Chrome Ore: IMSBC Code Schedule and Carriage

Chrome ore (chromite, FeCr2O4) is one of the densest mainstream dry bulk cargoes, with bulk density typically between 2,000 and 3,200 kg/m3 and a stowage factor of 0.31 to 0.50 m3/t. The IMSBC Code classifies lump and crushed chromite as Group C, meaning it is not liable to liquefy and carries no significant chemical hazard in its trivalent form, but the extreme density places tanktop structural loading at the centre of every chrome ore loading plan. Fines-grade chromite with elevated moisture may qualify as Group A and require Transportable Moisture Limit certification. The cargo moves in large volumes between South Africa, Kazakhstan, and Turkey on one side and Chinese stainless steel and ferrochrome plants on the other.

Chrome ore is the only commercial source of chromium, an element without which modern stainless steel, heat-resistant superalloys, chrome plating, and refractory linings for steelmaking furnaces would not be possible. Global seaborne chrome ore trade runs at approximately 12 to 18 million tonnes per year, a figure that has grown sharply since China’s stainless steel production expanded past 30 million tonnes per year in the early 2010s. The ore travels overwhelmingly in Supramax and Panamax bulk carriers from South African, Kazakhstani, and Turkish ports to Chinese receivers, with secondary flows to Japanese, South Korean, and Indian ferro-alloy plants.

The IMSBC Code, adopted by IMO Resolution MSC.268(85) and mandatory from January 2011, covers chrome ore under the CHROME ORE schedule entry in Appendix 1. Carriage rules differ between lump-grade chromite (Group C, no liquefiable character) and chrome ore fines with high moisture content (which may fall under Group A if the particle size distribution and moisture create a liquefaction risk). The dominant practical challenge for chrome ore is not chemical but physical: the cargo’s weight presses down on the tanktop with a force that can exceed the structural rating of the ship if loading is not carefully planned and distributed across holds.

IMSBC schedule entry and cargo classification

Schedule particulars

The IMSBC Code Appendix 1 schedule for CHROME ORE records the following principal parameters. These figures reflect the current consolidated edition as amended by Resolution MSC.539(107) (Amendment 07-23, mandatory from 1 January 2025):

The Group C classification for lump chrome ore means the cargo does not require Transportable Moisture Limit certification, is not subject to the can test screening requirement, and can be loaded without the pre-loading TML and moisture certificates that Group A cargoes demand. This is the key procedural distinction between chrome ore lump and chrome ore fines. The absence of a liquefaction requirement does not mean the cargo is without hazard; it means the principal hazards are structural and dust-related rather than stability-related.

Group A reclassification for chrome ore fines

Chrome ore fines with a particle size distribution where a significant proportion falls below 1 mm and the moisture content is elevated may exhibit a liquefaction-susceptible character. In that case, the shipper’s competent authority may require the cargo to be handled under Group A procedures, including laboratory TML determination and the shipper’s moisture content certification within seven days of loading. Amendment 07-23 did not alter the fundamental group assignment of lump chromite, but by requiring declared bulk density it tightened the information baseline for all solid bulk cargo declarations, including Group C cargoes.

The distinction matters operationally. A consignment of chrome ore described simply as “chrome ore” without particle size specification could be lump material handled as Group C, or it could be milled fines that belong in Group A. Cargo surveyors and the ship’s master should verify the particle size distribution in the shipper’s declaration before accepting the cargo classification. A cargo with more than 10 per cent of particles below 1 mm and more than 50 per cent below 10 mm, combined with a moisture content near the flow moisture point, is in practice a Group A cargo regardless of what commercial name the shipper assigns it.

The IMSBC Code schedule for CHROME ORE CONCENTRATE exists as a separate Appendix 1 entry covering beneficiated chromite from gravity separation or flotation milling. Chrome ore concentrate is explicitly Group A. That entry is distinct from the CHROME ORE entry and from the discussion in this article, but the boundary between “crushed chrome ore with fines” and “chrome ore concentrate” is not always obvious from the shipper’s documentation, and masters should request clarification if the declared product description is ambiguous.

The Amendment 07-23 bulk density requirement

Resolution MSC.539(107), adopted at MSC 107 on 8 June 2023 and mandatory from 1 January 2025, introduced a requirement for shippers to declare bulk density on cargo declarations for all solid bulk cargoes. For Group C chrome ore, this change is particularly consequential. Before Amendment 07-23, chrome ore shippers routinely provided only a general description of the cargo grade. A Panamax receiving chrome ore from the Bushveld Complex might work from a generic stowage factor of 0.40 to 0.45 m3/t without knowing whether the actual consignment was closer to 0.31 (dense lumpy ore) or 0.50 (fine crushed grade), a difference that directly affects whether the tanktop loading limit is approached or exceeded.

Post-Amendment 07-23, the shipper must provide an actual bulk density value, tested on the consignment or from a recent representative sample of that grade. This declared value becomes part of the cargo documentation the master must review before loading. If the declared bulk density indicates that loading the full cargo in the planned number of holds would exceed the class-rated tanktop loading capacity, the loading plan must be revised before the first tonne enters the hold.

The chromite mineral and trade fundamentals

Mineralogy and composition

Chromite is an iron-chromium oxide mineral with the formula FeCr2O4, a member of the spinel group. In the spinel structure, iron occupies octahedral sites and chromium occupies tetrahedral sites in the oxygen lattice. The crystal structure is unusually stable, which accounts for chromite’s resistance to reduction and its use as a refractory material in steelmaking furnace linings. Natural chromite ores vary in their Cr2O3 content from as low as 18 per cent in lean refractory grades to over 50 per cent in high-grade metallurgical ore.

Commercial chromite is sold into three distinct markets. Metallurgical-grade ore (Cr2O3 content typically 44 to 50 per cent, Cr:Fe ratio above 2.0) goes to ferrochrome production for stainless steel alloy additions. Chemical-grade ore (Cr2O3 40 to 46 per cent) feeds chromium compound manufacturing for chrome plating, pigments, and tanning agents. Refractory-grade ore (Cr2O3 as low as 30 per cent but with low silica and high alumina) goes to brickmaking for furnace linings. Each grade has a slightly different physical character, and bulk densities differ somewhat between them.

The spinel crystal structure gives chromite a relatively high specific gravity of 4.0 to 4.8, making it one of the heaviest naturally occurring industrial minerals. The bulk density of a cargo depends on how tightly the individual crystals and grain aggregates pack, which in turn depends on the lump size distribution and the degree of fines fill between the larger pieces. A coarse-lump cargo with minimal fines packs loosely; a mixed-grade cargo where fines fill the voids between lumps approaches the mineral’s specific gravity more closely. Reported bulk densities in commercial chrome ore shipments range from 1,950 kg/m3 for coarse lump with low fines fill to 3,200 kg/m3 for dense crushed ore with high fines content.

Global production and trade structure

South Africa’s Bushveld Igneous Complex is the world’s largest chromite deposit by a substantial margin, containing an estimated 5.5 billion tonnes of metallurgical-grade ore reserves. The Bushveld supplies roughly 44 to 50 per cent of annual global chromite output, exported through three principal port terminals: the Port of Richards Bay, Port Elizabeth (now Gqeberha), and Saldanha Bay. Richards Bay handles the largest tonnage, with dedicated chrome ore shiploaders and stackers at the bulk terminal. South Africa exported approximately 16 to 17 million tonnes of chrome ore in 2023 according to industry trade data, the majority to China.

Kazakhstan is the second-ranked exporter. The Donskoy ore mining complex in the Aktobe region and the Khromtau deposits supply high-grade metallurgical chromite to Russian and Chinese receivers. Kazakh exports move overland to Russian Black Sea ports or are trans-shipped through Caspian-Volga river routes in smaller volumes. Turkey has historically been a significant European supplier, with deposits in the Guleman, Elekdag, and Bursa regions. India exports chromite from the Sukinda valley in Odisha state, one of the largest chromite deposits outside South Africa, via Paradip and Dhamra ports on India’s east coast. Zimbabwe, with the Great Dyke complex, is a growing supplier. Albania, Finland, and Cuba supply minor volumes to regional European and North American receivers.

China absorbs approximately 60 to 65 per cent of global seaborne chromite imports. Chinese stainless steel production, which reached approximately 35 million tonnes in 2023, requires large quantities of ferrochrome alloy, and the country’s domestic chromite supply is far short of demand. Chinese ferrochrome producers import ore directly for smelting in coastal and inland facilities. India, despite being an exporter, imports specific high-grade metallurgical chromite for premium applications. Japan and South Korea import for established ferrochrome smelting operations.

Tanktop loading: the dominant structural concern

Why chrome ore stresses the tanktop

Tanktop structural loading is the primary operational concern for chrome ore, because the cargo’s high bulk density means a shallow fill of the hold exerts a very high pressure per unit area on the tanktop plates and the double-bottom structure beneath them. No other Group C cargo routinely reaches the pressures generated by a full chrome ore load in a standard bulk carrier hold.

The tanktop loading capacity of a bulk carrier is expressed in tonnes per square metre (t/m2) and is specified by the classification society for each hold. Typical ratings for Supramax and Panamax bulk carriers lie between 10 and 20 t/m2 depending on design vintage and class, though some older or lighter-construction vessels rate as low as 7.5 t/m2. The rating is the maximum uniform load that the tanktop structure can sustain without permanent deformation. A concentrated point load, such as a bulldozer track plate resting on the tanktop during trimming operations, is rated separately and usually at a lower limit.

The pressure a cargo column exerts on the tanktop is the product of the bulk density and the column height:

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 cargo column height in metres. Converting to practical units, a 2,800 kg/m3 chrome ore cargo loaded to a depth of $h$ metres exerts a pressure of $2800 \times 9.81 \times h$ Pa, or approximately $27.5h$ kPa. At a hold fill depth of 5 metres that is 137.5 kPa, equivalent to approximately 14.0 t/m2. A bulk carrier with a 12 t/m2 tanktop rating cannot accept that loading in any hold.

The loading planner’s task is to ensure that no hold, and no localised zone within any hold, receives a load exceeding the class rating. For chrome ore this typically means:

1. Calculating the maximum fill depth per hold that keeps the load at or below the tanktop rating, using the shipper’s declared bulk density.
2. Distributing the cargo across the maximum number of holds to reduce the per-hold tonnage.
3. Avoiding a single-hold plan or a plan where one or two holds take a disproportionate share, which would allow those holds to overfill while others are empty or lightly loaded.

The declared bulk density requirement introduced by Amendment 07-23 directly supports this calculation. Without a reliable declared density, the loading planner must use a conservative estimate, which may result in an unnecessarily restricted loading programme, or an optimistic estimate, which risks exceeding the structural limit.

Uneven load distribution and the 5% rule

Even within a correctly loaded hold, an uneven cargo surface creates uneven pressure distribution. A mound of chrome ore in the centre of a hold, with the tanktop exposed and unloaded near the hopper sides, places the full structural load on the central area while the periphery carries nothing. This localised concentration can exceed the tanktop rating even when the average load for the hold is within the rated value.

The IMSBC Code requires that bulk cargoes be trimmed so that the height difference between peaks and troughs does not exceed 5 per cent of the ship’s breadth. For a Supramax with a breadth of 32 metres, that is a maximum height difference of 1.6 metres. For dense chrome ore, a 1.6-metre difference in fill depth corresponds to a pressure difference of approximately 44 kPa at the peak relative to the trough, which is a structurally meaningful difference.

Trimming chrome ore manually in the hold requires careful attention to the bulldozer track loading limit. On vessels where the class certificate specifies a bulldozer weight and track plate area limit, exceeding that limit is a separate structural hazard distinct from the overall tanktop loading. Operators should confirm the bulldozer limits with the classification society’s certificate before deploying equipment in the hold.

Hog and sag bending moments

Beyond the tanktop, dense chrome ore affects the ship’s global bending moment. A fully loaded Panamax carrying chrome ore in all holds will produce a sagging bending moment in the midship region that may approach or exceed the permissible sagging limit in the stability instrument. The loading computer must be used to verify that both the shear force and bending moment at each section along the ship’s length remain within the permissible envelope throughout loading, not just at completion.

This concern is greatest during the intermediate stages of loading, when some holds are full and others are empty. The pattern of alternating full and empty holds, common in dense-cargo loading sequences, maximises the differential bending moment. Chrome ore loading plans should avoid any intermediate sequence that leaves adjacent holds at extreme fill differentials. A common practice is to load all holds simultaneously and progressively, keeping the distribution approximately balanced at every stage, rather than filling holds one by one.

Dust hazard and health protection

Dust generation and composition

Chrome ore generates dust during loading and discharge, during conveying operations, and when cargo is handled in windy conditions. The dust consists of fine chromite particles and associated gangue minerals, primarily silicate gangue (serpentine, talc, chlorite) from the surrounding rock matrix. For high-grade metallurgical chromite, the gangue content is low and the dust is predominantly chromite mineral. For lower-grade ores from some deposits, the silicate gangue fraction in the dust may be higher.

Trivalent chromium Cr(III), the form present in chromite spinel, is of low acute toxicity and is not classified as carcinogenic by major regulatory agencies at the exposure levels encountered in normal cargo handling. Hexavalent chromium Cr(VI), which is toxic and carcinogenic at low concentrations, can be present on the surface of chromite particles as a result of surface oxidation during weathering and stockpiling. The proportion of Cr(VI) in chrome ore dust from different deposits varies. Some sources report Cr(VI) levels below 0.1 per cent of total chromium in mine and port dust; others report higher fractions from ore that has been stored exposed to the weather for extended periods.

The IMSBC Code schedule for CHROME ORE notes that dust may be a health hazard and that personnel should avoid inhalation of dust. This reflects the uncertainty about Cr(VI) content rather than the toxicity of pure chromite. The precautionary approach, well-fitting respiratory protection, dust suppression during loading and trimming operations, and shower and change facilities for cargo workers, is appropriate regardless of the exact Cr(VI) fraction.

Hold atmosphere and crew entry

Chrome ore is not a self-heating cargo and does not generate flammable or toxic gases. The hold atmosphere after loading is not oxygen-depleted by chemical reaction as it would be with coal or some sulphide concentrates. Hold entry after a chrome ore voyage, for inspection or tank cleaning purposes, can be treated by normal enclosed-space entry procedures: check oxygen content with a calibrated instrument before entry, confirm the level exceeds 19.5 per cent by volume, and maintain continuous atmospheric monitoring during the entry period.

Dust accumulation on hatch coaming ledges, ventilators, and hold structure after chrome ore loading can become a source of airborne dust when the vessel is at sea in rough weather if hatches are opened. The dust residue on exterior surfaces of the hatch covers and deck should be washed down before departure to avoid contaminating the marine environment and the vessel’s superstructure.

Dust suppression at terminals

Major chrome ore export terminals, particularly at Richards Bay and Saldanha Bay in South Africa, operate dust suppression systems at shiploader transfer points and along conveyor belts to meet local environmental standards. These typically consist of water sprays at transfer points and enclosed conveyor gallery sections near the loading arm. The degree of dust suppression varies with the terminal’s infrastructure age and the regulatory environment of the port state.

Loading under conditions of strong onshore wind, particularly if the wind blows across the open hatch during loading, can carry dust from the cargo stream into accommodation areas and onto the ship’s navigation instruments. Vessel operators should assess wind direction before loading and, if necessary, request a change in berth orientation from the terminal to minimise dust exposure to the ship’s accommodation and open decks.

Hold preparation for chrome ore

Cleanliness requirements

Chrome ore is a Group C cargo with no chemical incompatibility concerns under normal circumstances. The IMSBC Code requires that holds be clean and dry before loading any solid bulk cargo. For chrome ore, the practical cleaning requirement is that no residues from previous cargoes remain in the hold, particularly residues of cargo types that could contaminate the chromite and reduce its quality. Chrome ore bought by ferrochrome smelters is often subject to tight assay specifications; contamination with salt, fertiliser, or incompatible mineral dust could lead to cargo claims.

The cleaning sequence after a previous bulk cargo is typically: dry sweep or mechanical shovel out of residues, manual inspection of structural recesses, bilge wells, and frames, water wash if the previous cargo was hygroscopic or chemically reactive, and final drying before inspection and acceptance by the loading surveyor.

For chrome ore following another dense mineral cargo such as iron ore or bauxite, a dry-clean-only sequence is generally sufficient. For chrome ore following coal, potash, fertiliser, or a sulphide concentrate, a fresh-water wash and thorough drying are essential.

Bilge well inspection

Bilge wells should be tested for suction before loading chrome ore. Chrome ore fines can migrate into bilge wells during loading and the sea passage, particularly if the cargo is on the finer end of the lump size range. Chromite fines that compact in bilge wells and suction pipes can be difficult to remove and may block suction during the voyage. Suction test results should be recorded in the ship’s log before departure.

Some operators fit canvas or burlap suction strainer bags over the bilge well openings before loading dense mineral cargoes to prevent fine particles from entering the suction system. This practice is noted in P&I club guidance but is not a mandatory IMSBC Code requirement for Group C chrome ore. Operators using this method should confirm that the strainer does not reduce suction capacity below the required pump-out rate.

Hatch cover inspection and maintenance

Chrome ore does not require sealed holds during the voyage, because it is not a cargo that generates toxic or flammable gases, and it does not need to be protected from moisture for the purpose of preventing cargo degradation. However, water ingress through defective hatch covers can raise the moisture content of fine-grade chrome ore to a point where the cargo becomes more fluid on discharge, and consistent water ingress over a long voyage can wet chrome ore fines to the point of creating drainage issues.

Hatch cover rubber seals should be inspected and confirmed to make proper contact with the coaming seal bars before loading. Damaged or missing sections of hatch cover drain channel rubber should be replaced. The chalk test, running a chalk-covered piece of rubber seal around the contact surface and verifying even chalk transfer to the coaming surface, is a practical check on hatch cover seal integrity.

Trimming chrome ore

Self-trimming characteristics

Lump chrome ore with a mixed particle size distribution self-trims reasonably well from a shiploader spout during loading. The cargo flows outward from the deposition point under gravity, distributing itself across the hold floor in a roughly conical pattern. As the hold fills, the cone flattens. For holds receiving cargo from a fixed or luffing shiploader boom, the deposition pattern can be adjusted by moving the vessel fore and aft along the berth or by swinging the shiploader boom.

The degree of self-trimming depends on the moisture content and the particle size distribution. Dry lump ore with little fines flows freely. Moist fine-crushed ore may pile under the spout without spreading adequately. In the latter case, mechanical trimming with a bulldozer or cargo redistribution by grab is needed to achieve a level surface within the 5 per cent of beam height-difference tolerance.

Trimming at hatch closure

Before the final hold is closed, the hatch covers must close without obstruction from the cargo surface. Chrome ore’s angle of repose of approximately 35 to 40 degrees means that material piled above the hatch coaming level will slide back into the hold when the coaming is approached by the cover, but only if the pile is not so high that the sliding cargo remains above the coaming lip after settling. The loading plan should ensure that the final fill leaves the cargo surface at or slightly below hatch coaming level after the self-trimming angle is accounted for.

If cargo protrudes above the coaming plane after the loading programme is complete, additional trimming is required before the covers are closed. Chrome ore that bridges the coaming and is caught between the cover and the coaming on closing will damage either the hatch cover edge or the sealing rubber. Damage at this stage may not be apparent until the vessel is at sea and rain water tests the seal.

Hold-to-hold sequencing during loading

Chrome ore loading at major South African terminals typically proceeds at high rates of 2,000 to 6,000 tonnes per hour for Supramax and Panamax vessels. At these loading rates, the vessel’s stability condition changes rapidly. The loading officer should monitor the stability computer at intervals no longer than every 500 tonnes and verify that the bending moment and shear force profiles remain within the permissible envelope at each stage. Vessels loading chrome ore on a departure-stability letter that describes a specific sequence must follow that sequence; deviating from it to accommodate a terminal’s loading convenience is a structural risk.

The typical loading sequence for a Panamax carrying chrome ore is to load the midship holds partially first to establish a baseline bending moment, then fill fore and aft alternately, maintaining approximate balance. End-hold filling at the extremes of the vessel while midship holds remain light creates sagging bending moments. Full filling of midship holds before end holds creates hogging. Either condition can approach or exceed permissible limits at maximum cargo weight on dense-cargo ships.

Draft survey and cargo quantity determination

Draft surveys are the standard method for determining the quantity of chrome ore loaded or discharged, because the cargo’s density and flowability make continuous weighbelt measurement less reliable than for lighter bulk cargoes. The cargo draught survey involves reading drafts at six points (fore, aft, and amidships on each side), correcting for trim, hull deflection, dock water density, and constant, and computing the displacement change between the pre-loading and post-loading conditions.

Chrome ore’s high density means that a Panamax carries a maximum chrome ore deadweight that is often limited by the tanktop loading constraint rather than by deadweight tonnage. A vessel rated at 76,000 tonnes deadweight might be limited to 55,000 to 60,000 tonnes of chrome ore by its tanktop capacity, carrying approximately 0.50 to 0.53 m3/t of stowage factor equivalent in void spaces. The draft survey will record a displacement change well within the vessel’s loadline limit even though the cargo hold is structurally fully loaded.

This partial loading condition can introduce errors in draft survey calculations if the surveyor applies standard allowances calibrated for a fully loaded vessel. The vessel’s stability booklet and hydrostatic tables remain the correct reference, but the constant (the difference between the calculated lightweight and the actual measured lightweight) should be verified before any cargo quantity dispute proceeds to formal survey.

Loading and discharge operations

Port terminal infrastructure

Chrome ore export terminals at Richards Bay (Bulk Terminal 1 and the dedicated chrome ore facility), Saldanha Bay, and Port Elizabeth (Gqeberha) operate continuous shiploaders fed by conveyor belts from open stockyards. Richards Bay Bulk Terminal can handle multiple vessel grades simultaneously. Loading rates at Richards Bay for chrome ore typically run at 3,000 to 5,000 t/h per shiploader. At Saldanha Bay, the terminal handles both iron ore and chrome ore through the same infrastructure; chrome ore loading rates are typically lower because the terminal is optimised for the higher-volume iron ore trade.

Kazakh exports transit overland through Russia to the port of Novorossiysk on the Black Sea, where chrome ore is loaded at multi-commodity bulk terminals. The terminal infrastructure at Novorossiysk is less specialised than South Africa’s dedicated chrome facilities, and loading rates are generally lower. Turkish exports load at Mediterranean ports including Mersin, Iskenderun, and Izmir, through general bulk terminals.

Loading plan and shipper communication

Before the vessel berths for loading, the ship’s officer should receive from the shipper or charterer:

• The cargo declaration confirming BCSN, group, bulk density (mandatory post-Amendment 07-23), chemical composition, and quantity per hold.
• The loading plan showing the intended quantity per hold, the loading sequence, and the anticipated loading rate.
• The cargo temperature certificate if the ore has been stored in conditions that could affect temperature (less relevant for chrome ore than for self-heating cargoes, but some ore from underground mines retains elevated temperatures after recent blasting).

The first officer should verify that the declared bulk density, combined with the intended fill depth per hold, keeps every hold within the class-rated tanktop loading capacity. Any hold that would exceed the rating under the proposed plan must be flagged to the terminal and the charterer for redistribution before loading starts.

Discharge operations and grab wear

Chrome ore discharges by shore grab crane at receiving terminals, which are typically adjacent to ferrochrome smelters or to railway and road connections serving inland smelters. Chromite is a hard mineral with a Mohs hardness of approximately 5.5 to 6.0, comparable to feldspar. Grab teeth, jaws, and the conveyor belts at receiving terminals experience measurable wear from chrome ore. This wear rate is higher than for coal, salt, or grain, but lower than for hard rock ballast or dense abrasive ores such as aluminium silicate.

Efficient grab discharge from a chrome ore cargo requires that the vessel maintain an even keel during discharge or that the trim be corrected progressively as cargo is removed. Chrome ore in the lower part of the hold, near the bilge well and sloping hopper sides, may not be accessible to the grab jaw and will require manual cleanup. Chrome ore that has compacted during the voyage, particularly if any moisture migration occurred, may form a firm consolidated mass in the lower cargo layers. Operators should be prepared to use small hydraulic excavators or manual methods for the final cleanup.

Sea passage considerations

Chrome ore does not require ventilation during the sea passage. The IMSBC Code schedule for chrome ore does not impose ventilation requirements because the cargo does not generate gases, does not heat, and does not suffer quality degradation from contained atmosphere. Hatch covers should remain closed during the voyage both to prevent water ingress and to prevent cargo dust from leaving the hold in the ventilation stream.

Monitoring bilge well levels during the passage is standard practice. Chrome ore should not generate significant bilge drainage on a Group C cargo basis. If bilge levels rise during the voyage at a rate that cannot be explained by condensation or minor hatch seal seepage, it may indicate that fine cargo migration is occurring into the bilge system. The master should record bilge sounding readings daily and investigate any upward trend before it becomes a drainage capacity problem.

The lump vs. fines distinction in practice

Commercial chrome ore grades and particle sizes

Chrome ore arrives at port in several particle size grades that reflect different stages of processing at the mine and concentrator:

• Run-of-mine lump (50 to 150 mm): the coarsest grade, directly blasted and screened, with low fines content. This grade has the lowest bulk density and highest stowage factor within the chrome ore range, typically 2,000 to 2,300 kg/m3 and 0.43 to 0.50 m3/t.
• Crushed lump (6 to 50 mm): primary crushing product, the most widely traded metallurgical grade. Bulk density typically 2,300 to 2,700 kg/m3.
• Lumpy fines (1 to 25 mm with significant sub-1 mm fraction): produced by crushing without screening, contains a mixed distribution. Bulk density 2,500 to 2,900 kg/m3.
• Chrome fines (below 10 mm, sometimes below 2 mm): the dust-generating grade, often a byproduct of lumpy ore processing, or a lower-grade ore that does not yield clean lump on crushing. Bulk density can approach 2,800 to 3,200 kg/m3 at high compaction. This is the grade where Group A reclassification becomes relevant at elevated moisture.

In the South African chrome market, “lumpy ore” typically refers to the 6 to 50 mm crushed grade, while “chrome fines” refers to material predominantly below 6 mm. Pelletised chrome (chrome ore pellets) is a distinct product produced from chrome fines by agglomeration with a binder, and is explicitly Group C regardless of moisture in its pelletised form, because pelletisation changes the physical character of the material. Chrome ore pellets have their own considerations, including pellet strength and tendency to generate fines from pellet breakage during loading and the voyage.

When chrome ore fines cross into Group A

The IMSBC Code does not set a bright-line particle size or moisture threshold at which chrome ore fines automatically become Group A. The Code’s general criterion for Group A classification is that a cargo may liquefy if shipped above its Transportable Moisture Limit, and the TML testing procedures in Appendix 2 are applied to the specific cargo in question.

For chrome ore fines in practice, competent authorities and cargo surveyors apply a similar approach to that used for iron ore and mineral concentrates: if the cargo has a substantial proportion (often taken as more than 10 per cent) of particles below 1 mm and the in-situ moisture content is elevated relative to historical TML values for similar grades, a TML test is prudent before proceeding on a Group C assumption. Several P&I clubs have published guidance recommending pre-loading TML testing for any chrome ore fines grade where the moisture content is declared above 3 to 4 per cent.

The incentive to avoid Group A classification is commercial: Group A imposes a certification cost and a loading delay if testing is needed, and requires the shipper to maintain moisture content below TML, which may mean additional drying or blending of stockpiled ore. Competent authorities in South Africa and Kazakhstan have issued guidance on which chrome ore grades require TML certification; masters loading at smaller or less regulated ports should not assume that the absence of a TML certificate means the cargo is unambiguously Group C.

Pelletised chrome ore: Group C regardless of moisture

Chrome ore pellets, where the fine chrome ore has been mixed with a binder, shaped into pellets of approximately 8 to 16 mm diameter, and hardened by baking or chemical binding, behave as Group C material even when the underlying chrome ore fines would be Group A in unprocessed form. This is because pelletisation changes the effective particle size and the physical character of the material: the pellets are discrete, self-supporting solid shapes rather than a fine granular mass, and they do not pack under vibration and pore water pressure in the same way that fine grains do.

The key practical caveat is pellet durability. Pellets that break down significantly during loading and the sea voyage into a high-fines mass can reacquire some Group A character. Where chrome ore moves in pelletized or briquetted form, crushing strength matters: pellets must be durable enough to survive handling without breaking down into a high-fines mass that could reacquire Group A character. Shippers should certify pellet quality, including crushing strength where relevant. A consignment of undersized or structurally weak pellets that breaks down heavily during loading should be treated with caution.

Cargo degradation and quality issues

Moisture effects on discharge quality

Group C chrome ore does not degrade in the way that coal or grain does when exposed to moisture during the voyage, because chromite is a chemically inert mineral stable in the presence of water. However, wet chrome fines compact under the weight of the overlying cargo during the voyage and become a dense consolidated mass that is harder to discharge by grab. Fine chrome ore that arrives at a Chinese receiving port in a wetted and compacted condition may attract a freight claim if the charter party specifies a maximum moisture content for the cargo.

Some smelter operators specify a maximum moisture content of 5 to 8 per cent for chrome ore fines because higher moisture increases the energy cost of pre-heating the ore before charging to the furnace. Monitoring hold ventilation closure and hatch cover integrity during the voyage, while not a formal IMSBC Code obligation for Group C chrome ore, protects the shipper’s quality interests as well as the vessel’s structural interests.

Silica content and dust toxicity

The gangue minerals in chrome ore from different deposits vary in silica content. South African Bushveld ore has relatively low silica; some Turkish and Indian deposits have higher silica gangue. High-silica chrome ore dust, particularly if it contains crystalline silica (quartz) rather than amorphous silica, is a respiratory hazard distinct from the chromium concern. Prolonged inhalation of respirable crystalline silica causes silicosis, a progressive fibrotic lung disease. Cargo handlers, stevedores, and ship’s crew working in dusty conditions during loading or discharge of high-silica chrome ore should have appropriate respiratory protection.

The IMSBC Code cargo schedule notes dust as a health concern for chrome ore but does not quantify the specific silica risk, reflecting the variability between ore sources. Operators loading at ports where the chrome ore origin and silica content are not well characterised should request the Material Safety Data Sheet (MSDS) or Safety Data Sheet (SDS) from the shipper and check the silica content declaration.

South Africa-to-China trade: route and vessel selection

The Panamax and Supramax segment

Chrome ore from South Africa to China travels approximately 11,800 nautical miles around the Cape of Good Hope, a voyage of approximately 30 to 38 days at a service speed of 12 to 14 knots. The cargo economics do not support the very large capesize vessels (180,000 dwt and above) that dominate iron ore trade, because chrome ore volumes per shipment are smaller and the receiving terminals in China are not universally capable of handling capesize drafts. Supramax (52,000 to 64,000 dwt) and Panamax (65,000 to 82,000 dwt) bulk carriers dominate the South Africa-to-China chrome ore trade.

For a Panamax carrying 55,000 to 60,000 tonnes of chrome ore, the tanktop loading constraint is the binding limit for most vessels. The cargo fills a smaller volume than the vessel’s grain capacity, leaving void space in each hold above the cargo surface. The vessel arrives at the discharge port with a draft well below its maximum allowable draft under the applicable loadline zone. This is expected and normal for dense mineral cargoes.

Ballast voyage and trading pattern

The Panamax chrome ore trade often pairs South Africa-to-China southbound chrome ore voyages with China-to-South Africa or China-to-Brazil iron ore ballast voyages. The vessel may ballast from Chinese discharge ports to Australian iron ore loading ports for a trans-Pacific voyage before returning to Southern Africa. Chrome ore’s trade pattern does not produce a tight triangular route; the ballast leg is an independent fixture.

Fuel consumption on a chrome ore voyage is higher per cargo tonne than on an iron ore voyage in a larger capesize, because the Panamax carries less cargo per unit of ship resistance. Slow steaming at 11 to 12 knots is common on the South Africa route to reduce fuel costs. The tanktop loading restriction means that the vessel’s fuel efficiency, measured in dollars per cargo tonne delivered, is inherently less favourable than for a capesize on an iron ore voyage.

Comparison with related dense mineral cargoes

Chrome ore shares its high bulk density and tanktop loading concern with several other dry bulk cargoes. Iron ore lump and iron ore pellets are also Group C but with a density range of approximately 1,900 to 2,600 kg/m3 for lump ore and 2,000 to 2,400 kg/m3 for pellets. Manganese ore has a bulk density of approximately 2,000 to 2,500 kg/m3, comparable to the lower end of the chrome ore range. Barytes (barium sulphate) is the densest common Group C bulk cargo, at approximately 2,400 to 2,900 kg/m3, and presents tanktop concerns similar to chrome ore.

The distinguishing feature of chrome ore among this group is the combination of high density across all size fractions (including the finer fractions that bring bulk density above 2,800 kg/m3 at high compaction) and the potential reclassification to Group A for fine grades. Iron ore pellets are Group C regardless of moisture. Manganese ore lump is Group C. Chrome fines can be Group A. This makes the particle size declaration and the Group assignment more important for chrome ore than for most comparable dense cargoes.

Nickel ore presents a different risk profile: its typical bulk density is lower (1,000 to 1,700 kg/m3), its moisture sensitivity is much higher, and it has caused some of the most notable Group A liquefaction casualties of the past two decades. Chrome ore lump does not share that liquefaction vulnerability, but operators who work across the dense-mineral bulk trade should recognise that chrome fines and nickel ore require quite different approaches to pre-loading certification.

IMSBC Code compliance checklist for chrome ore

The following steps reflect the IMSBC Code requirements as amended by MSC.539(107) for a Group C chrome ore cargo on a standard bulk carrier. They are not a substitute for the official Code text.

Before berthing for loading:

• Confirm receipt of the cargo declaration, which must include BCSN, hazard group, chemical composition, declared quantity, and declared bulk density (mandatory from January 2025).
• Verify that the bulk density declared, combined with the intended fill depth, keeps each hold within the class-rated tanktop loading capacity.
• Confirm the loading plan is approved by the master and the loading officer.
• Verify hold cleanliness and bilge suction test completion.
• Confirm hatch cover seal integrity by chalk test or equivalent.

During loading:

• Monitor the stability computer at regular intervals, not exceeding every 500 tonnes.
• Verify trim compliance (maximum height difference 5 per cent of ship breadth) at each hold before the hatch is closed.
• Observe dust conditions and ensure personnel in dusty work areas have appropriate respiratory protection.
• If the cargo appearance suggests unusually wet or fine material, contact the master and request independent surveyor attendance before continuing.

Before departure:

• Record bilge sounding readings as the pre-voyage baseline.
• Confirm hatch covers are fully closed and latched.
• Confirm deck dust wash-down has been completed.
• Verify the cargo declaration, bills of lading, and manifest are consistent with the quantity actually loaded.

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 official IMSBC Code text is the authoritative source; this article does not reproduce schedule tables verbatim and does not substitute for access to the current official text.

Bulk density values cited in this article are indicative ranges drawn from the IMSBC Code schedule, published commodity specifications, and trade practice. The actual bulk density of a specific chrome ore consignment must be declared by the shipper based on testing of that consignment or of a representative recent sample of the same grade. Density varies with particle size distribution, degree of fines compaction, and moisture content, and cannot be reliably assumed from the BCSN alone.

Tanktop loading capacity ratings are vessel-specific. The values described in this article as typical are illustrative; the actual rating for any vessel is in the vessel’s class certificate and stability booklet, and those documents govern. No calculation presented here should be used in place of the vessel’s own approved loading instrument.

The Group A reclassification discussion for chrome ore fines is based on the general principles of IMSBC Code Group A classification and on industry guidance. Whether a specific chrome ore fines consignment requires Group A treatment is a determination for the shipper’s competent authority and, where disputed, for an independent cargo surveyor. The IMSBC Code schedule for CHROME ORE, read with the Code’s general provisions, is the regulatory reference, not this article.

The trade statistics cited (South Africa export volumes, China import share, vessel sizes, voyage distances) are drawn from industry sources current to 2023 and 2024. Commodity trade volumes change from year to year with market conditions, mining output, and steel production cycles.

The dust hazard discussion reflects current understanding of Cr(III) toxicity and the variable Cr(VI) content of chrome ore dust. Operators should obtain the current Safety Data Sheet for the specific ore grade and source before loading, and consult occupational health guidance specific to the loading port jurisdiction.

See also

• IMSBC Code
• IMSBC Group C cargoes
• IMSBC Group A cargoes: Cargoes that may liquefy
• Iron Ore: IMSBC Code Schedule and Carriage
• Manganese Ore: IMSBC Code Schedule and Carriage
• Nickel Ore: IMSBC Code Schedule and Carriage
• Mineral Concentrates: IMSBC Code Schedule
• Cargo Draught Survey: Bulk Carriers
• Bulk Carrier

Related calculators:

• IMSBC Group A/B/C Classification
• IMSBC TML Moisture Check
• IMSBC Angle of Repose
• IMSBC Chromite
• IMSBC Group A - Liquefaction Risk