To supersede the requirements in the first part of Sentence 3.4.6.11.(3) prohibiting exit doors from opening onto a step, on the basis that a step of limited height will minimize the danger of door blockage from ice or snow without creating an undue risk of injury or delay.
This is to limit the probability that an accumulation of ice or snow outside the door will block the door, which could lead to persons being unable to leave the building in an emergency situation, which could lead to delays in the evacuation or movement of persons to a safe place, which could lead to harm to persons.