<P> Inert gas is produced on board crude oil carriers (above 8,000 tonnes) (from Jan 1, 2016) by using either a flue gas system or by burning kerosene in a dedicated inert gas generator . The inert gas system is used to prevent the atmosphere in cargo tanks or bunkers from coming into the explosive range . IG keeps 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 . IG is most important during discharging and during the ballast voyage when more hydrocarbon vapour 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 . </P> <P> 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 gas is produced . Too much air would result in an oxygen content exceeding 5%, 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, return of hydrocarbon gas to the engine room, or supply of IG with too high oxygen content . </P> <P> Gas tankers and product carriers cannot rely on flue gas systems (because they require IG with O 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 hold space around them is . This arrangement allows the tanks to be kept cool using a small heel of cargo while the vessel is in ballast while retaining the explosion protection provided by the inert gas . </P> <P> In gas tungsten arc welding (GTAW), inert gases are used to shield the tungsten from contamination . It also shields the fluid metal (created from the arc) from the reactive gases in air which can cause porosity in the solidified weld puddle . Inert gases are also used in gas metal arc welding (GMAW) for welding non-ferrous metals . Some gases which are not usually considered inert but which behave like inert gases in all the circumstances likely to be encountered in some use can often be used as a substitute for an inert gas . This is useful when an appropriate pseudo-inert gas can be found which is inexpensive and common . For example, carbon dioxide is sometimes used in gas mixtures for GMAW because it is not reactive to the weld pool created by arc welding . But it is reactive to the arc . The more carbon dioxide that is added to the inert gas, such as argon, will increase your penetration . The amount of carbon dioxide is often determined by what kind of transfer you will be using in GMAW . The most common is spray arc transfer, and the most commonly used gas mixture for spray arc transfer is 90% argon and 10% carbon dioxide . (Listed as many different names depending on the gas supplier). </P>

Why would an element be considered inactive or inert