Section 2(xv) in The Static and Mobile Pressure Vessels (Unfired) Rules, 2016
(xv)"Gas Cylinder" or "Cylinder" means any closed metal container having a volume exceeding 500 ml but not exceeding 1000 litres intended for the storage and transport of compressed gas, including any liquefied petroleum gas (LPG) container or compressed natural gas (CNG) cylinder fitted to a motor vehicle as its fuel tank but not including any other such container fitted to a special transport or undercarriage and includes a composite cylinder and cryogenic container, however, the water capacity of cylinders used for storage of CNG, nitrogen, compressed air, etc., may exceed 1000 litres up to 3000 litres provided the diameter of such cylinder does not exceed 60 cm;
