Haz Classification System
The UN Model Regulations use a classification system in which each dangerous substance or article is assigned to a CLASS, depending on the nature of the danger it presents. There are 9 Classes, some of which are sub-divided:
Class 1 – Explosives
Class 2 – Gases
Division 2.1 Flammable gas
Division 2.2 Non-flammable non toxic gas
Division 2.3 Toxic gas
Class 3 – Flammable liquids
Class 4 – Other flammables
Division 4.1 Flammable solids
Division 4.2 Substances liable to spontaneous combustion
Division 4.3 Substances which, in contact with water, emit flammable gases
Division 5.1 Oxidising agents
Division 5.2 Organic peroxides
Division 6.1 Toxic substances
Division 6.2 Infectious substances
Class 7 – Radioactive materials
Class 8 – Corrosives
Class 9 – Miscellaneous
Class 9 includes items such as asbestos, automotive airbags, lithium batteries and environmentally hazardous substances which don’t fit into any of the other 8 classes.
Whilst the CLASS defines the type of danger which a substance presents, a second classification, called the PACKING GROUP (PG) defines just how dangerous it is. There are three Packing Groups; PG I is the most dangerous, PG II represents a moderate danger and PG III is the least dangerous. Packing Groups are always written in Roman numerals to differentiate them from the Class numbers.
It is possible for a substance to appear in more than one Packing Group, depending on its concentration. For example, concentrated sulphuric acid is Class 8, PG II. A mild solution of the same acid, which might be marketed as a domestic drain cleaner, is still allocated to Class 8, but because of its lesser corrosivity could be PG III.