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Abstract

A sealed storage vessel containing volatile organic vapor over a bottom sludge layer is cleaned by (a) determining the level of free oil in the vessel and then using (b) either a two-stage or one-stage treatment regime, adding a cleaning agent thereto. If the free oil is greater than 2 volume percent the two-stage regime is used where an oil release agent is initially mixed with the sludge to separate the oil from solids in the sludge. The separated oil floats on the surface of water and is removed without substantially exposing the vessel's interior to the atmosphere, leaving within the vessel a mixture of water, solids, and trace amounts of hydrocarbons. Next, a predetermined amount of an emulsifying agent is added to substantially emulsify the trace hydrocarbons, so the level of volatile organic compounds remaining in the interior of the vessel is no greater than 5,000 ppmv, measured as methane, at least one hour after adding the emulsifying agent. If the free oil is less than 2 volume percent, the one-stage treatment regime is employed by only adding the emulsifying agent to achieve this same level of volatile organic compounds.

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First Claim