Exam Question
(a) Outline the potential causes of a crankcase explosion in a ship's machinery space. (8)
(b) Describe the function of crankcase relief doors. (4)
(c) Explain the purpose of oil mist detectors in preventing these events on a ship. (8)
Class 4 (4th Engineer)
SSEP
📅 Sep 2025
Reference Answer
### (a) Potential Causes of a Crankcase Explosion (8 Marks)
A crankcase explosion occurs when a flammable mixture of lubricating oil mist and air is ignited within the enclosed volume of an engine's crankcase. The event is governed by the principles of the fire triangle, which requires fuel, oxygen, and heat, all of which are present in a crankcase.
**Sequence of Events:**
1. **Formation of a 'Hot Spot':** The initial and most critical stage is the development of a localized area of high temperature within the crankcase. This 'hot spot' provides the ignition energy. Potential causes include:
A crankcase explosion occurs when a flammable mixture of lubricating oil mist and air is ignited within the enclosed volume of an engine's crankcase. The event is governed by the principles of the fire triangle, which requires fuel, oxygen, and heat, all of which are present in a crankcase.
**Sequence of Events:**
1. **Formation of a 'Hot Spot':** The initial and most critical stage is the development of a localized area of high temperature within the crankcase. This 'hot spot' provides the ignition energy. Potential causes include:
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