1. Compressed Gases – Nitrogen, Oxygen, Air, Carbon Dioxide, Helium 2. Liquefied Gases – LPG, Liquefied Nitrous Oxide 3. Dissolved Gases – Acetylene . Cryogenic vapour could also be considered as a gas but is dealt with in a separate document. Refer to . Storage, Transport and Handling of Cryogens Guideline for information on vapour from ...Web