To limit the probability that landings in exit stairs will be of insufficient size to permit efficient egress in an emergency situation, which could lead to congestion at landings, which could lead to delays in the evacuation or movement of persons to a safe place, which could lead to harm to persons.
To limit the probability that emergency responders will have insufficient space on a landing to perform their duties, which could lead to delays or ineffectiveness in emergency response operations, which could lead to delays in the evacuation or movement of persons to a safe place, which could lead to harm to persons.
To limit the probability that a person exiting onto a ramp will experience an immediate change in slope, which could lead to tripping or falling, which could lead to harm to persons.