Acetylene, LPG and other gases are commonly carried by tradesmen such as welders and motor vehicle repair technicians. Flammable gases are in Transport Category 2. Oxygen and gases such as carbon dioxide and argon are in Transport Category 3. Usually the small load threshold exemptions will apply,
The parts of ADR which apply are then
"Packages shall preferably be loaded in open or ventilated vehicles or open or ventilated containers. If this is not feasible and packages are carried in other closed vehicles or containers, the cargo doors of the vehicles or containers shall be marked with the following in letters not less than 25 mm high:
OPEN WITH CAUTION
This shall be in a language considered appropriate by the consignor."
HSE has published the leaflet "Working safely with acetylene" and the British Compressed Gases Association has a useful guidance note on the topic of carrying gas cylinders in vehicles, DN27 Guidance for the carriage of gas cylinders on vehicles. 2013. This and a wider range of BCGA publications can be found on their website. The UKLPG has also published its Code of Practice 27 "Carriage of LPG Cylinders by Road".