This S Slag hole has just been shut off with a soft clay plug fitted onto the end of a Dolly bar and pushed into place using a pneumatic ram. The face plate opening of the tap hole is water cooled to keep it from overheating during the tapping operation. Behind the face plate are large silicone carbide inserts capable of withstanding the high temperatures of the molten slag. Unlike the Matte, C Slag, and Blister tapping holes, these S slag holes are much bigger and do not require burning to open unless they're closed for over an hour. They are routinely in constant use, being closed only long enough to change the kress pot, and require only a pneumatic jack hammer to knock out the clay plug to restore flow. Under normal circumstances once the flow is started the molten slag flow will burn the tapping hole completely open on its own.