An automatic alarm fitted to an oily water separator that stops overboard discharge when oil content exceeds 15 parts per million.
In practice
Tampering with or bypassing the 15 ppm alarm — using a magic pipe, replacing the oily water sample with clean water, or defeating the solenoid valve — is among the most serious MARPOL violations and has led to criminal prosecutions, substantial fines, and imprisonment of officers in multiple jurisdictions including the United States. Engineers are required to maintain the alarm in full working condition, perform daily operational checks, and record any defects. Port state control officers inspect the alarm for evidence of modification, check calibration records, and may request a live test during inspection. The alarm must be included on the planned maintenance system with scheduled calibration intervals.
Regulatory detail & full definition
The 15 ppm bilge alarm is an automatic sampling and monitoring device fitted downstream of the oily water separator that continuously analyses the oil content of water intended for overboard discharge. When the oil content reaches or exceeds 15 milligrams per kilogram, the alarm activates and a solenoid valve automatically closes the overboard line, diverting the flow back to the bilge holding tank. The device must be approved to the performance standard in IMO Resolution MEPC.107(49), which specifies accuracy requirements, response time, and resistance to tampering.
Tampering with or bypassing the 15 ppm alarm — using a magic pipe, replacing the oily water sample with clean water, or defeating the solenoid valve — is among the most serious MARPOL violations and has led to criminal prosecutions, substantial fines, and imprisonment of officers in multiple jurisdictions including the United States. Engineers are required to maintain the alarm in full working condition, perform daily operational checks, and record any defects. Port state control officers inspect the alarm for evidence of modification, check calibration records, and may request a live test during inspection. The alarm must be included on the planned maintenance system with scheduled calibration intervals.