Shielding gas mechanisms for arc welding systems are shown and described. The shielding gas mechanisms each include a gas sensor configured to read and provide a measurement of the shielding gas and a shut-off mechanism configured to stop power to a welding gun when the measurement of the shielding gas falls below a minimum effective level. In some examples, the gas sensor is coupled to the gas line proximal to an inlet of a wire feed unit. In some other examples, the gas sensor is coupled to the gas line proximal to an outlet of the wire feed unit. In even other examples, the gas sensor is coupled to the welding gun.
