Question 1

You are asked to explain the purpose of a crankcase oil mist detector on a medium/large diesel engine, and what action is required if it alarms.

Accepted Answer

It monitors oil mist concentration within the crankcase to provide early warning of overheating components (bearings, pistons) that can lead to a crankcase explosion; on alarm, the engine must be slowed/stopped per the manufacturer's procedure and NOT immediately opened up, as residual heat and air ingress can trigger the very explosion the system is designed to prevent Crankcase explosions occur when oil mist from an overheating component (e.g. a failing bearing) reaches an explosive concentration and is then ignited by a hot spot, and the oil mist detector provides the critical early warning before this occurs. The well-documented correct response is to reduce load/stop the engine and allow it to cool for a prescribed period (often 20-30 minutes) before opening crankcase doors, because opening immediately introduces oxygen to an already hot, mist-laden atmosphere — several fatal crankcase explosions have resulted from doors being opened too soon after an alarm.

Question 2

You're draining a thermal oil system that was running normally a short time ago. Before opening the drain point, what should you confirm?

Accepted Answer

That the system has cooled and depressurised, and you are positioned clear of the drain point's discharge path On the dredger MV Amazone, two crew members draining a thermal oil system after months of contamination were sprayed with hot oil, suffering severe burns. The investigation found company procedures lacked clear instructions for safe drainage — confirming the system has cooled and depressurised, and standing clear of the discharge path, are essential before opening any drain point on a hot oil system.

Question 3

A thermal oil system has been contaminated and needs draining for cleaning. The written procedure tells you to open the drain valve but doesn't specify a cooling-down period or PPE. What should you do?

Accepted Answer

Treat the gap as a hazard in its own right: apply a suitable cooling/depressurising period and full PPE before proceeding, and raise the procedure gap with the Chief Engineer The FEBIMA investigation into the MV Amazone incident found that although the crew followed company procedures, those procedures lacked clear instructions for safely draining a thermal oil system. A procedure that's silent on cooling time and PPE for a hazardous task is a gap to be closed before the job starts — not a green light to skip those precautions.