To supersede the requirements of Sentence 9.9.4.2.(1) and not require a fire separation with a fire resistance rating, if certain conditions are met [i.e. smoke-tight barrier of not less than 12.7 mm gypsum board is installed on both sides of the walls and on the underside of floor-ceiling framing separating the exit from the remainder of the building], on the basis that the construction of rated fire separations may be cost prohibitive and the reduction in protection from spread of fire is offset by more stringent requirements for notification of occupants.
To limit the probability that fire will spread from one floor area to another floor area by means of an exit, which could lead to damage to the building.