IMSBC Group C Cargoes: Definition and Carriage

IMSBC Group C is the residual classification in the International Maritime Solid Bulk Cargoes Code: solid bulk cargoes that neither liquefy under vessel motion (the defining risk of Group A) nor present a chemical hazard during sea carriage (the defining risk of Group B). The Code’s current mandatory edition incorporates Amendment 06-21, which became mandatory on 1 December 2023, and Amendment 07-23, mandatory from 1 January 2025. Group C encompasses the bulk of the ordinary dry-bulk trade by cargo-name count and seaborne tonnage, including cement, clinker, salt, sand, iron ore lump, pig iron, and finished steel and non-ferrous metal products.

Group C’s lower hazard profile doesn’t mean low operational risk. The group includes the densest cargoes in maritime commerce, the cargoes most likely to overload hold structures, and the cargoes responsible for a large share of the steel-industry’s cargo-damage claims. The IMSBC Group A/B/C Classification calculator and the IMSBC Loading Density Constraint calculator are the primary computational tools for Group C cargo planning.

IMSBC Code framework and regulatory basis

SOLAS mandate

The IMSBC Code’s authority rests on SOLAS Chapter VI (Carriage of Cargoes and Oil Fuels), Regulation 1-6, which gives the Code mandatory force for all solid bulk cargoes carried on ships subject to SOLAS. Regulation 2 of Chapter VI defines a solid bulk cargo and requires its carriage to comply with the Code. Chapter XII (Additional Safety Measures for Bulk Carriers) adds structural and survey requirements for bulk carriers in heavy-cargo trades, a direct consequence of hold-structure failures in the iron ore and pig iron trades during the 1980s and 1990s.

The IMSBC Code itself entered mandatory force on 1 January 2011 under SOLAS Chapter VI Regulation 3, replacing the non-mandatory BC Code (Code of Safe Practice for Solid Bulk Cargoes, 1965 origin). The BC Code’s three-group classification survived the transition intact. Every subsequent amendment cycle has revised the cargo schedules in Chapter 9 and occasionally the framework provisions, but the Group A/B/C taxonomy has been stable since 1991.

Amendment currency

The 2021 edition of the IMSBC Code is the current base text. Two amendments are relevant for 2025:

Amendment 06-21 was adopted by IMO Resolution MSC.500(105) in April 2022 and became mandatory on 1 December 2023, with voluntary application permitted from 1 January 2023. It added new cargo schedules, introduced the dynamic-separation hazard definition for Group A, revised existing schedules including changes to several iron-ore and mineral-concentrate entries, and updated testing procedures in Chapter 8. Amendment 06-21 is the edition most ships’ libraries and flag-state type-approvals reference.

Amendment 07-23 was adopted by IMO Resolution MSC.539(107) on 8 June 2023. It became mandatory on 1 January 2025, with voluntary early application permitted from 1 January 2024. Amendment 07-23 added further cargo schedules, revised stowage-factor ranges for several mineral commodities, and incorporated updates to the moisture-content test methods for Group A cargoes. As of 2025, both amendments apply; shipowners should verify that their onboard IMSBC edition reflects Amendment 07-23.

Three-group taxonomy

IMSBC Code Section 1.7 defines the three groups:

Group A: Cargoes that may liquefy if shipped at moisture content above their Transportable Moisture Limit (TML). Liquefaction occurs when fine, water-saturated particles lose inter-granular friction under cyclic ship motion, converting the cargo from a solid heap into a viscous liquid that shifts to one side and can cause sudden list. Iron ore fines, nickel ore, bauxite, mineral sands concentrates, and many others. See IMSBC Group A cargoes.

Group B: Cargoes with a chemical hazard during sea carriage. This group includes cargoes liable to self-heating, to emitting flammable or toxic gases, to reacting with water, or carrying an IMDG Class 4.1-4.3, 5.1-5.2, 6.1, 8, or 9 designation in bulk form. Coal (methane emission, self-heating), direct-reduced iron (DRI, hydrogen emission and spontaneous combustion), and ammonium nitrate fertilizers are examples. The sub-category “Materials Hazardous only in Bulk (MHB)” identifies Group B cargoes that are classified as dangerous goods in bulk but not in packaged form. See IMSBC Group B cargoes.

Group C: Cargoes that are neither liable to liquefy (not Group A) nor possess chemical hazards (not Group B). Section 1.7 states explicitly that Group C is the residual: a cargo belongs to Group C if it fails both the Group A and Group B tests. A cargo can belong to both Group A and Group B simultaneously (for example, some nickel ore concentrates are both liquefiable and carry chemical hazard); it cannot be both Group A/B and Group C.

Group comparison table

Cargo-not-listed procedure

Not every cargo traded in bulk has a named schedule in IMSBC Chapter 9. When a shipper proposes to carry a solid bulk cargo that’s not listed, the Code requires a tripartite agreement under IMSBC Section 1.3. Three parties must each grant approval: the competent authority of the loading port, the competent authority of the discharge port, and the flag State of the carrying vessel. The agreement must document the cargo’s physical and chemical properties, the hazard assessment placing it in a Group (including the testing basis), and any special conditions of carriage.

Tripartite agreements are submitted to IMO and, if agreed for listing, incorporated into the next amendment cycle. Appendix 5 of the IMSBC Code lists cargoes currently moving under tripartite agreements, with their reference numbers. A shipper holding a tripartite agreement must carry copies of the agreement documentation for each voyage, and the master must sight the agreement before allowing loading.

Group C cargo schedules and their structure

Each Group C entry in IMSBC Chapter 9 follows a standard schedule template:

1. Description: Physical form, particle size, color, odor, any specific trade names.
2. Characteristics: Bulk density (t/m³), stowage factor (m³/t), size range, moisture content range, class (Group C confirmed), angle of repose where relevant.
3. Hazard: For Group C, typically “No special hazards” or a limited statement about dust or density-related structural loading.
4. Stowage and segregation: Hold preparation requirements, restriction on adjacent stowage if any.
5. Weather precautions: Whether cargo must be loaded in dry weather only (relevant for hygroscopic cargoes like cement and salt).
6. Loading: Specific instructions for loading rate, trim, avoidance of concentrated heap loading.
7. Carriage: Ventilation, monitoring, inspection interval.
8. Discharge: Dust suppression, residue management, equipment requirements.
9. Clean-up: Instructions for hold cleaning after discharge.
10. Emergency procedures: Emergency schedule reference (most Group C entries refer to EMS G-X “Not relevant”).

This structure gives the ship’s master a single-reference document for every operational decision involving that cargo. For Group C, the schedule is less prescriptive than Group A or B schedules, but it still defines baseline practice that P&I clubs and cargo underwriters treat as the minimum standard of care.

Major Group C cargoes

Cement and cement clinker

Cement is among the largest single dry-bulk commodities globally by seaborne tonne. Portland cement (CEM I per EN 197-1) is a fine grey powder with particle size 1-100 microns, bulk density 1.0-1.5 t/m³, and angle of repose approximately 25-30°. Its stowage factor is 0.67-1.0 m³/t. Bulk cement is carried on dedicated cement carriers fitted with pneumatic self-discharge systems or on conventional bulkers with shore-side pneumatic gear. See IMSBC Industrial Sand and the Shiptype: Cement Carrier profile for vessel specifications.

Cement clinker, the calcined-limestone intermediate from which cement is ground, is coarser (1-25 mm typical), denser (1.4-1.8 t/m³), and far more tractable for conventional grab-equipped bulkers. Clinker is the preferred form for long-haul trade where the receiving end operates its own grinding plant.

Both cement and clinker are firmly Group C. Neither self-heats, neither emits hazardous gas, neither reacts with water in a hazardous way (cement sets in water but this is not a IMSBC-hazard criterion). The operational challenges are dust, hold cleanliness, and abrasive wear on handling equipment. Respirable cement dust at concentrations above 4 mg/m³ (EU OEL for Portland cement dust, Directive 2017/164/EU) poses silicosis and lung-irritation risks for port workers and crew; loading in enclosed-chute systems with vacuum extraction is standard practice at major cement terminals.

Residual cement hardens on contact with moisture, making hold cleaning difficult and expensive. Cement-cargo charters routinely include strict cleanliness clauses specifying hold inspection procedures and penalty rates for residual cement that fails the standard. Vessels leaving cement cargoes for grain or sugar trades face the most stringent hold-preparation requirements.

Salt

Bulk salt is the largest single mineral commodity by seaborne tonnage, with major export points at Mexico’s Guerrero Negro and Isla del Carmen, Australia’s Dampier Salt operations, India’s Rann of Kutch, and rock-salt mines across Germany and Poland. Annual seaborne salt trade is approximately 100 million tonnes.

Three principal forms carry under the Salt schedule in IMSBC Chapter 9:

Rock salt: mined halite, coarse crushed, bulk density 1.2-1.4 t/m³, moisture typically very low. Loaded by conventional grabs.

Evaporated salt: chemically purer, finer particle size, bulk density 1.0-1.3 t/m³. Requires enclosed loading to prevent dust dispersion and loss.

Solar salt: produced by sea-water evaporation; composition and particle characteristics vary by producer. Some solar salt grades carry residual moisture that requires drainage management during voyage.

All salt forms are Group C. The operationally dominant concern is corrosion: salt is aggressively corrosive to unprotected mild steel, particularly in warm, humid holds where condensation cycles deposit brine on the hold lining. Vessels regularly in the salt trade apply heavy-duty epoxy hold coatings, with touch-up between cargoes. Post-salt hold cleaning requires thorough fresh-water washing, complete drying, and a full internal inspection for pitting corrosion before the next cargo. P&I clubs and class societies treat inadequate hold maintenance after salt cargoes as a significant contributor to structural-survey findings on older bulkers.

Sand, gravel, and crushed stone

Construction aggregates represent the largest single volume category in worldwide materials handling, although most of the tonnage moves on small coastal or inland craft rather than on Panamax or Capesize bulkers. Sand bulk density is 1.5-1.8 t/m³ for dry cargo and up to 2.0 t/m³ for wet-screened or dredged product.

Group C designation is unambiguous for properly drained aggregate. The operational factors are density (maximum allowable structural loading often reached before the hold is visually full), drainage (wet aggregate sheds free water into bilges throughout the voyage), and abrasion (quartz sand and crushed granite wear grab buckets, conveyor belts, and bilge-pump impellers faster than any other common Group C cargo).

Specialty grades that move on larger tonnage include silica sand for glass manufacturing (99%+ SiO₂, specific particle-size distribution) from operations in France, Vietnam, and Belgium, and frac sand for oil-and-gas hydraulic fracturing from the Midwest United States. These specialty grades command charter premiums because their chemical-purity specifications add hold-preparation requirements: any contamination with previous cargo residues can fail the quality test and result in cargo rejection.

Crushed limestone, granite, and basalt for civil-construction aggregate have similar bulk density (1.6-2.0 t/m³ depending on rock type and crushing gradation) and are straightforward Group C cargoes. The IMSBC Loading Density Constraint calculator provides the structural-load check for high-density aggregate cargoes on conventional bulkers.

Industrial clays and mineral products

Kaolin (china clay, the white aluminosilicate Al₂Si₂O₅(OH)₄) is a significant Group C tonnage from Brazil (Para state), China, and the UK (Cornwall). Kaolin bulk density is 1.0-1.3 t/m³; the cargo is fine, dusty, and susceptible to moisture-induced caking during a long voyage. Paper-grade kaolin requires tight moisture control during loading and carriage. Stowage factor is approximately 0.77-1.0 m³/t.

Gypsum (calcium sulphate dihydrate, CaSO₄·2H₂O) and gypsum plaster (the calcined half-hydrate) supply the global plasterboard industry. Major trade flows run from Spain, Mexico, Iran, and Thailand to plasterboard manufacturers in Europe, North America, and East Asia. The IMSBC - Gypsum Anhydrite calculator covers the cargo schedule’s key parameters. Bulk density 1.3-1.6 t/m³; structural loading on tank tops is the primary stowage constraint.

Talc, magnesite, vermiculite, perlite, pumice, zircon sand (see IMSBC - Zircon calculator), ilmenite, rutile, and chromite all appear as named Group C schedules in IMSBC Chapter 9. Manganese ore in coarse lump form is Group C; manganese ore fines with elevated moisture can cross into Group A.

Iron ore: lump and sintered

Iron ore is the single largest dry-bulk commodity globally, with approximately 1.6 billion tonnes seaborne annually, dominated by the Australia-to-China and Brazil-to-China corridors. The same chemical species, primarily hematite (Fe₂O₃) and magnetite (Fe₃O₄), carries under three different IMSBC groups depending on particle size and processing:

Iron ore fines: particles predominantly below 6.3 mm. Group A. Liquefaction risk when shipped above TML. See IMSBC Iron Ore Fines (IOF) calculator.

Iron ore concentrates: very fine particles from beneficiation plants. Group A. See IMSBC Iron Concentrate calculator.

Iron ore in lump form: dominant fraction above 6.3 mm, typically 8-30 mm. Group C. Covered by the IMSBC Iron Ore calculator. Bulk density 2.4-2.8 t/m³; stowage factor 0.36-0.42 m³/t.

Sintered ore (fines agglomerated in a sintering plant at 1,200-1,350°C into porous cake broken into 10-40 mm lumps) is Group C because sintering eliminates the fine-particle fraction that drives Group A liquefaction. Pellets (balled and indurated fines) are similarly Group C.

The Group A vs Group C distinction for iron ore is operationally critical and commercially charged. Australian and Brazilian exporters’ quality-assurance systems include particle-size distribution sampling at loading (per ISO 3082 sampling protocols) to confirm that the ore shipped meets lump specification and correctly belongs in Group C. A cargo declared as lump iron ore that in fact contains a fine fraction above Group A thresholds, loaded under a Group C declaration, would constitute a mis-declaration under IMSBC Section 4, with serious legal consequences for the shipper.

Pig iron

Pig iron, the rough cast-iron ingots (typically 8-15 kg each) produced in blast furnaces and shipped to electric-arc-furnace mini-mills or specialty steel producers, is one of the densest routine dry-bulk cargoes. Bulk density ranges from 3.5 t/m³ for loosely packed large pigs to 4.5 t/m³ for smaller pigs poured to a tight random pack. For comparison, iron ore lump bulk density is 2.4-2.8 t/m³; pig iron is 25-50% denser.

At 4.0 t/m³ average, a hold filled to only 25% of its geometric volume already reaches the maximum allowable tank-top load for most Handysize bulkers rated at 15-18 t/m². Pig iron stowage is therefore constrained by the tank-top design load long before the hold is visually full. The vessel’s loading manual must be consulted, and in some ships, dedicated pig-iron loading tables specify reduced acceptable weights below the general cargo rating.

The IMSBC Pig Iron calculator provides the stowage-factor and structural-load calculation for pig iron shipments. The cargo is Group C: no chemical hazard, no liquefaction risk. Hold structural overloading is the only significant casualty mechanism, and it’s not trivial. Several bulk carriers have suffered tank-top deformation and double-bottom damage from pig iron loaded without checking the structural load, particularly on older vessels whose actual tank-top strength had been reduced by corrosion.

Finished steel products

The global steel trade moves approximately 400 million tonnes of finished steel products per year as seaborne cargo. In bulk-carriage terms, the principal forms are:

Steel slabs: rough rectangles 8-30 cm thick, up to 1.5 m wide, up to 12 m long, mass 5-30 tonnes each. Bulk density in hold 2.5-3.5 t/m³ depending on stow efficiency. Stowed flat, typically single-layer or double-layer with separating dunnage.

Steel billets: square or rectangular cross-section, 100-200 mm side, 6-12 m long, 0.5-3 t each. Stacked horizontally in alternating orientations for stability.

Hot-rolled coils (HRC): coiled flat steel, 10-30 tonnes per coil, 1.0-2.0 m diameter, 0.5-2.0 m width. HRC stowage is demanding: coils are stored upright (eye-athwartship) in purpose-built hold cradles or in free stacks with bolster bars, requiring dedicated securing systems against transverse movement. The IACS Steel Grade Selection (UR W11) calculator covers the material specifications behind HRC certification.

Cold-rolled coils: similar dimensions to HRC but finer surface finish and tighter dimensional tolerances; surface damage in transit is a primary cargo-damage claim source.

Wire rod, rebar, and structural sections: long products in coils or bundles. Susceptible to edge and surface damage from inadequate dunnage placement.

All are Group C when carried as bulk or quasi-bulk cargo. Chemical hazard: none. Liquefaction: not applicable. The operational risks are structural overloading and cargo damage. Steel-products cargo-damage claims represent one of the highest-value categories of marine cargo insurance annually. Standard practice is to survey the cargo condition at loading, document hold preparation, record dunnage layout, and re-survey on arrival. See Marine Cargo Damage Investigation and Marine Cargo Securing and Lashing Systems.

Non-ferrous finished metals

Aluminium ingots: die-cast or open-mould ingots, typically 700-1,000 kg each, bundled in stacks with steel straps, bulk density approximately 2.7 t/m³ in hold. Major trade flows from aluminium smelter regions (Middle East, Iceland, Canada, Australia) to fabrication markets (Europe, North America, East Asia). The International Aluminium Institute estimates seaborne aluminium ingot trade at approximately 30 million tonnes annually.

Copper cathodes: electrorefined copper plates from tank-house operations, approximately 1.0 m × 1.0 m × 6-15 mm thick, 100-150 kg each. Bundled in stacks of 50-100 sheets with protective dunnage. Bulk density in hold 4.0-6.0 t/m³ depending on stow tightness. Copper is Group C; refined copper has no chemical hazard and no liquefaction mechanism.

Lead ingots: pig-shaped castings, 30-50 kg each. Density 11.3 t/m³ (pure lead). In the hold, even a conservative packing efficiency gives a stowed density above 8 t/m³, meaning structural loading constraints bind aggressively. A single standard Handysize hold filled to 20% of its volume with lead ingots exceeds most tank-top load ratings. Lead cargoes are therefore loaded in layers calculated from the loading manual, not to visual fill.

Zinc ingots and jumbo blocks: 20-25 kg standard ingots or 1-2 tonne jumbo slabs. Density 7.1 t/m³. Similar structural-loading constraints to lead.

Nickel briquettes, rounds, and cathodes: various refined-nickel forms from electrolytic and carbonyl refining, density 6-8 t/m³ in stow. Group C; the IMSBC Code’s nickel briquette schedule explicitly distinguishes this from unprocessed nickel ore (Group A) and from nickel carbonyl-contaminated material (Group B).

Scrap metal

Scrap classification is the most operationally awkward case in Group C, because the Group B boundary depends on cargo composition rather than cargo species.

Clean ferrous scrap (No. 1 Heavy Melt, No. 2 Heavy Melt, shredded auto bodies meeting the Group C oil-content criterion) is Group C. Processed scrap with oil contamination below the threshold set in the IMSBC ferrous scrap schedule is inert: no self-heating, no chemical hazard.

Oily or unprocessed ferrous scrap crosses to Group B, designated MHB(SH) (Materials Hazardous only in Bulk, Self-Heating category). The IMSBC Code’s ferrous scrap schedule includes a carriage condition requiring that the oil content not exceed the specified threshold; shippers are required to certify compliance and provide testing records. Several documented bulk-carrier cargo fires attributed to improperly certified scrap drove amendment 05-19 and 06-21 revisions to the ferrous scrap schedule.

Non-ferrous scrap (aluminium, copper, brass, lead, zinc in processed form) is typically Group C. Mixed, unprocessed, or contaminated non-ferrous scrap is generally not accepted for international bulk carriage under IMSBC and must be processed first.

The IMSBC Zinc Skimmings calculator covers a related non-ferrous material. Zinc skimmings carry a Group B designation in some grades, illustrating how zinc in refined-metal form (Group C) and zinc in drossing byproduct form (Group B) are different cargo species even from the same metal.

Classification boundary cases

Group A vs Group C: particle size determines group

The most practically important boundary is between Group A and Group C, because the same orebody, or even the same shipment, can fall on either side depending on how the material is processed and screened before loading.

The IMSBC Code defines the Group A boundary by moisture content relative to the TML, established by testing per Appendix 2 of the Code (Proctor-Fagerberg, flow table, penetration tests). But the TML itself is primarily a function of particle-size distribution: finer particles retain more moisture and are more susceptible to liquefaction. The practical industry distinction, used in contract terms and sampling programs for iron ore, is the 6.3 mm sieve threshold. Cargoes with dominant fraction above 6.3 mm are generally Group C candidates; those with more than 50% below 6.3 mm are Group A candidates and require formal TML testing before every shipment.

This boundary creates a financial incentive problem. Lump ore commands a price premium over fines. A shipper who declares fines as lump, or who screens inadequately, gains a commercial advantage while exposing the vessel to a liquefaction risk the master has no way to assess without independent sampling. The major iron-ore exporting terminals (Port Hedland, Dampier, Port Kembla, Tubarao, Ponta da Madeira) all operate formal quality-assurance programs with third-party sampling under ISO 3082 to certify lump specification. The IMSBC Iron Ore calculator reflects the lump specification parameters from Amendment 06-21.

Group B vs Group C: the MHB boundary

A cargo crosses from Group C to Group B if it carries a chemical hazard in bulk, whether or not it’s classified as a packaged dangerous good. The “Materials Hazardous only in Bulk (MHB)” label in Group B covers cargoes that are not regulated under IMDG in packaged form but present hazards when shipped in large bulk quantities.

The key MHB sub-categories with Group C implications:

MHB(SH) Self-Heating: ferrous and non-ferrous scrap above the oil-contamination threshold; some agricultural products.

MHB(D) Dust Hazard: no Group C cargo currently carries this designation in its schedule (Group B MHB(D) cargoes are separately listed), but very fine Group C cargoes approaching MHB(D) thresholds should be assessed case-by-case.

A cargo that tests below the MHB(SH) self-heating threshold and has no IMDG classification in packaged form is Group C. The IMSBC schedules for ferrous scrap and several ore concentrates include the testing criteria that place material on one side or the other of this boundary.

Stowage and operational requirements

Hold structural loading

For heavy Group C cargoes, the structural loading calculation, not the volumetric fill, is the binding constraint. The tank-top design load (expressed in t/m² of tank-top area in the vessel’s loading manual) defines the maximum weight that can sit on the hold bottom. For a bulk carrier with a tank-top load rating of 15 t/m² and a hold floor area of 600 m², the maximum cargo weight in that hold is 9,000 tonnes regardless of volumetric capacity.

A cargo with bulk density $\rho$ (t/m³) and a fill height $h$ (m) exerts:

Loading must stop when $q$ reaches the tank-top rating. For pig iron at 4.0 t/m³ and a tank-top rating of 15 t/m², the maximum fill height is 3.75 m, typically 20-30% of hold depth. For iron ore lump at 2.6 t/m³, the maximum fill height is about 5.8 m. For cement at 1.3 t/m³, the structural limit is rarely reached before volumetric capacity.

The IMSBC Loading Density Constraint calculator implements this check across multiple holds, matching cargo weight distribution to the bending-moment limits in the loading manual. Loading personnel who fill holds visually, to the hatch coaming, without checking the structural limit, have caused tank-top deformations and in severe cases double-bottom rupture with flooding.

Angle of repose and cargo trim

Group C cargoes don’t liquefy, but dry bulk cargo can still shift in heavy weather if loaded with surface slopes steeper than the cargo’s angle of repose. The IMSBC schedule for each cargo specifies the angle of repose where relevant; for coarse aggregate and lump ore, this is typically 35-45°. For fine powders like cement, the effective angle of repose in a loose heap is similar (25-35°) but the material compacts under vibration and is less susceptible to dynamic shift.

IMSBC Section 5 (Trimming procedures) requires that the cargo surface be leveled to within the trimming tolerance specified in the schedule. Untrimmed cargoes, with steep heap angles toward one side of the hold, can shift under heavy weather to create list. List compounds: cargo shift to the low side increases the angle, freeboard decreases, and water ingress through low-side hatches becomes possible. Several smaller-tonnage casualties in the coaster and short-sea fleet have involved Group C aggregate or salt cargo that was loaded quickly without proper trim and shifted in a North Sea or North Atlantic swell.

The IMSBC Angle of Repose calculator provides the geometric relationship for angle-of-repose compliance checks.

Hold preparation

Hold preparation requirements for Group C cargoes are set in the individual cargo schedule but follow the general framework in IMSBC Section 7:

Hold surfaces clean and free of previous cargo residue. Bilge wells clear and operational, covers in place and undamaged. Tank top in good structural condition: deformed or corroded frames must be repaired before dense cargo is loaded, because structural weakness is not visible from the surface and is only revealed under load. Hatch covers tested for watertightness on the voyage before loading.

Specific Group C requirements: cement holds must be substantially dry (residual moisture triggers premature set); salt holds require either full coating protection or a documented history of satisfactory salt-trade performance; iron ore lump holds often have removable tank-top sacrificial wear plates to reduce abrasion from grab-bucket discharge. See Cargo Hold Preparation Standards for the full inspection framework.

Dust management

Group C cargoes responsible for significant dust generation at loading or discharge terminals: cement, fly ash (when carried as Group C), gypsum, kaolin, finely-crushed limestone, silica sand, and some salt grades. The applicable industrial-hygiene standards are set by port-state regulation rather than the IMSBC Code. EU member state ports apply the OEL for inhalable dust (10 mg/m³) and for respirable dust (4 mg/m³ for inert dusts; lower for specific minerals like crystalline silica at 0.1 mg/m³ for respirable fraction under EU Directive 2017/2398/EU on crystalline silica).

Operational controls: enclosed chute loading with vacuum extraction at the discharge point, water misting at transfer points except for moisture-sensitive cargoes, dedicated PPE (P3 half-mask respirators) for crew working on deck during loading of dusty cargoes, and routing of accommodation ventilation away from the loading side.

Shipper’s cargo declaration

IMSBC Code Section 4.2 requires the shipper to provide the master with a cargo declaration before loading begins. For Group C, the declaration must state:

• BCSN (Bulk Cargo Shipping Name) per Chapter 9 of the Code.
• Group designation: Group C, with the schedule reference.
• Bulk density in t/m³ and stowage factor in m³/t.
• Angle of repose (if specified in the schedule or relevant to trim planning).
• Moisture content (where relevant to cargo condition and drainage).
• Particle size distribution (for cargoes like iron ore where particle size determines the group).
• Any specific hazards or precautions from the schedule.

The master is entitled to refuse loading if the declaration is missing, if the cargo’s visible condition contradicts the declared characteristics (for example, iron ore visually showing excessive fines suggesting Group A characteristics while declared as Group C lump), or if independent surveyor’s sampling results differ from the declaration. See Cargo Draught Survey for Bulk Carriers for the routine quantity-verification practice.

Relationship to the Cargo Securing Manual and CSS Code

The IMSBC Code governs cargoes in bulk, material loaded directly into the hold without unitization. When the same physical product is carried as packaged, unitized, or secured individual pieces, the applicable regime shifts to the Cargo Securing Manual (required under SOLAS Chapter VI Regulation 5.6) and the IMO CSS Code (Code of Safe Practice for Cargo Stowage and Securing, MSC.1/Circ.1352/Rev.1 as amended).

The boundary for steel products is the most frequently contested in practice. Hot-rolled coils loaded into dedicated hold cradles and secured with lashing wires and turnbuckles are argued by some operators to be “unitized” (CSS Code) rather than “bulk” (IMSBC). The practical test is whether the cargo can be handled without individual securing arrangements: bulk cargo by definition cannot, it relies on the hold structure to contain it. In most jurisdictions, coils carried in cradles with individual securing are classified as breakbulk and governed by the CSS Code rather than IMSBC; coils piled in a loose pyramid without individual securing fall under IMSBC. See Marine Cargo Securing and Lashing Systems for the securing-strength calculation framework.

Limitations

The Group C classification is a binary outcome for regulatory carriage purposes, not a full hazard characterization. Several important limitations apply:

The classification is cargo-specific, not vessel-specific. IMSBC Group C tells you the cargo is safe under standard bulk-carriage conditions. It doesn’t account for the fitness of a specific vessel to carry a specific Group C cargo at a specific density. A vessel with corroded tank tops or a loading manual that prohibits dense cargoes in specific holds can be seriously damaged by a Group C cargo that a fit vessel carries routinely.

Group determination depends on actual material loaded, not trade name. Iron ore fines declared as lump, oily scrap declared as clean, wet gypsum declared as dry: the BCSN and Group designation in the shipper’s declaration are only as reliable as the shipper’s quality-assurance system and the independent verification conducted at loading. Masters who accept cargo declarations without independent sampling for cargoes where Group A vs Group C is particle-size-dependent accept the consequent legal exposure.

Amendment currency matters. An IMSBC edition that predates Amendment 07-23 may carry superseded cargo-schedule parameters. Schedules revised in 07-23 (including updates to stowage-factor ranges for several mineral products and to moisture-content test methods) govern carriage from 1 January 2025 regardless of which edition is physically on the ship. Flag-state type approval of a specific edition doesn’t override the mandatory amendment schedule.

IMSBC does not address port safety. The Code governs sea carriage. Port-state occupational-health regulations, terminal design requirements for dust suppression, and environmental regulations for runoff from aggregate terminals are outside the IMSBC framework. Vessels operating in EU, US, or Australian ports carry additional compliance obligations that exceed IMSBC requirements.

Structural loading limits are vessel-specific. The tank-top load ratings in IMSBC cargo schedules are maximum design loads; a vessel’s actual capacity after years of service, corrosion, and previous structural damage may be lower. Class society survey findings on a vessel’s structural condition govern; the IMSBC schedule parameters are not a substitute for the loading manual.

See also

• International Maritime Solid Bulk Cargoes (IMSBC) Code
• IMSBC Group A cargoes (cargoes liable to liquefy)
• IMSBC Group B cargoes (cargoes with chemical hazards)
• SOLAS Chapter VI Carriage of Cargoes and Oil Fuels
• SOLAS Chapter XII Additional Safety Measures for Bulk Carriers
• Cargo Hold Preparation Standards
• Cargo Draught Survey for Bulk Carriers
• Cargo Securing Manual
• Marine Cargo Damage Investigation
• Marine Cargo Securing and Lashing Systems
• Cement Clinkers: IMSBC Code Schedule and Carriage

Related calculators

• IMSBC Group A/B/C Classification
• IMSBC Loading Density Constraint
• IMSBC Angle of Repose
• IMSBC Iron Ore
• IMSBC Iron Ore Fines (IOF)
• IMSBC Iron Concentrate
• IMSBC Pig Iron
• IMSBC Gypsum Anhydrite
• IMSBC Industrial Sand
• IMSBC Zircon
• IMSBC Zinc Skimmings
• IACS Steel Grade Selection (UR W11)
• Shiptype: Cement Carrier
• IMO IMSBC
• IMSBC Group A Liquefaction Risk