Some important points made above
Sites are fully liable for the safety of their staff
Liability under that, their insurance etc will require them to be responsible for the fill station and the site cylinders
They have no control over customer cylinders, when bottles are checked they can only make basic checks that it's uk legal, is in date, is the correct cylinder for the fill station and a passing glance over condition
They cannot be 100% sure of joe bloggs' cylinder, so unless their risk assessments & insurance state only staff operate fill stations then they offset that liability to the player
Idealy no one should get to touch the fill station without a basic check of the bottle, familiarization with the particular fill station and an assurance of basic air safety knowledge
Cue the ukpsf air pass
This was brought in a few years back to get a minimum level of 'competence' to players
The site says self fills are for air pass holders only, checks for an existing pass when players get bottles checked and runs a 15 minute session for those without (also over 18s only)
This has died down again, but as a new player ask for someone to show you what to do, preferably staff
See the air safety information / hpa 1 linked earlier in the thread for general information