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

S0300-A6-MAN-060including the Saybolt Second Universal (SSU) and Saybolt Second Furol (SSF) scalesused in the U.S. and the Redwood and Redwood Admiralty scales used in the UnitedKingdom. The scales differ in quantity of oil and orifice used to determine viscosity.The less viscous a material, the more readily it flows and spreads. Spills of low-viscosity oilsnecessitate rapid response to minimize spill migration.2-2.1.3 Pour Point. Pour point, related to viscosity, is the lowest temperature at which an oilflows. As the pour point is approached, spill spread decreases. Consequently, oils spread morerapidly in warm weather than in cold. Pour point can vary widely; some crude and residual oilsmay have pour points as high as 80°F, while the pour point of light diesel fuel is -60°F. The physicalstate of spilled oil influences containment and recovery methods. Both air and water temperaturesaffect oil state. Some oils may be solid or semisolid during cool nights and liquid during theday or solid when in contact with cool water and liquid when stranded on shore.2-2.1.4 Surface Tension. Surface tension is the attraction of a liquid for its own molecules.When oil is on water, the oil’s surface tension holds the oil molecules together and discouragesspreading, while the water’s surface tension works to pull the water molecules together, allowingthe oil to spread. Petroleum products with low surface tension spread readily over the water surface.Effective cleanup of spilled oil with low surface tension requires rapid response.2-2.1.5 Flash Point. Flash point is the lowest temperature at which a substance ignites understandard conditions. A highly volatile oil with a low flash point is a serious safety hazard thatgreatly complicates response.2-2.1.6 Emulsibility. Emulsibility is the tendency of spilled oil to form a stable suspension withwater. High emulsibility will cause oil to spread throughout the water column, increasing thethreat to the environment. This characteristic can force changes in cleanup priorities or methods.2-2.2 Chemical Properties. The chemical and physical properties of an oil are closely related, asboth are determined by the molecules that make up the oil.2-2.2.1 Boiling Point Range. Boiling point range indicates the relative volatility of an oil. Volatilityis the tendency of a liquid to evaporate and is related to boiling point; the lower the boilingpoint, the more volatile the liquid. Light (low-density) oils usually have lower boiling pointranges and are more volatile than heavy oils. Evaporation of highly volatile oils, such as JP-4 andgasoline, facilitates cleanup but may create an explosion hazard, especially in confined spaces. Asthe more volatile fractions of an oil evaporate, the remaining oil becomes denser and more viscous.When accounting for spilled oil, the portion that has evaporated must be included. Light, low boilingpoint range oils, such as gasoline or JP-4, may evaporate completely in a few days. Significantportions of spills of heavier oils, including fractions with boiling points above ambient, may belost to evaporation. Spilled Kuwait crude from the TORREY CANYON soon lost most of its fractionswith boiling point less than 570°F and it is estimated that as much as one-third of the total2-3