Editing Inert gas (section)

==Applications of inert gas==
Because of the non-reactive properties of inert gases, they are often useful to prevent undesirable [[chemical reaction]]s from taking place. Food is packed in an inert gas to remove oxygen gas. This prevents bacteria from growing.<ref>Maier, Clive & Teresa Calafut. ''Polypropylene: The Definitive User's Guide and Databook.'' Norwich, New York: Plastics Design Library, 1998. 105.</ref> It also prevents chemical oxidation by oxygen in normal air. An example is the rancidification (caused by oxidation) of edible oils. In [[food packaging]], inert gases are used as a passive preservative, in contrast to active preservatives like [[sodium benzoate]] (an [[antimicrobial]]) or [[butylated hydroxytoluene|BHT]] (an [[antioxidant]]).

Historical documents may also be stored under inert gas to avoid degradation. For example, the original documents of the [[U.S. Constitution]] are stored under humidified argon. Helium was previously used, but it was less suitable because it diffuses out of the case more quickly than argon.<ref>{{cite web | title = Charters of Freedom Re-encasement Project | publisher = National Archives | url = https://www.archives.gov/press/press-kits/charters.html | access-date = 2012-02-11}}</ref>

Inert gases are often used in the chemical industry. In a chemical manufacturing plant, reactions can be conducted under inert gas to minimize fire hazards or unwanted reactions. In such plants and in oil refineries, transfer lines and vessels can be [[purging (gas)|purged]] with inert gas as a fire and explosion prevention measure. At the bench scale, chemists perform experiments on [[air-sensitive compound]]s using [[air-free technique]]s developed to handle them under inert gas. Helium, neon, argon, krypton, xenon, and radon are inert gases.

===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.

===Inert gas systems on aircraft===
Inert gas is produced on board commercial and military aircraft in order to [[Passivation_(chemistry)|passivate]] fuel tanks. On hot days, fuel vapour in fuel tanks may otherwise form a flammable or explosive mixture which if oxidized, could have catastrophic consequences.  Conventionally, '''Air Separation Modules''' (ASMs) have been used to generate inert gas. ASMs contain selectively permeable membranes. They are fed compressed air that is extracted from a compressor stage of a gas turbine engine. The pressure drives the separation of oxygen from the air due to the increased permeability of oxygen through the ASMs in comparison to nitrogen. For fuel tank passivation, it is not necessary to remove all oxygen, but rather enough to stay below the lean flammability limit and the lean explosion limit. In contrast to the oxygen concentration of 21% in air, 10% to 12% in the [[ullage]] of a passivated fuel tank is common over the course of a flight.

===Welding===
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.<ref>Davis, J.R., ed. ''Corrosion: Understanding the Basics.'' Materials Park, Ohio: ASM International, 2000. 188.</ref> 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 penetration. The amount of carbon dioxide is often determined by what kind of transfer is used in GMAW. The most common in industrial applications is spray arc transfer, and the most commonly used gas mixture for spray arc transfer is 90% argon and 10% carbon dioxide.  In non-industrial applications, short circuit transfer is most commonly used, particularly in the US.  With short circuit transfer, a gas mixture made up of 75% argon and 25% carbon dioxide (referred to as C25) is most often used.  Outside the US, a mixture of 80% argon and 20% carbon dioxide is often used.

===Diving===
In [[underwater diving]] an inert gas is a component of the breathing mixture which is not metabolically active and serves to dilute the gas mixture. The inert gas may have effects on the diver, but these are thought to be mostly physical effects, such as tissue damage caused by bubbles in [[decompression sickness]]. The most common inert gas used in breathing gas for commercial diving is [[helium]].