Dangerous Goods Maritime Transport Under Carbon Neutrality: Restrictions of Biofuel-Powered Vessels on Class 9 Dangerous Goods Transportation

Driven by the global “dual carbon” goals, the maritime industry, as a key carbon-emitting sector, is accelerating its energy structure transformation. With its renewability and low-carbon emission characteristics, biofuel has become one of the core options for alternative marine fuels. However, Class 9 dangerous goods (miscellaneous dangerous substances and articles), covering pollutants, solid alcohol, magnetic substances and other special cargoes, have multiple conflicts between their transportation safety risks and the technical characteristics as well as operational specifications of biofuel-powered vessels. Based on the International Maritime Organization (IMO) 2025 ship emission reduction regulations, combined with the technical parameters of biofuel-powered vessels and the transportation requirements of Class 9 dangerous goods, this article systematically analyzes the restrictive factors faced by biofuel-powered vessels when carrying Class 9 dangerous goods, providing references for the industry to balance safety and emission reduction in the carbon neutrality transformation.

1. Background of Carbon Neutrality and Development of Biofuel-Powered Vessels

1.1 Urgent Demand for Carbon Neutrality in the Maritime Industry

The maritime industry contributes approximately 3% of global anthropogenic carbon emissions, among which dangerous goods transport vessels have a particularly prominent carbon footprint due to their large load capacity and long voyage cycles. In response to the emission reduction goals of the Paris Agreement, IMO has formulated the strategic target of “reducing greenhouse gas emissions from the shipping industry by 50% by 2050 compared with 2008”, and launched mandatory standards such as the Carbon Intensity Indicator (CII) and Existing Ship Energy Efficiency Index (EEXI). Against this backdrop, traditional fuel-powered vessels are facing elimination pressure, and alternative energy vessels such as biofuel, liquefied natural gas (LNG) and hydrogen fuel have become the direction of industrial transformation.

1.2 Technical Characteristics and Application Status of Biofuel-Powered Vessels

Biofuel-powered vessels use fatty acid methyl ester (FAME), hydrotreated vegetable oil (HVO) converted from vegetable oil and waste cooking oil as power sources. Their full-life-cycle carbon emissions are 60%-90% lower than traditional diesel, complying with IMO’s low-carbon fuel standards. Currently, more than 200 merchant ships worldwide have completed biofuel retrofitting or directly adopted biofuel power systems. Giants such as Maersk and COSCO Shipping have successively deployed biofuel transport fleets. However, biofuel itself has characteristics such as high viscosity, easy oxidation and large flash point differences, which put forward new requirements for ship power systems, storage conditions and operational safety compared with traditional fuel.

2. Transportation Characteristics and Safety Requirements of Class 9 Dangerous Goods

2.1 Classification and Core Risks of Class 9 Dangerous Goods

According to the International Maritime Dangerous Goods (IMDG) Code, Class 9 dangerous goods cover 7 sub-categories with diversified risk characteristics:

1. Pollutants: Such as oil-containing sludge and heavy metal waste liquids, which are toxic, corrosive and environmentally hazardous, requiring professional cleaning treatment after leakage;
2. Solid Flammable Substances: Such as solid alcohol and dry ice (solid carbon dioxide), which are prone to sublimation or combustion when exposed to high temperatures, requiring storage temperature control;
3. Magnetic Substances: Such as strong magnet components, which may interfere with ship navigation equipment when the magnetic field strength exceeds 0.159A/m;
4. Spontaneously Combustible Substances: Such as damp metal powder, which is prone to oxidation exothermic reactions when in contact with air, causing spontaneous combustion;
5. Substances Emitting Flammable Gases When Wet: Such as calcium hydride, which reacts with water to produce hydrogen, posing explosion risks;
6. Other Miscellaneous Dangerous Substances: Such as airbag inflation devices and high-temperature molten metal containers, which have special physical or chemical hazards;
7. Environmentally Hazardous Substances: Such as pesticide residue waste, which has long-term harm to aquatic organisms and ecosystems.

2.2 Mandatory Safety Standards for Class 9 Dangerous Goods Transportation

The IMDG Code has formulated strict specifications for Class 9 dangerous goods transportation: Pollutants must use leak-proof packaging and be equipped with emergency treatment agents; the transportation environment temperature of solid flammable substances must be at least 10℃ lower than their spontaneous combustion point; magnetic substances must undergo magnetic shielding treatment to ensure the normal operation of ship compasses and other equipment; all Class 9 dangerous goods must be affixed with special dangerous signs and handled by certified personnel for loading, unloading and escort. In addition, the EU REACH regulation requires the entire transportation process of Class 9 dangerous goods to retain carbon footprint records, further increasing transportation complexity.

3. Core Restrictions of Biofuel-Powered Vessels on Class 9 Dangerous Goods Transportation

The fuel characteristics, power system design and safety management system of biofuel-powered vessels have multiple contradictions with the transportation requirements of Class 9 dangerous goods, forming full-chain restrictions from loading to unloading, mainly concentrated in four dimensions: fuel compatibility, safety distance, equipment interference and emergency disposal.

3.1 Fuel and Dangerous Goods Compatibility Restrictions

1. Risk Superposition Caused by High Oxidizability of Biofuel: FAME-based biofuel has an oxygen content as high as 10%-12%, which is prone to oxidative degradation during storage and transportation, producing peroxides. If the vessel simultaneously carries spontaneously combustible substances in Class 9 (such as damp iron powder), leaked peroxides may accelerate their oxidation exothermic process and significantly reduce the spontaneous combustion temperature. A 2023 port simulation experiment showed that after FAME fuel leakage contacted damp iron powder, the spontaneous combustion time was shortened from the original 4 hours to 20 minutes, and the risk increased exponentially.
2. Damage of Pollutants to Fuel Quality: If pollutants such as oil sludge and heavy metal waste liquids in Class 9 leak and mix with biofuel, they will cause the fuel’s acid value to rise and viscosity to become abnormal, further clogging fuel injectors and damaging engine filters. A biofuel-powered vessel once had its engine shut down due to fuel tank contamination by a small amount of lead-containing waste liquid leakage, with maintenance costs as high as $280,000 and a maintenance cycle of 15 days, far exceeding that of traditional fuel-powered vessels.
3. Interaction Between Fuel Storage and Dangerous Goods Packaging: Biofuel needs to be stored in dedicated fuel tanks protected by inert gas, while substances such as solid alcohol and dry ice in Class 9 may release volatile gases (such as carbon dioxide and ethanol vapor) during transportation. If their storage areas are too close, volatile gases may penetrate into the fuel tanks, destroying the inert gas protection atmosphere and increasing the risk of fuel oxidation. Although not explicitly prohibited by the IMDG Code, most shipping companies have mandatory requirements for a minimum distance of 15 meters between them to avoid risks, which poses severe restrictions on the cargo hold layout of small and medium-sized biofuel-powered vessels.

3.2 Restrictions on Safety Distance and Ship Space

1. Isolation Requirements Between Fuel Tanks and Dangerous Goods Holds: Biofuel has a wide flash point range (HVO flash point is about 170℃, FAME flash point is about 120℃). Although higher than traditional diesel, it still belongs to flammable liquids. According to the SOLAS Convention, a fireproof isolation zone with a width of no less than 3 meters must be set between biofuel tanks and dangerous goods holds. The holds for pollutants and spontaneously combustible substances in Class 9 need additional leak-proof cofferdams, further occupying ship space. Taking a 4000TEU biofuel container ship as an example, the isolation zone and cofferdam alone occupy about 8% of the cargo hold area, reducing the loading capacity of Class 9 dangerous goods by 12%-15% compared with traditional fuel-powered vessels.
2. Safety Distance Conflict in Loading and Unloading Operations: The fuel filling port of biofuel-powered vessels and the loading/unloading port of Class 9 dangerous goods must maintain a safety distance of at least 10 meters, and they cannot operate simultaneously. This conflicts with the demand for efficient port loading and unloading—traditional fuel-powered vessels can conduct fuel filling and dangerous goods loading/unloading at the same time, while biofuel-powered vessels need to operate in phases, increasing the loading/unloading time per container by 20%-30%. In busy ports such as Tianjin Port and Rotterdam Port, this time delay may lead to increased ship demurrage fees, with a daily cost of up to $15,000.
3. Cross-Contamination Risk of Ventilation Systems: The fuel tank ventilation system of biofuel-powered vessels must operate independently, and the air outlet must be far away from dangerous goods holds. However, the transportation of magnetic substances and environmentally hazardous substances in Class 9 also requires dedicated ventilation equipment. If the ship’s ventilation system is unreasonably designed, it may cause cross-mixing of fuel vapor and dangerous goods volatile gases. For example, metal dust generated by damaged strong magnet packaging entering the fuel ventilation system may cause electrostatic sparks, posing explosion risks.

3.3 Restrictions on Equipment Interference and Ship Maintenance

1. Interference of Magnetic Dangerous Goods on Navigation and Fuel Systems: If strong magnet components in Class 9 (such as large electromagnets) are not effectively magnetically shielded, the magnetic field generated may interfere with the electronic navigation equipment (such as GPS and compass) of biofuel-powered vessels, while affecting the operation of fuel transfer pump motors. When a biofuel-powered vessel carried unshielded strong magnets, the fuel pump flow fluctuation deviation reached 15%, causing unstable engine power and forcing it to stop at a port for inspection midway.
2. Insufficient Maintenance Adaptability of Biofuel Power Systems: The engines, filters and other equipment of biofuel-powered vessels need regular maintenance with dedicated cleaning agents. However, corrosive dust and chemical residues may be generated during the transportation of Class 9 dangerous goods, which will accelerate wear after adhering to the equipment surface. For example, the replacement cycle of engine filters for biofuel-powered vessels transporting pesticide waste was shortened from the original 300 hours to 180 hours, increasing maintenance costs by 60%.
3. Compatibility Defects of Monitoring Equipment: The fuel level sensors and temperature monitors equipped on biofuel-powered vessels are mostly high-precision electronic equipment, while radioactive substances (small amounts of miscellaneous dangerous goods containing radioactivity) in Class 9 may cause ionizing radiation damage to the equipment. Even low-dose radiation may cause sensor data deviation, affecting the accuracy of fuel supply control and dangerous goods storage temperature monitoring.

3.4 Technical and Normative Restrictions on Emergency Disposal

1. Disposal Conflict of Leakage Accidents: Foam fire extinguishers are needed to cover and suppress biofuel leakage, while oil-absorbing mats are used to absorb the leakage of pollutants such as oil sludge in Class 9. The two disposal methods are different and cannot be mixed. If a biofuel-powered vessel has both biofuel and Class 9 dangerous goods leakage, emergency personnel need to dispose in different areas, leading to extended response time. In 2024, a biofuel-powered vessel in the Indian Ocean had a joint leakage of FAME fuel and mercury-containing waste liquid. Due to the disposal process conflict, the cleaning time was increased by 4 hours compared with the expected, and the pollution scope was expanded by 3 times.
2. Insufficient Adaptability of Fire-Fighting Systems: The fire-fighting system of biofuel-powered vessels needs to be designed according to fuel characteristics, adopting a combined water mist and dry powder fire-extinguishing method. However, the combustion of solid alcohol in Class 9 requires carbon dioxide fire extinguishers, and the fire of spontaneously combustible substances requires inert gas fire extinguishing. The existing fire-fighting systems are difficult to meet multiple fire-extinguishing needs simultaneously. Although some vessels are equipped with multiple types of fire extinguishers, their storage locations are scattered, increasing the emergency access time and possibly missing the best fire-extinguishing opportunity.
3. Dual Lack of Emergency Drills and Personnel Qualifications: Crew members of biofuel-powered vessels need to receive special training on safe fuel operation, while the transportation of Class 9 dangerous goods requires crew members to have IMDG Code special qualifications. Currently, less than 30% of crew members worldwide hold both qualifications, leading to prone operational errors during emergency disposal. In addition, most shipping companies have not formulated joint emergency drill plans for “biofuel + Class 9 dangerous goods”, resulting in weak crew capabilities in responding to compound risks.

4. Analysis of Underlying Causes of Restrictions

4.1 Lag of Technical Standards

As emerging entities, biofuel-powered vessels mainly refer to traditional fuel-powered vessels in their design and operation standards, lacking special specifications for dangerous goods transportation. Although IMO released the Safety Guidelines for Biofuel-Powered Vessels in 2024, it did not clarify the detailed rules for carrying Class 9 dangerous goods; ports in different countries also have different requirements for biofuel-powered vessels carrying Class 9 dangerous goods. For example, EU ports require additional fuel-cargo compatibility reports, while Southeast Asian ports have not yet introduced relevant regulations. The inconsistent standards lead to increased transportation restrictions.

4.2 Risk Superposition Characteristics of Fuel and Cargo

The oxidation characteristics and high viscosity of biofuel form a “1+1>2” superposition effect with the diversified risks of Class 9 dangerous goods. The risk management system of traditional fuel-powered vessels is designed based on a single fuel risk, while the interaction between biofuel and Class 9 dangerous goods may generate new risks (such as accelerated oxidation and equipment corrosion), which cannot be covered by existing risk assessment models. To reduce the claim rate, shipping companies actively add transportation restrictions.

4.3 Phased Constraints of Industrial Transformation

Currently, biofuel-powered vessels are still in the initial stage of large-scale application, and related technologies are not yet fully mature. For example, the low-temperature fluidity problem of biofuel has not been completely solved. When transporting substances requiring low-temperature storage in Class 9 in winter, the decreased fuel transportation efficiency may affect ship power, indirectly increasing transportation risks. At the same time, the coverage rate of biofuel filling facilities in ports is only 25%. To ensure fuel supply, vessels need to prioritize planning filling ports, restricting the transportation route selection of Class 9 dangerous goods.

5. Optimization Paths and Practical Explorations to Break Through Restrictions

5.1 Technological Upgrading: Building Compatible Ship Systems

1. Developing New Fuel-Cargo Isolation Technologies: Using vacuum insulation panels instead of traditional fireproof isolation zones, which reduces space occupation while improving thermal insulation performance. The minimum distance between biofuel tanks and Class 9 dangerous goods holds is shortened from 3 meters to 1.5 meters, increasing cargo hold utilization by about 6%.
2. Creating Intelligent Monitoring and Early Warning Systems: Integrating magnetic flux sensors, fuel quality detectors and dangerous goods leakage alarms to monitor parameters such as magnetic field strength, fuel acid value and volatile gas concentration in real time. When data is abnormal, isolation valves and ventilation switching devices are automatically activated, with response time controlled within 10 seconds.
3. Optimizing Fire-Fighting and Emergency Equipment Configuration: Adopting modular fire-fighting systems, equipping dedicated fire-extinguishing modules according to the sub-categories of Class 9 dangerous goods (such as carbon dioxide modules for solid alcohol and inert gas modules for spontaneously combustible substances), and realizing automatic fire type identification and rapid switching of fire-extinguishing modules through AI algorithms.

5.2 Standard Improvement: Establishing a Unified Normative System

1. Formulating Special Transportation Standards: Promoting IMO to issue the Technical Specifications for Biofuel-Powered Vessels Carrying Class 9 Dangerous Goods, clarifying the loading requirements (such as magnetic shielding standards for magnetic substances and packaging grades for pollutants), safety distance parameters and emergency disposal procedures for different sub-categories, to achieve unified standards in global ports.
2. Improving the Qualification Certification System: Establishing a “biofuel + dangerous goods” dual-qualification training and assessment mechanism, covering modules such as fuel characteristics, dangerous goods risks, equipment operation and emergency disposal. It requires 100% of crew members to hold certificates and incorporates qualifications into the bonus items of ship CII rating.
3. Establishing Risk Assessment Mechanisms: Developing a “fuel-cargo compatibility database” that collects interaction data between different biofuels (FAME, HVO, etc.) and sub-categories of Class 9 dangerous goods, providing intelligent suggestions for ship stowage. For example, reminding FAME-fueled vessels to avoid carrying oxidizable substances such as damp iron powder.

5.3 Operational Innovation: Exploring Adaptive Transportation Modes

1. Implementing “Targeted Routes + Fixed Categories” Transportation: For routes with complete biofuel filling facilities (such as Tianjin Port-Rotterdam Port), specially carrying low-risk Class 9 dangerous goods (such as magnetic substances and environmentally hazardous substances). Improving transportation efficiency and reducing stowage risks through fixed routes and categories.
2. Carrying Out Port-Ship Collaborative Maintenance: Setting up joint service stations for biofuel-powered vessels and Class 9 dangerous goods in major ports, providing one-stop services such as fuel quality testing, dangerous goods packaging inspection and equipment maintenance. Extending the ship maintenance cycle from 180 hours to 250 hours and reducing maintenance costs by 30%.
3. Piloting Blockchain Full-Process Traceability Management: Uploading biofuel filling records, dangerous goods packaging information, ship monitoring data and port inspection reports to the blockchain platform to achieve tamper-proof full-chain transportation data. It not only meets the carbon footprint traceability requirements of EU REACH regulations but also provides reliable data support for risk assessment.

5.4 Policy Support: Creating a Favorable Development Environment

1. Increasing R&D Subsidies: Providing subsidies of up to 50% of R&D costs for enterprises developing compatible ship systems, and 30% equipment purchase subsidies for vessels installed with intelligent monitoring systems, to accelerate technology application.
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