Class 2 - Gases

Gases are not assigned to Packing Groups as most other materials, but sub-divisions of Class 2 have been devised. This is because different gases have differing hazardous properties but still belong to the same generic family. Aerosols are also assigned to Class 2.

Class 2.1, Flammable gases:

These are the most common gases offered for transport and are familiar to all, usually as Liquefied Petroleum Gas (LPG), stored in pressurised cylinders similar to those shown in the photo above. LPG can in fact be two distinct gases, Butane or Propane.

Also included in this class are Methane, Ethylene Oxide, welding gases such as Acetylene and Hydrogen and items such as disposable cigarette lighters.

Class 2.2, Non-flammable, Non-toxic gases:

The main hazard posed by these materials is the pressure under which they are stored in their cylinders. In the event of an accident resulting in loss of the valve, a typical cylinder will become a fast moving steel torpedo. Typical examples of Class 2.2 include Compressed Air (diving gases), Carbon Dioxide, Nitrogen, Argon, Oxygen, Helium and Medical Gases (eg Entonox etc).

Though these materials are non-toxic and non-flammable, they may pose secondary risks.

Oxygen for example is the most powerful oxidising agent, it is this action that causes steel to rust in the atmosphere. However, put steel wool  into a pure oxygen environment and it will burst into flames in seconds. The presence of organic materials in the valves of oxygen cylinders (e.g. grease or p.t.f.e. tape) can result in explosions that have claimed lives in the past.

Some Class 2.2's can act as an asphyxiant . In the event of a release the gas will expand and displace the available oxygen in the air. Even a small drop in the volume of oxygen we breathe can lead to rapid unconsciousness, and death. Typically transported materials that could do this include Nitrogen and Carbon Dioxide.

Cryogenic gases:

In order to transport them more efficiently, some gases are reverted to their liquid state by super-cooling to form a cryogenic liquid. Skin contact with these materials will cause severe burns and widespread tissue death. Their main uses are cooling, the storage of biological specimens (cryopreservation), and the provision of inert atmospheres (blanketing).

Three of the commonest cryogenic materials are Liquid Nitrogen (-196^oC), Liquid Oxygen (-183^oC) and Liquid Helium (-269^oC).

Class 2.3, Toxic Gases:

The risks posed by these materials are self explanatory. Typical examples could include Chlorine, Sulphur Dioxide, Hydrogen Sulphide, Ammonia and a whole range of pesticides.

It's worth noting that hauliers who are not necessarily involved  in "chemical" transport may encounter Class 2.3 materials. It is common practice to fumigate containers of foodstuffs (e.g. bananas) to kill any native flora and fauna to prevent the spread of alien species. These containers are full of a toxic atmosphere until such time as they are safely vented, and their carriage may be regulated by dangerous goods laws. An example of additional marking of such containers can be seen by clicking HERE.

Drivers of vehicles carrying Class 2.3 materials must be provided with suitable Respiratory Protective Equipment (RPE) and be suitably trained in it's use.

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