IMSBC Code Solid Bulk Cargo Liquefaction & TML Guide

The carriage of solid bulk cargoes is governed internationally by SOLAS Chapter VI (Carriage of Cargoes and Oil Fuels), made mandatory through the International Maritime Solid Bulk Cargoes (IMSBC) Code (Resolution MSC.268(85)). The primary objective of the Code is to ensure the safe stowage and shipment of solid bulk cargoes by providing detailed information on the hazards associated with individual cargo schedules and instructions on cargo handling procedures.

The IMSBC Code is updated on a regular two-year amendment cycle. Amendment 07-23 (IMO Resolution MSC.539(107)) entered into force on 1 January 2025, introducing critical new requirements regarding dynamic separation, newly classified Group A cargo schedules (including specific bauxite and iron ore fines variants and leach residues), and enhanced shipper cargo declaration duties. This was followed by Amendment 08-25 (IMO Resolution MSC.575(110)) adopted in June 2025 (voluntary 1 January 2026, mandatory 1 January 2027), further standardizing testing protocols and schedule classifications.

Under SOLAS Regulation VI/2, the shipper must provide the Master or their representative with appropriate cargo information sufficiently in advance of loading to enable the necessary precautions for proper stowage and safe carriage to be put into effect. For solid bulk cargoes, this information must include the BCSN (Bulk Cargo Shipping Name), cargo group (A, B, or C), gross mass, moisture content, Transportable Moisture Limit (TML), flow moisture point (FMP), angle of repose, trimming procedures, and specific chemical hazards.

The IMSBC Code classifies solid bulk cargoes into three primary regulatory categories, each carrying specific risks and operational safeguards:

A critical development in modern bulk carrier safety is the distinction between bulk liquefaction and dynamic separation. While traditional liquefaction affects the bulk volume of moisture-dense concentrates (such as nickel ore from Indonesia or the Philippines), dynamic separation occurs predominantly in materials containing both coarse particles and cohesive fine fractions, such as bauxite. During vessel transit, vibration causes the fine particles and water to squeeze out of the coarser matrix, accumulating as a high-density, viscous slurry on the surface of the stow. This slurry exerts severe transverse dynamic forces against the hold bulkheads as the vessel rolls, degrading intact stability and causing rapid list without total cargo bed liquefaction.

For any Group A cargo, the fundamental safety rule of the IMSBC Code is unequivocal: Group A cargoes shall only be accepted for loading when the actual moisture content as certified by the shipper is less than its Transportable Moisture Limit (TML) (IMSBC Code § 4.1.2).

• Flow Moisture Point (FMP): The percentage moisture content (wet weight basis) at which a flow state begins to develop under specified test conditions in a laboratory apparatus (such as the Flow Table, Penetration Test, or Proctor/Fagerberg apparatus).
• Transportable Moisture Limit (TML): The maximum gross water content deemed safe for carriage in ships without specially fitted cargo hold shifting boards or wing tanks. Under standard IMSBC test procedures, TML is set at 90% of the Flow Moisture Point (TML = 0.90 × FMP).
• Accredited Laboratory Testing: TML determination must be carried out within six (6) months of loading unless the physical composition or source of the ore changes, in which case immediate re-testing is mandatory (IMSBC Code § 4.5.1).
• Moisture Content Sampling Within 7 Days: In contrast to the 6-month TML window, the sampling and testing for actual moisture content (MC) must be conducted within seven (7) days prior to the date of loading (IMSBC Code § 4.3.2).
• Rain and Stockpile Exposure: If significant rain, snowfall, or high humidity falls on open stockpiles or barges between sampling and loading, the original moisture certificate becomes legally invalid and the shipper must conduct fresh sampling and testing before the ship accepts the cargo.

Under SOLAS Regulation XI-2/8 and the IMSBC Code, the Master has the overriding authority to refuse or suspend the loading of any solid bulk cargo if they have reasonable grounds to suspect that the moisture content exceeds the TML or that the cargo poses a risk to the safety of the ship and crew.

To provide shipboard officers with a practical, field-level check, IMSBC Code Section 8.4 specifies the can test:

• Apparatus: A cylindrical can or rigid tin of 0.5 to 1.0 litre capacity, approximately 15 to 20 cm in height.
• Procedure: The can is filled approximately half-full with a sample drawn directly from the loading conveyor, barge, or hold stockpile (avoiding surface crusts). The can is raised to a height of approximately 0.2 metres (20 cm) and dropped sharply onto a solid steel deck 25 times at 1 to 2 second intervals.
• Evaluation: The sample is examined after 25 impacts. If moisture has migrated to the surface forming a visible sheen, fluid meniscus, or slurry boundary, the cargo exhibits high moisture and must be treated as liable to liquefy.
• Critical Legal Limitation: While a positive can test (appearance of free water) is definitive proof that the cargo is unsafe and justifies immediate loading suspension, a negative can test (no visible water) DOES NOT prove that the cargo is safe. Fine-particulate ores can fail dynamically under prolonged engine vibration even after passing a manual can test. A negative can test must never be used to override a questionable lab certificate.

Managing the risks of solid bulk cargoes requires rigorous execution of operational controls before, during, and after loading:

Special attention must be paid to cargo hold bilge systems and water ingress alarms. Under SOLAS Regulation XII/12, bulk carriers must be fitted with water level detectors in each cargo hold giving audible and visual alarms on the bridge at two distinct levels: a pre-alarm at 0.5 metres above the inner bottom, and a main alarm at not less than 15% of the hold depth (capped at 2.0 metres). Prior to loading bulk fines, bilge wells must be cleaned, tested under suction, and protected with burlap (hessian) filter cloth wrapped securely around the perforated strainer plates to prevent fine mineral particles from choking the bilge non-return valves and sounding pipes.