Gases are defined by dangerous goods regulations as substances which have a vapour pressure of 300 kPa or greater at 50°C or which are completely gaseous at 20°C at standard atmospheric pressure, and items containing these substances. The class encompasses gases, mixtures of one or more gases with one or more vapours of substances of other classes, articles charged with a gas, and aerosols. Substances of Class 2 are assigned to one of three divisions based on the primary hazard of the gas during transport. There are no assigned UN Packing Groups for Class 2 gases. 


The transport condition of a gas is described according to its physical state when packaged under pressure as: 

  • Compressed gas - a gas which is entirely gaseous at -50°C.

  • Liquefied gas - a gas which is partially liquid at temperatures above -50°C. Further, a high-pressure liquefied gas is a gas with a critical temperature between -50°C and +65°C, and a low-pressure liquefied gas is a gas with a critical temperature above +65°C.

  • Refrigerated liquefied gas - a gas which is made partially liquid because of its low temperature.

  • Dissolved gas - a gas which is dissolved in a liquid phase solvent.

  • Adsorbed gas - a gas which is adsorbed onto a solid porous material resulting in an internal receptacle pressure of less than 101.3 kPa at 20°C and less than 300 kPa at 50°C. 


Division 2.1 : Flammable Gases

These are gases which will burn. They are gases which at 20 °C and a standard pressure of 101.3 kPa are ignitable when in a mixture of 13 per cent or less by volume with air; or have a flammable range with air of at least 12 percentage points. Cylinders of flammable gases must always be transported standing upright and in a vehicle with a separate cab from the load carrying area.

Commonly transported Division 2.1 gases

  1. Acetylene / Oxyacetylene

  2. Butane

  3. Dimethyl ether (methoxymethane)

  4. Ethane

  5. Ethylene / Ethylene oxide

  6. Hydrogen / hydrogen compounds

  7. Hydrocarbon gas-powered devices

  8. Insecticide gases

  9. Isobutylene

  10. Lighters containing flammable gas

  11. Liquefied Petroleum gases (LPG)

  12. Methane

  13. Propane

  14. Propene / propylene

  15. Refrigerant gases

Division 2.2 : Non-Flammable, Non-Toxic Gases

These gases are usually compressed and therefore are a source of stored energy. They are either asphyxiants (by depletion of oxygen leading to do death by asphyxiation) or oxidisers (by causing or contributing to the combustion of other materials by providing oxygen.) Gases meeting the above criteria owing to their corrosivity are classified as toxic with a subsidiary corrosive hazard. Containers may rocket if valves are damaged or containers are involved in a fire.

NOTE. Per the ADG Code, non-flammable, non-toxic gases with a sub-risk of Class 5.1 (Oxidising Agent) may be displayed with the "Oxidising Gas" label, which is unique to Australia. It is often seen on Oxygen bottles.

Commonly transported Division 2.2 gases

  1. Air, compressed

  2. Argon, compressed

  3. Carbon dioxide

  4. Fertilizer ammoniating solution

  5. Fire extinguishers with compressed gas

  6. Fire extinguishers with liquefied gas

  7. Helium / helium compounds

  8. Neon, compressed

  9. Nitrogen / nitrogen compounds

  10. Nitrous oxide ("laughing gas")

  11. Oxygen, compressed

  12. Xenon


Division 2.3 : Toxic Gases

These are gases known or presumed to be so toxic or corrosive to humans as to pose a hazard to health. They may kill if inhaled.

Commonly transported Division 2.3 gases


  1.  Ammonia gases

  2. Anhydrous ammonia

  3. Anhydrous hydrogen chloride

  4. Carbon monoxide

  5. Chlorine gas

  6. Coal gas

  7. Fluorine gas, compressed

  8. Methyl bromide

  9. Nitric oxide, compressed

  10. Oil gas

  11. Oxygen difluoride, compressed

  12. Sulphur dioxide