Crankcase Explosion

Question 1

1. a) State the name of equipment used to give a warning of the presence of conditions that could lead to an explosion in the crankcase of a diesel engine.

Answer 1

a) Oil-mist detector

Question 2

b) Sketch and describe the device used to relieve any excess pressure that might develop as a result of a crankcase explosion in a diesel engine.

Answer 2

b) A strong spring seals the valve during normal conditions, however in the event of an excess of pressure cause by an explosion then overcomes the spring force for a brief period to allow the pressure to escape before reclosing. Flame gauzes fitted to stop flames expelling from the open valve, a guide also fitted to safely allow the force downwards to the deck plates.

Question 3

2. As EOOW explain the procedure to be followed in the event of a crankcase oil mist alarm on a bridge controlled constant speed main propulsion engine fitted with a controllable pitch propeller. (16)

Answer 3

• Inform the Chief Engineer and Bridge, request the engine to be stopped • Stop any auxiliary blowers, ER fans, open all indicator cocks, engage turning gear and maintain lubrication
• Evacuate the engine-room for at least half an hour whilst the engine is being turned No attempt must be made to enter the crankcase during this time.
• If the engine is not able to be stopped the engine-room must be evacuated and sealed, with emergency generator started and fire hoses set up outside ER space
• Space may only be entered if no explosion has occurred and after about 1hr of engine turning great care should still be taken
• The engine may only be re-started once a full check of the crankcase has been carried out and feel over of all bearing shells

Question 4

3. With reference to conditions which may cause an explosion in the crankcase of a large marine diesel engine:
   a) state FOUR possible sources of ignition (8)

Answer 4

Hot spots on bearing surfaces
Sparks from metal to metal contact
Fire outside the engine
Badly damaged piston rings and stuffing box

Question 5

3. With reference to conditions which may cause an explosion in the crankcase of a large marine diesel engine:
   a) state FOUR possible sources of ignition (8)
   b) state TWO methods which can be used to detect a potentially dangerous situation within the crankcase (4)

Answer 5

High oil mist alarm activation

High and rising crankcase pressure

Question 6

3. With reference to conditions which may cause an explosion in the crankcase of a large marine diesel engine:
   a) state FOUR possible sources of ignition (8)
   b) state TWO methods which can be used to detect a potentially dangerous situation within the crankcase (4)
   c) state TWO other indications which could signify a possible dangerous situation within the crankcase. (4)

Answer 6

Mist emitting from crankcase vent

Mist or sound from crankcase explosion doors