IMSBC Group A — Liquefiable cargoes

Group A of the IMSBC Code covers solid bulk cargoes that may liquefy if shipped with a moisture content above the Transportable Moisture Limit (TML). Liquefaction transforms an apparently solid cargo into a viscous fluid, producing a free-surface effect in the cargo hold and rapid, uncontrollable heel. Several vessels have capsized within minutes of liquefaction onset. The phenomenon is not unique to any single cargo type — it is a function of particle size, moisture content, and the vibration imparted by the ship's engines and sea state.

The physics of liquefaction

Free moisture and pore water pressure — Fine-grained particulate materials hold moisture in interstitial spaces. Under vibration (engine operation, sea state, cargo shifting), pore water pressure rises and grain-to-grain friction decreases. Once inter-particle friction is overcome, the bulk behaves as a fluid. This transition can be rapid and irreversible.
Structural change — Liquefaction collapses the granular structure. A cargo that appears compact and dry on the surface can have liquid layers beneath. The surface may re-solidify between wetting events, masking the hazard from a visual inspection.
Free-surface effect — Once liquefied, the cargo behaves like a liquid in a partially filled tank. Any heel causes the cargo to flow to the low side, increasing the heeling moment. Unlike liquid cargo in a proper tank, the hold structure provides no baffle effect. The vessel can capsize before crew can react.
TML and FMP relationship — The Flow Moisture Point (FMP) is the moisture content at which a cargo begins to flow under standard vibration conditions. The TML is set at 90% of the FMP, providing a safety margin for measurement uncertainty and natural variation across the shipment. Cargo with a moisture content at or below TML may be loaded; cargo above TML must not be loaded.

Common Group A cargoes

The IMSBC Code lists approximately 70 scheduled Group A or Group A+B cargoes. The following are among the most frequently shipped and the most frequently implicated in casualties:

Iron ore fines
Extremely common cause of liquefaction casualties. Fine particle size and high moisture content in tropical loading ports (India, Brazil, South Africa, Sierra Leone) create severe risk. Distinction between iron ore (lump) — Group C — and iron ore fines — Group A — is critical.
Nickel ore
Notoriously problematic from Indonesian and Philippine ports. High natural moisture content; TML can be very close to natural MC. A series of losses from 2009–2013 drove regulatory reform and led to the 2013 IMSBC amendments tightening nickel ore requirements.
Bauxite
Added to Group A in the 2015 amendments (in force 2017) following the loss of MV Bulk Jupiter in January 2015. Previously listed as Group C. Fine-grained bauxite from Guinea and Malaysia is susceptible to liquefaction despite its seemingly granular appearance.
Mineral concentrates
Copper, lead, zinc, and other metal concentrates from flotation processes. Often loaded with high residual moisture from the dewatering process. Some concentrates also carry Group B hazards (toxic heavy metals in dust).
Coal slurry / coal fines
Fine coal with high moisture content from washing plants can liquefy. Distinct from lump coal (Group B, self-heating). The fine fraction is often a by-product of coal handling and may not be tested separately from the parent cargo.
Laterite ore
High-moisture ore from tropical deposits. Loaded from barges in rivers or roads with natural moisture levels that vary with recent rainfall. Extremely difficult to control at source; independent survey is essential.
Fluorspar (fine)
Fine-grained calcium fluoride concentrate from ore processing. Dense but can liquefy under vibration. Requires TML certificate and moisture declaration in the same manner as other Group A cargoes.

Notable liquefaction casualties

Vinalines Queen2011Nickel ore (Philippines)
Lost with all 22 crew. The vessel sent a distress call reporting cargo shift and progressive listing before disappearing. Investigation confirmed liquefaction of the nickel ore cargo as the probable primary cause.
Bulk Jupiter2015Bauxite (Malaysia)
Lost with 18 of 19 crew. Sank within minutes of an acute list developing. MAIB/AAIB investigation concluded that the fine bauxite cargo had liquefied. Led directly to bauxite being reclassified from Group C to Group A.
Stellar Daisy2017Iron ore slurry (Brazil)
Lost with 22 of 24 crew. A VLOC (very large ore carrier) converted from a VLCC. Investigation pointed to a combination of structural hull failure and possible liquefaction of wet cargo. The two survivors were recovered after several days in the South Atlantic.
Trans Summer2009Nickel ore (Indonesia)
Capsized and sank in the Pacific. All crew lost. One of several nickel ore losses in 2009–2011 that triggered the IMO's review of Group A cargo controls.

Testing methods for TML

Proctor-Fagerberg methodISO 12742
Purpose: Laboratory determination of the Flow Moisture Point (FMP). A series of soil samples at increasing moisture content are subjected to vibration; the point at which free moisture appears on the surface is the FMP. TML = 90% of FMP.
Limitation: Requires a properly equipped laboratory. Result is valid for 6 months from the date of the test. The sample must be representative of the cargo to be loaded.
Flow table testIMSBC Code Appendix 2
Purpose: A standard geotechnical flow table is used to assess the flowability of a sample. The sample is placed in a mould and the table is dropped a specified number of times; spreading indicates flow behaviour.
Limitation: Older method; the Proctor-Fagerberg method is now preferred. Some competent authorities require both for certain cargoes.
Penetration testIMSBC Code Appendix 2
Purpose: A cone penetrometer is dropped into a sample to assess moisture-related shear strength. Low penetration resistance at the natural moisture content indicates a cargo near its flow moisture point.
Limitation: Qualitative screening tool. Cannot replace laboratory determination of TML.
Can test (on-board screening)IMSBC Code — informal
Purpose: Representative sample placed in a can or bucket; the can is dropped onto a hard surface from approximately 0.2 m several times. Moisture appearing on the surface indicates the cargo may be near or above its TML.
Limitation: Not a recognised test method for determining TML. A passing can test does not confirm a cargo is safe to load. Should be used only as a supplementary check. A failing can test justifies suspension of loading pending laboratory results.

Loading plan implications

Trim — Group A cargoes should be trimmed as level as possible in each hold. Excess trim (piling above the hatch coaming level) concentrates moisture and increases the risk of liquefied material flowing toward the ship's ends.
Ventilation — Hold ventilation is generally not recommended for Group A cargoes during the voyage, as introducing moist air can raise the moisture content of the surface layers and promote liquefaction. Hatches should be kept closed and sealed in heavy weather.
Monitoring — The Master should maintain a close watch on the vessel's trim and list throughout the loaded voyage. Any unexplained list or change in the ship's motion may indicate cargo movement. Sounding bilges under cargo holds regularly is essential.
Ballast strategy — Maintaining higher metacentric height (GM) through ballast management does not prevent liquefaction but may slow the rate of heel development, providing additional time to respond. However, high GM can also increase rolling accelerations, which aggravates liquefaction.