Dangerous Goods are articles or substances which are capable of posing a risk to health, safety, property or the environment.
Dangerous Goods are defined as those goods which meet the criteria of one or more of the nine UN hazard classes and where applicable, to one of the three UN packing. The classes relate to the kind of hazard & the packing groups relate to the degree of danger.

For packing purposes, Packing Group numbers I, II, III are assigned to dangerous goods classes according to the relative degree of danger presented by the article or substance.
Packing Group I: Substances causing high degree of danger
Packing Group II: Substances causing medium degree of danger
Packing Group III: Substances causing low degree of danger

Some Hazard Classes are subdivided in divisions due to the wide scope of the class. Please note that the order in which they are classified has nothing to do with the degree of danger they incur.

Division 1.1: Articles & substances having a mass explosion hazard.
Division 1.2: Articles & substances having a projection hazard but not a mass explosion hazard.
Division 1.3: Articles & substances having a fire hazard, a minor blast hazard &/or a minor projection hazard but not a mass explosion hazard.
Division 1.4: Articles & substances having presenting no significant hazard but not a mass explosion hazard.
Division 1.5: very insensitive substances having a mass explosion hazard.
Division 1.6: extremely insensitive articles which do not have a mass explosion hazard.

A Gas is a substance which:
a- at 122 F (50 C) has a vapor greater than 300kPa (3.0 bar, 43.5 lb/in2)
b- is completely gaseous at 68 F (20 C) at a standard pressure of 101.3 kPa (1.01 bar, 14.7 lb/in2)

Division 2.1: flammable gas
Division 2.2: Non-flammable gas
Division 2.3: Toxic gas.

The flash point of Flammable Liquid is the temperature at which a vapor from liquid could be ignited by a flame or spark. It is not the temperature at which it would ignite spontaneously. No Sub-Division available.

Division 4.1: Flammable solids
Division 4.2: Substances liable to spontaneous combustion
Division 4.3: Substances which, in contact of water, Emit Flammable Gases.

Division 5.1: Oxidizer
Division 5.2: Organic Peroxide

Division 6.1: Toxic Substances
Division 6.2: Infectious Substances.

Any material or combination of materials containing radionuclide where both the activity in the consignment exceeds a certain specified value. No Sub-Division available.

This class has no divisions. (Substance in this class causes damage to the skin and/or metal.)
Substances which by chemical action can cause severe damage when in contact with living tissue or, in the case of leakage will materially damage or even destroy, other goods or the means of transport. No Sub-Division available.

This class comprises substances whose properties are not included in any other hazard class, but would pose a risk to safety if not properly prepared for carriage. (Such as a hazardous waste). No Sub-Division available.