Understanding the whole picture. How to bunker liquefied hydrogen – safely

by Simen Diserud Mildal, Lead for Green Shipping Technologies, Norwegian Maritime Authority, and Torill Grimstad Osberg, Senior Principal Approval Expert, DNV

As the maritime industry seeks to reduce its greenhouse gas (GHG) footprint and transition to zero-emission fuels, hydrogen emerges as a promising option. The Maritime Technologies Forum (MTF), comprising leading classification societies and flag state administrations, has developed draft guidelines to address the complexities and safety concerns associated with liquefied hydrogen (LH2) bunkering. The latest report covers key aspects of the safe and efficient use of hydrogen as a marine fuel, and particularly how bunkering can be done in a way that minimizes safety concerns. The report has also been submitted to the 10th meeting of the International Maritime Organization’s (IMO) Sub-Committee on Carriage of Cargoes and Containers to support the discussion on completing the body’s guidelines for using hydrogen as a fuel.

IMO has set ambitious targets to reduce GHG emissions from ships, aiming for net zero by 2050. Hydrogen, with its zero-emission potential, is a viable candidate

to help achieve this goal. However, the maritime sector has limited experience with hydrogen, both as cargo and fuel. The MTF’s project aims to bridge this gap by drafting the first version of guidelines for the safe bunkering of LH2 .

Hydrogen itself – and its impact on materials and other particles

Hydrogen’s unique properties present both opportunities and challenges. It is highly flammable, with a wide flammability range (4-75% in air) and a high flame speed, increasing the risk of detonation. Hydrogen is also colourless and odourless, making leaks difficult to detect. Additionally, its small molecular size leads to high permeability and the risk of hydrogen embrittlement in metals. The extremely low boiling point of liquefied hydrogen (-253°C) necessitates careful material selection and extensive insulation to prevent equipment damage and ensure safety.

At -253°C, both oxygen and nitrogen in the air can condense and freeze. As such, one of the new aspects associated with LH2 , compared with the bunkering and operation with liquefied natural gas (LNG), is the risk of condensation and freezing of air both inside and outside the piping systems. If oxygen or nitrogen is present inside when LH2 is introduced, it can freeze and clog the systems, causing valves or other components to fail. The extremely low temperature of liquid hydrogen can also cause air to condense on the outside surfaces of piping and equipment. This can result in the formation of liquid oxygen, which poses a significant fire hazard due to its high reactivity. In addition, the accumulation of ice can lead to mechanical stresses and potential damage to the equipment.

These risks require meticulous design and operational procedures to mitigate. The use of more automated bunkering processes is one way to avoid air ingress. It may also be necessary to avoid the use of nitrogen for inerting after each bunkering operation. To prevent the condensation and freezing of air on the outside of the systems, more extensive use of vacuum insulation will be necessary. Liquid oxygen is highly reactive and can cause materials that are normally non-flammable to ignite and burn, so drip trays for collection of any frozen air is another relevant safeguard to help make sure that it does not reach organic materials.

The critical components & considerations

Currently, there are no specific international standards for LH2 bunkering. However, ongoing developments in ISO standards and experiences from the Norwegian ferry Hydra provide valuable insights. Hydra has been successfully conducting LH2 bunkering operations since April 2023. The solutions applied there offer practical reference.

IMO is also working on guidelines for the safe design of ships using hydrogen as fuel, with a target completion date of September 2024. These guidelines will focus on ship installations up to the bunkering manifold, but the details of bunkering operations are not within their scope. The work conducted by MTF aims to fill this gap by providing relevant recommendations for safe bunkering of LH2

An LH2 bunkering system consists of several critical components. First, the bunkering station: open facilities are preferred to allow for rapid dispersion of hydrogen in case of leaks. Dry disconnect type of bunkering connections should be used, like for LNG. Second, the bunker piping system: the high permeability of hydrogen leads to a need for careful material selection to prevent embrittlement and leakage. For handling the low temperatures, the piping system requires more extensive use of vacuum insulation, not only for the pipes but also for valves and hoses. Third, safety equipment: gas and fire detection systems of diverse types, as well as rapid emergency shutdown systems, are essential to ensure safety during bunkering operations.

The bunkering process for LH2 is more complex than for LNG due to hydrogen’s unique properties, requiring taking into account a few key considerations. First, emergency shutdown: rapid shutdown capabilities are crucial to prevent accidents. The emergency shutdown system should be activated from both the supplier and receiver sides and should not cause gas or liquid release. Second, purging: unlike LNG, nitrogen may not be a good choice for purging LH2 systems due to its freezing point. Instead, vacuum pumps and helium gas can be used to ensure the system is free of air and hydrogen before connections and disconnections. If nitrogen purging is applied, the complete removal of nitrogen traces will be a necessary part of the bunkering process. Third, personal safety: personnel involved in LH2 handling must wear appropriate personal protective equipment to protect against extreme cold and potential leaks. Automated processes are recommended to minimize human intervention.

Given the complexities of LH2 bunkering, crew training and certification are paramount. The safety management system should be updated to address the additional safety aspects of LH2 bunkering. Training programs should emphasize the unique properties of hydrogen, including its cryogenic temperatures and flammability.

Moving forward – in a safe manner

The use of LH2 as a marine fuel presents significant challenges but also offers substantial benefits in reducing GHG emissions. The newly proposed draft guidelines provide a framework for the safe and efficient bunkering of LH2, addressing the unique properties and risks associated with hydrogen. The main learning is that the bunkering systems and procedures as applied for LNG-fuelled ships cannot be copied directly due to the different properties of LH2.

The development of vessel-specific procedures, enhanced safety measures, and rigorous training programs are essential to mitigate the risks associated with LH2 bunkering. By fully understanding the special risk picture with LH2 and taking care to move forward in a safe manner, the maritime industry can pave the way for a cleaner, more sustainable future, and these guidelines will support the safe adoption of LH2 in maritime operations. ‚

MTF is a forum of flag states and classification societies established to provide technical and regulatory expertise to benefit the maritime industry. The role of the MTF is to work together on research that it publishes for the maritime sector and draw on regulatory expertise to be able to offer unbiased advice to the shipping industry. The flag state administrations include Maritime Bureau, Ministry of Land, Infrastructure, Transport and Tourism, Japan; the Norwegian Maritime Authority; the Maritime and Coastguard Agency, UK; and the Maritime and Port Authority of Singapore (MPA). The classification society members are ABS, DNV, LR, and ClassNK. Visit maritimetechnologiesforum.com to learn more.