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• For a fire or explosion to take place, there must be heat, oxygen and fuel

 

• 1. 1. In the crankcase of the main engine, the oil particles are churned into small 
     2. If a hot spot comes in contact with these small particles, forms mist, 
     3. These particles move towards the colder region inside the crankcase space and when in contact with the cold region, form a white mist. Over a period of time the formation of mist starts increasing
     4. When it reach the explosion limit, the mist comes in contact with the hot spot again and in the presence of sufficient temperature results into an explosion.
     5. Secondary explosion are caused by primary explosion reducing the size of oil droplets, producing more fuel for ignition. Explosion will cause Air to be sucked in, causing another explosion
     6. Hot spot produced as a result of rubbing between two metal surfaces or friction between two metals parts such as piston rod and gland, cross head guides, chain and gear drive etc.
     7.  The hot spot is generally caused by improper maintenance and insufficient or less clearance.

 

Crankcase inspection

• Apply for Immobilization permission of the main engine.
• After the permission is received the checklist has to be filled.
• Risk assessment and toolbox meeting conducted.
• When the engine is in “stopped” condition, the lubricating oil pump have to be stopped
• Open circuit breaker
• Proper sign and placards to be displayed regarding men at work.
• Since engine crankcase is an enclosed space, an enclosed space checklist is also to be filled.
• After stopping the engine and the pumps the crankcase doors have to be opened and sufficient time is to be given to cool and ventilate the space as the temperature inside is very hot and deprived of air.
• After the cooling and ventilating the space, the person entering the space should be with proper personnel protective equipments like boiler suit, safety harness, and anti slipping pads for shoes.
• Make sure there are no tools, pen etc in your pockets which might drop inside and cause damage to bearing and machinery parts

Inside Crankcase Following Checks are to be Made

1. Check the overall quality of oil whether it is clean or dirty with carbon particles.
2. Check for any distinguished smell, if found, this could be because of bacterial contamination of oil. The smell is generally of rotten eggs.
3. Check for any metal particles near the grating in the crankcase.
4. Check the condition and damage to the gratings.
5. Check the slip marks on the web; they should be in the same line. If slip is found then report is to be made to the company and classification society regarding this.
6. Check for any bluish dark patches, this indicates that hot spots are caused by friction of insufficient lubrication.
7. Check cross head for any damages.
8. Check cross head guides for damages and marks.
9. Check the bed plate for any welding cracks etc.
10. Check any metal seen near the bearings coming out due to wiping.
11. Check for piping and any loose connections between them.
12. Check the locking wires and locking washers on bolts of stuffing box.
13. Before coming out make sure there is nothing left inside.

[icedcappucino]

Early detection of over-heating and the prompt slowing down or stopping of the main engine as circumstances permit, will avoid conditions which might form an explosive mist in the crankcase.
In the majority of cases oil mist detectors are fitted to main engine crankcase to detect any buildup of a potentially explosive oil mist. All alarms from oil mist detectors, no matter how suspect the instrument may be, are to be treated as an emergency situation and the main engine stopped. Operation of a main engine with a positive alarm from a mist detector is only at the jurisdiction of the Master.
Under no circumstances is the alarm to be switched off until the main engine has been stopped. Great care must be exercised if the main engine has been stopped due to a positive alarm from an oil mist detector.
The most likely cause of such an alarm will be overheating of the bearing, or in the case of a trunk piston engine also the possibility of leaking piston rings. Sufficient time must elapse for cooling and mist dispersal before removing a crankcase door for examination.
In some ships bearing temperature sensors or bearing wear down monitoring systems are fitted for monitoring of the main engine bearing temperatures or wear down. Alarms are fitted to indicate high bearing temperatures and/or high bearing wear down. The alarms must be tested every 3 months.
CAUTION: Crankcase doors or inspection doors should not be opened until the engine has cooled down. DO NOT attempt to start the engine until reason of overheating has been ascertained. Ensure the LO flow is normal from all the bearings and LO pressure is normal. Ensure that bearing shells have not shifted or squeezed out.

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