Iron Ore: IMSBC Code Schedule and Carriage

Iron ore is the single largest seaborne dry-bulk commodity by volume, with global trade exceeding 1.6 billion tonnes per year. The IMSBC Code carries two separate schedule entries for it: IRON ORE (Group C, not liable to liquefy), which covers lump and coarse ore, and IRON ORE FINES (Group A, liable to liquefy), introduced as a mandatory schedule after a wave of casualties between 2009 and 2011. For Group C lump ore, the dominant practical hazard is not liquefaction but structural overloading: bulk densities of 2,000 to 3,500 kg/m3 rank iron ore among the heaviest cargoes carried on Capesize and Very Large Ore Carrier (VLOC) vessels, and SOLAS Chapter XII imposes specific structural assessment requirements for any bulk carrier loading a solid cargo at or above 1,780 kg/m3.

Iron ore’s position in maritime trade is defined by the mismatch between where the ore is geologically concentrated and where the steel industry consumes it. Australia’s Pilbara region and Brazil’s Iron Quadrangle together hold roughly half the world’s economically recoverable iron ore, while the world’s largest blast furnace capacity sits in China’s Hebei, Shandong, and Jiangsu provinces, thousands of nautical miles away. That gap sustains a dedicated fleet of Capesize and VLOC vessels that are among the largest dry-cargo ships afloat, operating routes that are the financial backbone of the bulk shipping industry.

Understanding the regulatory framework for iron ore carriage means understanding two distinct regulatory regimes packed under one commercial label: one for the coarse lump product that has been the backbone of the trade for decades, and one for the fine material that nearly destroyed the trade’s safety record between 2009 and 2017.

Iron ore as a cargo: mineralogy, grades, and forms

Ore types and iron grades

Iron ore is not a single mineral. Commercially significant iron ore deposits are dominated by two iron oxide minerals: hematite (Fe2O3, containing 69.9% Fe by mass) and magnetite (Fe3O4, containing 72.4% Fe by mass), with goethite (FeO·OH, containing 62.9% Fe by mass) as a significant secondary mineral in many lateritic and supergene deposits. The gangue minerals that dilute the iron content vary by deposit but typically include silica (SiO2), alumina (Al2O3), phosphorus-bearing apatite, and manganese-bearing minerals.

Direct-shipping iron ore (DSO) is ore that can be loaded and shipped to the blast furnace without beneficiation beyond crushing and screening. DSO quality varies by origin: Australia’s Pilbara produces predominantly hematite DSO at 58 to 62% Fe, while Brazil’s Carajas mine produces an exceptionally high-grade magnetite-hematite blend at 66 to 67% Fe. South Africa’s Northern Cape deposits (exported through Saldanha Bay) run 64 to 65% Fe. India’s Odisha and Jharkhand deposits, heavily traded before export restrictions, typically ran 55 to 63% Fe. The grade matters commercially because each percentage point of Fe content affects the blast furnace’s yield of hot metal per tonne of ore burden.

The cargo form that reaches a ship’s hold is either lump, fines, or a blend. Lump iron ore is crushed to 6 to 40 mm size, sorted out from fines by screening, and loaded directly as Group C cargo. Fines are the sub-6 mm fraction produced at every stage of mining, transport, and handling of lump ore. The ratio of lump to fines produced by any given ore body is broadly fixed by the ore’s physical character: hematite orebodies in the Pilbara typically yield 20 to 30% lump and 70 to 80% fines from any tonne mined. This lump-to-fines ratio has a direct regulatory consequence, since only the lump product is Group C and can be loaded without TML certification.

Physical properties governing carriage

The bulk density of iron ore at loading depends on ore type, moisture content, and the proportion of fines. Lump iron ore typically presents a bulk density of 2,000 to 2,600 kg/m3 at loading, giving a stowage factor of approximately 0.38 to 0.50 m3/tonne. Iron ore fines are denser at loading than lump ore because fine particles pack more efficiently: bulk densities of 2,300 to 3,200 kg/m3 are typical, with stowage factors of 0.31 to 0.43 m3/tonne. Some very high-grade magnetite ores produce fines with bulk densities approaching 3,500 kg/m3.

These densities sit at the high end of the solid bulk cargo universe. Coal, the second-largest dry-bulk trade by volume, loads at 750 to 900 kg/m3. Grain loads at 700 to 850 kg/m3. The structural loading consequence of iron ore’s density is not a minor consideration: a hold that grain fills to the hatch coaming, representing perhaps 10,000 tonnes of cargo, iron ore fills to perhaps 25 to 30% of that depth for the same tonne-count while pressing the tanktop at a force per square metre two to four times higher than grain.

Moisture content at loading depends on the ore’s surface area and the handling process. Lump iron ore is relatively dry, typically 2 to 6% moisture by wet weight, with the moisture concentrated on grain surfaces rather than in capillary pores. Iron ore fines hold more moisture because of their larger total surface area relative to mass and because fine particles create capillary structures that retain water. Fines moisture at loading commonly runs 6 to 11% and can rise significantly after rain events on open stockpiles.

The two IMSBC Code schedules: Group C and Group A

Why two schedules exist

The regulatory history of iron ore under the IMSBC Code reflects the discovery, through catastrophic losses, that “iron ore” as a commercial term can describe materials with completely different stability behaviour at sea. For most of the twentieth century, iron ore was treated as a single cargo category: heavy, dense, and essentially stable once loaded. The industry understood that the cargo was structurally demanding, but liquefaction was not considered a significant risk because the bulk of the trade in lump ore was genuinely stable.

The casualties of 2009 to 2011 demonstrated that iron ore fines exported from India and Indonesia behaved entirely differently from lump ore. The Jian Fu Star, Nasco Diamond, and Hong Wei were all lost in 2010 within months of each other, all carrying iron ore fines from Indonesia, all showing the same pattern: a progressive list developing at sea followed by rapid capsize. IMO’s Maritime Safety Committee treated the losses as an emergency and added the IRON ORE FINES schedule to the IMSBC Code in the 2013 amendment cycle (Resolution MSC.354(92)), giving the cargo its own Group A classification and a mandatory TML framework.

The MSC.500(105) amendments (Amendment 06-21, mandatory 1 December 2023) and the subsequent MSC.539(107) amendments (Amendment 07-23, mandatory 1 January 2025) have carried forward and refined both the IRON ORE and the IRON ORE FINES schedules. MSC.501(105) is the IMDG Code amendment and is not relevant to iron ore carriage; citing it in an IMSBC context is a common error to avoid.

The IRON ORE (Group C) schedule

The IMSBC Code schedule for IRON ORE applies to coarse material that does not meet the particle-size criteria for iron ore fines. The schedule carries the following key particulars:

Bulk Cargo Shipping Name (BCSN): IRON ORE

UN Number: not applicable (not a dangerous goods entry)

IMSBC Group: C (neither liable to liquefy nor a material hazard in chemical terms)

Stowage factor: approximately 0.38 to 0.50 m3/tonne for typical lump ore (schedule lists the range; actual cargo-specific values must be declared by the shipper)

Angle of repose: not applicable (the cargo is coarse enough that angle-of-repose limits on surface variation do not govern as they would for fine, low-cohesion materials)

Bulk density: 2,000 to 3,500 kg/m3 (depending on ore type and fines content)

Hazard class: no chemical hazard designation. The schedule notes that the cargo may have a residual moisture level that could be hazardous from dust generation and that the cargo is abrasive.

Special requirements: the schedule requires that the vessel’s master confirm that the ship is suitable for the intended cargo and that the loading plan respects the permitted tanktop loading limits. The high density of the cargo is explicitly called out: the schedule notes that the cargo density may be high enough to require assessment under SOLAS Chapter XII (high-density solid bulk cargo provisions). The master’s responsibility to refuse loading when tanktop limits cannot be respected within the approved distribution plan is preserved.

The IRON ORE FINES (Group A) schedule

The IRON ORE FINES schedule in the IMSBC Code is a separate entry, triggered by the particle-size characteristics of the cargo rather than by any chemistry or commercial designation. A cargo declared and commercially known as “iron ore” must be loaded under the IRON ORE FINES schedule if its particle size distribution meets the IMSBC Code’s definition: at least 10% of particles below 1 mm AND at least 50% of particles below 10 mm.

This definition is cargo-specific. Two shipments of “iron ore” from the same mine can fall into different schedule categories depending on how much fine material has been generated during stockpiling, reclaiming, and ship loading. A freshly screened batch with 8% below 1 mm is Group C; a batch from the same stockpile that has been rained on, re-handled, and degraded to 12% below 1 mm is Group A and cannot be loaded without TML certification.

IMSBC Group: A (liable to liquefy)

TML obligation: the shipper must provide a TML certificate (valid within six months of loading) and a moisture content certificate (based on testing within seven days before commencement of loading) confirming that the cargo’s actual moisture is below the TML.

Special requirements: the schedule requires that the cargo is trimmed level. The surface height difference between peaks and troughs must not exceed 5% of the ship’s breadth across any hold cross-section. It further requires continuous bilge monitoring during the voyage and prohibits ordinary vessels from loading when the declared moisture content equals or exceeds the TML.

Group classification comparison

The table below summarises the three iron ore family entries in the IMSBC Code. All three appear in the Code’s Appendix 1 (Schedule of Solid Bulk Cargoes). Iron ore concentrate has its own separate schedule and is covered in depth in the companion article on iron ore concentrate.

The distinctions in this table have direct safety consequences. Group C cargo requires no pre-loading testing; Group A cargo cannot legally be loaded on an ordinary bulk carrier above TML.

Distinguishing lump ore from iron ore fines: the critical assessment

Why the boundary matters

The Group C / Group A boundary is the most operationally significant regulatory determination made before an iron ore cargo is loaded. A master who accepts cargo as Group C when it actually meets the Group A particle-size definition has loaded without required documentation. If that cargo liquefies, the documentation gap is a primary basis for finding the vessel at fault in a cargo investigation, regardless of the shipper’s representations.

The boundary is not determined by the cargo’s commercial name, its iron grade, or its visual appearance. Fine material can look and feel very similar to borderline-compliant coarse material when both are dry. The determination is made by particle-size analysis of a representative sample using the sieve-based procedures in IMSBC Code Appendix 2.

In practice, Australian Pilbara lump product screened at the mine to 6 to 40 mm has essentially no ambiguity: it is a clear Group C cargo. But the same Pilbara operation’s fines stream, and the blends that miners sometimes produce to improve lump-to-fines revenue ratios, can sit very close to the 10% / 50% boundary. Indian and Indonesian iron ore historically presented many borderline cases; the 2010 casualties arose specifically from shipments whose fines content was either not assessed or was understated.

The 10% fines criterion and shipper responsibility

The IMSBC Code places the burden of correct classification on the shipper. The shipper must provide the master with a cargo declaration that includes the particle size distribution of the cargo, the fines content, and the resulting Group classification. If the shipper declares a cargo as Group C and the actual particle size distribution shows it meets the Group A criteria, the shipper has provided a false declaration. The master bears a secondary duty to review the declaration for plausibility and to request verification if there is reason to doubt it.

Reason to doubt can come from several sources: visual inspection of the cargo during loading showing a high proportion of fine, dusty material; cargo from an origin known to produce borderline product; or a declared moisture content that is higher than expected for a Group C lump product (high moisture on a purportedly coarse cargo is a sign that fines are present, since fines hold more water). The can test, properly applied, can also give indirect evidence of fines content: a coarse lump cargo at 5% moisture produces a dry, clean can test; a fines-rich cargo at the same nominal moisture can produce a glossy, wet-surface result.

What “trimming” means for fines under Group A

When a cargo meets the Group A criteria, the trimming requirement in the IRON ORE FINES schedule is not optional. The cargo surface height variation within any hold cross-section must not exceed 5% of the ship’s breadth. For a Capesize with a 50 m beam, that is 2.5 m variation maximum from peak to trough across any transverse section of the hold.

The reason for this limit is two-fold. An untrimmed cone of fines loaded through a central hatch creates an asymmetric pressure distribution across the tanktop, with the highest stress at the cone base and lower stress toward the hold boundaries. This asymmetry can push the highest-pressure zone to structural limits while the average pressure across the hold appears acceptable. Additionally, an untrimmed surface with pronounced peaks contains zones of lower packing density at the cone flanks; these zones drain more slowly and may reach higher degrees of saturation at equivalent moisture content, making them the first zones to liquefy under ship motion.

SOLAS Chapter XII and high-density cargo structural requirements

The threshold and its significance

SOLAS Chapter XII applies specifically to bulk carriers and sets out requirements that go beyond the general construction rules of SOLAS Chapter II-1. Regulation 12 of Chapter XII addresses structural requirements for bulk carriers carrying dense solid bulk cargoes and applies to vessels built on or after 1 January 2006 that carry solid bulk cargoes with a density at or above 1,780 kg/m3. Vessels built before that date carrying high-density cargoes are subject to assessment under Resolution MSC.277(85) and related guidance.

Iron ore, in all its forms, sits well above the 1,780 kg/m3 threshold. Lump iron ore at 2,000 to 2,600 kg/m3 and iron ore fines at 2,300 to 3,200 kg/m3 both trigger Chapter XII’s additional requirements. The implication is that every vessel entering the iron ore trade, whether as a one-off or as a dedicated ore carrier, must be structurally assessed for high-density cargo carriage and must operate with a loading manual that explicitly accounts for the tanktop and double-bottom structural limits.

Tanktop loading stress: the fundamental constraint

The structural load on a ship’s inner bottom from a column of cargo depends on the cargo’s bulk density, the depth of cargo loaded in the hold, and the area over which the load is distributed. The pressure at the tanktop surface is:

where $p$ is the pressure in Pascals, $\rho_b$ is the bulk density in kg/m3, $g$ is gravitational acceleration (9.81 m/s2), and $h$ is the depth of cargo above the tanktop in metres.

For iron ore fines at a bulk density of 3,000 kg/m3 loaded to a depth of 10 m in a hold:

Compare this to the same depth of coal at 800 kg/m3:

The iron ore column exerts nearly four times the tanktop pressure of a coal column of the same depth. A bulk carrier’s tanktop is typically designed to a permitted distributed load (PDL) expressed in tonnes per square metre (t/m2), specified in the loading manual for each hold. Capesize bulk carriers designed for the iron ore trade typically carry PDL values of 20 to 25 t/m2 on the tanktop, corresponding to the structural limit of the inner bottom plating, frames, and double-bottom girder system. A simpler form of the pressure calculation useful for checking against the PDL:

at $\rho_b$ in kg/m3 and $h$ in metres (dividing by 1,000 to convert kg/m2 to t/m2 and by gravity’s implicit 9.81 to mass units). For 3,000 kg/m3 at 8 m depth: PDL = 3,000 x 8 / 1,000 = 24 t/m2, close to the structural limit on many vessels. Adding any more cargo depth would exceed the limit.

This relationship explains why iron ore is typically loaded to a cargo depth well below the hold’s geometric capacity: the structural limit on tanktop pressure, not the hold volume, governs maximum cargo weight per hold.

Hull-girder bending and the loading sequence

The distribution of cargo between holds is as important as the tanktop check within any individual hold. A Capesize bulk carrier loading at a terminal with a single shiploader must cycle through holds in a planned sequence, and at any moment during loading some holds are full while others are empty. This creates longitudinal bending moments on the hull girder that change continuously as loading progresses.

Class rules and the vessel’s approved loading manual define maximum permissible hogging and sagging bending moments at each frame station along the hull, at every stage of loading. These limits are determined from the hull’s longitudinal strength calculation and must not be exceeded during loading, not merely at departure. Exceeding the hogging limit at a tanktop-loaded intermediate stage can cause buckling in the keel or bottom shell even if the fully loaded condition is within limits.

The practical implication for an iron ore voyage is that the chief officer must produce a loading plan before the vessel arrives at berth, compute the intermediate bending moments for each stage of the loading sequence, and confirm that every stage satisfies both the tanktop pressure limit and the hull-girder bending limit. At terminals loading at 10,000 to 16,000 tonnes per hour, a Capesize can fill a hold in under two hours. The loading plan is not a back-of-envelope exercise; it requires the vessel’s stability and hull-girder loading software to produce a compliant sequence before operations begin.

VLOC-specific structural considerations

Very Large Ore Carriers (VLOCs), vessels with deadweights from 250,000 to over 400,000 DWT, are a class in themselves. They were developed specifically for the Brazil-China and Australia-China long-haul trade routes where cargo volumes justify the economies of scale. VLOCs like those in the Vale fleet (Guaiba class, 325,000 DWT; Valemax class, 400,000 DWT) can load a full cargo of approximately 380,000 to 400,000 tonnes of iron ore in a single voyage, equivalent to roughly 250 Capesize voyages annually. The structural challenges of VLOCs are amplified by their sheer size: hull-girder bending moments at full load are enormous in absolute terms, and the double-bottom depth and stiffener spacing must handle tanktop loads at iron ore densities across holds that may be 30 m or more in depth.

The Stellar Daisy loss in March 2017 raised specific structural concerns about aged VLOCs. The Stellar Daisy was a converted ore-oil carrier, 35 years old, carrying 266,000 tonnes of Brazilian iron ore fines when it sank in the South Atlantic with the loss of 22 crew. The Marshall Islands Maritime Authority investigation identified structural failure in the conversion design as a contributing factor. Following the loss, the IMO and several flag states imposed enhanced structural survey requirements on VLOCs over 20 years of age, and the VLOC sector moved toward a more controlled fleet age profile.

Iron ore fines: the Group A hazard

The liquefaction mechanism for iron ore fines

Cargo liquefaction in iron ore fines follows the same pore-pressure accumulation mechanism that governs all IMSBC Group A cargoes, but iron ore fines have physical properties that make the hazard particularly severe. The fine particle size, typically with 50 to 80% below 10 mm in a typical iron ore fines shipment, gives the cargo a large total surface area relative to mass, which means it can hold substantial moisture in capillary pores even when it appears dry at the surface. The high bulk density, 2,300 to 3,200 kg/m3, means that when a volume of this material liquefies and shifts to one side, the resulting transverse moment is large relative to the vessel’s restoring moment.

Under ship motion in open ocean swell, cyclic stress pulses travel downward through the cargo column. In material fine enough to hold pore water without draining it between cycles, the water pressure between particles accumulates. At the critical point where accumulated pore pressure matches the effective weight of the overlying cargo, inter-particle friction falls to near zero and the material behaves as a dense slurry. The transition is not visible from the bridge: the cargo surface can remain intact as a solid crust while the mass below is effectively liquid. Progressive roll cycles cause the solid surface layer to shift toward the low side; the vessel develops a permanent list; and if the list angles the hatch coaming toward the water surface, flooding can begin.

Iron ore fines casualties tend to follow this sequence and to accelerate quickly once large-scale liquefaction is underway. The loss of the Jian Fu Star (2010), Nasco Diamond (2010), and Hong Wei (2010), all within months of each other, all carrying iron ore fines from Indonesian ports with improperly certified or uncertified moisture content, confirmed this pattern. The Stellar Daisy (2017), though complicated by structural factors, added a VLOC-scale example of the same hazard class.

Transportable Moisture Limit for iron ore fines

The IRON ORE FINES schedule requires TML determination by one of three methods prescribed in IMSBC Code Appendix 2: the flow table test, the penetration test, or the Proctor-Fagerberg test. For iron ore fines specifically, the Proctor-Fagerberg test became the mandated preferred method following the 2013 IMSBC amendment, because it was designed and validated for high-density fine-ore materials rather than for the broader range of grain sizes that the flow table test handles.

The Proctor-Fagerberg test determines TML directly as the moisture content corresponding to 70% degree of saturation on the compaction curve, without using the 0.9 x FMP formula that the flow table and penetration tests require. For iron ore fines, Proctor-Fagerberg TML values typically range from 9 to 14% depending on particle size distribution, clay mineral content, and ore type. Fines from Australian Pilbara operations, which tend to be coarser and lower in clay content, generally have higher TML values (12 to 14%) than fines from Indian or some South American origins (9 to 11%) where clay mineral content is higher and particles are finer.

The seven-day validity on moisture content certificates and the six-month validity on TML certificates must both be satisfied at the time loading commences, not at the time the ship arrives at berth. If a vessel berths on a Monday with a moisture certificate dated eight days earlier, new sampling and testing must be completed before any cargo enters the hold.

The can test applied to iron ore fines

The can test described in IMSBC Code Section 8 is an onboard screening procedure requiring no laboratory equipment. For iron ore fines the procedure is:

1. Collect a representative sample from the loading stream.
2. Fill a cylindrical metal can of 0.5 to 1 litre capacity to about half full.
3. Bring the base of the can down firmly onto a solid flat surface from 0.2 m height.
4. Repeat 25 times at one- to two-second intervals.
5. Inspect the surface for free moisture, a glistening sheen, or any tendency to pool at the edges.

A positive result means loading stops immediately and independent laboratory sampling is arranged. A negative (dry) result does not confirm that moisture is below TML; it only confirms that the cargo is not grossly over-wet. Iron ore fines at 95% of TML can produce a dry can test while retaining meaningful liquefaction risk. Can tests should be performed at the start of each loading shift, after any rain event, and whenever cargo appearance or texture changes during loading.

The global iron ore trade: routes, vessels, and terminals

Scale and origin

Global seaborne iron ore trade exceeded 1.6 billion tonnes in recent years, making it the largest single dry-bulk commodity trade by volume. Two countries dominate supply. Australia exports approximately 870 to 900 million tonnes per year, primarily from the Pilbara region in Western Australia: Rio Tinto’s Dampier and Cape Lambert terminals, BHP’s Port Hedland Finucane Island and Nelson Point facilities, Fortescue’s Herb Elliott port and Anderson Point terminals, and the Port Hedland facilities of smaller producers. Brazil exports 350 to 380 million tonnes per year, predominantly through Vale’s Ponta da Madeira terminal at Sao Luis (Carajas ore via the Carajas railway), Vale’s Tubarao complex at Vitoria, and CSN’s Itaguai terminal. Together, Australia and Brazil account for approximately 83 to 85% of global seaborne iron ore exports.

Secondary exporters include South Africa (50 to 60 million tonnes, primarily from Kumba Iron Ore’s Sishen and Kolomela mines via the Saldanha Bay terminal), Canada (30 to 40 million tonnes, primarily Quebec Cartier and ArcelorMittal Mines Canada through Sept-Iles), Sweden (LKAB through Narvik and Lulea), India (variable, 30 to 50 million tonnes depending on export policy), Ukraine (substantially reduced from 2022), and several smaller suppliers in West Africa (Guinea, Sierra Leone, Liberia) at early stages of mine development.

Destination: China’s steel industry

China imports roughly 70 to 75% of all seaborne iron ore, receiving 1,100 to 1,200 million tonnes per year at terminals across the Bohai Bay, Yangtze River delta, and Pearl River delta industrial areas. The key receiving ports are Qingdao (Huangdao and董家口), Caofeidian (Tangshan Steel complex), Tianjin, Zhanjiang, Ningbo-Zhoushan, and the Yangtze River terminals at Nantong, Zhangjiagang, and Taicang. Each of these terminals has been purpose-engineered for high-volume ore offloading with conveyor and shiploader systems sized for Capesize and VLOC vessels.

Japan and South Korea each import 100 to 130 million tonnes per year for domestic blast furnace and DRI operations. Europe imports 90 to 120 million tonnes split across Dunkirk, Rotterdam, Taranto, and several smaller terminals. The geographic distribution of receiving ports, all far from the supply centres in Australia and Brazil, sustains voyage durations of 14 to 18 days (Australia-China), 32 to 36 days (Brazil-China), and 20 to 24 days (Brazil-Europe) that make ship utilization and fleet size critical cost factors.

Capesize and VLOC fleet structure

The economics of iron ore shipping pushed the fleet toward large vessels decades before the VLOC category was formalised. A Capesize bulk carrier is broadly defined as a vessel too large for the Panama Canal, typically with a deadweight of 100,000 to 200,000 DWT, and the 170,000 to 180,000 DWT Newcastlemax is the modern working standard for vessels that can call at both Port Hedland and Chinese receiving terminals. The 210,000 DWT Guaibamax, and ultimately the 400,000 DWT Valemax class, were developed specifically for the deeper water at Ponta da Madeira and the receiving draft windows at designated Chinese terminals.

VLOC operation imposes vessel-specific requirements that go beyond those for standard Capesize. The draft at Ponta da Madeira for a fully loaded Valemax is approximately 23 m, requiring dedicated deepwater berths. Not all Chinese terminals can receive VLOCs; the trade to those terminals from Vale Brazil is therefore mediated by transshipment at dedicated floating transshipment platforms (FSTPs) such as those at Subic Bay in the Philippines and the Olingapo facilities, where cargo is transferred to Capesize feeder vessels for onward delivery to draft-restricted terminals.

Loading rates and operations at major terminals

The dedicated iron ore terminals at Port Hedland, Dampier, Ponta da Madeira, and Tubarao are among the highest-throughput cargo handling facilities in the world. Port Hedland’s combined terminal capacity exceeds 600 million tonnes per year, served by shiploaders capable of 10,000 to 16,000 tonnes per hour on individual machines. Ponta da Madeira’s four shiploaders can achieve a combined throughput of 24,000 tonnes per hour on a single vessel, filling a Capesize hold of 25,000 to 30,000 tonnes capacity in approximately 90 minutes.

These rates create important logistical considerations for the vessel. At 12,000 tonnes per hour, a 170,000 DWT Capesize can be fully loaded in 14 to 15 hours of net loading time. The chief officer must complete all pre-loading calculations and confirmations before the first cargo enters the hold, because once loading begins at terminal rates there is no practical pause for correction. Draft surveys to verify cargo weight are taken after loading; any significant discrepancy between the declared and actual cargo weight must be identified before departure.

Hold preparation and pre-loading requirements

Hold condition for Group C lump ore

Before accepting lump iron ore on a Group C basis, the master and chief officer should confirm:

• Bilge suction systems are tested clear and operational. Iron ore’s abrasive nature means even a small proportion of fines in a nominally lump cargo can migrate into bilge wells and block strainer baskets. Covering well openings with burlap or heavy canvas before loading provides a physical barrier that slows migration without blocking suction flow.
• Hatch covers close with seals intact. Lump iron ore is not sensitive to rain infiltration in the way that Group A fines are, but water entering through defective covers adds to the vessel’s free surface and corrodes structural members over time.
• Hold cleanliness is adequate for the cargo grade. Iron ore buyers at Chinese and Japanese terminals test the received ore against the declared grade specification; contamination from a previous cargo of a different ore type or from coal residue can cause a quality claim.
• Ventilation closure is confirmed. The vessel should not ventilate holds of iron ore during the voyage; natural ventilation provides minimal benefit and draws moist outside air over the cargo surface, potentially promoting surface corrosion and condensation.

Hold condition for Group A iron ore fines

In addition to the Group C checks, Group A iron ore fines require:

• Bilge well covers or strainers are fitted before loading commences.
• The bilge alarm system is operational and tested.
• Hatch cover seals are fully watertight. A Group A fines cargo that absorbs rain during the voyage through a defective seal becomes a vessel liability, not a shipper failure. The cost of hatch-cover seal replacement before loading is small relative to the cost of a casualty or a cargo claim.
• The loading officer confirms the cargo declaration in writing, including the TML and the moisture content certificate.
• A baseline bilge sounding is taken in each hold before loading begins and recorded in the log. Subsequent soundings are measured against this baseline.
• Can tests are scheduled and materials are ready.

Draft survey and cargo weight determination

A draft survey is the standard method for determining the weight of iron ore loaded onto or discharged from a vessel. The procedure involves measuring the vessel’s draft at six locations (forward, midship, and aft on both port and starboard sides), measuring list and trim, consulting the vessel’s hydrostatic tables to determine displacement, and calculating cargo weight as the change in displacement between the light departure condition and the loaded arrival condition (or vice versa).

For iron ore, the draft survey is particularly important because the cargo’s high density means relatively small changes in hold fill depth correspond to large changes in cargo weight. A Capesize vessel loaded with iron ore to a displacement difference of 170,000 tonnes has a total cargo weight measurement accuracy, with a well-conducted draft survey, of approximately plus or minus 0.3 to 0.5%, corresponding to plus or minus 500 to 850 tonnes. This precision is sufficient for commercial purposes but not for detecting small discrepancies in individual hold fills.

Iron ore’s high density also means draft survey errors propagate more severely than for lighter cargoes. A 1 cm reading error in a draft mark on a Capesize corresponds to approximately 100 to 150 tonnes of displacement error. Surveyors conducting iron ore draft surveys must use calibrated devices and read each draft mark independently from multiple angles to minimize systematic error.

The draft survey is typically conducted by a surveyor appointed by the vessel’s P&I club or the cargo interests. Both shipper and receiver surveyors often attend, and any significant discrepancy between their results requires resolution before the bill of lading is issued. For large VLOC cargoes, where the nominal cargo weight is 350,000 to 400,000 tonnes, even a 0.1% error represents 350 to 400 tonnes of discrepancy, a commercially significant sum at iron ore spot prices.

Dust: health and operational management

Iron ore dust is generated during conveyor transfer, shiploading, and grab discharge operations. The dust fraction varies by ore type: dusty, fine-grained hematite ores from some Australian origins can generate significant visible dust plumes during loading, while coarser, moister Carajas magnetite ore loads with minimal visible dust. The health significance of iron ore dust is relatively limited compared to silica-bearing dusts: iron oxide itself is not classified as a carcinogen, and the relevant occupational exposure limit for iron oxide fume in most jurisdictions is 5 mg/m3 as a general dust standard. Workers should wear dust protection rated for inert dust during holds inspections and cargo-adjacent operations.

During loading, dust generation is controlled at terminal level by water sprays on conveyor transfer points and by shiploader design features that minimize drop height. The master has limited ability to influence the terminal’s dust management. But the vessel’s own enclosed spaces must be protected: accommodation air intakes should be switched to internal recirculation mode during loading if the prevailing wind carries dust toward the superstructure, since iron ore dust is highly abrasive and can damage air conditioning components.

After loading, iron ore in the hold presents minimal respiratory hazard because the cargo’s moisture content at loading binds the surface dust. During grab discharge at the receiving port, dust generation picks up as the cargo surface is broken by the grab. Workers in the hold for trimming or cleaning operations must wear appropriate respiratory protection, since discharge of dry, surface-eroded iron ore generates the highest dust concentrations of any point in the voyage.

Cargo documentation and declaration

What the shipper provides

For Group C lump iron ore, the shipper must provide before loading: a cargo declaration stating the Bulk Cargo Shipping Name (IRON ORE), the IMSBC Group (C), the chemical composition (iron grade, major gangue elements), the moisture content (typically measured within seven days of loading), the bulk density, and the stowage factor. The bulk density declaration is mandatory from 1 January 2025 under Amendment 07-23 (MSC.539(107)). No TML certificate is required for Group C cargo.

For Group A iron ore fines, the shipper must also provide: a TML certificate from an accredited laboratory, valid within six months of the commencement of loading, stating the TML value and the test method; and a moisture content certificate confirming testing within seven days before commencement of loading and a measured moisture below TML. All documentation must reach the master before loading commences; a master who starts loading without the complete set has no regulatory basis for compliance if the cargo causes an incident.

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 Group A iron ore fines when documentation is absent, outdated, or shows moisture content equal to or above TML. This right extends to Group C lump iron ore when the master has reason to believe the cargo’s actual particle size distribution meets the Group A criteria. The master’s refusal right is not merely permissive; it is a duty. Operating under commercial pressure to load non-compliant cargo, and then having cargo liquefaction occur, places full legal exposure on the master and the vessel’s P&I insurer.

The master who refuses to load must document clearly: a written statement to the charterer and shipper citing the specific regulatory basis for refusal; contemporaneous records of any can tests performed and their results; and a formal request for independent laboratory sampling through the P&I correspondent. Charter party demurrage clauses do not override the master’s statutory duty.

Discharge operations

Iron ore is discharged at receiving terminals by grab cranes mounted on quayside gantries or floating cranes. Grab capacities at major terminals range from 25 tonnes to 65 tonnes per cycle; high-capacity grabs at terminals like Qingdao Huangdao or Caofeidian can achieve discharge rates of 5,000 to 8,000 tonnes per hour per crane. Multiple cranes working simultaneously can achieve total discharge rates of 15,000 to 20,000 tonnes per hour on a Capesize vessel, giving total discharge times of 12 to 18 hours for a full cargo under good conditions.

Iron ore is abrasive and damages grab bucket lips, cable fittings, and crane sheaves over time. Terminal operators factor grab wear into maintenance schedules; the vessel’s crew has no control over the grab design or condition. But the vessel’s cargo hold internals, including ladders, bilge well covers, and frame coatings, take significant abrasive damage from repeated grab discharge operations and should be inspected and repaired during dry-docking.

After discharge, the hold will contain a residual layer of iron ore “clinker,” the consolidated, partially dried material from the bottom of the hold that adheres to the tanktop and frames and cannot be reached efficiently by the grab. This residue must be removed by manual shovel work before the hold is clean enough for a subsequent clean-cargo (grain, fertiliser) voyage, and may require light-pressure water washing to remove staining. For iron ore-to-iron ore repeat voyages, the clinker can be left as part of the tare for the next cargo’s draft survey.

Voyage monitoring for Group A iron ore fines

Once a Group A iron ore fines cargo is at sea, the vessel is committed. No practical intervention can reduce the cargo’s moisture content or reverse an advanced liquefaction state. Monitoring is the only tool.

Bilge well soundings are the primary indicator. Rising bilge water in a hold carrying iron ore fines at a rate not attributable to rain infiltration, condensation, or known leaks indicates moisture migration through the cargo, which is an early sign of pore-pressure development. Soundings should be taken at every watch change and logged. Any rate of increase that exceeds the baseline taken before loading should trigger immediate reporting to the operator and P&I club, and consideration of heading for a nearby port of refuge.

Roll period monitoring can indicate changes in the vessel’s effective metacentric height. A cargo that is liquefying reduces the vessel’s effective GM as the free liquid surface of the slurry acts like a free surface in a liquid tank. The roll period lengthens as GM falls. Officers who know the vessel’s normal loaded roll period can detect a lengthening of 10% or more as a warning sign, though weather and loading state must be considered as alternative explanations.

Cargo surface visual inspection is only possible when holds are accessed, which should follow enclosed-space entry procedures under SOLAS. If an inspection reveals surface cracking, subsidence, or visible moisture sheens at the cargo surface, the situation should be treated as a probable liquefaction event.

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.

The particle-size boundary between Group C and Group A iron ore is cargo-specific. No determination can be made without representative sampling and sieve analysis of the actual cargo being presented for loading. Two shipments from the same mine and stockpile in the same week can fall on opposite sides of the 10% / 50% fines criterion depending on weather, stockpile age, and re-handling history.

TML values cited in this article are illustrative ranges drawn from published industry data and investigation reports. TML for any specific consignment of iron ore fines must be determined by laboratory testing of a representative sample from that consignment, following IMSBC Code Appendix 2 procedures, within the six-month validity window. Applying a generic TML value from tables or from a previous shipment to a new cargo is a regulatory non-compliance.

Tanktop permitted distributed load values cited in this article are illustrative. Every vessel has hold-specific PDL values specified in its approved loading manual. Masters must use those vessel-specific values, not industry generalizations.

The draft survey accuracy and trade volume data cited in this article reflect public reporting and professional literature available to mid-2026. Trade volumes shift with steel production cycles, port capacity expansions, and policy changes in exporting countries.

Regulatory requirements may differ between flag state and port state where the port state has implemented amendments the flag state has not yet adopted. Masters should confirm which edition of the IMSBC Code is applied by the competent authority of the loading port, particularly for ports in countries with historically delayed implementation of IMO amendments.

See also

• IMSBC Code
• IMSBC Group A Cargoes: Cargoes That May Liquefy
• IMSBC Group C Cargoes: Non-Hazardous Solid Bulk Cargoes
• Cargo Liquefaction: TML, FMP, and Group A Controls
• Iron Ore Concentrate: IMSBC Code Schedule and Carriage
• Iron Ore Pellets: IMSBC Code Schedule and Carriage
• Bulk Carrier
• SOLAS Chapter XII: Additional Safety Measures for Bulk Carriers

Related calculators:

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