Hydrogen Leak Risks Now Quantified: ClassNK Updates Alternative Fuel Ship
ClassNK’s Edition 3.1 guidelines incorporate IMO’s hydrogen safety rules and introduce hydrogen leak frequency.
Classification society ClassNK has updated its safety guidelines for vessels using alternative fuels, incorporating the latest international standards for hydrogen and introducing new structural requirements for methanol and ethanol fuel tanks. The revisions, published in Edition 3.1 of the Guidelines for Ships Using Alternative Fuels, aim to provide shipbuilders, designers, and owners with a clearer framework for compliance as the maritime industry accelerates its shift toward low-emission fuels.
The most notable change appears in Part D of the guidelines, which now fully integrates the International Maritime Organization’s (IMO) Interim Guidelines for the Safety of Ships Using Hydrogen as Fuel (MSC.1/Circ.1701). These IMO standards, finalized during the 11th session of the IMO Sub-Committee on Carriage of Cargoes and Containers (CCC 11) in September 2025, establish baseline safety protocols for hydrogen-fueled vessels.
ClassNK has supplemented these with a hydrogen leak frequency table, developed using a Bayesian statistical method and included as Appendix 2. This addition allows for more precise risk assessments during the design and approval process.
In Part A, which addresses methanol and ethanol-fueled ships, ClassNK has introduced new structural strength requirements for fuel tanks. Unlike the IMO’s existing guidelines for these fuels (MSC.1/Circ.1621), which did not specify tank integrity standards, ClassNK’s update fills this gap by standardizing design assessments. The requirements are based on the society’s experience reviewing methanol and ethanol vessel designs, ensuring a more efficient and consistent approach to tank construction and safety evaluations.
Structural Standards for Methanol and Ethanol Tanks: ClassNK
The updated guidelines reflect ClassNK’s role in aligning industry practices with evolving international regulations. By incorporating the IMO’s hydrogen standards and introducing quantified leak frequency estimates, the society provides a more rational basis for safety assessments—critical for securing approval from flag administrations. ClassNK’s participation in the IMO’s CCC 11 as part of Japan’s delegation further underscores its influence in shaping global maritime safety frameworks.
The revised guidelines are available to registered users on ClassNK’s website under the Guidelines section of My Page. The society continues to support the maritime sector’s transition to alternative fuels through certification, standard development, and technical guidance.
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