To permit drainage to a sewer system, if certain conditions are met [i.e. the effluent is water-miscible and does not create a fire hazard].
This is to limit the probability that escaped liquids, including contaminated water used for firefighting, will create a fire or lead to the spread of fire outside of the spill area, which could lead to harm to persons, including emergency responders, in other parts of the building, adjacent buildings or adjacent outdoor areas.