What Are ADR Classes? A Complete Guide to Dangerous Goods Categories
If you are considering ADR training or already carry dangerous goods by road, understanding the nine ADR classes is fundamental. The ADR (Accord Dangereux Routier) classification system divides hazardous materials into categories based on the type of danger they present. Each class has specific packaging, labelling, and documentation requirements — and drivers must hold the correct ADR certificate for the classes they carry.
This guide explains every ADR class in plain English, covering what falls into each category, the hazard labels you will see on vehicles, and what the rules mean for UK drivers in 2026.
The Nine ADR Hazard Classes
The ADR system uses nine primary classes, some of which are subdivided into divisions. The class number appears on the orange hazard panel displayed on ADR vehicles.
Class 1 — Explosives
Class 1 covers substances and articles that can explode, deflagrate, or react violently. It is divided into six divisions (1.1 through 1.6) based on the type of explosive hazard — from mass explosion (1.1) to very insensitive substances (1.6). Common examples include fireworks, ammunition, and airbag inflators. Class 1 requires a specialist ADR certificate and is one of the most tightly regulated categories.
Class 2 — Gases
Class 2 covers compressed, liquefied, dissolved, and refrigerated liquefied gases. It is subdivided into flammable gases (2.1), non-flammable non-toxic gases (2.2), and toxic gases (2.3). Examples include LPG, oxygen cylinders, carbon dioxide, and chlorine. Tanker drivers carrying bulk gases need both a core ADR certificate and a Tank (T) specialisation.
Class 3 — Flammable Liquids
Class 3 is one of the most common ADR classes in the UK. It covers liquids with a flash point below 60°C, including petrol, diesel, aviation fuel, acetone, and many industrial solvents. Fuel tanker drivers carrying Class 3 in bulk require the Tank specialisation. Class 3 is included in the standard ADR core certificate.
Class 4 — Flammable Solids
Class 4 has three divisions. Division 4.1 covers flammable solids such as matches and some metal powders. Division 4.2 covers substances liable to spontaneous combustion, including activated carbon and some organometallic compounds. Division 4.3 covers substances that emit flammable gases when in contact with water, such as sodium and calcium carbide. These materials require careful segregation from moisture and ignition sources.
Class 5 — Oxidising Substances and Organic Peroxides
Division 5.1 covers oxidising substances — materials that can cause or intensify a fire by releasing oxygen. Common examples include hydrogen peroxide, ammonium nitrate fertilisers, and sodium hypochlorite. Division 5.2 covers organic peroxides, which are thermally unstable and can decompose exothermically. Many organic peroxides require temperature-controlled transport.
Class 6 — Toxic and Infectious Substances
Division 6.1 covers toxic substances that can cause death or serious injury through inhalation, skin absorption, or ingestion. Examples include pesticides, cyanides, and certain industrial chemicals. Division 6.2 covers infectious substances — materials known or reasonably expected to contain pathogens. This includes clinical waste, diagnostic specimens, and biological cultures. Division 6.2 has strict UN packaging requirements (P650 for Category B).
Class 7 — Radioactive Material
Class 7 is regulated by both ADR and the International Atomic Energy Agency (IAEA). It covers materials emitting ionising radiation above specified thresholds. Transport of radioactive material requires specialist training beyond the standard ADR certificate. Examples include medical isotopes, industrial radiography sources, and nuclear fuel.
Class 8 — Corrosive Substances
Class 8 covers substances that can cause severe damage to living tissue or other materials by chemical action. Common examples include sulphuric acid, hydrochloric acid, sodium hydroxide (caustic soda), and battery acid. Many Class 8 substances are also toxic, requiring additional precautions. Bulk carriage of corrosives in tanks requires the Tank specialisation.
Class 9 — Miscellaneous Dangerous Substances and Articles
Class 9 is a catch-all for hazardous materials that do not fit neatly into Classes 1–8. It includes lithium batteries (UN3480, UN3481), dry ice (solid carbon dioxide), magnetised material, elevated temperature substances, and environmentally hazardous substances. The growth of e-commerce and electric vehicles has made lithium battery transport under Class 9 increasingly important for van and HGV drivers.
ADR Certificate Requirements by Class
| ADR Class | Core Certificate Required | Additional Specialisation |
|---|---|---|
| Class 1 (Explosives) | Yes | Explosives (E) |
| Class 2 (Gases — bulk) | Yes | Tank (T) |
| Class 3 (Flammable liquids — bulk) | Yes | Tank (T) |
| Classes 4, 5, 6.1, 8, 9 | Yes | None (core covers packaged goods) |
| Class 6.2 (Infectious) | Yes | None (specific packaging rules apply) |
| Class 7 (Radioactive) | Yes | Radioactive (RN) |
Hazard Labels and Orange Panels
Each ADR class has a distinctive diamond-shaped hazard label with a specific colour and symbol. Vehicles carrying dangerous goods in bulk must also display orange reflective panels — a plain orange panel at the front and rear, or a coded panel showing the Kemler code (hazard identification number) above and the UN number below.
For example, a fuel tanker carrying petrol would display the panel 33/1203 — "33" indicating a highly flammable liquid, and "1203" being the UN number for petrol. Understanding these panels is part of the ADR core training curriculum.
Exemptions and Thresholds
Not every load of dangerous goods requires a full ADR certificate. The ADR regulations include quantity thresholds (known as limited quantities and excepted quantities) below which simplified rules apply. For example, small quantities of Class 3 flammable liquids in consumer packaging may be transported without a full ADR certificate under the limited quantity provisions. However, exceeding these thresholds — or carrying in bulk — triggers the full ADR requirements including driver certification, vehicle marking, and documentation.
How GS Driver Training Can Help
GS Driver Training offers ADR training for UK drivers covering the core certificate and relevant specialisations. Our courses are delivered by experienced instructors familiar with the latest 2025 ADR regulations and DVSA requirements. Whether you are new to dangerous goods transport or renewing an existing certificate, we can help you get compliant and confident.
You can view full details and book your place online here: GS Driver Training ADR Courses.
Related Articles
- ADR Training Guide UK: Everything You Need to Know
- ADR Training Cost UK 2026: What to Expect
- ADR Certificate Renewal Guide: Step-by-Step Process
- ADR Hazard Classes Explained: Quick Reference Guide
- ADR Exemptions UK: When You Don't Need a Certificate
- ADR Licence Cost UK 2026: Full Breakdown
- Complete Guide to ADR Training UK 2026
Also in this series: How to Get Your ADR Licence | How to Get Your ADR Card | HGV ADR Driver Training UK | ADR Packaging Requirements UK
