ADR Dangerous Goods Classes Explained: A Driver's Guide for 2026
Understanding the ADR dangerous goods classification system is fundamental to safe and legal transport of hazardous materials by road. The ADR agreement divides dangerous goods into 9 main classes based on their primary hazard, and each class has specific requirements for packaging, labelling, documentation, and vehicle equipment. This guide explains each class in plain English, with practical information for professional drivers.
The 9 ADR Dangerous Goods Classes
The ADR classification system groups dangerous goods by their primary physical or chemical hazard. Many substances have secondary hazards and may be subject to requirements from more than one class. The 9 classes are:
| Class | Category | Examples |
|---|---|---|
| Class 1 | Explosives | Fireworks, ammunition, blasting explosives, airbag inflators |
| Class 2 | Gases | LPG, oxygen, acetylene, aerosols, carbon dioxide |
| Class 3 | Flammable Liquids | Petrol, diesel, ethanol, acetone, paint |
| Class 4.1 | Flammable Solids | Matches, metal powders, self-reactive substances |
| Class 4.2 | Spontaneously Combustible | White phosphorus, activated carbon, fish meal |
| Class 4.3 | Dangerous When Wet | Sodium, calcium carbide, aluminium powder |
| Class 5.1 | Oxidising Substances | Hydrogen peroxide, ammonium nitrate, bleach |
| Class 5.2 | Organic Peroxides | Benzoyl peroxide, methyl ethyl ketone peroxide |
| Class 6.1 | Toxic Substances | Pesticides, cyanides, arsenic compounds |
| Class 6.2 | Infectious Substances | Medical waste, biological samples, diagnostic specimens |
| Class 7 | Radioactive Materials | Medical isotopes, industrial radiography sources, nuclear fuel |
| Class 8 | Corrosive Substances | Sulphuric acid, hydrochloric acid, sodium hydroxide, batteries |
| Class 9 | Miscellaneous Dangerous Goods | Dry ice, lithium batteries, magnetised materials, elevated temperature substances |
Class 1: Explosives
Class 1 covers explosive substances and articles — materials that can detonate, deflagrate, or cause a rapid exothermic reaction. Class 1 is divided into 6 divisions (1.1 to 1.6) based on the type and severity of the explosion hazard. Division 1.1 covers substances with a mass explosion hazard (the most dangerous), while Division 1.6 covers extremely insensitive detonating articles.
Transporting Class 1 goods requires a specialist ADR Class 1 module in addition to the core qualification. Vehicles must carry specific fire-fighting equipment and display orange plates with the appropriate hazard identification number and UN number.
Class 2: Gases
Class 2 covers compressed gases, liquefied gases, dissolved gases, and refrigerated liquefied gases. It is divided into three sub-groups: flammable gases (2F), non-flammable non-toxic gases (2A), and toxic gases (2T). LPG (liquefied petroleum gas) is one of the most commonly transported Class 2 substances in the UK, used for domestic heating and industrial processes.
Tanker drivers transporting Class 2 gases require the ADR Tank module in addition to the core qualification. Gas tankers must be fitted with pressure relief valves and carry specific emergency equipment.
Class 3: Flammable Liquids
Class 3 is one of the most commonly encountered classes for UK HGV drivers, covering petrol, diesel, heating oil, ethanol, and many industrial solvents. A substance is classified as a flammable liquid if it has a flash point of not more than 60°C (or 65°C for certain transport conditions).
Fuel tanker drivers — one of the largest groups of ADR-certified drivers in the UK — primarily work with Class 3 goods. The Tank module is required for tanker operations, and vehicles must display orange plates with the appropriate hazard identification number (e.g., 33 for highly flammable liquids) and UN number (e.g., UN 1203 for petrol).
Class 4: Flammable Solids and Related Hazards
Class 4 is divided into three sub-classes covering different types of solid fire hazards. Class 4.1 (flammable solids) includes matches and metal powders that can ignite easily. Class 4.2 (spontaneously combustible substances) includes materials that can ignite without an external ignition source. Class 4.3 (substances dangerous when wet) includes materials that react with water to produce flammable gases — sodium metal is a classic example.
Class 5: Oxidising Substances and Organic Peroxides
Class 5.1 covers oxidising substances — materials that can cause or contribute to the combustion of other materials by providing oxygen. Ammonium nitrate (used in fertilisers and explosives) and hydrogen peroxide are common Class 5.1 substances. Class 5.2 covers organic peroxides, which are thermally unstable and may decompose exothermically.
Class 6: Toxic and Infectious Substances
Class 6.1 covers toxic substances that can cause death or serious injury if inhaled, swallowed, or absorbed through the skin. Pesticides, cyanide compounds, and many industrial chemicals fall into this class. Class 6.2 covers infectious substances — biological materials known or reasonably expected to contain pathogens. Medical waste and diagnostic specimens are common Class 6.2 goods.
Class 7: Radioactive Materials
Class 7 covers radioactive materials — substances that spontaneously emit ionising radiation. Transport of Class 7 goods is strictly regulated and requires a specialist ADR Class 7 module. Radioactive materials are transported in specially designed packages (Type A, Type B, or Type C) depending on the activity level and type of radiation. Common Class 7 goods include medical isotopes for hospitals and industrial radiography sources.
Class 8: Corrosive Substances
Class 8 covers substances that can cause full-thickness destruction of skin tissue or corrode steel or aluminium at a specified rate. Sulphuric acid, hydrochloric acid, and sodium hydroxide (caustic soda) are common Class 8 substances. Lead-acid batteries (such as vehicle batteries) also fall into Class 8 when transported in bulk.
Class 9: Miscellaneous Dangerous Goods
Class 9 is a catch-all category for substances and articles that present a danger during transport but do not fit neatly into Classes 1–8. Lithium batteries (including those in electric vehicles) are one of the most significant Class 9 goods in 2026, given the growth of EV transport. Dry ice (solid carbon dioxide), magnetised materials, and elevated temperature substances also fall into Class 9.
UN Numbers and Hazard Identification Numbers
Every dangerous substance transported under ADR is assigned a UN number — a four-digit code that uniquely identifies the substance. Vehicles must display orange plates showing the UN number and, for tankers, a hazard identification number (HIN) that describes the nature of the hazard. For example:
- UN 1203 — Petrol (Gasoline)
- UN 1011 — Butane
- UN 1789 — Hydrochloric Acid
- UN 3480 — Lithium Ion Batteries
Understanding UN numbers and HINs is a core part of ADR training and is tested in the DVSA examinations.
Packing Groups
Many dangerous goods are assigned to a packing group (I, II, or III) that indicates the degree of danger they present. Packing Group I indicates great danger, Packing Group II indicates medium danger, and Packing Group III indicates minor danger. The packing group affects the packaging requirements and the exemption thresholds that determine whether ADR documentation and certification are required.
Frequently Asked Questions
How many ADR dangerous goods classes are there?
There are 9 main ADR classes, but Class 4 is divided into three sub-classes (4.1, 4.2, 4.3), Class 5 into two (5.1, 5.2), and Class 6 into two (6.1, 6.2), giving 13 distinct categories in total. Each class has its own labelling, packaging, and documentation requirements.
Do I need ADR training for all 9 classes?
No. ADR training is structured so that you only need to be certified for the classes of dangerous goods you will actually be transporting. The core (packages) qualification covers all classes for packaged goods, but specialist modules are required for tanks, explosives (Class 1), and radioactive materials (Class 7).
What class is diesel?
Diesel is classified as a Class 3 flammable liquid under ADR, with UN number 1202. It has a flash point above 23°C and up to 60°C, placing it in Packing Group III (minor danger). However, when transported in bulk in tankers, full ADR Tank certification is still required.
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