What are the nine classes of dangerous goods?

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

Is hazmat the same as dangerous goods?

Yes, in practice. US law says hazardous material; the UN, IMO and IATA say dangerous goods. Both use the same UN classes and numbers, though the US rules may cite an older edition of the international codes.

Which code covers dangerous goods at sea?

The IMDG Code, made mandatory under SOLAS chapter VII. Amendment 42-24 has been mandatory since 1 January 2026, and IMO amends the code every two years.

Term

Dangerous goods (DG)

Dangerous goods — hazardous materials in US law — are substances and articles that can endanger health, safety or property in transport. The UN sorts them into nine classes by their main hazard, and each mode carries them under its own code: the IMDG Code at sea, IATA's regulations by air, ADR on Europe's roads and 49 CFR in the US.

Also called DG, hazmat, hazardous materials, dangerous goods classes, hazardous cargoUpdated 14 October 2026

The nine classes

Class	Covers
1	Explosives
2	Gases — flammable, non-flammable non-toxic, and toxic
3	Flammable liquids
4	Flammable solids; substances liable to spontaneous combustion; substances that give off flammable gases in contact with water
5	Oxidizing substances and organic peroxides
6	Toxic and infectious substances
7	Radioactive material
8	Corrosive substances
9	Miscellaneous dangerous substances and articles

Each substance or article goes to the class of its hazard, or of the most predominant one if it has several. The numbers are not a ranking: the IMDG Code says the order of the classes is not their degree of danger. Within most classes, packing groups I, II and III mark high, medium and low danger.

Which code applies

Mode	Code	Status
Sea	IMDG Code, mandatory under SOLAS chapter VII	Amendment 42-24, mandatory from 1 January 2026
Air	ICAO Technical Instructions; IATA's Dangerous Goods Regulations	2027 DGR, in force 1 January 2027
Road, EU	ADR, through Directive 2008/68/EC	Annexes A and B apply, with 'Member State' in place of 'contracting party'
United States	The Hazardous Materials Regulations, 49 CFR	Still cite the UN 22nd revised edition and IMDG 41-22

IMO amends the IMDG Code on a two-year cycle. US rules also let a shipper offer hazardous materials under the ICAO Technical Instructions or the IMDG Code, with conditions — so the same cargo can be described under two rulebooks of different dates.

Worked example: which IMDG edition applies

Sailing June 2025 → Amendment 42-24 may be applied voluntarily · sailing February 2026 → 42-24 is mandatory · US leg of the same move → 49 CFR still incorporates Amendment 41-22 (eCFR, 9 October 2026)

42-24 was adopted on 23 May 2024, could be used voluntarily from 1 January 2025 and entered into force on 1 January 2026 (IMO resolution MSC.556(108)). The sailings are illustrative.

The mistake people make

Assuming a product that is safe to sell is safe to ship. Gasoline and lithium ion batteries are everyday goods, yet one is class 3 and the other class 9, and the batteries are forbidden on passenger aircraft under US rules. Classify from the product's actual hazard and the code for the mode, before booking — not after the carrier asks.

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