Wednesday, September 22, 2010

Air Compressors for Contaminants and Air Purity Classification

ISO 8573 Certification of Air Compressors for Contaminants and Air Purity Classification

Rudy Pina

The undertaking to certify a compressed air system for purity classification in accordance with the ISO document 8573 can result in the Original Equipment Manufacturer (OEM)’s opening the proverbial “Pandora’s Box.” The manufacturer may not realize, at the onset, the potentially massive undertaking from an engineering and cost standpoint that may be required.

In order to minimize unforeseen obstacles, such as costly engineering modifications, facility renovations, and/or management commitments to this undertaking of qualifying an existing or designed air compressor to the standard “Compressed Air Contaminants and Purity Classes ISO 8573 Part 1,” a series of fundamental steps should be pondered in order to determine if your compressor will meet a set of prescribed requirements in order to achieve the desired classification.

The first step, for all interested parties, is to become familiar with the appropriate documents. ISO 8573 is broken into nine equal parts as listed in INTERNATIONAL STANDARD ISO 8573-1:2001 as follows:

Part 1: Contaminants and Purity Classes
Part 2: Test methods for aerosol content
Part 3: Test methods for measurement of humidity
Part 4: Test methods for solid particle content
Part 5: Determination of oil vapor and organic solvent content
Part 6: Determination of content of gaseous contaminants
Part 7: Test methods for viable microbiological contaminant content
Part 8: Contaminants and purity classes (by mass concentration of solid particles)
Part 9: Test methods for liquid water content

Note: Each part addresses the requirements to certify the compressor. Part 1, “specifies purity classes of compressed air in respect of particles, water, and oil regardless of the source of the compressed air.” 1

This article will address only those compressors used to supply air for general use where the quality is measured in accordance with specifications set forth in one, or a combination, of the specifications in 8573. Other applications may or may not apply. In addition this article is a subjective approach to the assessment of the compressor and may or may not apply for all applications regarding the attempt to classify a compressor to the ISO standard 8573.2

There are various compressor designs which include but are not limited to: screw type, single stage centrifugal, and oil driven compressors, however each has an intake and out-take finished product.

The manufacturer should be aware that the initial design of the air compressed system may not lend itself to accurately determine if it can be inspected and tested in order to meet the classification criteria as stipulated in Part 1: Purity Classification. Therefore a few simple questions should be considered:

A. Has a target classification been selected? Considerations as to the different aspects of the standard and the design of the compressor should be made so that the air compressor can accurately be tested. A CLASS ZERO is the most stringent and most costly classification to attain.

B. Is the compressor modified from an engineering standpoint, to allow air testing to be performed that accurately measures the air quality of the compressor? For instance a measurement of the finished product (compressor air discharge) will allow you to characterize the air quality and subsequently classify your compressor. However if the compressor’s air intake (compressor ambient air inlet) is not considered prior to the assessment, the outcome (compressor air discharge) may result in a higher or less favorable than expected classification.

C. Did you select the ISO 8573 sections which you wish to use to classify your compressor? For example if you want to classify your compressor as OIL FREE, you may want to review ISO 8573 Part(s) 1, 2, 4, 5, and 6. If microbiological assessment is desired Part 7 may be appropriate.

D. Select the appropriate section(s) for which you plan to certify your compressor. The ISO standards address similar attributes in different ISO 8573 sections, therefore careful planning to ensure the appropriate section is used for the assessment.

One of the most important, yet overlooked, aspects of certifying a compressor is the environment where the testing will be performed. The environment to conduct the assessment is selected; however, in some cases very little attention is given as to the initial quality of air the compressor will use in its operational phase. This may be important, especially when critical and extremely low classifications are sought. A classification of ZERO may require that the air intake also be equal to the quality of air sought for in the classification. Some important factors to consider here if classification is sought:

A. Is there a pre filter and if so what are the specifications of the pre filter? What is the particulate micron pore size rating? A pre filter micron rating may affect the outcome of the test classification. Serious consideration should be given to assessing the classification sought and the particulate micron filtration efficiency of the pre filter in order to achieve the target classification in some cases.

B. Are there environmental conditions that may adversely impact the classification process? Dust storms, oil vapor, and/or a climate inversion may present complications to the ultimate goal of achieving the expected classification. If any one of these attributes are encountered, a closed environment similar to a pharmaceutical cleanroom may be required to achieve the target classification. Specifically the quality and characteristics (micron size and concentration of particulates) of the environmental air should be assessed prior to testing to ensure the quality of air-intake does not adversely affect the particulate test results.

The compressor, as designed, will supply air that is potentially not at the operating characteristics the manufacturer wishes to be at for the classification process. Here are some tips which may need to be considered before the assessment process starts:

A. Have your compressor prepared for testing. Engineering sampling ports may be required to sample UPSTREAM AND DOWNSTREAM flow patterns. Sampling ports can be described as fittings which allow for air sampling in the flow-stream. The downstream is considered finished product (air discharge), and the upstream is considered the control sample and is usually the inlet air. A compressor should be engineered with sampling ports to sample both sources of air. A clear understanding of this section is required to ensure accurate assessment.

B. Have your compressor cleaned for testing. Approved solvents are available that may be useful in cleaning any foreign matter, particulate, oil deposits, and or gasket lubricants from the air pathway to minimize potentially misleading results.

C. Remove and replace stored water supplies for Water Jacketed compressors if microbiological testing is to be performed. Stagnant water may harbor bacteria over extended periods of time.

The approach to classification should take into consideration the attributes desired, and subsequently the selection of the appropriate ISO 8573 standard, and appropriate Part. Once this has been determined, a methodical approach based on the recommendations (at a minimum) listed here should be considered.

In addition the sampling apparatus in some cases is diagramed for the actual testing in the ISO 8573 Parts 1 through 9. If the sampling apparatus is not available then in-house design and or outsourcing will be required.

This article does not address the approach to testing due to the diversity of compressor design, size, and variability and approach to testing. Professional and experienced assistance is recommended to ensure compliance to the ISO Standard 8573 and ultimately interpretation of results.


  1. International Standard ISO 8573-1: 2001 Compressed Air- Part 1: Contaminants and Purity Classes
  2. Testing Compressed Air Lines for microbiological contamination, Controlled Environments Magazine Vol.9 No. 5, May 2006.

Rudy Pina is President of Dynatec Scientific Laboratories, Inc. He has 30 years of laboratory experience in the medical device industry, and most recently has acquired third party recognition for air compressor certification for ISO 8573 in accordance with TUV SUD America. Dynatec is locat

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