Liquid hydrogen is emerging as a key energy carrier for decarbonizing maritime transport, particularly for deep-sea shipping. Its adoption requires specialized bunkering infrastructure, stringent safety protocols, and adaptations to port operations. The International Maritime Organization has begun developing guidelines for hydrogen bunkering, though comprehensive regulations are still in progress. Current IMO discussions focus on the International Code of Safety for Ships Using Gases or Other Low-flashpoint Fuels, which will incorporate liquid hydrogen handling requirements. These include mandatory risk assessments, leak detection systems, and crew training standards specific to hydrogen’s properties.

Bunker vessels for liquid hydrogen must address extreme cryogenic conditions, with storage temperatures maintained at minus 253 degrees Celsius. Modern designs incorporate vacuum-insulated double-walled tanks, often using stainless steel or aluminum alloys to prevent embrittlement. Capacity typically ranges between 1,000 to 20,000 cubic meters, with advanced systems achieving boil-off rates below 0.2 percent per day. Transfer systems employ cryogenic pumps and specially designed loading arms that maintain thermal isolation during operation. Safety features include pressure relief valves, emergency shutdown systems, and vapor recovery units to manage hydrogen gas during transfer operations.

Port infrastructure demands for liquid hydrogen bunkering are substantial. Dedicated berths require exclusion zones of at least 50 meters during operations, based on current industry best practices. Storage terminals need vaporizers to convert liquid hydrogen to gas when required, along with extensive monitoring systems for leaks. The energy required to maintain cryogenic temperatures makes land-based storage more complex than conventional fuels, with power consumption estimates ranging between 5 to 10 percent of the stored hydrogen’s energy content. Some ports are considering shared infrastructure with liquefied natural gas facilities to reduce costs, though material compatibility issues require careful evaluation.

Ammonia bunkering presents distinct advantages and challenges compared to liquid hydrogen. Storage occurs at minus 33 degrees Celsius or at ambient temperature under pressure, significantly reducing energy requirements for temperature maintenance. Ammonia’s higher volumetric energy density allows for smaller storage tanks, with existing bunker vessel designs requiring less modification than for hydrogen. However, ammonia’s toxicity necessitates stricter safety measures, including gas detection systems capable of sensing concentrations as low as 5 parts per million and water deluge systems for leak mitigation. Transfer operations require additional personal protective equipment due to the chemical’s caustic nature.

The bunkering process duration differs substantially between the two fuels. Liquid hydrogen transfers are typically slower due to the need for precise temperature control, with flow rates currently limited to approximately 200 cubic meters per hour. Ammonia can be transferred using conventional liquid cargo handling equipment, achieving rates comparable to marine gas oil at over 1,000 cubic meters per hour. This operational difference impacts port throughput and vessel turnaround times, particularly for large fuel demands.

Infrastructure costs show clear divergences between the two options. Liquid hydrogen bunkering requires investment in cryogenic equipment throughout the supply chain, with current estimates suggesting capital costs three to four times higher than equivalent ammonia infrastructure. Ammonia leverages existing chemical handling technologies, though modifications for maritime safety add approximately 20 to 30 percent to conventional liquid bulk terminal costs. Both fuels require extensive safety training, but ammonia’s well-established industrial handling procedures give it an advantage in workforce availability.

Energy losses across the bunkering chain favor ammonia for long-distance maritime applications. Liquid hydrogen experiences boil-off during storage and transportation, with typical losses of 0.5 to 1 percent per day even with advanced insulation. Ammonia demonstrates negligible losses during storage, though energy penalties occur during cracking back to hydrogen if required for end use. Well-to-wake analyses indicate ammonia maintains 75 to 80 percent of its original energy content upon delivery, compared to 65 to 70 percent for liquid hydrogen under optimal conditions.

Regulatory frameworks for ammonia are more developed due to its established use in agriculture and industry. The IMO’s existing International Code for the Construction and Equipment of Ships Carrying Liquefied Gases in Bulk provides a foundation for ammonia bunkering standards, requiring fewer amendments than hydrogen-specific regulations. Classification societies have already issued guidelines for ammonia-fueled vessels, while hydrogen-specific rules remain under development. This regulatory gap creates uncertainty for early adopters of liquid hydrogen in maritime applications.

Safety protocols during bunkering operations reflect the different risk profiles of each fuel. Liquid hydrogen requires continuous monitoring for leaks due to its wide flammability range and invisible flame characteristics. Ammonia operations focus on toxic gas detection and respiratory protection, with emergency response plans emphasizing vapor suppression rather than ignition prevention. Both fuels mandate exclusion zones during transfer, but ammonia’s heavier-than-air vapor behavior necessitates different ventilation strategies compared to hydrogen’s rapid dispersion.

The choice between liquid hydrogen and ammonia for maritime bunkering involves trade-offs across technical and operational parameters. Liquid hydrogen offers carbon-free combustion but demands more extensive infrastructure modifications. Ammonia provides easier integration with existing port systems but introduces new toxicity concerns. Industry adoption patterns suggest ammonia may dominate initial deployments for deep-sea shipping, while liquid hydrogen could find earlier acceptance in short-sea routes with smaller bunkering volumes. Both pathways require continued regulatory development and standardization to achieve scale in the maritime sector.

Future infrastructure planning must account for potential synergies between hydrogen and ammonia bunkering systems. Some ports are evaluating dual-purpose terminals capable of handling both fuels, though the technical differences in storage and handling make true integration challenging. Standardization of coupling systems and safety interfaces will be critical as the industry moves toward multi-fuel capabilities. The maritime sector’s decarbonization timeline will ultimately determine whether liquid hydrogen or ammonia emerges as the predominant bunkering solution, or if both will develop parallel pathways for different vessel types and operational profiles.