Air cascade systems may consist of either DOT cylinders or ASME cylinders. They may be used as a cascade refilling system or bulk refilling system. They can be arranged vertically or horizontally too. ASME storage vessels never have to be hydrostatically retested, where DOT, UN/ISO cylinders do require scheduled hydrostatic retesting of the cylinder to insure it is safe to use.
UN/ISO air cascade cylinders are the most prolific cylinders used to refill your self-contained breathing apparatus (SCBA) with either cascade or bulk filling methods. This picture depicts a stationary air cascade system with UN/ISO/DOT cylinders, with CGA nuts/nipples, pipe tees, flexible 6000 PSI pigtails, pressure adjustable regulator, fill hose assembly and a wall mounting bracket for the cylinders.