It is fundamental for safety in the transport chain that detailed information on the hazards presented by any dangerous goods are known and readily available for all parties involved in the carriage. Therefore, the first key task of a shipper of dangerous goods is to identify the hazard that his dangerous goods present by carrying out the correct UN classification.

The UN Manual of Tests and Criteria contains criteria, test methods and procedures to be used for classification of dangerous goods for transport in all modes, and of chemicals presenting physical hazards according to the Globally Harmonized System of Classification and Labelling of Chemicals (GHS).

These test methods include laboratory procedures for establishing explosivity, toxicity of liquids, gases and solids, flash points of flammable liquids, temperature thresholds for flammable solids and self-reactive substances, stability of peroxides, degree of corrosivity of acids and alkalis, propensity of substances to polymerize, environmental damage potential and many other hazardous characteristics.

At the end of the process, dangerous goods are classified into one of nine hazard classes, allocated a formal Proper Shipping Name and UN identification number, and where applicable, graded by packing group into high, medium or low hazard. Where substances have more than one hazard, all the hazards should be identified in the Proper Shipping Name but the most significant hazard, in accordance with the Table for Precedence of Hazards⁵, takes prominence.

Classification and hazard identification of the most commonly shipped base chemicals are well established. Shippers of these will have manufacturer’s authenticated laboratory test reports available and will not need to repeat those tests.

However, shippers of products consisting of innovative combinations of two or more chemicals whose hazardous characteristics are not established will need to arrange for tests to be done that identify the hazard class(es) and UN Number according to the UN Manual of Tests and Criteria before the substance can be offered for sale and transport. They cannot be accurately documented for the IMDG Code or other transport modes until those tests are done, except as small samples dispatched for test purposes.

Shippers that design and develop chemical products would normally have personnel with the required skills to test and classify their own products to UN criteria, but shippers who only buy and sell dangerous substances need to obtain the hazardous classification from the original manufacturer in the form of a Safety Data Sheet. This will contain the information required for the dangerous goods transport document.

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⁵ IMDG Code, 2022 Edition Amendment 41-22, Section 2.0.3.6

Section B, the reference section to this guide (the tinted pages) explains the principles of the UN classification system as used in the IMDG Code (and other UN transport protocols). The laboratory methods used to identify the hazard classification of a substance are outside the scope of this guide, and the hazard classification process for a substance is done by specialists.

All dangerous goods are classified⁶ into one of nine hazard classes:

Class 1 – Explosives

Class 2 – Gases

Class 3 – Flammable liquids

Class 4 – Flammable solids; substances liable to spontaneous combustion; substances which, in contact with water, emit flammable gases

Class 5 – Oxidizing substances and organic peroxides

Class 6 – Toxic and infectious substances

Class 7 – Radioactive material

Class 8 – Corrosive substances

Class 9 – Miscellaneous dangerous substances and articles (Class 9) and environmentally hazardous substances

One very significant classification criteria is the Packing Group. This indicates the overall degree of danger presented by the substance, and influences the size and type of packaging options available:

Packing Group I – high degree of danger
Packing Group II – medium degree of danger
Packing Group III – low degree of danger

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⁶ IMDG Code, 2022 Edition Amendment 41-22, Part 2

It is necessary to have a professional knowledge of chemistry to carry out many of the UN tests to initially classify a dangerous substance, but once that classification has been obtained the classification details are entered on the safety data sheet, which are made freely available by manufacturers.

However, a key point of the IMDG Code is that specialised knowledge of chemistry is not required to produce an IMDG compliant consignment. Given access to the classification details in the safety data sheet, any person trained to understand the layout and meaning of the IMDG Code can prepare a legally compliant dangerous goods transport document, can check that the packaging is suitable, and can mark and label the packages correctly, ready for packing into a cargo transport unit.

All stakeholders need to exercise care to ensure that the safety data sheet is accurate and current. There are many instances of forged or otherwise inappropriate data sheets being presented.