Editing Inert gas (section)

===Inert gas systems on ships===
Inert gas is produced on board crude oil carriers (above 8,000 tonnes from Jan 1, 2016) by burning kerosene in a dedicated [[inert gas generator]]. The inert gas system is used to prevent the atmosphere in cargo [[tank]]s or [[bunker]]s from coming into the explosive range.<ref>International Maritime Organization. ''Tanker yes Familiarization'' London: Ashford Overload Services, 2000. 185.</ref> Inert gases keep the [[oxygen]] content of the tank atmosphere below 5% (on crude carriers, less for product carriers and gas tankers), thus making any air/hydrocarbon gas mixture in the tank too rich (too high a fuel to oxygen ratio) to ignite. Inert gases are most important during discharging and during the ballast voyage when more [[hydrocarbon]] vapor is likely to be present in the tank atmosphere. Inert gas can also be used to purge the tank of the volatile atmosphere in preparation for gas freeing - replacing the atmosphere with breathable air - or vice versa.
The flue gas system uses the boiler exhaust as its source, so it is important that the fuel/air ratio in the boiler burners is properly regulated to ensure that high-quality inert gases are produced. Too much air would result in an oxygen content exceeding 5%, and too much fuel oil would result in the carryover of dangerous hydrocarbon gas.
The flue gas is cleaned and cooled by the [[scrubber]] tower. Various safety devices prevent overpressure, the return of hydrocarbon gas to the engine room, or having a supply of IG with too high oxygen content.

Gas tankers and product carriers cannot rely on flue gas systems (because they require IG with O<sub>2</sub> content of 1% or less) and so use inert gas generators instead. The inert gas generator consists of a combustion chamber and scrubber unit supplied by fans and a refrigeration unit which cools the gas. A drier in series with the system removes moisture from the gas before it is supplied to the deck. Cargo tanks on gas carriers are not inerted, but the whole space around them is.