Discharging from a protected stairway (I take it that is the case?) into an enclosed carpark and by so many people is a big problem. This coupled with a locked final exit gate and the lack of detection on some floors including the staircases is a recipe for disaster if override facilities are envisaged.
As an interim measure I would insist that the gate is maintained open (even if that exit point has to be manned for security purposes 24/7) at all times that anyone is on the premises. I would then have a risk assessment carried out without delay.
I agree nearlythere but we would assume that the car park is in a seperate compartment and people will not all arrive at the same instant and as employees they can be familiarised with the arrangements? Or have I had too much medication again (takes rose tinted glasses off nose and polishes them)