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Simulation, Not Assumptions: How ABS Is Building a Safety Case for Ammonia at Sea

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Simulation, Not Assumptions: How ABS Is Building a Safety Case for Ammonia at Sea

Ammonia is fast emerging as a front-runner in shipping’s race to net zero.

But turning a carbon-free fuel into a safe, workable reality onboard requires more than new engines — it demands a fundamental rethink of maritime safety management.

As the industry pushes beyond LNG and methanol toward zero-carbon fuels, ammonia is gaining traction for one key reason: it burns without producing carbon dioxide and can be scaled for global supply.

According to American Bureau of Shipping (ABS), however, technical feasibility alone is not enough. Confidence in ammonia as a marine fuel will depend on how well the industry understands — and manages — its risks.

The safety equation: toxicity first

Unlike conventional fuels, ammonia presents immediate toxicity risks even at relatively low concentrations. Exposure can threaten crew health within minutes, making emergency response speed and accuracy critical.

Flammability and corrosive properties add further complexity, but toxicity remains the central operational challenge. For chief engineers and masters, this shifts risk management from fire containment toward rapid detection, plume control and evacuation strategy.

Training is another major hurdle.

Current international standards under the International Maritime Organization framework — particularly the International Convention on Standards of Training, Certification and Watchkeeping for Seafarers (STCW) — were largely shaped by experience with LNG. ABS notes that ammonia-specific competencies will need significant updates, covering toxicity response, material compatibility and new emergency procedures.

While ammonia expertise exists in industries such as refrigeration and fertilizer production, scaling that knowledge across the global seafaring workforce is a different challenge altogether.

Building the safety baseline: HAZID, HAZOP and CFD

ABS is applying a structured, layered methodology to address these risks.

The starting point remains traditional hazard identification tools — HAZID and HAZOP workshops — where multidisciplinary teams assess potential failure modes across bunkering, fuel preparation and engine room operations. These workshops go beyond equipment failure to include human-factor risks, such as maintenance exposure and emergency decision-making under stress.

From there, analysis becomes more technical.

Computational Fluid Dynamics (CFD) simulations are used to model how ammonia would behave if released — whether during ship-to-ship bunkering or from a vent mast. These simulations predict plume formation, vapor dispersion and concentration levels under varying wind, temperature and atmospheric conditions.

For operators, this means emergency planning can be informed by realistic dispersion modelling rather than assumptions.

Importantly, simulation can be conducted before vessel construction, allowing designers to optimize layout, ventilation and safety systems at the design stage.

Moving beyond drills: agent-based modelling

Live emergency drills remain essential. But they are costly, limited in scope and cannot safely replicate worst-case toxic releases.

To bridge that gap, ABS is advancing what it calls agent-based probabilistic risk analysis.

In simple terms, this approach models how individual crew members — treated as “agents” — might behave during an ammonia incident. Each agent has defined characteristics such as location, reaction time, mobility and stress response. Their interactions are then simulated within a dynamic environment that incorporates CFD plume data and hazard scenarios.

Using Monte Carlo techniques, thousands of variations can be run to account for uncertainty in both ammonia dispersion and human behaviour. The result is not a single predicted outcome, but a statistical range of possible evacuation flows, bottlenecks and response effectiveness.

For shipowners, port operators and bunkering facilities, this provides a more realistic picture of how an incident might unfold — and where vulnerabilities lie.

A dynamic, time-sensitive risk model

One of the key advantages of this integrated approach is that it treats emergencies as evolving events.

As environmental conditions change — wind shifts, ventilation systems activate, responders move — the probability of different outcomes shifts as well. The modelling framework accounts for time delays, resource availability and operational constraints, reflecting the reality that minutes matter during toxic exposure events.

This time-sensitive dimension is particularly relevant for confined spaces such as engine rooms and fuel preparation areas, where ammonia concentration can escalate rapidly.

ABS argues that combining structured hazard workshops, CFD simulation and agent-based modelling provides a comprehensive framework to de-risk ammonia adoption.

Why this matters

  • For shipowners: Robust simulation-backed safety cases will be essential for class approval, insurance confidence and regulatory compliance as ammonia-fuelled vessels enter service.
  • For chief engineers and crew: Ammonia shifts the risk profile from traditional fire response to rapid toxic exposure management — requiring new training, drills and decision-making protocols.
  • For designers and yards: Early-stage CFD and agent-based modelling allow safety systems and layouts to be optimized before steel is cut.
  • For regulators and operators: Data-driven risk assessment strengthens the case for ammonia while identifying where international training standards must evolve.
Ammonia may offer a carbon-free pathway. But without rigorous, simulation-driven safety management, it will not gain the trust of the people who operate ships every day.

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