Reducing the environmental and climate impact of shipping propelled by liquefied natural gas (LNG) requires the introduction of alternative fuels such as liquid biogas/biomethane (LBG) (Jivén et al., 2022). Today, only a small part of the biomethane produced in Sweden is liquefied into LBG and an even smaller part is used as fuel for shipping. The price and availability of biogas is governed by supply and demand in an international market where shipping, industry and heavy trucks demand biogas. The biogas then needs to be processed into upgraded biogas (biomethane) or LBG quality in order to be transported and used in the respective sectors inside and outside of Sweden. The trend is for a larger proportion of biogas to be liquefied into LBG. The market has thus gone from a local market, where biogas was produced in the city's wastewater treatment plant and the city buses ran on biogas, to an international market where biogas often is transported in the same way as fossil gas and marketed using the fossil gas together with certificates. The project "Renewable liquid biogas (LBG) for shipping in practice" was carried out by IVL Swedish Environmental Research Institute and RISE in 2023 together with stakeholders from the shipping sector, ports and industry organizations for biogas. The project has studied the conditions required to make LBG available to shipping in practice at Swedish ports. The study shows that the major obstacles to an established use of LBG in the shipping sector in Sweden today are pricing/willingness to pay that is affected by international market prices, lack of suitable logistical solutions as well as the absence of the piece of the puzzle that is the business model and cooperation needed to make available the large volumes of biogas that shipping may demand. The stakeholders in the project estimate their total need of biogas to 3 TWh in a short term, and 10 TWh in a longer term. The project has identified a number of conclusions and recommendations for future work, including that the potential for biogas is large and untapped, but that new solutions for the distribution and logistics of LBG are needed. There is a clear interest from maritime actors as they see biogas as a strategic solution and the dialog between actors in the industry remains important. A change in the tax system could be needed so that more actors can use the green gas principle for LBG. In addition, a functioning "marketplace" is needed, which simplifies for sellers and buyers of LBG, and agreements/contracts are needed that are longterm and to a greater extent based on the costs of producing and providing LBG.

Society is changing ever faster, and tunnels are complex systems where performance is affected by many different stakeholders. These conditions suggest that safety management needs to be proactive and based on a systems perspective that acknowledges socio-technical theories. Although systems thinking principles are foundational in overarching European regulations and goals, system principles generally don’t affect tunnel fire safety design principles or engineering practice. In the countries investigated in this study, tunnel fire safety management (TFSM) builds on experience-based and risk management-based principles that are optimized independently system by system. This is usually done with limited consideration of how these systems are interconnected and affect the overall tunnel system. The purpose of this paper is to investigate how systems thinking could support existing engineering practice. The work presented in this article is the outcome of a collaboration between fire safety researchers and practitioners from five countries and three continents. Through three workshops, current TFSM principles have been compiled and discussed. It is suggested that tunnel safety regulations be redesigned to strengthen the ability of engineers to work in design teams using systems thinking principles.

Vehicles that are powered by gaseous fuel, e.g., compressed natural gas (CNG) or hydrogen (H2), may, in the event of fire, result in a jet flame from a thermally activated pressure relief device (TPRD), or a pressure vessel explosion. There have been a few incidents for CNG vehicles where the TPRD was unsuccessful to prevent a pressure vessel explosion in the event of fire, both nationally in Sweden and internationally. If the pressure vessel explosion would occur inside an enclosure such as a road tunnel, the resulting consequences are even more problematic. In 2019 the authors investigated the fire safety of CNG cylinders exposed to localized fires. One purpose of the tests conducted in 2021 reported in this paper is to investigate whether extinguishment with water, e.g., from a tunnel deluge system, may compromise the safety of vehicle gas cylinders in the event of fire. Steel cylinders handles the situation with localizde fire and/or cooling with water well. Composite tanks can rupture if the fire exposure degrades the composite material strength, and the TPRD is not sufficiently heated to activate, e.g., if the fire is localized or if the TPRD is being cooled by water, which prevents its activation.

The increased use of electric vehicles has raised a concern about firefighting measures including water spray fire suppression systems (often denoted “drencher systems”) and tactics and equipment used for manual firefighting on ro-ro cargo and ro-ro passenger ships. A test series involving testing of two pairs of geometrically similar internal combustion engine vehicles (ICEV’s) and battery electric vehicles (BEV’s) under as equal test conditions as possible were conducted to investigate the performance efficiency of the drencher system. In addition, manual firefighting equipment and tactics was evaluated on three BEV fire tests. It is concluded that a fire in the two types of vehicles is different but share similarities. However, a fire in a BEV does not seem to be more challenging than a fire in an ICEV for the drencher system design given in current international recommendations. Similarly, there are common (e.g., handheld fire extinguishers and hoses) and new (e.g., fire blanket and water-cooling device) manual firefighting equipment that effectively can be used to control or limit a BEV fire.

These proceedings include papers and extended abstracts from the 7th International Conference on Fires in Vehicles – FIVE 2023, held in Stavanger, Norway, April 24-25, 2023. The proceedings include an overview of research and regulatory actions coupled to state-of-the-art knowledge on fire related issues in vehicles, such as passenger cars, buses, trucks and trains, or related infrastructure, such as car parks or vehicle transport at sea. Fires in transport systems are a challenge for fire experts. New fuels that are efficient and environmentally friendly are rapidly being introduced, with emphasis on high energy density batteries. This rapid development, however, introduces new fire risks not considered previously and we risk getting a situation where we do not have enough knowledge to tackle them. In this context FIVE represents an important forum for discussion of the fire problem and for exchange of ideas. Fire protection in road, rail, air, and sea transport is based on international regulations since vehicles cross borders and the safety requirements must be the same between countries. Therefore, understanding of safety and regulations must be developed internationally and the FIVE-conference has a significant role to play as a place to exchange knowledge. FIVE attracts researchers, operators, manufacturers, regulators, rescue services and other key stakeholders. Of particular value is the mix of expertise and the international participation in the conference. The conference is unique as it includes fires in different types of vehicles. In recognition of the fact that many of the fire problems faced by these vehicles are the same, the solutions to them can also be similar. In the proceedings you will find papers on vehicle fire development, bus fires, alternative fuel and electric vehicles, and car park fires. We are grateful to the renowned researchers and engineers presenting their work and to the keynote speakers setting the scene. We sincerely thank the scientific committee for their expert work in selecting papers for the conference.

This publication includes the Proceedings of the 10th International Symposium on Tunnel Safety and Security (ISTSS) held in Stavanger, Norway, April 26-28, 2023. The Proceedings include 45 papers and 16 posters. The papers were presented in 16 different sessions, i.e., Keynote sessions, Alternative Fuel Vehicle Safety, Risk Management & Explosion, Digitization, Explosion, Poster Corner, Ventilation 1&2, Fixed Fire Fighting Systems, Tenability and Evacuation, Emergency Management, Evacuation, Safety Management, Fire Dynamics and Resistance. Each day was opened by invited Keynote Speakers (in total five) addressing broad topics of pressing interest. The Keynote Speakers, selected as leaders in their field, consisted of Ove Njå (University of Stavanger, Norway), Vladimir Molkov (Ulster University, UK), Ulf Lundström (Swedish Transport Administration, Sweden), Mirjam Nelisse (TNO, The Netherlands), and Gunnar Jenssen (SINTEF, Norway). We are grateful that the keynote speakers were able to share their knowledge and expertise with the participants of the symposium.

RISE has previously studied alternative fuels, such as batteries and gaseous fuels including liquid and compressed hydrogen (GH2). Each fuel has its unique risks. Liquid hydrogen (LH2) is a cryogenic fluid and is thus stored in cooled liquid form, which entails specific risks. The purpose of this report is to, based on the current state of research, map the risks of hydrogen in underground facilities in relation to conventional fuels and investigate which technical measures can be taken to reduce the risks. Unlike diesel, hydrogen (and for instance methane or gasoline) has such a low flash point that an emission can be ignited at normal temperature by a small ignition source. Hydrogen is also very buoyant, with strong diffusion and dispersion characteristics, accordingly it accumulates at high points in a subsurface environment. Hydrogen requires very low energy to ignite at or near stoichiometric mixing with air at around 30%. The lower flammability limit is, compared to other flammable fuel/air mixtures high at around 4%, which means that many smaller releases in ventilated spaces will be too lean. Explosions would require a higher hydrogen concentration, above 8% or more. In subsurface environments, containment contributes to a higher increase in pressure, as well as an increased risk of explosion for both GH2 and LH2. The handling of hydrogen underground can therefore be seen as problematic. When it comes to hydrogen as a vehicle fuel, however, there are safety measures to achieve equivalent safety with conventional vehicles. For example, the shut-off valve (mandatory in regulation) on each tank that reduces the risk of leakage, and through the development of explosion-free composite tanks (not mandatory in regulation) in the event of fire that provide a less dangerous fire scenario than a diesel or gasoline tank in case of fire. When it finally comes to transporting hydrogen, pipelines are the long-term sustainable (and safe) alternative. Transport of compressed hydrogen gives a low amount of gas per trailer and entails relatively higher risks than CNG underground, for example in tunnels. The usage of liquid hydrogen, so far, has an impressive safety record, events like BLEVE or fireballs appear to be rare. The transport of liquid hydrogen provides a larger amount of hydrogen per trailer (than for compressed hydrogen) with a relatively lower risk than, for example, LNG in the open, but a slightly higher risk for explosion of accumulated gas compared to GH2 in enclosed spaces. The safety requirements for transport of compressed hydrogen are less stringent than for road vehicles, e.g., with regard to shut-off valves and melt-fuses and could be improved. Several risk mitigation measures for tunnels and other underground facilities have been identified.