• 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

(c) Procedure in the event of overheating being evident

• 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.

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.