Japanese classification society ClassNK has tightened its alternative-fuel safety guidance with new hydrogen leak-frequency benchmarks and structural strength requirements for methanol and ethanol fuel tanks in Edition 3.1 of its Guidelines for Ships Using Alternative Fuels, according to ClassNK.
The revision updates Part D for hydrogen-fuelled ships by incorporating the International Maritime Organization’s Interim Guidelines for the Safety of Ships Using Hydrogen as Fuel, MSC.1/Circ.1701.
ClassNK has also added estimated hydrogen leak frequencies to Appendix 2, using a Bayesian method to derive figures that can be applied in ship design and safety assessments required for administration approval.
The classification society took part in the Japanese delegation to the IMO Sub-Committee on Carriage of Cargoes and Containers at CCC 11 in September 2025, where the hydrogen guidelines were finalised.
The IMO Maritime Safety Committee approved them at MSC 111 in London in May 2026. Part A has meanwhile been revised with structural strength requirements for methanol and ethanol fuel tanks.
ClassNK developed and standardised the requirements from its experience of design reviews because specific provisions are not included in MSC.1/Circ.1621.
The guidelines cover methanol, ethanol, LPG, ammonia and hydrogen, setting requirements for equipment, controls and safety devices. Work on mandatory IMO provisions for methyl and ethyl alcohol is due to continue at CCC 12 in September 2026.
Nippon Kaiji Kyokai, known as ClassNK, is an independent non-profit ship classification society founded in 1899. It also conducts statutory surveys and certification on behalf of more than 100 flag administrations.