Dangerous goods

Dangerous goods and the IMDG Code

Published 28 August 2026 · updated 17 October 2026

An enquiry that reads “5,000 tonnes IMO cargo, Antwerp to Jebel Ali” does not tell you what the cargo is. Dangerous goods are identified by four pieces of information. Until you have all four, nobody can say which ships may carry the parcel, where on board it may go, what it may sit next to, or whether the fixture is possible at all.

The four identifiers, and why all four

• UN number. A four-digit number that identifies the substance or article. This is the key, because everything else in the system is looked up from it.
• Proper shipping name. The name the Code uses. It is often not the name the trade uses, and it is never the manufacturer’s brand name.
• Class or division. The type of hazard, numbered one to nine.
• Packing group. Where it applies, this is the level of danger within the class: I is high, II medium and III low. It sets the packaging standard and sometimes decides how far the cargo must be kept from other goods.

Two substances can share a class and behave in completely different ways, so the class alone tells you very little. Two substances with the same UN number, on the other hand, are treated the same at every step of transport, which is the purpose of the number.

The nine classes

The Code, and the fact that it moves

The International Maritime Dangerous Goods (IMDG) Code is the IMO's rulebook for dangerous goods carried in packages. SOLAS chapter VII makes it law, and its environmental part links to MARPOL Annex III. That link is why ships use a marine pollutant mark in addition to the hazard labels.

The Code is amended every two years, and each amendment is mandatory. A chartering desk feels the effect directly. A safety data sheet or a declaration that cites an out-of-date amendment does not just contain a small error; it will be refused. Amendment 42-24, in the 2024 edition, became mandatory on 1 January 2026, and every shipment after that date must be declared against it.

Segregation is the part that decides the stowage plan

The central working idea of the Code is segregation: certain goods must be kept apart from certain other goods, and the Code says by how much. The levels are "away from", "separated from", "separated by a complete compartment or hold from", and "separated lengthways by a complete compartment or hold in between". These are defined distances, not loose descriptions, and their effects add up quickly. One parcel of class 5.1 booked late can make half the stowage plan illegal.

The same logic reaches the terminal, because much of the Code deals with packing and marking the cargo unit rather than with the ship. The IMO, ILO and UNECE Code of Practice for Packing of Cargo Transport Units (the CTU Code) covers what happens inside the container. It exists because most of the failures a ship sees were created ashore, by people who never saw the ship.

Bulk dangerous goods are not IMDG

Many people get this wrong. A solid cargo carried loose in the hold with a chemical hazard does not fall under the IMDG Code. It is a Group B cargo under the IMSBC Code, the code for solid bulk cargoes, and follows that cargo's own schedule. Coal that heats itself and uses up oxygen is a Group B cargo, not a class 4.2 package. Liquid chemicals in bulk fall under the IBC Code and MARPOL Annex II, and oil in bulk falls under MARPOL Annex I.

So a hazardous cargo can fall under three different sets of rules, and what decides between them 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 accidents that make the news are almost never caused by a correctly declared cargo behaving in an unexpected way. They are caused by cargo declared as something it is not, to avoid a surcharge, a refused booking or the cost of proper packaging, and then stowed on that false basis. A shipper who books calcium hypochlorite as a general chemical has started a fire on a ship whose stowage plan assumed there was nothing to burn.

That is why the paperwork is the most important part, not a formality. The dangerous goods declaration, and for a container the container packing certificate, are how the carrier learns the truth. If they are wrong, every later decision rests on the wrong facts. Afterwards, the charterparty's dangerous goods clause and the shipper's indemnity are all that is left to argue about.

What this means for a fixture

In practice, on a dry cargo or multipurpose desk:

• Get the UN number before you send the cargo to owners. An enquiry without one cannot be answered honestly, and offering ships against it wastes the owner's time and damages your credibility.
• Expect the ship to have limits. A ship's document of compliance for dangerous goods states which classes it may carry and in which spaces. Not every ship may carry every class, and this detail is rarely on a position list.
• Expect the ports to have limits too. Terminals and port authorities set their own restrictions and notice periods for hazardous parcels. These are local rules that no code makes uniform.
• Price the segregation. A parcel that makes the space around it unusable costs more than its own volume, and the freight should reflect that.

The Code is long, and the desk does not need to know all of it. It needs to know that the four identifiers exist, that everything else starts from them, 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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