Air Quality Testing

Compressed air is used in a wide variety of manufacturing and commercial applications, and in some industries the quality of the air is extremely important.

Compressed air typically has three main contaminants which are water, particles and oil.

Contaminants originate from three general sources:

  1. Contaminants in the surrounding area of the compressor are drawn into the air system through the intake of the air compressor. Ingested contaminants appear in the form of water vapour, hydrocarbon vapours, natural particles and airborne particulates.
  2. As result of the mechanical compression process, additional impurities may be introduced into the air system. Generated contaminants include compressor lubricant, wear particles and vaporised lubricant.
  3. A compressed air system will contain in-built contamination. Piping distribution and air storage tanks, more prevalent in older systems, will have contaminant in the form of rust, pipe scale, mineral deposits and bacteria.

If the compressed air system has not been designed for your industry specific requirements, it has potential to cause major problems to product quality and operating expenses.

This is especially important for industries such as food and beverage and pharmaceutical if the air comes into direct contact with the product or indirect contact with the packaging.

In order to be compliant with industry standards, the quality of your compressed air should be considered as part of the hazard analysis and critical control point (HACCP) activity.

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At Direct Air, we offer advice about your current compressed air system and provide quality solutions to ensure you achieve the air quality your business requires. To achieve the stringent air quality levels required for today’s modern production facilities, a careful approach to system design, commissioning and operation must be employed.

Treatment at one point alone is not enough and it is highly recommended that the compressed air be treated prior to entry into the distribution system to a quality level suitable for protecting air receivers and distribution piping.

Point of use purification should also be employed, with specific attention being focused on the application and the level of air quality required.
This approach to system design provides the most cost-effective solution for high quality compressed air.

Before we do anything, we ask the question: ‘what air quality do you require?’ We ensure our analysis and recommendations align 100% with industry standards, including taking into account environmental factors in accordance with your system design.

A thorough understanding of compressed air quality and testing is indispensable when designing your system to achieve the purity levels your application requires.

The International Organisation for Standardisation (ISO) sets three such standards, ISO 8573, ISO 12500, and ISO 7183.

Which standards you should apply will depend on the specific contaminants your aim to remove and the purification equipment you will rely on to do so.

Compressed air purity classes for particles

ISO8573-1:2010 CLASS

Solid Particulate Water Oil
Maximum number of particles per m³ Mass Concentration mg/m³ Vapour Pressure Dewpoint Liquid g/m³ Total Oil (aerosol liquid and vapour)
0.1 – 0.5 micron 0.5 – 1 micron 1 – 5 micron mg/m³
0 As specified by the equipment user or supplier and more stingent than Class 1
1 ≤ 20,000 ≤ 400 ≤ 10 ≤ -70℃ 0.01
2 ≤ 400,000 ≤ 6,000 ≤ 100 ≤ -40℃ 0.1
3 ≤ 90,000 ≤ 1,000 ≤ -20℃ 1
4 ≤ 10,000 ≤ +3℃ 5
5 ≤ 100,000 ≤ 7℃
6 ≤ 5 ≤ -10℃
7 5 – 10 ≤ 0.5
8 0.5 – 5
9 5 – 10
X > 10 > 10 10

Air Quality Testing

Direct Air offers air quality testing services to meet your systems specific requirements.

ISO 8573 Testing 

ISO 8573 is an internationally recognised standard that defines major contaminants in compressed air and presents a comprehensive system for air purity designations. The implementation of this standard supports accurate testing of the major contaminants in compressed air – particles, water, oil, and microorganisms. ISO 8573 is used widely throughout the compressed air industry, acting as a common language available to the manufacturer, compressed air system supplier, and compressed air testing laboratory.

For applications where the quality of compressed air is critical, Direct Air can measure to the limits of ISO8573 standards.

If the compressed air system has not been designed for your specific requirements, it has the potential to cause major problems to product quality and operating expenses. We look after many of the UK’s leading food, beverage and pharmaceutical companies and can assist in this matter.

Our trained engineers can visit your site with our calibrated ISO 8573 air quality testing equipment*. We can conduct periodic compressed air purity testing at point of use with certified results that can be measured against ISO: 8573-1 standards, testing for particle content, dew point and oil vapour concentration.

At Direct Air, we also offer advice about your current compressed air systems and provide quality solutions to ensure you achieve the air quality your business requires.

ISO 8573-1:2010 Class 0 Compressed Air:

  • Does not mean zero contamination
  • Has purity levels jointly defined in writing by users and/or equipment manufacturers or suppliers
  • Does not account for purity levels greater than those measurable by methods defined by ISO 8573-2 to 8573-9 standards

* There is no air quality testing equipment available to test oil measurement onsite. However, it is a great tool for quality testing, as vapour is always present alongside liquid and aerosol oil but can still be present when the liquid and aerosol contents are filtered out. Using a PID sensor can provide accurate and repeatable measurement of vapour in high purity systems, to guide maintenance and provide client confidence in the effectiveness of the air treatment system.


Breathing Air Testing

All employers have a duty of care to their employees to ensure that the breathing air they are supplied with is adequate for the respiratory protective equipment (RPE) they are using and safe to breathe, whether this is supplied via a fresh hose or a source of compressed air.

Compressed gas for breathing should not contain contaminants at a concentration which cause harmful effects. In any event, all contaminants shall be kept to as a low a level as possible and shall be less than 1/10 of a national 8-hour exposure limit.

Periodically testing air quality makes sure that the control measures you have put in place are delivering the air quality required by BS EN 12021. The frequency of such tests should be the result of a risk assessment and take place at least every three months if not sooner. Direct Air can perform regular air quality checks to help keep your facility safe and compliant to current regulations and advised standards. Because compressors themselves can generate and concentrate a wide range of contaminants, we take extra care in assuring air quality.

Records of completed breathing air checks must be retained in either physical or electronic form for a minimum of 5 years. Direct Air can perform regular air quality checks to help keep your facility safe and compliant to current regulations and advised standards.

Do you require Class 1 air?

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We offer complete compressed air solutions including design, installation, servicing & WSE inspections.


We consider your entire compressed air system from the compressor to downstream equipment & pipework.

Industry / Sector

Whatever the industry and whatever the application, there's a growing demand for higher-quality compressed air.