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Liquid hydrogen (LH2) is believed to play a pivotal role in the energy transition. The main issue of this technology is the boil-off of the cryogenic liquid, particularly in the presence of critical heat sources, such as an external fire. Typically, in addition to the insulation system, safety barriers, such as water deluge systems and water curtains, are introduced as shields to protect the vessel from the fire radiation. Thus, the heat received from the cryogenic equipment depends on the effectiveness of those barriers. The present study aims at providing a dynamic quantification of the time to failure of an LH2 cryogenic tank, based on the performance of the abovementioned safety barriers. The results of this analysis highlight how different parameters affect the effectiveness of the safety systems, suggesting how to implement the most effective configurations. Moreover, the results obtained in terms of heat fluxes are precious input data useful for the definition of the boundary conditions in mathematical models (e.g., analytical and computational fluid dynamic models) used to investigate the behavior of cryogenic tanks engulfed in a fire.

Glass is one of the most ubiquitous materials in the world. Due to the extremely high temperatures required in the melting process, the glass industry is considered a hard-to-abate sector and poses major challenges to meet the net-zero target in the next decades. Since the highest share of emissions from glass production stems from the combustion of natural gas, its replacement with hydrogen is considered a promising solution to reduce the sector's environmental impact. This is the aim of the H2GLASS project, launched by the European Union at the beginning of 2023. In this context, addressing hydrogen-safety-related aspects is a top priority. In fact, due to hydrogen’s peculiar flammability properties (e.g., wide flammability range, low ignition energy), its utilisation in furnaces may pose significant risks. In this study, a computational fluid dynamic (CFD) model is developed in Ansys Fluent to investigate hydrogen diffusion in enclosures following an accidental release. A grid and time-step sensitivity analyses are carried out to identify the best setup. The model is then validated against experimental data. The results of this work can be used as the starting point to build a CFD model suitable for studying hydrogen releases in large domains, such as glass manufacturing facilities, where obstacles and mechanical ventilation systems are present.

Hydrogen is assuming a pivotal role in the energy sector, intending to lead the decarbonization and overcome the fossil fuel use. In evaluating its key applications, the role of hydrogen in mobility stands out. It could transform one of the most polluting sectors, drastically reducing emissions without changing the drivers’ needs. In this perspective, the focus should be placed on hydrogen refueling infrastructures, which are a key factor, along with fuel cell vehicles, for extending the hydrogen chain in the mobility sector. Given this, the study analyzes the hydrogen refueling station performance, investigating the hydrogen flow features, and estimating the evolution of pressure and temperature within the vehicle tank. An ad-hoc model for hydrogen performance analysis is used by customizing its main blocks. In addition, the main safety aspects of the hydrogen refueling stations are evaluated. The behavior of each component of the refueling infrastructure, such as hydrogen storage tanks, compressors, and cooling systems, is examined and introduced in the model, characterizing the whole system. The model is then validated by comparing its performance with experimental data. The results show the pressure, temperature, and mass flow rate between the dispenser and the vehicle tank. These findings could help boost hydrogen use in mobility since crucial aspects are investigated and important information is provided for promising integrated systems, based on the interconnection between infrastructures and vehicles.

Liquid hydrogen (LH2) is a versatile and efficient energy carrier with numerous applications in space exploration, hydrogen fuel cell vehicles, industrial processes, and the maritime sector. However, its extremely low boiling point and low density present unique challenges in handling, storage, and transportation, particularly in the prevention of loss of containment scenarios. At present, there is still limited knowledge available on the thermodynamics of liquid hydrogen contained in cryogenic storage tanks. This scientific paper delves into an examination of insulation techniques and the operation of liquid hydrogen tanks. Also, self-pressurization is explained and set into context. Furthermore, modelling of specific parameters such as temperature distribution, pressure increase and liquid level play an important role in understanding the thermodynamics inside of LH2 tanks and enable to draw conclusions for the efficient operation when avoiding the loss of hydrogen by releasing boil off gas. The ramifications of this study hold critical importance for industries reliant on hydrogen. The insights gained will facilitate the development of prediction models to enhance operational directives, and the development of effective storage systems.

The interest towards hydrogen skyrocketed in the last years. Thanks to its potential as an energy carrier, hydrogen will be soon handled in public and densely populated areas. Therefore, accurate models are necessary to predict the consequences of unwanted scenarios. These new models should be employed in the consequence analysis, a phase of risk assessment, and thus aid the selection, implementation, and optimization of effective risk-reducing measures. This will increase safety of hydrogen technologies and therefore favour their deployment on a larger scale. Hydrogen is known to be an extremely flammable gas with a low radiation flame compared to hydrocarbons. However, luminous fireballs were generated after the rupture of both compressed gaseous and liquid hydrogen tanks in many experiments. Moreover, it was demonstrated that conventional empirical correlations, initially developed for hydrocarbon fuels, underestimate both dimension and duration of hydrogen fireballs recorded during small-scale tests (Ustolin and Paltrinieri, 2020). The aim of this study is to obtain an analysis of hydrogen fireballs to provide new critical insights for consequence analysis. A comparison among different correlations is conducted when predicting fireball characteristics during the simulation of past experiments where both gaseous and liquid hydrogen tanks were intentionally destroyed. All the models employed in this study are compared with the experimental results for validation purposes. Specific models designed for hydrogen can support the design of hydrogen systems and increasing their safety and promote their future distribution.

Liquid hydrogen (LH2) may be employed to transport large quantities of pure hydrogen or be stored onboard of ships, airplanes and trains fuelled by hydrogen, thanks to its high density compared to gaseous compressed hydrogen. LH2 is a cryogenic fluid with an extremely low boiling point (-253°C at atmospheric pressure) that must be stored in double-walled vacuum insulated tanks to limit the boil-off formation. There is limited knowledge on the consequences of LH2 tanks catastrophic rupture. In fact, the yield of the consequences of an LH2 tank explosion (pressure wave, fragments and fireball) depend on many parameters such as tank dimension, filling degree, and tank internal conditions (temperature and pressure) prior the rupture. Only two accidents provoked by the rupture of an LH2 tank occurred in the past and a couple of experimental campaigns focussed on this type of accident scenario were carried out for LH2. The aim of this study is to analyse one of the LH2 tank explosion consequences namely the fragments. The longest horizontal and vertical ranges of the fragments thrown away from the blast wave are estimated together with the spatial distribution around the tank. Theoretical models are adopted in this work and validated with the experimental results. The proposed models can aid the risk analysis of LH2 storage technologies and provide critical insights to plan a prevention and mitigation strategy and improve the safety of hydrogen applications.

Hydrogen is widely considered a promising energy carrier capable of mitigating human environmental impact. Nevertheless, safety aspects represent one of the major bottlenecks for the widespread utilization of hydrogen technologies. Industrial equipment operating in hydrogen environments is prone to hydrogen-induced damages, which may manifest through a reduction of mechanical properties, fracture toughness, and fatigue performance. They may cause component failures at stress levels significantly below the design level, therefore determining loss of containment. The occurrence of hydrogen embrittlement (HE) relies on the synergy of several factors, such as hydrogen concentration, operating conditions, level of internal and applied stress, microstructure and chemical composition of the material. However, the interlinked dependence of these factors makes a direct and clear evaluation challenging, subsequently creating serious difficulties in planning inspection and maintenance activities. In this study, a comprehensive review of the experimental data of tensile tests carried out in hydrogen was performed and analyzed through an advanced machine learning approach. This study can provide critical insights into the susceptibility to hydrogen embrittlement for several materials operating under different environmental conditions. In particular, the Embrittlement Index was estimated and used as determining parameter to predict the likelihood of component failures. The model demonstrated accurate and reliable predicting capabilities. The outcome of this study can increase the understanding of hydrogen-induced material damages and facilitate decision-making processes in planning the inspection and maintenance of hydrogen technologies.

Hydrogen is considered a promising energy carrier to achieve the ambitious target of a zero-emission society in the forthcoming years. Despite its environmental advantages, hydrogen-induced material damages represent a serious safety concern. Hence, inspection and maintenance activities must be performed to guarantee the equipment's integrity. The risk-based inspection (RBI) is the most beneficial methodology for inspection planning but has never been adopted for components operating in hydrogen environments. The probability of failure of each piece of equipment is quantified through the definition of the damage factor, a parameter that accounts for the damage mechanism likely to occur. Hydrogen embrittlement (HE) is the main active degrading mechanism in equipment exposed to hydrogenated environments; if not appropriately accounted for, it can cause failures at unexpectedly low stress levels. This study aims to bridge a gap in knowledge by proposing a qualitative methodology to assess the degradation of equipment operating in hydrogenated environments and potentially subjected to HE. The environmental severity is estimated based on the operating conditions, while the material’s susceptibility depends on microstructure, strength, and adoption of post-weld heat treatments. This study could set the basis for the application of the RBI methodology to industrial equipment for producing, handling, and storing hydrogen. Hence, it will facilitate the inspection and maintenance of emerging hydrogen technologies.

Hydrogen has not only the potential of tackling climate-related issues by replacing fossil fuels, but it also plays a main role in the energy transition which will have several geopolitical implications. According to the International Renewable Energy Agency (IRENA), relations between countries and communities will be transformed by “a new energy age” changing the concept of power, security, energy independence and prosperity. For these reasons, the interest in hydrogen recently skyrocketed as shown by the hydrogen strategies developed by many countries in the world. This will result in a considerable increase of hydrogen produced, stored, and consumed worldwide in the near future. Safety aspects must always be considered during the whole hydrogen lifecycle. The aim of this study is to pinpoint the consequences of failure for hydrogen technologies and the most common types of techniques developed and validated to assess them. Different types of models including theoretical and numerical ones were adopted to assess these consequences in the past. The advantages and drawbacks of these types of techniques are highlighted in this work. The intent is to provide critical insights to analysts carrying out the risk assessment in order to improve the overall safety of hydrogen technologies.

The adoption of hydrogen has been largely indicated as a feasible solution to support society in achieving its ambitious targets for a low-carbon future. The increased knowledge in liquefaction techniques has encouraged the study of technological solutions based on liquid hydrogen (LH2). Moreover, handling and distribution under cryogenic conditions represent attractive options due to the elevated energy density of LH2. Despite these advantages, the bottleneck for its widespread adoption is represented by safety aspects. Considering that an LH2 tank truck has a probability of suffering a car accident like all other road vehicles, an emergency auto-thermal burner has been designed in this work. This safety system has the purpose to dispose of the content of a tank truck to avoid the loss of containment. The disposal process includes the vaporization and pre-heating of the LH2, the mixing with ambient air, and its combustion. This device is completely self-supporting since the heat required to vaporize the LH2 is entirely provided by the combustion of the fuel itself. Firstly, the equation of energy balance around the burner was numerically solved to estimate the temperature of flue gases. Then, inner and outer heat transfer coefficients were determined for each section of the coiled-tube heat exchanger. Finally, the heat transfer surface was calculated. The spontaneous conversion between two spin isomers of hydrogen was considered. From the perspective of the heating process, the enthalpy of conversion represents an additional energy request. If the decrease of para-hydrogen fraction was neglected, the length of the heat exchanger would be significantly underestimated. Based on the obtained results, it is possible to conclude that the designed device can be transported on-site and started up easily, making it suitable for emergency response.

Hydrogen can play a central role in the energy transition thanks to its unique properties. However, its low density is one of the main drawbacks. The liquefaction process can drastically increase its density up to virtually 71 kg m-3 at atmospheric pressure and -253°C (NIST, 2019). The safety knowledge gap on physical explosions is still broad in the case of liquid hydrogen (LH2). For instance, it is unclear what are the consequences yields as well as the probabilities of a catastrophic rupture of an LH2 tank. A boiling liquid expanding vapour explosion (BLEVE) might arise after this top event. In this case, the expansion of the compressed gaseous phase is followed by the flashing of a fraction of the liquid. Moreover, combustion may occur for hydrogen since it is highly flammable. This complex phenomenon was not widely explored for LH2 yet. This study focused on the physical explosion by also considering the combustion process. Many integral models were adopted to estimate the mechanical energy developed by the explosion. The tank pressure prior to the rupture was considered below the critical one (1.298 MPa (NIST, 2019)). It was assumed that both liquid and gaseous phases are present inside the tank. The influences of the filling degree of the tank (liquid level) and the temperatures of the liquid and gaseous phases on the explosion energy were analysed. The results were compared with the ones of a previous study where similar models were employed to estimate the mechanical energy of an LH2 tank with different initial conditions (Ustolin et al., 2020a). In particular, the effect of the combustion process on the explosion energy and shock wave overpressure was not accounted for. The aim of this study is to conduct a comparison between different models and assess which are the most and the least conservative. The outcomes of this work provide critical suggestions on the consequence analysis of cryogenic liquefied gas vessels explosions.

Hydrogen can be adopted as a clean alternative to hydrocarbons fuels in the marine sector. Liquid hydrogen (LH2) is an efficient solution to transport and store hydrogen onboard of large ships. LH2 will be implemented in the maritime field in the near future. Additional safety knowledge is required since this is a new application and emerging risk might arise. Recently, a series of LH2 large-scale release tests was carried out in an outdoor facility as well as in a closed room to simulate spills during a bunkering procedure and inside the ship’s tank connection space, respectively (Aaneby et al., 2021). The extremely low boiling point of hydrogen (-253°C (NIST, 2019)) can cause condensation or even solidification of oxygen and nitrogen contained in air, and thus enrich with oxygen the flammable mixture. This can represent a safety concern since it was demonstrated that a burning mixture of LH2 and solid oxygen may transition to detonation (Litchfield and Perlee, 1965). In this study, the experimental data of an LH2 release test series recently carried out were analysed by means of an advanced machine learning approach. The aim of this study was to provide critical insights on the oxygen condensation and solidification during an LH2 accidental release. In particular, a model was developed to predict the possibility and the location of the oxygen phase change depending on the operative conditions during the bunkering operation (e.g. LH2 flowrate). The model demonstrated accurate and reliable predicting capabilities. The outcomes of the model can be exploited to select effective safety barriers such as a water deluge system to prevent the oxygen change phase.

Hydrogen is one of the most suitable candidates in replacing heavy hydrocarbons. Liquefaction of fuels is one of the most effective processes to increase their low density. This is critical especially in large-scale or mobile applications such as in the maritime or aeronautical fields. A potential loss of integrity of the cryogenic storage equipment might lead to severe consequences due to the properties of these substances (e.g. high flammability). For this reason, this critical event must be avoided. The aim of this study is to analyse the behaviour of the cryogenic vessel and its lading when it is exposed to a fire and understand how to prevent a catastrophic rupture of the tank during this accident scenario. A two-dimensional computational fluid dynamic (CFD) analysis is carried out on a cryogenic liquid hydrogen (LH2) vessel to investigate its thermal response when engulfed in a fire. The model accounts for the evaporation and condensation of the substance and can predict the tank pressurization rate and temperature distribution. It is assumed that the vessel is completely engulfed in the fire (worst-case scenario). The CFD model is validated with the outcomes of a small-scale fire test of an LH2 tank. Critical indications on the dynamic response of the cryogenic tank involved in a worst-case accident scenario are provided. Tank pressurisation and temperature distributions of the case study can be exploited to provide conservative estimations of the time to failure (TTF) of the vessel. These outcomes represent useful information to support the emergency response to this type of accident scenario and can aid the selection of appropriate and effective safety barriers to prevent the complete destruction of the tank.

Large-scale experiments have been performed to investigate the possible consequences of realistic amounts of liquified hydrogen (LH2) encountering water. The experiments aimed at simulating an accidental release of LH2 onto water, for instance during the fuelling of a ship. For liquified natural gas (LNG), it has been demonstrated that physical explosions may occur when it is spilled onto water. These phenomena are referred as rapid phase transitions (RPTs). It cannot be excluded that RPTs are also possible in the case of LH2. The tests were performed at the Test Site Technical Safety of the Bundesanstalt für Materialforschung und –prüfung (BAM) in Horstwalde, Germany. The tests were performed in a 10 m x 10 x 1.5 m basin filled with water. LH2 releases of up to about 1 kg/s were established releasing directly from a trailer carrying LH2. The releases occurred from a height of 50 cm above the water surface pointing downwards, 30 cm under the water surface pointing downwards and 30 cm under the water surface pointed along the water surface. All release configurations resulted in a very chaotic LH2-water mixing zone, causing considerable evaporation and resulting in minor over pressures. No RPTs were observed. The main phenomenon to be observed is, however, an ignition of the released gas cloud resulting in significant blast wave overpressures and heat radiation to the surroundings. The ignition occurred in all under-water releases and in about 90 % of the releases above the water surface.

Experiments have been performed to determine the consequences of a storage vessel containing liquified hydrogen (LH2) is engulfed by a fire. The tests were performed at the Test Site Technical Safety of the Bundesanstalt für Materialforschung und –prüfung (BAM) in Germany within a research cooperation between BAM and Gexcon as part of the SH2IFT program. Three tests were performed using double-walled vacuum insulated vessels of 1 m3 volume varying the orientation of the vessel and the effect of the insulation material used (perlite or multi-layer insulation (MLI)). The degree of filling of the vessel was approximately 35 % in each of the tests performed. The fire load was provided by a propane fed burner positioned under the storage vessel and designed to give a homogeneous fire load. In one of the tests a rupture of the storage vessel occurred causing a blast, a fireball and fragments. Apart from measuring these consequences, the conditions in the vessel (e.g. temperatures and pressure) during the heating process were monitored in all three tests. The work described was undertaken as part of the project Safe Hydrogen fuel handling and Use for Efficient Implementation (SH2IFT).

The European Green Deal aims to transform the EU into a modern, resource-efficient, and competitive economy. The REPowerEU plan launched in May 2022 as part of the Green Deal reveals the willingness of several countries to become energy independent and tackle the climate crisis. Therefore, the decarbonization of different sectors such as maritime shipping is crucial and may be achieved through sustainable energy. Hydrogen is potentially clean and renewable and might be chosen as fuel to power ships and boats. Hydrogen technologies (e.g., fuel cells for propulsion) have already been implemented on board ships in the last 20 years, mainly during demonstration projects. Pressurized tanks filled with gaseous hydrogen were installed on most of these vessels. However, this type of storage would require enormous volumes for large long-range ships with high energy demands. One of the best options is to store this fuel in the cryogenic liquid phase. This paper initially introduces the hydrogen color codes and the carbon footprints of the different production techniques to effectively estimate the environmental impact when employing hydrogen technologies in any application. Afterward, a review of the implementation of liquid hydrogen (LH2) in the transportation sector including aerospace and aviation industries, automotive, and railways is provided. Then, the focus is placed on the maritime sector. The aim is to highlight the challenges for the adoption of LH2 technologies on board ships. Different aspects were investigated in this study, from LH2 bunkering, onboard utilization, regulations, codes and standards, and safety. Finally, this study offers a broad overview of the bottlenecks that might hamper the adoption of LH2 technologies in the maritime sector and discusses potential solutions.

The hydrogen consumption is expected to grow in the near future, and a forecasted energy transition after the COVID-19 pandemic may increment such growth. For this reason, there is the need for a solution to increase the hydrogen density for both storage and transportation purposes. The release of hydrogen from its handling equipment is a scenario that must be assessed to define the technology feasibility. Both confined and unconfined hydrogen releases have been broadly studied in the scientific literature. However, the focus has been placed mainly on the release and dispersion of compressed gaseous hydrogen. Hydrogen distribution to the future gas refuelling stations in liquid (cryogenic) phase rather than compressed gas is one of the options to increase the truck payload. For this reason, potential liquid hydrogen (LH2) release with a consequent pool formation and gas dispersion is one of the scenarios to consider by the associated risk assessment. The aim of this study is to comprehend the hydrogen behaviour after a liquid release in a refuelling station, which represents a semi-confined space, by means of a commercial computational fluid dynamics (CFD) tool: the FLame ACceleration Simulator (FLACS). The LH2 pool formation as well as the dispersion of the hydrogen gas cloud in the surrounding were investigated. Different parameters such as the variation in density of the extremely cold gas and the lower flammability limit (LFL) of the gas cloud were measured. As expected, the wind speed and direction significantly affect the position and dilution of the flammable gas cloud within and outside the facility. Few solutions to prevent further consequences from the LH2 releases such as a vapour cloud explosion were proposed to spark the interest on future studies on safety barriers for this type of accident scenario.

Historically, electrical system networks have been designed to allow a small number of centralized electricity generating facilities to distribute electricity to many consumers. With the deployment of the means of production in renewable energies, necessary to reach the objectives of Paris Agreements, the means of energy production multiply and decentralize. This decentralization leads to an additional cost of electricity due to the need to strengthen the distribution and transport networks, as well as the exchange capacities at the borders. In addition, these means of producing renewable energy (whether wind turbines, photovoltaic panels, hydraulic central) have intermittences both daily and seasonal. Within the framework of the “Smart Energy Systems” ERA-Net (European Research Area Network), the recently funded “H2 CoopStorage” project responds to the challenges posed by the deployment of renewable energy production means, by improving local balancing, by reducing renewable intermittences and by intensifying the production of renewable energy. More specifically, the project aims to develop methodological tools and software allowing the deployment and management of a multi-energy (electric, heat, hydrogen) energy community integrating hybrid storage (electrochemical and fuel cell) to be able to respond to the storage of daily and seasonal energy needs. The tools will be developed on the real Mortsel pilot site (Belgium), responding in a global manner to the challenges posed by technological, societal and legal barriers. The project is also innovative in its approach because the actors of the energy community will participate in the development of tools through a co-construction process. This is fundamental to ensuring that the tools developed meet the needs of all stakeholders. This contribution aims at providing both a detailed description of the project activities ahead and the preliminary results already obtained.

A fireball may occur after the catastrophic rupture of a tank containing a flammable substance such as a fuel, if an ignition source is present. The fireball is identified by the combustion of the flammable cloud created after the fuel release and composed by the mixture of the latter and air. In particular, the fuel concentration is higher at the center of the fireball compared with the external layers where the ignition takes place. After its formation, the fireball tends to rise vertically due to the buoyancy of the hot gases involved in the combustion. Moreover, the fireball emits its energy mainly through radiant heat. Hence, the fireball formation may be one of the consequences of both a liquid and a compressed gaseous hydrogen tank explosion. For instance, the fireball is a consequence of a boiling liquid expansion vapor explosion (BLEVE). A BLEVE may occur after the catastrophic rupture of a tank containing a liquid at a temperature higher than its boiling point at atmospheric pressure. The explosion is characterized by the rapid expansion of the liquid and vapor phases due to the depressurization of the vessel. The aim of this study is to model a liquid hydrogen (LH2) fireball generated subsequently the BLEVE phenomenon. Different empirical correlations were selected to estimate the fireball dimensions and duration. Moreover, the fireball radiation was estimated by means of a theoretical model. As case study, the fireball generated from the explosion of the LH2 tank with a volume of 1 m3, which will be tested during the safe hydrogen fuel handling and use for efficient implementation (SH2IFT) project, was simulated. The results achieved from the fireball numerical models can be employed to estimate the safety distance from an LH2 tank and propose appropriate safety barriers. Furthermore, these outputs can aid the writing of critical safety guidelines for hydrogen technologies. Finally, the outcome of this study will be validated with the experimental results during the SH2IFT project.

Light hydrocarbons and hydrogen can replace high-alkane fuels with the benefit of reduced CO2 emissions. Their liquefaction to a cryogenic state is one of the most suitable solutions for storage and transport. An unexpected release of these fuels might lead to a rapid phase transition (RPT). RPT is a physical explosion well-known for liquefied natural gas (LNG), and may occur when this substance is spilled onto water. The heat provided by the water to the cryogenic fuel might lead to a sudden evaporation of the liquid, resulting in an explosion. The generated blast wave has the potential to damage equipment and personnel. The RPT phenomenon can also occur in different types of industrial applications when molten metals accidentally come in contact with water. In these cases, the water is the cold fluid which expands violently. In this study, the RPT phenomenon is investigated for cryogenic fluids (liquefied hydrocarbons, nitrogen and hydrogen) as well as for smelts (molten inorganic salts) and molten metals (aluminum). The contribution has a twofold purpose as it addresses relevant past accidents and lay the foundation for future modelling activities to simulate the cryogenic-pool formation on water, triggering of an RPT event and the RPT explosion consequences. Furthermore, the RPT theories and mechanisms comprehension is critical to qualitatively evaluate the probability for a liquid hydrogen (LH2) RPT. In particular, a comparison between liquid nitrogen (LN2) and LH2 is conducted to understand under which conditions an LH2 RPT might occur. The results of this study are to be validated through the Safe Hydrogen Fuel Handling and Use for Efficient Implementation (SH2IFT) project, in which a series of LH2 spill tests onto water will be conducted.

The Energy System lab at the University of Trieste has carried out a study to investigate the reduction in performance of high temperature polymer electrolyte membrane (HTPEM) fuel cell membrane electrode assemblies (MEAs) when subjected to different ageing tests. In this study, start and stop cycles, load cycles, open circuit voltage (OCV) permanence and constant load profile were considered. Polarization curves (PC) together with electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) data were recorded during the ageing tests to assess the fuel cell performance. In this paper, experimental data are presented to confirm the test methodology previously proposed by the authors and to quantitatively correlate the performance degradation to the operational profiles. It was demonstrated that OCV condition, start and stop and load cycling increase degradation of the MEAs with respect to constant load operation. As expected, the OCV is the operational condition that influences performance degradation the most. Finally, the MEAs were analyzed with synchrotron small angle X-ray scattering (SAXS) technique at the Austrian SAXS beamline at Elettra-Sincrotrone Trieste to analyze the nano-morphological catalyst evolution. As for the catalyst morphology evolution, the ex situ SAXS methodology proposed by the authors is confirmed in its ability to assess the catalyst nanoparticles aggregation.

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, potential 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 posterior 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 used in this study. Critical conditions identified by the numerical simulation models are identified and considered for subsequent update of the overall system risk assessment.

Liquid hydrogen (LH2) spills share many of the characteristics of liquefied natural gas (LNG) spills. LNG spills on water sometimes result in localized vapor explosions known as rapid phase transitions (RPTs), and are a concern in the LNG industry. LH2 RPT is not well understood, and its relevance to hydrogen safety is to be determined. Based on established theory from LNG research, we present a theoretical assessment of an accidental spill of a cryogen on water, including models for pool spreading, RPT triggering, and consequence quantification. The triggering model is built upon film-boiling theory, and predicts that the mechanism for RPT is a collapse of the gas film separating the two liquids (cryogen and water). The consequence model is based on thermodynamical analysis of the physical processes following a film-boiling collapse, and is able to predict peak pressure and energy yield. The models are applied both to LNG and LH2, and the results reveal that (i) an LNG pool will be larger than an LH2 pool given similar sized constant rate spills, (ii) triggering of an LH2 RPT event as a consequence of a spill on water is very unlikely or even impossible, and (iii) the consequences of a hypothetical LH2 RPT are small compared to LNG RPT. Hence, we conclude that LH2 RPT seems to be an issue of only minor concern.