The purpose of the shielding gas is to prevent the atmosphere from contaminating the weld area and the tungsten electrode. Critical factors in shielding efficiency are nozzle size, flow rates and the type of gas used. Welding grade argon and nitrogen are supplied with a purity of 99.995% or greater. Since argon is a heavy gas with an atomic weight of 40, lower flow rates are required for it to provide a good shield.

Generally, the shield gas is delivered around the tungsten electrode through a concentric nozzle, which must be of adequate size to provide coverage of the weld area. Automatic welding setups may include leading or trailing shields to increase the coverage area.

Argon is obtained from the liquefaction of air, and argon, oxygen and nitrogen are the primary products of air separation plants. Argon is readily available even though it makes up less than 1% of the yield. Helium is mostly obtained from wells controlled by the U.S. Bureau of Mines. Limited availability places a premium on helium. Shielding gas systems using less than 10,000 ft3 per month normally use individual cylinders. For higher consumption rates, distribution manifolds fed by cylinder banks or trailers are used.