Preventing Starting Air Line Explosion

Fire on merchant vessels has led 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 damage and loss. One of the several reasons for the fire in the main engine system of the ship is Starting an airline explosion.

 

 

Starting Air Line Component

 
 
For a fire to happen, it has to complete the three sides of the fire triangle namely-Heat, Fuel & Air. In an air starting system of the main engine, fuel may be present in the form of lube oil carried over from the air compressor. Moreover, oxygen is present in the system in abundance.
 
The heat source may come from a leaking starting air valve fitted on the cylinder head and the combination of these three in the proper ratio will lead to an airline explosion.
 
Precaution and Prevention
 
For precaution against explosion on starting airlines, 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 a relief valve is it will sit back after removing the excess pressure and thus continuous air is available to the engine in case of manoeuvring or traffic
  • Bursting Disc: It is fitted in the starting air pipe and consists of a perforated disc protected by a sheet of material that will burst in case of excessive pressure caused due to airline explosion. It also consists of a protective cap constructed so 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, the air is available for the engine at all times.
  • 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 the unidirectional property of the 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 a leaking start air valve. It is fitted on every cylinder before the start air valve.
 
For the prevention of starting airline explosions following measures are to be performed:

  • Ensure that all safety devices fitted are working correctly
  • Draining of the air bottle is carried out on every watch
  • Auto drain to be checked for proper functioning
  • The Air compressor is well maintained to avoid oil carryover
  • The oil separator at the discharge of the compressor is working efficiently
  • The starting air manifold pipe is to be cleaned and checked for paint deformation which will indicate overheating of the pipe
  • Starting air valve to be overhauled regularly to avoid leakage

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