Discover how the Risk-Based Assessment Tool (RBAT) supports safer decarbonization in shipping. Learn how the IMO integrates RBAT into regulatory frameworks to guide green fuel adoption, system safety, and future-proof maritime operations.”
Why this topic matters in modern maritime operations
Decarbonizing the global shipping fleet is no longer an option—it’s an international obligation. The International Maritime Organization (IMO) adopted its revised GHG Reduction Strategy in July 2023, setting ambitious targets for greenhouse gas (GHG) cuts from international shipping. These include reducing total annual GHG emissions from ships by at least 20% by 2030 (with a stretch goal of 30%) and reaching net-zero emissions “by or around 2050.”
As shipowners, designers, and operators race to meet these goals, many are turning to alternative fuels such as methanol, hydrogen, ammonia, biofuels, and electrification. But these new technologies bring unfamiliar risks—from ammonia toxicity to hydrogen flammability to battery fires.
To manage these risks effectively, the IMO is increasingly endorsing the use of Risk-Based Assessment Tools (RBATs) to supplement prescriptive rules and ensure safety is maintained during the transition to green fuels. This article explores how RBAT supports safer decarbonisation, how it fits into the IMO’s regulatory approach, and what maritime professionals and students need to know to stay ahead.
What is RBAT and how does it support IMO objectives?
A Risk-Based Assessment Tool (RBAT) is a structured approach used to assess the safety of novel systems, fuels, and operational models. Instead of relying solely on rigid regulations, RBAT allows for evidence-based justification that a new fuel or technology is at least as safe as conventional alternatives, even if it falls outside standard regulations.
RBAT typically follows methodologies rooted in:
- Formal Safety Assessment (FSA) as per IMO guidelines (MSC-MEPC.2/Circ.12/Rev.2)
- ISO 31000 Risk Management Principles
- The ALARP (As Low As Reasonably Practicable) risk acceptance model
- The IGF Code equivalency process under SOLAS Regulation I/5
By using RBAT, engineers and operators can demonstrate compliance with international conventions while adopting innovative solutions that support the IMO’s climate targets.
How the IMO uses RBAT within its regulatory framework
Formal Safety Assessment (FSA) and RBAT alignment
The IMO’s Formal Safety Assessment (FSA) methodology forms the foundation for most RBAT processes. The FSA consists of five steps:
- Hazard identification (HAZID)
- Risk assessment
- Risk control options (RCOs)
- Cost-benefit assessment
- Recommendations for decision-making
This structure is applied in projects involving non-standard systems—especially those involving green fuels with no long history of maritime use. The IMO encourages Member States and companies to submit FSA-based proposals during the development of new rules or amendments.
IGF Code and the need for equivalency
The International Code of Safety for Ships using Gases or other Low-Flashpoint Fuels (IGF Code) is currently focused on fuels such as LNG. However, its general structure provides a framework for managing low-flashpoint fuel risks. When shipowners seek to use fuels not explicitly covered (e.g., ammonia or hydrogen), they must apply for equivalency approval under SOLAS Regulation I/5, which often relies on RBAT to demonstrate comparable or better safety levels.
Flag administrations frequently request RBAT submissions as part of this process. For example, both the Norwegian Maritime Authority (NMA) and Transport Canada have accepted RBAT-led safety cases for hydrogen and methanol fuel systems.
Integration into IMO model courses and training
The IMO is gradually incorporating risk-based thinking into training frameworks, such as:
- STCW amendments aligned with alternative fuel handling (STCW A-V/3)
- IMO Model Courses on energy efficiency and GHG reduction (e.g., 4.05 and 4.06)
- Future training elements addressing ammonia and hydrogen-specific risks
Students and officers trained in RBAT methodologies will be better prepared to meet compliance and lead safety innovation.
Technologies and developments accelerating RBAT use
Hydrogen systems and fuel cells
Hydrogen introduces risks such as:
- Flammable gas dispersal in enclosed spaces
- Embrittlement of tank materials
- Cryogenic storage and boil-off gas management (for liquid hydrogen)
RBAT is used to model worst-case release events, simulate venting patterns using CFD software, and assess the reliability of ESD systems.
Class societies like DNV and Lloyd’s Register are publishing dedicated hydrogen safety guides that embed RBAT templates.
Ammonia fuel engines
Ammonia is a zero-carbon fuel but is toxic, corrosive, and prone to forming NOx and N2O. RBAT helps:
- Map toxic exposure scenarios
- Design double-walled piping and leak detection systems
- Assess evacuation procedures and PPE effectiveness
The Green Corridor Project in Asia and the AFC Ammonia Consortium have used RBAT to vet ammonia bunkering and engine room safety concepts.
Methanol dual-fuel designs
Methanol poses flammability and toxicity challenges. IMO and flag states require RBAT to assess:
- Fire detection system coverage
- Bunkering interface risks
- Impact of blend quality on combustion and emissions
RBAT also supports crew training scenario development and incident response drills.
Batteries and hybrid propulsion
RBAT is being applied to thermal runaway risks in lithium-ion battery systems. For instance:
- Fault Tree Analysis (FTA) identifies fire ignition pathways
- Event Tree Analysis (ETA) models smoke propagation and response effectiveness
Hybrid-electric ships using green fuel and batteries are often subject to dual RBAT reviews.
Case studies: IMO, RBAT, and safer decarbonisation
MF Hydra: Hydrogen ferry approved by Norwegian Maritime Authority
MF Hydra became the world’s first hydrogen ferry in 2023. Its safety case, accepted by the Norwegian Maritime Authority, was based on RBAT and included:
- CFD simulations of hydrogen dispersal during bunkering
- Triple redundancy in detection and shutdown systems
- Crew PPE and remote monitoring protocols
Hydra’s successful certification now informs IMO work on hydrogen regulatory development.
Maersk methanol-fueled containerships (2024)
Maersk’s new methanol dual-fuel ships passed RBAT-driven approval processes with:
- IGF Code equivalency via SOLAS Reg. I/5
- DNV-reviewed bunkering safety case using HAZID and CBA
- Crew safety training aligned with new IMO STCW course models
These vessels are now operating under EU FuelEU Maritime compliance, showing RBAT’s practical benefits.
EMSA-DNV RBAT for MASS and alternative fuels
The European Maritime Safety Agency (EMSA) partnered with DNV to develop RBAT templates for Maritime Autonomous Surface Ships (MASS) and alternative fuel systems. These tools are designed for:
- Functional decomposition (e.g., fuel handling, navigation, remote control)
- Hazard and risk mapping
- Documented evidence for flag approval
Though focused on European context, these RBAT frameworks are influencing IMO discussions on MASS regulation under MSC.
Challenges and regulatory evolution
No single global RBAT standard (yet)
Despite growing use, there is no universally mandated RBAT template under IMO. This leads to variations between flag States and classification societies. However, work is ongoing:
- MSC and MEPC subcommittees are reviewing how to standardise equivalency evaluations
- The IMO’s Correspondence Groups on Alternative Fuels are incorporating RBAT as part of rule development for hydrogen and ammonia
Keeping pace with technology
The fuel landscape is changing faster than regulation. RBAT helps regulators and industry keep pace, but the learning curve is steep. New fuels like e-methane, liquid organic hydrogen carriers (LOHCs), and nuclear propulsion may require RBAT adaptation.
Training and workforce gaps
There is still a shortage of seafarers and designers trained in applying RBAT methods. Flag authorities like Transport Malta and Singapore MPA have started integrating RBAT awareness into cadet programs and port safety audits.
FAQ: RBAT and the IMO’s role in green maritime transition
Does the IMO mandate RBAT use?
Not directly. But the IMO encourages RBAT as part of FSA and equivalency evaluations, especially under the IGF Code and SOLAS Regulation I/5.
Is RBAT only for alternative fuels?
No. RBAT can also be used for autonomous ship systems, innovative cargo handling designs, and unusual engine configurations.
What is the difference between FSA and RBAT?
FSA is the IMO’s five-step methodology for safety assessment. RBAT typically applies FSA structure but is adapted for specific project or national use.
Is RBAT software?
No. It is a methodology. However, RBAT includes tools like HAZID worksheets, CFD software, FTA/ETA diagrams, and cost-benefit analysis spreadsheets.
Who reviews RBAT submissions?
Typically, the flag State and classification society (e.g., DNV, ABS, BV) review RBAT documentation to assess compliance and safety equivalency.
Where can students learn RBAT methods?
Through IMO Model Courses, university modules on marine risk engineering, or class society guidance (e.g., DNV’s RBAT guides).
Conclusion: A vital bridge between innovation and regulation
As the maritime sector transitions to a cleaner future, it must not sacrifice safety. RBAT provides a structured, evidence-based path to assess the unfamiliar risks of green fuels, novel systems, and hybrid propulsion.
By aligning with the IMO’s safety and environmental goals, RBAT becomes more than a risk tool — it becomes a policy enabler.
For maritime professionals, students, and regulators, mastering RBAT principles means:
- Enabling safe fuel innovation
- Navigating regulatory uncertainty with confidence
- Future-proofing ship design and operations
Call to action: Explore RBAT case studies, study FSA and ISO 31000, and look for real-world IMO equivalency submissions. The future of sustainable shipping depends not only on bold fuels — but on smart, safe systems that RBAT helps deliver.
References (hyperlinked)
- IMO. (2023). GHG Strategy 2023
- IMO. (2020). IGF Code
- DNV. (2023). Hydrogen in Shipping
- Lloyd’s Register. (2022). Alternative Fuel Safety Insights
- EMSA & DNV. (2022). RBAT for MASS
- Norwegian Maritime Authority. (2023). Hydra Approval
- ISO. (2018). ISO 31000 Risk Management Guidelines
- IMO. (2020). FSA Guidelines MSC-MEPC.2/Circ.12/Rev.2