Short answer
IMDG is the international code governing the carriage of dangerous goods by sea, applied under SOLAS. It sets out the rules for packaging, labelling, declaration, segregation and stowage. Its difference from ADR lies in requirements specific to sea transport: the container packing certificate, deck-versus-hold stowage categories, and the marine pollutant mark.
What the IMDG Code is
IMDG — the International Maritime Dangerous Goods Code. It is the international code governing the carriage of dangerous goods by sea. The obligation to apply it derives from the SOLAS convention.
The classification logic is the same as under ADR: nine classes, a UN number, a packing group. The difference emerges in the additional requirements specific to sea transport.
Differences from ADR
Container packing certificate. The party loading dangerous goods into a container declares that the loading was carried out in accordance with IMDG rules. This document commits to the suitability of the packaging, securing, and compliance with segregation rules.
Stowage categories. Where each substance may be carried on the ship is defined: in the hold, on deck, or on deck only. The category is assigned according to the ability to respond in the event of fire or leakage. Some substances cannot be carried in an enclosed hold.
Marine pollutant mark. Substances that harm the environment when they enter the sea are marked separately. This mark is independent of the class label; a substance need not be Class 9 to be a marine pollutant.
Segregation tables. Segregation between classes is regulated in more detail at sea: there are graduated requirements such as “away from,” “separated from,” “separated by a complete compartment from,” and “separated longitudinally by a complete compartment from,” which determine placement within the ship.
The declaration chain
The process runs in this order:
- Classification from the SDS — UN number, class, packing group
- Packaging — UN-marked, certified packaging
- Labelling and marking — class label, UN number, and the marine pollutant mark where required
- Dangerous goods declaration — issued by the shipper
- Container packing certificate — issued by the party loading the container
- Booking and bill of lading — dangerous goods information is entered on the document
If any link in the chain is missing, the container is not accepted at the terminal or is not taken on board.
Acceptance restrictions
Not every carrier accepts every dangerous good. Carriers and ports have their own acceptance policies; some classes are refused, and additional requirements are applied to others.
Class 1 and Class 7 are subject to special permits and have a much narrower network of services.
The practical consequence: scope must be confirmed before booking. A refusal discovered after loading has been planned disrupts the whole schedule.
Common mistakes
Loading a container without declaring the class. If this is discovered later, the container is unloaded and the entire cost falls on the shipper.
Overlooking the segregation rule in a consolidated load. Two substances that cannot be carried together in the same container cause a problem even if each has been correctly declared on its own.
Forgetting the marine pollutant mark. It is confused with the class label; the two are separate obligations.
Handing over a load prepared for ADR unchanged for sea transport. Packaging and labelling requirements can differ between modes.
This page is general information, not legal advice. Regulations change; confirm the current position before acting.