To supersede the requirements of Sentence 3.1.8.3.(1), which would otherwise require the space between a horizontal service space or other concealed space, and a required vertical fire separation, to be divided at the fire separation, if certain conditions are met.
This is to limit the probability that a fire in one fire compartment will spread to another fire compartment by means of the horizontal service space or concealed space, which could lead to damage to the building.