• If a hotspot exists in the crankcase, some lube oil will come in contact with it and will be vaporised.
• The vapour will circulate to cooler parts of the crankcase and condense to form a white oil mist
• The oil droplets in this white mist are very small. If this oil mist circulates back to the hotspot in such concentration (with typical particle sizes of around 0.5 to 5 microns in diameter, density between 30 to 50 mg/L (milligrams per litre)), it will be ignited, and a primary explosion will occur.
• The explosion can cause a flame front and pressure wave to accelerate through the crankcase, vaporising further oil droplets in the path.
• The pressure shock wave may build up sufficiently to rupture crankcase doors if not relieved.
• If the relief valves do not reseal after lifting, it will cause fresh air to enter into the crankcase, resulting in another flammable mixture to be developed, leading to a secondary or major explosion.

• Modern engines often have sensors to monitor bearing temperatures.
• Feeling the crankcase door for excessive heat.
• Measuring the temperature of oil returning from bearings.
• Unusual sounds from the crankcase might indicate component wear or malfunction.
• A visible and dense mist from the breather pipe suggests significant oil vaporisation.
• Overheating can cause paint to peel or discolour on the crankcase or doors.
• Irregular running of engine

However, the following measures ensure that the possibility of explosion is less:

• Ensure the OMD is correctly calibrated and alarms are set appropriately.
• Ensure the automation system slows the engine down when the OMD activates.
• Regularly inspect the crankcase for lubrication conditions and signs of overheating.
• Adhere strictly to the manufacturer's recommended maintenance schedules.
• Regularly check and clean relief valves and flame traps.
• Do not operate the engine beyond its designed capacity.
• Maintain adequate lubrication to minimise friction and heat generation.
• Ensure the bearing high-temperature alarm is functioning correctly.

• In the event of overheating being evident, start the stand-by generator and
• Inform bridge, C/E and 2/E about the situation, if the vessel is not in navigational danger, stop the engine. This will help in cooling the hotspot.
• Evacuate all personnel from the engine room. This prevents injury to personnel if there is an explosion.
• Continue to run the lubricating oil pumps to help cool down the hotspot.
• Do not go near crankcase relief valves. This is to prevent injury in case there is an explosion.
• Wait at least 20 minutes before opening the crankcase doors. Allowing oxygen by opening the doors may cause an explosion.
• Isolate the engine (shut off start air, stop LO pumps, engage turning gear) this is to prevent accidental start
• Open crankcase doors and find the cause of overheating.
• Repair/ rectify the cause of overheating. This could be due to a bearing, chain rubbing, piston rod fouling on the stuffing box, cracked piston, etc. The engine should not be restarted until the cause is established and corrected.
• Before restarting, check the oil flow through the bearings, chains/ jet sprayers, and piston cooling return. Turn the engine and monitor the load on the turning gear motor (to check the engine is not binding on the tight spot)
• When restarting, keep a close eye on any repairs. Use an IR temperature gun to monitor the location of overheating. Stop the engine after 30 seconds, 2 minutes and 10 minutes running at low load and check for overheating. To prevent reoccurrence.
• Increase load over 2 hours, keeping a close eye on bearings temperature and oil mist detector.
• If the engine is fully operational, when the Chief Engineer is satisfied with the running of the engine, hand it back to bridge control.