I love Colins answer, concise and straight to the point. Fire Awareness and Training including Wardens is essential.
I look after a number of similar sites, one of which is full of dealers who just will not move, for fear of loss of money.
I find that the answer is to remind the management that if they allow the practice to continue, then they may be considered as encouraging it and therefore liable.
I also strongly indicate on any Fire Drills the areas where persons did not evacuate, or where slow to evacuate, from during fire drills.
This has had 2 effects, 1 the management now are much stronger in relation to ensuring staff leave, and 2, they have changed the Fire wardens in certain areas to managers, who are less likely to be ignored when telling people to leave.
The Sweep System is the preferred method, in my opinion, with Wardens reminded that their role is not to waste time "discussing" with persons that they should leave, if someone refuses, they are left to their own devices, then it is reported, I note on the evac report, that the premises was not satisfactorily evacuated, and that loss of life would be likely in a fire situation. That gets results.
Bill