| Gas | Formula | Cylinder identification | IS shade | UN number |
|---|---|---|---|---|
| Acetylene | C₂H₂ | Maroon | IS 4379 shade 541 | 1001 |
| Oxygen | O₂ | Black | IS 4379; medical O₂ follows IS 3933 | 1072 |
| Nitrogen | N₂ | French grey + Black band | IS 4379 shade 630 + black neck band | 1066 |
| Argon | Ar | Peacock blue | IS 4379 shade 103 | 1006 |
| Carbon dioxide | CO₂ | Black + White band | IS 4379 — white band distinguishes it from oxygen | 1013 |
| Hydrogen | H₂ | Signal red | IS 4379 shade 537 | 1049 |
| Helium | He | Middle brown | IS 4379 shade 411 | 1046 |
| Nitrous oxide | N₂O | Blue | Medical gas — IS 3933 | 1070 |
| Compressed air | Air | French grey | IS 4379 shade 630 — NO band (nitrogen has a black band) | 1002 |
The black-cylinder trap
Oxygen and carbon dioxide both have black bodies. The only colour difference is the white neck band on CO₂. On a mixed site — a fabrication shop running oxy-fuel next to a MIG line — that single band is what separates an oxidiser from an asphyxiant.
The same trap exists at the other end of the chart: compressed air and nitrogen are both french grey, distinguished only by nitrogen's black neck band. Always read the stencilled gas name and formula as well as the colour. Under IS 4379 every cylinder must carry both.
How to read a band
Band width must be at least a quarter of the cylinder's outside diameter. Where a cylinder carries two bands, red or blue sits nearest the valve, with yellow between. Colour numbers refer to the ready-mixed paint shades in IS 5.
Industrial and medical cylinders follow different standards
IS 4379 covers industrial gas cylinders. Medical gas cylinders are identified under IS 3933 instead, which is why a medical oxygen cylinder does not necessarily match the industrial oxygen cylinder beside it. Never infer a medical cylinder's contents from the industrial chart.
One further caution: the 1981 edition of IS 4379 is what the black oxygen cylinders in service across India actually follow. A later ISO-harmonised revision uses different assignments — including white for oxygen. If you are specifying new cylinders rather than identifying existing ones, confirm which edition your inspecting authority requires.