Can a listed UST be installed as an AST?
A. No, at least not unless the UST has also been evaluated and listed by U.L. as an aboveground liquid storage tank. While several manufacturers produce both USTs and ASTs, the OSFM is not aware of any singular tank that is listed for installation as either an UST or AST. USTs are designed to have backfill serve as an essential part of the structural support for the tank, especially the tank ends. Therefore, when an UST is installed aboveground, without the assistance of backfill to offer structural support, it is subject to failure. In addition, USTs are not designed with emergency venting because they are not subjected to fire/high heat conditions.
