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

S0300-A6-MAN-060Light, volatile oils burn more readily than heavy oils. Ignition and sustained combustion is difficultto achieve in weathered oil because light components have evaporated. Some refined oils sustaincombustion on the water surface only when aided by a burning agent. Oil slicks do not burncompletely; residue must be removed mechanically. Removal by burning is a tradeoff betweenremoving oil pollution from the water and releasing combustion products into the atmosphere.Research by the U.S. Department of Commerce indicates that the combustion products are nomore hazardous than the gases released by evaporating oil. Despite this evidence, the smoke andvisible air pollution are objectionable to most communities. Open in situ burning of oil and oilydebris is therefore used most often in remote areas.Oil contained in cargo or bunker tanks of a ship supports combustion much more readily than freeoil. A rule of thumb is that at least ten percent of the area over the oil in a cargo or bunker tankmust be open to the atmosphere for sustained combustion. It is difficult to burn oil completelyfrom deep cargo tanks that are not open to the sea. As oil is consumed, the oil level and consequentlythe combustion zone, falls within the tank. As the burning oil surface falls deeper into theenclosed tank, it becomes more difficult for air to reach the fire. The fire becomes very smoky andmay go out altogether. The sides of the tank must be opened to admit air if the burning is to continue,a difficult and dangerous proposition on a hot and fire-weakened structure. In tanks open tothe sea on stranded vessels, the oil level falls only slightly as oil is burned off because water flowsinto the tank to compensate for the reduced weight of oil.6.5.2 Approval. The National Contingency Plan requires burning agents to be approved by theFOSC, with concurrence from RRT representatives from the EPA and states with jurisdictionover the navigable waters threatened by the oil. Consultation is also required with the Departmentsof Commerce and Interior when natural resources for which they have trustee responsibilityare threatened. Approval for burning agents is given on a case basis, with no pre-approval. TheEPA does not include burning agents on the National Contingency Plan Product Schedule.6.6 SINKING AGENTSA sinking agent is an additive applied to oil discharges to sink floating pollutants below the watersurface. Sinking agents are made from the dust of dense materials with a high absorption capacity.Cement, coal dust, chalk and clay are such materials. When the dust is spread on an oil slick, itbonds to oil and settles to the bottom in small globules.Sinking agents neither remove oil from the water nor change the form of oil to enhance its degradationby natural means. The application of sinking agents merely substitutes one form of environmentalimpact for another. For instance, an offshore seabed can be sacrificed to protectshorelines, adjacent areas of seabed or water areas that are deemed more sensitive for environmentalor commercial reasons. Sinking agents do biological harm by suffocating bottom dwelling(benthic) organisms on the seabed. Once oil is moved to the seabed by a sinking agent, there is arisk that some oil may return to the surface. Sinking agents should be applied in the water deepenough that the bottom is unaffected by wave surge, which tends to resurface the oil. Becausesinking agents merely move oil to the bottom, where it is least vulnerable to natural degradationand may do grave harm to the environment, regulatory authorities seldom permit sinking agentsfor oil spill response.6-11