To exempt openings leading to ducts from the requirements of Sentence 220.127.116.11.(1), which would otherwise not permit openings in rated ceiling membranes, if certain conditions are met [i.e. the ducts, the amount of openings and their protection conform to the requirements of Appendix B].
This is to limit the probability that openings into rated ceiling membranes will contribute to the spread of fire within the ceiling space, which could lead to the premature failure or collapse of the structure within the ceiling space, which could lead to damage to the building.
To make the provisions in Appendix B mandatory with respect to: