Exam Question
(a) Describe indications of crank case explosion in main engine. (4)
(b) Describe actions to be taken, if there is crank case explosion in main engine. (8)
(c) Describe means of prevention of crank case explosion (4)
Class 4 (4th Engineer)
MEP
📅 Jun 2023
Reference Answer
### (a) Indications of a Crankcase Explosion
A crankcase explosion is preceded by the formation of an explosive mixture of oil mist and air, which is then ignited by a hot spot. The indications are therefore related to the detection of this mist and the presence of the hot spot.
1. **Oil Mist Detector (OMD) Alarm**: This is the most critical and reliable early warning. The OMD continuously samples the atmosphere from various points within the crankcase. It will trigger an audible and visual alarm in the Engine Control Room when the oil mist concentration reaches a pre-set level, typically 2.5% of the Lower Explosive Limit (LEL). This provides time for corrective action before a flammable concentration is reached.
2. **Physical and Sensory Indications**:
A crankcase explosion is preceded by the formation of an explosive mixture of oil mist and air, which is then ignited by a hot spot. The indications are therefore related to the detection of this mist and the presence of the hot spot.
1. **Oil Mist Detector (OMD) Alarm**: This is the most critical and reliable early warning. The OMD continuously samples the atmosphere from various points within the crankcase. It will trigger an audible and visual alarm in the Engine Control Room when the oil mist concentration reaches a pre-set level, typically 2.5% of the Lower Explosive Limit (LEL). This provides time for corrective action before a flammable concentration is reached.
2. **Physical and Sensory Indications**:
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