label or decal should always be checked for product identification. European cylinder colours The colours below are specific shades, defined in the European Standard in terms of RAL coordinates. The requirements are based on a combination of a few named gases, otherwise on the primary hazard associated with the gas contents: Specific gases Based on gas properties Gas mixtures, mostly for diving Diving cylinders are left unpainted (for aluminium), or painted to prevent corrosion (for steel), often in bright colors, most often fluorescent yellow, to increase visibility. This should not be confused with industrial gases, where a yellow shoulder means chlorine. See also References Notes Standards ISO 32: Gas cylinders for medical use—Marking for identification of content. CEN EN 1089-3: Transportable gas cylinders, Part 3 - Colour Coding. External links Virtual Anesthesia Machine - 6 different color codes for medical gas cylinders, hoses and outlets British Compressed Gases Association – Colour Coding of Cylinders. Air Products – European Gas Cylinder Identification Chart. Compressed Gas Association (U.S.) Gases and Welding Distributors Association (U.S.) European Industrial Gases Association (E.U.) British Compressed Gases Association (UK) Anesthesia Gases Welding Breathing gases Pressure vessels Gas technologies Industrial gases Fuel containers de:Gasflasche