AJM
CAO 20.9, S 4.2.2 covers it in detail and you're correct, pax must be advised before fuel is loaded.
The only airline I've experienced that does this routinely is Jetstar, who in their boarding PA and Welcome to PA state something like, "As the aircraft may be being refuelled, passengers are reminded ....."
I've been on a B747 being refuelled at the gate after an air return where nothing was said, and a 737 which made a tech stop for fuel due to a U/S centre tank where nothing was said and every one still had belts on and the belt sign stayed on.