The Transport of Dangerous Goods – An Overview


Classification, Packaging, Marking, Labelling and Documentation

Classification of dangerous goods for transport

In order to transport dangerous goods as safely as possible across all modes of transport, it is necessary to identify the hazards presented and classify the goods appropriately. 

The United Nations (UN) Recommendations and Model Regulations for the safe transport of dangerous goods, otherwise known as the UN Orange Book set out the provisions for a uniform classification system.

This system assigns each dangerous substance or article a class that defines the type of danger the substance presents. 

There are 9 dangerous goods classes, some of which have divisions:

Class 1: Explosives, divisions 1.1-1.6

Class 2: Gases

  • 2.1: flammable gas
  • 2.2: non-flammable, non-toxic gas
  • 2.3: toxic gas

Class 3: Flammable liquids

Glass 4: Flammable solids

  • 4.1: substances liable to spontaneous combustion
  • 4.2: substances which in contact with water emit flammable gases

Class 5: Oxidising substances (5.1) and organic peroxides (5.2)

Class 6: Toxic (6.1) and Infectious (6.2) substances

Class 7: Radioactive material

Class 8: Corrosive substances

Class 9: Miscellaneous dangerous goods

Dangerous goods typically fall into more than one hazard class; additional classes are assigned as sub risks and form part of the transport classification, along with packing group (PG) where applicable.

The packing group determines the degree of dangerous within the hazard class: 

Packing Group I: high danger

Packing Group II: medium danger

Packing Group III: low danger

The class and PG determine how dangerous goods should be packaged, marked and labelled for transport.

Whereas the Orange Book sets out Model regulations, variation exists within the different modes of transport regulation, due to transport across very different environmental media, by very different means of transportation. Transport by road involves a variety of vehicles e.g. tankers, which must be identified as carrying dangerous goods and conform to specific test requirements. Marine environments will be more sensitive to some chemicals and freshwater ecosystems more susceptible to others.

Packaging of dangerous goods for transport

Packaging must be designed and constructed to UN specification standards and undergo tests to ensure that it is fit for purpose e.g. withstand conditions encountered during transport, such as stacking and vibration.

UN approved packaging is marked with the prefix ‘UN’ and is coded with the specification for the packaging, to include the type of packaging, packing group for which the packaging has been tested, last two digits of the year of manufacture, state authorising the mark and certificate identification.

UN 4G/Y/…/18/GB/****

The mark will also include further information depending on the type of packaging and what it intended to contain. This information will follow the packing group specification.

Limited and Excepted Quantities

The modal regulations include provision for ‘limited’ and ‘excepted’ quantities of dangerous goods, with reduced requirements to reflect lower risk. Consignments of limited and excepted quantities of dangerous goods must be contained within good quality packaging but are not required to conform to UN specification standards. Other relaxation to transport regulation also applies to limited and excepted quantities of dangerous goods, depending on the mode of transport.

Marking, labelling and documentation

Marking refers to UN number, the ‘proper shipping name’, UN specification mark and other markings, such us orientation arrows, marine pollutant mark, limited quantity mark, etc. 

Labelling mainly refers to the hazard class labels and are required for primary hazard and sub risk.

The proper shipping name associated with the UN number for the item classification is provided in the dangerous goods lists of the modal regulations. 


Dangerous goods must normally be accompanied by a transport document declaring the description and nature of the goods. Documentation must be in accordance with the specification set by the dangerous goods regulation applicable to the mode of transport.

Page published 11 July 2018