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Vapor Recovery 101
Vapors emitted by gasoline contain high levels of Volatile Organic Compounds. When mixed with sunlight and heat, these pollutants aide in the formation of ground-level ozone. While effective in protecting Earth in the stratosphere, ozone is harmful to humans, animals and vegetation when located closer to Earth’s surface. For more information regarding ground-level ozone and its effects, visit EPA's Ozone - Good Up High Bad Nearby webpage.
By recapturing these vapors during loading and refueling, vapor recovery prevents the release of gasoline vapors from various activities into the atmosphere. There are two different categories of vapor recovery: Stage I and Stage II.
Stage I Vapor Recovery
Stage I vapor recovery regulates the release of gasoline vapors from storage tanks at bulk plants and terminals as well as vapors released during the transfer of gasoline from the terminal to delivery trucks. It also controls the release of gasoline vapors between delivery trucks and other storage tanks, generally at gasoline dispensing facilities.
In the image to the left, the black arrows represent the gasoline flowing into the tanks, while the red arrows represent the vapors being forced, by the pressure of the loading, from the tank back into the truck. The truck then takes these vapors back to a terminal where they are burned off or condensed back into gasoline.
Submerged fill is also used during Stage I deliveries. The drop tube of the tank extends down to within 6” of the bottom of the tank. This allows gasoline to be pumped into the tank below the surface of the liquid, which minimizes splashing and turbulence at the surface, which in turn minimizes vapor formation.
However, if an excess amount of positive or negative pressure is created inside the tank, the tanks are also connected to a Pressure/Vacuum valve which will open and close in order to maintain the proper balance of air inside the gasoline tanks.
EPA created an informational video describing Stage I gasoline filling requirements per their Federal Regulations 40 CFR 63 Subparts BBBBBB (6B) and CCCCCC (6C), but it does an excellent job of illustrating the components of a typical Stage I Vapor Recovery system.
Stage II Vapor Recovery
Stage II Vapor Recovery is the capture and control of gasoline vapors that would normally be released into the atmosphere during the refueling of motor vehicles at a GDF. The image to the right represents a typical refueling utilizing Stage II Vapor Recovery. The black arrows represent the gasoline being pumped from the storage tank to the automobile. The red arrows show the flow of the vapors from the automobile tank back into the storage tank. These vapors are held in the storage tank until the next gasoline delivery when they are returned to the truck.
Stage II Vapor Recovery is generally categorized by the “boot” on the nozzle that allows it to capture vapors during refueling. The hose used is a coaxial hose specially designed to allow gasoline to flow through an inner hose surrounded by larger hose that allows the vapors to be pushed back down to the storage tank. CARB used an infrared camera to document the release of gasoline vapors from a non-Stage II nozzle.
The movement of the vapors from the automobile to the storage tank is done without the use of a pump. The vapors are pushed out of the tank by the incoming gasoline filling the tank. This is called a “balance system.” In some states, Vapor-Assist systems are used which actively pull vapors from the automobile into the storage tank when refueling. Missouri has approved only balance systems. For more information on equipment approved for use in Missouri, see the MOPETP webpage.