The European Agreement concerning the International Carriage of Dangerous Goods by Road (ADR) is a treaty ratified by member European countries in Geneva on the 30th of September 1957 and fully implemented more than ten years later on the 29th January 1968.
Under the ADR, there are nine classes of goods that are considered dangerous and subject to regulations (in some cases, prohibition), but there are some exceptions depending on the tonnage and circumstances.
Continue reading to find out more about the nine different classes of ADR – and check out our sister article on the differences in ADR regulations between the UK and the EU.
In this post:
What Are ADR Classes?
Classes of ADR apply to the different categories of dangerous goods that are regulated when being transported on roads within the European Economic Area (EEC).
These goods are classified into nine categories (more on these below). They must be properly labelled and transported within containers specific to their categories. The vehicles that carry them must also be compliant to ADR standards.

ADR Classification System
The United Nations Economic Commission for Europe, or UNECE, seeks to harmonise the classifications of dangerous goods being transported on roads within the EEA.
The classification system makes it easier to assess compliance in terms of labels, containers, vehicles, and personnel.
The 9 Classes of ADR Dangerous Goods
The nine classes under the ADR categories of dangerous or hazardous goods have specific provisions. They are:
Class 1 – Explosives
Class 2 – Gases
Class 3 – Flammable liquids
Class 4 – Flammable solids
Class 5 – Oxidising agents
Class 6 – Toxics
Class 7 – Radioactive
Class 9 – Miscellaneous dangerous substances and articles
These classes apply to storage, handling, compatibility, level of necessary protection, the training or competence of the personnel handling/transporting chemicals, and the type or design of vehicles transporting them.
Let’s explore each of the ADR classes in more detail.
Class 1: Explosives
Explosives are defined as substances capable of very rapid chemical reactions which produce gases and high temperatures, and can cause damage to surroundings. Examples of explosives include pyrotechnics, ammunition, propellants, and fireworks.
Class 2: Gases
Gases can be pure gas, mixtures of different gases, or a mixture of a gas with another substance or substances.
Gases are considered dangerous because they are usually pressurised. However, there are gases, such as hydrogen fluoride, that are classified under Class 8 because they are highly corrosive.
Class 3: Flammable Liquids
Class 3 flammables are in a liquid state under definition 1.2.1 of the ADR manual. This definition states that flammable liquids are those not completely gaseous at 20°C at 101.3 kPa, have a vapour pressure under 300 kPa at 50°C, and a flash point under 60°C.
Class 4: Flammable Solids
Flammable solids are defined to be in solid state under standard conditions, those which are readily combustible, or may cause fire through friction. They may be granular or powdered, such as metal powder. They are difficult to extinguish when ignited.
Class 5: Oxidising Substances & Organic Peroxides
Class 5 substances aren’t necessarily combustible, but they readily release oxygen and may contribute to the combustion of other materials. They’re commonly used as chemical catalysts, and include oxidising liquids, oxidising solids, and organic peroxides.
Class 6: Toxic & Infectious Substances
Toxic and infectious substances are classified into subcategories of their own within Class 6, but are in the same class because they can have a direct affect on our health, whether that’s due to chronic or acute exposure.
Toxic substances are chemicals that may cause poisoning, such as pesticides. For the purposes of ADR classification, infectious substances are those that are expected to contain pathogens and prions, which may cause diseases. Examples of infectious substances are live specimens being cultured, and intentionally infected animals used in scientific studies.
Class 7: Radioactive Material
Substances in Class 7 contain radionuclides. These are either fissile nuclides, such as uranium-223, or low dispersible radioactive material. They are either usable fuel sources or waste products of nuclear reactions.
Class 8: Corrosive Substances
Corrosive substances are those that can cause injuries to your skin’s epithelial tissue and mucous membrane. They may also cause damage to other objects, such as metals and leather items. They maybe liquid, solid, or even gas, such as in the case of hydrogen fluoride that we mentioned in Class 2.
Class 9: Miscellaneous Dangerous Goods
Class 9 substances may pose a danger, but aren’t covered under any of the other classes. They are subdivided into several subcategories, and include lithium batteries, substances in the form of fine dust, and substances that may form dioxins when burned.
Why Do ADR Classes Matter?
ADR classes specify not only the categories of dangerous substances, but also the required labelling and specific packaging for them. They also specify what type of vehicle should be used.
This means that the safety of handling and transporting these substances is significantly improved. This is important not only for the chemical industry, chemical repacking, and transportation sectors, but mainly for the general public.
How to Identify ADR Classes in Packaging
Classes of ADR can be identified on packaging labels, as well as on the type of packaging materials and design. For example, they may contain certification markings, such as UN symbols and package codes.
There are also four basic types of ADR packaging based on volume and weight:
- P – a capacity of up to 450 litres or 400kg net, such as substances in crates and drums
- IBC – large bulk containers with a capacity greater than 450 litres or 400kg net
- R – light metal packaging with a capacity of up to 40 litres or 50kg net
- N – large packaging with a capacity greater than 450 litres or 400kg net
Safety & Risk Management
ADR classes are meant for efficient and standardised management of safety and handling of risks.
They help vehicle operators, personnel, and consignees effectively handle the products being transported. They can make calculated decisions to avoid mishaps while maintaining fast and reliable delivery of goods.
Conclusion
ADR classes are an efficient and comprehensive means of classifying various types of dangerous goods that are transported by road within the European Economic Area. The categories provide specific guidelines for packaging, labelling, and transporting dangerous goods. This system helps track the movements of the goods, and also helps ensure public safety.