Some medical and para-medical staff carry items such as compressed oxygen or nitrous oxide mixtures ("Entonox"), sometimes in their cars.
In these cases the cylinder is likely to form part of a "ready to use" set which includes a regulator, hose and mask. As such it is regarded as exempt from ADR by virtue of paragraph 220.127.116.11(b). There is a simple condition:
"….measures have been taken to prevent any leakage of contents in normal conditions of carriage"
This should mean no more than ensuring that the cylinder valve is properly closed and that the equipment is carried securely in the vehicle. Usually the equipment is carried in purpose-made bags or cases and this would be regarded as satisfactory.
Dutyholders will still need to carry out a risk assessment and provide appropriate training under other legislation such as the Management of Health and Safety at Work Regulations and the Provision and Use of Workplace Equipment Regulations.