cylinders are often color-coded, but the codes are not standard across different jurisdictions, and sometimes are not regulated. Cylinder color can not safely be used for positive product identification; cylinders have labels to identify the gas they contain. Common cylinder sizes The below are example cylinder sizes and do not constitute an industry standard. (US DOT specs define material, making, and maximum pressure in psi. They are comparable to Transport Canada specs, which shows pressure in bars. A 3E-1800 in DOT nomenclature would be a TC 3EM 124 in Canada.) Gas storage tubes For larger volume high pressure gas storage units, known as tubes, are available. They generally have a larger diameter and length than high pressure cylinders, and usually have a tapped neck at both ends. They may be mounted alone or in groups on trailers, permanent bases, or intermodal transport frames. Due to their length, they are mounted horizontally on mobile structures. In general usage they are often manifolded together and managed as a unit. Gas storage banks Groups of similar size cylinders may be mounted together and connected to a common manifold system to provide larger storage capacity than a single standard cylinder. This is commonly called a cylinder bank or a gas storage bank. The manifold may be arranged to allow simultaneous flow from all the cylinders, or, for a cascade filling system, where gas is tapped off cylinders according to the lowest positive pressure difference between storage and destination cylinder, being a more efficient use of pressurised gas. Gas storage quads A gas quad is a group of high pressure cylinders mounted on a transport and storage frame. There are commonly 16 cylinders, each of about 50 litres capacity mounted upright in four rows of four, on a square base with a square plan frame with lifting points on top and may have fork-lift slots in the base. The cylinders are usually interconnected as a manifold for use as a unit, but many variations in layout and structure are possible. See also – Small gas cylinder typically used for specialty gasses – a small, inexpensive, disposable metal gas cylinder for providing pneumatic power References External links NASA — Safety Standards for Oxygen and Oxygen Handling Pressure vessels Anesthetic equipment Containers Gas technologies Industrial gases