To exempt certain walls from the requirements of Sentence 9.10.17.3.(1), which would otherwise limit surface flame-spread rating to 25 on at least 90% of the exposed wall surface, and permit a maximum surface flame-spread rating of 25 on at least 75% of the exposed wall surface, on the basis that the increased surface area where the flame-spread rating may be more than 25 will not contribute significantly to the spread of flame.
To limit the probability that certain finishes having an inappropriately high flame-spread property will be used in a lobby used as an exit, which could lead to the spread of fire across the exposed surfaces of the finishes, which could lead to delays in the evacuation or movement of persons to a safe place, which could lead to harm to persons.