International Maritime Dangerous Goods Code

Overview

The International Maritime Dangerous Goods Code (IMDG Code) is the International Maritime Organization’s (IMO) mandatory global rulebook for carrying dangerous goods and marine pollutants by sea in packaged form. First published in 1965, it became mandatory on 1 January 2004 under the Safety of Life at Sea (SOLAS) Convention, and it governs how hazardous cargo is classified, packaged, labelled, documented, stowed and segregated aboard ships (CHEMTREC; IMO publication).

The Code aims at enhancing “the safe carriage of dangerous goods while facilitating the free unrestricted movement of such goods and preventing pollution to the environment” (Djadjev, University of Groningen). It applies to all ships flying the flag of a SOLAS contracting party that carry dangerous goods, and its reach is near-universal: at least 150 countries, whose combined merchant fleets account for more than 98% of the world’s gross tonnage, use it as the basis for regulating sea transport of hazardous materials (Djadjev, University of Groningen; PHMSA).

From recommendation to mandatory law

For nearly four decades the Code operated as a respected but voluntary recommendation: governments were urged to adopt it, and many did, but compliance gaps remained. That changed at the IMO’s Maritime Safety Committee (MSC), which at its seventy-fifth session in May 2002 confirmed its decision to make the Code mandatory in international law; Amendment 31 then became mandatory on 1 January 2004, without any transitional period, under the umbrella of Chapters VI and VII of SOLAS 1974, as amended (IMO publication). From that date the Code has been a mandatory instrument by force of SOLAS Chapter VII and Annex III of the International Convention for the Prevention of Pollution from Ships (MARPOL), with only a few provisions still recommendatory (Djadjev, University of Groningen).

The Code is kept current on a two-year amendment cycle, maintained by the IMO’s Carriage of Cargoes and Containers (CCC) Sub-Committee with its Editorial and Technical Group harmonizing new provisions with the latest UN Recommendations on the Transport of Dangerous Goods (MCA; PHMSA). New amendments typically open with a voluntary-application year before becoming mandatory: Amendment 42-24, adopted by the MSC at its 108th session in May 2024 through resolution MSC.556(108), could be applied voluntarily from 1 January 2025 and became mandatory internationally on 1 January 2026 (MCA).

How the Code works: classify, pack, label, document, stow, segregate

Every dangerous good is assigned to one of nine hazard classes, given a four-digit UN number and a Proper Shipping Name, and — where applicable — a Packing Group indicating the degree of danger: Packing Group I (high), II (medium) or III (low) (CHEMTREC). The Code’s Dangerous Goods List sets out each entry across 18 columns, including class, subsidiary risks, packing group, stowage and segregation requirements, and properties and observations, so a carrier can look up any substance by its UN number (Djadjev, University of Groningen).

Class	Hazard	Examples
1	Explosives	Fireworks, ammunition
2	Gases	Propane, oxygen
3	Flammable liquids	Gasoline, paint
4	Flammable solids	Matches, sulfur
5	Oxidizing substances and organic peroxides	Hydrogen peroxide, bleach
6	Toxic and infectious substances	Pesticides, medical waste
7	Radioactive material	Uranium, medical isotopes
8	Corrosives	Battery acid, drain cleaner
9	Miscellaneous dangerous goods	Lithium batteries, dry ice

Packaging must be UN-certified and matched to the hazard class and packing group; common types include UN-certified containers, Intermediate Bulk Containers and portable tanks (CHEMTREC). Packages carry diamond-shaped hazard labels showing the class symbol and number, plus a MARINE POLLUTANT mark where applicable and an elevated-temperature mark for hot cargo (CHEMTREC; Djadjev, University of Groningen). The shipper must supply a dangerous goods transport document — including the UN number, Proper Shipping Name, hazard classes and packing group — with a signed declaration that the consignment is properly packaged, marked and labelled, and both shipper and carrier must retain copies for at least three months; the ship must also carry a special list, manifest or stowage plan showing each dangerous good, its quantity and its location aboard (Djadjev, University of Groningen).

Stowage and segregation are where the Code gets physically precise. General cargo uses five stowage categories — A, B and E (on deck or below deck), C and D (on deck only) — with separate categories for Class 1 explosives (Djadjev, University of Groningen). Incompatible goods must be kept apart by defined degrees: “away from” means 3 metres of separation, “separated from” means 6 metres, “separated by a complete compartment or hold from” means 12 metres, and “separated longitudinally by an intervening complete compartment or hold from” means 24 metres (Djadjev, University of Groningen). Even goods in the same class can require segregation — alkalis and acids in Class 8, for example — which is why the Dangerous Goods List entry, not the class alone, governs (Djadjev, University of Groningen). Emergency response is covered by the Code’s Supplement, which contains the Emergency Response Procedures for Ships Carrying Dangerous Goods (EmS Guide) and the Medical First Aid Guide (MFAG); in any incident, the safety of the crew takes priority over pollution prevention (Djadjev, University of Groningen; IMO flyer).

The Code in the wider dangerous-goods regime

The IMDG Code is the sea leg of a single global system. It is based on the UN Model Regulations — the UN Recommendations on the Transport of Dangerous Goods — but adds maritime-only requirements for marine pollutants, freight-container loading, stowage and segregation, and shipboard safety that the Model Regulations do not cover (PHMSA). In 1996 the Maritime Safety Committee agreed to reformat the Code to match the UN Model Regulations’ format, and each biennial amendment keeps it harmonized with the requirements for the carriage of dangerous goods in other modes of transport (IMO publication; MCA).

Within the IMO family, the Code sits alongside the International Maritime Solid Bulk Cargoes (IMSBC) Code for bulk cargo and the INF Code for packaged irradiated nuclear fuel, plutonium and high-level radioactive waste: in 2001, resolution MSC.118(74) amended the INF Code to align it with IMDG Code Amendment 30, which had added a new transport schedule 14 (Djadjev, University of Groningen; Resolution MSC.118(74)). For the most sensitive cargoes the Code defers to specialist regulators: the International Atomic Energy Agency’s Regulations for the Safe Transport of Radioactive Material are the principal rules for Class 7, and the World Health Organization’s guidance governs infectious substances in Class 6.2 — neither of which requires the ship’s Document of Compliance (Djadjev, University of Groningen).

Enforcement runs through national law and port scrutiny rather than through the IMO itself. Ships intended to carry dangerous goods must hold a Document of Compliance, issued by the competent authority after a satisfactory survey, certifying which classes may be carried and where each may be stowed; port officials strictly scrutinize all dangerous-goods documentation, and irregularities can result in fines or detention of the vessel (Djadjev, University of Groningen). Governments implement the Code domestically — the United Kingdom does so through the Merchant Shipping (Carriage of Dangerous Goods and Harmful Substances) (Amendment) Regulations 2024, and the United States Hazardous Materials Regulations authorize the IMDG Code as a means of compliance where a leg of the journey is by sea (MCA; PHMSA). The stakes are not theoretical: the academic analysis cites the sinking of the Kapitan Sakharov (1993) after undeclared hazardous cargo in deck containers, the total loss of the Thor Emilie (2000) carrying misdeclared cargo, and the sinking of the Ythan (2004) after an explosion of misleadingly described direct reduced iron cargo (Djadjev, University of Groningen).

Frequently asked questions

When did the IMDG Code become mandatory? Amendment 31 became mandatory on 1 January 2004 under SOLAS 1974, after the Maritime Safety Committee confirmed the decision at its 75th session in May 2002. Before that, the Code had operated as a voluntary recommendation since its first publication in 1965.

Which amendment of the IMDG Code is currently in force? Amendment 42-24, adopted by resolution MSC.556(108) at the Maritime Safety Committee’s 108th session in May 2024. It could be applied voluntarily from 1 January 2025 and became mandatory internationally on 1 January 2026, including new UN numbers for sodium-ion batteries and battery-powered vehicles.

What are the nine classes of dangerous goods? Class 1 explosives, Class 2 gases, Class 3 flammable liquids, Class 4 flammable solids, Class 5 oxidizing substances and organic peroxides, Class 6 toxic and infectious substances, Class 7 radioactive material, Class 8 corrosives, and Class 9 miscellaneous dangerous goods such as lithium batteries and dry ice.

Who enforces the IMDG Code? Enforcement runs through national authorities, not the IMO directly. Ships must hold a Document of Compliance from the competent authority, port officials scrutinize dangerous-goods documentation, and irregularities can mean fines or detention. The UK implements the Code through 2024 merchant shipping regulations; US rules authorize it for sea legs.

How does the IMDG Code relate to the INF Code? The INF Code governs ship design, construction and equipment for packaged irradiated nuclear fuel, plutonium and high-level radioactive waste, while the IMDG Code supplies the classification and schedule framework it references. Resolution MSC.118(74) in 2001 aligned the INF Code with IMDG Amendment 30.

What this profile does not claim

This profile does not reproduce the Code’s text, which is a paywalled IMO publication, and it does not give operational stowage or packaging instructions for any specific substance — the Code itself is the only authoritative source for those. It does not detail the road, rail or air sibling regimes built on the same UN Model Regulations, because no fully-read source in this pass covered them. It does not assess how well any flag state or port actually enforces the Code in practice, nor does it claim that the casualty cases cited are the only misdeclaration incidents — they are the three examples given by the academic source. The 1965 first-publication year rests on a single tier2 source (see openItems), and the profile does not state details of any Amendment 43-26, which were not verified from a fully-read source.