The International Maritime Dangerous Goods (IMDG) Code is the IMO's international rulebook for carrying packaged dangerous goods by sea. It sorts dangerous goods into nine classes, gives each substance a UN number and a proper shipping name, and sets the rules for packaging, labels, placards, documents and segregation on board. This article is an introductory educational reference only; it is not a substitute for the official edition of the IMDG Code, certified training or advice from a dangerous goods specialist.
What the IMDG Code is for
Misdeclared or poorly packed dangerous goods can cause fires, explosions, toxic leaks or marine pollution. The IMDG Code gives shippers, forwarders, carriers, terminals and crews a common language so that everyone knows the hazard and how to handle it. It is mandatory through SOLAS Chapter VII and also covers marine pollutants. The code is updated every two years. Amendment 42-24 could be applied voluntarily from 1 January 2025 and is mandatory from 1 January 2026. For air transport, the IATA Dangerous Goods Regulations (DGR) apply, not the IMDG Code.
In Indonesia, the term B3 (bahan berbahaya dan beracun, hazardous and toxic materials) is common in everyday use, but sea shipments are classified under the IMDG Code. Carriers usually require a separate dangerous goods request and approval before accepting a booking, and terminals may have their own storage rules. Check the requirements of the carrier, the terminal and the local port authority. The code also requires training for shore-side staff involved in classifying, packing, marking, documenting or loading dangerous goods into containers, matched to their duties.
The nine classes
| Class | Category | Divisions | Typical examples |
|---|---|---|---|
| 1 | Explosives | 1.1–1.6 | Fireworks, ammunition |
| 2 | Gases | 2.1 flammable, 2.2 non-flammable non-toxic, 2.3 toxic | Aerosols, LPG, oxygen cylinders |
| 3 | Flammable liquids | — | Paint, thinner, alcohol-based perfume |
| 4 | Flammable solids | 4.1 flammable solids, 4.2 spontaneously combustible, 4.3 dangerous when wet | Matches, calcium carbide |
| 5 | Oxidizers and organic peroxides | 5.1 oxidizing substances, 5.2 organic peroxides | Certain ammonium nitrate fertilisers, hydrogen peroxide |
| 6 | Toxic and infectious | 6.1 toxic, 6.2 infectious | Pesticides, medical specimens |
| 7 | Radioactive | — | Medical isotopes |
| 8 | Corrosive | — | Sulphuric acid, wet batteries |
| 9 | Miscellaneous | — | Lithium batteries, dry ice, environmentally hazardous substances |
The examples are illustrative only. Final classification always comes from the Safety Data Sheet (SDS), laboratory testing where needed and the Dangerous Goods List in the IMDG Code.
UN numbers, proper shipping names and packing groups
Every dangerous substance or article has a four-digit UN number, such as UN 1263 for paint. It is paired with a Proper Shipping Name (PSN), the standard name that must appear exactly on documents and packages. A trade name cannot replace the PSN.
The packing group (PG) indicates the degree of danger: PG I high, PG II medium and PG III low. It determines how strong the packaging must be; UN-approved packaging carries a specification code showing which packing groups it was tested for. Not every class uses packing groups.
Marks, labels and placards
- On packages: the UN number and PSN, diamond-shaped hazard labels (generally at least 100 × 100 mm), and additional marks such as the marine pollutant mark or orientation arrows where required.
- On the container: placards (generally at least 250 × 250 mm) on all four sides, meaning both long sides plus the front and rear ends. In certain cases the UN number must be displayed as well.
- Lithium batteries: the IMDG Code has a dedicated Class 9 lithium battery label.
Old or irrelevant labels and placards must be removed once the container is emptied or reused for other cargo. An ordinary shipping mark, such as one from the shipping mark generator, does not replace hazard labels.
Documents: the DG Declaration and Container Packing Certificate
The Dangerous Goods Declaration lists the UN number, PSN, class, packing group, number and type of packages, total quantity and additional information such as flashpoint for Class 3 or marine pollutant status, together with the shipper's signed declaration. The Container Packing Certificate confirms that the container is fit for use, the goods are packed and secured according to the rules, in-container segregation is respected, and marks and placards are fixed. Cargo securing should also follow the CTU Code and lashing principles, and the container still needs a declared VGM.
Worked example: filling in the declaration
A factory ships 80 drums of paint, 20 litres each and 26 kg gross per drum, in one 20-foot container. Assume the SDS-based classification is UN 1263, PAINT, Class 3, PG III (an example only; the packing group for paint depends on its flashpoint and viscosity).
| Entry | Calculation | Result |
|---|---|---|
| Number of packages | 80 drums | 80 drums |
| Net quantity | 80 × 20 L | 1,600 L |
| Gross mass of goods | 80 × 26 kg | 2,080 kg |
| Container placards | 2 sides + 2 ends | 4 Class 3 placards |
The 2,080 kg gross mass is added to the container tare and securing material for the VGM. Container sizes and tare weights are in the container size table.
Segregation, lithium batteries and limited quantities
Segregation keeps apart dangerous goods that could react with each other. The levels are "away from", "separated from", "separated by a complete compartment or hold from" and "separated longitudinally by an intervening complete compartment or hold from". The IMDG segregation table sets the level required between classes, plus rules for segregation groups such as acids and alkalis. Final positions on board are decided by the ship planner in the stowage plan.
Lithium batteries fall under Class 9, with separate UN numbers for lithium ion and lithium metal, and for batteries shipped alone, packed with equipment or contained in equipment. Damage, short circuits and inadequate packaging are the main risks; follow the applicable special provisions.
Limited quantities and excepted quantities are provisions for dangerous goods in very small inner packagings. Requirements are lighter, for example a special mark replacing some labels, but there are still per-package limits, documentation duties and loading rules. Limits differ for each UN number; check the Dangerous Goods List.
Common mistakes
- Not declaring dangerous goods at all. Perfume, aerosols, batteries and battery-powered devices are often shipped as "general cargo".
- Using a trade name instead of the PSN.
- Packaging without UN certification or not rated for the packing group.
- Incomplete placarding or old labels left on the container.
- Ignoring segregation when several products share one container.
- Working from a different IMDG edition than the carrier.
Plan with care
Use the 3D planner to visualise drum layout and securing, then prepare the VGM form. A planner layout is a simulation and does not replace official weighing, VGM, the vessel's loading computer or operator approval. For dangerous goods, always follow the current official edition of the IMDG Code and involve trained staff or a dangerous goods specialist.