Safety

International ships carrying liquefied fuel are strongly recommended to install vent masts to control the pressure of cargo tanks in the event of an emergency. However the gas emitted from a vent mast may be hazardous for the crew of the ship. In the present study the volume and length of the flammable zone (FZ) created by the emitted gas above the ship was examined. Various scenarios comprising four parameters namely relative wind speed arrangement of vent masts combination of emissions among four vent masts and direction of emission from the vent-mast outlet were considered. The results showed that the convection acts on the volume and length of an FZ. The volume of an FZ increases when there is a reduction in convection reaching the FZ and when strong convection brings hydrogen from a nearby FZ. The length of the FZ is also related to convection. An FZ is elongated if the center of a vortex is located inside the FZ because this vortex traps hydrogen inside the FZ. The length of an FZ decreases if the center of the vortex is located outside the FZ as such a vortex brings more fresh air into the FZ.

The climate emergency is one of the biggest challenges humanity must face in the 21st century. The global energy transition faces many challenges when it comes to ensuring a sustainable reliable and affordable energy supply. A likely outcome is decarbonizing the existing gas infrastructure. This will inevitably lead to greater penetration of hydrogen. While the introduction of hydrogen into natural gas  transmission and distribution networks creates challenges there is nothing new or inherently impossible about the concept. Indeed more than 4000 kilometers of hydrogen pipelines are currently in operation. These pipelines however were (almost) all built and operated exclusively in accordance with specific hydrogen codes which tend to be much more restrictive than their natural gas equivalents. This means that the conversion of natural gas pipelines which have often been in service for decades and have accumulated damage and been subject to cracking threats (e.g. fatigue or stress corrosion cracking (SCC)) throughout their lifetime can be challenging. This paper will investigate the impact of transporting hydrogen on the crack management of existing natural gas pipelines from an overall integrity perspective. Different cracking threats will be described including recent industry experience of those which are generic to all steel pipelines but exacerbated by hydrogen and those which are hydrogen specific. The application of a Hydrogen Framework to identify characterise and manage credible cracking threats to pipelines in order to help enable the safe economic and successful introduction of hydrogen into the natural gas network will be discussed.

This review examines the central role of hydrogen particularly green hydrogen from renewable sources in the global search for energy solutions that are sustainable and safe by design. Using the hydrogen square safety measures across the hydrogen value chain—production storage transport and utilisation—are discussed thereby highlighting the need for a balanced approach to ensure a sustainable and efficient hydrogen economy. The review also underlines the challenges in safety assessments points to past incidents and argues for a comprehensive risk assessment that uses empirical modelling simulation-based computational fluid dynamics (CFDs) for hydrogen dispersion and quantitative risk assessments. It also highlights the activities carried out by our research group SaRAH (Safety Risk Analysis and Hydrogen) relative to a more rigorous risk assessment of hydrogenrelated systems through the use of a combined approach of CFD simulations and the appropriate risk assessment tools. Our research activities are currently focused on underground hydrogen storage and hydrogen transport as hythane.

A Lagrangian-based one-dimensional approach has been developed using Cantera to study the dynamics of spherically expanding flames. The detailed reaction model USC-Mech II has been employed to examine flame propagating in hydrogen-air mixtures. In the first part our approach has been validated against laminar flame speed and Markstein number data from the literature. It was shown that the laminar flame speed was predicted within 5% on average but that discrepancies were observed for the Markstein number especially for rich mixtures. In the second part a detailed analysis of the thermo-chemical dynamics along the path of Lagrangian particles propagating in stretched flames was performed. For mixtures with negative Markstein lengths it was found that at high stretch rates the mixture entering the reaction-dominated period is less lean with respect to the initial mixture than at low stretch rate. This induces a faster rate of chemical heat release and of active radical production which results in a higher flame propagation speed. Opposite effects were observed for mixtures with positive Markstein lengths for which slower flame propagation was observed at high stretch rates compared to low stretch rates."

The ability to remotely monitor hydrogen and map its concentration is a pressing challenge in large scale production and distribution as well as other sectors such as nuclear storage. We present a photonicsbased approach for the stand-off sensing and mapping of hydrogen concentration capable of detecting and locating <0.1% concentrations at 100m distance. The technique identifies the wavelength of light resulting from interaction with laser pulses via Raman scattering and can identify a range of other gas species e.g. hydrocarbons ammonia by the spectroscopic analysis of the wavelengths present in the return signal. LIDAR Light Detection and Ranging – analogous to Radar is used for ranging. Laserbased techniques for the stand-off detection of hydrocarbons frequently employ absorption of light at specific wavelengths which are characteristic of the gas species. Unfortunately Hydrogen does not exhibit strong absorption however it does exhibit strong Raman scattering when excited in the UV wavelength range. Raman scattering is a comparatively weak effect. However the use of solid-state detectors capable of detecting single photons known as SPADS (Single Photon Avalanche Photodiode) enables the detection of low concentrations at range while making use of precise time-of-flight range location correlation. The initial safety case which necessitated our development of stand-off hydrogen sensing was the condition monitoring of stored nuclear waste supported and funded by Sellafield and the National Nuclear Laboratory in the UK. A deployable version of the device has been developed and hydrogen characterisation has been carried out in an active nuclear store. Prior to deployment a full ignition risk assessment was carried out. To the best of our knowledge this technique is the strongest candidate for the remote stand-off sensing of hydrogen.

Hydrogen combustion inside a post-accident nuclear reactor containment may pose a challenge to the containment integrity which could alter the fission-product release source term to the public. Combustion-generated overpressures may be relieved by venting to adjacent compartments through relief panels or existing openings. Thus an improved understanding of the propagation of lean hydrogen deflagrations in inter-connected compartments is essential for the development of appropriate management strategies. GOTHIC is a general purpose lumped parameter thermal-hydraulic code for solving multi-phase compressible flows which is accepted as an industry-standard code for containment safety analyses. Following the Fukushima accident the application of three-dimensional computational fluid dynamics methods to high-fidelity detailed analysis of hydrogen combustion processes has become more widespread. In this study a recently developed large-eddy-simulation (LES) capability is applied to the prediction of lean premixed hydrogen deflagrations in large-scale vented vessels of various configurations. The LES predictions are compared with GOTHIC predictions and experimental data obtained from the large-scale vented combustion test facility at the Canadian Nuclear Laboratories. The LES methodology makes use of a flamelet- or a progress-variable-based combustion model. An empirical burning velocity model is combined with an advanced finite-volume framework and a mesh-independent subfilter-scale model. Descriptions of the LES and GOTHIC modelling approaches used to simulate the hydrogen reactive flows in the vented vessels along with the experimental data sets are given. The potential and limitations of the lumped parameter and LES approaches for accurately describing lean premixed hydrogen deflagrations in vented vessels are discussed.

Adopting proton exchange membrane fuel cells fuelled by hydrogen presents a promising solution for the shipping industry’s deep decarbonisation. However the potential safety risks associated with hydrogen leakage pose a significant challenge to the development of hydrogen-powered ships. This study examines the safe design principles and leakage risks of the hydrogen gas supply system of China’s first newbuilt hydrogen-powered ship. This study utilises the computational fluid dynamics tool FLACS to analyse the hydrogen dispersion behaviour and concentration distributions in the hydrogen fuel cell room based on the ship’s parameters. This study predicts the flammable gas cloud and time points when gas monitoring points first reach the hydrogen volume concentrations of 0.8% and 1.6% in various leakage scenarios including four different diameters (1 3 5 and 10 mm) and five different directions. This study’s findings indicate that smaller hydrogen pipeline diameters contribute to increased hydrogen safety. Specifically in the hydrogen fuel cell room a single-point leakage in a hydrogen pipeline with an inner diameter not exceeding 3 mm eliminates the possibility of flammable gas cloud explosions. Following a 10 mm leakage diameter the hydrogen concentration in nearly all room positions reaches 4.0% within 6 s of leakage. While the leakage diameter does not impact the location of the monitoring point that first activates the hydrogen leak alarm and triggers an emergency hydrogen supply shutdown the presence of obstructions near hydrogen detectors and the leakage direction can affect it. These insights provide guidance on the optimal locations for hydrogen detectors in the fuel cell room and the pipeline diameters on hydrogen gas supply systems which can facilitate the safe design of hydrogen-powered ships.

There is growing interest in utilizing existing infrastructure for storage and distribution of hydrogen. Gaseous hydrogen for example could be added to natural gas in the short-term whereas entire systems can be converted to transmission and distribution networks for hydrogen. Many active programs around the world are exploring the safety and feasibility of adding hydrogen to these networks. Concerns have been raised about the structural integrity of materials in these systems when exposed to hydrogen. In general the effects of hydrogen on these materials are grossly misunderstood. Hydrogen unequivocally degrades fatigue and fracture resistance of structural steels in these systems even for low hydrogen partial pressure (-l bar). In most systems however hydrogen effects will not be apparent because the stresses in these systems remain very low. Another misunderstanding results from the kinetics of the hydrogen  effects:  hydrogen  degrades   fatigue  and  fracture  properties  immediately  upon  exposure  to gaseous hydrogen and those effects disappear when the hydrogen environment is removed even after prolonged exposure. There is also a misperception that materials selection can mitigate hydrogen effects. While some classes of materials perform better in hydrogen environments than other classes for most practical   circumstances  the  range  of  response  for  a  given  class  of  material  in  gaseous  hydrogen environments is rather narrow. These observations can be systematically characterized by considering the  intersection  of  materials  environmental  and  mechanical  variables   associated  with  the  service application. Indeed any safety assessment of a hydrogen pressure system must quantitatively consider these aspects. In this report we quantitatively evaluate the importance of the materials environmental and mechanical variables in the context of hydrogen additions to natural gas piping and pipeline systems with  the  aim  of  providing  an  informed   perspective  on  parameters relevant for assessing  structural integrity of natural gas systems in the presence of gaseous hydrogen.

The increasing demand for renewable energy storage may position hydrogen as one of the major players in the future energy system. However to introduce such technology high level of safety must be offered. In particular for the accident scenarios with combustion or explosion of the unintendedly released hydrogen in partially or fully confined volumes such as e.g. road tunnel the effective countermeasures preventing or reducing the risk of equipment damages and person injuries should be established. A mitigation strategy could be the use of existing fire suppression system which can inject water as a spray. The shock waves resulted from hydrogen explosion could be weakened by the water droplets met on the shock path. In the presented work an attenuation effect of water droplets presence on the strength of the passing shock was studied. The analysis of the different attenuation mechanisms was performed and estimation of the effect of spray parameters such as droplet size and spray density on the shock wave was carried out. For the quantitative evaluation of the attenuation potential a numerical model for the COM3D combustion code was developed. The novel model for the droplet behavior accounting for the realistic correlations for the fluid (water) particle drag force linked with the corresponding droplet breakup model describing droplet atomization is presented. The model was validated against literature experimental data and was used for the blind simulations of the hydrogen test facility in KIT.

One of China’s ambitious hydrogen strategies over the past few years has been to promote fuel cells. A number of hydrogen refueling stations (HRSs) are currently being built in China to refuel hydrogen-powered automobiles. In this context it is crucial to assess the dangers of hydrogen leaking in HRSs. The present work simulated the liquid hydrogen (LH2) leakage with the goal of undertaking an extensive consequence evaluation of the LH2 leakage on an LH2 refueling station (LHRS). Furthermore the utilization of an air curtain to prevent the diffusion of the LH2 leakage is proposed and the defending effect is studied accordingly. The results reveal that the Richardson number effectively explained the variation of plume morphology. Furthermore different facilities have great influence on the gas cloud diffusion trajectory with the consideration of different leakage directions. The air curtain shows satisfactory prevention of the diffusion of the hydrogen plume. Studies show that with the increase in air volume (equivalent to wind speed) and the narrowing of the air curtain width (other factors remain unchanged) the maximum flammable distance of hydrogen was shortened.