NBN EN 13077:2004

This European Standard specifies the characteristics and the requirements of air gap with non-circular overflow (unrestricted) Family A Type B for nominal flow velocity not exceeding 3 m/s. Air gaps are devices for protection of potable water in water installations from pollution. This standard applies to air gaps in factory assembled products and to constructed air gaps in situ, and defines the physico-chemical characteristics of materials of construction used for the purpose and application to ensure compliance with this standard during normal working use.
The annex A gives a relationship for rectangular overflow and the annex B is a note for alternative constructions.