There are various systems for the abatement of oil pollution at sea: the "Load-on-top" system involves passing the washing from tank cleaning operations and residue from discharge of the original ballast water to an empty cargo tank nominated as the "slop" tank. Fresh oil cargo is loaded on top of the final residue left after further discharges of water, the resulting mixture being acceptable to refineries despite some additional cost in removing the salt and water. Under the International Convention for the Prevention of Pollution from Ships, 1973, all oil-carrying ships will be required to be capable of operating with this method of retention, or alternatively to discharge to reception facilities. Another method consists in spraying on the oil dispersives and/or blasting straw and sawdust, functioning as "blotting paper", onto water, beaches, rocks and docks. The Vikoma System for the containment of oil spills at sea, developed by British Petroleum, a seaboom of about 500 metres in length, is inflated and towed downwind of the oil slick and formed into a U-shape; under the influence of wind, the oil becomes trapped within the boom.