To supersede the requirements of Sentence 9.10.9.11.(1) by increasing the required fire-resistance rating between residential occupancies and specific other major occupancies [i.e. mercantile or medium hazard industrial occupancies] from 1 to 2 hours, on the basis that these other specific occupancies pose a higher fire risk than residential occupancies.
This is to limit the probability that fire will spread from one major occupancy to an adjacent major occupancy having a different degree of fire risk, which could lead to damage to the building.