It depends, ADR considers them as Transport Category 4 and as such small load exemptions apply. Thus no documentation would be required for GB domestic transport. The key remaining requirements are as follows: Train the driver at least to "general " standards (ADR 8.2.3 and 1.3) Carry one 2 kg fire extinguisher Ensure stowage complies with 7.5.7 However, and interstingly, the HSE express the view that ADR applies Viz: Class 2 (compressed and liquefied gases). In ordinary service these items are not emptied in any conventional way and it would be difficult (and possibly dangerous without specialist equipment) to determine residual contents. The main operators in this field treat all cylinders as full and do not seek to utilise the small load exemptions. Enforcement officers should also take this view (that is, that the cylinders cannot be regarded as TC4). I would offer the opinion that TC4 applies.