The three main standards are: ISO8573 Series / ISO12500 Series / ISO7183. The most commonly used standard is the ISO8573 Series and in particular ISO8573-1:2010.

The compressed air quality standard ISO8573 consists of nine separate parts:

•  Part 1 Compressed air – Contaminants and purity classes

•  Parts 2 to 9 – specifying the methods of testing for a range of contaminants.

ISO8573-1:2010             Specifies the amount of contamination allowable in each cubic metre of compressed air

ISO8573-2:2007             Specifies the test method for oil aerosol content 

ISO8573-3:1999             Specifies the test method for the measurement of humidity

ISO8573-4:2001             Specifies the test method for solid particle content

ISO8573-5:2001             Specifies the test method for oil vapour and organic solvent content

ISO8573-6:2003             Specifies the test method for gaseous containment content

ISO8573-7:2003             Specifies the test method for viable microbiological contaminant content

ISO8573-8:2004             Specifies the test for solid particle content by mass concentration

ISO8573-9:2004            Specifies the test method for liquid water content

Air quality (purity) in accordance with ISO8573-1:2010

ISO8573-1 is the primary document used from the ISO8573 series as it is this document which specifies the amount of contamination allowed in each cubic metre of compressed air.

ISO8573-1 lists the main contaminants as solid particulate, water and oil. The purity levels for each contaminant can be found in the table below.

Compressed air purity levels are shown within ISO 8573.1 in table form. The horizontal headings show the three major contaminants of solid particulate, water and oil. The vertical headings show ‘purity classes’ identified by a number. Alongside each purity class, is a maximum permissible amount of contamination per cubic metre. 

When specifying purity classes, a different purity class should be selected for each contaminant and is written as shown in the following example :

ISO 8573.1 : 2010 Class 1.2.1 

The first number refers to purity level class 1 for solid particulate, the second number refers to purity level class 2 for water and the third number refers to purity level class 1 for oil. 

Selecting an air purity class of 1.2.1 would specify the following air quality: 

•  Class 1 Particulate 

No more than 100 particles in the 0.1 – 0.5 micron size range allowed in each cubic metre of compressed air.

No more than 1 particle in the 0.5 – 1 micron size range allowed in each cubic metre of compressed air.

No particles in the 1 – 5 micron size range allowed in each cubic metre of compressed air.

•  Class 2 Water

No liquid water allowed. Pressure dewpoint of -40°C or better. 

•  Class 1 Oil 

Not more than 0.01mg of oil allowed in each cubic metre of compressed air. This refers to a combined level for both oil aerosol and oil vapour.

The quality of air required throughout a typical compressed air system can vary. The extensive range of filtration equipment available from companies such as BEKO Technologies allows the end user to specify the quality of air for every application, from a general purpose ring main filtration, through to critical clean dry air systems for medical or instrumentation purposes.

Matching equipment to system requirement  

ISO8573-1:2010 Class zero

•  Class 0 does not mean zero contamination

•  Class 0 requires the equipment manufacturer and the end user to agree contamination levels as part of a written scheme/specification

•  The agreed contamination levels for a Class 0 specification should be within the measurement capabilities of the test equipment and test methods as shown in ISO8573 Part 2 to Part 9

•  The agreed Class 0 specification must be written on all documentation to be in accordance with the standard

•  Stating Class 0 without an agreed specification will mean it is not in accordance with the standard

 •  A compressor delivering air to Class 0 will be dependent upon what is drawn into the compressor air intake and will still require purification equipment in both the compressor room and at the point of use for the Class 0 to be maintained at the point of use

 •  Air for critical applications such as instrumentation, food, breathing air or medical air typically will require air to Class 2.2.1 or Class 2.1.1

 •  Class 0 air purity is best achieved at the point of use to minimise cost.