Fire on merchant vessels has lead to massive devastations in the past and has been the biggest cause of causalities on ships. If such fire has its source in the main propulsion engine, then the ship might lose its control, leading to severe damages and loss. One of the several reasons of fire in the main engine system of the ship is Starting air line explosion.
How Can Air Line Explode?
For a fire to happen, it has to complete the three sides of the fire triangle namely-Heat, Fuel & Air.
The heat source may come from a leaking starting air valve fitted on the cylinder head and the combination of these three in proper ratio will lead to an air line explosion.
Precaution and Prevention
For precaution against explosion on starting air line different safety devices and arrangements are fitted. They are
- Relief Valve: It is fitted on the common air manifold which supplies air to the cylinder head. Normally fitted at the end of the manifold and it lifts the valve in the event of excess pressure inside the manifold. The advantage of relief valve is it will sit back after removing the excess pressure and thus continuous air is available to engine in case of manoeuvring or traffic.
- Bursting Disc: It is fitted in the starting air pipe and consist of a perforated disc protected by a sheet of material which will burst in case of excessive pressure caused due to air line explosion. It also consist of a protective cap such constructed that if the engine is required to run even after the disc has been ruptured, the cap will cover the holes when it is turned. This will ensure that in manoeuvring or traffic air is available for engine at all time.
- Non Return Valve: Positioned in between the Air Manifold and Air Receiver, it will not allow the explosion and its mixture to reach the air bottle because of unidirectional property of N.R. valve.
- Flame Arrestor: It is a small unit consisting of several tubes which will arrest any flame coming out of the cylinder through leaking start air valve. It is fitted on every cylinder before the start air valve.
For prevention of starting air line explosion following measures to be performed:
- Ensure that all safety devices fitted are working correctly
- Draining of the air bottle is carried out every watch
- Auto drain to be checked for proper functioning
- Air compressor is well maintained to avoid oil carry over
- The oil separator at discharge of the compressor is working efficiently
- The starting air manifold pipe to be cleaned and check for paint deformation which will indicate overheating of the pipe
- Starting air valve to be overhauled regularly to avoid leakage
- Starting air valve seat to be inspected and lapped
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