IMSBC Group B: solid bulk cargoes with chemical hazards

Group B of the International Maritime Solid Bulk Cargoes Code covers cargoes which possess a chemical hazard which could give rise to a dangerous situation on a ship. That is the whole definition, at section 1.7 of the Code as amended by resolution MSC.539(107). It sits against Group A , cargoes which possess a hazard due to moisture that may result in liquefaction or dynamic separation , and Group C , cargoes which are classified as neither group A nor group B.

Group B is where coal, direct reduced iron, sulphur, seed cake, fishmeal, charcoal, petroleum coke, ferrosilicon, ammonium nitrate fertilizer and quicklime are regulated. It is the part of the Code that decides whether a hold is inerted or ventilated, whether the fire response is to batten down or to open the hatches, and whether a stevedore who opens an access hatch is walking into an atmosphere that will kill in eight minutes.

This article works from the Code’s own text at amendment 07-23. Bulk Cargo Shipping Names are quoted exactly as the Code writes them, which means British spellings such as SULPHUR and ALUMINIUM FERROSILICON POWDER appear in capitals even though the surrounding prose is US English. A shipping name that is not written exactly as Appendix 1 has it is not a Bulk Cargo Shipping Name.

The three populations inside Group B

Group B is not one class of cargo but three, and section 9.1 says so directly: solid bulk cargoes which may possess chemical hazards during transport are in group B, and these materials can be classified as dangerous goods under 9.2.2 not possessing additional chemical hazards specified in 9.2.3, as MHB under 9.2.3, or as dangerous goods also possessing additional chemical hazards specified in 9.2.3.

The practical difference shows up in the Characteristics table of any individual schedule . A dangerous good carries an entry in the Class cell and usually a UN number: SULPHUR UN 1350 reads class 4.1, FERROSILICON reads class 4.3 with subsidiary hazard 6.1. An MHB cargo reads “Not applicable” in Class and carries letters in the MHB cell instead: DIRECT REDUCED IRON (B) reads SH and/or WF. A cargo in the third population carries both.

That split is not bookkeeping. It decides which SOLAS chapter applies, which certificates the ship needs, and whether the Document of Compliance is required at all.

The eight hazard classes recognized at section 9.2.2 are class 4.1 flammable solids, class 4.2 substances liable to spontaneous combustion, class 4.3 substances which in contact with water emit flammable gases, class 5.1 oxidizing substances, class 6.1 toxic substances, class 7 radioactive material, class 8 corrosive substances, and class 9 miscellaneous dangerous substances and articles. Environmental harm is not one of them: it enters the Code on a separate axis, at 4.2.2.17, as the declaration of whether the cargo is harmful to the marine environment under appendix I of MARPOL Annex V .

Materials hazardous only in bulk: the seven codes

MHB means materials which may possess chemical hazards when carried in bulk other than materials classified as dangerous goods in the IMDG Code . Section 9.2.3.1.1 adds that these materials present a significant risk when carried in bulk and require special precautions. The category exists because a substance can be harmless in a drum and lethal in a 60,000-tonne stow, and the IMDG classification tests do not measure that.

The notation table at 9.2.3.1.5 has seven rows:

Two edition designations carry the weight of that table and rarely get cited. GHS in amendment 07-23 means the ninth revised edition, ST/SG/AC.10/30/Rev.9. The UN Manual of Tests and Criteria means the seventh revised edition, ST/SG/AC.10/11/Rev.7 with Amendment 1. Both are named in the section 1.7 definitions, and a laboratory result against an older edition is not a result against the Code as it now stands.

OH is the one most often misdescribed. It is not a list of phenomena such as dust explosion or oxygen depletion. Section 9.2.3.1.4 defines it as a deviation from the six named hazards which shall be properly recorded with justifications, and which is to be included in the section for Hazard in the individual schedule. Whatever the OH hazard is on a given cargo, the Hazard cell of that schedule is where it is written down.

Section 9.2.3.1.3 opens a route that needs no laboratory at all: a material may be classified MHB by analogy with similar cargoes of known hazardous properties, or by records of accidents. Casualty history is a valid classification basis under the Code.

How the MHB notation is written, and where it lives

The MHB codes are written as bare letters, joined by “and/or”, in the MHB cell of the Characteristics table. COAL reads “CB and/or SH and/or WF and/or CR”. DIRECT REDUCED IRON (B) reads “SH and/or WF”. LIME (UNSLAKED) and MAGNESIA (UNSLAKED) both read “SH and/or CR”. PETROLEUM COKE reads “SH”.

The subsection headings in section 9.2.3 use a second form, with a space: “9.2.3.3 Self-heating solids: MHB (SH)”. The closed form MHB(SH), which circulates widely in commercial guidance, has never been the Code’s notation in any amendment.

Before amendment 05-19 the notation sat inside the Class cell and was written “MHB (CR)”. Resolution MSC.462(101) moved it out and gave the Hazard classification block its present four columns: Class, Subsidiary hazard(s), MHB, Group. So a schedule photocopied from a pre-2021 edition has the codes in a different place, which is a common source of confusion when a shipper’s declaration is checked against an old printout.

Where the MHB codes came from

The sub-categorisation arrived in three amendments, not one, and the chain matters when an older reference has to be read against the current text.

Amendment 04-17, resolution MSC.426(98), is often credited with creating the scheme. It did not. Its six references to MHB are applications of existing codes to individual schedules, of the form “In Characteristics, under Class, after the word MHB, add (SH) and/or (CR) and/or (TX)”. The amendment cycle applies codes to cargoes on every pass; it created them only twice.

How to read a Group B cargo schedule

Every schedule in Appendix 1 carries the same fourteen fields in the same order, and the template is published in the Code itself at section 1.3.3, as the format a competent authority uses when submitting a new cargo:

1. Bulk Cargo Shipping Name , in capitals, with a qualifying sub-line where the schedule has one
2. Description
3. Characteristics, one table in two blocks: Size, Angle of repose , Bulk density and Stowage factor ; then Class, Subsidiary hazard(s), MHB and Group
4. Hazard
5. Stowage and segregation
6. Hold cleanliness
7. Weather precautions
8. Loading
9. Precautions
10. Ventilation
11. Carriage
12. Discharge
13. Clean-up
14. Emergency procedures, itself four cells: Special emergency equipment to be carried, Emergency procedures, Emergency action in the event of fire, and Medical first aid

Two variations sit outside the list. Some schedules carry a trailing Remarks field: COAL’s reads that the use of CO2 or inert gas, if available, should be withheld until fire is apparent. And COAL carries a full appendix to the schedule holding its segregation, ventilation, monitoring and carriage content, which is why its Stowage and segregation cell says only “Refer to the appendix to this schedule”.

The presence of the Emergency procedures block is the cleanest Group C marker there is. Section 1.3.3 makes it conditional, “if necessary”, and Group C schedules do not carry it. If a schedule has one, the cargo is Group A, Group B, or both.

Transportable moisture limit and moisture content never appear as schedule fields. They are declaration items at 4.2.2.10 and certificate items at 4.3.2, and they are Group A business.

What in a schedule is mandatory and what is not

Section 1.4.2 draws the line, and it puts more of a Group B schedule on the informative side than most practitioners expect. Recommendatory or informative: section 11 except 11.1.1, section 12, section 13, appendices other than 1 and 5, and the texts in the sections for Description, Characteristics other than Hazard classification, Hazard, and Emergency procedures of individual schedules in appendix 1.

Read against a Group B schedule, that means the Hazard cell is informative. So is the Emergency procedures block, including “Do not use water” and the 120°C diversion instruction on DRI. What is mandatory is the Hazard classification block, that is Class, Subsidiary hazard, MHB and Group, together with the operational cells from Stowage and segregation through Clean-up.

Section 1.2.1 reinforces the point on the physical properties: they are given only for guidance, and current valid information must be obtained from the shipper before loading. A bulk density range printed in the schedule does not govern the stowage plan. The shipper’s declared figure does, and SOLAS regulation XII/10 is what requires it on a bulk carrier of 150 m in length and upwards.

The informative status of the Emergency procedures block is worth carrying into any dispute about what the master was obliged to do. It does not make the instruction bad advice. It means the obligation to follow it comes from the ISM Code safety management system and from ordinary seamanship, not from a “shall” in the Code.

Segregation: the Code carries two matrices, both mandatory

The IMSBC Code does have explicit segregation matrices, built on the same four-term model as the IMDG Code. Section 9.3.3 governs a Group B bulk cargo against packaged dangerous goods, with rows for classes 4.1, 4.2, 4.3, 5.1, 6.1, 7, 8 and 9 plus a row for MHB, and columns running from division 1.1/1.2/1.5 through class 9. Section 9.3.4 governs one bulk cargo against another, as a lower-triangular table over the same classes plus MHB.

The four terms, from the note under the 9.3.3 table:

• Away from: effectively segregated so that incompatible materials cannot interact dangerously in the event of an accident, but they may be carried in the same hold or compartment or on deck provided a minimum horizontal separation of 3 metres, projected vertically, is provided.
• Separated from: in different holds when stowed under deck. Provided an intervening deck is resistant to fire and liquid, a vertical separation, that is in different compartments, may be accepted as equivalent.
• Separated by a complete compartment or hold from: either a vertical or a horizontal separation. If the decks are not resistant to fire and liquid, then only a longitudinal separation is acceptable.
• Separated longitudinally by an intervening complete compartment or hold from: vertical separation alone does not meet this requirement.

“Segregate from” is not one of them, and a charterer’s clause using that phrase has not specified anything.

The MHB row is where the two matrices become interesting. In 9.3.3 it reads X against every packaged class except class 7, where it is 3. In 9.3.4 it reads X against every bulk class except class 7, where it is 2. So an MHB-only cargo has no default segregation from anything at all except radioactive material, and everything else falls to the individual schedule. That is why COAL’s segregation lives in its appendix, and why the appendix has to spell out that the cargo is separated from goods of classes 1 (division 1.4), 2, 3, 4 and 5 in packaged form and from solid bulk materials of classes 4 and 5.1, that stowage of class 5.1 above or below the cargo is prohibited outright, that the master shall ensure the cargo is not stowed adjacent to hot areas, and that it is separated longitudinally by an intervening complete compartment or hold from goods of class 1 other than division 1.4.

Section 9.3 also carries thirteen general requirements at 9.3.1 that no matrix expresses. Segregation from combustible materials does not include packaging material, ceiling or dunnage, which shall be kept to a minimum. Different grades of the same cargo in one space take the most stringent provisions applicable to any grade. Incompatible materials shall not be handled simultaneously, with hatch covers closed and decks cleaned of residue between cargoes. After discharge of toxic or oxidizing cargoes the spaces shall be inspected for contamination before reuse. And where a schedule requires hatches to be opened in an emergency, those hatches shall be kept capable of being opened, which is a hatch cover maintenance obligation dressed as a segregation rule.

Amendment 08-25 reformats the 9.3.3 table without changing its logic: division 1.6 is added to the fourth column heading, “Radioactive materials” becomes “Radioactive material”, the word MHB is deleted from the second column heading, and segregation term 3 opens “Either” rather than “Means either”.

The shipper’s declaration and the certificates behind it

Section 4 is titled Assessment of acceptability of consignments for safe shipment, and the cargo information it requires at 4.2.2 runs to eighteen items. Seven of them are what separate a Group B declaration from a Group C one, because the “if applicable” qualifier hands them to Group B and takes them away:

• .3 the IMO class of the cargo
• .4 the UN number, preceded by the letters UN
• .12 toxic or flammable gases which may be generated by the cargo
• .13 flammability, toxicity, corrosiveness and propensity to oxygen depletion
• .14 self-heating properties, and the need for trimming
• .15 properties on emission of flammable gases in contact with water
• .16 radioactive properties

Item .10, the certificate on moisture content and transportable moisture limit, is Group A only. Item .7, bulk density, is flagged in the Code itself as required by SOLAS regulation XII/10.

The MHB codes reach the declaration through the form at 4.2.3 rather than through the item list. The form’s single relevant line reads “Chemical properties if potential hazard, e.g. class and UN No. and/or MHB hazard(s)”. The same form carries four group checkboxes, two MARPOL Annex V checkboxes, and four additional-certificate checkboxes, of which the weathering certificate and the exemption certificate are the Group B ones.

Certification for a chemically hazardous cargo runs through 4.3.6, and its wording is the general rule under which the charcoal weathering statement, the coal competent-person certificate and the fishmeal antioxidant certificate all sit:

Where certification is required by the individual schedules for cargoes possessing chemical hazards, the certificate shall contain, or be accompanied by, a statement from the shipper that the chemical characteristics of the cargo are, to the best of their knowledge, those present at the time of the ship’s loading. However, it is important to ensure that the samples taken are representative of the whole depth of the stockpile.

Nothing in section 4 gives the master a power to refuse. That power comes from IMSBC 5.1.3, SOLAS regulation VI/7.5, the express conditions in a schedule, and ISM Code paragraph 5.2. The master’s right to refuse cargo is a separate chain from the declaration one.

Documents on board, and the Document of Compliance

Section 4.8 sets out what a ship carrying dangerous goods in solid form in bulk must have on board, and it is the part of the Code that most often surprises a superintendent preparing for port state control . Three requirements:

• 4.8.1: a special list or manifest of the dangerous goods on board and their location, per SOLAS regulation VII/7-2.2, or a detailed stowage plan identifying by class in its place.
• 4.8.2: appropriate instructions on emergency response to incidents involving the cargoes shall be on board. Section 3.1.3 imposes the same duty separately, and the Medical first aid cell of every Group B schedule points at the IMO, WHO and ILO Medical First Aid Guide .
• 4.8.3: cargo ships of 500 GT and over constructed on or after 1 September 1984, and cargo ships under 500 GT constructed on or after 1 February 1992, subject to SOLAS regulation II-2/19.4, shall have a Document of Compliance when carrying dangerous goods in solid form in bulk, except class 6.2 and class 7.

The Document of Compliance is the sharpest test of whether a cargo is an MHB or a dangerous good, and the answer runs backwards from where most people look. SOLAS regulation VII/7 defines dangerous goods in solid form in bulk as material “which is covered by the IMDG Code”. An MHB-only cargo is by definition not covered by the IMDG Code. So a laden Capesize full of coal does not need the Document of Compliance, while a Handysize with 20,000 tonnes of SULPHUR UN 1350 does.

The ship-side equipment that goes with it lives in SOLAS chapter II-2 rather than in the IMSBC Code, and section 13.2 of the Code is the map: regulation II-2/19 for ships carrying dangerous goods, II-2/19.3.4 for ventilation with the unified interpretations at MSC.1/Circ.1434 and MSC.1/Circ.1120, II-2/19.3.6.1 and II-2/19.3.6.2 for protective clothing and self-contained breathing apparatus with FSS Code chapter 3, II-2/10.10 for fire-fighter’s outfits, II-2/19.3.8 for the A-60 insulation standard, IEC 60092-506 for equipment safe in an explosive atmosphere, and IEC 60092-352 for cable penetrations. The fixed fire-fighting picture is completed by MSC.1/Circ.1395, the list of solid bulk cargoes for which a fixed gas fire-extinguishing system may be exempted or is ineffective, which amendment 08-25 updates from Revision 6 to Revision 7.

The SOLAS chain, regulation by regulation

The IMSBC Code sits under two SOLAS chapters, and its own section 1.6 reproduces the text that says which: parts A and B of chapter VI and part A-1 of chapter VII deal with the carriage of solid bulk cargoes and the carriage of dangerous goods in solid form in bulk respectively. Chapter VII part A is packaged dangerous goods and part B is dangerous liquid chemicals; neither applies to a solid bulk parcel.

Under chapter VI :

• VI/1-1.1 defines the IMSBC Code by reference to MSC.268(85) as may be amended, and is the gateway every amending resolution recites.
• VI/1-2 is the mandatory hook, in one sentence: the carriage of solid bulk cargoes other than grain shall be in compliance with the relevant provisions of the IMSBC Code.
• VI/2 places the cargo-information duty on the shipper and routes solid bulk content to IMSBC section 4. The group declaration itself is required by IMSBC 4.2.2.2, not by SOLAS.
• VI/3, Oxygen analysis and gas detection equipment, is the SOLAS provision most directly about Group B and the least cited: when transporting a solid bulk cargo which is liable to emit a toxic or flammable gas, or cause oxygen depletion in the cargo space, an appropriate instrument for measuring the concentration of gas or oxygen in the air shall be provided together with detailed instructions for its use, to the satisfaction of the Administration. It is the parent of IMSBC 3.2.5.
• VI/6 covers acceptability for shipment and VI/7 covers loading, unloading and stowage, including VI/7.5 on the master’s right to suspend.

Under chapter VII part A-1, five regulations run from VII/7 Definitions to VII/7-5 Requirements. Regulation VII/7-1.2 is blunt: the carriage of dangerous goods in solid form in bulk is prohibited except in accordance with the provisions of this part. Regulation VII/7-4 adds the incident-reporting duty that MHB-only cargoes escape.

Chapter XII is not group-specific, but regulation XII/10 is the source of the bulk density declaration that IMSBC 4.2.2.7 and the declaration form both cross-reference.

Coal: Group A and B by default

Coal is classified group A and B unless it is classified group B only, and most cargo officers have it the other way round. The COAL schedule provides that coal shall be classified as group A and B unless classified as group B only by a test determined by the appropriate authority, or where not more than 10 percent by weight of particles are less than 1 mm and not more than 50 percent by weight are less than 10 mm. A blend of two or more coals is group A and B unless every original coal in the blend is group B only.

There is one COAL schedule, not four. Its Description reads “Coal (bituminous and anthracite) is a natural, solid, combustible material consisting of amorphous carbon and hydrocarbons”, and no sub-bituminous or lignite schedule exists. The adjacent entries are COAL SLURRY, which is Group A, COAL TAR PITCH , which is Group B with MHB TX and/or CR and a carcinogenic dust profile that has nothing to do with coal, and BROWN COAL BRIQUETTES .

The COAL schedule reads MHB “CB and/or SH and/or WF and/or CR” and Group “B (and A)”. Its Hazard cell names four hazards and one Group A risk: coal may create flammable atmospheres, may heat spontaneously, may deplete the oxygen concentration, may corrode metal structures, and may liquefy if shipped at a moisture content in excess of its transportable moisture limit.

Instruments and monitoring on a coal cargo

The COAL appendix requires the ship to be suitably fitted and to carry appropriate instruments for measuring four things without requiring entry into the cargo space: methane, oxygen, carbon monoxide, and the pH value of cargo space bilge samples. The bilge pH is the one most often skipped, and it is the leading indicator of the acid mechanism that produces both the hydrogen and the corrosion.

Temperature measurement is recommended, not required. The appendix says only that it is recommended that means be provided for measuring cargo temperature in the range 0°C to 100°C without entering the space. What is mandatory is atmosphere monitoring, at a frequency determined from the shipper’s information and from the analysis results, and daily in any event.

Ventilation runs for the first 24 hours after departure from the loading port, not after completion of loading, which on a ship that sits at berth for two days is a real difference. During that period the atmosphere is monitored once from one sample point per space, with ventilation stopped for an appropriate period before the reading. The openings are closed afterwards only when methane is at an acceptably low level; if it is not, surface ventilation continues until it is.

The gas sampling arrangement is specified: a hole of diameter approximately 12 mm positioned as near to the top of the hatch coaming as possible, one sample point per space, with two provided port and starboard for flexibility in adverse weather. In an unventilated hold one measurement per day is sufficient as a precautionary measure, but if carbon monoxide levels are higher than 30 ppm the frequency rises to at least twice a day at suitably spaced intervals. In a ventilated hold the ventilators are closed before measurement, and the appendix recommends that the shutdown be not less than 4 hours, held constant so that readings compare.

The two coal trigger figures

Methane: additional precautions apply where the shipper has advised that the cargo is liable to emit methane, or the atmosphere indicates the presence of methane in excess of 20 percent of the Lower Explosion Limit. The appendix gives the methane range as 5 percent to 16 percent by volume in air.

Self-heating: at 50 ppm carbon monoxide in any cargo space, or a steady rise over three consecutive days, a self-heating condition may be developing and the master informs the shipper and the company. The report carries eight items: the cargo spaces involved with their carbon monoxide, methane and oxygen results; the cargo temperature with location and method of measurement; the time the gas sample was taken; the times ventilators were opened and closed; the quantity of coal in the holds involved; the type of coal per the cargo information; the date loaded and the ETA at the intended discharge port; and the master’s comments.

Loading acceptance for a self-heating coal is capped at 55°C. That figure is a gate at the berth, not a voyage alarm, and reading it as an alarm setpoint is the most common error in commercial coal guidance.

Where carbon monoxide is increasing steadily, the appendix requires the space to be completely closed and all ventilation ceased, with expert advice sought immediately. On water it is explicit: water shall not be used for cooling material or fighting coal cargo fires at sea, but may be used for cooling the boundaries of the cargo space. The Emergency action cell adds “Batten down. Exclusion of air may be sufficient to control the fire. Do not use water. Seek expert advice and consider heading to the nearest port.”

Amendment 07-23 also carries a dedicated regime for gravity-fed self-unloading bulk carriers : the segregation paragraph and the 24-hour ventilation paragraph need not apply, tunnel ventilation runs positive-pressure if methane is detected and negative-pressure if carbon monoxide is detected, entry into cargo or unloading spaces above 30 ppm carbon monoxide requires breathing apparatus, and owners are notified at a steady rise or 50 ppm.

Direct reduced iron: four schedules and two opposite strategies

There are four DRI schedules in amendment 07-23, and none of them carries a UN number or an IMDG class. All four read “Not applicable” in both Class and Subsidiary hazard, and all four read MHB “SH and/or WF”.

DRI (A) is defined as moulded at a temperature greater than 650°C with a density greater than 5,000 kg/m3, and fines and small particles under 6.35 mm not exceeding 5 percent by weight. The Code sets a floor on the moulding temperature, not a band. Its Hazard cell allows for a temporary increase in temperature of about 30°C due to self-heating after material handling in bulk, and its Weather precautions cell permits non-working hatch covers to be left open for a minimum of 1 hour after completion of each pour when weather permits, to allow cooling.

DRI (B) covers cold-moulded briquettes, defined as those moulded below 650°C or with a density under 5,000 kg/m3, alongside lumps and pellets. The ageing provision offers three routes, not one: aged for at least 3 days, or treated with an air-passivation technique, or another equivalent method that reduces the reactivity to the same level as the aged product, with the ageing process approved by the competent authority which also provides a certificate. Cargo that has been wetted, or is known to have been wetted, shall not be loaded.

Inerting is prescriptive and carries one prohibition that catches ships out. Dry inert gas is introduced at tank top level so that it purges the air from the cargo and fills the free volume above, nitrogen preferred, with all vents, accesses and coaming drains closed and sealed. Sufficient inert gas is then introduced to achieve an oxygen concentration less than 5 percent throughout the space. And: the ship’s fixed CO2 fire-fighting system shall not be used for this purpose. A ship without a separate nitrogen supply cannot lawfully carry DRI (B).

The sailing gate is three conditions: all loaded spaces correctly sealed and inerted, the cargo temperature stabilized at all measuring points and not exceeding 65°C, and the hydrogen concentration in the free space stabilized and not exceeding 0.2 percent by volume. During the voyage the hold stays tightly sealed with the inert condition maintained, and hydrogen and oxygen are measured at regular intervals, not continuously, because every measurement costs inert gas. Records are kept on board for a minimum of two years.

Two voyage thresholds run through DRI (B) and DRI (C): 1 percent hydrogen by volume, which the Code writes as greater than 25 percent of the lower explosive limit, and 65°C. The emergency threshold is 120°C, at which the ship should make for the nearest appropriate port to discharge the affected cargo, with preparations made for grab discharge. Water, steam and CO2 are all prohibited on a DRI fire; flooding the affected hold is contemplated only as a last resort.

DRI (C) adds a 30-day ageing requirement, a prohibition on loading or transferring during ANY precipitation with the capitalization in the Code’s own text, and a duty to discharge without delay any cargo wetted beyond its natural moisture content or in which reactions have started and the temperature has exceeded 120°C. Its Hazard cell ends on a sentence rare in a regulatory instrument: the reactivity of this cargo is extremely difficult to assess due to the nature of the material that can be included in the category, and a worst case scenario should therefore be assumed at all times.

DRI (D), the schedule that inverts the strategy

DRI (D) is new in resolution MSC.539(107) and runs opposite to (B) and (C). Instead of keeping fines bone dry and sealed, it keeps them deliberately wet and vented, which is why it is the only DRI schedule classified group A and B and why it carries a transportable moisture limit.

Loading requires a certificate that the cargo does not meet the criteria for class 4.2 materials, natural ageing for a minimum of 30 days, and a stockpile temperature log taken by the shipper on three consecutive days, measured 20 cm to 30 cm below the surface at 3-metre intervals over the length and width of the pile. The cargo is not loaded above 65°C. Hatch covers stay open after loading, weather permitting, once thermocouples are placed.

The ship then waits 24 hours before sailing, or longer if required, until all holds are closed and sealed, the cargo temperature is stable and not above 65°C for at least 12 consecutive hours, and the hydrogen concentration in the head space has stabilized and does not exceed 1 percent by volume for at least 12 consecutive hours.

The Ventilation cell is the most quantitative in the Code. Mechanical surface ventilation runs in each hold to keep hydrogen below 1 percent by volume, sized to enable an airflow of at least 1.2 cubic metres per hour per tonne of cargo when needed, with adequate capacity to ventilate down to 0.2 percent hydrogen or less. Two spare sets of ventilation equipment of a certified safe type for an explosive atmosphere must be on board, with a crew member or other person able to install them, and availability is tied to Load Line Convention Annex I regulation 19(3) or to measures that keep the system usable in rough seas. A time-based gas prediction curve is established before sailing and updated during the voyage.

The Precautions cell recommends an experienced cargo technician appointed by the shipper on board during loading and throughout the voyage, and strongly recommends weather routing.

Sulphur: the larger trade is Group C

Two sulphur schedules exist, and the group split runs against intuition. SULPHUR UN 1350 (crushed lump and coarse grained) is class 4.1 with no MHB code and Group B. SULPHUR (formed, solid), covering prills, granules, pellets, pastilles and flakes, is Group C. Because the formed product is the larger seaborne trade, most sulphur parcels are Group C, and the sulphur schedule that carries the chemical-hazard regime governs the minority of them.

The Group B schedule opens with a prohibition: fine grained sulphur, that is flowers of sulphur, shall not be transported in bulk. Its Description records that sulphur is loaded in a damp or wet condition, which is the deliberate dust-suppression practice that produces the corrosion problem downstream.

The Precautions cell is where the schedule earns its group. When the cargo is involved in a fire, a toxic, very irritating and suffocating gas is evolved. The cargo forms explosive and sensitive mixtures with most oxidizing material. It has a liability to dust explosion , which may occur especially after discharge and during cleaning. The hold trimming plates and tank tops shall be lime-washed or coated with paint to prevent corrosion, and upper sections shall have a sound coating of paint. Electrical circuits in the cargo spaces unsuitable for an explosive atmosphere shall be isolated by removal of links other than fuses. Ventilators shall be fitted with spark-arresting screens.

The Clean-up cell answers the corrosion question more precisely than any commercial guidance does. The cargo spaces and other structures which may have been in contact with the cargo or the dust shall not be swept; they are washed out with fresh water to remove all residues and then thoroughly dried, because wet dust or residues may form highly corrosive sulphurous acid, which is extremely dangerous to personnel and corrosive to steel. The ban on sweeping is a dust-explosion control, and it is why hold washing water handling on a sulphur trade differs from every other dry bulk.

Carriage is bilge-led: bilges shall be pumped regularly to prevent accumulation of water and acid solution, which makes bilge well preparation a load-bearing item on this cargo rather than a routine one.

Molten sulphur is outside the Code, and the reason is simple rather than special: the IMSBC Code covers solid bulk cargoes, and molten sulphur is a liquid carried in dedicated tankers. Its dangerous goods entry is UN 2448, SULPHUR, MOLTEN, class 4.1, packing group III. It is not the class 9 elevated temperature liquid entry, because a named entry displaces an n.o.s. entry.

Seed cake, fishmeal and copra: oil, moisture and time

The self-heating oilseed and marine-protein family is the largest group of Group B schedules and the one where the classification boundaries are numeric and unforgiving. Five seed cake schedules exist:

The route out of class 4.2 is not a general oil threshold but a closed list of named commodities with paired figures. UN 2217 excludes solvent-extracted rape seed meal, rape seed pellets, soya bean meal , cotton seed meal and sunflower seed meal at not more than 1.5 percent oil and not more than 11 percent moisture. UN 1386 (b) carries a different five-limb list: those same solvent-extracted meals at not more than 4 percent oil and 15 percent oil and moisture combined; mechanically expelled citrus pulp pellets at 2.5 percent and 14 percent; mechanically expelled corn gluten meal at 11 percent and 23.6 percent; mechanically expelled corn gluten feed pellets at 5.2 percent and 17.8 percent; and mechanically expelled beet pulp pellets at 2.8 percent and 15 percent. Each exclusion needs a certificate from a person recognized by the competent authority of the country of shipment.

Operating requirements across the seed cake family:

• UN 1386 (a) may be carried in bulk only with special permission from the competent authority.
• Loading temperature for UN 1386 (a) and the MHB residues schedule is capped at ambient temperature plus 10°C or 55°C, whichever is lower.
• Ageing is required but no period is stated: before shipment the cargo shall be properly aged, and the duration of ageing required varies with the oil content. Any specific figure in commercial guidance does not come from the Code.
• Temperature is measured regularly at a number of depths and recorded. At 55°C and still rising, ventilation stops; if self-heating continues, carbon dioxide or inert gas is introduced. For solvent-extracted seed cakes the gas is withheld until fire is apparent, because introducing inert gas into a solvent-laden hold before there is a fire is the wrong move.
• Where the planned interval between commencement of loading and completion of discharge exceeds 5 days, UN 1386 (b) and UN 2217 shall not be accepted for loading unless carried in a space equipped with facilities for introducing carbon dioxide or inert gas.
• UN 1386 (a) shall not be mechanically ventilated during the voyage except in an emergency. The other three take surface ventilation as necessary, for removing residual solvent vapour, with caution against self-heating.
• Where the bulkhead between the cargo space and the engine room is not insulated to class A-60 standard, UN 1386 (b) and UN 2217 shall be stowed away from that bulkhead.
• Loading dry pellets with cargo blowers presents a dust explosion risk: blower equipment shall be earthed, and piping shall be electrically continuous or earthed. The same warning covers rapeseed meal .

Fishmeal was rewritten in amendment 07-23 and its classification changed. The current entry is FISH MEAL (FISH SCRAP), STABILIZED, Anti-oxidant treated, with no UN number, no IMDG class, MHB SH and Group B. Under amendment 05-19 it was FISH MEAL (FISH SCRAP), STABILIZED UN 2216, class 9. There is no FISHMEAL FLAKED shipping name.

The antioxidant requirement is a choice of three, each with its own figure: at least 50 ppm ethoxyquin, or 100 ppm BHT, or 250 ppm of a tocopherol-based antioxidant which may be blended with rosemary extract, applied at the time of production and within twelve months before shipment. Composition limits are fat not more than 15 percent and moisture greater than 5 percent and not exceeding 12 percent. Loading temperature is capped at 35°C or 5°C above ambient, whichever is higher, and voyage temperature is taken at eight-hour intervals.

The European Union withdrew the feed-additive authorization for ethoxyquin, which is a regional overlay on the cargo rather than a change to the Code: a fishmeal parcel treated to the IMSBC figure remains compliant for carriage while facing a separate restriction on entry into the EU feed chain.

Copra is the outlier for time rather than chemistry. COPRA (dry) UN 1363 requires either weathering for at least one month before shipment, or a certificate from a person recognized by the competent authority of the country of origin that the moisture content is not more than 5 percent. It shall not be accepted for loading when wet, and it shall not be stowed on or adjacent to heated surfaces including fuel oil tanks. Ventilation is surface only; there is no inerting requirement anywhere in the schedule.

Ferrosilicon: the cargo where measurement is not the control

Ferrosilicon is the Group B family that evolves toxic gas rather than heat, and the schedules split on silicon content into an entry carrying class 4.3 with subsidiary hazard 6.1 and one carrying MHB WF and/or WT. ALUMINIUM FERROSILICON POWDER UN 1395 is class 4.3 with subsidiary 6.1, requires a detector covering four gases including silane, and requires two sets of self-contained breathing apparatus over and above the SOLAS regulation II-2/10.10 fire-fighter’s outfits.

The shared ferrosilicon appendix sets numbers the rest of the Code rarely states:

• Ventilation: at least two separate explosion-proof fans giving a total of at least 6 air changes per hour based on an empty cargo space, running from commencement of loading until the space is free of ferrosilicon. The ventilation is continuous; the monitoring is not.
• Monitoring: at least once during every 8 hours during the voyage, at each outlet ventilator and in any accessible adjacent space, logged. While anyone is inside the cargo space, checks run at 30-minute intervals.
• Entry gate: entry is prohibited above 0.3 ppm phosphine, above 0.05 ppm arsine, or below 18 percent oxygen.
• Loading: a 3-day weathering certificate, not a moisture-content verification.

The appendix also records the clinical fact that makes arsine and phosphine different from every other Group B gas: arsine poisoning generally shows a delay before onset, sometimes of a day or so, and the early symptoms are indefinite, with severe anaemia and jaundice appearing after a day. A crew member who feels well after working near a ferrosilicon hold has not thereby escaped an exposure.

The gap between the entry gate and portable instrument resolution is the reason the practical control on this cargo is exclusion and ventilation rather than measurement. The US NIOSH recommended exposure limit for arsine is a 15-minute ceiling of 0.002 mg/m3, roughly 0.0006 ppm, some eighty times below the OSHA permissible exposure limit of 0.05 ppm and far below what a shipboard multigas detector can resolve.

Charcoal and petroleum coke

Charcoal reads MHB CB and/or SH and is one of the few Group B cargoes whose schedule turns on a stated period. The manufacturer or shipper gives the master, before loading, a statement that the cargo is not class 4.2 on a test approved by the competent authority, and that it has been weathered for not less than 13 days. Charcoal that is class 4.2 shall not be carried in bulk, the actual moisture content shall not exceed 10 percent, and hot screenings above 55°C shall not be loaded. Segregation is as for class 4.1 materials.

There is no ACTIVATED CARBON schedule, so the familiar comparison between activated and lump charcoal has no basis in the Code. What the Code does carry is the test that distinguishes them, at Appendix 2 section 6: a carbon self-heating test at 140°C plus or minus 2°C over 12 hours, with a 200°C pass mark for non-activated carbon and 400°C for activated carbon.

The documented casualty record for charcoal is a container record rather than a bulk one, and it bears directly on how much the 13-day statement is worth. The German Federal Bureau of Maritime Casualty Investigation investigated the charcoal fires on MSC Katrina in the Elbe estuary on 20 November 2015 and Ludwigshafen Express in the Red Sea on 21 February 2016 in a single report, and found that both consignments had passed the UN N.4 test and were not classified as self-heating. Its conclusion was that the hazardous properties of charcoal cannot be fully determined from that test alone. On Yantian Express in January 2019 the same bureau found the probable cause to be self-ignition of coconut charcoal misdeclared as coconut pellets, roughly 22,150 kg of pyrochar in one 40-foot container, material that again did not meet the class 4.2 criteria, and it noted that in large quantities the self-ignition temperature can fall to as low as 50°C. The fire burned for three weeks and damaged 662 containers.

Petroleum coke has one schedule, PETROLEUM COKE (calcined or uncalcined), with no class, MHB SH and Group B, and the Appendix 4 index lists both grades as B. The variable that takes petcoke outside the schedule is temperature, not calcination: the provisions should not apply to material below 55°C when loaded.

Hot loading is the operationally distinctive part. Where a fuel tank below the space contains fuel or other material with a flashpoint under 93°C, a layer at least 0.6 m thick of cargo at 44°C or lower is loaded first throughout the space; where the layer to be loaded would be thicker than 1.0 m, it is loaded first within a layer between 0.6 m and 1.0 m. Cargo above 107°C shall not be loaded at all, and the master posts high-temperature warnings near the cargo spaces. Segregation is separated from foodstuffs, and every other operational cell reads “No special requirements”.

Ammonium nitrate: the fire response that inverts

Ammonium nitrate is the Group B family where every instinct trained on coal is wrong. The mechanism is self-sustaining decomposition rather than combustion, so excluding oxygen does not stop it, and the Emergency action instruction is to open the hatches, treat the fixed gas system as inadequate, use copious amounts of water and isolate any heat source. Flooding may be considered with due regard to stability, and the Loading cell requires the hatches to be kept free so that they can be opened.

Five schedules cover the family, and the article of trade most often shipped is not the pure salt:

The MHB entry is new in amendment 07-23 and applies where the ammonium nitrate content is 20 percent or more and the chloride content is 2 percent or more. Where either the ammonium nitrate is below 20 percent or the chloride is below 2 percent, the Group C schedule applies. That two-variable boundary is what a surveyor checks first on an ammonium nitrate fertilizer parcel, and it does not depend on particle size at all.

Combustible-material limits are not a single figure. The ceiling is 0.2 percent for pure ammonium nitrate and for the limb of UN 2067 above 90 percent ammonium nitrate, 0.4 percent elsewhere, and unrestricted below 45 percent ammonium nitrate.

The rest of the UN 1942 regime is about keeping hydrocarbons away from the stow. The loading temperature limit is 40°C, the lowest in the Code. Fuel tanks under the cargo spaces must have been pressure tested for leakage of manholes and piping before loading. Bunkering of fuel oil shall not be allowed during loading, and pumping of fuel oil in spaces adjacent to the cargo spaces, other than the engine room, is prohibited, with the same rule at discharge. The cargo spaces shall not be ventilated during the voyage, and temperature is monitored and recorded daily to detect decomposition. The MHB entry adds daily oxygen monitoring with trend assessment.

Two investigated casualties give the decomposition scenario its shape. The German Federal Bureau of Maritime Casualty Investigation reported on the Purple Beach, a Marshall Islands-flagged bulk carrier that developed heavy smoke from the cargo hold area with a fertiliser cargo in the German Bight west of Helgoland in May 2015; the crew were evacuated ashore and the self-heating was stopped by cooling the shell and flooding the holds. The Isle of Man Ship Registry reported on the MV Cheshire, a supramax carrying roughly 42,500 tonnes declared as Ammonium Nitrate Based Fertilizer (Non-hazardous) and declared not liable to self-sustaining decomposition, which began decomposing three days out of Norway in August 2017, drifted off the Canary Islands for about two and a half weeks and became a constructive total loss. Its recommendations were to rename the cargo Ammonium Nitrate Based Fertilizer (not otherwise classified), to require manufacturers to supply behaviour and carriage information, to review the adequacy of the IMO test for self-sustaining decomposition , and to open the hatches immediately on detecting decomposition. The warning signs it listed are oxygen depletion, water accumulation, visible vapours, temperature rise and a smell of ammonia.

Calcium hypochlorite has no IMSBC schedule. The word hypochlorites appears three times in resolution MSC.539(107) and every occurrence is inside a segregation list in an ammonium nitrate schedule, naming it as a material the fertilizer must be separated from. It is a packaged class 5.1 oxidiser , its marine casualty record is a container record, and a proposal to carry it in bulk would have to run the section 1.3 route from the beginning.

Quicklime and unslaked magnesia

Quicklime is a Group B cargo because of heat, not gas. LIME (UNSLAKED) reads MHB SH and/or CR, and its Hazard cell states that unslaked lime combines with water to form calcium hydroxide or magnesium hydroxide, that the reaction develops a great deal of heat which may be sufficient to cause ignition of nearby combustible materials, and that it is corrosive to eyes and mucous membranes. The danger the Code identifies is not that the cargo burns but that it ignites something else.

The Appendix 4 index routes both “Calcium oxide” and “Quicklime” to LIME (UNSLAKED) , so those are synonyms and only the shipping name may be written on a declaration.

The Stowage and segregation cell is unusually broad: separated from all packaged dangerous goods and solid bulk cargoes in group B. Weather precautions require the cargo to be kept as dry as practicable and not handled during precipitation, with non-working hatches closed during handling. Precautions cover bilge wells kept clean, dry and covered, machinery and accommodation spaces protected from the dust, and goggles or equivalent dust eye-protection and dust filter masks for anyone exposed. Ventilation and Carriage both read “No special requirements”. Discharge carries one line: do not discharge during precipitation. And the fire response is “Nil (non-combustible). Do not use water.”

MAGNESIA (UNSLAKED) is the same regime one step down in reactivity: it combines with water to form magnesium hydroxide with an expansion in volume and a release of heat, may ignite materials with low ignition temperatures, and is described by the Code itself as similar to LIME (UNSLAKED) but less reactive.

MAGNESIA (DEADBURNED) is Group C, and the split is a matter of what the product is rather than where it sits on a reactivity scale. Its Description reads that deadburned magnesia is natural magnesite calcined at very high temperatures, which results in a non-reactive magnesium oxide which does not hydrate or produce spontaneous heat. Its only precaution is a declaration from the shipper or manufacturer that the cargo has been sufficiently heat-treated and is ready for loading.

Cargoes the Code refuses to carry in bulk

A Group B article that lists only conditions misses the sharpest category the Code has: cargoes it will not carry in bulk at all, under any conditions. Four appear in amendment 07-23:

• Fine grained sulphur, that is flowers of sulphur, from the note to SULPHUR UN 1350.
• Charcoal that meets class 4.2, from the CHARCOAL Precautions cell.
• CASTOR FLAKE, CASTOR MEAL and CASTOR POMACE UN 2969, each marked in the Appendix 4 index as carriage in bulk prohibited, alongside CASTOR BEANS UN 2969 , which may be carried.
• Ammonium nitrate material liable to self-heating sufficient to initiate decomposition.

The prohibited-in-bulk list is short, and each entry is a case where the Code concluded that no combination of ventilation, segregation and monitoring would do.

Monitoring: what the Code sets, and what it does not

Section 3, Safety of personnel and ship, contains no temperature threshold, no gas concentration, no alarm setpoint and no monitoring interval. It is entirely qualitative, and every numeric monitoring figure that applies to a Group B cargo comes from that cargo’s own schedule.

What section 3 does carry is a set of duties that apply across the group. Section 3.2 requires attention that cargo spaces and adjacent spaces may be oxygen-depleted or contain toxic or asphyxiating gases, and names the liable cargoes: most vegetable products and forest products, ferrous metals, metal sulphide concentrates and coal cargoes. Section 3.2.4 requires appropriate procedures before enclosed space entry , taking into account the recommendations developed by the Organization, with the warning that small oxygen-deficient or fume-bearing areas may persist after a space has tested safe. Section 3.2.5 requires the gas and oxygen measuring instruments to be provided; 3.2.6 restricts emergency entry to trained personnel in self-contained breathing apparatus and protective clothing under a responsible officer.

Section 3.4.2 extends gas monitoring to enclosed spaces adjacent to the cargo spaces, which is where the fatalities actually happen. Section 3.5 carries five mandatory ventilation rules, of which 3.5.6 is the one behind every “surface ventilation only” cell in the Code: when a cargo may heat spontaneously, ventilation other than surface ventilation shall not be applied, and on no account shall air be directed into the body of the cargo. Section 3.5.1 splits the requirement by hazard: toxic-gas cargoes get mechanical or natural ventilation, flammable-gas cargoes get mechanical.

Section 3.1.2 carries the Code’s only express cross-reference into the safety management system: routine onboard operational fire safety risk assessments by the crew for cargo handling areas on self-unloading bulk carriers with internally installed conveyor systems, detailed in the ship’s SMS together with a recommended timing for regular reassessment.

One current defect in the Code is worth stating plainly because it will mislead anyone following its own footnotes. Section 13.2.12 still points section 3.2.4 at “Resolution A.1050(27), 30 November 2011”. The current instrument is resolution MSC.581(110), adopted 27 June 2025, whose operative paragraph 3 invites the Assembly to revoke A.1050(27). Amendment 08-25 does not correct the cross-reference, so a ship following the Code’s footnote is working to a superseded instrument.

Exposure limits are not entry criteria

The single most common confusion in Group B practice is treating an occupational exposure limit as an entry threshold. They are different instruments, made by different bodies, doing different jobs, and only one of them is maritime.

The IMSBC Code states occupational concentrations in very few places, and the ferrosilicon appendix holds most of them: 0.3 ppm phosphine and 0.05 ppm arsine as entry gates, with a note that arsine at 250 ppm is dangerous to life after 30 minutes’ exposure and 6.25 to 15.5 ppm after 30 to 60 minutes. The charcoal family carries a recommended threshold limit value of 50 ppm for carbon monoxide exposure, which is a different quantity from the 50 ppm coal reporting trigger even though the numbers coincide.

On oxygen, the Code sets no general figure. The instrument-stated values are: 21 percent in the wood pellet schedules as an entry criterion with carbon monoxide below 100 ppm; 21 percent in the charcoal family as the level below which self-contained breathing apparatus is required on entry; 18 percent in the ferrosilicon appendix as an entry prohibition; and 20.9 percent as the level recommended by resolution MSC.581(110). Everything else in circulation is national or conventional:

Carbon monoxide runs the same way. The 1,200 ppm immediately dangerous to life or health figure is a US NIOSH value, not an IMO one, though MSC.581(110) Appendix 5 now carries it alongside intermediate danger levels of 400 ppm and 800 ppm. The working limits are national: OSHA’s enforceable permissible exposure limit is 50 ppm as an 8-hour time-weighted average, NIOSH recommends 35 ppm with a 200 ppm ceiling, the EU indicative limit under Commission Directive (EU) 2017/164 is 20 ppm over 8 hours, and California sets 25 ppm.

For flammable ranges the Code publishes figures only inside the COAL appendix, and they are worth quoting because they differ from the values in general circulation: methane 5 percent to 16 percent, carbon monoxide 12 percent to 75 percent, hydrogen 4 percent to 75 percent. The appendix adds that carbon monoxide is odourless, slightly lighter than air, and toxic by inhalation with an affinity for blood haemoglobin over 200 times that of oxygen.

What the casualty record actually supports

The Group B casualty record is thinner and more specific than commercial guidance suggests, and the honest position is that no public dataset counts cargo fires at all. INTERCARGO’s Bulk Carrier Casualty Report 2025, published 10 June 2025, records 20 bulk carriers of 10,000 dwt and above lost between 2015 and 2024 with 89 seafarer lives, excluding three Red Sea war-risk losses, and identifies cargo liquefaction as the largest single cause of loss of life at 55 lives, 61.8 percent of the total. But it counts total losses, so a coal fire that reaches a refuge port and discharges never enters the series. The same report records that the average time for flag-state accident investigation reports to reach the IMO Global Integrated Shipping Information System exceeds two years, which is itself why a frequency figure cannot be built.

Three investigated casualties carry the Group B lessons that generalize.

Enclosed-space entry on a coal cargo. The UK Marine Accident Investigation Branch reported on the Berge Mawson, a post-panamax bulk carrier at the Bunyu Island anchorage in Indonesia on 27 June 2022, in report 5/2025, published 20 March 2025. Loading 150,000 tonnes of coal from barges with hatches closed for heavy rain, a stevedore descended unsupervised into the No.8 cargo hold forward access space and collapsed; a second stevedore and the assistant foreman entered to rescue him and also collapsed. Three men died. The measured atmosphere in the access space was 0.9 percent oxygen by volume, and no atmosphere testing had been carried out before entry, contrary to the ship’s own procedures. The report records that below 6 percent oxygen death follows in roughly six to eight minutes, and its recommendations went to INTERCARGO, InterManager and RightShip for a minimum operational safety standard for stevedores.

The pattern in that casualty is the one that repeats across the group: the dead were not in the hold. They were in a space connected to the cargo, which is exactly what section 3.4.2 and the enclosed space entry drill regime under SOLAS regulation III/19 are aimed at.

Methane migrating out of the hold. The United States Coast Guard issued Safety Alert 07-25 on 13 February 2025 after consecutive explosions in the two forward cargo holds of a coal-laden bulk carrier approximately 100 nautical miles off Virginia on 27 November 2024. The vessel suffered significant structural damage, and the other five holds were then found to hold methane approaching the lower explosive limit. The operational point is that a single explosion is not the end of the emergency: every hold gets tested, not only the damaged ones.

Declaration failure as the common cause. Bulk Jupiter, Cheshire, Purple Beach and Yantian Express all began with a declaration that turned out not to describe the cargo as loaded. That is not a Group B fact so much as a fact about section 4, and it is why 4.3.6 requires the shipper’s statement that the chemical characteristics are those present at the time of loading rather than at the time of manufacture.

Cargoes not listed in Appendix 1

A cargo that is not in Appendix 1 can still be shipped, under section 1.3, and the route splits on whether Group A or B hazards are present.

The shipper provides the competent authority of the port of loading with the characteristics and properties of the cargo in accordance with section 4, before loading, and the authority assesses acceptability. Where the cargo may present group A or B hazards, advice is sought from the competent authorities of the port of unloading and of the flag State, and the three set the preliminary suitable conditions for carriage. Where no specific hazards are found, the loading port authorizes the carriage and merely advises the other two. That second limb is a unilateral authorization with notification, and it is the Group C route.

The Code never uses the word “tripartite”. It does not appear anywhere in resolution MSC.539(107), and it is the industry name for the three-authority mechanism rather than a term of art. Guidance on the mechanism is MSC.1/Circ.1453/Rev.2 of 26 June 2023, approved at MSC 107, which expressly supersedes Revision 1. The unlisted-cargo route closes with a duty on the loading port authority to issue a certificate to the master and to submit an application to IMO within one year from the issue of that certificate, to incorporate the cargo into Appendix 1.

Section 1.5 runs a parallel and less-used route. A competent authority, being the port State of departure, the port State of arrival or the flag State, may authorize any other provision by exemption if satisfied it is at least as effective and safe. Validity is not more than five years, a copy goes to IMO and to the ship, and the authorizing authority shall take action to amend the Code to include the provisions covered by the exemption. Together with the one-year application at 1.3.2, that is the Code’s second self-amending feedback loop, and it is why the schedule list grows on every amendment cycle.

The amendment cycle and what governs today

The IMSBC Code is amended on a roughly two-year cycle, with each set entering into force on 1 January of an odd-numbered year and one exception. The two-digit suffix is the drafting-cycle year and not always the adoption year: it matches for 01-11 through 05-19 and for 07-23 and 08-25, but amendment 06-21 was adopted in 2022.

Each resolution carries the same four operative paragraphs: it adopts the amendments, sets a tacit-acceptance date, provides for entry into force upon that acceptance, and agrees that Contracting Governments may apply the amendments in whole or in part on a voluntary basis from a stated earlier date. Voluntary application is a permission given to Contracting Governments, not a transitional phase, and a shipper cannot invoke it against a flag State that has not taken it up.

Amendment 07-23 governs every voyage to 31 December 2026. Amendment 08-25 was tacitly accepted on 1 July 2026, is not in force, and may be applied voluntarily since 1 January 2026. At the framework layer 08-25 changes very little: the 9.3.3 table reformatting described above, and updates to the cross-references at section 13.2.3, 13.2.6 and 13.2.9. Everything else in it is individual schedules.

Amendments are adopted under SOLAS article VIII(b)(iv), tacitly accepted under article VIII(b)(vi)(2)(bb), and enter into force under article VIII(b)(vii)(2), with regulation VI/1-1.1 as the gateway every resolution recites. Between amendments the work runs through the IMO Sub-Committee on Carriage of Cargoes and Containers. Amendment 09-27 is in preparation, with cargoes agreed in principle at CCC 11 in September 2025 and referred to the editorial and technical group for drafting.

Limitations

This article states the Code as amended by resolution MSC.539(107) and read against resolution MSC.575(110). It is a reference to the framework and to the schedules that carry the largest Group B trades, not a substitute for the schedule itself, and a cargo officer works from the current Appendix 1 text for the cargo in hand.

Four limits are worth stating explicitly.

The Code publishes no count of cargo schedules or of cargoes per group, in section 1, in Appendix 4 or in any adopting resolution. Independent parses of the Appendix 4 index disagree with each other, because index entries wrap across lines, secondary names carry cross-references, and several Bulk Cargo Shipping Names carry more than one hazard classification table. What is checkable by inspection is that Group C is the largest of the three by entry count. Any specific total in circulation is a third-party count of a particular amendment.

Physical properties in a schedule are informative under section 1.4.2, and the shipper’s declared figures govern the stowage plan. Ranges quoted here reproduce the schedule and are not carriage values.

Occupational exposure limits are jurisdictional. Where this article gives an OSHA, NIOSH or EU figure it names the body, and the value that applies on a given ship in a given port depends on the flag State, the port State and the manning agreement, not on the IMSBC Code.

Casualty frequency for Group B cargoes is not published anywhere. INTERCARGO’s series counts total losses, which excludes every fire that ended in a discharge, and flag-state reporting to IMO GISIS runs more than two years behind. Loss frequency in these trades is held by underwriters and P and I clubs and is not a public number.

Related Articles

• International Maritime Solid Bulk Cargoes (IMSBC) Code
• IMSBC Group A cargoes: cargoes that may liquefy
• IMSBC Group C cargoes: cargoes that are neither Group A nor Group B
• Materials hazardous only in bulk (MHB)
• IMSBC segregation requirements
• The IMSBC individual cargo schedule
• IMSBC schedule mandatory and informative fields
• IMSBC section 4: the shipper’s declaration
• IMSBC loading temperature limits
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• SOLAS Chapter VI: carriage of cargoes and oil fuels
• SOLAS Chapter VII: carriage of dangerous goods
• IMDG Class 4: flammable solids
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• Self-heating and spontaneous combustion of solid bulk cargoes
• Oxygen depletion in cargo spaces
• Marine confined space entry and tank inspection
• Place of refuge
• Bulk carrier
• Ship-shore safety checklist for solid bulk cargoes