17 September, 2021

ISO8573 – When quality counts

01 September, 2021

Roy Brooks, technical development officer for the British Compressed Air Society (BCAS), talks us through ISO 8573, the international standard for air purity and explains why operators should consider all parts of a compressed air system during the specification process.


Compressed air is not clean. In fact, it can contain up to 10 different contaminants, which need to be treated correctly. These tend to be combined into three distinct categories: particles (including viable and non-viable microbiological organisms), water and oil. ISO 8573-1 refers to the main contaminants in this format.

When selecting purification equipment, don’t forget that contaminants will be in one of three different phases (states of matter). For example, water and oil in a compressed air system will be found in liquid form, as an aerosol (fine mist) and in a vapour (gaseous) phase and a different purification technology will be required depending upon the phase of the contaminant.

Which standard?

Depending on the application, there are number of different compressed air standards and best practice guidelines which can assist. ISO8573 series is the most commonly used standard for compressed air (excluding breathing air or medical air). It is made up of nine separate parts.

Part 1 refers to air purity (quality), while parts two to nine provide details on the equipment and methodology to be used to measure for different contaminants in a compressed air system (and meet the air purity (quality) classifications shown in part one).

ISO8573-1 – International Standard Relating to Compressed Air Purity (Quality) ISO8573-1 provides guidance on specifying the air purity (quality) required for the entire compressed air system and/or for individual usage points, based upon application requirements.

In addition, there are also specific requirements for compressed air that comes in to direct or indirect contact with food or beverage products as well as the HTM02-1 purity recommendation for medical and surgical air and HTM2022 for dental air. Finally, BS EN 12021:2014 is the specified standard for breathable air, indicating maximum permitted contaminant levels both in the UK and the EU.

Specifying correctly

To achieve the degree of air purity (quality) specified by ISO8573-1, a careful approach to system design, commissioning and operation must be adopted.

Best practice is to treat compressed air prior to entry into the distribution system and at critical usage points and application, to ensure that contamination already in the distribution system is removed.

Purification equipment should ideally be installed where the air is at the lowest possible temperature, i.e., downstream of air receivers, but also protected from freezing. Point-of-use purification equipment should be installed as close as possible to the application.

To allow correct sizing and selection of purification equipment, operators should have the following operating parameters to hand:

The maximum compressed air flow rate into the filters/dryer

The maximum operating temperature into the filters/dryer

The maximum ambient air temperature where the equipment is to be installed (required for some dryer technologies)

The required dewpoint (dryers)

Individually, each of the primary operating parameters can influence product sizing, however collectively they can have a major impact on product sizing and performance. Many manufacturing plants only need a proportion of the compressed air to be treated to a very high purity (quality). In these cases, excellent savings are achievable by treating all the generated air to the minimum acceptable level and improving the purity (quality) to the desired level at the usage point.

If most of the compressed air is needed at a high purity (quality), it can make sense to treat all the compressed air to the level required by the highest purity (quality) application. To find out more about BCAS’s dedicated ISO 8573 training course visit https://bit.ly/BCAS-ISO8573.

In addition, detailed guidance can be found in the ‘Filtration and Drying of Compressed Air – Best Practice Guide 104 at www.bcas.org.uk/airtreatment.




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