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IMSBC Group A cargoes: Cargoes that may liquefy

IMSBC Group A of the International Maritime Solid Bulk Cargoes Code covers solid bulk cargoes that may liquefy if shipped at moisture content above their Transportable Moisture Limit (TML). Liquefaction occurs when fine-particle cargoes shift from a solid-like packed state into a viscous fluid under the cyclical motion of the vessel; the resulting free surface effect destroys vessel stability and is responsible for some of the worst dry-bulk casualties on record. Notable Group A cargoes include iron ore fines (IOF, particularly Brazilian and Australian fine grades), nickel ore (Indonesian, Philippine, New Caledonian), bauxite (under specific conditions, after the MV Bulk Jupiter loss in 2015), mineral concentrates (zinc, lead, copper, sulphide ores), coal slurries and certain construction materials (sand, fluorspar). The IMSBC Code requires every Group A shipment to be accompanied by a TML and Moisture Content (MC) declaration with MC less than TML at the time of loading, with sampling per ISO 3082 and TML determination per one of three standardised tests: the Flow Table Test (ISO 12742, suitable for fine concentrates), the Penetration Test (suitable for porous or coarse cargoes) or the Proctor-Fagerberg Test (suitable for iron ore fines, with three variants F1, F2 and F3 corresponding to typical loading and storage configurations). The shipper bears the legal responsibility for the declaration; the master has the right to refuse loading if the declaration is missing, late, or evidently inconsistent with the visible cargo condition. Casualties from undeclared or under-declared moisture include the MV Vinalines Queen 2011 (Cape Capricorn-shape, total loss with 22 fatalities), the MV Bulk Jupiter 2015 (Supramax bauxite carrier, total loss with 18 fatalities) and the MV Stellar Daisy 2017 (VLOC iron ore, total loss with 22 fatalities). ShipCalculators.com hosts the principal computational tools that support Group A cargo handling: the TML calculator, the moisture content calculator, the Flow Moisture Point calculator, the Proctor-Fagerberg calculator, the free surface effect calculator, the stability before loading IMSBC calculator, the draft survey calculator and the bulk cargo loading calculator. A full listing is available in the calculator catalogue.

Contents

Background

What liquefaction is

Liquefaction is the process by which a fine-particle solid cargo, packed and apparently dry on inspection, transitions into a viscous fluid under the cyclical motion of the vessel at sea. The mechanism:

  1. The cargo as loaded contains some moisture distributed between the particles (in the pore spaces and as adsorbed films on particle surfaces).
  2. Vessel motion (rolling, pitching, heaving) causes fine particles to consolidate; gaps close; pore-water pressure rises.
  3. If the moisture is above the cargo’s Transportable Moisture Limit, the rising pore-water pressure exceeds the inter-particle friction; the cargo loses its solid-like character.
  4. The cargo flows toward the lower side of the hold, creating a free surface effect that dramatically reduces the vessel’s transverse metacentric height (GM).
  5. Reduced GM means the vessel cannot recover from a roll; it lists, develops further free surface, lists more, and ultimately capsizes.

The process can be very fast, a vessel may be apparently stable at sunset and capsize before sunrise. Crew typically have minutes to react once the list begins.

Why TML matters

The Transportable Moisture Limit (TML) is the maximum moisture content at which the cargo can be safely transported. TML is a cargo-specific property that depends on the particle size distribution, the mineralogy, and the consolidation behaviour. TML is determined by laboratory testing of a representative sample.

For a given cargo:

  • If moisture content (MC) < TML: the cargo is safe to ship as Group A (or as Group C if no liquefaction property exists).
  • If MC = TML: the cargo is at the boundary. Most flag administrations treat MC ≥ TML as unsafe.
  • If MC > TML: the cargo will liquefy under vessel motion. Loading is prohibited.

The TML calculator computes the safety margin between MC and TML for a sample.

Distinction from Group B and Group C

  • Group A: liquefaction risk. The principal hazard mechanism.
  • Group B: chemical hazard (oxidiser, self-heating, toxic, corrosive). Some cargoes are both A and B (sulphide concentrates that are both liquefaction-prone and chemically reactive).
  • Group C: no special hazards. The largest category by tonnage (clean coal, grain, salt, gypsum).

The same chemical species may fall in different groups depending on the form: lump iron ore is Group C; iron ore fines below a particle-size threshold are Group A.

TML determination

Three standard test methods

The IMSBC Code Appendix 2 specifies three TML test procedures:

Flow Table Test (ISO 12742) is the standard for fine mineral concentrates. A wet sample is placed on a brass flow table and shaken at a standard frequency. The moisture content at which the sample ‘flows’ (loses cohesion and slumps off the table) is the Flow Moisture Point (FMP). TML = 0.9 × FMP.

Penetration Test uses a standard penetrometer dropped into a wet sample bed. The moisture content at which the penetrometer readings exceed a threshold is the FMP. TML = 0.9 × FMP. Suitable for cargoes that do not respond well to the flow table (porous or angular particles).

Proctor-Fagerberg Test compresses the sample at standard pressure to determine the moisture-density relationship. The ‘optimum’ moisture content corresponds to the FMP. Suitable for cargoes with significant fine-content variability. Three variants:

  • F1: low compaction (typical of grab loading and short voyage).
  • F2: medium compaction (typical of conveyor loading).
  • F3: high compaction (typical of long voyage and large stack height).

The Proctor-Fagerberg calculator returns the F1/F2/F3 TML for a sample given the test data.

Sampling per ISO 3082

Representative sampling is the foundation of a valid TML measurement. ISO 3082 specifies:

  • Sample increment count: minimum 16 increments per cargo lot of 1,000 tonnes.
  • Increment locations: distributed across the loaded face or stockpile per a defined grid pattern.
  • Increment mass: minimum 0.5 kg or 5 × the maximum particle dimension, whichever is greater.
  • Combination: increments combined into a gross sample, then sub-sampled by riffle splitter or coning-and-quartering.
  • Conditioning: sample protected from moisture loss or gain during transport to the laboratory.

Failure to follow ISO 3082 sampling protocol is a frequent reason for declarations being challenged at the loading port.

Stowage and loading

Hold preparation

Group A cargo holds must be:

  • Dry (no residual ballast water, no leaks from hatch covers).
  • Free of any prior cargo residue that could contaminate the sample.
  • Bilge wells inspected and bilge pumps tested.
  • Hatch covers verified to be weathertight (rain ingress on Group A cargo at sea is a recipe for liquefaction).

Loading

  • Multi-spout loading preferred to single-spout to avoid centrifugal moisture concentration.
  • Trimming to remove peaks and valleys that concentrate moisture.
  • Visual monitoring for any sign of free water on the cargo surface (a ‘splashing’ sound during loading, visible water layer at the bottom of the loading chute) is a red flag for over-moisture.
  • Loading rate moderated when rain is forecast or visible.

During the voyage

  • Frequent hold inspection by the chief officer, particularly in the first 48 hours.
  • Bilge sounding to detect any moisture migration to the hold bottom.
  • Routing decisions that minimise heavy-weather encounters in the first week of voyage.
  • Vessel motion monitoring via accelerometers (some modern bulk carriers have automated alert systems).

Master’s right to refuse

The master has the legal right to refuse loading if:

  • The shipper’s declaration is missing or late.
  • The cargo visible at the loading point is evidently wetter than the declaration claims.
  • A surveyor’s challenge to the declaration is unresolved.

Refusal carries commercial consequences (the vessel may incur demurrage, deviation costs); but the master’s safety responsibility prevails over the commercial pressure. Industry guidance (BIMCO, INTERCARGO, P&I Clubs) all support master refusal as the correct response when in doubt.

Notable casualties

MV Vinalines Queen 2011

The Vietnamese-flag Cape Capricorn-shape bulk carrier MV Vinalines Queen capsized and sank in the Pacific Ocean off the Philippines in December 2011 carrying nickel ore from Indonesia to China. 22 of 23 crew were lost; one survived in a life raft for two days before rescue. The investigation found the cargo had been loaded at moisture content above TML; rapid liquefaction in heavy weather caused the capsize. The casualty drove the 2011 Indonesia nickel ore export ban (later relaxed) and the Philippines Coast Guard pre-loading inspection regime.

MV Bulk Jupiter 2015

The Supramax bulk carrier MV Bulk Jupiter sank in the South China Sea in January 2015 carrying bauxite from Malaysia. 18 of 19 crew were lost. Until Bulk Jupiter, bauxite was widely considered Group C (no liquefaction risk); the casualty established that fine bauxite under certain moisture conditions can liquefy, and the IMSBC Code was amended in 2017 (and again in 2023) to classify some bauxite grades as Group A. The investigation drove the Bauxite Working Group at the IMO that produced the current bauxite-specific provisions.

MV Stellar Daisy 2017

The Marshall Islands-flag VLOC (Very Large Ore Carrier) MV Stellar Daisy sank in the South Atlantic in March 2017 carrying iron ore from Brazil to China. 22 of 24 crew were lost. The vessel was a converted VLCC (originally a tanker) and structural failure combined with possible cargo shift. The casualty drove the post-conversion structural assessment requirements for VLOCs converted from tankers (a programme that resulted in many such vessels being scrapped) and the iron ore loading procedure review.

MV Cape Capricorn 2010

The MV Cape Capricorn capsized in the South China Sea in October 2010 carrying nickel ore from the Philippines. The casualty preceded Vinalines Queen by 14 months and was an early indicator of the nickel ore liquefaction problem that drove the subsequent IMSBC amendments and flag-administration interventions.

Documentation

Shipper’s declaration

For every Group A shipment, the shipper must provide:

  • Cargo name (per the IMSBC Code Schedule for Group A cargoes).
  • TML in % moisture content (with test method and lab name).
  • MC at the time of loading (with sampling protocol).
  • Particle size distribution (size grading).
  • Stowage factor (cubic metres per tonne).
  • Angle of repose.
  • Specific reference to IMSBC Code Schedule.
  • 24-hour shipper contact for emergencies.

Master verification

The master should verify:

  • Declaration contains all required fields.
  • Signing authority has appropriate qualifications.
  • TML test was within the validity window (typically 30 days for nickel ore, 90 days for many concentrates).
  • Sample identification on the declaration matches the cargo at the loading point.
  • Visual inspection of the cargo at loading is consistent with the declared MC.

If any of the above checks fails, the master should suspend loading and request clarification or re-sampling.

See also

References

  • IMO, International Maritime Solid Bulk Cargoes Code (IMSBC Code), current edition with 06-21 amendments, International Maritime Organization, 2021.
  • IMO, Resolution MSC.500(105) - Amendments to the IMSBC Code (bauxite), 2022.
  • ISO, ISO 3082 Iron ores - Sampling and sample preparation procedures, current edition.
  • ISO, ISO 12742 Iron ores - Determination of moisture content of a lot, current edition.
  • ISO, ISO 3087 Iron ores - Determination of the moisture content of a lot, current edition.
  • INTERCARGO, Bulk Carrier Casualty Report (Annual), INTERCARGO, current edition.
  • INTERCARGO and BIMCO, Industry Guidance on Bauxite Cargoes, joint publication, 2017 (revised 2023).
  • BIMCO, The Master’s Guide to IMSBC Cargo, BIMCO, current edition.
  • P&I Clubs (various), Loss prevention bulletins on liquefaction casualties, ongoing.