Safety

Hydrogen vehicles may emerge as a leading contender to replace today’s internal combustion engine powered vehicles. A Phenomena Identification and Ranking Table exercise conducted as part of the European Network of Excellence on Hydrogen Safety (HySafe) identified the use of hydrogen vehicles in road tunnels as a topic of important concern. An internal project called HyTunnel was duly established within HySafe to review identify and analyse the issues involved and to contribute to the wider activity to establish the true nature of the hazards posed by hydrogen vehicles in the confined space of a tunnel and their relative severity compared to those posed by vehicles powered by conventional fuels including compressed natural gas (CNG). In addition to reviewing current hydrogen vehicle designs tunnel design practice and previous research a programme of experiments and CFD modelling activities was performed for selected scenarios to examine the dispersion and explosion hazards potentially posed by hydrogen vehicles. Releases from compressed gaseous hydrogen (CGH2) and liquid hydrogen (LH2) powered vehicles have been studied under various tunnel geometries and ventilation regimes. The findings drawn from the limited work done so far indicate that under normal circumstances hydrogen powered vehicles do not pose a significantly higher risk than those powered by petrol diesel or CNG but this needs to be confirmed by further research. In particular obstructions at tunnel ceiling level have been identified as a potential hazard in respect to fast deflagration or even detonation in some circumstances which warrants further investigation. The shape of the tunnel tunnel ventilation and vehicle pressure relief device (PRD) operation are potentially important parameters in determining explosion risks and the appropriate mitigation measures.

A turbulent combustion model based on the Linear Eddy Model for Large Eddy Simulation (LEM- LES) is currently proposed to study self-ignition events of rapidly expanding hydrogen jets. The model is a one-dimensional treatment of a diffusion-reaction system within each multi-dimensional LES cell. This reduces the expense of solving a complete multi-dimensional problem while preserving micro-scale hotspots and their effects on ignition. The current approach features a Lagrangian description of fluid particles on the sub-grid for increased accuracy. Also Adaptive Mesh Refinement (AMR) is implemented for increased computational efficiency. In this paper the model is validated for various inviscid laminar 1-D mixing and ignition problems shock tube problems flames and detonations.

This paper shows numerical investigation related to hydrogen-air deflagration venting. The aim of this study is to clarify the influence of concentration gradient on the pressure histories and peak pressures in a chamber. The numerical analysis target is a 27 m3 cubic chamber which has 2.6 m2 vent area on the sidewall. The vent opening pressure is set to be gauge 10 kPa. Two different conditions of the hydrogen concentration are assumed which are uniform and gradient. In the uniform case 15 20 25 30 and 35 vol.% concentrations are assumed. In the gradient case the concentration linearly increases from 0 vol.% (at the ground) to 30 40 50 60 70 vol.% (at the ceiling). The initial total mass of hydrogen inside the chamber is the same as the uniform case. Moreover three different ignition points are assumed: on the rear center and the front of the chamber relative to the vent. The deflagrations are initiated by a single ignition source. In most gradient cases the highest peak is lower than in the uniform case though the initial total mass of hydrogen inside the chamber is the same as in the uniform case. This is because the generated burned gas per time is smaller in the gradient case than in the uniform case. In 15 vol.% gradient case however the peak pressure gets higher than in the uniform case. This is because in 15 vol.% gradient case the burning velocity around the ignition point gets faster and the flame surface gets larger which induces larger amount of burned gas per time.

Contrary to several reports in the recent literature the use of oxygen sensors for indirectly monitoring ambient hydrogen concentration has serious drawbacks. This method is based on the assumption that a hydrogen release will displace oxygen which is quantified using oxygen sensors. Despite its shortcomings the draft Hydrogen Vehicle Global Technical Regulation lists this method as a means to monitor hydrogen leaks to verify vehicle fuel system integrity. Experimental evaluations that were designed to impartially compare the ability of commercial oxygen and hydrogen sensors to reliably measure and report hydrogen concentration changes are presented. Numerous drawbacks are identified and discussed.

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.

Evaluations of the uncertainties resulting from risk assessment tools to predict releases from the various hydrogen storage types are important to support risk informed safety management. The tools have to predict releases from a wide range of storage pressures (up to 80 MPa) and temperatures (at 20K) e.g. the cryogenic compressed gas storage covers pressures up to 35 MPa and temperatures between 33K and 338 K. Accurate calculations of high pressure releases require real gas EOS. This paper compares a number of EOS to predict hydrogen properties typical in different storage types. The vessel dynamics are modelled to evaluate the performance of various EOS to predict exit pressures and temperatures. The results are compared to experimental data and results from CFD calculations.

Computational Fluid Dynamics (CFD) is applied to investigate the near exit jet behavior of high pressure hydrogen release into quiescent ambient air through different types of orifices. The size and geometry of the release hole can affect the possibility of auto-ignition. Therefore the effect of release geometry on the behavior and development of hydrogen jet issuing from non-axisymmetric (elliptical) and expanding orifices is investigated and compared with their equivalent circular orifices. A three-dimensional in-house code is developed using the MPI library for parallel computing to simulate the flow based on an inviscid approximation. Convection dominates viscous effects in strongly underexpanded supersonic jets in the vicinity of release exit justifying the use of the Euler equations. The transport (advection) equation is applied to calculate the concentration of hydrogen-air mixture. The Abel-Nobel equation of state is used because high pressure hydrogen flow deviates from the ideal gas assumption. This work effort is conducted to fulfill two objectives. First two types of circular and elliptic orifices with the same cross sectional area are simulated and the flow behavior of each case is studied and compared during the initial stage of release. Second the comparative study between expanding circular exit and its fixed counterpart is carried out. This evaluation is conducted for different sizes of nozzle with different aspect ratios.

The present work proposes a parametric study on the influence of the height of the release source on the helium dispersion regimes inside a naturally ventilated enclosure. Several configurations were experimentally addressed in order to improve knowledge on dispersion considering conditions close to hydrogen energy systems in terms of operating characteristics and design. Thus the varying parameters of the study were mainly the height of the release and also the releasing flow rate the volume and the geometry of the enclosure. Experimental results were compared to existing analytical models and considered through model improvements allowing a better approach of these specific cases for hydrogen systems risk assessment.

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.

Gas sensors are applied for facilitating the safe use of hydrogen in for example fuel cell and hydrogen fuelled vehicles. New sensor developments aimed at meeting the increasingly stringent performance requirements in emerging applications are presented based on in-house technical developments and a literature study. The strategy of combining different detection principles i.e. sensors based on electrochemical cells semiconductors or field effects in combination with thermal conductivity sensor or catalytic combustion elements in one new measuring system is reported. This extends the dynamic measuring range of the sensor while improving sensor reliability to achieve higher safety integrity through diverse redundancy. The application of new nanoscaled materials nano wires carbon tubes and graphene as well as the improvements in electronic components of field-effect resistive-type and optical systems are evaluated in view of key operating parameters such as sensor response time low energy consumption and low working temperature.

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.

The commercial deployment of hydrogen will often involve housing portable hydrogen fuel cell power units in 20-foot or 40-foot shipping containers. Due to the unique properties of hydrogen hazards identification and consequence analysis is essential to safe guard the installations and design measures to mitigate potential hazards. In the present study the explosion of a premixed hydrogen-air cloud enclosed in a 20-foot container of 20’ x 8’ x 8’.6” is investigated in detail numerically. Numerical simulations have been performed using HyFOAM a dedicated solver for vented hydrogen explosions developed in-house within the frame of the open source computational fluid dynamics (CFD) code OpenFOAM toolbox. The flame wrinkling combustion model is used for modelling turbulent deflagrations. Additional sub-models have been added to account for lean combustion properties of hydrogen-air mixtures. The predictions are validated against the recent experiments carried out by Gexcon as part of the HySEA project supported by the Fuel Cells and Hydrogen 2 Joint Undertaking (FCH 2 JU) under the Horizon 2020 Framework Programme for Research and Innovation. The effects of congestion within the containers on the generated overpressures are also investigated.

Distributed hydrogen optical fiber sensor with Brillouin scattering is an innovative solution to measure hydrogen in harsh environment as nuclear industry. Glass composition is the key point to enhance the sensing parameter of the fiber in the target application. Several optical fiber with different doping element were used for measuring hydrogen saturation. Permeability of optical plays a major role to the kinetic of hydrogen diffusion. Fluorine doped fiber increase the sorption and the desorption of hydrogen.

Hydrogen safety issue in a ventilation system of a generic nuclear containment is studied. In accidental scenarios a large amount of burnable gas mixture of hydrogen with certain amount of oxygen is released into the containment. In case of high containment pressure the combustible mixture is further ventilated into the chambers and the piping of the containment ventilation system. The burnable even potentially detonable gas mixture could pose a risk to the structures of the system once being ignited unexpectedly. Therefore the main goal of the study is to apply the computational fluid dynamics (CFD) computer code – GASFLOW to analyze the distribution of the hydrogen in the ventilation system and to find how sensitive the mixture is to detonation in different scenarios. The CFD simulations manifest that a ventilation fan with sustained power supply can extinguish the hydrogen risk effectively. However in case of station blackout with loss of power supply to the fan hydrogen/oxygen mixture could be accumulated in the ventilation system. A further study proves that steam injection could degrade the sensitivity of the hydrogen mixture significantly.

The spontaneous ignition of hydrogen released from the high pressure tank into the downstream pipes with different lengths varied from 0.3m to 2.2m has been investigated experimentally. In this study the development of shock wave was recorded by pressure sensors and photoelectric sensors were used to confirm the presence of a flame in the pipe. In addition the development of jet flame was recorded by high-speed camera and IR camera. The results show that the minimal release pressure in different tube when self-ignition of hydrogen occurred could decrease first and then increase with the increase of the aspect of pipe. And the minimum release pressure of hydrogen self-ignition was 3.87MPa. When the flame of self-ignition hydrogen spouted out of the tube Mach disk was observed. The method of CFD was adopted. The development of shock wave at the tube exit was reproduced and structures as barrel shock the reflected shock and the Mach disk are presented. Because of these special structures the flame at the nozzle is briefly extinguished and re-ignited. At the same time the complete development process of the jet flame was recorded including the formation and separation of the spherical flame. The flame structure exhibits three typical levels before the hemispherical flame separation.

This paper aims to improve prediction capability of the vent sizing correlation presented in the form of functional dependence of the dimensionless deflagration overpressure on the turbulent Bradley number similar to our previous studies. The correlation is essentially upgraded based on recent advancements in understanding and modelling of combustion phenomena relevant to hydrogen-air vented deflagrations and unique large-scale tests carried out by different research groups. The focus is on hydrogen-air deflagrations in low-strength equipment and buildings when the reduced pressure is accepted to be  below 0.1 MPa. The combustion phenomena accounted for by the correlation include: turbulence generated by the flame front itself; leading point mechanism stemming from the preferential diffusion of hydrogen in air in stretched flames; growth of the fractal area of the turbulent flame surface; initial turbulence in the flammable mixture; as well as effects of enclosure aspect ratio and presence of obstacles. The correlation is validated against the widest range of experimental conditions available to date (76 experimental points). The validation covers a wide range of test conditions: different shape enclosures of volume up to 120 m3; initially quiescent and turbulent hydrogen-air mixtures; hydrogen concentration in air from 6% to 30% by volume; ignition source location at enclosure centre near and far from a vent; empty enclosures and enclosures with obstacles.

Efficient storage of hydrogen is crucial for the success of hydrogen energy markets (early markets as well as transportation market). Hydrogen can be stored either as a compressed gas a refrigerated liquefied gas a cryo-compressed gas or in hydrides. This paper gives an overview of hydrogen storage technologies and details the specific issues and constraints related to the materials behaviour in hydrogen and conditions representative of hydrogen energy uses. It is indeed essential for the development of applications requiring long-term performance to have good understanding of long-term behaviour of the materials of the storage device and its components under operational loads.

The Australian Capital Territory (ACT) has legislated and aims to be net zero emissions by 2045. Such ambitious targets have implications for the contribution of hydrogen and its storage in gas distribution networks Therefore we need to understand now the impacts on the gas distribution network of the transition to 100% hydrogen. Assessment of the viability of decarbonising the ACT gas network will be partly based on the cost of reusing the gas network for the safe and reliable distribution of hydrogen. That task requires each element of the natural gas safety management system to be evaluated.

This article describes the construction of a test facility in Canberra Australia used to identify issues raised by 100% hydrogen use in the medium pressure distribution network consisting of nylon and polyethylene (PE) as a means of identifying measures necessary to ensure ongoing validity of the network's regulatory safety case.

Evoenergy (the ACT's gas distribution company) have constructed a Test Facility incorporating an electrolyser a gas supply pressure reduction and mixing skid a replica gas network and a domestic installation with gas appliances. Jointly with Australian National University (ANU) and Canberra Institute of Technology (CIT) the Company has commenced a program of “bench testing” initially with 100% hydrogen to identify gaps in the safety case specifically focusing on the materials work practices and safety systems in the ACT.

The facility is designed to assess:

•  Materials in use including aged network materials and components
•  Construction and installation techniques both greenfield and live gas work
•  Purging and filling techniques
•  Leak detection both underground and above ground
•  Emergency response and make safe techniques
•  Issues associated with use of hydrogen in light commercial and domestic appliances.

To educate and train:

•  Technicians and gas fitters on infrastructure installation and management
•  Emergency response services on responding to hydrogen related emergencies in a network environment; and
•  Manage public perceptions of hydrogen in a network environment.

Australia has an enviable safety record for the safe and reliable transport distribution and use of natural gas. The ACT natural gas network owned and operated by Evoenergy is one of the newest in Australia and has leveraged off the best materials and practices in Australia to build its network.

The paper addresses major safety issues relating to the production/storage distribution and consumer end use of hydrogen injected into existing gas distribution networks. The analysis is guided by the Safety Management System. The Hydrogen Testing Facility described in the paper provide tools for evaluation of hydrogen safety matters in the ACT and Australia-wide.

Testing to date has confirmed that polyethylene and nylon pipe and their respective jointing techniques can contain 100% hydrogen at pressures used for the distribution of natural gas. Testing has also confirmed that current installation work practices on polyethylene and nylon pipe and joints are suitable for hydrogen service. This finding is subject to variation attributable to staff training and skill levels and further testing has been programmed as outlined in this paper.

Testing of gas isolation by clamping and simulated repair on the hydrogen network has established that standard natural gas isolation techniques work with 100% hydrogen at natural gas pressures.

Explosion venting is a frequently used measure to mitigate the consequence of gas deflagrations in closed environments. Despite the effort to predict the vent area needed to achieved the protection through engineering formulas and CFD tools work has still to be done to reliably predict the outcome of a vented gas explosion. Blind-prediction exercises recently published show a large spread in the prediction of both engineering formula than CFD tools. University of Pisa performed experimental tests in a 25 m3 facility in inhomogeneous conditions and with the presence of simple obstacles constituted by plates bolted to HEB beams. The present paper is aimed to share the results of hydrogen dispersion and deflagration tests and discuss the comparison of maximum peak overpressure generated with different blockage ratio and repeated obstacles sets. Description of the experimental set-up includes all the details deemed necessary to reproduce the phenomenon with a CFD tool.

Hydrogen leakage in a closed space is one of the causes of serious accidents because of its high detonability. Assuming the situation that hydrogen is accumulated in a closed space two-dimensional numerical simulation for hydrogen oxygen detonation which propagates in stratified fuel and oxidizer with concentration gradient is conducted by using detailed chemical reaction model. The concentration gradient between fuel and oxidizer is expressed by changing the number of hydrogen moles by using sigmoid function. Strength of discontinuity at the boundary is controlled by changing the gain of the function. The maximum pressure history shows that the behaviour of triple points is different depending on the strength of discontinuity between the two kind of gas. In without concentration gradient case the transverse waves are reflected at the boundary because of the sudden change of acoustic impedance ratio between two kind of gas. In contrast in with concentration gradient case the transverse wavs are not reflected in the buffer zone and they are flowed into the oxidizer as its structures are kept. As a result the confined effect declines as the strength of discontinuity between the two kind of gas is weakened and the propagating distance of detonation changes

Emerging hydrogen energy technologies are creating new avenues for bring hydrogen fuel usage into larger public domain. Identification of possible accidental scenarios and measures to mitigate associated hazards should be well understood for establishing best practice guidelines. Accidentally released hydrogen forms flammable mixtures in a very short time. Ignition of such a mixture in congestion and confinements can lead to greater magnitudes of overpressure catastrophic for both structure and people around. Hence understanding of the permissible level of confinements and congestion around the hydrogen fuel handling and storage unit is essential for process safety. In the present study numerical simulations have been performed for the hydrogen-air turbulent deflagration in a well-defined congestion of repeated pipe rig experimentally studied by [1]. Large Eddy Simulations (LES) have been performed using the in-house modified version of the OpenFOAM code. The Flame Surface Wrinkling Model in the LES context is used for modelling deflagrations. Numerical predictions concerning the effects of hydrogen concentration and congestion on turbulent deflagration overpressure are compared with the measurements [1] to provide validation of the code. Further insight about the flame propagation and trends of the generated overpressures over the range of concentrations are discussed.

Transport by pipe is one the most usual way to carry liquid or gaseous energies from their extraction point until their final field sites. To limit explosion risk or escape to avoid pollution problems and human risks it is necessary to assess nocivity of defect promoting fracture. This need to know the mechanical properties of the pipes steels. Hydrogen is considered to day as a new energy vector and its transport in one of the key problems to extension of its use. Within the European project NATURALHY it has been proposed to transport a mixture of natural gas and hydrogen. 39 European partners have combined their efforts to assess the effects of hydrogen presence on the existing gas network. Key issues are durability of pipeline material integrity management safety aspects life cycle and socio-economic assessment and end-use. The work described in this paper was performed within the NATURALHY work package on ’Durability of pipeline material’. This study makes it possible to emphasize the hydrogen effect on mechanical properties of several pipe steels as X52 X70 or X100 in fatigue and fracture and in two different environments: air and hydrogen electrolytic.

The temperature of the hydrogen cylinder needs to be carefully controlled during fuelling process. The maximum temperature should be less than 85℃ according to the ISO draft code. If the fuelling period is reduced the maximum temperature should increase. In this study temperature change of a Type IV cylinder was measured during the hydrogen fuelling process up to 35 MPa. Fuelling period was 3 to 5 minutes. Twelve thermocouples were installed to measure inside gas temperature and seven were attached on the outside of the cylinder. An infrared camera was also used for measuring temperature distribution of outside of cylinder. The maximum gas temperature was higher than 85℃ inside of the cylinder. Significant temperature difference between the upper and lower part of the vessel was observed. Temperature near the plug and the valve was quickly increased and maintained higher than that of the other region. Temperature increases for the partial refuelling process were also discussed.

Any experimental study of catalysts and catalytic recombining devices for removal of hydrogen gas from industrial environments is known to carry a risk of ignition of hydrogen. Experiments conducted in an atmosphere with a high concentration of hydrogen present a particular danger. Here a technique is reported that allows conducting such experiments with relative safety. This technique has been developed and applied by the company ‘Russian Energy Technologies’ for the last five years without any significant incident.<br/>A “Gas stream method” for testing and analysis of the characteristics of a catalyst for hydrogen/oxygen recombination is proposed. Tests with a variety of catalysts in a passive recombining device were carried out in a climatic chamber (86 l in volume) with a hydrogen/air mixture containing up to 20% (v/v) hydrogen flowing through it. The balance equation for hydrogen and oxygen flows entering reacting and exiting the chamber led to a formula for calculating the efficiency of a catalyst or a catalytic device under stationary conditions.<br/>Fluctuations in local temperatures of the catalyst and other parts of the chamber along with variation in the concentration of hydrogen gave the authors an insight into the thermal regime of an active catalyst. This enabled them to develop new catalysts for removal of hydrogen from the environment using industrial recombining devices.

In the context of the French DIMITRHY project ANR-08-PANH006 experiments have been carried out to measure helium injections in a cubic 1 m3 box - GAMELAN in a reproducible and quantitative manner. For the present work we limit ourselves to the unique configuration of a closed box with a small hole at its base to prevent overpressure. This case leads to enough difficulties of modelisations to deserve our attention. The box is initially filled with air and injections of helium through a tube of diameter 20 mm is operated. The box is instrumented with catharometres to measure the helium volume concentration within an accuracy better than 0.1%. We present the CFD (Fluent and CASTEM ANSYS-CFX and ADREA-HF) calculations results obtained by 5 different teams participating to the benchmark in the following situation: the case of a plume release of helium in a closed box (4NL/min). Parts of the CFD simulations were performed in the European co-funded project HyIndoor others were performed in the French ANR-08-PANH006 DimitrHy project.