Hi jonny,
Refuelling can take 20 mins or more, (A320/321), and that is simply too much of the 45-50 minutes turnaround to 'waste' by doing it separately.
Some airports mandate the attendance of a fire tender whilst refuelling with passengers on board.
Instructions on how to operate the doors are on the safety card in front of your seat - it is always worth studying this - as soon as you've sat down.
Passengers would not be able to watch and listen to a safety brief given while they were still boarding.
Last edited by Uplinker; 23rd Jan 2016 at 16:47.