The energy transition in shipping
The safety risks of ammonia as a ship fuel
The energy transition in the shipping industry, with its shift towards alternative fuels, could introduce significant safety risks. The potential future use of ammonia as a ship fuel raises serious safety and security concerns which warrant particularly close attention, including around safeguarding vessels, crew and the wider population from state and non-state actor threats.
Decarbonisation efforts in shipping are driven by directives from the International Maritime Organisation (IMO), the European Union (EU) and national governments. Both the IMO and EU are pushing for net-zero emissions from greenhouse gases (GHG) by 2050. In April, the IMO adopted a mandatory Net-Zero Framework – effective from 2027 – including a new marine fuel standard and a global GHG emissions pricing mechanism. In January, the FuelEU Maritime Regulation took effect, requiring vessels over 5,000 gross tonnes (GT) calling at EU ports – regardless of flag – to reduce the GHG intensity of their energy use. From 2024, shipping has been included in the EU emissions trading scheme.
The volumes of ‘high energy density’ fuels required in shipping make the transition challenging and limit options. Alternatives – such as biofuels, methanol, wind and nuclear – all vary in suitability depending on ship type and operational requirements. Industry approaches this challenge in different ways, and without a clear frontrunner in viable ‘net-zero’ fuels, liquefied biogas, methanol and ammonia have emerged as key contenders. The shift to alternative fuels and multi-fuel vessels improves flexibility and optimisation, but introduces risks – including lower flashpoints, toxic vapour clouds and liquefied natural gas (LNG) or methanol fires – which must be understood and carefully managed.
Ammonia, a colourless toxic gas, is considered by some to be a promising future fuel because of its ability to burn with close to zero COâ‚‚ emissions at relatively low cost and much greater efficiency than other options such as methanol. However, using anhydrous ammonia as a ship fuel poses significant safety risks due to its toxicity. Even low concentrations can burn and damage mucous membranes, while leaks may be life-threatening if inhaled or absorbed through the skin. While used successfully in agriculture and transported as cargo on gas carriers, using it as a ship fuel introduces significant safety risks. As a result, many shipowners have dismissed it as a viable alternative.
Using ammonia as a ship fuel presents major operational and competency challenges related to ‘bunkering, onboard storage, supply and consumption’. It requires specialised storage – pressurised or at low temperatures – and advanced safety-rated systems. The primary risk arises from direct exposure to leaks, even minor ones, raising serious crew safety concerns, especially given increased human interaction and the long-term effects of engine vibrations. Mitigating these risks will require additional regulations, extensive safety procedures and comprehensive crew training to understand the challenges which come with handling such a toxic fuel. This places additional pressure on an already limited pool of seafarers, and requires changes to ship management and organisation.
Ammonia is often cited as a viable ship fuel based on its use in transporting energy from Australia to Japanese power plants, but this is a very different case. In these controlled corridors, ammonia is used to move solar energy to secure, closed power plants using specialised vessels with highly trained crews.
The safety and security risks are especially concerning. While ammonia carries the risk of explosion, the greatest danger lies in its extreme corrosiveness and ability to form dense, toxic clouds which can drift into populated areas. A major release – whether accidental or deliberate – could cause mass casualties. Given the volume required to power a ship, ammonia-fuelled vessels present a serious risk of severe accidents or targeted attacks, effectively becoming ‘floating bombs’. This threat is amplified by the vulnerability of commercial ships in the face of growing threats in the maritime environment, especially given the largely unregulated nature of shipping practices while at sea.
Current commercial fuel storage regulations do not address new hazards of alternative fuels like ammonia, nor do they consider the impact of naval weaponry. A missile fragment striking an ammonia tank would take out the entire crew. While attacks on commercial vessels in the Red Sea have caused few casualties to date, ammonia-fuelled ships would become far more dangerous and appealing targets. Any expansion of ammonia use in shipping must therefore directly confront these risks. Ensuring acceptable safety levels will require sweeping new regulations, robust protective measures and significant resources.
Looking beyond security, new regulations for adopting ammonia as a ship fuel are not expected to be in place until 2028. Many tend to leverage the complexity of the transition and system to delay real change, outlining ambitious net-zero newbuilding plans. While green ammonia holds promise as a zero-carbon fuel, the primary concern remains that of safety. The question then becomes: at what cost?
Accidents highlight the dangers of hazardous materials like ammonia, particularly in densely populated areas. On 24th March 1992, a leak from an anhydrous ammonia tank in Dakar, Senegal, killed 129 people and injured over 1,150 after 22 tonnes were released – well above the tank’s 17.7 tonne capacity. Even smaller leaks below 10 tonnes have triggered large-scale evacuations. An accident or attack on an ammonia-powered ship in port would have catastrophic consequences beyond inflicting casualties on the crew. As such, the movements of ammonia-fuelled vessels would require strict oversight and continuous monitoring.
While anhydrous ammonia is not inherently explosive, its use as a ship fuel poses a major strategic risk by making vessels high-value targets for hostile actors. A breach of a 2,000 tonne ammonia tank – whether through accident or attack – could be devastating. The recent collision between a tanker and container ship off the British coast illustrates how easily accidents can happen, even under ‘normal’ conditions. The prospect of such vessels drifting into ports raises serious safety concerns. Who would feel safe living or working near ports visited regularly by ammonia-fuelled vessels? This is not merely a logistical concern; it is a critical security issue.
As the industry moves towards decarbonisation, fuels like ammonia introduce complex safety, training and risk management challenges. Given their reliance on commercial shipping for logistics and supply, modern militaries must understand how the energy transition will impact the future fleet and resilience of global supply chains.
The energy transition in shipping isn’t just about cleaner fuels, but also about new risks. As the maritime domain becomes more contested, shipping is increasingly viewed as a strategic asset to target and weaponise. Adopting fuels like ammonia provides state and non-state actors with new vulnerabilities to exploit. To ensure resilience, decarbonisation efforts must be carefully monitored to identify potential risks and mitigate them.
Charlotte Kleberg is an Associate Fellow at the Council on Geostrategy and an Associate Fellow at the Royal Navy Strategic Studies Centre. She holds various project and board advisory roles in the Ro-Ro shipping sector through Wallenius Lines, Wallenius Marine and United European Car Carriers.
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