To limit the probability that a fire that has spread into a lobby from an adjacent floor area will lead to untenable conditions in the exit, which could lead to delays in the evacuation or movement of persons to a safe place, which could lead to harm to persons.
To supersede the requirements of Sentence 9.9.4.2.(1), which would otherwise require the exit to be separated from adjacent floor areas by a fire separation having a minimum fire-resistance rating.