The work presented in this thesis was undertaken as part of the safety work package of the NATURALHY project which was an integrated project funded by the European Commission (EC) within the sixth framework programme. The purpose of the NATURALHY project was to investigate the feasibility of using existing natural gas infrastructure to assist a transition to a hydrogen based economy by transporting hydrogen from its place of production to its place of use as a mixture of natural gas and hydrogen. The hydrogen can then be extracted from the mixture for use in fuel cells or the mixture used directly in conventional combustion devices. The research presented in this thesis focused on predicting the consequences of explosions and fires involving natural gas and hydrogen mixtures, using engineering type mathematical models typical of those used by the gas industry for risk assessment purposes. The first part of the thesis concentrated on modifying existing models that had been developed to predict confined vented and unconfined vapour cloud explosions involving natural gas. Three geometries were studied: a confined vented enclosure, an unconfined cubical region of congestion and an unconfined high aspect ratio region of congestion. The modifications made to the models were aimed at accounting for the different characteristics of a natural gas/hydrogen mixture compared to natural gas. Experimental data for the laminar burning velocity of methane/hydrogen mixtures was obtained within the safety work package. For practical reasons, this experimental work was carried at an elevated temperature. Predictions from kinetic modelling were employed to convert this information for use in models predicting explosions at ambient temperature. For confined vented explosions a model developed by Shell (SCOPE) was used and modified by adding new laminar burning velocity and Markstein number data relevant to the gas compositions studied. For vapour cloud explosions in a cubical region of congestion, two models were used. The first model was developed by Shell (CAM2), and was applied using the new laminar burning velocity and other composition specific properties. The second model was based on a model provided by GL Services and was modified by generalising the flame speed model so that any natural gas/hydrogen mixture could be simulated. For vapour cloud explosions in an unconfined high aspect ratio region of congestion, a model from GL Services was used. Modifications were made to the modelling of flame speed so that it could be applied to different fuel compositions, equivalence ratios and the initial flame speed entering the congested region. Predictions from the modified explosion models were compared with large scale experimental data obtained within the safety work package. Generally, (apart from where continuously accelerating flames were produced), satisfactory agreement was achieved. This demonstrated that the modified models could be used, in many cases, for risk assessment purposes for explosions involving natural gas/hydrogen mixtures. The second part of thesis concentrated on predicting the incident thermal radiation from high pressure jet fires and pipelines fires involving natural gas/hydrogen mixtures. The approach taken was to modify existing models, developed for natural gas. For jet fires three models were used. Fuel specific input parameters were derived and the predictions of flame length and incident radiation compared with large scale experimental data. For pipeline fires a model was developed using a multi-point source approach for the radiation emitted by the fire and a correlation for flame length. Again predictions were compared with large scale experimental data. For both types of fire, satisfactory predictions of the flame length and incident radiation were obtained for natural gas and mixtures of natural gas and hydrogen containing approximately 25% hydrogen.

Vätgas är en energibärare som kan vara en av pusselbitarna i omställningen till en mer klimatneutral värld. Infrastrukturen byggs ut, industrin växer och vätgasfordon blir vanligare. Vätgas är ett ämne med de bra egenskaperna att det kan lagra kemisk energi och från förnybar el tillverkas med elektrolys, men det har också den riskabla egenskapen att det är mycket brandfarligt. Vid läckage av vätgas finns risken att en jetflamma med höga temperaturer uppstår vilket påverkar omgivningen där det sker. Standarder för jetbrandtester är idag baserade på tester med propan, men då vätgas har andra egenskaper behövs ökad kunskap för att minska riskerna vid olyckor. Studien syftar till att via litteraturstudier samla information om storskaliga jetbrandtester, vilken utrustning som används, hur material påverkas av jetflammor och vilka standarder som finns för jetflammor och jetbrandtester. Ett av syftena är också att med intervjustudie ta reda på hur räddningstjänsten i Luleå ser på utvecklingen av vätgasinfrastruktur och om de har några rutiner för olyckor med vätgas. Det finns en vision vid Luleå tekniska universitet att det i framtiden ska finnas en anläggning för att utföra jetbrandtester av vätgas och andra bränslen i Luleå. Studien syftar därför också till att via intervju ta reda på om räddningstjänsten i Luleå skulle ha någon användning för en sådan anläggning. Jetbrandtester kan enligt standarden SS-ISO 22899-1:2021 utföras i mindre skala med propan som bränsle och ändå ge liknande resultat som vid storskaliga jetbrandtester med naturgas. Jetbrandtestet utförs för att testa brandmotstånd genom integritet (E) och isolerande förmåga (I) för passiva brandskyddsmaterial som används till rör, paneler, konstruktionsstål och rör- och kabelgenomföringar. Testerna utförs enligt standarden med utrustning såsom munstycke, åter-cirkuleringskammare, skyddskammare, med mera. Enligt standarden SS-ISO 22899-1:2021 träffas testobjektet vid ett jetbrandtest med en jetflamma av propan på 1 meters avstånd. Det korta avståndet medför att propanet inte fullt hinner förbrännas vilket skapar temperaturskillnader på testobjektets yta när det träffas av flamman. Det bildas en ”kall” och en ”varm” zon på ytan där den ”kalla” zonen är den punkt som i direkt kontakt med jetflamman utsätts för mekanisk kraft i form av erosion. För vätgas hinner flamman stabilisera sig på en meters avstånd vilket gör att testobjektet träffas av en fullt utvecklad flamma och därför både utsätts för termiska laster i form av en enhetlig ”varm” zon och mekaniska laster i form av erosion. Denna skillnad kan göra att passiva brandskyddsmaterial vid jetflammor av vätgas inte klarar av att upprätthålla det krav på brandmotstånd som ställs. Detta är främst aktuellt att undersöka för reaktiva passiva brandskyddamaterial då de är mer känsliga för erosion än icke-reaktiva passiva brandskyddsmaterial. Om så är fallet att passiva brandskyddsmaterial inte klarar av att motstå jetflammor av vätgas lika bra som för propan kanske en standard för jetbrandtester med vätgas skulle behöva tas fram. Det kan vid intervjun med PärJohan Fredrickson som är sektionschef för myndighetsutövningen vid Luleå räddningstjänst konstateras att de verkar vara väl informerade om utvecklingen av vätgasinfrastrukturen och att de har varit delaktiga i vätgasfrågor sedan några år tillbaka. De har samarbeten med andra räddningstjänster och de försöker tidigt vara med i dialogen när nya processer och verksamheter utvecklas. De har i dagsläget inte några operativa övningar med jetflammor av vätgas men de arbetar förebyggande genom att ta fram insatsplaner tillsammans med de industriella verksamheter som hanterar vätgas. De kan från ett förebyggande perspektiv se hur räddningstjänsten kanske skulle kunna ha användning av en anläggning för att genomföra jetbrandtester med vätgas. Men om det finns något operativt behov behöver vidare utredas med personal på räddningstjänsten som arbetar inom de operativa resurserna. / Hydrogen is an energy-carrier that can be a piece in the change for a climate neutral world. The infrastructure and industry expand, and hydrogen vehicles becomes more common. Some good characteristics with hydrogen are that it from renewable energy can be produced through electrolysis and store chemical energy, but it also has the risky characteristic that its very flammable. If hydrogen gas would leak from a container there is the risk of a jet flame with high temperatures that can affect the surroundings. Today’s standards for jet fire testing are based on propane gas, but because hydrogen has so many different characteristics there might be a need for more knowledge to prevent risks and accidents. Through a literature study this report aims to gather information about large scale jet fire testing, what equipment that is used, how materials react to jet flames, and what standards that are current for jet fire testing and jet flames. A purpose is to through an interview-study figure out how the rescue service in Luleå sees on the development in hydrogen infrastructure and if they have any routines for accidents with hydrogen. Luleå University of Technology has a vision to in the future have a facility in Luleå where they can perform jet fire testing with hydrogen and other flammable fuels. One purpose of the study is therefore to interview the rescue service in Luleå to investigate if they would have any interest in such facility and what use they could have of it. According to the standard SS-ISO 22899-1:2021, jet fire tests with propane gas can be performed in a smaller scale and still give similar results as for large scale jet fire tests with natural gas. The jet fire test is performed to determine the fire resistance regarding integrity (E) and isolating capacity (I) for passive fire protection materials that are used for pipes, panels, structural steelwork, and pipe penetration seals. The gear that is used for the tests are a nozzle, flame re-circulation chamber, protective chamber etc. A propane flame hits the object of testing from 1 meter according to the standard. Because of the short distance, the propane flame does not reach full combustion which leads to a temperature difference on the object of testing that is encountered with the jet flame. A “cold” and “hot” zone is therefore created at the surface where the “cold” zone appears at the center core of the jet flame. At this core, the object of testing is exposed to a higher mechanical force in terms of erosion than other parts of the object. For hydrogen the jet flame stabilizes in 1 meter which changes how the flame affects the object of testing. The object is instead hit by a fully combusted jet flame that exposes it to high thermal load with a uniform “hot” zone and mechanical load of erosion. That difference could change how passive fire protection (PFP) materials are able to resist jet flames with hydrogen as the tests for PFP materials are done with propane. This would mainly be topical for reactive PFP materials as they are more sensitive to erosion than non-reactive PFP materials and a standard for jet fire tests with hydrogen may become relevant if PFP materials fail to maintain the requirements that are set for propane. The interview with section manager PärJohan Fredrickson that works at Luleå rescue service shows that Luleå rescue service seems to be well informed about the development of hydrogen infrastructure. Since a few years back they have been involved with questions relating to hydrogen, they have collaborations with other rescue services around the country and they try to get involved as early as possible when new processes and operations are formed. They do not seem to do any exercises where they train for jet fire accidents with hydrogen involved but they are working to prevent accidents with hydrogen. Action plans has been and are being developed together with the operations that are handling the hydrogen. The rescue service could from a preventive perspective have a use of a facility for jet fire testing with hydrogen. But it must be further investigated if there is an operative need to use such a facility.