Safety requirements for hydrogen-, methanol- and ethanol-fuelled ships had been revised, Japanese classification society ClassNK said on Tuesday.
The changes are contained in Edition 3.1 of its Guidelines for Ships Using Alternative Fuels.
ClassNK is a third-party certification body that develops technical standards and provides classification and certification services for ships.
The revised section covering hydrogen-fuelled vessels incorporated the International Maritime Organization’s (IMO) Interim Guidelines for the Safety of Ships Using Hydrogen as Fuel, the society said.
It also introduces estimated hydrogen-leak frequencies that may be used in safety assessments required under the IMO guidelines for the approval of alternative-fuelled vessels by administrations.
A Bayesian statistical method had been used to derive the estimates by combining newly observed data with existing information, ClassNK said.
The hydrogen-leak frequency estimates have been included in an appendix to the revised guidelines.
They were intended to enable ship designs and the associated safety assessments to be conducted on a more consistent basis, said the society.
The IMO’s interim guidelines were finalised during the 11th session of its Sub-Committee on Carriage of Cargoes and Containers in September 2025 and issued this year.
ClassNK participated in their development as a member of the Japanese delegation to the subcommittee, the society said.
The revised edition also introduces structural-strength requirements for fuel tanks used on methanol- and ethanol-fuelled vessels.
Those requirements were not specifically stipulated in the IMO’s 2020 guidelines for the safety of ships using methanol and ethanol as fuel, said ClassNK.
They were developed using the society’s experience in reviewing the design of methanol- and ethanol-fuelled ships and are intended to standardise fuel-tank structural assessments.
ClassNK’s alternative-fuel guidelines also set out requirements for equipment, controls and safety devices on vessels using liquefied petroleum gas and ammonia.
