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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.

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.

Hydrogen er den mest lovende kandidaten for å erstatte fossilt brensel ettersom det under forbrenning ikke produserer karbondioksid så vel som det er rikelig i naturen og inneholder høy gravimetrisk energitetthet. Det har potensial til å bli brukt som et lavutslippsdrivstoff i transportsektoren, deponerer elektrisk energi, oppvarming og kjøling osv. Dette har ført til nødvendigheten av å forsterke hydrogenøkonomien ved å utvikle alle fire seksjoner, produksjon, lagring, transport og applikasjon beskrevet i hydrogenverdikjeden. Hydrogen kan lagres i forskjellige tilstander, for eksempel i flytende, komprimert gassform og fast form, samt kan transporteres til sluttbrukere gjennom rørtilhengere, jernbane eller skip. Selv om hydrogen utvilsomt har utmerkede egenskaper som energikilde, utfolder det flere sikkerhetsproblemer under lagrings- og leveringsprosessen. Derfor er det nødvendig med sikker og pålitelig infrastruktur for å formidle hydrogen siden den forbinder etterspørselen og tilbudet av gassen. I denne rapporten studeres transport av hydrogen i komprimert gassform ved hjelp av rørtilhengere siden det krever den enkleste infrastrukturen og har økonomisk fordel fremfor andre alternativer. Oppgaven presenterer en detaljert risikoanalyse for rørtilhengertransport av komprimert gassformig hydrogen og identifiserer potensielle ulykkesscenarier som utvikler seg fra de initierende hendelsene til sluttkonsekvensene. Siden de initierende hendelsene er de første indikatorene på avvik fra normal driftstilstand i et system, blir teknologier for å umiddelbart oppdage avviket ved å studere ytelsen til forskjellige komponenter gjennomgått i denne studien. Dette vil føre til tidlig identifisering av farlige forringelser i systemet som kan håndteres i tide, og store ulykker kan også forhindres. Prosesssikkerhetsindikatorer er også nevnt i denne rapporten for overvåkingsteknologiene for de initierende hendelsene for å sikre dobbel sikkerhet. Siden det ikke er noen retningslinjer for hvilke fysiske mengder/parametre som skal overvåkes under transport av hydrogen gjennom rørtilhengere, anbefales en overvåkingsstrategi for MCE-selskap basert på dette forskningsarbeidet som kan tas i bruk for å etablere en sikker leveringsmetode for komprimert gassformig hydrogenrørtilhenger. . Til slutt, sammenligning mellom overvåkingstilnærmingene brukt for hydrogenrørhenger og LPG, blir CNG-transporterende kjøretøy utført for å studere forskjellene. Videre foreslås fremtidig arbeidsområde i denne forbindelse også i denne rapporten. Hydrogen is the most promising candidate for replacing fossil fuels as during combustion it does not produce carbon dioxide as well as it is abundant in nature and contains high gravimetric energy density. It has the potential to be employed as a low emission fuel in transportation sector, depositing electrical energy, heating, and cooling purposes etc. This has led to the necessity of reinforcing hydrogen economy by developing all four sections, production, storage, transportation, and application described in hydrogen value chain. Hydrogen can be stored in different states for instance, in liquid, compressed gaseous and solid forms as well as can be transported to the end users through tube trailers, railway or ship. Though hydrogen has undoubtedly excellent properties as a source of energy, it unfolds several safety issues during its storage and delivery process. Hence, safe and reliable infrastructure is needed to convey hydrogen since it connects the demand and supply of the gas. In this report, transportation of hydrogen in compressed gaseous form using tube trailers is studied since it requires the simplest infrastructure and has economic benefit over other options. The thesis presents a detailed risk analysis for tube trailer transportation of compressed gaseous hydrogen and identifies the potential accident scenarios developing from the initiating events to the end consequences. Since the initiating events are the first indicators of deviation from normal operating condition within a system, technologies to instantly detect the deviation by studying performance of different components are reviewed in this study. This will lead to early identification of any dangerous deterioration within the system which can timely be handled, and major accidents can be prevented as well. Process safety indicators are also mentioned in this report for the monitoring technologies of the initiating events to ensure dual assurance. Since there is no guideline about what physical quantities/ parameters are to be supervised while transporting hydrogen through tube trailers, a monitoring strategy is recommended for MCE company based on this research work that can be adopted to establish a safe compressed gaseous hydrogen tube trailer delivery method. Finally, comparison between the monitoring approaches adopted for hydrogen tube trailer and LPG, CNG transporting vehicles is conducted to study the differences. Moreover, future scope of work in this regard is also suggested in this report.

Nye karbonutslippsmål for 2050 er i topp interesse for markedet for hydrogen som en alternativ energikilde. MCE, en leverandør av løsninger for veitransport, ba om støtte til planlegging og beslutningstaking angående muligheter for transport av komprimert hydrogengass. Oppgavearbeidet er en videreføring av spesialiseringsprosjektet høstsemesteret 2020 rettet mot domenet for risikoanalysen av lagringsutstyret under transport, spesielt for komprimerte hydrogentanker. Oppgaven presenterer risikoanalysen av de potensielle konsekvensene basert på flere scenarier angående transport av komprimert hydrogentank og førerhusets sikkerhet. Hovedfokus har vært på konsekvensmodellering av brudd i hydrogentanken ved bruk av computational fluid dynamics (CFD) modellering for å simulere og evaluere virkningen av eksplosjonsbølgen generert på førerhuset og det omkringliggende miljøet når det gjelder trykk og temperaturprofiler. Resultatene støtter analysen av tiltak som er nødvendige for å forhindre og minimere konsekvensene. Imidlertid gjenstår det ytterligere arbeid med å etablere klare retningslinjer for å sikre transport av hydrogengass i form av forskrifter som den European Agreement concerning the International Carriage of Dangerous Goods by Road (ADR). New carbon emissions targets for 2050 are peaking interest in the market for hydrogen as an alternative energy source. MCE, a supplier of road transportation solutions, requested the support of their planning and decision-making regarding options for the transport of compressed hydrogen gas. The thesis work is the continuation of the specialization project of fall semester 2020 directed towards the domain of the risk analysis of the storage equipment under transport in particular for compressed hydrogen tanks. The thesis presents the risk analysis of the potential consequences based on multiple scenarios regarding the transportation of the compressed hydrogen tank and the driver’s cabin safety. The major focus has been on the consequence modeling of rupture of the hydrogen tank using computational fluid dynamics (CFD) modeling to simulate and evaluate the impact of the blast wave generated on the driver’s cabin and the surrounding environment in terms of pressure and temperature profiles. The results support the analysis of measures required to prevent and minimize the effects of the consequences. However, additional work remains toward establishing clear guidelines for safeguarding the transport of hydrogen gas in terms of regulations such as the European Agreement concerning the International Carriage of Dangerous Goods by Road (ADR).

Hydrogen er en lovende kandidat for å erstatte konvensjonelle drivstoff og oppnå målet for klimagassutslipp. Dette har resultert i en større interesse for utviklingen av hydrogen som energibærer. Til tross for fremskritt innen teknologiene relatert til hydrogen, er sikkerhet fortsatt en stor bekymring for hydrogens sosiale aksept. Selv om det er en mengde forskning for å designe sikkerhetsbarrierer i tilfelle den katastrofale eksplosjonen av hydrogen, mangler det forskningsarbeid om førerens sikkerhet under transport av hydrogen via tilhengere, selv om det er mange rapporterte hydrogen- relaterte ulykker der sjåførene var de første rapporterte omkomne. Målet med studien er å utvikle konsekvensreduserende barrierer for tap av inneslutning av komprimert gassformig hydrogen (CGH2) under transport. På grunn av det teoretiske grunnlaget som ble etablert i masterns spesialiseringsrapport med MCE AS, ønsket selskapet å studere videre utformingen av førerhusets sikkerhetssystem mot høytrykkssprengning forårsaket av tap av CGH2-inneslutning. Studien fokuserer på utformingen av en ny kontinuerlig vegg mellom førerhuset og lagringstankene for hydrogen. Valget av veggen er basert på modellering av et potensielt storeffektulykkesscenario, med trykkstøt mot veggen. Deretter er alternativene for konstruksjon av veggen basert på tilgjengelige materialer i samsvar med MCEs teknologiske evner, styrken på materialene og tillatte veggdimensjoner. Studien evaluerer et utvalg av designhensyn for valg av sikkerhetsbarrierevegg, der sammenligninger blir gjort mellom den enkle barriereveggen, den forsterkede veggen og den femkantede armerte barrieren. Responsen på eksplosjonens overtrykkeffekt studeres og det konkluderes med at det ved hjelp av en forsterket femkantet vegg med en tykkelse på 50 mm er mulig å beskytte førerhuset mot den kritiske hendelsen av hydrogentankeksplosjon. Hydrogen is a promising candidate for replacing conventional fuels and achieving the greenhouse gaseous emissions target. This has resulted in a greater interest in the development of hydrogen as an energy carrier. Despite advances in the technologies related to hydrogen, safety remains a major concern for hydrogen's social acceptance. Even though there is a body of research to design safety barriers in the case of the catastrophic explosion of hydrogen, there is a lack of research work on the safety of the driver during the transport of hydrogen via trailers even though there are many reported hydrogen-related accidents where the drivers were the first reported casualties. The objective of the study is to develop consequence-reducing barriers for the loss of containment of compressed gaseous hydrogen (CGH2) in transportation. Due to the theoretical foundation established in the master's specialization report with MCE AS, the company wanted to study further the design of the driver's cabin safety system against the high-pressure blast caused by the loss of CGH2 containment. The study focuses on the design of a novel continuous wall between the driver’s cabin and hydrogen storage tanks. The selection of the wall is based on modeling a potential high-impact accident scenario, with pressure shocks against the wall. Then, the options for the construction of the wall are based on the available materials consistent with MCE’s technological capabilities, the strength of materials, and allowable wall dimensions. The study evaluates a selection of design considerations for choosing a safety barrier wall, where comparisons are made between the simple barrier wall, reinforced wall, and the pentagonal reinforced barrier. The response to the overpressure effect of the explosion is studied and it is concluded that by using a reinforced pentagonal wall of 50mm thickness, it is possible to safeguard the driver’s cabin against the critical event of hydrogen tank explosion.