An apparatus for blocking discharge from a flanged pipe coupling, including a strap configured to surround, and cover a gap between flanges. The apparatus includes a tensioning mechanism with a lever pivotally coupled to the strap, a clamp pin mounted on the opposing end of the strap, and an adjustment pin on a side of the clamp pin opposite the lever. Holes extend through ends of the clamp and adjustment pins. The tensioning mechanism includes a bolt having ends, and a mid-portion looped around the lever, so that portions of the bolt on opposing ends of the mid-portion are generally parallel and project through the holes. A fastener is mounted onto each bolt end on a side of the adjustment pin opposite the clamp pin. When the lever pivots away from the clamp pin, contact between the lever and bolt urges the ends of the strap together, increasing tension therein.