Iron Ore Concentrate: IMSBC Code Schedule

Iron ore concentrate is a Group A cargo under the IMSBC Code: a beneficiated iron mineral product with a fine, uniform particle size that may liquefy and destabilise a bulk carrier if loaded above its Transportable Moisture Limit. The cargo is the primary feedstock for iron ore pellet plants worldwide, shipped in volumes of tens of millions of tonnes annually from Brazil, Chile, Peru, Iran, and Russia to Asian steelmaking terminals. Its Group A status places it in the same regulatory category as iron ore fines and mineral concentrates, with strict pre-loading testing, shipper certification, and the master’s right and duty to refuse non-compliant cargo.

Iron ore concentrate’s position in maritime regulation is shaped by two facts that distinguish it from the other iron ore family entries in the IMSBC Code. First, it is a manufactured product in the sense that its properties result from a deliberate beneficiation process rather than from natural geology: the particle size, iron grade, and moisture content at loading reflect decisions made at the processing plant, not the character of the original ore deposit. Second, that beneficiation process inevitably produces a fine particle size that creates exceptional conditions for pore-pressure build-up under ship motion. The resulting cargo liquefaction risk is not a marginal concern; bulk carriers carrying iron ore family Group A cargoes have capsized with the loss of entire crews, and iron ore concentrate has been at the centre of the regulatory tightening that followed those losses.

The cargo: what iron ore concentrate is and how it is made

Beneficiation and the steel-making supply chain

Iron ore concentrate enters the maritime world because pellet plants, the facilities that agglomerate fine iron ore feedstock into the small spherical pellets fed to blast furnaces and direct-reduction plants, cannot use coarse run-of-mine ore or even standard direct-shipping ore directly. Pelletising requires a feed with iron content typically above 65% Fe and a particle size predominantly below 45 micrometres to ensure uniform pellet strength and metallurgical performance. Natural ores, even high-grade deposits in Brazil’s Quadrilatero Ferrifero or Sweden’s Kiruna mine, rarely meet these specifications without processing.

Beneficiation takes a lower-grade ore, typically 30 to 60% Fe depending on deposit type, and upgrades it by removing the silica, alumina, phosphorus, and other gangue minerals that dilute the iron content and harm blast furnace chemistry. The process has three main steps. The ore is first crushed and then wet-ground in ball mills to liberation size, the particle size at which the iron minerals (magnetite or hematite) are mechanically separated from the surrounding gangue. For magnetite ores, liberation size is typically 50 to 100 micrometres; for hematite, it is often finer, down to 25 to 75 micrometres. The iron minerals are then separated from gangue: magnetite by low-intensity magnetic drums that attract the ferromagnetic magnetite grains, hematite by flotation using reagents that selectively collect the iron minerals on rising bubbles, or by gravity spirals and cyclones that exploit the density difference between iron minerals (5.2 g/cm3 for magnetite, 5.3 g/cm3 for hematite) and silicate gangue (2.6 to 2.7 g/cm3). The separated concentrate slurry, which contains 50 to 70% water by volume at this stage, is then thickened in large settling tanks and filtered to reduce the moisture content for transport.

The final moisture content at which the concentrate leaves the plant is typically 7 to 11% on a wet-mass basis, reflecting a balance between the cost of further drying, the specifications of the receiving pellet plant, and the IMSBC Code’s TML requirement. Over-drying is expensive in energy terms and creates dust-handling problems during conveyor transfer and shiploading; under-drying risks delivering a cargo at or above TML. The business incentive is to dry to exactly the TML, which is why iron ore concentrate cargoes are routinely presented very close to their loading limit.

Physical properties of iron ore concentrate

The beneficiation process gives iron ore concentrate a set of physical properties that define its behaviour as a maritime cargo.

Iron content typically runs 65 to 70% Fe for magnetite concentrates and 63 to 68% Fe for hematite concentrates, substantially above the 58 to 65% Fe of direct-shipping lump iron ore and iron ore fines. This elevated iron grade is the primary commercial value of the product.

Particle size is the key safety-determining property. Grinding to liberation size produces a material where more than 90% of particles are below 1 mm and a significant fraction, typically 20 to 50%, is below 100 micrometres. The 100-micrometre threshold is significant for the IMSBC Code: material with a high fraction below this size transmits pore-water pressure efficiently under cyclic loading and has limited drainage capacity, making it more susceptible to liquefaction than coarser material.

Bulk density at loading is approximately 2,500 to 3,000 kg/m3 for magnetite concentrate and somewhat lower, around 2,000 to 2,500 kg/m3, for hematite concentrate. These values are higher than for many other Group A cargoes: copper concentrate runs 1,800 to 2,300 kg/m3 and zinc concentrate 2,400 to 2,800 kg/m3. High bulk density amplifies the heeling moment produced when a volume of cargo shifts: a 1% shift of 50,000 tonnes of iron ore concentrate at 2,700 kg/m3 generates a far larger transverse moment than the same volume shift of a lighter cargo. This is why bulk carriers carrying high-density Group A cargoes can capsize so quickly once large-scale liquefaction begins.

The stowage factor runs approximately 0.33 to 0.40 m3/tonne, meaning large capesize and very large ore carrier (VLOC) vessels can carry iron ore concentrate to their full deadweight in a partially filled configuration, with considerable freeboard. The structural loading implications are discussed below.

Moisture content at loading, typically 7 to 11%, is close to TML values that commonly fall in the 9 to 13% range, leaving narrow safety margins. The exact values depend on mineralogy, grind size, clay content in the ore, and the plant’s dewatering equipment.

IMSBC Code schedule: the three iron ore family entries

The IMSBC Code’s Appendix 1, which lists individual cargo schedules, includes three separate entries for iron ore family cargoes. These three entries have different Group classifications, different TML obligations, and different loading precautions.

IRON ORE (Group C): lump material

Lump iron ore is the direct-shipping product of mining natural high-grade deposits without beneficiation, crushed only to a size suitable for direct charging into blast furnaces. The lump size fraction, typically greater than 6 mm and up to 30 mm or more, drains freely and does not build up pore pressure under cyclic loading. The IMSBC Code classifies it Group C: not liquefiable, no TML or moisture content certification required. Brazil’s Carajas mine and Australia’s Pilbara operations produce some of the world’s most widely traded lump iron ore under this category.

Group C status does not mean carriage is without hazard. Lump iron ore has high bulk density, and incorrect loading distribution can cause structural damage to the tanktop or to the vessel’s frame in way of the cargo hold boundaries. But the catastrophic stability-loss mechanism of liquefaction does not apply.

IRON ORE FINES (Group A): natural fine fraction

Iron ore fines entered the IMSBC Code as a named schedule entry in 2013, following a wave of casualties in 2009 to 2011. The key defining events were the losses of the Jian Fu Star, Nasco Diamond, and Hong Wei in 2010 within months of each other, all carrying iron ore fines from Indonesian ports. The Stellar Daisy loss in March 2017 in the South Atlantic, with 22 lives lost, reinforced the urgency of the issue.

The IMSBC Code defines iron ore fines as material with at least 10% of particles below 1 mm AND at least 50% of particles below 10 mm. This size-based definition captures the natural fine fraction produced during mining, stockpiling, and ship loading of iron ore, which can have variable moisture content and particle size depending on the ore type and handling conditions. Iron ore fines are Group A, subject to the same TML and moisture content certification framework as iron ore concentrate.

IRON ORE CONCENTRATE (Group A): beneficiated product

Iron ore concentrate has a separate schedule entry from iron ore fines, reflecting its distinct origin and physical character. Where iron ore fines are a natural product of the ore’s particle size distribution, concentrate is a manufactured product whose particle size, grade, and moisture result from deliberate processing choices. The concentrate schedule applies to magnetite and hematite concentrates from beneficiation plants. The particle size is finer and more uniform than iron ore fines: the grinding step that achieves mineral liberation produces a much tighter particle size distribution, with minimal coarse material above 1 mm. The IMSBC Code’s concentrate entry captures this character, and the Proctor-Fagerberg test is the preferred test method precisely because it was developed and validated for fine ore concentrates rather than for the broader range of iron ore fines particle sizes.

The Group A liquefaction hazard

How the mechanism works

Cargo liquefaction begins not at the moment of loading but at the moment when cyclic loading from ship motion begins to accumulate pore-water pressure faster than the water between the particles can drain away. In iron ore concentrate, the fine particle size gives both a high pore-water retention capacity and a low permeability: water enters easily when cargo is deposited but drains slowly once confined. This combination is precisely what makes the cargo dangerous.

At the particle level, fine iron ore concentrate grains are held in contact by both direct friction and by capillary tension in the thin water films between them. The cargo feels solid when first poured into a hold: you can walk on it, push into it with a hand, and see no free moisture. But under the cyclic loading of ocean swells, each roll of the ship transfers a pulse of stress downward through the cargo column. This stress pulse generates a brief spike of pore-water pressure. With coarse, permeable material, the water moves quickly through the pore space and the pressure dissipates between cycles. With fine iron ore concentrate, the pressure from cycle N has not fully dissipated before cycle N+1 arrives. The residual pressures accumulate. Over hours or days at sea, the accumulated pore pressure in the lower layers of a deep hold can approach the weight of the overlying cargo, at which point the inter-particle contact forces go to zero and the cargo ceases to behave as a solid.

The result is not immediately visible from the bridge. The cargo surface above a liquefied lower layer remains dry and coherent: the overlying solid layer floats on the liquefied material beneath without breaking through. What changes is the cargo’s ability to resist transverse acceleration. On a roll to port, the liquefied base allows the solid upper layer to shift bodily to port. The ship rights, but the cargo does not shift back symmetrically; surface tension and the viscosity of the slurry below resist the return. With each successive roll, the cargo surface tilts further. At some critical inclination, the shift becomes permanent and the vessel takes a fixed list. If the list angles the free surface toward the hatch coaming, water can enter. Many casualties have followed a pattern of a developing list reported to the charterer, then rapid capsize within the following hour.

Magnetite versus hematite concentrate: liquefaction behavior

Both magnetite and hematite concentrates are Group A cargoes, but their physical differences produce some variations in liquefaction behavior worth understanding for cargo officers.

Magnetite (Fe3O4) has a density of 5.18 g/cm3, significantly higher than hematite (Fe2O3) at 5.26 g/cm3. The difference in mineral density is small, but the denser packing of magnetite concentrate typically produces higher bulk densities at loading and slightly higher TML values at equivalent particle size distributions. Magnetite concentrate from Brazil’s Samarco operation or from Chilean Compania Minera del Pacifico plants has bulk densities typically running 2,600 to 3,000 kg/m3, while hematite concentrates from Australian or some Brazilian operations may run 2,000 to 2,500 kg/m3.

The higher bulk density of magnetite concentrate means the heeling moment produced by a given volume shift of liquefied cargo is larger. A vessel carrying 80,000 tonnes of magnetite concentrate in a capesize hold configuration faces more severe stability consequences from a 2% cargo shift than one carrying the same deadweight of a lighter commodity.

Magnetite is also ferromagnetic, which means that a ship’s steel structure can acquire a slight magnetic character over multiple voyages carrying magnetite, though this is more a navigational consideration than a cargo safety issue.

The narrow moisture margin

The liquefaction hazard is most acute because iron ore concentrate producers face competing commercial pressures when setting the loading moisture. Further drying costs energy and reduces throughput; over-wet concentrate fails the TML requirement and cannot be loaded. The practical outcome is that many commercial shipments arrive at port with moisture content between 85% and 98% of TML, measured on fresh samples taken by the shipper. The 10% safety margin built into the TML formula does not accumulate on top of this; it is already factored into the TML value through the 0.9 multiplier applied to the FMP.

Any event between sampling and loading that adds moisture to the cargo surface creates actual conditions above what the certificate measured. Rain falling on open stockpiles at the port, re-handling of cargo by front-end loader from a wet stockpile section, or mixing of a wetter cargo batch with the certified batch are all documented mechanisms for certificate compliance to be undermined between the laboratory and the hatch coaming.

Transportable Moisture Limit: the regulatory framework

Definitions and the TML formula

The IMSBC Code defines two critical thresholds for Group A cargo management:

Flow Moisture Point (FMP) is the moisture content at which a sample of the cargo, subjected to the prescribed laboratory test (flow table or penetration), first exhibits a flowing state. FMP is measured by the laboratory; it is not the regulatory limit but the measurement from which TML is derived.

Transportable Moisture Limit (TML) is the maximum moisture content at which the cargo may be loaded on an ordinary bulk carrier without risk of liquefaction. For the flow table test and the penetration test, the relationship is:

The 10% factor serves two purposes. It compensates for the inherent variability of sampling and testing, acknowledging that a TML determined on a 1 kg laboratory sample may not represent exactly the moisture of 50,000 tonnes of cargo. It also acknowledges that the FMP is determined on a static or gently agitated laboratory sample, while the cargo in a loaded hold is subjected to much higher dynamic loading from ocean swell. The true critical moisture in the ship is lower than the laboratory FMP by an amount that the 10% factor is designed to cover.

The Proctor-Fagerberg test does not use FMP at all. Instead, it constructs a compaction-saturation curve from multiple compaction tests at different moisture levels and identifies TML as the moisture content corresponding to 70% degree of saturation. This approach produces a TML directly without the 0.9 multiplier step.

What TML compliance means in practice

A TML of 11% on a certified cargo means the FMP is approximately 12.2% (since 0.9 x 12.2 = 11%). A shipper measuring cargo moisture at 10.5% is technically compliant, but operating with a 0.5 percentage-point margin against a limit that already incorporates a 10% safety factor. If sampling variability is plus or minus 0.5%, and if the cargo stockpile has heterogeneous moisture distribution, some portions of the cargo entering the hold may already be at or above TML.

Moisture content certificates must be based on samples taken no more than seven days before the commencement of loading. TML certificates must be based on tests conducted within six months of loading. The seven-day window for moisture testing reflects how quickly surface moisture can change due to weather; the six-month window for TML reflects that the cargo’s fundamental physical properties, its particle size and mineral composition, do not change significantly over months of production.

When cargo cannot be loaded

The IMSBC Code’s Section 7 creates a narrow exemption: specially constructed or fitted ships, with flag state approval, may carry Group A cargo with moisture above TML. The vessel must have reinforced double-bottom structure, a bilge system capable of handling partially liquefied material, and stability calculations certified for the liquefied condition. No ordinary Handysize, Supramax, Ultramax, or Capesize bulk carrier meets these requirements. The practical consequence is that when a shipper cannot certify moisture below TML, no standard commercial vessel can legally carry the cargo. The cargo must wait, be dried further, or be blended with drier material.

Laboratory test methods

Proctor-Fagerberg test

The Proctor-Fagerberg test is the IMSBC Code’s preferred method for fine ore concentrates and is the test most commonly used by accredited laboratories in Australia, Chile, Brazil, Peru, and other major concentrate-exporting countries. It was developed specifically for the high-density, fine-particle concentrates that the flow table method handles poorly.

In the test, a cargo sample is compacted into a cylindrical mould in three layers using a specified hammer and drop height, and the resulting dry density and moisture content are measured. This procedure is repeated at multiple moisture levels across the range of interest. The data points are plotted as a compaction curve (dry density versus moisture) and a saturation curve (the theoretical maximum dry density at each moisture for zero air voids). The TML is read from the intersection of the compaction curve with the 70% degree-of-saturation line, meaning the moisture content at which 70% of the void space between particles is filled with water.

This approach avoids the visual judgment required by the flow table test and produces a TML that reflects the cargo’s actual compaction behavior under mechanical loading. For iron ore concentrate, the Proctor-Fagerberg TML tends to be slightly higher than the flow table TML on the same material, by around 0.5 to 1.5 percentage points, because the test captures how the dense, well-graded concentrate packs tightly and requires relatively high moisture to reach the critical saturation level.

The test requires careful sample preparation: the sample must be representative, and preliminary drying and reconstituting at different moisture levels must follow the procedure precisely. P&I clubs have documented cases where different accredited laboratories returned Proctor-Fagerberg TML values differing by 2 to 3 percentage points on the same cargo lot, which is sufficient to flip a borderline cargo from compliant to non-compliant depending on which result the shipper presents.

Flow table test

The flow table test is the original IMSBC Code Appendix 2 method and is applicable to material with a maximum grain size up to 1 mm (with some scope up to 7 mm for coarser fractions). A weighed sample is placed in a brass mould on a standardised table, tamped to a defined density, and the mould is then removed. The table is lifted through 12.5 mm and dropped 25 times in 15 seconds. The spread diameter of the resulting cargo patty is measured and compared to the reference diameter. The process is repeated at increasing moisture levels until the cargo spreads by more than 3 mm beyond the reference, identifying the FMP. TML is then 0.9 x FMP.

The flow table test is familiar to laboratories in Asia and to ports with a long history of coal TML testing. Its principal limitation is that the identification of the flow state depends on operator judgment of when the 3 mm spread threshold is crossed, and this subjectivity can introduce test-to-test variability of 1 to 2 percentage points in reported FMP values.

For iron ore concentrate with its very fine, uniform particle size, the flow table test can also produce erratic results because the material’s cohesive fine fraction sometimes prevents the cone from spreading cleanly regardless of moisture content. The Proctor-Fagerberg test’s mechanical approach is less sensitive to this behaviour, which is one reason it became the preferred method for concentrates in the major mining countries.

Penetration test

The penetration test provides an objective, measurable flow state criterion by eliminating the visual spread judgment of the flow table test. The cargo sample sits on a vertically oscillating platform. Brass weights placed on the sample surface penetrate when the cargo approaches its FMP. The FMP is the average moisture between the last non-penetrating test and the first test where weights penetrate more than 50 mm. TML = 0.9 x FMP.

The penetration test is applicable up to 25 mm top size, making it versatile for coarser materials. For very fine iron ore concentrate with particle sizes mostly below 100 micrometres, the cargo’s cohesive character can affect penetration behavior, and the test should be verified as applicable to the specific material before being used as the sole certification basis.

Which method applies

The IMSBC Code does not mandate a single method for iron ore concentrate universally. The cargo schedule entry specifies the preferred method and the shipper’s TML certificate must state which method was used. Where the cargo’s particle size characteristics fall within all three methods’ applicability ranges, the Proctor-Fagerberg result governs in practice at most major trading ports because it is the method historically validated for concentrates and is most familiar to the major accredited laboratories serving the concentrate trade. Any of the three methods is permissible if the laboratory can document that the specific cargo characteristics fall within the method’s stated applicability range.

The can test: shipboard screening

The can test described in IMSBC Code Section 8 is a quick shipboard check that the master and cargo officers can perform from the first cargo entering the hold without specialised equipment. It does not replace laboratory certification; it is a trip-wire for gross moisture excess.

The procedure: collect a representative sample from the loading stream, fill a cylindrical metal container of 0.5 to 1 litre to about half its capacity, and bring it down sharply onto a solid flat surface from a height of about 0.2 metres. Repeat 25 times at one- to two-second intervals. Then examine the sample surface carefully for free moisture, a glistening wet sheen, or any tendency for the material to flow or pool at the edges.

If free moisture appears, loading stops immediately. The master contacts the operator and arranges independent laboratory sampling and TML determination by a surveyor jointly appointed with the shipper’s interests. No loading resumes until the laboratory confirms moisture is below TML. The cost of delay is the shipper’s consequence, not the vessel’s.

A dry can test result tells the officer that the cargo is not grossly over-wet. It does not tell the officer that moisture is below TML. A cargo at 95% of TML may produce a dry can test result while still carrying a meaningful liquefaction risk in ocean swell. The Code makes this limitation explicit. The can test catches the top of the risk scale; it provides no useful information about the lower portion.

Officers performing can tests for iron ore concentrate should note the cargo’s texture and behaviour. Fresh magnetite concentrate has a characteristic dark, metallic grey appearance and a slightly heavy feel; hematite concentrate is brick-red to reddish-brown. Either should present as a damp but coherent mass under the can test at compliant moisture levels. If the sample feels unusually sticky, pours sluggishly, or shows any tendency to flatten and spread under its own weight after impacts, the cargo should be treated as suspect even if no free water is visible.

Can tests should be performed:

• At the start of each loading shift, before cargo from a new part of the stockpile enters the hold.
• Whenever the cargo appearance or texture changes during loading, which may indicate a switch to a different moisture batch.
• After any rain event during loading, on samples taken from the topmost layer of cargo in the open hold.
• Whenever bilge monitoring indicates unexpected moisture accumulation.

Cargo declaration and certification

What the shipper must provide before loading

The IMSBC Code Section 4 and SOLAS Regulation VI/2 require the shipper to provide the master, in writing, before loading commences:

1. A cargo declaration stating: the Bulk Cargo Shipping Name (BCSN) as “IRON ORE CONCENTRATE,” the IMSBC Group (Group A), the chemical composition including total iron content and any significant impurities, the declared moisture content on a wet-mass basis, and the bulk density (mandatory from 1 January 2025 under MSC.539(107)).
2. A TML certificate issued by an accredited laboratory within six months of the commencement of loading, stating the TML value, the test method used, and the applicability basis.
3. A moisture content certificate confirming that the moisture was measured within seven days before the commencement of loading and that the measured value is below the TML.

All three documents must arrive before cargo operations begin. A master who commences loading without the complete set has no regulatory basis for claiming compliance if the cargo subsequently causes an incident.

Bulk density declaration

The requirement to declare bulk density, made mandatory from 1 January 2025 under Amendment 07-23 (MSC.539(107)), addresses a practical gap. Masters and loading computers using generic iron ore concentrate density figures from tables can be substantially wrong for specific cargoes. A lower-grade, higher-clay hematite concentrate at 2,000 kg/m3 and a dense magnetite concentrate at 2,900 kg/m3 have profoundly different implications for tanktop loading stress and for the vessel’s GM as cargo is distributed across multiple holds. The declared density is the basis for the loading computer’s structural load and stability calculations.

TML certificate validity and rain events

The six-month validity of the TML certificate is intentionally long because the TML reflects the physical character of the cargo as a product type. A concentrate from a specific plant, processed from a consistent ore body with consistent grinding parameters, has a stable TML that does not change materially month to month.

The seven-day window for moisture content testing is short because moisture changes quickly. After a rain event at the port, a shipper must test again and issue a new moisture certificate before loading can proceed on the basis of the new data. P&I casualty analyses have repeatedly identified cases where shippers presented the original moisture certificate without re-testing after rainfall, loading cargo already above TML while technically appearing compliant on paper.

Structural loading: high density and hold distribution

Tanktop loading stress

Iron ore concentrate’s bulk density of 2,500 to 3,000 kg/m3 places it among the densest Group A cargoes in the bulk carrier trade. The structural loading consequence is that a fully filled hold of iron ore concentrate exerts far higher tanktop pressure per unit area than any grain, fertiliser, or coal cargo, and higher pressure than most other concentrates except lead concentrate.

Bulk carriers carrying iron ore concentrate must not overstress the tanktop or the double-bottom structure. The vessel’s loading manual specifies maximum permitted hold weights, typically expressed as tonnes per hold or as a maximum tonnes-per-square-metre pressure on the tanktop. For a Capesize with nine holds, the permitted maximum may be around 8,000 to 10,000 tonnes per hold for structural limit reasons, even though the hull’s total deadweight is much larger. The shipmaster must confirm that the planned cargo distribution respects these limits.

The combination of high density and partial loading (when only some holds carry cargo while others are empty or partially filled during loading) creates significant longitudinal bending stress. Capesize bulk carriers loading iron ore concentrate at single-berth terminal facilities often alternate filled and empty holds during the loading sequence, producing bending moments that must be calculated and compared against the hull girder’s permitted hogging and sagging limits at each stage of loading.

Trimming and cargo distribution

The IMSBC Code requires that Group A cargoes be trimmed so that the height difference between peaks and troughs in the cargo surface does not exceed 5% of the ship’s breadth. For a Capesize with a beam of 50 m, this means the surface should not vary by more than 2.5 m from peak to trough across any cross-section of the hold. This rule prevents uneven pressure distribution that would create zones of higher effective stress, which are more prone to local liquefaction initiation, and prevents a static off-centre transverse moment from cargo piled to one side.

Iron ore concentrate self-trims reasonably well through a spout or shiploader during loading. The cargo is dense and flows readily at compliant moisture levels. Most terminal shiploaders can achieve good trim without mechanical intervention in the hold. However, trimming issues arise when loading through multiple hatch positions in a large hold with a single shiploader, where the cargo’s angle of repose (approximately 30 to 35 degrees at compliant moisture) governs how far the cone from any one loading point extends.

Any trim correction requiring crew to enter the hold must be preceded by an atmosphere check. Iron ore concentrate itself presents no toxic gas hazard (unlike sulphide concentrates), but the enclosed hold space should be checked for oxygen depletion before entry, following standard enclosed-space entry procedures under SOLAS.

Hold preparation before loading

Before accepting iron ore concentrate, the master should confirm:

• Bilge suction systems are tested and operational. Fine particles from concentrate can migrate into bilge wells and block suction strainers. Covering the bilge well openings with burlap or canvas strainer protection before loading reduces blocking risk.
• Hatch covers close fully with undamaged seals. Water-tight integrity prevents rain infiltration from raising cargo moisture above TML after loading. A defective hatch cover that admits rain during the voyage is not a shipper failure; it becomes a vessel liability.
• The hold is free of residue from previous cargoes that might react with iron ore concentrate or compromise the moisture balance.

Loading precautions and master’s authority

Loading operations

Iron ore concentrate is loaded via shore conveyor and shiploader at purpose-built terminal facilities. The cargo is dense and flows readily at compliant moisture. Loading rates at major terminals range from 5,000 to 15,000 tonnes per hour on capesize vessels.

The chief officer should monitor the moisture appearance and texture of cargo entering the hold continuously throughout loading. The can test schedule described above provides structured checkpoints. Bilge soundings should be taken before loading commences to establish a baseline and then at regular intervals during loading; any rise in bilge level not attributable to ballast operations or rainfall indicates moisture migration from the cargo.

Loading must stop immediately during precipitation. Rain falling into an open hatch onto partially loaded concentrate raises surface moisture rapidly in the upper layers. The rate of moisture absorption depends on the cargo’s existing moisture content and surface area, but even a moderate rain shower of 20 minutes can raise surface moisture to or above TML in a cargo that was borderline compliant before the rain. The IMSBC Code requires loading to stop during rain; the master must enforce this regardless of commercial pressure.

After rain stops, a can test should be performed on samples from the top layer of cargo in the hold before loading resumes. If the can test shows free moisture, or if the cargo surface appears unusually glossy or wet, loading stays suspended until laboratory testing confirms moisture is below TML.

The master’s right and duty to refuse

SOLAS Chapter VI and IMSBC Code Section 4 preserve the master’s authority to refuse or suspend loading of iron ore concentrate if the required documents are absent, outdated, or show moisture content equal to or above TML. This is not merely a right; it is a regulatory duty. A master who loads in violation of these requirements cannot use the shipper’s documentation failures as a defence in casualty investigations or in insurance claims.

Exercising the refusal right requires the master to document clearly: a written communication to the charterer and shipper stating the specific regulatory basis for refusal (stating which document is absent or invalid and why), contemporaneous records of can tests performed during loading with results and times, and a request for independent sampling by a surveyor appointed through the master’s P&I correspondent.

Charter parties often impose demurrage liability on the vessel for delays caused by refusing to load. This commercial exposure does not override the master’s statutory duty. P&I clubs routinely support masters who refuse loading for documented moisture reasons and advise that the cost of demurrage is far lower than the cost of a casualty. Where the master accepts cargo under reservation, every concern must be noted in writing in the cargo declarations, in the mate’s receipt at the time of loading, and in a contemporaneous message to the operator.

Voyage monitoring

Once loaded and at sea, iron ore concentrate cannot be safely inspected, ventilated, or corrected. The vessel is committed. Monitoring during the voyage is therefore the only means of detecting developing problems.

Bilge well levels are the primary observable indicator. Rising bilge levels in a hold carrying iron ore concentrate, at a rate that cannot be explained by normal condensation or hatch seal weeping, indicate moisture migration through the cargo. This is an early warning of potential liquefaction. Masters should record bilge soundings at standard intervals and investigate any rate of increase that exceeds the baseline.

Roll period monitoring can also detect changes in the vessel’s metacentric height. As a cargo liquefies, the free liquid surface reduces the vessel’s effective GM, lengthening the roll period. Officers who know the vessel’s normal loaded roll period can detect a lengthening that might indicate cargo deterioration, though other factors including ballast state and sea state affect roll period and must be considered.

The IMSBC Code advises that bilge wells should be monitored continuously for Group A cargoes during the voyage. In practice this means checking at every watch change and immediately investigating any significant change from the baseline readings.

Major seaborne trade flows

Iron ore concentrate seaborne trade is driven by the geography of magnetite and hematite deposits that require beneficiation, and by the location of pellet plants that require fine concentrate feedstock.

Brazil is the largest single exporter. Vale’s Samarco joint venture at Ponta Ubu, before its 2015 tailings dam failure and subsequent partial restart, was one of the world’s largest single concentrate and pellet export operations. Vale also exports concentrate through Tubarão and Ponta da Madeira. The Samarco operation, producing magnetite concentrate from the Iron Quadrangle region, illustrates the scale of the trade: before the suspension, Samarco shipped approximately 30 million tonnes of concentrate per year.

Chile exports magnetite concentrate from the Atacama and Coquimbo regions, principally through Guacolda and Coquimbo terminals operated by Compania Minera del Pacifico (a CAP Group subsidiary), primarily to Asian steel mills. Peru exports iron concentrate from the Marcona mine, operated by Shougang Hierro Peru, through the port of San Juan de Marcona.

Iran exports concentrate from the Gol-e-Gohar, Chadormalu, and Sangan mines through Bandar Abbas and Imam Khomeini Port on the Persian Gulf, primarily to China. Iran’s iron ore concentrate exports grew from under 10 million tonnes in the early 2010s to over 40 million tonnes by the mid-2020s, making it a major supplier to Chinese steel mills.

Russia exports concentrate from the Kursk Magnetic Anomaly region, the world’s largest iron ore deposit, through Novorossiysk on the Black Sea and through Murmansk and other Baltic and Arctic ports. Ukraine, before 2022, was a significant Black Sea exporter of iron ore concentrate from Kryvyi Rih basin operations.

Receiving ports are overwhelmingly Chinese. Qingdao, Bayuquan, Caofeidian, Tangshan, Zhanjiang, and Ningbo-Zhoushan are the principal terminals for iron ore concentrate imports, supplied to pellet plants attached to major steel complexes. Japan and South Korea also import significant concentrate volumes for domestic pellet plant operation.

The vessels carrying this trade range from Handymax and Supramax vessels on shorter routes to large Capesize and VLOC vessels on the Brazil-China and Australia-China routes. Vessel selection depends on terminal draft limits, jetty loading capacity, and the economics of scale for each trade route.

Relationship to iron ore pellets

Iron ore pellets, the product of pelletising plants that use iron ore concentrate as feedstock, are a separate IMSBC Code schedule entry and a very different maritime cargo. Pellets are approximately 9 to 16 mm spherical agglomerates, produced by mixing wet concentrate with a small amount of binder (typically bentonite clay or an organic binder), forming green pellets in a disk or drum pelletiser, and firing them in a kiln at around 1,300 degrees Celsius. The firing produces a hard, strong pellet with an iron content similar to the concentrate feedstock but dramatically different physical properties.

Fired iron ore pellets are Group C under the IMSBC Code: they do not liquefy. The pelletising process converts the fine, moist, liquefiable concentrate into a coarse, dry, strong product that is safe to carry on standard bulk carriers without TML certification. The pelletising step is, in physical terms, a liquefaction-risk elimination step for the iron ore. The trade-off is that pelletising adds significant processing cost: building and operating a pellet plant at the mine site or at the export port requires capital investment of several hundred million to over one billion US dollars for a plant processing 7 to 10 million tonnes per year.

Some producers ship concentrate rather than pellets because they lack pellet plant capacity or because their buyers prefer to pelletise domestically. Others ship pellets to avoid the maritime liquefaction risk and to deliver a higher-value product. The economics of the pellet premium versus the cost of a pelletising plant, and the maritime risk premium on concentrate shipping, determine which route a specific mine and buyer combination selects.

Documented losses and the regulatory response

The liquefaction hazard for iron ore family Group A cargoes is not theoretical. The loss record includes:

The MV Stellar Daisy sank in the South Atlantic in March 2017, carrying Brazilian iron ore fines (not concentrate, but the same Group A mechanism). Twenty-two of the 24 crew died. The Marshall Islands Maritime Authority investigation found structural failure in the VLOC’s aged hull contributed, but the incident sharpened global focus on the liquefaction-prone iron ore cargo class. The Stellar Daisy loss led to enhanced survey requirements for very large ore carriers under the Marshall Islands flag and contributed to subsequent IMSBC amendment discussions.

The Jian Fu Star, Nasco Diamond, and Hong Wei all sank in 2010 carrying iron ore fines from Indonesian ports. The near-simultaneous loss of three vessels within months of each other carrying the same cargo class from the same origin triggered the emergency IMO action that added the Iron Ore Fines schedule to the IMSBC Code in 2013.

The Asian Forest (2009) and Black Rose (2009) were earlier iron ore fines losses that set the pattern later bulk carriers would repeat. The Bulk Jupiter (2015), carrying bauxite, contributed to the understanding that the Group A classification needed to be more precisely defined and applied to newly recognised liquefiable cargoes, which eventually led to the dynamic separation concept being added to the IMSBC Code under Amendment 06-21.

Each of these casualties shares a common investigative finding: the vessel departed port with documentation that, on its face, appeared compliant. The conditions producing liquefaction were already present at loading or developed from moisture ingress after departure. The IMSBC Code’s certification framework, when followed rigorously, prevents these conditions from arising; the failures occur when the framework is circumvented or inadequately applied.

Limitations

The information in this article reflects the IMSBC Code as amended by Resolution MSC.539(107) (Amendment 07-23, mandatory from 1 January 2025). The definitive regulatory text is the official IMO publication; this article is a reference guide, not a reproduction of the schedule.

TML values are cargo-specific. No value stated in this article should be applied to a specific shipment without laboratory testing of that shipment’s representative sample. TML for iron ore concentrate varies with mineralogy, grind size, clay mineral content, and the specific dewatering equipment at the processing plant. Two concentrates from two different operations, both correctly declared as “IRON ORE CONCENTRATE,” may have TML values differing by 4 to 6 percentage points.

The Proctor-Fagerberg test results from different accredited laboratories on the same cargo have been documented to differ by 2 to 3 percentage points in P&I club case studies. Shippers or masters dealing with borderline cargoes should consider requesting duplicate testing by two independent laboratories.

The Group A classification and the TML framework apply to iron ore concentrate as carried on ordinary bulk carriers. Vessels specifically constructed to IMSBC Code Section 7 requirements may carry cargo above TML under flag state conditions. No standard commercial bulk carrier meets those requirements without specific structural modification and certification.

The casualty accounts in this article are drawn from published investigation reports and from P&I club analyses. Where liquefaction is cited as the cause, this reflects the official or most widely accepted finding of the responsible investigation authority. In several historical cases, the exact cargo conditions at the time of sinking were not fully reconstructed because the vessel and evidence were lost.

Regulatory requirements can differ between the flag state and port state where the flag state has not yet implemented IMO amendments. Masters should confirm that the version of the IMSBC Code applied by the competent authority of the loading port corresponds to the current mandatory edition.

See also

• IMSBC Code
• IMSBC Group A Cargoes: Cargoes That May Liquefy
• Cargo Liquefaction: TML, FMP, and Group A Controls
• Iron Ore: IMSBC Code Schedule and Carriage
• Iron Ore Pellets: IMSBC Code Schedule and Carriage
• Mineral Concentrates: IMSBC Code Schedule
• Copper Concentrate: IMSBC Code Schedule and Carriage
• Zinc Concentrate: IMSBC Code Schedule and Carriage
• Lead Concentrate: IMSBC Code Schedule and Carriage
• Nickel Ore: IMSBC Code Schedule and Carriage
• Bulk Carrier

Related calculators:

• IMSBC Group A - Liquefaction Risk
• IMSBC TML Moisture Check
• IMSBC - Iron Concentrate
• IMSBC - Iron Ore Fines (IOF)
• IMSBC Group A/B/C Classification