IMSBC Code

The International Maritime Solid Bulk Cargoes Code (IMSBC Code) is the mandatory international instrument governing the safe carriage of solid bulk cargoes by sea. Adopted by IMO Resolution MSC.268(85) in December 2008 and entering into force on 1 January 2011 as a mandatory requirement under SOLAS Chapter VI, the Code superseded the voluntary BC Code that had been in service since 1965. It classifies every solid bulk material into one of three Groups - A (liable to liquefy), B (presenting a chemical hazard), or C (neither) - and prescribes individual schedules for hundreds of named commodities, specifying stowage factors, angles of repose, moisture testing protocols, and emergency response data. The Code is revised biennially through numbered amendment cycles; the 07-24 amendments apply from 2026. Its requirements interact directly with SOLAS load-line provisions, grain carriage rules, and the structural design standards for bulk carriers. ShipCalculators.com provides a suite of IMSBC calculators covering cargo group classification, transportable moisture limit checks, angle-of-repose assessment, liquefaction risk, and individual commodity schedules.

Contents

Background and history

The carriage of solid bulk commodities predates any formal international regulation by many centuries. Coal, grain, ore, and salt were moved between ports in unpackaged form long before the concept of cargo classification existed. The hazards specific to bulk carriage - shift of cargo causing list, the generation of explosive or toxic gases in enclosed holds, and the conversion of granular material into a fluid slurry when moisture content is excessive - were documented in casualty records from the 19th century onward, yet codified international rules did not emerge until the second half of the 20th century.

The BC Code and its predecessor frameworks

The Code of Safe Practice for Bulk Cargoes, universally abbreviated to the BC Code, was published by IMO in 1965. It was a voluntary instrument and its uptake depended entirely on the willingness of flag states to incorporate its recommendations into national legislation. The BC Code introduced the conceptual framework that underpins the current IMSBC Code: individual schedules for named cargoes, moisture-related testing requirements for cargoes liable to liquefy, and the segregation of materials presenting chemical hazards. However, voluntary status meant that enforcement was inconsistent and that commodity schedules lagged behind the growth of new bulk trades, particularly concentrated mineral ores from developing exporters in the Asia-Pacific region and West Africa.

The BC Code was revised and reissued several times - notably in 1994 - but successive casualties involving liquefaction and chemical hazards highlighted the inadequacy of a voluntary framework. The 1990s and 2000s saw a series of total-loss incidents in which bulk carriers laden with mineral concentrates or nickel ore sank with all hands, and the casualty pattern became impossible for the IMO to ignore.

Adoption of the IMSBC Code

The IMO Maritime Safety Committee adopted the IMSBC Code as Resolution MSC.268(85) at its 85th session in December 2008. The text restructured and substantially expanded the BC Code’s content while preserving its tripartite classification system. SOLAS Chapter VI Regulation 1-2, as amended, made compliance with the IMSBC Code mandatory for ships carrying solid bulk cargoes from 1 January 2011, with a one-year transitional period during which administrations could permit continued use of the old BC Code up to 1 January 2012.

The mandatory character of the instrument was a significant regulatory step. Flag-state administrations were now required to enforce the Code’s requirements, and port state control officers gained a clear legal basis for detaining ships whose cargo documentation or loading practices were non-compliant.

Amendment cycles

The IMSBC Code is amended on a two-year cycle, with each amendment set identified by a sequential number and the year of the IMO session that adopted it. The first set of amendments (01-09) entered into force on 1 January 2011 simultaneously with the Code itself. The 02-13 amendments, adopted by MSC 91, incorporated a schedule for iron ore fines (IOC) that had previously been absent, following investigations into casualties attributed to the liquefaction of this commodity. The 06-21 and 07-24 amendment cycles are among the most substantive; the 07-24 amendments apply from 2026 and contain revised testing requirements for several Group A materials and updated emergency procedures for Group B substances.

Structure of the IMSBC Code

The IMSBC Code is organised into 13 sections and five appendices.

Sections 1 to 7: general provisions

Section 1 defines the scope and application of the Code. It applies to all ships to which SOLAS Chapter VI applies, meaning seagoing cargo vessels other than passenger ships and fishing vessels below certain sizes. Section 2 provides general principles covering acceptability of cargoes for shipment, documentation obligations, and the role of the master in refusing shipment where the cargo condition is uncertain. Section 3 deals with the safety of personnel and the management of risks during loading and discharge, including requirements for atmosphere testing in cargo holds before entry.

Section 4 specifies the assessment of acceptability for loading, including the shipper’s obligation to provide a cargo declaration. Section 5 addresses trimming, a term that in the bulk cargo context means the levelling of cargo within holds to reduce free-surface effects and improve transverse stability. Poor trimming practice is a recognised contributory factor in bulk carrier casualties. Section 6 covers loading and discharge operations as they interact with the ship’s structure and stability, linking to the BLU Code (Code of Practice for the Safe Loading and Unloading of Bulk Carriers, MSC.159(78), 2004). Section 7 deals with the stowage of dangerous goods in solid form within bulk loads, which arise most commonly when a Group B cargo is present.

Sections 8 to 13: specific hazard management

Section 8 addresses cargoes that may liquefy (Group A), setting out in detail the tests required to determine the flow moisture point (FMP) and from it the transportable moisture limit (TML). Section 9 covers materials that are hazardous only in bulk (MHB), a category that encompasses many Group B cargoes. Section 10 provides provisions for coal and other materials that emit flammable gases or generate oxygen-depleting or toxic atmospheres. Sections 11, 12, and 13 address trimming requirements in more detail, provisions applicable to specific vessel types, and the handling of cargo residues, respectively.

Appendices

The five appendices include the individual commodity schedules (Appendix 1), which form the operationally critical part of the Code for day-to-day use; test procedures for determining TML (Appendix 2); properties of bulk cargoes considered relevant to emergency response (Appendix 3); emergency schedules (Appendix 4); and a glossary (Appendix 5).

The three-group classification system

The IMSBC Code assigns every solid bulk cargo to one of three groups based on its hazard profile. The assignment determines which documentary requirements, moisture limits, atmosphere monitoring protocols, and stowage conditions apply.

Group A: cargoes liable to liquefy

Group A comprises solid bulk cargoes that, when the moisture content exceeds the transportable moisture limit, may undergo liquefaction - the process by which a particulate solid loses its shear strength and begins to behave as a liquid. Liquefaction is initiated by the cyclic vibration of the ship’s hull and machinery acting on saturated fine-grained material. A cargo that appears firm and stable alongside can transition to a viscous slurry at sea, producing a free-surface effect that reduces the ship’s metacentric height and can cause a rapid, irrecoverable list, capsize, or sinking.

Principal Group A cargoes include iron ore fines (IOC), nickel ore, bauxite fines, mineral concentrates (copper, zinc, lead, and others), and various sands and residues with a significant fine-particle fraction. The critical distinguishing parameter is the particle size distribution combined with the moisture content. Coarse material with good internal drainage rarely presents a liquefaction hazard at practicable moisture contents; fine-grained material with a high proportion of particles below 1 mm can reach its flow moisture point at surprisingly low absolute moisture levels.

The IMSBC Code requires the shipper to provide a certificate of analysis from an accredited laboratory showing the actual moisture content and the TML, and to state the method by which the TML was determined. The IMSBC TML check calculator assists compliance officers and cargo surveyors in comparing the declared moisture content against the TML to determine acceptability for shipment. The IMSBC liquefaction Group A checker extends this to an integrated liquefaction risk assessment. A related tool, the iron ore fines moisture checker, is specific to IOC cargoes. Where moisture content M exceeds TML, loading must be refused or postponed until the cargo dries to an acceptable level; the condition M < TML is the fundamental acceptability criterion.

Group B: cargoes presenting a chemical hazard

Group B encompasses solid bulk cargoes that may present a chemical hazard during carriage but that do not meet the Group A liquefaction criterion. Chemical hazards in this context include self-heating, spontaneous ignition, generation of flammable or toxic gases, explosive reactivity with water or other substances, and oxidising properties.

Coal is the most commercially significant Group B cargo by volume. Bituminous coal self-heats through oxidation of exposed carbon surfaces, and this process generates carbon monoxide (CO) as an early indicator gas and can progress to smouldering or open fire in a hold. Coal also emits methane from included gas that was trapped in the coal seam at formation. The combination of methane accumulation and the possibility of an ignition source from spontaneous heating makes coal cargo monitoring essential. The bulk coal methane ventilation calculator and the IMSBC coal self-heating assessment are used to evaluate ventilation requirements and thermal hazard levels. The IMSBC bituminous coal schedule and IMSBC anthracite schedule provide commodity-specific parameters.

Direct reduced iron (DRI) in its various forms is another critical Group B commodity. DRI is produced by removing oxygen from iron ore using reducing gases, leaving a highly reactive metalite sponge product that reacts with water to generate hydrogen and with atmospheric oxygen to generate heat. Ship fires and explosions involving DRI have caused casualties. The IMSBC Code distinguishes DRI Type A (briquettes, hot), DRI Type B (briquettes, cold), and DRI Type C (fines and cold), each with distinct schedules and transport conditions. The IMSBC DRI-A schedule, IMSBC DRI-B schedule, and IMSBC DRI fines schedule cover these three forms. A related tool, the bulk iron DRI passivation calculator, addresses the passivation treatment required for safe DRI carriage.

Ammonium nitrate-based fertilisers occupy a special position within Group B. Ammonium nitrate (AN) is both a commonly shipped fertiliser and an explosive substance. The IMSBC Code distinguishes UN 1942 (pure ammonium nitrate) from UN 2067 (ammonium nitrate-based fertilisers with no explosive ingredient) and from materials that fall outside the ammonium nitrate schedules entirely. The IMSBC ammonium nitrate UN1942 schedule and IMSBC ammonium nitrate-based fertilisers UN2067 schedule provide the applicable parameters. Port Authorities typically apply additional national restrictions on the handling of these materials at berth.

Fishmeal presents a combination hazard. It is classified as Group B because of self-heating and the potential for spontaneous combustion, particularly when moisture is elevated, but it can also emit toxic and flammable gases including ammonia and hydrogen sulphide. The IMSBC fishmeal schedule applies to stabilised (antioxidant-treated) fishmeal; unstabilised fishmeal is generally prohibited from bulk carriage. Sulphur in bulk, both granular and lump forms, is combustible and can generate sulphur dioxide during a fire; it has a low electrical conductivity that promotes dust explosion hazards during loading. The bulk sulphur explosion risk calculator covers this aspect, and the IMSBC granular sulphur schedule provides the standard parameters.

Group C: cargoes not liable to liquefy and not presenting a chemical hazard

Group C is the residual category. It comprises cargoes that do not meet either the Group A or Group B criteria. Common Group C commodities include coarse iron ore (as distinct from iron ore fines), cement, gypsum, sand, salt, limestone, and most grades of grain carried under SOLAS Chapter VI (though grain additionally attracts the International Grain Code). Group C cargoes still require a shipper’s declaration and still have individual schedules, but those schedules do not require moisture limit testing or chemical hazard monitoring. The IMSBC cement schedule, IMSBC gypsum schedule, and IMSBC coarse iron ore schedule illustrate the simpler documentation profile for Group C commodities.

The IMSBC cargo group classifier allows operators to identify the applicable group for a named cargo and retrieve the baseline parameters from the Code schedule.

Transportable moisture limit and testing methods

The transportable moisture limit is defined in the IMSBC Code as 90% of the flow moisture point (FMP), where the FMP is the moisture content at which a granular solid becomes sufficiently saturated that it exhibits flow behaviour under mechanical vibration. The relationship is expressed as: TML = 0.9 × FMP. A 10% safety margin is embedded in this relationship to account for spatial variation in moisture distribution within a cargo parcel and for the imprecision inherent in field sampling.

The IMSBC Code Appendix 2 specifies three test methods, each suited to different material types.

Flow Table Test

The Flow Table Test (also called the Modified Proctor-Fagerberg approach in older literature, though the two are now distinct) subjects a prepared specimen of the material to a standardised impact sequence on a mechanical flow table. The moisture content at which the specimen first shows flow - that is, spreads laterally across the table under impact - is recorded as the FMP. The test is suitable for fine-grained materials with cohesive properties. It has been criticised for yielding conservative (lower) FMP values for some materials, leading to lower TML values than may be necessary, but it remains the primary test required by the Code for most concentrates.

Penetration Test

The Penetration Test uses a falling metal rod or cone that penetrates a specimen of the material compacted in a standardised mould. Moisture content is varied systematically, and the penetration depth at each moisture level is plotted. The FMP corresponds to the moisture level at which penetration increases sharply, indicating loss of shear strength. The Penetration Test is faster to conduct in the field than the Flow Table Test and is permitted as an alternative for certain materials.

Proctor-Fagerberg Test

The Proctor-Fagerberg Test, originally developed for phosphate rock and later modified for wider application, uses compaction energy (similar to the standard Proctor compaction test used in geotechnical engineering) to determine the moisture content at which a specimen compacts to a minimum dry density at a given vibration energy. The modified Proctor-Fagerberg method has been specifically mandated in the IMSBC Code for iron ore concentrate (IOC) since the 02-13 amendments took effect, following investigations that showed the standard Flow Table Test gave inconsistent results for some high-density concentrates. The IMSBC angle of repose calculator and the IMSBC moisture and flow moisture point calculator support the evaluation of individual test results. The IMSBC cargo density and stowage factor calculator provides the related density parameters.

Sampling requirements

The reliability of any TML determination depends critically on the representativeness of the sample. The IMSBC Code requires sampling at the point of loading from the cargo stream, using a mechanical cross-belt sampler or an equivalent manual sampling protocol that takes increments at regular intervals across the full cross-section of the material flow. A single grab sample from the top of a stockpile is not an acceptable substitute. The sample must be dispatched promptly to an accredited laboratory; delay degrades accuracy because moisture can redistribute or evaporate from the sample container. International standards for sampling procedures include ISO 3082 (iron ore) and ISO 4296 (manganese ore), and similar standards exist for individual concentrate types.

Shipper’s declaration and cargo information requirements

The IMSBC Code places the primary obligation for cargo information on the shipper. Before loading, the shipper must provide the master with a cargo declaration containing:

the Bulk Cargo Shipping Name (BCSN), being the name of the cargo as listed in the IMSBC Code schedule or the most appropriate NOS (not otherwise specified) entry;
the cargo group (A, B, or C);
the stowage factor in cubic metres per tonne (m³/t), representing the volume occupied by one tonne of the cargo in a hold;
the angle of repose in degrees, defining the maximum slope at which the cargo will rest without sliding;
for Group A cargoes: the actual moisture content and the TML, with the method used to determine TML and a certificate from an accredited laboratory;
for Group B cargoes: the relevant IMO hazard class, UN number, packing group, and emergency schedule reference;
any special requirements from the commodity schedule.

The master is entitled to refuse cargo or to require additional testing if the documentation is incomplete, if the declared moisture content is close to the TML, or if the physical appearance of the cargo is inconsistent with the declaration. This right of refusal is codified in SOLAS Regulation VI/2.

The IMSBC group classifier and the individual commodity schedule calculators - including IMSBC nickel ore, IMSBC bauxite fines, IMSBC iron ore fines, and IMSBC copper concentrate - summarise the required declaration parameters for each commodity.

Notable Group A cargoes

Iron ore fines

Iron ore fines and concentrates are high-density, fine-grained materials produced as a by-product of iron ore crushing and screening at mine sites. The proportion of fines exported from major producers - Brazil, Australia, India - has grown as blast-furnace and sintering technology has become more tolerant of fine material, and as mines progressively exploit lower-grade deposits that require more crushing. The IMSBC Code did not include a specific schedule for iron ore fines until the 02-13 amendments of 2013 (adopted at MSC 91). Before that, iron ore fines were often shipped under the generic coarse iron ore schedule, which did not require TML testing, a practice that contributed to a series of casualties.

The Stellar Daisy, a converted very large ore carrier (VLOC) of approximately 266,000 deadweight tonnes, sank in the South Atlantic on 31 March 2017 with the loss of 22 lives. The investigation pointed to structural failure exacerbated by the likelihood that the iron ore fines cargo was partially liquefied. At MSC/MEPC 99, mandatory reporting requirements were introduced for VLOCs over a threshold size, and a casualty investigation framework was strengthened for this vessel type. The IMSBC iron ore fines schedule calculator and the iron ore fines moisture checker address the TML requirements for this category.

Nickel ore

Nickel ore, typically shipped from mines in the Philippines, Indonesia, New Caledonia, and the Solomon Islands, has been responsible for a disproportionate share of bulk carrier liquefaction casualties. The ore is lateritic in character - a weathered surface deposit with high natural moisture content and a wide particle size distribution that includes a significant fine and clay fraction. Its FMP can be low, and because the ore is mined in tropical regions with high rainfall, moisture contents at the point of loading frequently approach or exceed the TML.

The MV Jianfu Star sank on 3 November 2010 north-east of the Philippines with the loss of 13 lives after listing severely. Cargo was nickel ore from the Philippines. The MV Vinalines Queen sank in the South China Sea on 25 December 2011 with the loss of 22 lives, again laden with nickel ore. These casualties, occurring within months of each other, prompted the Philippines and Indonesia to tighten sampling and testing procedures and led directly to the enhanced Group A monitoring provisions in subsequent IMSBC Code amendments. The IMSBC nickel ore schedule provides the applicable parameters.

Bauxite fines

Bauxite in its coarser forms (Group C) is a major commodity in Handymax and Kamsarmax trades. However, bauxite fines - the residue remaining after screening coarser grades - present a liquefaction hazard when the fines fraction is significant. The MV Bulk Jupiter sank on 2 January 2015 in the South China Sea with the loss of 18 of the 19 crew members aboard. The vessel was carrying approximately 46,000 tonnes of bauxite from Indonesia to China. The IMO investigation concluded that liquefaction of the bauxite cargo was the probable cause. Following the Bulk Jupiter casualty, MSC 94 (May 2014, convened before the loss but responding to growing concerns) and subsequent sessions tightened the bauxite schedule and classified certain bauxite grades under Group A rather than Group C. The IMSBC bauxite fines schedule and IMSBC bauxite schedule reflect the post-amendment classification.

Mineral concentrates

Copper, zinc, lead, iron, and other metallic mineral concentrates are produced from mined ore by concentration processes (flotation, gravity separation, and magnetic separation) that generate a product with a high metallic content but also a very fine particle size - typically with 80% or more of particles below 75 micrometres. At this particle size, even modest moisture contents can bring the material close to or above its TML. Concentrates are high-density (typically 2.0 to 4.5 t/m³) and have low stowage factors. They are shipped in large quantities from South America, Australia, and southern Africa to smelters in Asia and Europe. The IMSBC zinc concentrate schedule, IMSBC lead concentrate schedule, IMSBC copper concentrate schedule, and IMSBC iron concentrate schedule provide commodity-specific parameters.

Interaction with stability and structural requirements

Free-surface effect from liquefied cargo

When a Group A cargo liquefies at sea, it behaves as a free liquid surface within the hold. The free-surface effect reduces the ship’s effective metacentric height (GM) by an amount proportional to the second moment of area of the liquid surface divided by the displacement volume. For large holds characteristic of bulk carriers, the reduction can be substantial, potentially eliminating the positive GM entirely. This is discussed in detail in the free-surface effect article. Partial liquefaction, where only the lower layers of the cargo have fluidised while the surface crust remains apparently solid, is particularly dangerous because it may not be detectable from visual inspection of the cargo surface.

The interaction between liquefaction risk and ship stability is complex. A ship with adequate positive GM at departure can become unstable as the voyage progresses and as vibration induces progressive liquefaction of the cargo mass. The damage stability framework does not contemplate liquefaction as a flooding source, so the Code relies on pre-loading moisture control rather than post-casualty damage limitation to manage this risk.

Load line and freeboard

The IMSBC Code interacts with freeboard and load line requirements through its provisions on cargo density and stowage factor. The stowage factor of a bulk cargo determines the volume occupied per unit mass, which in turn affects how deeply the ship sits in the water for a given cargo weight. High-density cargoes (iron ore at approximately 0.3 to 0.5 m³/t, concentrates at 0.2 to 0.5 m³/t) frequently result in ships being weight-limited rather than volume-limited, meaning that full deadweight cannot be loaded without exceeding the appropriate load line. Shippers and operators who are unfamiliar with the interaction between the stowage factor, deadweight, and load line assignment risk inadvertent overloading. The IMSBC cargo density and stowage factor calculator assists in these calculations.

Bulk carrier structural standards

Bulk carriers are constructed to IACS Common Structural Rules for Bulk Carriers (CSR-BC), which prescribe minimum scantlings for hold frames, transverse watertight bulkheads, corrugated bulkheads, and hatch cover coamings. The IMSBC Code interfaces with these structural standards because the density and loading pattern of the cargo determines the maximum pressure on hold tank top plating and on hoppers. High-density cargoes loaded non-uniformly can induce local structural overstress even within the overall deadweight limit. Vessels trading regularly in iron ore or concentrates are subject to enhanced structural survey requirements under IACS surveys and classification society rules.

The BLU Code

The Code of Practice for the Safe Loading and Unloading of Bulk Carriers, universally known as the BLU Code (adopted by IMO Resolution MSC.159(78) in May 2004 at MSC 78), is a companion instrument to the IMSBC Code that addresses the interface between the ship and the shore terminal during loading and discharge operations. While the IMSBC Code focuses on the properties of the cargo itself and the conditions under which it may be safely carried, the BLU Code prescribes how the loading process should be managed to avoid structural damage, excessive sloshing of cargo during transfer, over-stressing of holds from uneven distribution, and flooding from hatch cover damage.

The BLU Code requires terminals to provide a terminal representative and a ship/shore safety checklist. It specifies the sequence of hold loading to avoid hogging and sagging stress concentrations, the rate of loading for different cargo densities, and the responsibilities of the terminal operator and the master during cargo operations. The BLU Manual, a supplementary guidance document, provides detailed worked examples and background material. The BLU Code is referenced in SOLAS Chapter VI Regulation 7, which requires that bulk carriers comply with both the IMSBC Code and the terminal/ship interface provisions. The bulk carrier loading rate and stress calculator assists in planning loading sequences that comply with BLU Code structural limits.

Amendment history and current status

01-09 amendments (2011)

The 01-09 amendment set entered into force simultaneously with the Code on 1 January 2011. It contained corrections and clarifications to several commodity schedules, and adjusted the reference to the IMDG Code to maintain consistency as that Code also updated.

02-13 amendments (2013)

Adopted at MSC 91 (November 2012) and entering into force on 1 January 2015, the 02-13 amendments introduced the iron ore fines (IOC) schedule as a distinct Group A commodity, with mandatory TML testing using the modified Proctor-Fagerberg method. This was the most consequential single amendment since the Code’s initial adoption, addressing a gap that casualty investigators had identified repeatedly. Additional material schedules were revised and a number of new cargoes added.

03-15 amendments (2015)

The 03-15 amendments incorporated further new schedules and updated emergency procedures for several Group B materials, with particular attention to DRI handling.

05-19 and 06-21 amendments

The 05-19 amendments (entering force 2021) and the 06-21 amendments (entering force 2023) consolidated a growing body of research on bauxite classification, revised testing requirements for certain agricultural products prone to self-heating (fishmeal, seedcakes), and updated the schedule for ammonium nitrate-based fertilisers in the wake of the Beirut port explosion of 4 August 2020, which killed over 200 people and destroyed a significant portion of Beirut’s port infrastructure and adjacent urban areas, drawing global attention to ammonium nitrate storage and handling risks.

07-24 amendments (2026)

The 07-24 amendments, the most recent cycle, apply from 2026. Key changes include revised Group A moisture testing protocols for several mineral concentrates, updated emergency response data aligned with the 2024 edition of the IMDG Code, and new or revised schedules for a range of materials. The ShipCalculators.com calculator catalogue incorporates parameters from the 07-24 amendment schedules where applicable.

Enforcement and port state control

The IMSBC Code is enforced through the port state control (PSC) framework. Under the Tokyo MOU, Paris MOU, and other regional PSC agreements, inspectors may examine cargo documentation, request verification of moisture content certificates, inspect hold conditions, and detain vessels where cargo is loaded without an adequate shipper’s declaration or where the declared moisture content exceeds the TML. PSC inspections of bulk carriers regularly cite IMSBC Code deficiencies as grounds for detention, including: missing or inadequate shipper’s declarations; certificates issued by non-accredited laboratories; declared moisture content data that is out of date relative to actual loading conditions; and missing emergency schedules for Group B materials.

Flag-state administrations are required to issue guidance to masters on the right to refuse cargo and the procedure for reporting non-compliance to the competent authority. In practice, the commercial pressure to load and sail on schedule is often cited as a factor in masters accepting cargoes with marginal or non-compliant documentation. Industry guidance from the International Group of P&I Clubs, INTERCARGO, and INTERTANKO reinforces the legal and practical basis for refusal.

Grain carriage

Grain presents a distinct suite of hazards that overlap with, but are not identical to, the IMSBC Code framework. Grain is classified as Group C under the IMSBC Code because it does not liquefy under normal cargo moisture conditions and does not present a chemical hazard in the Group B sense. However, it can shift - particularly in partially-filled holds - causing a list, and it can generate carbon dioxide and oxygen-depleting atmospheres through biological respiration. The International Grain Code (adopted under SOLAS Chapter VI, Part C, Regulation 9) applies in parallel with the IMSBC Code to ships carrying grain in bulk. The IMSBC wheat schedule, IMSBC corn schedule, IMSBC soybeans schedule, and IMSBC rice bran schedule cover the principal traded grain and oilseed varieties. Grain shift and its effect on the bulk cargo displacement and grain stability calculation are critical voyage planning inputs.

The grain heel stability calculator computes the maximum permissible heeling moment from grain shift under the International Grain Code, which requires a residual positive area under the righting lever (GZ) curve after applying the assumed shift moment.

Individual commodity schedules

The operative core of the IMSBC Code is Appendix 1, the individual commodity schedules. Each schedule is a standardised data sheet for a named cargo, containing a defined set of parameters that master, mate, cargo officer, and cargo surveyor use to plan and execute the voyage. Understanding the schedule structure is essential for compliance.

Schedule format and mandatory fields

Every schedule contains at minimum the following fields: the Bulk Cargo Shipping Name (BCSN); description of the cargo (physical appearance, colour, odour, particle size range); the cargo group or groups; the stowage factor in cubic metres per tonne; the angle of repose in degrees (or a statement that the cargo does not have a defined angle of repose because it is always handled as a slurry); the moisture content range and, for Group A cargoes, the TML; the size of cargo particles; class (the relevant IMO hazard class under the IMDG Code, if applicable); UN number (for dangerous goods); segregation requirements; hazard and emergency response data; and carriage conditions (ventilation, trimming, special requirements, entry precautions, and any prohibition on carriage).

The stowage factor is particularly important for voyage planning. A cargo with a stowage factor of 0.30 m³/t occupies 30 per cent less space per tonne than a cargo with a stowage factor of 0.40 m³/t. For high-density commodities, the ship will typically reach its deadweight limit before its volume limit, and the stowage factor determines how much volumetric space remains unused. For low-density materials such as wood chips (stowage factor approximately 2.0 to 3.0 m³/t), the ship reaches its volume limit before its deadweight limit. The IMSBC cargo density and stowage factor calculator assists operators in computing the expected cargo intake for a given hold volume and stowage factor.

Angle of repose

The angle of repose is the steepest angle at which a heap of the material will rest without sliding or collapsing. It is measured in degrees from the horizontal. Cargoes with a high angle of repose (for example, lump coal at approximately 38 to 45 degrees) retain their shape when loaded into a hold and do not slump significantly under vibration. Cargoes with a low angle of repose (for example, wet concentrate at 20 to 25 degrees) spread more readily and present a greater risk of cargo shift if the hold is not trimmed level. The angle of repose is also used to calculate the maximum surface slope permissible in a partially-filled hold, which interacts with longitudinal bending moment calculations under the BLU Code. The IMSBC angle of repose calculator computes the maximum permissible cargo surface slope based on declared angle of repose values.

Not otherwise specified schedules

Where a cargo does not match any named schedule, the shipper may apply the most appropriate NOS (not otherwise specified) entry. NOS entries exist for several broad categories, including Metal Sulphide Concentrates (general) and Seed Cake (non-hazardous). The IMSBC metal sulphide concentrates schedule covers a range of mixed metallic sulphide products. NOS entries apply more conservative default conditions than specific schedules and require the competent authority of the loading state to approve the carriage conditions before loading. This approval mechanism - known as the competent authority condition - allows novel cargoes to be carried under the Code while a specific schedule is developed through the IMO amendment process.

Hold atmosphere management

The management of hold atmospheres is a dimension of bulk cargo safety that the IMSBC Code addresses in depth, particularly for Group B cargoes. Three atmospheric hazards are relevant: oxygen depletion, flammable gas accumulation, and toxic gas accumulation.

Oxygen depletion

Several bulk cargoes consume oxygen through oxidation reactions within the cargo mass. Coal, DRI, and certain agricultural products (copra, wood chips, fishmeal) all consume oxygen at rates that can reduce the hold atmosphere below the minimum safe concentration of 20.9% down to levels that are immediately dangerous to life. The IMSBC Code requires that hold atmospheres be tested before personnel entry and that a suitable atmosphere testing instrument be carried on board. Specifically, the O₂ concentration must be at or above 20.9% (or within a defined safe range appropriate to the cargo) before entry. For coal cargoes, CO concentration is also monitored as an early indicator of self-heating, and the relevant threshold is typically 50 ppm CO as a first alert level, with higher levels triggering escalating responses.

The IMSBC coal self-heating assessment evaluates the risk profile for a coal cargo based on the coal’s reported properties and provides guidance on monitoring intervals and ventilation requirements.

Methane from coal

Coal seams trap methane gas at formation, and this gas is released progressively from the coal matrix after mining. The rate of outgassing depends on the coal rank, the particle size, the temperature, and the time since mining. In a sealed cargo hold, methane can accumulate to concentrations within the explosive range (5 to 15% by volume in air, the lower and upper explosive limits respectively). The IMSBC Code requires that holds carrying coal be ventilated at intervals to prevent methane accumulation, and that a methane-capable gas detector be available on board. The bulk coal methane ventilation calculator computes the minimum ventilation exchange rate required to maintain methane below 20% of the lower explosive limit (LEL), providing a margin of safety consistent with the Code’s approach.

Toxic gases

Certain cargoes emit toxic gases. DRI generates hydrogen when wet and can accumulate hydrogen sulphide. Fishmeal emits ammonia and hydrogen sulphide during decomposition. Coal can emit hydrogen sulphide from pyrite oxidation. Ammonium nitrate decomposes to nitrogen oxides at elevated temperatures. The IMSBC Code schedules for these materials specify the testing instruments required, the safe entry conditions, and in some cases an absolute prohibition on entry while the cargo is loaded. The requirement to test hold atmospheres for O₂, CO, CH₄, and H₂S (and in some cases NO₂) before entry requires the ship to carry calibrated multi-gas detectors, the calibration records of which are subject to PSC inspection.

Voyage planning under the IMSBC Code

Compliance with the IMSBC Code is not a one-time pre-departure exercise. It requires ongoing attention throughout the voyage.

Pre-loading planning

Before the ship arrives at the loading port, the cargo officer should obtain from the shipper or chartering party the proposed BCSN, the declared cargo group, and the provisional stowage plan. For Group A cargoes, the pre-loading documentation should include the most recent TML certificate from an accredited laboratory, dated within 30 days of the anticipated loading date under most flag-state administrations’ guidance (the Code itself does not specify an absolute expiry period for TML certificates, but IMO and industry guidance consistently recommend a short validity period given the time-sensitivity of moisture data).

The cargo officer should calculate the expected draft at completion of loading using the stowage factor and the hold volumes, then verify that the expected draft does not exceed the applicable load line for the zone and season. For dense cargoes, the trim and list arising from asymmetric loading must also be checked. The trim and list calculator addresses the trim contribution from cargo weight distribution across holds. The load line article describes the zone and seasonal mark system that governs the maximum permissible draft.

During loading

During loading, the cargo officer should monitor the actual moisture content of each lot of cargo as it is loaded, particularly in regions with variable weather. If rain falls during loading operations, loading should be suspended and the exposed cargo surface assessed. The IMSBC Code requires that loading be suspended if the moisture content of the cargo being loaded exceeds the TML, and resumed only when the moisture content has been confirmed to be below TML by re-testing. This provision is difficult to enforce in practice when there is commercial pressure to load continuously, and the requirement to retain and present re-test data is one of the IMSBC deficiencies most commonly cited by PSC inspectors.

Hold trimming requirements must be met as loading progresses. For Group A cargoes, the Code requires that the cargo be trimmed level to reduce free-surface effects. Inadequate trimming leaves a cargo peak or slope that can shift under ship motion, reducing transverse stability further before liquefaction has even begun. Section 5 of the Code specifies the trimming methodology in detail.

At sea

Group B cargoes require regular monitoring during the voyage. For coal, this means daily measurement of hold CO concentration and temperature, with results logged in the cargo logbook. Holds are typically surface-ventilated during the voyage to prevent methane accumulation, but the ventilation arrangement must not introduce water into a cargo that is sensitive to moisture. The cargo officer must balance the conflicting requirements of ventilating to dilute flammable gas and minimising the ingress of salt spray.

For DRI cargoes, holds must be maintained with an inert gas atmosphere (typically nitrogen or carbon dioxide) to suppress the oxidation and water-reactivity hazards. The nitrogen or CO₂ supply must be adequate for the full duration of the voyage plus a reserve, and the hold atmosphere must be monitored continuously. The IMSBC DRI-A schedule specifies the required inerting conditions and monitoring intervals.

At each port stop during a multi-port voyage, the cargo status must be reassessed before re-entering holds or handling residues.

Accreditation, laboratories, and certificate validity

The IMSBC Code’s effectiveness depends critically on the quality and independence of the moisture testing regime. A shipper who falsifies or manipulates moisture certificate data can cause a casualty even if the Code’s procedural requirements are nominally met. The Code requires that TML determination be carried out by a laboratory recognised by the competent authority of the state in which the laboratory is located. Accreditation typically requires ISO 17025 certification and demonstration of proficiency through inter-laboratory comparison exercises. The Code does not specify a global accreditation body; each flag state and loading state maintains its own list of recognised laboratories.

A persistent challenge is the geographic concentration of credible accredited laboratories relative to the locations of bulk cargo loading ports. Nickel ore is loaded at numerous small Indonesian ports where access to accredited laboratory facilities is limited and where sample transport to the nearest accredited laboratory can take several days, potentially compromising sample integrity. The 2011-2012 spate of nickel ore casualties led to enhanced requirements in Indonesia and the Philippines for in-country laboratory capability and for port authority oversight of sampling, but independent assessments have found continued inconsistency.

Certificate date validity is a related issue. The Code requires moisture content certificates to reflect the condition of the cargo at the time of loading, not weeks or months earlier when a previous lot from the same source was tested. In practice, shippers sometimes present certificates that were issued for an earlier cargo lot as representative of the current one. Chartering party guidance from organisations such as the International Group of P&I Clubs recommends that shipowners’ representatives attend sampling and insist on witnessing the preparation of samples for laboratory analysis, particularly for high-risk Group A commodities.

Connection to the SOLAS and MARPOL regulatory framework

The IMSBC Code sits within the broader SOLAS Convention architecture as a mandatory code under SOLAS Chapter VI. SOLAS Chapter XII (Additional Safety Measures for Bulk Carriers) applies to the structural and operational safety of bulk carrier vessels, including requirements for double-skin or single-skin construction standards that interact with the cargo density assumptions of the IMSBC Code. The MARPOL Convention intersects with bulk cargo carriage through Annex V (Garbage) and the residue management provisions for cargo holds after discharge, and through Annex I restrictions on bilge water discharge contaminated with cargo residues.

The ISM Code, implemented under SOLAS Chapter IX, requires shipping companies and ships to maintain a Safety Management System (SMS) that explicitly addresses the risks of bulk cargo carriage, including procedures for obtaining and verifying cargo declarations, testing moisture content, and refusing to load non-compliant cargoes. Classification societies such as Lloyd’s Register, DNV, Bureau Veritas, and the American Bureau of Shipping provide additional guidance and surveyor review at loading for high-risk commodities.

Relationship with the IBC Code

The International Bulk Chemical Code (IBC Code) governs the carriage of hazardous and noxious liquid chemicals in bulk. While the IMSBC Code deals exclusively with solid bulk cargoes, the two codes share regulatory logic in several areas: the hazard-based classification system, the requirement for individual commodity schedules specifying carriage conditions, the obligation on shippers to provide accurate cargo information, and the interface with the IMDG Code for packaged dangerous goods. A chemical tanker operator managing a cargo of liquid fertiliser (typically urea-ammonium nitrate solution) operates under the IBC Code, while a bulk carrier operator managing the same fertiliser in solid granular form operates under the IMSBC Code. The conceptual boundary is the physical state - solid versus liquid - rather than the chemical identity of the cargo.

Relationship with port state control and classification society oversight

Port state control deficiency patterns

INTERCARGO’s annual bulk carrier casualty reports and the published deficiency databases of regional PSC memoranda of understanding consistently show IMSBC Code deficiencies among the top ten categories for bulk carriers. Common deficiencies cited in detention reports include: missing or incomplete shipper’s declarations at the time of loading; TML certificates issued by non-accredited or unrecognised laboratories; actual moisture content at loading exceeding TML without the mandatory refusal or postponement of loading; absence of emergency schedules for Group B materials; failure to carry calibrated hold atmosphere testing instruments; and absence of documented hold trimming records.

Detention of a bulk carrier for IMSBC Code violations carries financial consequences beyond the daily rate of detention. Demurrage penalties may be imposed by the cargo interest if the delay exceeds the allowed laytime; insurance P&I cover may be compromised if a casualty is traced to a known and unresected deficiency; and classification society survey requirements may be accelerated following a PSC detention. Under the Paris MOU’s ship targeting system, bulk carriers with prior detentions for cargo documentation violations receive higher targeting priority, increasing the probability of future inspections.

Classification society surveys

Major classification societies - Lloyd’s Register, DNV, Bureau Veritas, ClassNK, American Bureau of Shipping, and others - do not directly survey IMSBC Code compliance as part of statutory certification (that responsibility falls to the flag state), but they do survey the structural elements that interact with bulk cargo: hatch cover watertightness, hold bilge pumping arrangements, sounding pipe locations, and the structural integrity of hopper and topside tank boundaries. Class rules for Enhanced Survey Programme (ESP) apply to bulk carriers over a certain age and require periodic in-water examination of hold frames and transverse bulkheads - elements whose failure under the combination of cargo pressure and sea sloshing has contributed to bulk carrier losses. The interaction between cargo density (a key IMSBC parameter) and hold structural loading is therefore a point at which classification society oversight and IMSBC Code compliance intersect directly.

Flag state requirements and additional national restrictions

Flag state administrations may impose requirements more stringent than the IMSBC Code minimum. Several major flag states have issued circulars requiring that TML certificates be renewed at intervals shorter than the Code’s implicit guidance, or requiring the master to obtain an independent moisture measurement before accepting cargo declarations at face value. Australia’s Australian Maritime Safety Authority (AMSA) has issued explicit guidance on acceptable laboratory accreditation bodies and on the sampling protocols that must be followed for nickel ore and bauxite loaded at Australian ports. Similar guidance has been issued by the Maritime and Port Authority of Singapore and by the Philippine Coast Guard for mineral ore trades through their respective ports.

Modern developments and ongoing challenges

Real-time moisture monitoring

One of the structural weaknesses of the IMSBC Code’s moisture-limit framework is its reliance on laboratory testing of samples taken before loading, which may not reflect the condition of the cargo at the point of loading hours or days later, particularly in ports subject to heavy rainfall. Research programmes have explored real-time moisture sensors that can be integrated into the cargo conveyor system to provide continuous moisture data during loading, but as of 2026 no mandatory real-time monitoring requirement exists in the Code.

Small vessel and barge carriage

The IMSBC Code applies to seagoing vessels, but a substantial volume of solid bulk cargo moves on inland waterways and in coastal barge trades that fall outside its scope. Several national administrations have implemented equivalent provisions for coastal bulk carriage, but harmonisation is incomplete. The IMO has under consideration at various sessions whether equivalent provisions should apply to small seagoing vessels below the SOLAS threshold, particularly in regions such as South-East Asia and West Africa where loss incidents have occurred.

Autonomous and remotely operated vessels

The anticipated introduction of Maritime Autonomous Surface Ships (MASS) creates new questions for IMSBC Code compliance. The Code’s provisions on cargo inspection, master’s right to refuse, and atmosphere testing before hold entry are framed around the assumption of a manned bridge and crew capable of exercising professional judgment. Adaptation of these provisions for MASS is under review at IMO as part of the broader MASS regulatory framework.

Climate-driven moisture variation

Climate change is altering precipitation patterns at major bulk cargo export terminals. Increased rainfall frequency and intensity at mining and port locations in tropical and subtropical regions is raising the baseline moisture content of cargoes at the point of loading. This trend makes the current TML framework more operationally binding, and may require revision of the safety factor embedded in the TML = 0.9 × FMP relationship if the statistical distribution of moisture content at loading shifts systematically upward.

References

IMO, International Maritime Solid Bulk Cargoes (IMSBC) Code, 2008 Edition (MSC.268(85)), International Maritime Organization, London, 2008.
IMO, SOLAS Convention, Chapter VI (Carriage of Cargoes and Fuel Oil), as amended to 2024.
IMO, BLU Code: Code of Practice for the Safe Loading and Unloading of Bulk Carriers, Resolution MSC.159(78), 2004.
IMO MSC 91/22 (2012) - Report of the Maritime Safety Committee, 91st session, incorporating adoption of IMSBC Code 02-13 amendments including iron ore fines schedule.
IMO MSC-MEPC.5/Circ.15 (2017) - VLOC mandatory reporting following Stellar Daisy sinking.
Marine Accident Investigation Branch (MAIB), Report on the Loss of MV Bulk Jupiter, London, 2015.
Transport Safety Investigation Bureau of China (TSIB), Sinking of MV Jianfu Star, 2011.
INTERCARGO, Bulk Carrier Casualty Report 2023, International Association of Dry Cargo Shipowners, London, 2024.
IMO, IMSBC Code 07-24 Amendments, MSC.510(105), London, 2024.
ISO 3082:2017, Iron ores - Sampling and sample preparation procedures, International Organization for Standardization.

External links

IMO IMSBC Code page - official IMO resource for the Code text and amendments
INTERCARGO - shipowners’ association with bulk cargo safety guidance
Nautical Institute: Bulk Carrier Safety - professional guidance for deck officers