Why Should Compressed Air Be 'Clean'?

Compressed air is an energy carrier used in numerous processes in manufacturing, such as motor power, conveying, filling, blowing, drying, and packaging. However, a significant portion of this air comes into direct or indirect contact with the product, packaging, or process surfaces. The moment this contact occurs, any contaminants in the air become a source of contamination.

Air drawn in from the atmosphere contains dust, aerosols, water vapor, and microorganisms. When a compressor compresses this air, it also concentrates these contaminants; furthermore, compressor oil, abrasion particles, and rust/sediment from the pipes can enter the system. As a result, untreated compressed air poses a serious risk of contamination if it comes into contact with the product.

Therefore, compressed air quality needs to be defined within an objective, measurable, and internationally accepted framework. The ISO 8573 series precisely addresses this need. This content is an informational document prepared to introduce the ISO 8573 framework to manufacturers.

• Air in contact with the product, packaging, or process surface = potential contamination.
• Compression concentrates pollutants in the atmosphere.
• Compressor oil, wear particles, and pipe deposits are additional sources.
• Quality cannot be managed unless it is defined by measurable metrics.

Structure of the ISO 8573 Series

ISO 8573 is not a single document, but a series of complementary standards. ISO 8573-1, the core document of the series, identifies contaminants in compressed air and defines purity (quality) classes for each contaminant. Other sections describe how these classes are measured in the field, i.e., the measurement and sampling methods.

The measurement sections are separated according to the type of contaminant. Thus, a class claim becomes not merely an objective, but a verifiable result based on a defined method. This structure of the series separates the functions of 'defining quality' from 'measuring quality'.

• ISO 8573-1: Contaminants and purity classes (the basis of the framework)
• ISO 8573-2: Method for measuring oil aerosol content.
• ISO 8573-3: Moisture/water vapor content measurement method
• ISO 8573-4: Method for measuring solid particle content.
• ISO 8573-5: Method for measuring oil vapor and organic solvent content.
• ISO 8573-6: Measurement of gaseous pollutants.
• ISO 8573-7: Measurement of viable microbiological contaminants.
• ISO 8573-8: Measurement of solid particles by mass concentration.
• ISO 8573-9: Measurement of liquid water content.

Three Main Pollutants: Particulate Matter, Moisture, and Oil

ISO 8573-1 addresses compressed air quality through three main contaminants: solid particles, water (moisture), and oil. Since these three contaminants can exist in different physical forms (solid, liquid, vapor, aerosol), each is evaluated on its own separate scale.

Solid particles include dust, rust, wear products, and particles from the external environment, and can affect valves, nozzles, and sensitive surfaces. Water is critical both in terms of corrosion and freezing risks, as well as microbial growth. Oil, which can be found in liquid, aerosol, and vapor forms, is one of the least acceptable contaminants in sensitive processes such as food, pharmaceuticals, and electronics.

Because the standard classifies these three contaminants separately, a system might be in a very clean class in terms of particulate matter, for example, but in a lower class in terms of oil. This approach allows each process to focus on its own critical contaminant.

• Solid particles: dust, rust, abrasive particles, and external particles.
• Water/moisture: risk of corrosion, freezing, and microbial growth.
• Oil: liquid, aerosol and vapor forms are all important separately.
• Each pollutant is classified separately; no single, general rating is given.

Purity Class Logic (Class 0 – Class X)

ISO 8573-1 defines purity classes for each pollutant, numbered from the strictest to the laxest. The general logic is: the smaller the class number, the lower the amount of pollutant allowed, meaning the air is cleaner. Additionally, for particles, the number of particles allowed according to their size ranges is also considered.

Class 0, often referred to as the most stringent level in the series, is not a fixed numerical limit; it requires the user or equipment supplier to define and demonstrate better performance than the relevant class in a written technical specification. Therefore, the designation 'Class 0' alone is meaningless without documented targets and measurements behind it.

A quality objective is typically expressed in three numbers, representing particle, water, and oil classes, respectively. Precise class-limit numbers are deliberately omitted in this text; the aim is to convey the class logic. The numerical class values corresponding to a specific application must be verified from the current text of the standard and from the assessment of a qualified engineer.

• Lower grade number = fewer pollutants = cleaner air.
• The number per size range in the particle is also taken into account.
• Class 0: not a fixed limit, but the strictest grade defined by written specifications.
• The target is expressed with separate class values for particle-water-oil.

The Concept of Pressure Dew Point (PDP)

At the heart of humidity classifications lies the concept of the pressure dew point (PDP). The PDP is the temperature at which water begins to condense under compressed air pressure. The lower the PDP, the drier the air and the less risk of condensation.

Defining the PDP at the operating pressure is important because the dew point changes when the same air expands to atmospheric pressure. Therefore, when evaluating moisture performance, the dew point should always be considered in conjunction with the relevant pressure condition. For lines at risk of freezing or sensitive filling processes, low PDP targets can be crucial.

The moisture classifications in ISO 8573-1 are based on these PDP values for water in vapor form, while water in liquid and aerosol forms is considered separately. Thus, moisture is positioned as a pollutant evaluated according to its form, not a single temperature value.

• PDP: the temperature at which water begins to condense at the operating pressure.
• Lower PDP = drier air = less risk of condensation.
• The dew point should always be read in conjunction with the relevant pressure condition.
• Water vapor is evaluated with PDP, and liquid/aerosol water is evaluated separately.

Measurement Points and Sampling

A purity class claim is only valid at a specific point in the system. ISO 8573-1 states that classes can be defined regardless of location in the system; however, in practice, air quality varies significantly between the compressor outlet, after the dryer, at the filter outlet, and at the point of use. Therefore, where the measurement is taken directly affects the result.

Measurement and sampling are performed according to the methods described in the relevant measurement sections (particle, moisture, oil aerosol, oil vapor, etc.). Accurate results are critical to sampling conditions, including steady-state line operation, appropriate flow, and clean sampling lines. Improper sampling can lead to results that deviate from actual performance.

Therefore, when evaluating whether a target has been met, the target class, measurement point, measurement method, and measurement conditions should be considered as a whole. Planning and interpreting the measurement strategy is a matter requiring the technical assessment of a qualified engineer.

• Quality differs at different points in the system: the output is different, the point of use is different.
• The measurement method is defined in the relevant section according to the type of pollutant.
• A steady regime, proper flow, and a clean sample line are critical for the result.
• The target, measurement point, and method should be evaluated together.

Which Sectors and General GMP/Food Safety Expectations?

Compressed air quality is crucial, especially in sectors where air comes into contact with the product or packaging. In food and beverage production, strict requirements regarding oil and microbiological safety are generally emphasized for air in contact with the product. In pharmaceutical and GMP-compliant production, the contact air is expected to be managed according to a defined and traceable quality objective.

In electronics and semiconductor manufacturing, particle and moisture control is critical for protecting sensitive components. In paint and surface treatment applications, oil and water are major causes of surface defects. In medical applications, air purity is directly related to safety.

In general, food safety and GMP approaches are consistent with the measurable class logic provided by ISO 8573, with risk assessment, defined quality objectives for contact compressed air, and expectations of regular verification. Which classes are required for a specific facility should be determined by a qualified engineer's assessment based on the product, process, and relevant industry requirements.

• Food and beverage: priority given to fat and microbiological control.
• Pharmaceuticals/GMP: defined, traceable quality target expectation.
• Electronics/semiconductors: particles and moisture are critical.
• Paints and medical: oil, water, and purity directly affect quality/safety.

Information Note and Scope of AES

AES (aesinn.com) operates as a TÜRKAK-accredited Type A inspection body. AES's accreditation scope is '6.1 Electrical Installation'. This content is an informational study aimed at introducing compressed air quality and the ISO 8573 framework, and is not a statement of AES's accreditation scope.

AES is NOT an accredited inspection/certification body in this context. The content is for informational purposes only and is subject to technical evaluation by an authorized engineer.

Determining the class objectives, selecting measurement methods, and interpreting results under ISO 8573 must be based on the current text of the standard and the assessment of a qualified engineer. The information contained in this document does not replace an on-site technical assessment.

• AES: A TURKAK accredited Type A inspection body.
• Accreditation scope: '6.1 Electrical Installation'‘
• This content is for informational purposes only and does not constitute a statement of scope.
• Classification and measurement decisions require expert engineering assessment.

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Frequently Asked Questions

What exactly does ISO 8573 define?

ISO 8573 is a series of standards defining contaminants in compressed air and their corresponding purity classes. The core section, ISO 8573-1, identifies the contaminants and their classes, while the other sections (8573-2 through 8573-9) describe how these contaminants should be measured. This informational text aims to introduce the framework; precise class-limit values should be verified against the current text of the standard.

Does Class 0 mean 'zero pollution'?

No. Class 0 does not mean zero pollution or a fixed numerical limit. As the strictest measure, it requires the user or equipment supplier to define and demonstrate better performance than the relevant class in a written technical specification. Therefore, a 'Class 0' claim must be evaluated in conjunction with the written specification and measurement behind it.

Why is the pressure dew point (PDP) important?

PDP (Pelvic Dew Point) is the temperature at which water begins to condense under compressed air operating pressure, and it forms the basis of humidity classifications. A lower PDP means drier air and less risk of condensation. Since the dew point varies depending on pressure, it should always be evaluated in conjunction with the relevant pressure condition.

Why are three separate classes discussed for a system instead of a single quality metric?

Because ISO 8573-1 classifies the three main contaminants (solid particles, water/moisture, and oil) separately. A system might be in a very clean class in terms of particles but in a lower class in terms of oil. Therefore, the quality target is usually expressed with separate class values for particles, water, and oil.

Does the point where the measurement is taken affect the result?

Yes. Air quality varies significantly between the compressor outlet, dryer, and after-filter, and the point of use. Therefore, a class claim only makes sense when considering the point of measurement, the measurement method used, and the measurement conditions.

Does AES conduct any measurements or certifications within this scope?

AES is not an accredited inspection/certification body in this context. AES's TÜRKAK accreditation scope is '6.1 Electrical Installation'. This content is for informational purposes only and is within the framework of authorized engineer technical evaluation.