What colour identifies each medical gas?

WHO notes that different standards for colour coding, labelling and connections apply in different countries, and describes two predominant cylinder colour systems: the ISO system, in which oxygen cylinders have a white shoulder, and the United States system, in which oxygen cylinders are completely green. In the ISO chart reproduced by WHO, nitrous oxide is blue and air is shown in black and white quarters. WHO describes outlet front covers that use the same colour code as the cylinders, and adds that local and international standards may vary.

Two official codes compared

In the US, the federal rule assigns these colours to the shoulder of high-pressure medical gas cylinders and to the labels of portable cryogenic containers; a mixture carries the colours of each component gas. NHS England's HTM 02-01 (2026 edition) asks for pipelines to be identified to BS 1710 with colour bands within 300 mm of valves and junctions and on both sides of walls, plus a label naming the gas at intervals of no more than 3 m and arrows for flow direction. For cylinders, HTM 02-01 Part B notes that cylinder colours may change with regulatory updates while the shoulder colour stays constant, and sends users to the suppliers' current charts. In Portugal, ACSS specification ET 03/2006 asks for networks to be identified with the colour code of ISO 7396 and lists NP EN 1089-3 for cylinder colours.

Colour and gas-specific connections

HTM 02-01 ensures identity of supply by giving every terminal unit and user-replaceable component a gas-specific connection, identified also by symbol and colour. WHO describes the same two combined methods at the wall outlet: colour coding and connectors shaped so that a hose for one gas cannot fit another.