Abstract: This invention relates to an improvement in an above-ground storage system for volatile liquids wherein there is a horizontally extending cylindrical storage tank located in a dike, the tank having a top vent through which liquid may escape; the vent being surrounded by a collar and top cover to form a chamber around the vent and the collar having an outlet to drainage means down into the dike; the improvement comprising a weir so positioned in the collar that a limited overflow of liquid from the tank through the vent is retained by the weir within the collar at the top of the tank and escaping to the dike only when the capacity of the weir is exceeded.

Abstract: A storage system for liquid is disclosed which includes an external containment vessel which is open on top and an internal storage tank mounted within the external containment vessel so as to extend above it. The internal tank and the containment vessel are constructed and arranged so as to have a substantial outer storage space formed between them. This storage space is covered by a roof structure which extends from a point below the top of the internal storage tank to cover the containment vesel. A venting structure is provided at a location on the internal tank above the roof structure, where it is exposed to the atmosphere, and a drainage structure provides liquid coupling from the venting structure to the outer storage space.