The International Maritime Solid Bulk Cargoes Code is the IMO regulation governing the safe transport of solid bulk cargoes by sea. The IMSBC Code is mandatory under the SOLAS Convention for any solid bulk cargo carried in dedicated bulk carrier ships, the open-hold ships that move iron ore, coal, grain, fertiliser, and bulk chemicals at scale. Cargoes are classified into three groups based on hazard: Group A for cargoes that may liquefy under conditions of moisture and motion, Group B for cargoes possessing chemical hazards (which can overlap with IMDG classifications), and Group C for cargoes that present neither liquefaction nor chemical hazards.
The three groups
| Group | Hazard | Examples |
|---|---|---|
| A | Liquefaction risk if moisture content exceeds the Transportable Moisture Limit (TML) | Iron ore concentrates, copper concentrates, coal slurries, bauxite (some grades), nickel ore |
| B | Chemical hazard (some Group B cargoes are also IMDG-classified) | Sulphur (UN 1350), aluminium nitrate (UN 1438, also IMDG), wood pellets, ammonium sulphate (UN 9028 IMSBC) |
| C | Neither liquefaction nor chemical hazard | Cement clinker, gypsum, soda ash, salt, refined sugar |
A cargo can be Group A only, Group B only, Group A and B (both liquefaction and chemical hazard), or Group C. The classification is published in the IMSBC Code Schedule for each named cargo.
The Group A liquefaction problem
The most consequential IMSBC issue in chemical and mineral shipping is Group A liquefaction. A cargo with moisture content above its Transportable Moisture Limit can transition from solid-like behaviour to fluid-like behaviour under the cyclical motion of the ship at sea. The shifted cargo affects vessel stability and has caused several catastrophic ship losses since the regulation was tightened in the 2010s.
For affected cargoes the master must verify the moisture content is below TML before loading. The shipper provides:
- A Mineral Cargoes Declaration with the cargo’s TML
- Test results showing the actual moisture content of the loading lots is below TML
- For high-risk cargoes, additional sampling and witness verification at the load port
A cargo lot above TML cannot load. The master refuses; the shipper must dry the cargo or reblend with drier material before loading.
Group B chemical hazards
Group B cargoes possess chemical hazards distinct from the liquefaction question. Many Group B cargoes are also IMDG-classified, sulphur (UN 1350) is both Group B under IMSBC and Class 4.1 under IMDG. The two regimes apply in parallel: the IMSBC Code addresses bulk-handling-specific rules (loading temperature, ventilation, fire-fighting), while IMDG addresses the substance hazard generally.
Some Group B cargoes are not IMDG-classified, wood pellets, for example, are Group B for self-heating risk in the bulk but are not commonly shipped as IMDG packaged DG.
How IMSBC applies to bulk chemicals from China
For chemical buyers, IMSBC primarily affects:
- Solid bulk fertilisers: ammonium sulphate, urea, potassium chloride, NPK granular blends. Routine Chinese export from northern ports. Most are Group C; some forms of ammonium nitrate fertiliser are Group B with strict additional rules.
- Sulphur in bulk: UN 1350 (formed) is Class 4.1 IMDG; the cargo also carries Group B IMSBC requirements. Volume export from Chinese refining and gas-processing operations.
- Mineral concentrates: copper, zinc, lead concentrates from Chinese mining. Group A; TML verification mandatory.
- Bulk catalysts and bulk specialty solids: occasionally moved as IMSBC bulk for very large volume shipments (5,000+ tonnes); usually Group B with chemistry-specific requirements.
For routine containerised chemical shipping (the bulk of chemical sourcing), IMSBC does not apply, the cargo moves under IMDG packaged-cargo rules.
Documentation chain for bulk shipping
For an IMSBC bulk shipment the documentation differs from packaged DG:
- Mineral Cargoes Declaration / IMSBC Cargo Declaration identifying the cargo, group, and key parameters
- TML certificate for Group A cargoes
- Sampling and moisture-content certificate issued by the load-port surveyor
- For Group B IMDG-classified cargoes: the bulk-equivalent of the DG declaration, including the chemical hazard data
- Bill of lading identifying the bulk cargo
The load-port surveyor’s involvement is the structural quality control. For Chinese-origin Group A concentrates, the surveyor (typically SGS, Bureau Veritas, or a Chinese state inspection agency) takes physical samples and runs the TML and moisture tests at the port. Results below TML clear loading.
Operator note: the rainy-season TML problem
Chinese coastal ports run higher humidity and frequent rain in summer (Shanghai, Ningbo, Tianjin) and during the southern monsoon (Guangdong, Fujian). Group A concentrates stockpiled at port in covered or partly covered storage can absorb moisture between drying at origin and loading. A cargo that tested below TML at the mine site can be above TML at the port a week later.
Buyers under spot contracts for Group A concentrates from China should:
- Specify the moisture-content requirement in the PO (“Maximum 8.5% moisture; certificate at load port”)
- Allow time for drying or reblending if the load-port test is above TML
- Not rely on origin-side moisture certificates more than 7 days old
The TML failure mode is a vessel ready to load with cargo above TML and a 5-7 day drying delay before loading can begin. Build the contingency into voyage planning for high-moisture-risk cargoes.
Related terms
IMDG is the parallel code for packaged DG. MARPOL Annex II covers bulk liquid pollution (different mode but related framework). Marine pollutant designation can apply to IMSBC Group B cargoes.