Oil Mist Detector

An oil mist detector is a continuous monitoring instrument fitted to the crankcase of diesel engines above a defined size, required by SOLAS II-1/40.2.1 and IACS Unified Requirement M10 to provide early warning of overheating bearings before crankcase pressure builds to the point where an explosive mixture forms. The device draws air samples from each crank bay through a light scattering or optical obscuration sensor and alarms when the oil mist concentration rises above a set threshold, triggering automatic engine slowdown or shutdown depending on the system design. The detector must be maintained in clean condition because oil deposits on optical surfaces will cause false alarms or, worse, desensitise the instrument to a genuine mist event. Engineers calibrate the detector at regular intervals using standard mist concentration references supplied by the manufacturer and verify alarm set points during planned maintenance. When an oil mist alarm activates, SOLAS requires the engine to be stopped as soon as safely practicable and not restarted until the source of overheating has been identified and rectified. Investigating officers must treat oil mist alarms with the highest urgency, as a crankcase explosion can destroy the engine and kill personnel in the vicinity.