Bilge alarm

The bilge alarm, also called the 15 ppm alarm, is the monitoring device that watches the discharge from a ship’s oily-water separator and trips when the oil content of the effluent reaches 15 parts per million. On the trip it sounds an alarm and drives a three-way valve that recirculates the discharge back to a holding tank instead of overboard, so no water above 15 ppm reaches the sea. The equipment is required by MARPOL Annex I Regulation 14 and type-approved to IMO Resolution MEPC.107(49). Tampering, a bypass line, or a defeated alarm is a primary detention and prosecution trigger at port state control.