Dangerous goods

Dangerous goods and the IMDG Code

Published 28 August 2026 · updated 22 September 2026

An enquiry that reads “5,000 tonnes IMO cargo, Antwerp to Jebel Ali” has not told you what the cargo is. Dangerous goods are identified by four things, and until all four are on the table nobody can say which ships may carry the parcel, where it may be stowed, what it may be stowed next to, or whether the fixture is possible at all.

The four identifiers, and why all four

• UN number. A four-digit number identifying the substance or article. This is the key. Everything else in the system is looked up from it.
• Proper shipping name. The name the Code uses, which is frequently not the name the trade uses and never the manufacturer’s brand name.
• Class or division. The nature of the hazard, one to nine.
• Packing group. Where applicable, the degree of danger within the class: I is high, II medium, III low. It drives packaging standards and sometimes segregation.

Two substances can share a class and behave completely differently, so the class alone answers nothing. Two substances can share a UN number and be identical for every purpose in the transport chain, which is the point of having one.

The nine classes

The Code, and the fact that it moves

The International Maritime Dangerous Goods Code is the IMO instrument for dangerous goods carried in packaged form. It is given force by SOLAS chapter VII, and its environmental half connects to MARPOL Annex III, which is why the marine pollutant mark exists alongside the hazard labels.

It is amended on a two-year cycle and the amendments are mandatory, which has a practical consequence a chartering desk feels directly: a safety data sheet or a declaration citing a superseded amendment is not a document with a small error in it, it is a document that will be refused. Amendment 42-24, in the 2024 edition, became mandatory on 1 January 2026, and shipments after that date have to be declared against it.

Segregation is the part that decides the stowage plan

The Code’s central operational idea is that certain goods must be kept apart from certain other goods, and it says by how much: away from, separated from, separated by a complete compartment or hold from, separated longitudinally by an intervening complete compartment or hold from. Those are defined distances, not adjectives, and they cascade. One parcel of class 5.1 booked late can make half the stowage plan illegal.

The same logic runs into the terminal, because a great deal of the Code is about the packing and marking of the unit rather than the ship. The IMO, ILO and UNECE Code of Practice for Packing of Cargo Transport Units, the CTU Code, is the companion document for what happens inside the box, and it exists because most of the failures the ship sees were created ashore by someone who never saw the ship.

Bulk dangerous goods are not IMDG

This trips people up regularly. A solid cargo in bulk with a chemical hazard is not handled under the IMDG Code; it is a Group B cargo under the IMSBC Code and works to that cargo’s individual schedule. Coal that self-heats and depletes oxygen is a Group B cargo, not a class 4.2 package. Liquid chemicals in bulk are the IBC Code and MARPOL Annex II. Oil in bulk is MARPOL Annex I.

So a hazardous cargo has three possible regimes and the deciding question is the packaging, not the substance. The same chemical is IMDG in drums, IBC Code in a chemical tanker and IMSBC in a hold.

Misdeclaration is the real hazard

The failures that make the news are almost never a correctly declared cargo behaving unexpectedly. They are cargoes declared as something they are not, in order to avoid a surcharge, a booking refusal or the cost of proper packaging, and then stowed accordingly. A shipper who books calcium hypochlorite as a general chemical has caused a fire on a ship whose stowage plan assumed there was nothing to burn.

Which is why the paperwork is the substance of the thing rather than a formality around it. The dangerous goods declaration and, for a container, the container packing certificate are the documents by which the carrier is told the truth. If they are wrong, everything downstream is built on the wrong facts, and the charterparty’s dangerous goods clause and the shipper’s indemnity are what is left to argue about afterwards.

What this means for a fixture

Practically, on a dry cargo or multipurpose desk:

• Get the UN number before you circulate the cargo. An enquiry without one cannot be answered honestly and offering against it wastes the owner’s time and your credibility.
• Expect the ship to have limits. A ship’s document of compliance for the carriage of dangerous goods states which classes she may carry and in which spaces. Not every ship may carry every class, and this is a particulars question that is rarely on a position list.
• Expect the ports to have limits too. Terminals and port authorities impose their own restrictions and notice periods for hazardous parcels, and those are local rules that no code harmonises.
• Price the segregation. A parcel that sterilises adjacent stowage costs more than its own volume, and the freight should say so.

The Code is long and the desk does not need to know it. It needs to know that four identifiers exist, that they are the entry point to everything else, and that an enquiry without them is not yet an enquiry.

References

• International Maritime Organization, The International Maritime Dangerous Goods (IMDG) Code. IMO, dangerous goods
• International Maritime Organization, IMDG Code, 2024 edition, incorporating Amendment 42-24, mandatory from 1 January 2026. IMO publications
• IMO, ILO and UNECE, Code of Practice for Packing of Cargo Transport Units (CTU Code), 2014. IMO, CTU Code
• International Maritime Organization, International Maritime Solid Bulk Cargoes (IMSBC) Code, for Group B cargoes with a chemical hazard carried in bulk. IMO, cargoes in bulk
• International Maritime Organization, Raft of shipping rules in force from 1 January 2026. IMO press briefing

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