Storage tanks are containers that hold liquids, compressed gases (gas tank; or in U.S.A “pressure vessel”, which is not typically labeled or regulated as a storage tank) or mediums used for the short- or long-term storage of heat or cold. In the USA, storage tanks operate under no (or very little) pressure, distinguishing them from pressure vessels. Storage tanks are often cylindrical in shape, perpendicular to the ground with flat bottoms, and a fixed frangible or floating roof. There are usually many environmental regulations applied to the design and operation of storage tanks, often depending on the nature of the fluid contained within.