Most introductions to dangerous goods teach “the nine classes”. That comes from the UN Recommendations, which ADR, IMDG, IATA and US rules all build on. The explainer this post is based on is a general overview that isn’t tied to any regime, and it uses US wording like “gasoline”. It also isn’t precise enough to use behind the wheel. ADR 2.1.1.1 splits the nine headings into thirteen classes, and those subdivisions change the labels, the paperwork and the equipment you carry.
Nine headings, thirteen ADR classes
Each class has its own criteria in Chapter 2.2 of ADR. The consignor classifies the goods. The driver doesn’t. Your job is to recognise what the documents and labels are telling you.
| ADR class | What it covers | Typical road example |
|---|---|---|
| 1 | Explosive substances and articles | Commercial blasting explosives, fireworks |
| 2 | Gases: compressed, liquefied, dissolved or refrigerated | Propane UN 1978, helium |
| 3 | Flammable liquids | Petrol UN 1203, diesel UN 1202 |
| 4.1 | Flammable solids, self-reactive and polymerising substances, solid desensitised explosives | Safety matches UN 1944, sulphur UN 1350 |
| 4.2 | Substances liable to spontaneous combustion | White phosphorus UN 1381 |
| 4.3 | Substances that give off flammable gas in contact with water | Sodium UN 1428, calcium carbide UN 1402 |
| 5.1 | Oxidising substances | Hydrogen peroxide solutions, ammonium nitrate fertiliser UN 2067 |
| 5.2 | Organic peroxides | Resin hardeners and curing agents |
| 6.1 | Toxic substances | Many pesticides |
| 6.2 | Infectious substances | Clinical waste UN 3291 |
| 7 | Radioactive material | Medical isotopes |
| 8 | Corrosive substances | Battery fluid, acid UN 2796 |
| 9 | Miscellaneous dangerous substances and articles | Lithium batteries, environmentally hazardous substances UN 3082, asbestos UN 2212 |
Class 2 has no subdivisions in ADR. Gases carry a classification code instead, such as A (asphyxiant), F (flammable) or T (toxic), and the package shows label 2.1, 2.2 or 2.3.
Where the general explanation needs correcting
A broad overview is a fine starting point, but several of its claims would mislead an ADR driver:
| Claim in the video | The ADR position |
|---|---|
| Class numbers show the level of danger | Class numbers describe the type of hazard, not how severe it is. Within most classes, severity comes from the packing group: I (high), II (medium), III (low). |
| Class 4 is “flammable solids”, with metals as an example | Class 4 is three separate classes. Reactive metals are often 4.3 (they react with water) or 4.2, not 4.1. |
| Peroxides in hair bleach are “Class 5” | Hydrogen peroxide solutions are 5.1 oxidisers. Organic peroxides are 5.2, a different class, and some need temperature control. |
| Pesticides are Class 6 | It depends on the formulation. Many are 6.1, but a flammable liquid pesticide can be Class 3 with a toxic subsidiary hazard. |
| Dry ice is a Class 9 hazard in a closed container | On the road, the provision drivers usually meet is 5.5.3: dry ice used as a coolant, the asphyxiation warning mark, and ventilating before anyone enters. |
The Class 1 division is the one place where the number after the dot does describe how the goods behave:
| Division | Hazard |
|---|---|
| 1.1 | Mass explosion |
| 1.2 | Projection, no mass explosion |
| 1.3 | Fire with minor blast or projection |
| 1.4 | No significant hazard outside the package |
| 1.5 | Very insensitive, but with a mass explosion hazard |
| 1.6 | Extremely insensitive articles |
Fireworks can fall anywhere from 1.1G to 1.4S, depending on how they are classified. Never assume the division from the product type. Read it from the label and the transport document. Our guide to reading a UN packaging mark covers how packing groups and packaging codes fit alongside the class.
What the class changes for you on the road
Knowing the class matters because so many of your duties depend on it:
| Duty | ADR reference | How the class affects it |
|---|---|---|
| Package labels | 5.2.2 | The label model follows the class or division, plus any subsidiary hazards |
| Placards and orange plates | 5.3 | Placards show the class. Orange plates on tanks and bulk loads carry the hazard identification number and UN number. |
| Transport document | 5.4.1 | Lists the UN number, proper shipping name, label models, packing group and tunnel code |
| Load threshold | 1.1.3.6 | Uses the transport category, not the class. Check both. |
| Mixed loading | 7.5.2 | Some label combinations can’t be loaded together on the same vehicle |
| Crew equipment | 8.1.5.3 | An escape mask is needed for labels 2.3 or 6.1. A shovel, drain seal and collecting container are needed for solids and liquids with labels 3, 4.1, 4.3, 8 or 9. |
| Driver certificate | 8.2.1 | Class 1, Class 7 and tank carriage each need a specialisation on top of the basic course |
If what’s on the vehicle doesn’t match the paperwork, for example a 6.1 label with no escape mask on board or goods that can’t be loaded together, don’t set off until it has been sorted out. Carrying above the 1.1.3.6 threshold without the right certificate, placards and equipment isn’t a grey area. Our vehicle equipment checks guide goes through the 8.1.5 kit list item by item.
How ADR Driver Pro Fits Into This
ADR Driver Pro organises its 13 modules around the core course and the individual hazard classes, so you can revise 4.1 and 4.3, or 5.1 and 5.2, as separate topics rather than lumping them together. There are 1820 revision questions in total, and 110 of them are free.
The 6 driver routes separate what everyone needs from the specialist material for packages, tanks, explosives and radioactive goods. The 8 quick reference sets give you the class, label and equipment detail at a glance. The 5 calculators include the load-points calculator for 1.1.3.6, and the 6 field tools are there when you need to check something beside the vehicle. None of it replaces the transport document or advice from your DGSA, but it will help you spot when something doesn’t add up.
