The nine UN dangerous goods classes
Every regulated dangerous good is assigned to one of nine UN classes based on its primary hazard. These classes are shared across the road (ADR), rail (RID), sea (IMDG) and air (IATA/ICAO) regulations, and drive the diamond label, packing group and documentation a shipment needs.
The complete class and division breakdown
| Class | Name | Key divisions | Label colour |
|---|---|---|---|
| 1 | Explosives | 1.1 mass explosion, 1.2 projection, 1.3 fire, 1.4 minor hazard, 1.5 blasting agents, 1.6 | Orange |
| 2 | Gases | 2.1 flammable, 2.2 non-flammable non-toxic, 2.3 toxic | Red, Green, or White |
| 3 | Flammable liquids | — | Red diamond |
| 4 | Flammable solids / reactive | 4.1 flammable solids, 4.2 spontaneously combustible, 4.3 dangerous when wet | White-red stripes, red/white, blue |
| 5 | Oxidising / organic peroxides | 5.1 oxidisers, 5.2 organic peroxides | Yellow |
| 6 | Toxic / infectious | 6.1 toxic, 6.2 infectious | White with skull, biohazard |
| 7 | Radioactive | — (categories I, II, III within) | Yellow/white |
| 8 | Corrosives | — | Black/white |
| 9 | Miscellaneous | Lithium batteries, dry ice, magnetised, hazardous to environment | White with stripes |
How classes are assigned and used
The class is determined by the substance’s dominant danger — a flammable liquid is Class 3, a corrosive acid is Class 8, a radioactive source is Class 7. Many classes split into divisions that pin down the specific risk: Class 2 gases divide into 2.1 flammable, 2.2 non-flammable non-toxic, and 2.3 toxic. The class and division appear together on the hazard diamond and in the dangerous goods entry.
A substance with more than one hazard receives a primary class plus one or more subsidiary risk labels. For example, a flammable toxic liquid would be Class 3 (primary) with a 6.1 subsidiary label. The primary class drives which placard goes on the vehicle or container; subsidiary risks add further placards. Always work from the substance’s UN number and its proper shipping name to identify all hazards, not the class alone.
Packing groups and how they relate to class
Classes 3, 4, 5.1, 6.1, and 8 assign a packing group (PG I, II, or III) that indicates the degree of hazard within the class:
- PG I: great danger — strictest packaging, quantity limits, and documentation.
- PG II: medium danger — standard regulated requirements.
- PG III: minor danger — lighter requirements and higher quantity limits.
Class 1 (explosives) and Class 7 (radioactive) use their own compatibility and category systems instead of packing groups. Class 9 entries such as lithium batteries use special provisions rather than packing groups.
Common examples and traps
- Petrol: Class 3, Packing Group II, UN 1203, red diamond, flammable liquid.
- Chlorine gas: Class 2.3, UN 1017, white skull diamond.
- Lithium-ion batteries in equipment (e.g. laptops): Class 9, UN 3481, special provisions PI965/PI966 limit quantity per cell and per battery.
- Dry ice (solid CO₂): Class 9, UN 1845, specific marking requirements for ventilation, not a hazard diamond.
- Ammonia solution: dual-hazard — Class 8 corrosive primary with Class 6.1 toxic subsidiary, depending on concentration.
This reference is an educational summary. For actual shipping, consult the current ADR/IMDG/IATA texts and the full dangerous goods entry for your specific UN number.