Originally Posted by
James Duffin
No backflow device needed as long as there is an air gap..
Which in and of itself is a backflow prevention device. But not all cross connections are allowed to use air gaps as air gaps are not always reliable for the prevention of a cross connection.
Contamination can cross the air gap, spillage, splashing, evaporation, a number of different reasons, including backpressure (in this case, an air gap could overflow if the DWV line clogged and backed up).