The IMDG Code is the IMO regulation that governs how dangerous goods move on container ships. Every hazardous chemical leaving China by sea, solvents, peroxides, corrosives, toxic substances, oxidizers, is classified, packed, labelled, declared, and segregated according to the IMDG Code. Carriers refuse cargo that does not match. There is no negotiating this on the dock.
The nine DG classes
The IMDG Code groups dangerous goods into nine classes by physical hazard. The five we ship most often:
| Class | Hazard | Typical cargo |
|---|---|---|
| 3 | Flammable liquids | IPA, MEK, NMP, MTBE, perchloroethylene |
| 4 | Flammable solids | Sulphur, certain metal powders |
| 5 | Oxidizers and organic peroxides | Hydrogen peroxide solutions, persulfates |
| 6.1 | Toxic substances | Acrylonitrile, certain pesticide intermediates |
| 8 | Corrosives | Sodium hydrosulfide, hydrobromic acid, sulphuric acid |
Classes 1 (explosives), 2 (gases), 7 (radioactive), and 9 (miscellaneous) exist but are rare in industrial chemical sourcing.
What the factory must produce before the container can sail
The IMDG documentation set the carrier and port require:
- Multimodal Dangerous Goods Form (DG Declaration). Lists proper shipping name, UN number, class, packing group, quantity, and packaging type. Signed by the shipper.
- Certified UN packaging. The drum, IBC, or pail must carry a UN code stamp showing the packaging has been tested to the right packing group. Non-UN packaging is grounds for cargo rejection at the load port.
- MSDS in English. The carrier’s chemist verifies the MSDS matches the DG Declaration.
- Labels and placards. Hazard labels on each package, placards on the container.
- Segregation check. Some DG classes cannot share a container or even a deck position. The carrier’s stowage plan handles this, but the booking has to be made under the right class so segregation is computed correctly.
If any of those five fail, the container does not load. We have caught more booking failures from a missing UN packaging stamp than from any other single cause.
Packing groups (PG I, II, III)
Within most classes, the packing group sets how stringent the packaging requirements are. PG I is the most hazardous, PG III the least. A Class 8 PG II corrosive (e.g. sodium hydrosulfide) needs more robust packaging than a Class 8 PG III corrosive (e.g. dilute acetic acid). The packing group is determined by the substance’s properties, not by the importer’s preference.
Why DG is a moat for an experienced sourcer
A first-time importer trying to ship a Class 6.1 toxic substance from China will hit the same five obstacles in sequence: factory misclassifies the cargo, factory provides non-UN packaging, factory writes a non-compliant MSDS in Chinese only, the carrier rejects the booking, the port refuses the container. Twenty years of doing this is twenty years of pre-empting those five obstacles before the deposit is paid. There are not many shortcuts.
Practical filing discipline for Chinese exporters
For chemical cargo originating in China, the IMDG documentation chain involves three parties: the factory (which produces the goods and the SDS), the freight forwarder (which prepares the DG declaration and books carrier space), and the carrier (which accepts the cargo and applies the IMDG segregation rules on board). Each handoff is a potential failure point. The factory may underspec the hazard profile to keep the carrier-side surcharge low; the forwarder may file a generic DG declaration that does not match the actual cargo; the carrier may reject the booking on a final-stage segregation review. The buyer’s defensive move is to require the factory to provide a full UN-number-specific DG declaration and an English-language SDS at proforma stage, before the order is placed. Confirming the UN number, IMDG class, packing group, and any sub-risk classifications at this point catches under-declared cargo before it becomes a port-side problem.
How IMDG amendments roll out
The IMDG Code is updated on a two-year cycle. The current edition is IMDG 42-24, in force from 1 January 2026. The previous edition (IMDG 41-22) remains valid for transitional cargoes through 30 June 2026. After that date, any DG cargo on board a vessel must comply with the current edition. For first-shipment relationships, confirm the factory’s SDS references the current edition and that the DG packaging meets the current UN-certified-packaging requirements. Older packaging certified to a prior edition is sometimes still acceptable but the discipline rewards forcing the factory onto the current standard.
Related terms
MSDS is the safety data sheet that travels with every DG shipment. COA certifies the chemical content. UN Number is the four-digit substance identifier on the DG Declaration.