagration and detonation experimental data sets in order to improve its hydrogen combustion modeling capabilities in industrial settings. The code employs an algorithm for the propagation of reactive interfaces RDEM which includes a combustion wave as an integrable part of the Reactive Riemann problem propagating with a fundamental flame speed (being a function of initial mixture properties as well as gas dynamics parameters). An improvement of the combustion model is searched in a direction of transient interaction of flames with regions of elevated vorticity/shear in obstacle-laden channels and vented enclosures.

Hydrogen fuelling in the US is unattended activity although this precedent is not without several challenges that have been addressed in the past decade. This paper provides the recent history and the generic safety case which has established this precedent for hydrogen. The paper also explores the longer history of unattended gasoline fuelling and attempts to help place hydrogen fuelling into the longer history of fuelling personal vehicles.

Various studies and market trends show that the number of hydrogen fuelling stations will increase to the thousands in the US by 2050. NFPA 2 Hydrogen Technologies Code (NFPA2) the nationally adopted primary code governing hydrogen safety is relatively new and hydrogen vehicle technology is a relatively new and rapidly developing technology. In order to effectively aid and accelerate the deployment of standardized retail hydrogen fuelling facilities the permitting of hydrogen fuelling stations employing outdoor bulk liquid storage in the state of California.

In an effort to better understand how the applicants consultants and more importantly the Authorities Having Jurisdiction (AHJ)s are interpreting and applying the NFPA 2 especially for complex applications the newest hydrogen stations with the largest amount of bulk hydrogen storage in urban environment settings were identified and the permit applications and permit approval outcomes of the said stations were analysed. Utilizing the pubic record request process LH2 station permit applications were reviewed along with the approval outcomes directly from the municipalities that issued the permits. AHJs with H2 station permitting experience were interviewed. Case studies of permit hydrogen fuelling station permit applications were then complied to document both the perspectives of the applicant and the AHJ and the often iterative and collaborative nature of permitting.

The current permitting time for Liquid Hydrogen (LH2) stations can range from 9 to 18 months in the California. Five out of the six LH2 stations applications required Alternative Means & Methods (AM&Ms) proposals and deviations from the prescriptive requirements of the Code were granted. Furthermore AHJs often requested additional documents and studies specific to application parameters in addition to NFPA 2 requirements.

The Hydrogen Incident Reporting and Lessons Learned website (www.h2incidents.org) was launched in 2006 as a database-driven resource for sharing lessons learned from hydrogen-related safety events to raise safety awareness and encourage knowledge-sharing. The development of this database its first uses and subsequent enhancements have been described at the Second and Third International Conferences on Hydrogen Safety [1] [2]. Since 2009 continuing work has not only highlighted the value of safety lessons learned but enhanced how the database provides access to another safety knowledge tool Hydrogen Safety Best Practices (http://h2bestpractices.org). Collaborations with the International Energy Agency (IEA) Hydrogen Implementing Agreement (HIA) Task 19 – Hydrogen Safety and others have enabled the database to capture safety event learning’s from around the world. This paper updates recent progress highlights the new “Lessons Learned Corner” as one means for knowledge-sharing and examines the broader potential for collecting analyzing and using safety event information.

Hydrogen is a valuable option of clean fuel to keep the global temperature rise below 2°C. However one of the main barriers in its transport and use is to ensure safety levels that are comparable with traditional fuels. In particular liquid hydrogen accidents may not be fully understood (yet) and excluded by relevant risk assessment. For instance as hydrogen is cryogenically liquefied to increase its energy density during transport Boiling Liquid Expanding Vapor Explosions (BLEVE) is a potential and critical event that is important addressing in the hazard identification phase. Two past BLEVE accidents involving liquid hydrogen support such thesis. For this reason results from consequence analysis of hydrogen BLEVE will not only improve the understanding of the related physical phenomenon but also influence future risk assessment studies. This study aims to show the extent of consequence analysis influence on overall quantitative risk assessment of hydrogen technologies and propose a systematic approach for integration of overall results. The Dynamic Procedure for Atypical Scenario Identification (DyPASI) is used for this purpose. The work specifically focuses on consequence models that are originally developed for other substances and adapted for liquid hydrogen. Particular attention is given to the parameters affecting the magnitude of the accident as currently investigated by a number of research projects on hydrogen safety worldwide. A representative example of consequence analysis for liquid hydrogen release is employed in this study. Critical conditions detected by the numerical simulation models are accurately identified and considered for subsequent update of the overall system risk assessment.

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.

Car park fires are known to be dangerous due to the risk of fast fire spread from one car to another. In general no fatalities are recorded in such fires but they may have a great cost in relation to damaged cars and structural repair. A very recent example is the Liverpool multi-storey car park fire from December 31 2017. It destroyed 1400 cars and parts of the building structure collapsed. This questions the validity of current design praxis of car parks. Literature studies assumes a 12 minutes period for the fire spread from one gasoline fuelled car to another. Statistical research and test from the European commission of steel structures states that in an open car park at most 3-4 vehicles are expected to be on fire at the same time.<br/>A number of investigations have been made concerning vehicles performance in car park fires but only a few are concerned with hydrogen-fuelled vehicles (HFV). It is therefore important to investigate how these new vehicles may contribute to potential fire spread scenario. The aim of the paper is to report the outcome of car park fire spread simulations involving common fuelled and hydrogen fuelled cars. The case study is based on a typical car park found in Denmark. The simulation applied numerical models implemented in the Fire Dynamic Simulator (FDS). In particular the focus of the study is on the influence of the parking distance to fire spread to adjacent vehicles in case a TPRD is activated during a car fire. The results help understanding whether different design rules should be envisaged for such structures or how a sufficient safety level can be obtained by ensuring specific parking condition for the hydrogen-fuelled cars.

The reproducibility of fire test protocol in the UN Global Technical Regulation on Hydrogen and Fuel Cell Vehicles (GTR#13) is not satisfactory. Results differ from laboratory to laboratory and even at the same laboratory when fires of different heat release (HRR) rate are applied. This is of special importance for fire test of tank without thermally activated pressure relief devise (TPRD) the test requested by firemen. Previously the authors demonstrated a strong dependence of tank fire resistance rating (FRR) i.e. time from fire test initiation to moment of tank rupture on the HRR in a fire. The HRR for complete combustion at the open is a product of heat of combustion and flow rate of a fuel i.e. easy to control in test parameter. It correlates with heat flux to the tank from a fire – the higher HRR the higher heat flux. The control of only temperature underneath a tank in fire test as per the current fire test protocol of UN GTR#13 without controlling HRR of fire source is a reason of poor fire test reproducibility. Indeed a candle flame can easily provide a required by the protocol temperature in points of control but such test arrangements could never lead to tank rupture due to fast heat dissipation from such tiny fire source i.e. insufficient and very localised heat flux to the tank. Fire science requires knowledge of heat flux along with the temperature to characterise fire dynamics. In our study published in 2018 the HRR is suggested as an easy to control parameter to ensure the fire test reproducibility. This study demonstrates that the use of specific heat release rate HRR/A i.e. HRR in a fire source divided by the area of the burner projection A enables testing laboratories to change freely a burner size depending on a tank size without affecting fire test reproducibility. The invariance of FRR at its minimum level with increase of HRR/A above 1 MW/m2 has been discovered first numerically and then confirmed by experiments with different burners and fuels. The validation of computational fluid dynamics (CFD) model against the fire test data is presented. The numerical experiments with localised fires under a vehicle with different HRR/A are performed to understand the necessity of the localised fire test protocol. The understanding of fire test underlying physics will underpin the development of protocol providing test reproducibility.

Radiative heat fluxes from small to medium-scale hydrogen jet flames (<10 m) compare favorably to theoretical predictions provided the product species thermal emittance and optical flame thickness are corrected for. However recent heat flux measurements from two large-scale horizontally orientated hydrogen flames (17.4 and 45.9 m respectively) revealed that current methods underpredicted the flame radiant fraction by 40% or more. Newly developed weighted source flame radiation models have demonstrated substantial improvement in the heat flux predictions particularly in the near-field and allow for a sensible way to correct potential ground surface reflective irradiance. These updated methods are still constrained by the fact that the flame is assumed to have a linear trajectory despite buoyancy effects that can result in significant flame deformation. The current paper discusses a method to predict flame centerline trajectories via a one-dimensional flame integral model which enables optimized placement of source emitters for weighted multi-source heat flux prediction methods. Flame shape prediction from choked releases was evaluated against flame envelope imaging and found to depend heavily on the notional nozzle model formulation used to compute the density weighted effective nozzle diameter. Nonetheless substantial improvement in the prediction of downstream radiative heat flux values occurred when emitter placement was corrected by the flame integral model regardless of the notional nozzle model formulation used.

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.

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.

The formation of a flammable hydrogen-air mixture is a major safety concern especially for closed space. This hazardous situation can arise when considering permeation from a car equipped with a composite compressed hydrogen tank with a non-metallic liner in a closed garage. In the following paper a scenario is developed and analysed with a simplified approach and a numerical simulation in order to estimate the evolution of hydrogen concentration. The system is composed of typical size garage and hydrogen car’s tank. Some parameters increasing permeation rate (i.e. tank’s material thickness and pressure) have been chosen to have a conservative approach. A close look on the top of tank surface showed that the concentration grows as square root of time and does not exceed 8.2×10-3 % by volume. Also a simplified comparative analysis estimated that the buoyancy of hydrogen-air mixture prevails on the diffusion 35 seconds after permeation starts in good agreement with simulation where time is at about 80 seconds. Finally the numerical simulations demonstrated that across the garage height the hydrogen is nearly distributed linearly and the difference in hydrogen concentration at the ceiling and floor is negligible (i.e. 3×10-3 %).

The paper presents an overview of the main results of the EC NOE HySafe activity to estimate an allowable hydrogen permeation rate for automotive legal requirements and standards. The work was undertaken as part of the HySafe internal project InsHyde.<br/>A slow long term hydrogen release such as that due to permeation from a vehicle into an inadequately ventilated enclosed structure is a potential risk associated with the use of hydrogen in automotive applications. Due to its small molecular size hydrogen permeates through the containment materials found in compressed gaseous hydrogen storage systems and is an issue that requires consideration for containers with non-metallic (polymer) liners. Permeation from compressed gaseous hydrogen storage systems is a current hydrogen safety topic relevant to regulatory and standardisation activities at both global and regional levels.<br/>Various rates have been proposed in different draft legal requirements and standards based on different scenarios and the assumption that hydrogen dispenses homogeneously. This paper focuses on the development of a methodology by HySafe Partners (CEA NCSRD. University of Ulster and Volvo Technology) to estimate an allowable upper limit for hydrogen permeation in automotive applications by investigating the behaviour of hydrogen when released at small rates with a focus on European scenario. The background to the activity is explained. reasonable scenarios are identified a methodology proposed and a maximum hydrogen permeation rate from road vehicles into enclosed structures is estimated The work is based on conclusions from the experimental and numerical investigations described by CEA NCSRD and the University of Ulster in related papers.

For large-scale distribution and use of energy carriers classified as hazardous material in many countries as a method to assist land use planning to grant licenses to design a safe installation and to operate it safely some form of risk analysis and assessment is applied. Despite many years of experience the methods have still their weaknesses even the most elaborated ones as e.g. shown by the large spread in results when different teams perform an analysis on a same plant as was done in EU projects. Because a fuel as hydrogen with its different properties will come new in the daily use of many people incidents may happen and risks will be discussed. HySafe and other groups take good preparatory action in this respect and work in the right direction as appears from various documents produced. However already a superficial examination of the results so far tells that further cooperative work is indispensable. To avoid criticism skepticism and frustration not only the positive findings should be described and general features of the methods but the community has also to give strong guidance with regard to the uncertainties. Scenario development appears to be very dependent on insight and experience of an individual analyst leak and ignition probability may vary over a wide range of values Computational Fluid Dynamics or CFD models may lead to very different result. The Standard Benchmark Exercise Problems SBEPs are a good start but shall produce guidelines or recommendations for CFD use or even perhaps certification of models. Where feasible narrowing of possible details of scenarios to the more probable ones taking into account historical incident data and schematizing in bowties more explicit use of confidence intervals on e.g. failure rates and ignition probability estimates will help. Further knowledge gaps should be defined.

The UK has committed to significantly reduce greenhouse gas emissions by 2050 to help address climate change. Decarbonising heating is a key part of this and using hydrogen (H2) as a replacement to natural gas (NG) can help in achieving this. The objective of current research including HyDeploy is to demonstrate that NG containing levels of H2 beyond those currently allowed of 0.1 vol% (1000 ppm) [1] can be distributed and utilised safely and efficiently. Initial projects such as HyDeploy are studying the effects of introducing up to 20 vol% H2 in NG but later projects are considering using up to 100 vol% H2.

A key element in the safe operation of a modern gas distribution system is gas detection. However the addition of hydrogen to NG will alter the characteristics of the gas and the impact on gas detection must be considered. It is important that sensors remain sufficiently sensitive to the presence of hydrogen natural gas carbon monoxide (CO) and oxygen (O2) deficiency and that they don’t lead to false positive or false negative readings. The aim of this document is to provide a summary of the requirements for gas detection of hydrogen enriched natural gas for the gas distribution industry and other potentially interested parties. As such it is based on gas detectors presently used by the industry with the only major differences being the effects of hydrogen on the sensitivity of flammable gas sensors and the cross sensitivity of carbon monoxide gas sensors to hydrogen.

There is further information of gas detector concepts and technologies in the appendices.

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Wet dust removal systems used to control dust in the polishing or grinding process of Mg alloy products are frequently associated with potential hydrogen explosion caused by magnesium-water reaction. For purpose of avoiding hydrogen explosion risks we try to use a combination of chitosan (CS) and sodium phosphate (SP) to inhibit the hydrogen evolution reaction between magnesium alloy waste dust and water. The hydrogen evolution curves and chemical kinetics modeling for ten different mixing ratios demonstrate that 0.4% wt CS + 0.1% wt SP yields the best inhibition efficiency with hydrogen generation rate of almost zero. SEM and EDS analyses indicate that this composite inhibitor can create a uniform smooth tight protective film over the surface of the alloy dust particles. FTIR and XRD analysis of the chemical composition of the surface film show that this protective film contains CS and SP chemically adsorbed on the surface of ZK60 but no detectable Mg(OH)2 suggesting that magnesium-water reaction was totally blocked. Our new method offers a thorough solution to hydrogen explosion by inhibiting the hydrogen generation of magnesium alloy waste dust in a wet dust removal system.

The Hydrogen Incident and Accident Database (HIAD) is being developed as a repository of systematic data describing in detail hydrogen-related undesired events (incidents or accidents). It is an open web-based information system serving various purposes such as a data source for lessons learnt risk communication and partly risk assessment. The paper describes the features of the three HIAD modules – the Data Entry Module (DEM) the Data Retrieval Module (DRM) and the Data Analysis Module (DAM) – and the potential impact the database may have on hydrogen safety. The importance of data quality assurance process is also addressed.

An increase in use of hydrogen for energy storage and clean energy supply in a future energy and mobility market will strengthen the focus on safety and the safe handling of hydrogen facilities. The ability to simulate the whole chain of physical phenomena that may occur during an accident is mandatory for future safety studies on an industrial or urban scale. Together with the RWTH Aachen University Forschungszentrum Jülich (JÜLICH) develops numerical methods to predict safety incidents connected with the release of either LH2 or GH2 using the commercial CFD code ANSYS CFX. The full sequence from the release distribution or accumulation of accidentally released hydrogen till the mitigation of accident consequences by safety devices is considered. For specific phenomena like spreading and vaporization of LH2 pools or the operational behavior of passive auto-catalytic recombiners (PAR) in-house sub-models are developed and implemented. The paper describes the current development status gives examples of the validation and concludes with future work to provide the full range of hydrogen release and recombination simulation.

Natural ventilation is an efficient and well-known way to mitigate a hydrogen build-up in the case of an accidental release in confined enclosures. However for some hydrogen energy applications natural ventilation is not possible or is not efficient enough to reach defined safety strategy. Thus mechanical or forced ventilation can be interesting means to avoid critical concentration of hydrogen considering degraded operation and associated potential hazardous events. To better understand the impact of mechanical ventilation on the hydrogen build-up and distribution a dedicated study was led. First accidental release scenarios were experimentally simulated with helium in a 1-m3 enclosure. Several configurations of release and ventilation modes were tested and are presented in this study. Secondly analytical and numerical – Computational Fluid Dynamics – calculation approaches were applied and adjusted to propose a simplified methodology taking into account mechanical ventilation for assessment of hydrogen accumulation and for design optimization of the applications.

We numerically investigated the initial behaviour of leakage and diffusion from high-pressure hydrogen storage tank assumed in hydrogen station. First calculations are carried out to validate the present numerical approach and compare with the theoretical distribution of hydrogen mass fraction to the direction which is vertical to the jet direction in the case of hydrogen leaking out from the circular injection port whose diameter is 0.25 mm. Then performing calculations about hydrogen leakage and diffusion behaviour on different tank pressures the effects are examined to reduce damage by gas explosion assumed in the hydrogen station. There is no significant difference in the diffusion distance to the jet direction from a start to 0.2 ms. After 0.2 ms it is seen the difference in the diffusion distance to the jet direction in different pressure. As tank pressures become large the hydrogen diffusion not only to the jet direction but also to the direction which is vertical to the jet direction is remarkably seen. Then according to histories of the percentage of the flammable mass to total one in the space it drastically increases up to 30%2between 0 and 0.05 ms. After 0.05 ms it uniformly increases so it is shown that the explosion risk becomes high over time. The place where mass within flammability range distributes at a certain time is shown. Hydrogen widely diffuses to jet direction and distributes in each case and time. Therefore it is found that when it is assumed that ignition occurs by some sources in place where high-pressure hydrogen is leaked and diffused the magnitude of the explosion damage can be predicted when and where ignition occurs.

Compressed hydrogen is delivered by trailers in steel cylinders at 19.6 MPa in Japan. Kawasaki Heavy Industries Ltd. developed two compressed hydrogen trailers with composite cylinders in collaboration with JX Nippon Oil in a project of the New Energy and Industrial Technology Development Organization (NEDO).<br/>The first trailer which was the first hydrogen trailer with composite cylinder in Japan has 35 MPa cylinders and the second trailer has 45 MPa cylinders. These trailers have been operated transporting hydrogen and feedstock to hydrogen refuelling stations without the accident. This paper describes the safety design including compliance with regulations the influence of vibrations and safety verification in case of a collision.

An engineering tool is presented to predict steady state two-phase choked flow through a discharge line with variable cross section with account of friction and without wall heat transfer. The tool is able to predict the distribution of all relevant physical quantities along the discharge line. Choked flow is calculated using the possible-impossible flow algorithm implemented in a way to account for possible density discontinuities along the line. Physical properties are calculated using the Helmholtz Free Energy formulation. The tool is verified against previous experiments with water and evaluated against previous experiments with cryogenic two-phase hydrogen.

This paper deals with the build-up of concentration when a continuous source of helium is supplied in an air-filled enclosure. Our aim is to reproduce the results of a small-scale experimental study. To begin with the size of the experiment is reduced from 1/10 to 3/5 for the present analysis. Hypotheses are made in order to reduce the dimension of the real problem. Numerical simulations are carried out on fine grids without any turbulence modelling. The flow structure and the concentration profile of the resulting flow are analyzed and compared with theoretical results.

Hydrogen Infrastructures are currently being built up to support the initial commercialization of the fuel cell vehicle by multiple automakers. Three primary markets are presently coordinating a large build up of hydrogen stations: Japan; USA; and Europe to support this. Hydrogen Fuelling Station General Safety and Performance Considerations are important to establish before a wide scale infrastructure is established.

This document introduces the ISO Technical Report 19880-1 and summarizes main elements of the proposed standard. Note: this ICHS paper is based on the draft TR 19880 and is subject to change when the document is published in 2015. International Standards Organisation (ISO) Technical Committee (TC) 197 Working Group (WG) 24 has been tasked with the preparation of the ISO standard 19880-1 to define the minimum requirements considered applicable worldwide for the hydrogen and electrical safety of hydrogen stations. This report includes safety considerations for hydrogen station equipment and components control systems and operation. The following systems are covered specifically in the document as shown in Figure 1:

• H2 production / supply delivery system
• Compression
• Gaseous hydrogen buffer storage;
• Pre-cooling device;
• Gaseous hydrogen dispensers.
• Hydrogen Fuelling Vehicle Interface

The draft TR 19880-1 (and current plan for the standard) also gives guidance for the fueling validation with safety considerations relevant to the interaction between the hydrogen station and hydrogen road vehicles (during fuelling).. Through a cross-industry risk assessment carried out between OEMs Hydrogen Suppliers and existing vehicle fuelling station providers & operators (e.g. oil and industrial gas companies) the hydrogen fueling protocol SAE J2601 and associated dispenser hardware was evaluated."

We at Kawasaki Heavy Industries have proposed a "CO2-Free H2 supply chain" using abundant brown coal of Australian origin as the energy source. This chain will store CO2 generated during the process for producing hydrogen from brown coal in a project (Carbon Net) that the Australia Government is promoting. Thus Japan can import CO2-free hydrogen. The supply chain consists of the hydrogen production system the hydrogen transport/storage system and the hydrogen use system. Related to their designs we have to consider their hazards polluted scenarios and safety measures via a safety assessment process that is compliant with international risk assessment standards. To verify safety designs related experiments and analyses will be conducted. This paper describes the approach to safety design for especially the related liquid hydrogen facilities.

A high-pressure hydrogen jet released into the air has the possibility of igniting in a tube without any ignition source. The mechanism of this phenomenon called spontaneous ignition is considered to be that hydrogen diffuses into the hot air caused by the shock wave from diaphragm rupture and the hydrogen-oxidizer mixed region is formed enough to start chemical reaction. Recently flow visualization studies on the spontaneous ignition process have been conducted to understand its detailed mechanism but such ignition has not yet been well clarified. In this study the spontaneous ignition phenomenon was observed in a rectangular tube. The results confirm the presence of a flame at the wall of the tube when the shock wave pressure reaches 1.2–1.5 MPa in more than 9 MPa burst pressure and that ignition occurs near the wall followed by multiple ignitions as the shock wave propagates with the ignitions eventually combining to form a flame.

There is a significant potential for nuclear combined heat and power (CHP) in quite a number of industries. The reactor concepts of the next generation would be capable to open up in particular the high temperature heat market where nuclear energy is applicable to the production processes of hydrogen (or liquid fuels) by steam reforming or water splitting. Due to the need to locate a nuclear facility near the hydrogen plant an overall safety concept has to deal with the question of safety of the combined nuclear/industrial system by taking into account a qualitatively new class of events characterized by interacting influences. Specific requirements will be determined by such factors as the reactor type the nature of the industrial process the separation distances of the industrial facility and population centers from the nuclear plant and prevailing public attitudes. Based on the Japanese concept of the GTHTR300C nuclear reactor for electricity and hydrogen cogeneration theoretical studies were conducted on the release dispersive transport and explosion of a hydrogen cloud in the atmosphere for the sake of assessing the required minimum separation distance to avoid any risk to the nuclear plant's safety systems. In the case of sulfur-iodine water splitting the accidental release of process intermediates including large amounts of sulfur dioxide sulfur trioxide and sulfuric acid need to be investigated as well to estimate the potential risk to nuclear installations like the operators' room and estimate appropriate separation distances against toxic gas propagation. Results of respective simulation studies will be presented.

In order to monitor a trace amount of Hydrogen in millisecond portable H2 sensor (Sx) was made by using mass spectrometer. The method of monitoring the hydrogen pulse of millisecond in exhaust gas is the increasing needed. Determining H2 concentration both inside and outside of the Fuel Cell Vehicle (FCV) for the optimized operations is becoming a critical issue. The exhaust gas of Fuel Cell Vehicle H2 consumption flushing and disposal around Fuel cell the real time monitoring of H2 in highly humid conditions is the problematic. To solve this issue the system volume of the sampling route was minimized with the heater and the dehumidifier to avoid condensation of water droplets. And also for an automatic calibration of H2 concentration the small cylinder of specific H2 concentration was mounted into the system.<br/>Our basic experiment started from a flow pattern analysis by monitoring H2 concentration in narrow tube. The flow patter analysis was carried out. When H2 gas was introduced in the N2 flow or air in the tube the highly concentrated H2 front phases were observed. This H2 sensor can provide the real time information of the hydrogen molecules and the clouds. The basic characterization of this sensor showed 0-100% H2 concentrations within milliseconds. Our observations showed the size of the high concentration phase of H2 and the low concentration phase after mixing process. The mixed and unmixed H2 unintended concentration of H2 cloud the high speed small cluster of H2 molecules in purged gas were explored by this system.  

This paper introduces the 3D risk management (3DRM) concept with particular emphasis on hydrogen installations (Hy3DRM). The 3DRM framework entails an integrated solution for risk management that combines a detailed site-specific 3D geometry model a computational fluid dynamics (CFD) tool for simulating flow-related accident scenarios methodology for frequency analysis and quantitative risk assessment (QRA) and state-of-the-art visualization techniques for risk communication and decision support. In order to reduce calculation time and to cover escalating accident scenarios involving structural collapse and projectiles the CFD-based consequence analysis can be complemented with empirical engineering models reduced order models or finite element analysis (FEA). The paper outlines the background for 3DRM and presents a proof-of-concept risk assessment for a hypothetical hydrogen filling station. The prototype focuses on dispersion fire and explosion scenarios resulting from loss of containment of gaseous hydrogen. The approach adopted here combines consequence assessments obtained with the CFD tool FLACS-Hydrogen from Gexcon and event frequencies estimated with the Hydrogen Risk Assessment Models (HyRAM) tool from Sandia to generate 3D risk contours for explosion pressure and radiation loads. For a given population density and set of harm criteria it is straightforward to extend the analysis to include personnel risk as well as risk-based design such as detector optimization. The discussion outlines main challenges and inherent limitations of the 3DRM concept as well as prospects for further development towards a fully integrated framework for risk management in organizations.

To examine the effect of initial turbulence on vented explosions experiments were performed for lean hydrogen–air mixtures with hydrogen concentrations ranging from 12 to 15% vol. at elevated initial turbulence. As expected it was found that an increase in initial turbulence increased the overall flame propagation speed and this increased flame propagation speed translated into higher peak overpressures during the external explosion. The peak pressures generated by flame–acoustic interactions however did not vary significantly with initial turbulence. When flame speeds measurements were examined it was found that the burning velocity increased with flame radius as a power function of radius with a relatively constant exponent over the range of weak initial turbulence studied and did not vary systematically with initial turbulence. Instead the elevated initial turbulence increased the initial flame propagation velocities of the various mixtures. The initial turbulence thus appears to act primarily by generating higher initial flame wrinkling while having a minimal effect on the growth rate of the wrinkles. For practical purposes of modelling flame propagation and pressure generation in vented explosions the increase in burning velocity due to turbulence is suggested to be approximated by a single constant factor that increases the effective burning velocity of the mixture. When this approach is applied to a previously developed vent sizing correlation the correlation performs well for almost all of the peaks. It was found however that in certain situations this approach significantly under predicts the flame–acoustic peak. This suggests that further research may be necessary to better understand the influence of initial turbulence on the development of flame–acoustic peaks in vented explosions.

"The current practise of focusing the periodic retesting of composite cylinders primarily on the hydraulic pressure test has to be evaluated as critical - with regard to the damage of the specimen as well as in terms of their significance. This is justified by micro damages caused to the specimen by the test itself and by a lack of informative values. Thus BAM Federal Institute of Materials Research and Testing (Germany) uses a new approach of validation of composite for the determination of re-test periods. It enables the description of the state of a population of composite cylinders based on destructive tests parallel to operation.<br/>An essential aspect of this approach is the prediction of residual safe service life. In cases where it cannot be estimated by means of hydraulic load cycle tests as a replacement the creep or burst test remains. As a combination of these two test procedures BAM suggests the ""slow burst test SBT"". On this a variety of about 150 burst test results on three design types of cylinders with plastic liners are presented. For this purpose both the parameters of the test protocol as well as the nature and intensity of the pre-damage artificially aged test samples are analysed statistically. This leads first to an evaluation of the different types of artificial ageing but also to the clear recommendation that conventional burst tests be substituted totally if indented for assessment of composite pressure receptacles."

The aim of this study is to assess the probability of the damage to hydrogen fuelling station personnel exposed to the hydrogen explosion shock wave. A three-dimensional mathematical model of the explosion of hydrogen-air cloud formed after the destruction of the high-pressure storage cylinders is developed. A computer technology how to define the personnel damage probability field on the basis of probit analysis of the generated shock wave is developed. To automate the process of computing the "probit function-damage probability" tabular dependence is replaced by a piecewise cubic spline. The results of calculations of overpressure fields impulse loading and the probability of damage to fuelling station personnel exposed to the shock wave are obtained. The mathematical model takes into account the complex terrain and three-dimensional non-stationary nature of the shock wave propagation process. The model allows to obtain time-spatial distribution of damaging factors (overpressure in the shock wave front and the compression phase impulse) required to determine the three-dimensional non-stationary damage probability fields based on probit analysis. The developed computer technology allows to carry out an automated analysis of the safety situation at the fuelling station and to conduct a comparative analysis of the effectiveness of different types of protective facilities.

The availability of repair garage infrastructure for hydrogen fuel cell vehicles is becoming increasingly important for future industry growth. Ventilation requirements for hydrogen fuel cell vehicles can affect both retrofitted and purpose-built repair garages and the costs associated with these requirements can be significant. A hazard and operability (HAZOP) study was performed to identify key risk-significant scenarios related to hydrogen vehicles in a repair garage. Detailed simulations and modeling were performed using appropriate computational tools to estimate the location behaviour and severity of hydrogen release based on key HAZOP scenarios. This work compares current fire code requirements to an alternate ventilation strategy to further reduce potential hazardous conditions. It is shown that position direction and velocity of ventilation have a significant impact on the amount of flammable mass in the domain.

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.

An increase in the number of hydrogen-fuelled applications in the marketplace will require a better understanding of the potential for fires and explosion associated with the unintended release of hydrogen within a structure. Predicting the temporally evolving hydrogen concentration in a structure with unknown release rates leak sizes and leak locations is a challenging task. A simple analytical model was developed to predict the natural and forced mixing and dispersion of a buoyant gas released in a partially enclosed compartment with vents at multiple levels. The model is based on determining the instantaneous compartment over-pressure that drives the flow through the vents and assumes that the helium released under the automobile mixes fully with the surrounding air. Model predictions were compared with data from a series of experiments conducted to measure the volume fraction of a buoyant gas (at 8 different locations) released under an automobile placed in the center of a full-scale garage (6.8 m × 5.4 m × 2.4 m). Helium was used as a surrogate gas for safety concerns. The rate of helium released under an automobile was scaled to represent 5 kg of hydrogen released over 4 h. CFD simulations were also performed to confirm the observed physical phenomena. Analytical model predictions for helium volume fraction compared favourably with measured experimental data for natural and forced ventilation. Parametric studies are presented to understand the effect of release rates vent size and location on the predicted volume fraction in the garage. Results demonstrate the applicability of the model to effectively and rapidly reduce the flammable concentration of hydrogen in a compartment through forced ventilation.

In this study the spread of cryogenic liquid due to a limited period of release is investigated for the first time to clarify the unclear conventional concept regarding two release types continuous and instantaneous release. In describing instantaneous release a discharge time has been assumed to be infinitesimally small; however such an assumption is unreal because there exists a finite period of release no matter how rapid it is. If the discharge time is less than the entire time domain the instantaneous release model should be added to the continuous model from the end of the time. This combined release that consists of the initial continuous model and subsequent instantaneous model is more realistic than the instantaneous release. The physical phenomenon is governed by three parameters: the evaporation rate per unit area release time and spill quantity. Third-order perturbation solutions are obtained and compared with a numerical solution to verify the perturbation solution. For the same spill quantity the combined model that consists of continuous and subsequent instantaneous model is necessary for small release times whereas the continuous model is only required for large release times. Additionally the combined release model is necessary for a small spill quantity at a fixed release time. These two release models are clearly distinguished using the perturbation solution.

We report the development and testing of a novel hydrogen sensor that shows a very peculiar response to hydrogen exposure due to its micro-structured palladium surface. The fabrication of the wrinkled Pd surface is obtained using an innovative fast and cheap technique based on the deposition of a thin Pd film on to a thermo-retractable polystyrene sheet that shrinks to 40% of its original size when heated. The buckling of the Pd surface induced by shrinking of the substrate produces nano and micro-wrinkles on the sensor surface. The micro-structured sensor surface is very stable even after repeated hydrogen sorption/desorption cycles. The hydrogen sensing mechanism is based on the transitory absorption of hydrogen atoms into the Pd layer leading to the reversible change of its electrical resistance. Interestingly depending on hydrogen concentration the proposed sensor shows the concurrent effect of both the usually described behaviors of increase or decrease of resistance related to different phenomena occurring upon hydrogen exposure and formation of palladium hydride. The study reports and discusses evidences for an activation threshold of hydrogen concentration in air switching the behavior of sensor performances from e.g. poor negative to large positive sensitivity and from slow to fast detection.

In this study a solution for a liquid pool spreading model with a continuous spill is compared with that for a liquid pool spreading model with an instantaneous spill under the same total release volume. As reducing spill time in completely releasing liquid from a tank it is evaluated whether the solution for a continuous spill approaches to that for an instantaneous spill or not. Also effects of the viscous term in the liquid pool spreading model with continuous and instantaneous spills on the liquid pool spreading behaviour are investigated.

Hydrogen is seen as an ideal energy carrier for stationary and mobile applications. However the use of high energy density condensed hydrogen storage materials such as NH3BH3 comes with risks associated with their high reactivity with water exposure and their decomposition products reactivity in air. To predict their behaviour under these circumstances idealized finite element models of hypothetical accident scenarios have been developed. Empirical thermodynamic calculations based on precise thermal gravimetric analysis (TGA) and calorimetric experiments have been performed in order to quantify the energy and hydrogen release rates and to quantify the reaction products resulting from water and air exposure.

Two vehicle fire tests were conducted to investigate the spread of fire to adjacent vehicles from a hydrogen fuel cell vehicle (HFCV) equipped with a thermal pressure relief device (TPRD) : – 1) an HFCV fire test involving an adjacent gasoline vehicle 2) a fire test involving three adjoining HFCV assuming their transportation in a carrier ship. The test results indicated that the adjacent vehicles were ignited by flames from the interior and exterior materials of the fire origin HFCV but not by the hydrogen flames generated through the activation of TPRD.

The states of Regulations Codes and Standards (RCS) of hydrogen refueling stations (HRSs) in Japan and France are compared and specified items to understand correspondence and differences among each RCSs for realizing harmonization in RCS. Japan has been trying to reform its RCSs to reduce HRS installation and operation costs as a governmental target. Specific crucial regulatory items such as safety distances mitigation means materials for hydrogen storage and certification of anti-explosion proof equipments are compared in order to identify the origins of the current obstacles for disseminating HRS.

The effect of irregular polygonal grain size and random grain boundary on hydrogen diffusion in polycrystalline nickel is investigated. Hydrogen diffusion behavior in micropolycrystalline nickel is compared with that in nanopolycrystalline nickel through numerical analysis. The two dimensional computational finite element microstructural and nanostructural analyses are based on Fick's law corresponding to heterogeneous polycrystalline model geometry. The heterogeneous polycrystalline model consists of random irregular polygonal grains. These grains are divided into internal grain and grain boundary regions the size of which is determined from the grain size. The computational analysis results show that hydrogen diffusion in nanostructural irregular polycrystalline nickel is higher in magnitude than the microstructural irregular polycrystalline nickel. However models of voids traps and micro and nano clustered grains are yet to be included.

The use of and interpretation of Regulations Codes and Standards is important input when developing hydrogen systems and applications. This paper presents the work related to standardisation undertaken by DNV as part of the EU supported project H2SusBuild. During the H2SusBuild project a renewable (solar and wind) based full scale energy system with components for hydrogen storage hydrogen production by electrolysis and hydrogen consumption by fuel cell and burner was built and integrated into an existing office building in Lavrion Greece. The relevant standards identified and applied the standardisation gaps identified and the recommendations made for further standardisation activities are presented.