Technology Unit

A Fixed Roof Tank is a type of Storage Tank used to store Liquids, consisting of a Cone- or Dome-Shaped Roof that is permanently affixed to a Cylindrical Shell. Newer Storage Tanks are typically fully welded and designed to be both Liquid- and Vapor-tight. Older Tanks, however, are often riveted or bolted, and are not Vapor tight. A Breather Valve (Pressure-Vacuum Valve), commonly installed on many Fixed Roof Tanks, allows the Tank to operate at a slight internal pressure or vacuum. This Valve prevents the release of Vapors during very small changes in temperature, barometric pressure, or Liquid level.^[1] Fixed Roof Tanks without Breather Valves will generally be freely vented, thus the Emissions from a Fixed Roof Tank can be non-trivial. Gauge Hatches, Sample Wells, Float Gauges, and Roof Manholes provide accessibility to these Tanks, and also act as potential sources of Volatile Emissions.