To limit the probability that in a straight run and where the stairway turns less than 90 degrees, landings 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 landings will be of insufficient size for persons to negotiate a change of direction, which could lead to congestion, collisions or other risk of injuries, which could lead to harm to persons.