U.S. Navy Ship Salvage Manual Volume 6 - Oil Spill Response

S0300-A6-MAN-060begin to draw water instead of oil. The thickness of the water bottom can be increased by drawingoil from the top of the tanks with portable pumps, allowing water to flow in through the breachedplating. In the initial stages of the incident, salvors or spill responders should attempt to create orincrease water bottoms in damaged tanks, especially if lightering capacity is limited and severaltanks are leaking. Water bottoms should be deep enough to ensure that several feet of waterremains beneath the oil at the lowest anticipated tide. As operations continue, water bottoms canbe systematically increased until the tanks are completely discharged. The U.S. Navy SalvageManual, Volume 5, S0300-A6-MAN-050, discusses the use of water bottoms and methods toremove liquids from damaged vessels.The effectiveness of water bottoms is limited for water soluble liquids or liquids with a specificgravity very near one. Water bottoms cannot be created at all under liquids with specific gravitiesgreater than one. Many bulk chemicals fall into this category, as well as some crude oils and bunkerfuels.3-5.1.2 Preventing Further Discharge. Spills are prevented by taking appropriate precautionswhen handling pollutants. In many cases, spills are best prevented by removing the potential pollutantfrom the damaged vessel or by removing the vessel with the pollutant completely contained.The act of removing a pollutant carries the risk of accidental spill. The potential gain mustbe weighed against the possibility of a spill during transfer. U.S. Navy Salvage Manual, Volume 5,S0300-A6-MAN-050, describes procedures to minimize incident potential during POL transfer.3-5.1.3 Containment. Oil and other pollutants are most often contained with purpose-builtbooms. Booms are also used to corral, move or funnel spilled oil to recovery devices or to divert itaway from sensitive areas. Trained aircraft spotters should be deployed to track oil movement,guide skimmers and recommend locations for placement of protective containment booms.Booms range in height from under one foot for protecting calm water areas to over seven feet foroffshore use. Smaller booms are less expensive, lighter, easier to deploy and require less power totow. Deployment of large offshore booms requires larger boats and heavier equipment thansmaller booms. Specialized equipment is sometimes required. Most booms become ineffective incurrents greater than one knot or wave heights greater than six feet, as oil is entrained in the currentand swept under the boom. Systems designed for severe conditions in the Norwegian sectorof the North Sea are required by the Norwegian government to be effective in nine-foot wavesand 1.5 knot currents. Even with booms built to these standards, efficiency is greatly reduced insix- to nine-feet seas. When wave height exceeds nine feet, oil is whipped into the water andsplashed over booms; little containment or recovery is possible.Boom heights of 18 to 80 inches have been used for offshore oil containment. Available evidencesuggests that the largest booms are no more effective at containing oil than booms in the 32- to42-inch height, but larger booms are useful for providing increased towing resistance to slowdown boats that otherwise could not maintain the one- to two-knot speeds required for boom andskimmer towing.Booms for sheltered waters can be field-fabricated from linked chains of logs, empty oil drums,small craft, etc. Effectiveness can be increased by adding weighted plastic or canvas skirts. Sor-3-15