ClassNK revises alternative-fuel ship guidelines with updated hydrogen, methanol and ethanol safety requirements

ClassNK has released a revised edition of its Guidelines for Ships Using Alternative Fuels, incorporating updated safety requirements for hydrogen, methanol and ethanol-fuelled vessels.

The revised guidelines, Edition 3.1, were announced on 18 August 2026 and are intended to support shipyards, designers and shipowners in carrying out the design and safety assessment of alternative-fuelled ships in line with international standards.

Hydrogen-fuelled ships

For hydrogen-fuelled vessels, ClassNK has incorporated the IMO’s Interim Guidelines for the Safety of Ships Using Hydrogen as Fuel, MSC.1/Circ.1701, into Part D of the guidelines.

The revision also introduces a hydrogen leak frequency table for use in safety assessments required under the IMO guidelines. ClassNK applied a Bayesian method to estimate hydrogen leak frequencies for ships, with the estimates included in Appendix 2 of Part D.

According to ClassNK, the revised requirements are intended to support more consistent and reliable ship design and safety assessments required for administrative approval of alternative-fuelled vessels.

Methanol and ethanol-fuelled ships

Part A of the guidelines, covering methanol and ethanol-fuelled ships, now includes structural strength requirements for methanol and ethanol fuel tanks.

These requirements were developed based on ClassNK’s experience in reviewing the designs of such vessels and address aspects not specifically covered by the relevant IMO guidelines, MSC.1/Circ.1621.

The standardized requirements are intended to support more efficient assessments of fuel tank designs.

Alignment with IMO safety requirements

The revisions come as the use of alternative fuels expands in response to efforts to reduce greenhouse gas emissions from shipping.

ClassNK’s guidelines cover safety requirements for ships using methanol, ethanol, LPG, ammonia and hydrogen. They address equipment, control systems and safety devices intended to manage risks associated with alternative fuels to ships, seafarers and the environment.

For hydrogen-fuelled ships, ClassNK incorporated the IMO’s latest interim guidelines following the development of those requirements at the IMO Sub-Committee on Carriage of Cargoes and Containers (CCC). ClassNK participated in the discussions as part of the Japanese delegation.

The revised Edition 3.1 is intended to provide shipyards, designers and shipowners with a consolidated framework for assessing alternative-fuelled ship designs while incorporating additional requirements and technical guidance developed by ClassNK.