Working time regulations Exempt from 48 hour work week

UK Wales,

Apparently jobs that require 24/7 staffing are exempt.

However there are many places now open 24/7.

So when does a business that is open 24/7 become exempt from the 48hr weekly limit?

Is there a list somewhere.

I know that regardless an employer still has a requirement around "duty of care" to their employees to manage fatigue etc but sometimes a hard rule is easier to argue.