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Horizons article 02 September 2023

Ammonia as fuel: Quantitative Risk Assessment ranks safety issues

  • Marine energy transition
  • Ammonia
Issue 66

As marine engine designers prepare to launch ammonia-ready dual fuel engines in just a few months’ time, experts have been assessing the risks relating to the toxic chemical both from ship design and human element perspectives.

Carbon-free ammonia, already widely carried by sea as cargo, could provide a new and relatively fast-track marine fuel in support of the sector’s increasingly urgent decarbonisation drive. Leading engine builders are already working on ammonia combustion and engine hardware and the first ‘ammonia-ready’ engines are expected to be commissioned on ships in 2024.

But ammonia comes with a number of risks for which global shipping is not yet prepared. These include toxicity, dispersion, risks to crew, an absence of class rules on its use as fuel, and a need for rapid personnel upskilling.

To address these concerns, the Lloyd’s Register Maritime Decarbonisation Hub and the Maersk Mc-Kinney-Møller Center for Zero Carbon Shipping (MMMCZS) have recently completed a multi-disciplinary programme to assess the design challenges and identify the risks to seafaring personnel from the use of ammonia as a marine fuel. This collaboration has resulted in the publication of– Recommendations for Design and Operation of Ammonia-Fuelled Vessels Based on Multi-disciplinary Risk Analysis.

LR and MMMCZS decided on a Quantitative Risk Assessment (QRA) approach to the safety analysis, with the specific aim of identifying design and operational measures that would reduce risks to ships’ crews to a ‘tolerable’ level. QRAs provide a systematic approach to quantifying the risks associated with the operation of an engineering process: they are widely used in the oil and gas and nuclear energy sectors but are relatively new in the maritime field.

The iterative data-driven QRA process enables the assessment of risk in a quantitative and granular way. Crucially, the process can be used to estimate the effectiveness of risk mitigations by making different modifications to the QRA model and observing their relative impact on the risk outcome. For the QRA to have validity, however, the term ‘tolerable’ needed to be defined. Clearly, a high level of risk is unacceptable for ships’ crews and the environment, but how far should designers and operators take risk mitigation?

The project used thresholds published by the International Maritime Organization and the UK Health and Safety Executive as benchmarks against which to assess risk. A project target was set based on these thresholds and the mitigation process repeated until risk levels were below this target.

The analysts chose three ammonia-fuelled reference ship designs to put through the QRA model. A 3,500 TEU feeder container ship had a fully refrigerated prismatic fuel tank below deck just forward of the ship’s accommodation storing liquid ammonia at ambient pressure and a temperature of minus 33°C.

Next was an 80-100,000dwt bulk carrier with a fully pressurised Type C fuel tank located on deck aft of the accommodation. This design was based on the carriage of liquid ammonia at ambient temperature and a pressure of 18 bar.

The third reference vessel was a 50,000dwt medium-range tanker with a Type C semi-refrigerated tank located on deck, forward of the accommodation. In this case, the liquid ammonia fuel was shipped at a pressure of four bar.

The QRA enabled the experts to identify a range of factors that have a bearing on the design and operation of ammonia-fuelled ships. These were divided into three groups: high priority recommendations relating to measures that significantly reduce risks 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
  • The fuel preparation room should be divided 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 minimised, monitored, and controlled
  • Ventilation outlets from spaces containing ammonia equipment should be placed in a safe location adequately separated from areas accessed by crew to avoid accidental release of toxic concentrations of ammonia affecting personnel
  • Multiple sensors of different types should be installed to detect ammonia.


  • 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 in both 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.

The human element

A key component of the Lloyd’s Register / Maersk McKinney Møller study was a focus on new human factors that could be encountered from the use of ammonia as a marine fuel. The two organisations commissioned LR’s Human Factors experts to undertake the study. Here, we identify some of the key findings in the 44-page report.

Hazards associated with marine fuels are, of course, nothing new, but unlike conventional fuels, ammonia is toxic to personnel and therefore presents a whole new range of potential risk factors. And, unless these can be carefully assessed and managed, they will remain a hindrance to its take-up.

The team assessed a series of human related factors, ranking them into three categories of risk – high, medium, and low. Its analysis then identified the aspects of ship operation likely to be affected by these risks.

The four ‘high’ risk areas highlighted by the analysts were:

  • Competence: seafarers’ technical and non-technical skills, knowledge, understanding, and application
  • Process and Procedures: documented processes and work practices
  • Occupational Health Hazards: exposure to toxicity, fire, noise, muscoskeletal risks, trips and falls, etc
  • Process Safety Hazards: human involvement in the contribution, exacerbation, and recovery of a major accident.

Two ‘medium’ risk areas were identified:

  • Ergonomics Design: workspace arrangements and human machine interface
  • Management of Change: organisational, operational and technical changes that must be managed to achieve final ammonia preparedness and the process of change itself.

Two ‘low’ risks were also noted:

  • Roles and Responsibilities: organisational structure and assigned roles
  • Resourcing and Personnel: workload distribution and number of personnel.

The expert team also repeated the high-priority recommendations, set out above, which could well affect the design of ammonia-fuelled ships in the future. In conclusion, they said: “If the marine industry addresses the human factors considerations, builds upon existing marine industry experience with low flash-point fuels / cargo and ensures sufficient safeguards are provided for the various ammonia risks, then ammonia can provide an acceptable alternative to conventional fuel use.”

Human Factors Considerations: Ammonia Fuel End-of-Stage Report
Front cover of "Human Factors Considerations: Ammonia Fuel End-of-Stage Report

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