Understanding Low Sulphur Fuel Oils (LSFOs) and their spill response challenges
At OSRL, we are constantly evolving our response techniques and studying the effects of different fuels that we may be faced with during an incident. It’s important that our responders are aware of the characteristics and behaviours of each type of fuel they are dealing with, to ensure an effective clean-up operation. This article looks at what responders need to be aware of when potentially dealing with future LSFO incidents.
The global transition towards reducing sulphur oxide (SOx) emissions in the maritime industry has introduced Low Sulphur Fuel Oils (LSFOs) as a cleaner alternative to traditional marine fuels. The significance of these new-generation fuels was highlighted in July 2020, when the MV Wakashio ran aground in Mauritius, spilling LSFO into the marine environment. At the time, this fuel type was still relatively new to the market, and concerns arose about its unpredictable behaviour and response challenges.
We’re taking a look at what we collectively know about LSFOs, how they behave when spilled, and the five critical characteristics that oil spill responders need to consider when planning for and responding to LSFO incidents.
The evolution of marine fuels and emission regulations
Historically, the maritime industry primarily used Fuel Oil (FO) and Marine Diesel Oil (MDO). FO, a thick, high-viscosity fuel, required preheating before combustion, whereas MDO, a lower-viscosity fuel, was used for manoeuvring during port operations.
In recent decades, international regulations have aimed to reduce atmospheric pollution caused by traditional marine fuels. The International Maritime Organization (IMO), through the Marine Environment Protection Committee (MEPC), has implemented a series of measures to mitigate emissions associated with shipping, particularly:
- Sulphur Oxides (SOx)
- Nitrogen Oxides (NOx)
- Volatile Organic Compounds (VOCs)
- Particulate Matter (PM)
Between 2007 and 2012, shipping emissions accounted for 3% of global man-made CO₂ emissions (IMO, 2015). The Paris Agreement has further reinforced the need for stricter environmental policies, leading to the introduction of the Global Sulphur Cap on 1st January 2020.
This regulation limits sulphur content in marine fuels to 0.5% globally and 0.1% in designated Emission Control Areas (ECAs). Ship operators can comply by:
Using compliant low-sulphur fuels, including Very Low Sulphur Fuel Oil (VLSFO, ≤0.5%) and Ultra-Low Sulphur Fuel Oil (ULSFO, ≤0.1%).
Retrofitting vessels with exhaust gas scrubbers to remove sulphur from emissions.
As a result, next-generation fuels have emerged, designed to comply with these stringent environmental standards. However, the spill response implications of LSFOs remain a challenge to response specialists due to their variable properties and unpredictable behaviour in marine environments.
Five critical behaviour characteristics of LSFO spills
Whenever an unfamiliar oil type is spilled, responders need to answer five key questions to determine the most effective response strategy.
- Will it flow?
The pour point of an oil determines whether it will remain liquid or solidify under environmental conditions. Traditional high-sulphur fuel oils tend to have high pour points, meaning they harden in cold waters, limiting their spread but complicating recovery.
However, LSFOs vary significantly in composition, and their pour points can be lower than ambient sea temperatures. This means that some LSFO blends remain fluid and spread extensively, increasing the complexity of containment and recovery. - Will it spread?
An oil's viscosity determines how easily it spreads over a water surface. Marine Diesel Oil (MDO), for example, has a low viscosity and spreads rapidly.
In contrast, LSFOs exhibit a wide range of viscosities, making their behaviour unpredictable. During the MV Wakashio spill, responders observed unusually fluid LSFO, which spread rapidly through Mauritius' tidal lagoons, surprising many experts.
This variability underscores the need for case-by-case spill response assessments, as LSFO behaviour cannot be assumed based on previous fuel oil spills. - Can it be dispersed?
Chemical dispersants are commonly used in crude oil spills but have limited effectiveness on heavy fuel oils due to high viscosity. However, some LSFO blends are less viscous, potentially expanding the dispersant application window.
While dispersants were not used during the Mauritius LSFO spill due to environmental constraints, further research is required to determine if certain LSFOs could be effectively dispersed in offshore environments. - Can it be recovered?
The effectiveness of mechanical recovery techniques, such as skimmers, depends on an oil’s viscosity and adhesiveness.
Traditional FO is highly sticky, allowing it to adhere to containment materials, while MV Wakashio’s LSFO was less adhesive, penetrating improvised booms. This highlights the need for tailored recovery strategies based on the specific properties of the spilled fuel. - How can response planning be improved?
LSFOs introduce new response challenges, and scientific institutions like SINTEF and CEDRE are actively researching their behaviour. Key projects, such as IMAROS and EPPR-PAME, are focusing on:
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- Understanding LSFO fate and behaviour in marine environments.
- Identifying effective response techniques for different LSFO blends.
- Bridging gaps in spill preparedness and response training.
One of the major challenges is the lack of real-world spill data. Unlike crude oils, LSFOs do not have standardised spill behaviour models, and Safety Data Sheets (SDS) typically focus on combustion properties rather than environmental fate.
Improving response preparedness requires:
- More detailed LSFO characterisation in spill scenarios.
- Greater collaboration between the shipping industry and spill response organisations.
- Application of updated oil characterisation guidelines to new fuel types.
The future of marine fuels and spill response
The shift to low-sulphur fuels is only one phase of a broader maritime decarbonisation strategy. The industry is now exploring alternative fuel technologies, including:
- Liquefied Natural Gas (LNG)
- Liquefied Petroleum Gas (LPG)
- Methanol & Biofuels
- Synthetic Methane & Hydrogen
- Ammonia & Future Clean Marine Fuels
As these fuels emerge, it is essential to consider their spill risks and response challenges before widespread adoption. The MV Wakashio experience serves as a reminder that proactive planning, preparedness, and research are critical to mitigating future marine fuel spills.
By continuously evolving response strategies and enhancing industry knowledge, OSRL and the wider spill response community can ensure that environmental protection keeps pace with maritime fuel innovation.
The wider conversation
In this article, we’ve focused on the response challenges in the transition from conventional marine fuels to a broad range of low-sulphur variations that are now used in ships worldwide.
This is just one aspect of a much broader transition taking place to make shipping cleaner and more efficient. As the industry heads towards decarbonisation, some ships are already powered by Liquified Natural Gas (LNG).
Other fuels that have the potential to contribute to this revolution include Liquified Petroleum Gas (LPG), methanol, biofuels, synthetic methane, hydrogen, ammonia, and many others.
As new fuels are developed and brought to market, we need to reflect on our experience with the MV Wakashio incident. Planning and preparedness remain key for effective response and consideration should be given to the potential response challenges that we might face.
