# ISO 8573-1: compressed air purity classes

ISO 8573-1:2010 is the ISO standard that defines purity classes for compressed air with respect to particles, water and oil. It is a general compressed air standard: hospitals use it for technical air, while the quality of medical air is set by the pharmacopoeia.

## What the standard covers

ISO 8573-1, Compressed air, Part 1: Contaminants and purity classes, gives a common way to state how clean compressed air is. A purity designation gives one class each for particles, water and oil, the three contaminants that have purity classes in the standard. It is a general compressed air standard, not a medical gas monograph.

The Portuguese ACSS specification for technical compressed air in hospital buildings, ET 08/2010 (last revised November 2025), shows how it is used: centrally produced technical air must meet at least ISO 8573-1:2010 class [2:4:2].

## Edition in force and status

The edition in force is ISO 8573-1:2010, the third edition, published in April 2010. On 22 October 2026 ISO lists it at stage 90.92, to be revised, so a new edition may follow. Check iso.org before fixing the edition in a specification.

## What it means for a hospital or designer

- Medical air is not defined by an ISO 8573-1 class. In Europe its quality is set by the European Pharmacopoeia monograph Air, medicinal (1238), which makes medical air a medicine with defined limits.
- Technical (non-medical) hospital air is specified with ISO 8573-1 classes. In Portugal, [ACSS ET 08/2010](https://library.ultracontrolo.com/standards/acss-et-08/) sets class [2:4:2] as the minimum, and the medical gas specification is a separate document, ACSS ET 03/2006.
- Oil: EDQM notes that the oil test in monograph 1238 is only relevant when the air is produced with an oil-lubricated compressor, so the compressor choice affects how medical air is tested.
- PSA oxygen plants: the WHO technical specifications for PSA oxygen plants (interim guidance, 8 June 2020; superseded by WHO's technical specifications of 31 December 2024) listed ISO 8573-1 among the product performance standards and accepted a feed air compressor that is oil-free, filtered oil-injected or oil-lubricated rotary screw.

## Related standards

- Ph. Eur. 1238: Air, medicinal.
- [ACSS ET 08/2010](https://library.ultracontrolo.com/standards/acss-et-08/): technical compressed air in Portuguese hospital buildings.
- [WHO technical specifications for PSA oxygen plants](https://library.ultracontrolo.com/standards/who-psa-plant-specifications/) (2020).

In the Ultra Controlo range, the ACIH industrial compressed air system for hospitals exists because hospital standards prohibit the use of medical air for industrial purposes, and it complies with the ACSS ET 08/2010 technical specifications, according to its datasheet. ULTRAK activated carbon towers are rated ISO 8573-1 quality class 0/1 for oils, according to their datasheet.

### Is an ISO 8573-1 class the same as medical air?

No. ISO 8573-1 classes, including class 0, describe contaminant levels in compressed air; medical air in Europe has to meet the European Pharmacopoeia monograph Air, medicinal (1238).

### What does [2:4:2] mean in ACSS ET 08/2010?

It is the minimum ISO 8573-1:2010 purity designation that ACSS sets for centrally produced technical compressed air, with one class each for particles, water and oil.

## Sources

- [ISO 8573-1:2010, Compressed air, Part 1: Contaminants and purity classes (iso.org)](https://www.iso.org/standard/46418.html)
- [ACSS ET 08/2010 V.2025, Especificações técnicas para ar comprimido técnico em edifícios hospitalares](https://www.acss.min-saude.pt/wp-content/uploads/2016/10/ET-08_2010_V.2025_VF.pdf)
- [ACSS, list of technical specifications](https://www.acss.min-saude.pt/2016/10/04/especificacoes-tecnicas/)
- [EDQM Knowledge database, monograph 1238 Air, medicinal](https://extranet.edqm.eu/4DLink1/4DCGI/Web_View/mono/1238)
- [EDQM, history of monograph 1238](https://extranet.edqm.eu/4DLink1/Web_mono_hist?1238)
- [WHO, Technical specifications for PSA oxygen plants: interim guidance (8 June 2020)](https://iris.who.int/server/api/core/bitstreams/d53996d5-380c-44ae-9fe8-9e529d3270cd/content)
- [ACIH datasheet, p. 2](https://www.ultracontrolo.com/products/acih)
- [ULTRAK datasheet, p. 2](https://www.ultracontrolo.com/products/ultrak)
- [WHO, Technical specifications for health facility based medical oxygen systems (31 December 2024), note on the oxygen generator plant specification (supersedes the 2020 interim PSA specifications)](https://iris.who.int/server/api/core/bitstreams/ff437601-add3-44c8-8149-b85f0cdb2b52/content)

Reviewed: 2026-10-22. Ultra Controlo engineering. https://library.ultracontrolo.com/standards/iso-8573-1/