All pipework must be appropriately labelled to inform employees, contractors and emergency services about the contents of the pipe
Regulations + Standard = Compliance
The British, European and International Standards are slightly different ways to achieve the same goal, which is to comply with the Regulations.
In the UK it is the Health & Safety (Safety Signs & Signals) Regulations 1996 which stipulate that pipes must be marked and gives general guidance about what is required.
Then it’s down to the accepted Standard to specify in greater detail the appropriate colour coding, size, placement of markers etc. which will demonstrate compliance.
All three Standards are recognised in complying with the Regulations. They share many common elements in colour and GHS symbols for example, but there are variations size and layout.
Any is a valid choice but if you already have some pipe marking in place or you have multiple sites then it is recommended to maintain a common standard.