'Vessels should only be transported in lifts when covered by a safe system of work which takes account of the hazards, including that due to oxygen deficiency when a lift is stopped for a period between floors' (Transportable Vacuum Insulated Containers of not more than 1000 Litres Volume - BCGA Code of Practice CP27).
In practice, this means that pressurised vessels (and Dewars) must not be accompanied in lifts. If a goods lift or passenger lift is used then it should be closed to all passengers. The vessel should be manoeuvred into the lift and the lift sent to its destination floor to be met by an individual.