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Setting the standard for compressed air quality

10 January 2024

THE BRITISH Compressed Air Society’s (BCAS) best practice guide entitled The Filtration and Drying of Compressed Air helps operators and specifiers make an informed choice on which type of compressed air treatment equipment is best suited to the air quality required. There are a variety of different compressed air standards that should be considered when assessing the air purity levels required for the application.

Introducing the guide

The guide was produced with the input of leading engineers from BCAS members in the field of air treatment and purification. It is designed to help demystify not only the selection of the correct air treatment equipment but to provide practical advice on which contaminants can be present and their impact on the processes that compressed air is being used for.

It is aimed at typical industrial compressed air applications operating at low pressure, with a range between 7 bar g to 20 bar g.  

Selecting the correct air purity (quality)

Depending on the application for which the compressed air is to be used, there are number of different compressed air standards and best practice guidelines which can assist the end user. 

This is as an important consideration as any oversights as this early specification stage can impact significantly on the quality of the air being used by the process, potentially resulting in product spoilage or production downtime.

Prior to the purchase of new compressed air treatment equipment, the user should assess carefully the air purity (quality) requirements of the system or application. This information should be provided to all suppliers to assist during the product selection and specification.

International standards - ISO8573 series

The ISO8573 series is the most commonly used standard for compressed air (excluding breathing air or medical air). It comprises nine separate parts. Part one 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.

ISO8573-1 - International standard relating to compressed air purity (quality)

ISO8573-1 provides a methodology for specifying the air purity (quality) required for the entire compressed air system and/or for individual usage points, based upon application requirements. It also allows equipment manufacturers to demonstrate product performance easily and specify purification equipment to meet the end user’s air purity (quality) specification.

In ISO8573-1, compressed air contaminants are grouped into particulate, water and total oil.  Different levels of contamination are then assigned ‘purity (quality) classes.’  

Food grade air

The Food Grade Compressed Air Best Practice Guideline 102 was prepared by BCAS with advice from the British Retail Consortium Trading. It details the HACCP process and enables informed decisions to be made on the type of compressed air equipment that is required, how it should be installed as well as maintained and importantly the requirements for the air purity (quality).

Microbiological contaminants and ISO 8573-7

Microbiological contaminants such as bacteria require water to maintain viability.  To reduce the viability for microbiological contaminants to be present in the compressed air system, it is important that the humidity of the compressed air is reduced.

Typically, adsorption dryers (commonly described as desiccant dryers) provide the highest levels of compressed air dryness and are best suited for reducing the humidity to levels that are low enough to suppress microbiological activity within the system.

Using a test method specified in ISO 8573-7, the presence of microbiological contaminants can be established. The BCAS best practice guideline recommends that compressed air purity (quality) should be tested and verified at least twice per year, unless otherwise identified in the HACCP (Hazard analysis critical control point) process. 

Breathing air

The specified standard for breathable air is EN 12021: 2014 - 'Respiratory protective devices and states that: "Compressed gas for breathing shall not contain contaminants at a concentration which can cause toxic or harmful effects. In any event, all contaminants shall be kept as low as possible and shall be less than one tenth of a national eight hour exposure limit. For breathing air only, the limit shall be less than one sixth of a national eight hour exposure limit. 

For breathing at hyperbaric pressures greater than 10 bar or exposure times greater than eight hours, the levels shall be revised to consider the effects of pressure and exposure times."

BS EN 12021:2014, the UK National Annex NA.4.2, states: "Samples should be taken and analysed at least every three months or more frequently if there has been a change in, or concerns relating to, the production process".

Assisting with the entire specification process

The Filtration and Drying of Compressed Air guide does not only provide guidance on the relevant standards applicable for air purity (quality) assurance, It is also invaluable during the entire specification process, covering all stages of system design; from an overview of the sources of contamination, such as solid particles, water and oil to the extensive range of air purification technologies available and how these operate, including after-cooling, dryers, air receivers, filtration grades and condensate management.

With compressed air energy costs now a major contributing factor to a site’s overall electricity consumption, the guide also focuses on the varying energy efficiencies of the different treatment technologies available as well as guidance on the ongoing maintenance of the system.

A hardback copy or digital download version of the Filtration and Drying of Compressed Air guide can be purchased from the BCAS online shop at: https://elearning.bcas.org.uk/publications/


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