Inert Gas Marine notes (Overview)

• Inert Gas (IG) is the backbone of the tanker.

• Inert is something which does not support combustion.

• Since tankers (Gas Ships) carry payload which is highly flammable (and toxic) in nature, and to support combustion oxygen is essential, Inert Gas is use to lower the oxygen percent from the tank so as to eliminate the risk of explosion hazard.

1. Less than 11% oxygen is safe, theoretically, no gas-air mixture burn at this percentage.
2. But for practical purpose and to allow safety margin, 8% is taken as the level of oxygen at which no air-hydrocarbon mixture can burn by any means.
3. But on tankers, IG is maintained at 5% oxygen and it is ensure Oxygen does not exceed 8%.

There are mainly 3 ways to generate Inert Gas on board the Vessel.
1) Boiler
2) Inert Gas Generator (IGG)
3) Carbon Molecular Sieve

• Every pump in IG system has duplicate Pump(stand-by pump) except the Scrubber pump.

• Most of the IG equipment are located at very high point, normally nobody goes there, a visit and inspection is taken during survey.

• There is a counter which count for how much time a machinery is being running.

Few terms worth noting:

1. Flue Gas : left over of the combustion process in the boiler which come out as the exhaust. 
2. Taint : Tainting means change of color when IG is produce by boiler combustion which was not proper(indicated by black smoke at the outlet funnel) therefore Soot goes into the cargo tank and react with cargo and changes it color. The customer may refuse to take-in the cargo which has been tainted, for example the Aviation Oil is the lightest and most refined oil, and even a slightest soot goes into the cargo tank carrying A.O it will taint the oil which maybe unfit for usage.
3. Toxicity : when gas reaches it's threshold value without lowing its oxygen(21%) content which do harm.
4. Soot : a deep black powdery or flaky substance consisting largely of amorphous carbon, produced by the incomplete burning.