Dangerous Goods Classes: The 9 UN Classes Explained

Dangerous Goods Classes: The 9 UN Hazard Classes Explained

Dangerous goods are classified into nine UN hazard classes based on the primary risk they pose — from explosives (Class 1) to miscellaneous hazards (Class 9). The class, UN number, and packing group determine how cargo must be packed, labelled, documented, segregated, and whether a given vessel or aircraft will carry it.

The nine classes

Class 1 Explosives; Class 2 Gases (flammable, non-flammable, toxic); Class 3 Flammable liquids; Class 4 Flammable solids and substances liable to spontaneous combustion or emitting flammable gas in water; Class 5 Oxidizers and organic peroxides; Class 6 Toxic and infectious substances; Class 7 Radioactive material; Class 8 Corrosives; Class 9 Miscellaneous dangerous substances (including lithium batteries and environmentally hazardous goods).

Each item is identified by a four-digit UN number (e.g., UN1950 = aerosols) and, for most classes, a packing group indicating danger level: PG I (high), II (medium), III (low). The same UN classification underpins both sea and air, but the rulebooks and quantity limits differ: ocean follows the IMDG Code (updated biennially), air follows the IATA DGR (updated annually), with air far more restrictive — and air adds the crucial CAO vs PAX split (Cargo Aircraft Only vs passenger-and-cargo), which changes what quantities can fly and on what aircraft.

What shipping DG actually requires

Moving dangerous goods is document- and process-heavy, and the constraints override normal flow. A signed Dangerous Goods Declaration (the Shipper's Declaration for Dangerous Goods in air) is mandatory; ocean stuffed containers also need a Container Packing Certificate. Segregation rules forbid stowing incompatible classes together, so a multi-commodity DG container needs a segregation check. Many consolidators refuse DG in LCL groupage, effectively forcing FCL. DG surcharges apply, and certain classes are barred from specific terminals, aircraft, or routes entirely.

The core operational truth: DG cannot be treated as ordinary cargo that happens to have a label. It must be flagged at the very start — at quote and booking — because the class, packing group, and mode dictate feasibility, price, routing, and paperwork. A DG shipment discovered late is a shipment that misses its sailing or gets rejected at the gate, which is why competent desks screen for hazard classification before quoting, not after.

Frequently Asked Questions

What are the 9 classes of dangerous goods?

Class 1 Explosives, 2 Gases, 3 Flammable liquids, 4 Flammable solids, 5 Oxidizers and organic peroxides, 6 Toxic and infectious substances, 7 Radioactive material, 8 Corrosives, and 9 Miscellaneous dangerous goods (including lithium batteries). Each is grouped by its primary hazard.

What is the difference between IMDG and IATA dangerous goods rules?

IMDG governs dangerous goods by sea (updated every two years); IATA DGR governs them by air (updated annually) and is generally far stricter on quantities. Both use the same UN classification, but limits and requirements differ significantly by mode.

What is a packing group?

A packing group indicates the degree of danger within a class: PG I is high danger, PG II medium, PG III low. It affects packaging standards and quantity limits. Not all classes use packing groups (for example, explosives and radioactives use their own systems).

Can dangerous goods ship as LCL?

Often not. Many consolidators refuse dangerous goods in shared LCL containers because one shipper's hazard and segregation requirements constrain everything else in the box. DG cargo is frequently planned as FCL by default.