To limit the probability that persons using an exit stair in an emergency situation and encountering obstructions or hazardous conditions will not be able to leave the exit and gain access to a floor area, which could lead to harm to persons.
To limit the probability that persons using an exit stair in an emergency situation and encountering obstructions or hazardous conditions will not be familiar with which floor areas are accessible, which could lead to delays in leaving the exit and gaining access to a floor area, which could lead to harm to persons.