Shutoff device for hollow electrodes supplying particulate feed material to and/or removing furnace gas from electrothermal reduction furnaces, arc melting furnaces, e.g., calcium carbide or similar furnaces. The inner shell of the hollow electrode has an inclined pipe socket secured to it, preferably welded thereto, which in turn has detachably secured to it a sleeve with an inflatable bag therein. The bag is displaceable by means of a thrust rod from inside the sleeve to a position inside the hollow electrode, and inflated therein using gas under pressure to effect shutoff of the hollow electrode.