Part of the requirement of aeroplane manufacturers to build planes that allow passengers to exit within 90 seconds is to have enough exits to get "X" number of passengers out of the plane in 90 seconds. Does that make sense?
I am not sure what the ratio of passengers to exits is.
IF the plane sits (with landing gear down) at a certain height, planes are required to have the inflatable slides.
It sounds if that the slides did not deploy properly in this incident...but this was a quote from a passenger.