A process to detect metal impurities in a gas or gas mixture including the steps of directing the gas or gas mixture through non-metallic pipings to a sampling device and sampling the gas or gas mixture for metal impurities detection, wherein the sampling device is close to an inlet and/or outlet of a machine employing the gas or gas mixture as a processing gas, the machine being surrounded by a booth containing a gaseous atmosphere which is continuously circulated in the booth, partially renewing said atmosphere continuously, and exhausting excess atmosphere.