Medical Gas Reference
The medical gas systems, their US color codes, the copper and brazing requirements, the operating pressures, and how the piping is sized — per NFPA 99. This is life-safety work: medical gas is engineered per project and installed and verified by certified professionals. The color codes and pressures below are the fixed facts every technician needs.
Medical gas systems
| Gas / system | Label color | Lettering | Operating pressure |
|---|---|---|---|
| Oxygen (O₂) | Green | White | 50–55 psi |
| Medical air | Yellow | Black | 50–55 psi |
| Medical/surgical vacuum | White | Black | 15–30 in Hg (12 in Hg code min) |
| Nitrous oxide (N₂O) | Blue | White | 50–55 psi |
| Nitrogen (N₂) | Black | White | 160–185 psi |
| Carbon dioxide (CO₂) | Gray | Black | 50–55 psi |
| WAGD (waste anesthetic gas) | Purple / violet | White | Vacuum |
Copper, pressure, and the sizing framework
Medical-grade cleaned seamless copper to ASTM B819 — Type L is standard; Type K is required where operating pressure exceeds 185 psi and pipe size is larger than NPS 3. Joints are brazed under a continuous oil-free nitrogen purge to prevent internal oxidation.
Sizing itself is engineered for each facility rather than looked up. The framework is:
- Count the number and type of terminals (outlets/inlets) each pipe segment serves.
- Apply the flow demand per outlet with a simultaneous-use (diversity) factor — not every outlet flows at once.
- Hold the allowable pressure drop to the farthest outlet, keeping the required delivery pressure (50–55 psi for most gases, 160–185 psi for nitrogen, the required level for vacuum).
- Choose the copper inside diameter that carries the total design flow within that drop.
This is life-safety work
Life-safety work under NFPA 99 — installed by certified brazers, purged with nitrogen during brazing, and verified after installation (pressure, cross-connection, and purity tests) by a party independent of the installer. Outlets are gas-specific and non-interchangeable.
Because it is life-safety, this reference deliberately stops at the fixed facts — the gases, colors, pressures, copper, and the sizing framework — and does not publish per-outlet flow tables or diversity factors, which are engineered per room type from the licensed NFPA 99 standard and belong in a project design, not a general chart.
Common questions
What are the medical gas color codes?
In the US (CGA C-9, referenced by NFPA 99): oxygen is green, medical air is yellow, medical/surgical vacuum is white, nitrous oxide is blue, nitrogen is black, and carbon dioxide is gray, with waste anesthetic gas disposal (WAGD) purple. Nitrogen (black) and medical air (yellow) are the two most often confused — they are different gases at very different pressures.
What pipe is used for medical gas?
Medical-grade cleaned seamless copper to ASTM B819 — Type L is the standard choice, and Type K is required where the operating pressure exceeds 185 psi and the pipe is larger than NPS 3. Joints are brazed under a continuous flow of oil-free nitrogen to keep the inside of the tube from oxidizing, which would contaminate the gas.
How is medical gas pipe sized?
It is engineered per project, not read from a generic chart. You count the terminals each segment serves, apply the flow demand per outlet with a simultaneous-use (diversity) factor, hold the allowable pressure drop to the farthest outlet at the required delivery pressure, and choose the copper size that carries the total flow within that drop. The per-outlet flows come from the current NFPA 99 tables for the specific facility.
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