Recommendations for Design and Operation of Ammonia-Fueled Vessels Based on Multi-disciplinary Risk Analysis

Published — June 23, 2023

Executive summary

The implementation of alternatives to conventional fossil-based fuels is key to decarbonization of the global shipping industry. Ammonia is currently one of the frontrunners among alternative shipping fuels, as it can be combusted with almost no carbon dioxide emissions. However, using ammonia as a shipping fuel involves safety hazards: primarily toxicity, but also onboard fires and explosions. Therefore, it is crucial to understand these risks and the safeguards that can be implemented to reduce them to tolerable levels.

To this end, we have pioneered an innovative multi-disciplinary approach to assess and address the onboard safety risks to a ship’s crew of ammonia as a shipping fuel. Our project is a collaboration between the Lloyd’s Register Maritime Decarbonisation Hub (MDH) and the Mærsk Mc-Kinney Møller Center for Zero Carbon Shipping (MMMCZCS), with contributions from other partners. This report outlines the results of this project.

The first main section of this report summarizes the results of an iterative quantitative risk assessment (QRA) analysis applied to three reference designs for ammonia-fueled vessels. QRA is a powerful data-driven method that allows users to assess risk in a quantitative and granular manner. Importantly, QRA can be used to quantitatively estimate the effectiveness of risk mitigations by adding different modifications to the QRA model and observing their impact on the risk calculation. In our project, we used this capability of QRA to characterize risk levels across different vessel types, place these in the context of existing risk criteria, and identify design and operational measures that would reduce risk to crew to a tolerable level.

Based on our analysis, we highlight several recommendations and findings for the design and operation of ammonia-fueled vessels. We divided these into three groups: high-priority recommendations relating to measures that contribute significantly to reduction of risk to crew; findings that demonstrate the importance of existing good practice, guidelines, or rules; and other recommendations.

High-priority recommendations:

  • Lower storage temperature reduces the safety risk from ammonia fuel.
  • Divide the fuel preparation room into two or more separate spaces containing different groups of equipment that could leak ammonia.
  • Access to and length of time spent in spaces containing ammonia equipment should be minimized, monitored, and controlled.
  • Ventilation outlets from spaces containing ammonia equipment should be placed in a safe location adequately separated from areas accessed by crew, in order to avoid accidental release of toxic concentrations of ammonia affecting personnel.
  • Multiple sensors of different types to detect ammonia leaks should be installed.


  • Secondary containment mechanisms, such as double-walled piping, used for ammonia-related equipment outside of already-restricted areas have been proven to significantly reduce risk.
  • Ventilated gas-tight enclosures installed around any gas valve units in engine rooms also reduce risk.
  • Ventilation of spaces containing ammonia equipment provides mitigation of toxic effects for many smaller, but not all, potential ammonia leaks. This mitigation is particularly efficient for smaller leaks. Consideration of additional precautions is required for personnel entering these spaces.
  • Ventilation of spaces containing ammonia equipment reduces the risk of ammonia concentrations reaching a flammable level. Although ammonia is much less flammable than some other fuels, the flammability hazard should not be ignored.
  • Ammonia leak alarms should be installed both in controlled areas (for example, the fuel preparation room) and near potential leak sources.
  • The fuel system should be subject to rapid and reliable manual and automated shutdown in the event of an ammonia leak.

Other recommendations:

  • Depending on storage conditions and ammonia tank location, shutdown of the ventilation for crew accommodation should be made possible in the event of an ammonia leak.
  • A distinctive, vessel-wide audible toxicity alarm for ammonia leaks should be implemented.

To complement this quantitative analysis, the second main section of this report summarizes insights from an analysis of human factors considerations, such as training and work practices, that will be impacted by a transition to ammonia fuel use. Through a series of collaborative workshops, we identified relevant human factors considerations based on the three reference designs used for QRA and rated their impact as low, medium, or high. This report explains and discusses ways to address the highest-impact human factors considerations based on our analysis. These factors relate to the following areas:

  • Competence and training: specific training and upskilling will be needed to prepare crew for operation and maintenance on ammonia-fueled vessels.
  • Process and procedures: safe work practices and standard procedures need to be updated and should be implemented through systematic change management programs.
  • Occupational health hazards: effective occupational health safeguards, such as personal protective equipment (PPE), need to be developed and implemented.
  • Process safety hazards: appropriate safety management procedures for emergency response and other events need to be developed.

Taken together, we conclude that the risks to crew of using ammonia as an alternative maritime fuel can be kept to a tolerable level, provided that the maritime industry can:

  • Ensure suitable and sufficient technical barriers and administrative safeguards are implemented to protect the crew against various ammonia risks;
  • Address human factors considerations, such as those outlined above; and
  • Build upon existing maritime industry experience with gas as fuels and cargo and carry over learnings from other industries with considerable experience in safely handling, transferring, and storing ammonia.

The recommendations and results from this report can and should be used to further inform specific regulations, guidelines, and best practices that will allow ammonia-fueled vessels to be acceptably safe for the crew.

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