How do IMDG classes relate to UN dangerous goods classes?

The IMO adopted the United Nations dangerous goods class system, so the class numbers are the same. An IMDG Class 3 substance is also UN Class 3. The IMDG Code adds maritime-specific detail such as divisions, packing groups, and segregation rules for carriage by sea.

What are the nine main dangerous goods classes?

Class 1 explosives, Class 2 gases, Class 3 flammable liquids, Class 4 flammable solids and reactive substances, Class 5 oxidisers and organic peroxides, Class 6 toxic and infectious substances, Class 7 radioactive material, Class 8 corrosives, and Class 9 miscellaneous dangerous substances and articles.

What do the division numbers like 2.1 or 4.3 mean?

Some classes are split into divisions for more specific hazards. Class 2 divides into 2.1 flammable gas, 2.2 non-flammable non-toxic gas, and 2.3 toxic gas. Class 4 divides into 4.1 flammable solids, 4.2 spontaneously combustible, and 4.3 dangerous when wet.

What is the difference between IMCO and IMO?

IMCO, the Inter-Governmental Maritime Consultative Organization, was the former name of the body now called the IMO, the International Maritime Organization. The IMDG Code is its set of rules for carrying dangerous goods by sea, so IMCO class and IMDG class refer to the same scheme.

Which class covers lithium batteries?

Lithium batteries are assigned to Class 9, miscellaneous dangerous goods. Class 9 covers substances and articles that present a danger during transport not covered by the other classes, which also includes dry ice, marine pollutants, and asbestos.

What is the IMDG / IMO Class to UN Class Cross-Reference?

Reference table mapping IMO IMDG hazard classes and divisions to UN dangerous goods class numbers for maritime transport. Filter by class, division, or hazard to find the matching UN class, hazard name, and example substances. It runs free in your browser on Gera Tools, with nothing uploaded.

IMDG / IMO Class to UN Class Cross-Reference

Name: IMDG / IMO Class to UN Class Cross-Reference
Creator: Gera Tools
License: https://creativecommons.org/licenses/by/4.0/

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Mapping IMDG classes to UN classes

When dangerous goods move by sea they are regulated by the IMO’s IMDG Code, but the hazard classes themselves come from the United Nations dangerous goods system. This reference cross-references each IMDG class and division to its UN class number, with the hazard name and example substances, so you can confirm the class for a cargo or read a shipping document quickly.

How it works: the class numbers are identical

The key fact is that the IMO adopted the UN class scheme wholesale, so there is no renumbering between the two systems — the class digit is always the same:

IMDG Class 3   ==  UN Class 3   (flammable liquids)
IMDG Class 4.3 ==  UN Class 4.3 (dangerous when wet)
IMDG Class 8   ==  UN Class 8   (corrosives)

What the IMDG Code adds on top of the UN base classification is maritime-specific detail: explosive divisions 1.1 to 1.6, packing groups I to III for the degree of danger within a class, and segregation tables stating which classes must be stowed apart on board ship. Divisions like 2.1, 2.2, 2.3 or 4.1, 4.2, 4.3 refine the broad class into specific sub-hazards.

All nine dangerous goods classes

Class	Name	Example substances
1	Explosives	Fireworks, ammunition, detonators
2	Gases	LPG (2.1), compressed nitrogen (2.2), chlorine (2.3)
3	Flammable liquids	Petrol, ethanol, acetone
4	Flammable solids / reactive	Matches (4.1), white phosphorus (4.2), sodium (4.3)
5	Oxidisers / organic peroxides	Hydrogen peroxide (5.1), benzoyl peroxide (5.2)
6	Toxic / infectious	Pesticides (6.1), medical waste (6.2)
7	Radioactive material	Uranium ore, medical radioisotopes
8	Corrosives	Sulphuric acid, sodium hydroxide
9	Miscellaneous	Lithium batteries, dry ice, marine pollutants

Class divisions in detail

Class 1 — Explosives. Divided 1.1 to 1.6 based on the type of explosion risk: mass explosion hazard (1.1), blast or fragment hazard without mass explosion (1.2), fire hazard without blast (1.3), no significant hazard (1.4), very insensitive substances (1.5), and extremely insensitive articles (1.6). The division number matters enormously for stowage and segregation.

Class 2 — Gases. Division 2.1 is flammable gas (LPG, hydrogen), 2.2 is non-flammable non-toxic gas (compressed air, helium, oxygen), and 2.3 is toxic gas (chlorine, phosgene, ammonia). These require different segregation from oxidisers and flammable materials.

Class 4 — Flammable solids. Division 4.1 covers solid materials that burn readily (sulphur, magnesium powder, matches). Division 4.2 covers spontaneously combustible materials that ignite on contact with air (white phosphorus, charcoal). Division 4.3 — dangerous when wet — covers materials that react with water to produce flammable gases (sodium, calcium carbide, potassium).

Practical notes

The older abbreviation IMCO (Inter-Governmental Maritime Consultative Organization) is the former name of the IMO. IMCO class labels refer to the same scheme as IMDG classes.
For any specific substance, the authoritative source is its UN number and proper shipping name in the IMDG dangerous goods list, which fixes the class, division, packing group, and special provisions together.
Marine pollutants and lithium batteries both fall under Class 9, but they have very different segregation and marking requirements — Class 9 is not a uniform catch-all.