IMSBC Group B cargoes: Cargoes with chemical hazards

Background

What Group B is

The IMSBC Code’s three-group classification, Group A liquefaction-risk cargoes, Group B chemical-hazard cargoes, and Group C cargoes that are neither A nor B, was introduced in the consolidated 2008 IMSBC Code (then voluntary, made mandatory under SOLAS Chapter VI on 1 January 2011). Each cargo listed in the IMSBC Cargo Schedules (Chapter 9) is assigned to one or more groups based on the dominant hazard. A cargo can be Group A only, Group B only, both Group A and Group B (the so-called “A and B” cargoes such as some sulphide concentrates that both liquefy and present a chemical hazard), or Group C only.

Group B is defined by Section 1.7.2 of the IMSBC Code as: “cargoes which possess a chemical hazard which could give rise to a dangerous situation on a ship”. The chemical hazards explicitly recognised include: combustible solids (Class 4.1 if classified as a packaged dangerous good); spontaneously combustible solids (Class 4.2); substances which on contact with water emit flammable gases (Class 4.3); oxidising substances (Class 5.1); toxic substances (Class 6.1); corrosive substances (Class 8); environmentally hazardous substances; and substances with miscellaneous hazards (Class 9), including substances that are toxic at elevated temperatures or that emit asphyxiating gases.

Group B cargoes that are also dangerous goods

Many Group B cargoes are also assigned UN numbers and IMDG classes when transported in packaged form. The IMSBC Cargo Schedules indicate this dual regulatory status by labelling such cargoes as “MHB” (Materials Hazardous only in Bulk) when they present a hazard only in bulk but not as a packaged dangerous good, or by listing the corresponding UN number and IMDG class when the bulk cargo is also a regulated dangerous good in packaged form. For example:

• Direct Reduced Iron (B), UN 2870, IMDG Class 4.2 in packaged form. The bulk cargo schedule applies because shipping DRI as packaged goods would be commercially unworkable.
• Ammonium nitrate fertiliser, UN 2067 (Class 5.1) for IMDG packaged shipments and as a Group B cargo under IMSBC for bulk shipments. The bulk schedule cross-references the IMDG provisions.
• Coal, designated MHB(SH) (self-heating) and MHB(WT) (water reactive, in some grades) and MHB(CB) (combustible) under the new MHB sub-categorisation introduced in IMSBC Amendment 04-17.
• Wood pellets, designated MHB(WF) for water-reactive and MHB(SH) for self-heating.

The combined IMSBC + IMDG regulatory regime ensures that a substance carried in any quantity from a single packaged drum to a 200,000-tonne Capesize bulker is subject to consistent hazard controls. See SOLAS Chapter VII Part A for the dangerous-goods carriage gate.

MHB sub-categorisation

IMSBC Amendment 04-17 (in force 1 January 2019) introduced a more granular sub-categorisation within Group B for cargoes that are not themselves classified as IMDG dangerous goods but which present specific chemical hazards in bulk:

• MHB(CB), Combustible solid in bulk: the cargo can burn but does not necessarily self-heat.
• MHB(SH), Self-heating solid in bulk: the cargo undergoes exothermic oxidation that, if heat is not dissipated, can lead to spontaneous ignition.
• MHB(WT), Solid that emits flammable gas when wet: hydrogen evolution from ferrosilicon, methane evolution from coal in some conditions.
• MHB(WF), Solid that becomes a flowable solid when wet: similar to liquefaction but distinct from Group A in mechanism (typically wood-pellet swelling rather than fine-particle pore-pressure rise).
• MHB(TX), Solid that emits toxic gas in bulk: arsine and phosphine from ferrosilicon containing arsenic or phosphorus impurities.
• MHB(OH), Other hazards including dust explosion (sulphur dust, aluminium powder), corrosive properties (calcium oxide quicklime), or oxygen-depletion in unventilated holds (wood pellets, soya bean meal, copra).

The MHB labelling appears in each cargo schedule’s headline “Hazards” entry and drives the corresponding hold preparation, ventilation, monitoring and emergency response requirements.

How a cargo gets onto Group B’s list

A cargo can be added to the IMSBC Cargo Schedules in Chapter 9 only by amendment to the IMSBC Code, adopted by the IMO Maritime Safety Committee. The amendment cycle proceeds in two-year intervals, with each amendment introduced first as voluntary application from a specified date and then mandatory after a transition period. The most recent amendments are IMSBC Amendment 06-21 (adopted by IMO Resolution MSC.500(105), entered into force 1 December 2023) and Amendment 05-19 (Resolution MSC.462(101), in force 1 January 2021).

For a cargo not listed in Chapter 9 but presenting characteristics of Group B hazards, the competent authority of the loading port (or, where relevant, of the port of discharge and the flag state) must issue a tripartite assessment under IMSBC Section 1.3 confirming the cargo’s group classification and the schedule under which it may be carried, pending formal listing in the next amendment cycle. Tripartite agreements are common for new agricultural by-products, mining intermediates, and recycled materials.

The cargo schedule structure

Each Group B cargo in IMSBC Chapter 9 is documented in a standardised cargo schedule containing the following standard sections:

1. Description, physical form, particle size range, source mineralogy or processing route.
2. Characteristics, angle of repose, bulk density, stowage factor, hazard class.
3. Hazard, including MHB sub-category and IMDG class where applicable.
4. Stowage and segregation, IMDG-style segregation requirements from incompatible cargoes.
5. Hold cleanliness, clean and dry hold standards, removal of previous cargo residues.
6. Weather precautions, restrictions on loading during rain or with high humidity.
7. Loading, trim and ventilation arrangements, restrictions on rough loading.
8. Precautions, temperature monitoring, gas monitoring, no-smoking enforcement.
9. Ventilation, surface ventilation only, mechanical ventilation, no ventilation, or specific airflow rates.
10. Carriage, temperature recording frequency, gas sampling, ullage entry restrictions.
11. Discharge, special handling for hot-spots, dust suppression, residue management.
12. Clean-up, final hold inspection criteria, cargo residue disposal.

The schedule also lists emergency procedures for fire, exposure, and spillage. Many Group B cargoes have specific emergency entries that depart from the IMDG EmS schedules because the bulk-cargo fire-fighting context is different from a packaged-cargo fire (no separation between cargo, structural water tightness compromised by hatch covers under fire condition, etc.).

Coal

The dominant Group B cargo

Coal is by tonnage the largest Group B cargo and one of the largest dry-bulk commodities globally, approximately one billion tonnes of seaborne coal trade per year, dominated by thermal coal (for power generation) and metallurgical coal (for steel-making coke). Coal is shipped as bituminous, sub-bituminous, anthracite or lignite depending on rank, and the IMSBC schedules treat each rank with slightly different hazard profiles. See the per-rank calculator for bituminous coal and anthracite.

Hazards

Coal in bulk presents three principal hazards that drive its IMSBC schedule:

1. Self-heating leading to spontaneous combustion. All coals oxidise exothermically at ambient temperature; the rate of oxidation is determined by coal rank, particle size, moisture content, oxygen access and ambient temperature. Lower-rank coals (sub-bituminous, lignite) and freshly-mined high-volatile coals self-heat fastest. The exothermic heat evolved during oxidation is small per unit cargo per unit time, but if it cannot be dissipated to the surroundings the cargo temperature rises; above approximately 60-70°C the oxidation rate accelerates further (positive feedback through the Arrhenius dependence); above 100°C steam evolution begins; above 150-200°C ignition occurs.

2. Methane emission. Many coals contain adsorbed methane (firedamp in mining terminology) which is released during transport, particularly in the early hours after loading as the coal de-pressurises. Methane is flammable in air at concentrations between 5% (lower flammable limit, LFL) and 15% (upper flammable limit, UFL); in sealed cargo holds the methane concentration can rise into the explosive range and be ignited by any spark, hot bearing, or smoking violation. The Coal Methane Ventilation Rate calculator supports surface-ventilation airflow specification to keep methane below 20% of LFL.

3. Oxygen depletion in cargo holds and adjacent enclosed spaces. The same oxidation that produces self-heating also consumes oxygen and produces carbon monoxide. Oxygen levels in unventilated coal holds can drop from atmospheric 20.9% to single digits within hours; carbon monoxide concentrations of several thousand ppm are routinely measured in coal-cargo enclosed spaces. Both hazards are fatal to anyone entering without enclosed-space entry procedures including supplied-air respiratory protection.

Coal monitoring and ventilation regime

The IMSBC coal schedule requires:

• Temperature monitoring at multiple depths in each hold, recorded at least once per watch (every four hours) and trended throughout the voyage. A rising trend, especially above the 55°C threshold, requires immediate enhanced ventilation and notification to the master. The Coal Self-Heating Indicator calculator implements the trending logic.
• Gas monitoring for methane, oxygen and carbon monoxide before any enclosed-space entry. Many vessels are equipped with permanent fixed-gas monitoring systems for coal cargoes that read continuously and alarm on threshold excursion.
• Surface ventilation for the first 24 hours after loading to dissipate methane peak. After 24 hours the schedule typically requires hatches battened with no surface ventilation (because surface ventilation supplies oxygen that accelerates self-heating), the so-called “self-extinguishing” hold preparation.
• No naked lights, no smoking, no welding in or near holds throughout the voyage.

Coal hold preparation

Holds must be clean and dry before loading, with no oily residue from previous cargoes (oil films can absorb oxygen and themselves self-ignite at elevated temperature). The steel hatch coamings must be in good condition with intact rubber gaskets to prevent water ingress. Bilge wells should be tested for proper drainage and the bilge system (which serves as the primary firefighting water source if internal flooding becomes necessary) verified operational.

Coal stowage

Coal is normally trimmed level across the hatch to minimise the surface area exposed to oxygen access. Trimming arrangements that pile coal high in the centre of the hold create chimneys, channels through which air can flow into the cargo mass and accelerate self-heating. Some terminals trim coal hard against the bulkheads to compress the pile and reduce permeability.

Coal fires at sea

A coal cargo fire at sea is one of the most difficult casualties to manage. The IMO recommended response is:

1. Do not open the hatches, opening the hatch supplies oxygen and can accelerate fire from a smouldering hot spot to flaming combustion.
2. Battened-hold smothering, close all ventilation and rely on oxygen depletion within the sealed hold to extinguish the fire.
3. Bilge water flooding as a last resort, with attention to vessel stability when introducing thousands of tonnes of water above the cargo mass.
4. Inert gas injection, some specialised vessels carry CO₂ or N₂ injection systems for coal-fire suppression, but most do not.
5. Diversion to refuge port, fire-management decisions almost always include diversion to a designated coal-fire refuge port (the IMO maintains a list); discharge under shore-supplied hydraulic and thermal monitoring is standard.

Sulphur

Forms shipped

Elemental sulphur is shipped in bulk in three main forms: prilled (pelletised) sulphur, molten sulphur (carried at 130-150°C as UN 3257 in dedicated tank vessels, see IMDG Class 9 for elevated-temperature substances), and bright yellow crushed lump sulphur. Bulk solid sulphur (prills, lumps) is the IMSBC Group B cargo; molten sulphur is regulated under MARPOL Annex II / IBC Code as a chemical tanker cargo and not under IMSBC.

Hazards

Solid sulphur is flammable with a low autoignition temperature (around 232°C), but the more pressing hazards are:

• Dust explosion. Sulphur dust forms explosive mixtures in air at concentrations as low as 35 g/m³. The minimum ignition energy is approximately 15 mJ, easily met by static discharge from cargo handling equipment, vehicle electrical systems, or even falling material in the cargo stream. The Bulk Sulphur Dust Explosion Risk calculator supports the airflow and dust-suppression specification.
• Toxic gas emission. Hot sulphur produces sulphur dioxide (SO₂) and hydrogen sulphide (H₂S) in trace quantities. In a closed hold containing self-heating sulphur or sulphur in contact with moisture, these concentrations can rise into the irritant or fatal range.
• Corrosion of structural steel. Sulphur in contact with moisture forms sulphurous and sulphuric acid that aggressively corrodes hold steel. Long-distance sulphur trades have caused chronic structural corrosion in older bulk carriers; modern sulphur-trade vessels apply special protective coatings.

Sulphur loading and discharge

Sulphur is loaded with substantial dust generation. Most modern terminals use enclosed conveyor systems with dust suppression (water spray, foam, vacuum extraction). The vessel side must verify that hold openings are sealed against dust ingress to the accommodation, machinery and deck spaces. Smoking is prohibited within several hundred metres of any sulphur cargo operation. After loading, the vessel typically washes down decks with water to remove deposited sulphur dust.

Direct Reduced Iron and Hot Briquetted Iron

What DRI is

Direct Reduced Iron (DRI) is solid iron produced by reducing iron oxide ore (haematite, magnetite, pellets) with hydrogen and carbon monoxide at temperatures below the iron melting point. The resulting product is approximately 90-95% iron in a porous metallic form. DRI is an alternative to traditional blast-furnace pig iron and is produced increasingly using natural gas and (in newer plants) green hydrogen as the reducing gas, making it a key feedstock for low-carbon steel-making.

Three forms: A, B, C

The IMSBC schedules recognise three forms of DRI with different hazard profiles:

• DRI (A) Hot Briquetted Iron (HBI), DRI fines compressed at 650-700°C into dense briquettes with apparent density >5,000 kg/m³ and very low porosity. The briquetting process passivates the surface and substantially reduces re-oxidation potential. HBI is the safest DRI form for sea transport and the schedule reflects this with reduced monitoring requirements.

• DRI (B) Lumps, pellets, cold-moulded briquettes, DRI in larger fragments that has not been hot-briquetted but has been allowed to passivate at ambient temperature for a defined period (typically 72+ hours) before loading. The schedule requires inerting of cargo holds with nitrogen before loading and during transit, plus continuous gas monitoring. The DRI Passivation Requirement calculator supports the passivation-time check. See also IMSBC DRI (B).

• DRI (C) Fines, by-product fines, DRI fines and dust that has not been briquetted or pelletised. This is the most hazardous form because the high specific surface area enables rapid re-oxidation and hydrogen evolution on contact with water. The schedule requires extensive precautions and many flag states restrict or prohibit DRI (C) carriage. See IMSBC DRI Fines (C).

DRI hazards

The principal DRI hazards are re-oxidation (the metallic iron reacts with oxygen and water vapour to form iron oxide, releasing heat and consuming oxygen) and hydrogen evolution (the metallic iron reacts with water to form hydrogen gas and iron oxide, with hydrogen being explosive in air at 4% to 75% concentration). Both reactions accelerate at elevated temperatures, and once initiated can become self-sustaining if heat dissipation and gas removal are inadequate.

DRI inerting and monitoring

DRI (B) and DRI (C) cargoes typically require nitrogen inerting of cargo holds to maintain oxygen below 5% by volume. Nitrogen is supplied either from shore-based plant before sailing or from on-board membrane or PSA generators. Continuous monitoring of hydrogen, oxygen and carbon monoxide is required at multiple hold depths. Temperature monitoring follows the same regime as for coal but with tighter excursion thresholds (alarm at 50°C versus 55°C for coal).

DRI casualties

DRI cargoes have a notable casualty record. The 2002 fire on the bulk carrier Pavlina off Indonesia, the 2011 fire on Jian Hua, and several enclosed-space fatalities reported by classification societies in the 2010s have driven progressive tightening of the DRI schedule. The IMSBC working group has continued to review DRI provisions across multiple amendments.

Fishmeal and seed cake

Fishmeal hazards

Fishmeal is a Group B cargo because of its strong tendency to self-heat through fat oxidation. Fishmeal contains oil (5-15% depending on species and processing) that oxidises exothermically; the oxidation generates heat that accelerates further oxidation in a positive feedback similar to coal but mediated by a different chemistry (lipid peroxidation rather than coal-rank oxidation). Untreated fishmeal in bulk can self-heat to 200°C+ within weeks and ignite spontaneously.

Antioxidant requirement

Fishmeal in international trade is required to be stabilised with an antioxidant prior to shipment, typically:

• Ethoxyquin at 100-1,500 ppm (formerly the dominant antioxidant; subject to EU restrictions since 2020),
• BHA (butylated hydroxyanisole) and BHT (butylated hydroxytoluene) as alternative or supplementary antioxidants,
• TBHQ (tert-butylhydroquinone) in some jurisdictions.

The shipper must provide a certificate of antioxidant treatment showing the concentration applied, the application date, and the cargo’s age relative to the antioxidant decay curve. Antioxidant-stabilised fishmeal is normally stable for several months under ordinary stowage conditions; un-stabilised or under-stabilised fishmeal may require refrigerated containerised carriage instead of bulk transport. See the IMSBC Fishmeal and IMSBC Fishmeal Flaked cargo schedules.

Seed cake

Seed cakes (the protein-rich pressed residue from oil-seed processing, soya bean meal, rapeseed meal, sunflower meal, copra, palm kernel meal, cottonseed meal) are similar to fishmeal in their self-heating mechanism (residual oil oxidation) but with different antioxidant requirements and different hazard profiles by species. The IMSBC schedules distinguish:

• Seed cake (non-hazardous), seed cakes with sufficiently low residual oil content (typically ≤1.5%) and tested moisture content that they do not present significant self-heating risk; classified as Group C. See IMSBC Seed Cake (non-hazardous).
• Seed cake (UN 1386, UN 2217, UN 1374 derivatives), seed cakes with higher oil content or higher moisture that present self-heating risk; classified as Group B with specific schedules.
• Copra (dried coconut), particularly hazardous because its fat content can exceed 30%; typically requires special hold preparation including pre-loading inerting.

The 2013 fire on the MV Hantian (copra cargo from the Philippines) and similar incidents have driven progressive tightening of the seed-cake schedules.

Wood pellets

What wood pellets are

Wood pellets are compressed sawdust and wood-shavings cylinders used as a renewable biomass fuel for power generation. The trade has grown substantially since 2010 as European and East Asian power utilities have converted coal-fired stations to biomass co-firing. Annual seaborne wood-pellet trade is now several tens of millions of tonnes.

Wood pellet hazards

Wood pellets present three principal hazards:

1. Self-heating through residual lignocellulose oxidation. The reaction is similar to fishmeal/seed-cake oxidation but involves different chemistry. Self-heating is most pronounced in pellets shipped within weeks of manufacture; aged pellets are substantially safer.

2. Carbon monoxide and oxygen depletion. Wood pellets in bulk consume oxygen and produce carbon monoxide at rates that have caused multiple enclosed-space fatalities at port-side handling facilities. CO concentrations in unventilated wood-pellet silos and ship holds have been measured at thousands of ppm, far above the immediately dangerous to life and health (IDLH) threshold of 1,200 ppm.

3. Dust explosion. Wood-pellet dust formed during loading and discharge is combustible and forms explosive mixtures in air. Dust explosions in pellet-handling facilities have caused several major casualties; the 2010 Imperial Sugar refinery explosion in the United States (which involved sugar dust, not wood pellets, but illustrates the mechanism) and several pellet-plant fires in North America have driven progressive tightening of dust-management requirements.

The IMSBC Wood Pellets schedule covers ventilation, gas monitoring and entry restrictions.

Charcoal and petroleum coke

Charcoal

Charcoal (produced by partial pyrolysis of wood) is a classic self-heating cargo. The hazard depends on the production method:

• Activated charcoal (high specific surface area, used for filtration and adsorption applications) is the most hazardous; activation produces a porous structure with extremely high surface area (typically 500-2,000 m²/g) that promotes oxygen adsorption and exothermic oxidation.
• Lump charcoal (low surface area, used for cooking and metallurgy) is less hazardous but still classified as Group B MHB(SH).

Both grades require at least seven days of cooling between manufacture and loading, with shipper certification of the cooling period. The 2003 fire on the Thomson Spirit (one of several charcoal-cargo incidents) illustrates the consequences of inadequate cooling. See IMSBC Charcoal.

Petroleum coke

Petroleum coke (petcoke), the solid carbon residue from heavy-oil refining, is shipped in two forms: green petcoke (uncalcined, high volatile content) and calcined petcoke (heated to 1,200-1,400°C to drive off volatiles). Green petcoke is Group B MHB(CB) because of its higher volatile content; calcined petcoke is generally Group C unless specific hazards apply.

Both grades present dust hazards during loading (similar to coal), and the schedule requires dust suppression, water-spray on conveyor systems, and verification that the vessel’s accommodation and machinery air intakes are protected.

Ferrosilicon and aluminium ferrosilicon

Composition and hazards

Ferrosilicon (FeSi) is a steel-industry alloy used to deoxidise and silicon-alloy steel. Aluminium ferrosilicon (AlFeSi) contains both aluminium and silicon. Both alloys can react with water in the cargo hold to evolve hydrogen gas, plus traces of arsine (AsH₃) and phosphine (PH₃) if the alloy contains arsenic and phosphorus impurities, which it generally does at trace levels:

• Hydrogen evolved at sufficient rate creates explosive atmospheres (4-75% in air).
• Arsine and phosphine are highly toxic at parts-per-million concentrations; both have caused enclosed-space fatalities.

Ferrosilicon stowage

The IMSBC schedule for ferrosilicon requires:

• Strictly dry holds, verified moisture content of the cargo before loading, and complete sealing of hold accesses to prevent water ingress during voyage.
• Continuous gas monitoring for hydrogen, arsine and phosphine.
• Restricted enclosed-space entry, only with full breathing apparatus and gas-detection meters.
• Voyage-end de-gassing before discharge personnel enter the holds.

See IMSBC Ferrosilicon.

Ammonium nitrate fertilisers

Group B/IMDG Class 5.1 overlap

Ammonium nitrate (AN) is the principal nitrogen fertiliser worldwide. The IMSBC schedules cover several AN grades:

• Ammonium nitrate-based fertiliser (UN 2067), Class 5.1 oxidiser when packaged; Group B when in bulk. Restricted by particle size and combustible-material content.
• Calcium ammonium nitrate fertiliser, typically lower hazard than pure AN; specific schedule.
• Urea ammonium nitrate solution (UAN), IBC Code chemical-tanker cargo, not IMSBC. See IBC Urea Ammonium Nitrate.

The hazard profile of bulk AN is shaped by the Texas City 1947, Toulouse AZF 2001 and Beirut 2020 disasters discussed in IMDG Class 5. The IMSBC schedule for bulk AN requires:

• Verification that combustible-material content is below threshold (typically 0.2% for fertiliser grade).
• Rigorous separation from oils, fuels, solvents and combustibles.
• Hold cleanliness verification, no residual oil films from previous cargoes.
• Specific weight and stowage limits per hold.
• Contingency planning including external cooling capability if temperature monitoring shows excursion.

Calcium hypochlorite (UN 2880)

Calcium hypochlorite is a Group B oxidising solid that self-heats and decomposes when wet, releasing chlorine gas. The schedule requires strictly dry holds, segregation from organic cargoes, and gas monitoring throughout the voyage.

Quicklime, magnesia and water-reactive Group B cargoes

Quicklime (calcium oxide)

Quicklime (CaO) reacts vigorously with water to form calcium hydroxide and release substantial heat. In a cargo hold breached by water ingress (heavy weather, hatch-cover failure, bilge flooding) the reaction can heat the cargo mass to several hundred degrees Celsius and damage structural steel. The IMSBC schedule requires verification of hold dryness, intact hatch covers, and a cargo-securing arrangement that does not concentrate water around any single cargo region.

Calcined magnesia

Calcined magnesia (MgO from calcining magnesium carbonate) similarly reacts with water but with somewhat less violence. Some grades of calcined magnesia are classified Group C if their reactivity is below the threshold; reactive grades fall under Group B MHB(WT).

Self-heating monitoring and ventilation regimes

Temperature monitoring

The general principle for self-heating Group B cargoes is daily (and ideally per-watch) temperature recording at multiple depths in each hold, trended against the cargo’s specific schedule thresholds:

• Initial alarm typically at 55°C for coal, 50°C for DRI, lower for fishmeal/seed cake.
• Intervention threshold typically at 65-70°C, the master is required to take active steps (enhanced ventilation, course/speed adjustment to reduce roll, diversion consideration).
• Critical threshold at 80°C+, emergency response, potentially diversion to refuge port.

Temperature is recorded by inserted thermometers, fixed thermocouples in some specialised vessels, or thermal-imaging surveys of hold surfaces. The trend (rate of rise) is often a more meaningful indicator than the absolute value: a steady 50°C is less concerning than 40°C rising at 2°C per day.

Gas monitoring

Group B cargoes that emit gases require per-watch gas measurement at hold ullage points before any access:

• Methane for coal cargoes (LFL = 5%; alarm at 20% LFL = 1% methane).
• Hydrogen for DRI and ferrosilicon cargoes (LFL = 4%; alarm at 20% LFL = 0.8%).
• Carbon monoxide for self-heating cargoes (alarm at 50 ppm; IDLH 1,200 ppm).
• Oxygen for all enclosed spaces (alarm if below 20.5% or above 23.5%).
• Hydrogen sulphide for sulphur, certain ores (alarm at 5 ppm).

Ventilation regimes

The IMSBC schedules specify ventilation regimes by cargo:

• Surface ventilation only, natural air movement above the cargo surface, no air supply into the cargo mass. Used for most Group B cargoes including fishmeal, seed cake, wood pellets in most grades.
• No surface ventilation, hatches battened, no airflow whatsoever. Used for coal after the initial methane-dissipation period.
• Mechanical ventilation, powered fans drawing air across hold surface at specified airflow rate. Used for cargoes with high gas-emission rates and for the methane-dissipation period of coal cargoes.
• Inert atmosphere, nitrogen blanket maintained throughout voyage. Used for DRI (B) and DRI (C) cargoes.

Stowage and segregation

Group B segregation under IMSBC

The IMSBC Code does not have an explicit segregation matrix on the same model as the IMDG Code. Instead, each cargo schedule specifies the cargoes from which segregation is required. Common segregation rules:

• Self-heating Group B cargoes must be segregated from oxidisers (ammonium nitrate, calcium hypochlorite), the combination has driven several historical fires.
• Water-reactive cargoes (ferrosilicon, calcium oxide) must be segregated from cargoes that may contain or release water (some sulphide concentrates, certain agricultural products).
• Oxidisers must be segregated from organic cargoes, hydrocarbon residues and combustibles.
• Toxic-emitting cargoes must not be co-stowed with foodstuffs.

Segregation from packaged dangerous goods

When a Group B cargo is co-stowed on a vessel that also carries packaged dangerous goods, the segregation rules of the IMDG Code apply for the relationship between the bulk cargo and the packaged goods. For example, a bulk coal cargo (MHB(SH)) must be segregated from packaged Class 5.1 oxidisers.

Documentation

Shipper’s declaration

Every Group B cargo shipment requires a shipper’s declaration under IMSBC Section 4 stating:

• Cargo name and Bulk Cargo Shipping Name (BCSN) per the schedule.
• Group classification (A, B, A and B, or C) and any MHB sub-categories.
• UN number and IMDG class if applicable.
• Stowage factor and angle of repose.
• Moisture content where applicable.
• Antioxidant treatment (for fishmeal and seed cake).
• Passivation status (for DRI).
• Certificate of cooling period (for charcoal).
• Source of the cargo and processing route.

Hold inspection certificate

Pre-loading hold inspection by an independent surveyor is standard practice for many Group B cargoes (coal, sulphur, DRI). The inspection certificate documents hold cleanliness, dryness, integrity of structures, and operational status of monitoring equipment.

Voyage records

The master maintains continuous logbook records of temperature, gas concentration, ventilation regime adjustments, and any anomalous observations. These records are available to flag-state, port-state and class-society inspection on request.

Notable casualties

Coal cargo fires

Coal-cargo fires occur multiple times per year across the world fleet. Notable cases:

• MV Sage Sagittarius 2012, Australian coal carrier, fatal ITF investigation revealed unsafe coal-loading practices; multiple injuries.
• MV Vega Auriga 2009, coal cargo fire in the Indian Ocean; vessel diverted to Cape Town for refuge; six-month cargo discharge under shore-supplied cooling.
• Many additional coal fires every year reach refuge ports without major media attention but contribute to the underwriting profile of the trade.

MV Cougar Ace 2006

The PCTC Cougar Ace (carrying around 4,800 vehicles, primarily Mazdas) heeled severely during ballast exchange in the North Pacific in July 2006. While not strictly a Group B casualty, the incident illustrates how dry-bulk-style stability margins differ from packaged-cargo vessels and reinforces the importance of hold-by-hold loading sequencing for any bulk operation.

Wood-pellet enclosed-space fatalities

A series of fatalities at wood-pellet handling facilities and on board pellet carriers in the 2010s, including incidents at European pellet-receiving terminals and on board feeder vessels in the North American Great Lakes, drove the wood-pellet schedule’s tighter enclosed-space entry requirements. The fatalities have generally involved port-side workers entering silos or holds without atmospheric testing, finding oxygen levels below 10% and CO levels above the IDLH threshold.

DRI fires

DRI cargoes have caused multiple bulk-carrier fires, with the MV Pavlina 2002 and MV Jian Hua 2011 as the most-cited examples. Both involved DRI (B) or DRI (C) cargoes with inadequate inerting or with water ingress through compromised hatch covers; the fires required diversion to refuge port and lengthy salvage operations.

Sulphur fires

The MV Buochsa 1996 sulphur cargo fire is one of several incidents that drove progressive tightening of the sulphur schedule. Sulphur-cargo fires are typically smaller in scale than coal fires (because of the lower energy content per tonne) but are particularly dangerous because of the SO₂ and H₂S emissions, which can incapacitate or kill rescue personnel.

See also

• International Maritime Solid Bulk Cargoes (IMSBC) Code
• IMSBC Group A cargoes (cargoes that may liquefy)
• IMDG Class 5: Oxidisers and Organic Peroxides
• IMDG Class 4 Flammable Solids
• IMDG Class 9 Miscellaneous Dangerous Goods
• SOLAS Chapter VI Carriage of Cargoes and Oil Fuels
• SOLAS Chapter VII Carriage of Dangerous Goods
• SOLAS Chapter XII Additional Safety Measures Bulk Carriers
• MARPOL Annex III Harmful Substances Carried in Packaged Form
• Cargo hold preparation standards
• Cargo draught survey for bulk carriers

References

• International Maritime Organization. International Maritime Solid Bulk Cargoes (IMSBC) Code, 2022 edition (Amendment 06-21). Sections 1.7 (group classification), 4 (assessment of cargo and shipper’s declaration), 7 (hold cleanliness and weather precautions), 8 (test procedures), 9 (cargo schedules), 10 (transport of solid wastes in bulk), 11 (security provisions), Appendix 1 (BCSN list), Appendix 2 (test methods).
• IMO Resolution MSC.500(105) adopting IMSBC Code Amendment 06-21 (May 2022).
• IMO Resolution MSC.462(101) adopting IMSBC Amendment 05-19.
• IMO Resolution MSC.426(98) adopting IMSBC Amendment 04-17 (introducing MHB sub-categorisation).
• International Convention for the Safety of Life at Sea, 1974 (SOLAS), Chapter VI Carriage of Cargoes and Oil Fuels, Chapter VII Part B Carriage of Dangerous Goods in Solid Form in Bulk, Chapter XII Additional Safety Measures for Bulk Carriers.
• International Maritime Dangerous Goods (IMDG) Code, 2022 edition, for cross-reference where Group B cargoes also have UN-number IMDG classification.
• ISO 3082, ISO 3087, ISO 12742, ISO 21246, sampling and moisture-determination standards.
• IACS Recommendation No. 110 on Hold Preparation and Cargo Operations on Bulk Carriers.
• IACS Recommendation No. 116 on Cargo Hold Steel Structure Inspection on Bulk Carriers.
• INTERCARGO Bulk Carrier Casualty Report (annual), statistical analysis of bulk-carrier total losses, including cargo-induced casualties.
• BIMCO standard contractual clauses for bulk-cargo voyages, including the Solid Bulk Cargo Clause, Hold Cleanliness Clause and DRI Cargo Clause.
• Marine Accident Investigation Branch (UK), Australian Transport Safety Bureau (ATSB), Federal Bureau of Maritime Casualty Investigation (Germany), published casualty reports for cited incidents including the MV Pavlina, MV Jian Hua and various coal-cargo fire investigations.
• World Coal Association and International Energy Agency seaborne-coal trade statistics.
• World Steel Association DRI production and trade statistics.
• INTERFISH and IFFO global fishmeal trade data and antioxidant treatment guidance.
• US Pellet Fuels Institute (PFI) and European Bioenergy Industry standards for wood-pellet handling and stowage.