Marine Engineer: Starting Air Line Explosion

Starting air line explosion occurs when oil accumulated in starting air manifold or piping gets ignited under high pressure air.

Sources of ignition can be:

A leaky air start valve - whilst the engine is running hot gases produced in cylinder as fuel burns [at above 1200degree celsius] leak past a valve which has not seated properly.Branch pipe to manifold gets heated to red hot.If engine has stopped and restarted before cooling down, oil vapour in the air can be ignited leading to explosion.
Fuel leaking into the cylinder whist engine is stopped, gets ignited when piston compresses the air inside the cylinder in starting sequence.When air start valve opens as the piston comes to TDC, the pressure in the cylinder is higher than start air pressure.Burning combustion gases passes into the air start manifold and ignite oil entrained resulting in explosion.
Oil deposited on inner surface of start air manifold can get auto ignited because of high temperature created by inflow of high pressure air. At about 400 degree celsius, oil deposits in manifold self ignite resulting in explosion.

*Starting air pipe to cylinder exploded

To minimize the risk of explosion:

Oil carryover from compressor to be minimum.
Air intake mist catcher, oil seperator of compressor to be properly maintained and cleaned.
Non return valve at starting of air supply to engine[incorporated in auto start valve]
As per IACS, In direct reversing engines with bore dia >230mm should have flame arrestor, bursting disc between manifold and cylinder start valve.A relief valve may be fitted in manifold where flame arrestors are fitted.

*Bursting disc

*Bursting disc MAN B&W

Safety devices:

Marine Engineer