This technical report addresses evaporative loss from internal floating-roof tanks (IFRTs) with closed vents. When the vents in the fixed roof of an IFRT are closed, rather than open, estimation of emissions is shown to be highly complex.

This subject is not covered in other API standards such as the Manual of Petroleum Measurement Standards (MPMS), Chapter 19.1, which specifically excludes fixed-roof tanks that have an internal floating roof, and MPMS Chapter 19.2, which specifically excludes closed internal floating-roof tanks (that is, tanks vented only through a pressure-vacuum relief vent, blanketed with an inert gas, vented to a vapor processing unit, or otherwise restricted from being freely vented).