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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. Experimental Investigation into the Consequences of Release of Liquified Hydrogen onto and under Water

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).

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.

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 autothermal 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.

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.

Hydrogen is one of the most suitable candidates to replace hydrocarbons and reduce the environmental pollution and CO2 emissions. Hydrogen is valuable energy carrier, potentially clean and renewable thanks to its peculiar properties. However, hydrogen has a few characteristics, such as high flammability and low density that must be taken into account when stored or handled, especially in relation to the associated safety. For this reason, this PhD study aims to increase the knowledge on safety of hydrogen technologies. Hydrogen safety is a broad topic which involves several disciplines. This PhD focusses on the modelling of atypical accident scenarios of liquid hydrogen (LH2) technologies by adopting a multidisciplinary approach. This type of accident scenarios is called atypical because they have low probability to happen but high consequences. A few times, the neglection of these scenarios by conventional risk assessment techniques led to major accidents. For this reason, the atypical accident scenario cannot be omitted during a risk assessment and must be further analysed. Firstly, through a comprehensive literature review, this PhD study investigates the causes of loss of integrity (LOI) and loss of containment (LOC) of hydrogen equipment since the atypical accident scenarios always occurred after these critical events. The consequences of an LH2 release are then analysed. The focus is placed on the boiling liquid expanding vapour explosion (BLEVE) and the rapid phase transition (RPT) explosions for liquid hydrogen technologies because a significant dearth of knowledge is still present. Secondly, the possibility for the BLEVE to occur after the catastrophic rupture of an LH2 vessel is theoretically assessed by gathering information on previous accident and applying accepted thermodynamic theories for this event. The consequences of a potential BLEVE for LH2 (pressure wave, missiles and fireball) are evaluated. Unique experimental series on LH2 bursting tank scenario and fire tests are simulated. Different approaches are employed for the BLEVE event: analytical models, empirical correlations and CFD analysis. Finally, the time to failure of an LH2 tank exposed to a fire is estimated with a thermal node model. Thirdly, the RPT event is analysed from a more theoretical approach since no records of LH2 RPT are found in literature. The knowledge gained for other substances such as liquefied natural gas (LNG) and liquid nitrogen (LIN) is applied to LH2. The consequences of a hypothetical LH2 RPT are evaluated by means of an analytical model and compared to the LNG RPT aftermath. The main contributions of this PhD study are the following: • investigation on the causes of LOI of hydrogen technology; • identification of the LH2 release consequences; • understanding of the BLEVE feasibility for LH2 storage systems; • determination of the LH2 BLEVE consequences; • estimation of the time to failure of LH2 tanks exposed to a fire; • analysis of the theories and mechanisms of RPT explosions; • determination of the LH2 RPT consequences. This PhD study provides relevant safety indications on the causes of LOI of hydrogen technologies as well as on the BLEVE and RPT phenomena for LH2 technologies. The knowledge gap in these topics is highlighted and partially fulfilled. The limitations of existing models for the simulation of these explosions are emphasised. The results of this thesis serve as a starting point for future studies.

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. This journal provides immediate open access to its content on the principle that making research freely available to the public supports a greater global exchange of knowledge. Our policy is to permit Authors to reuse part of their CET articles or to self-archive the published version of their work in Institutional Repository, provided that AIDIC/CET is acknowledged as the source. The version to be used is the Publisher’s PDF. No embargo period is required.

Data analysis of vessels routes show that shipping is responsible of about 2,6% of world CO2e (carbon dioxide equivalent) emissions. The effect on environment is increased as most of the emissions are concentrated in coastal areas. IMO and other bodies are making growing efforts to impose severe limits on shipping pollutions. Different technical and operational improvements have been made but hydrogen and fuel cells remain one of the best candidates to substantially reduce emissions and fuel consumption. This paper gives an updated review of the fuel cells applications in the marine sector and analyses the potential of different fuel cells technology for the on board installation. The analysis shows the advantages that fuel cells can give in terms of emissions reductions and fuel saving. The benefits are dependent on the type of ship and the operating profiles. Nevertheless, even if some fuel cells types are today ready for marine application, costs, hydrogen availability and certifications issues still hamper the full exploitation of the technology.

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. Copyright © 2019, AIDIC Servizi S.r.l.

Nowadays the urgency to address climate change and global warming is growing rapidly: the industry and the energy sector must be decarbonized. Hydrogen can play a key role in the energy transition: it is expected to progressively replace fossil fuels, penetrating economies and gaining interest from the public. However, this new possible energy scenario requires further investigation on safety aspects, which currently represent a challenge. The present study aims at making a little contribution to this field. The focus is on the analysis and modeling of hazardous scenarios concerning liquid hydrogen. The investigation of BLEVEs (Boiling Liquid Expanding Vapor Explosion) consequences lies at the core of this research: among various consequences (overpressure, radiation), the interest is on the generation and projection of fragments. The goal is to investigate whether the models developed for conventional fuels and tanks give good predictions also when handling hydrogen. The experimental data from the SH2IFT - Safe Hydrogen Fuel Handling and Use for Efficient Implementation project are used to validate those models. This project’s objective was to increase competence within safety of hydrogen technology, especially focusing on consequences of handling large amounts of this substance.

Hydrogen regnes som en av de mulige løsningene for å redusere klimagassutslippene. Det er imidlertid problemer knyttet til produksjon, lagring og sikkerhet som må løses før hydrogen kan bli tatt i bruk på verdensbasis. I denne avhandlingen studeres ildkuler som genereres etter katastrofale brudd på hydrogentanker. Spesielt evalueres den termiske faren ved ildkuler ved hjelp av eksperimentelle data samlet inn under SH2IFT-prosjektet. Modellene som vanligvis brukes til å forutsi ildkulenes størrelse og varighet, analyseres og sammenlignes med empiriske data fra litteraturen. Til slutt foreslås noen nye modeller som bedre beskriver de eksperimentelle dataene. Hydrogen is considered one of the possible solutions to reduce greenhouse gas emissions. However, there are production, storage, and safety issues to be solved before it might start to be widely used worldwide. In this thesis, the fireballs generated after the catastrophic rupture of hydrogen tanks are studied. In particular, the fireball thermal hazard is evaluated by means of experimental data collected during the SH2IFT project. Also, the models generally used to predict the fireball dimension and duration are analyzed and compared with empirical data from the literature. Finally, some new models that better describe the experimental data are proposed.

Hydrogen kan være en passende erstatning for fossilt brensel takket være dets unike egenskaper. Etter produksjon,hydrogen kan transporteres og distribueres ved hjelp av rørledninger, tankbiler, rørtilhengere eller skip. Transport med rørhengere er godt etablert for relativt små mengder over korte avstander (opp til 200 km). Komprimert gassformig hydrogen (CGH2) kan transporteres med sylindere eller buntede rør på rørhenger på lastebiler med trykk mellom 20-70 MPa. Men sikker bruk og håndtering av komprimert gassformig hydrogen byr på ulike utfordringer på grunn av hydrogens lette lekkasje, lav tenning energi på 0,017 mJ og bredt utvalg av brennbare drivstoff-luftblandinger på 4-75 %, oppdrift og sprøhet. Derfor er sikkerhet en stor bekymring for den nye hydrogeninfrastrukturen. Et viktig prinsipp underliggende sikker hydrogenbruk er å søke design og operasjoner som minimerer alvorlighetsgraden av konsekvensene av et potensielt uhell. Dette kan gjøres ved bruk av alarmer og varslingsenheter (inkludert hydrogen- og branndetektorer), områdekontroll rundt et hydrogensystem og bruk av personlig verneutstyr utstyr. Det er imidlertid foreløpig ingen indikasjon på hvordan man kan utvikle et system for å oppdage lekkasjer for transport av komprimert gassformig hydrogen ved hjelp av rørhengere. I dette arbeidet, et lekkasjedeteksjonssystem for rørhengere sammen med automatiske sikkerhetsbarrierer er utviklet. Sammen med gjennomføringen av et lekkasjedeteksjonssystem, kreves det forsikring om dets tiltenkte og effektive drift. Derfor, en modifikasjon av "HSG254: Developing Process Safety Indicators" ble vedtatt, og sikkerhetsindikatorer ble utviklet. Gjennom implementeringen av det utviklede lekkasjedeteksjonssystemet og vedta det relevante sikkerhetsindikatorer, risikoene knyttet til transport av komprimert gassformig hydrogen ved hjelp av rørhengere forventes å bli kontrollert i stor grad. Hydrogen may be a suitable substitute to fossil fuels thanks to its unique properties. After production, hydrogen can be transported and distributed using pipelines, tanker trucks, tube trailers, or ships. Transportation by tube trailers is well established for relatively small quantities over short distances (up to 200 km). Compressed gaseous hydrogen (CGH2) can be transported by cylinders or bundled tubes on tube trailer on trucks with pressures between 20-70 MPa. However, the safe usage and handling of compressed gaseous hydrogen poses different challenges due to hydrogen’s ease of leaking, low ignition energy of 0.017 mJ and wide range of combustible fuel-air mixtures of 4-75%, buoyancy and embrittlement. Therefore, safety is a major concern for the emerging hydrogen infrastructure. An important principle underlying safe hydrogen use is to seek designs and operations that minimize the severity of the consequences of a potential mishap. This can be done by use of alarms and warning devices (including hydrogen and fire detectors), area control around a hydrogen system and use of personal protective equipment. However, there is currently no indication on how to develop a system for detecting leakages for transporting compressed gaseous hydrogen using tube trailers. In this work, a leakage detection system for tube trailers along with automatic safety barriers has been developed. Along with the implementation of a leakage detection system, the assurance of its intended and effective operation is required. Therefore, a modification of ‘HSG254: Developing Process Safety Indicators’ was adopted, and safety indicators were developed. Through the implementation of the developed leakage detection system and adopting its relevant safety indicators, the risks regarding the transportation of compressed gaseous hydrogen using tube trailers are expected to be controlled to a large extent.

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 large amounts of hydrogen, thus it is suitable for the maritime field. 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 operation and inside the ship’s tank connection space, respectively. The extremely low boiling point of hydrogen (-253°C) can cause condensation or even solidification of air components, thus enrich with oxygen the flammable mixture. This can represent a safety concern in case of ignition of the flammable mixture of LH2 and solid oxygen, since it was demonstrated that the resulting fire may transition to detonation. In this study, the abovementioned LH2 release experiments were analysed by using 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 spill and to evaluate whether the hydrogen concentration within the gas cloud formed due to the LH2 evaporation would reach the lower flammability limit. In particular, a model was developed to predict the possibility and the location of the oxygen phase change and of the hydrogen concentration above the lower flammability limit depending on the operative conditions during the bunkering operation (e.g. LH2 flow rate). The model demonstrated accurate and reliable predicting capabilities. The outcomes of the model can be exploited to select effective safety barriers and adopt the most appropriate safety measures in case of liquid hydrogen leakage.