# What is synthetic medical air?

**What is synthetic medical air made by mixing oxygen and nitrogen, and what does ISO 7396-3 cover?**

Synthetic medical air is made by blending oxygen and nitrogen in defined proportions instead of compressing and treating ambient air; ISO 7396-3:2025 covers the proportioning units that produce it as a source of supply for a medical gas pipeline.

HTM 02-01 (2026) says medical compressed air can be obtained from compressor systems and from cylinders. Synthetic medical air takes a third route: an oxygen supply and a nitrogen supply are mixed in a proportioning unit to give a gas with the oxygen content of air. The European Pharmacopoeia has a separate monograph for it, 1684 Air, synthetic medicinal, alongside monograph 1238 for medical air.

## What ISO 7396-3 covers

ISO 7396-3:2025, first published in July 2025, applies to proportioning units that produce synthetic medical air, and air for driving surgical tools, by mixing oxygen and nitrogen in defined proportions. The units are sources of supply for medical gas supply systems feeding a pipeline built to ISO 7396-1. The rule that a supply system has at least three sources of supply is outside ISO 7396-3 and is dealt with in ISO 7396-1.

## Quality criteria

HTM 02-01 (2026) gives synthetic air its own acceptance criteria: oxygen between 95% and 105% of the nominal value of 21% to 22.5%, carbon monoxide up to 5 ppm, carbon dioxide up to 300 ppm and water vapour up to 67 vpm, drier than a −46 °C dew point. It lists quarterly quality control testing for synthetic air plants, as it does for medical air compressor plants.

## Where it is used

HTM 02-01 does not recommend mixing gaseous oxygen and nitrogen from cryogenic liquid supply sources, which it calls synthetic air. Requirements differ by country, so the national specification decides whether a proportioning unit can be a source of supply.

ULTRAAR SC medical air plants from Ultra Controlo take the compressor route: oil-free scroll compressors with air treatment, dryers and sterile pressure reduction, built to EN ISO 7396-1.

### Is synthetic medical air the same as medical air?

No. The European Pharmacopoeia has separate monographs, 1238 Air, medicinal and 1684 Air, synthetic medicinal, and HTM 02-01 sets different acceptance criteria for each.

### Does ISO 7396-3 say how many proportioning units are needed?

No. ISO 7396-3:2025 leaves the rule of at least three sources of supply, and how they combine, to ISO 7396-1.

## Sources

- [ISO 7396-3:2025, Medical gas pipeline systems, Part 3: proportioning units (iso.org)](https://www.iso.org/standard/86136.html)
- [EDQM, Ph. Eur. monograph 1684 Air, synthetic medicinal](https://extranet.edqm.eu/4DLink1/4DCGI/Web_View/mono/1684)
- [EDQM, Ph. Eur. monograph 1238 Air, medicinal](https://extranet.edqm.eu/4DLink1/4DCGI/Web_View/mono/1238)
- [NHS England, HTM 02-01 Medical gas pipeline systems (2026), Part A, 7.1, Table 33 and Table 34](https://www.england.nhs.uk/wp-content/uploads/2016/05/health-technical-memorandum-02-01-medical-gas-pipeline-systems-part-a-design-installation-validation-verification-aug-2026.pdf)
- [ULTRAAR SC datasheet, p. 2](https://www.ultracontrolo.com/products/ultraar-sc)

Reviewed: 2026-10-22. Ultra Controlo engineering. https://library.ultracontrolo.com/answers/what-is-synthetic-medical-air/