Purge and shield gasses shall be delivered to the welding machine via exclusively stainless delivery lines fitted with adequate, calibrated regulators for controlling and monitoring of gas flow rates. Regulators shall be constructed of stainless steel. Brass regulators shall be allowed if all wetted areas of the regulator are constructed with stainless steel. In order to prevent the possibility of loss of shield gas causing a detrimental weld, all purge and shield gas supplies shall have a backup source routed via an automatic, switching manifold capable of ensuring uninterrupted gas supply should the primary source empty during the weld.