To exempt certain soil-or-waste stack installations from the requirement for a yoke vent, where alternative venting is provided.
This is to limit the probability that inadequate venting will lead to back pressure in drainage systems, which could lead to trap seal failure, which could lead to the entry of sewer gases into occupied space, which could lead to negative effects on indoor air quality, which could lead to harm to persons [see Sentence 2.5.4.3.(1)].