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 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.