What is ADR? Hazardous goods classes and transport rules

What is ADR

ADR is the European agreement on the international carriage of dangerous goods by road. It sets out the conditions that the vehicle, the driver, the packaging, the labelling and the declaration must satisfy.

The hard part in this field is not the transport itself but correct classification and a complete declaration. A wrongly declared load is stopped at the border, at the port, or at the terminal.

The nine classes

Class	Content	Example
1	Explosives	Fireworks, explosive substances
2	Gases	Compressed, liquefied, dissolved gas; aerosols
3	Flammable liquids	Paint, thinner, alcohol, fuel
4	Flammable solids; substances liable to spontaneous combustion; substances that emit flammable gas on contact with water	Matches, metal powder
5	Oxidising substances and organic peroxides	Hydrogen peroxide, fertiliser components
6	Toxic and infectious substances	Pesticides, medical samples
7	Radioactive material	Medical and industrial sources
8	Corrosives	Acid, base, battery electrolyte
9	Miscellaneous dangerous substances and articles	Lithium batteries, environmentally hazardous substances

Classes 1 and 7 are subject to a special permit regime and are not accepted by every carrier; the scope must be separately confirmed before loading.

UN number and packing group

Every hazardous substance has a four-digit UN number; the substance is identified by this number.

The packing group indicates the degree of hazard and determines which packaging may be used:

• I — high danger
• II — medium danger
• III — low danger

Packing groups are not used for Classes 1, 2 and 7; these classes have their own classification logic.

Starting point: the safety data sheet

The foundation of the process is the SDS (safety data sheet). The classification, UN number, packing group and the precautions to be taken are all read from it.

The manufacturer supplies the form. Before transport, it must be confirmed as current — forms get revised, and a declaration made against an outdated version can turn out to be wrong.

Responsibility lies with the consignor. For a substance about which there is any doubt, written confirmation should be obtained from the manufacturer.

Packaging, labelling, segregation

Packaging must be certified. A load sent in packaging that does not carry the UN mark is rejected even if the contents were correctly declared.

Labelling includes the class labels, the UN number and, where required, the environmentally hazardous substance mark. The vehicle carries an orange plate.

Segregation rules state that certain substances cannot be carried in the same unit, and that others must be kept at a distance from one another. These rules directly shape the stowage plan in consolidated loads — and explain why hazardous goods LCL shipments are scheduled less frequently than dry cargo.

Relationship with other modes

The same substance is subject to IMDG rules by sea and IATA DGR rules by air. The rule sets are close to one another but not identical: packaging, labelling and declaration requirements can differ between modes.

In an intermodal shipment, the strictest rule set in the chain governs.

Common mistakes

Leaving classification to the carrier. Responsibility lies with the consignor.

Misusing the limited quantity exemption. Thresholds vary by substance; declaring a shipment that exceeds the threshold under the exemption is a misdeclaration.

Using uncertified packaging. The load is rejected even if the contents are correctly declared.

Declaring against an outdated SDS. The form may have been revised.