ISO 8573-1 Guide to the quality of compressed air for food production

Compressed air is one of the least visible but most important "ingredients" in modern food and beverage production. It is used in packaging, products and equipment in the dairy industry, bottled water and many other applications, but its quality is often unknown or considered "good enough".

ISO 8573-1 is the international standard that defines what "clean" compressed air actually means. It classifies air quality according to particles, water and oil so that companies can prove that they protect product integrity, comply with food safety standards and operate efficiently. Filters and compressed air dryers are the tools that make this standard a reality: They transform the air delivered by a compressor into air that is safe for food and reliable for audits, while keeping energy and life cycle costs under control.

This article provides a comprehensive overview of the ISO 8573-1 classification for compressed air and shows how quality managers and production managers can ensure product and process safety with an effective filtration strategy.

What the standard covers (and what it doesn't)

ISO 8573-1 defines cleanliness classes for compressed air based on three types of contaminants: Solid particles, water (as moisture, liquid water or vapor) and oil (as liquid, aerosol and vapor). It does not itself define microbial limits, and gases such as carbon monoxide or sulphur dioxide are dealt with in other parts of the ISO 8573 series or in separate guidelines. In practice, ISO 8573-1 is used in food and beverage production together with food safety systems such as SQF, BRC or FSSC 22000.

For quality managers, this means that ISO 8573-1 forms the technical basis for statements such as "compressed air must be clean and must not pose a risk to food safety". It provides concrete numerical limits for each contamination dimension that you can test, document and present to auditors.

How ISO 8573-1 cleanliness classes work - the [A:B:C] system

The standard expresses air quality with a three-part designation [A:B:C]. The first position indicates the particle class, the second position the water class (usually via the pressure dew point) and the third position the oil class. Lower numbers indicate cleaner air; class 0 indicates a customer-specific requirement that is stricter than class 1 and must be defined with a numerical limit value.
For example, the designation [2:2:1]:
- Particle class 2: Particle count limited to a defined maximum in the relevant size ranges.
- Water class 2: Pressure dew point of -40 °C or better, which is cold enough to significantly limit the risk of condensation and microbial growth.
- Oil Class 1: Total oil content (liquid, aerosol and vapor) at or below 0.01 mg/m³.

Description: Overview table in English for the compressed air classes according to ISO 8573-1

These designations are independent of the compressor type. They describe the air quality at a specific point in the system, e.g. at the outlet of a dryer or at an end-use filter.

Compressors produce compressed air, but they do not determine its final quality. Even oil-free compressors draw in dust, moisture and hydrocarbons from the atmosphere, and the compression process itself concentrates contaminants. The elements that actually deliver a specific ISO class are the air treatment components: Dryers, which control humidity and dew point, and filters, which remove particulates and oil.

An adsorption dryer makes it possible to achieve water class 2 or better by constantly reaching a dew point of -40 °C. Coalescence filters, Particle Filters and Activated Carbon Filters ensure compliance with the particle and oil classes by removing solid contaminants as well as oil aerosols and vapors. According to the measuring point for ISO 8573, sterile end-use filters form a final barrier for microorganisms and the finest particles at critical points. When testing conformity with ISO 8573-1, the decisive question is not "Which compressor?", but "Which dryer and which filter chain at which points?".

Food safety, regulations and audits

Food safety regulations and standards address compressed air as a potential source of indirect food additives and contamination. In the US, 21 CFR 110.40 requires that compressed air in direct contact with food or food contact surfaces must be handled in a manner that does not contaminate food. Global programs such as SQF, BRC and FSSC 22000 require facilities to consider compressed air in their prerequisite programs, including the definition of acceptable quality, controls and verification through testing.

Industry bodies such as the British Compressed Air Society (BCAS) and organizations working on guidelines for food grade compressed air have translated this into practical recommendations. For example, a common guideline for direct contact applications is ISO 8573-1 class [2:2:1], while for indirect contact applications (where the air is discharged close to the product) [2:4:2] can be specified. The German VDMA guidelines suggest similar or slightly stricter classes, depending on whether the product is dry, moist or sterile. These recommendations are increasingly being used as reference points by auditors and customers.

Direct vs. indirect contact - where the risk really lies

Direct contact means that the compressed air touches the product or primary packaging in such a way that contamination could realistically be transferred. Typical examples include blowing out PET bottles before filling in a water or dairy plant, transporting powders such as milk powder or cocoa, or using air knives to dry or clean surfaces in contact with the product. In these cases, compressed air is essentially a food contact medium.

Indirect contact includes applications in which the air is not directed directly at the product, but is expelled in its vicinity. Examples of this include blowing off contaminants from the outside of Packaging or driving pneumatic components whose exhaust air enters the production environment. Indirect contact also poses risks - contaminants can settle on surfaces - but the likelihood and severity are generally lower than with direct contact.

Quality managers need to differentiate between these scenarios as they determine the required class according to ES 8573-1 at each point. Direct contact applications typically require a more stringent class and a more robust combination of compressed air dryers and filters, especially sterile filtration at the point of use.

Hidden contaminants - microbes, water and oil

Ambient air naturally contains bacteria, spores and fungi. When this air is compressed, the concentration of microorganisms increases and any moisture present in the system creates an ideal environment for the growth of biofilms in pipes, Header Tanks and filters. Biofilms can regularly release large quantities of microorganisms into the air stream, often without this being visually apparent. For ready-to-eat products and sensitive categories such as UHT milk or bottled water, this poses a serious risk to safety and shelf life.

Water is also a mechanical problem. Condensation can cause powder to clump and stick in hoppers and filling lines. Oil aerosols and vapors from lubricated compressors or from hydrocarbon sources in the environment can cause a foreign taste and odor and violate both legal limits and customer specifications. Filters and compressed air dryers are key tools to remove water and oil and limit microbial risk by controlling the dew point and ensuring fine and sterile filtration when required.

Dryers - control of water and microbial risk

The water class in ISO 8573-1 is expressed as a pressure dew point. Class 2 (corresponding to a dew point of -40 °C) is the typical benchmark for direct contact with food, as no condensation can occur in the piping at this dryness under normal operating conditions. Suitable drying technology is required to reliably achieve this dew point.

Refrigeration dryers cool compressed air down to a dew point of around +3 °C (class 4), which is sufficient for many general industrial applications and some indirect food contact applications. For direct contact and more critical applications, adsorption dryers are required. These systems use adsorption materials to remove moisture from the air and can deliver dew points of -40°C (Class 2) or -70°C (Class 1) depending on the configuration.

From a quality manager's perspective, the choice of dryer is not just a technical question, but a risk and cost decision. An adsorption dryer that reliably maintains a dew point of -40 °C under peak load conditions gives the assurance that the risk of microbial growth and condensation is under control. Modern adsorption dryers also offer energy-saving features. This allows systems to maintain strict dew points while reducing unnecessary flushing losses and energy consumption.

Filters - determining particle and oil classes

Filters determine the particle and oil classes according to ISO 8573-1 at each sampling point. A typical treatment plant comprises several filter stages, each of which fulfills a specific task:

• A pre-filter to remove liquid water and large particles, protecting downstream equipment.
  A coalescence filter to remove fine liquid droplets and oil aerosols.
• A fine particle filter to capture small solid particles down to a size of less than one micrometer.
• An Activated Carbon Filters if the removal of oil vapors and odors is required for very low oil classes.
• A point-of-use sterile or final filter for direct contact with the product or Packaging, with a retention efficiency of typically around 0.01 µm and a high microbial retention efficiency.

Rather than thinking only in micron ratings, it may make more sense to specify filters based on the ISO 8573-1 classes they achieve for particulates and oil in a given configuration. Many modern filters are tested and published with a performance expressed in these terms. This makes it easier to design a system that reliably meets, for example, particle class 2 and oil class 1 on a filling machine, and to justify that design to auditors.

In food or beverage production, the compressor can be oil-free or lubricated, existing or new. The downstream components are decisive for the air quality. A typical setup for a direct contact application could be as follows:

• Compressor and aftercooler: supply compressed air at a suitable temperature.
• Cyclone separator and drain: remove liquid build-up.
• Coalescence filter: removes residual liquid and oil aerosols.
• Fine particle filter: cleans the air down to the required particle class.
• Dryer: a refrigeration dryer or an adsorption dryer to achieve the desired dew point.
• Activated Carbon Filters (if required): Reduces oil vapors and odors.
• Point-of-use sterile filter: installed immediately before the critical contact point (e.g. blow molding station or filling line).

Description: Example of a filter process for compressed air in food and beverage production in accordance with ISO 8573 with coalescence and Particle filters, Activated Carbon Filters and sterile Filter Elements

TCO and energy - why pressure drop and drying are important

Compressed air is one of the most expensive operating resources in a plant, and energy accounts for most of its life cycle costs. Every millibar of pressure drop across filters and dryers forces the compressors to work harder. This increases power consumption and, in many regions, the associated CO₂ emissions. Over the years, small differences in pressure drop and flushing losses add up to considerable costs.

Filters contribute to pressure drop over time due to their media and housing design as well as the increase in differential pressure by being loaded with contaminants. Adsorption dryers can cause internal pressure drops and also consume purge air. Selecting low pressure drop filters and energy-optimized dryers and maintaining them on an appropriate schedule is therefore key to both compliance with the ISO 8573 standard and controlling total cost of ownership.

Modern dryers with dew point dependent control reduce energy consumption by adapting operation to the actual moisture load instead of running continuously at full capacity. High efficiency filters use advanced media structures to combine high retention efficiency with a low initial pressure drop and a slower increase over time. It makes sense for a quality manager to look at air treatment not just as a compliance cost, but as a controllable lever in the plant's energy and sustainability strategy.

The selection of filters and dryers can be seen as a decision based on return on investment. Under-specifying the treatment may reduce the purchase price, but can lead to more frequent product quality problems, higher risk during audits and increased energy consumption due to incorrectly sized or prematurely clogged filters. Over-specification without consideration of pressure drop can also waste energy and money.

A structured selection process takes this into account:

• The required ISO 8573-1 classes at each point of use.
• The existing compressor configuration and demand profile.
• The dew point required throughout the year to meet safety margins.
• Maintenance options and intervals.

Based on this information, filtration specialists can propose a configuration that meets quality targets at minimum life cycle cost. This allows quality managers to justify investments from a total cost of ownership perspective: reduced risk of non-compliance and recalls, less unplanned downtime and lower energy and maintenance costs over the life of the system.

Step 1 - Record the uses of compressed air and the required classes

Start by identifying where and how compressed air is used in your process. Determine for each point:

• Whether the air comes into direct contact with the product or primary packaging.
• Whether it is indirect, but close enough to be a contamination route.
• Whether it is used exclusively for supply purposes or for non-product contact purposes.

Use your HACCP study to officially record each use of compressed air as a potential hazard and assign a required class according to ISO 8573-1. For example, blowing PET bottles in a dairy plant could be assigned to class 1:2:1, while the outlet of a pneumatic actuator in a supply room may not require a specific food grade class. This step converts standard guidelines and customer expectations into specific targets per plant or machine.

Step 2 - Determine the correct filter and dryer combination

Once the required classes have been defined, work backwards to the required combinations of filters and compressed air dryers. This is where the added value of Hengst's filtration experts comes into play. Define for each compressed air branch or each group of branches:

• Dryer type and capacity: refrigerant or desiccant; target dew point and capacity.
• Filter stages and classes: Pre-filter, coalescing filter, fine filter, activated carbon if required.
• Sterile filters at the point of use at all direct contact points.
• Expected pressure drops and their impact on compressor set points.

The result should be a clear strategy showing the process flow for each zone and the ES 8573-1 classes for which it is designed. This document is part of your audit evidence and serves as an internal technical reference.

Step 3 - Measure, monitor and document

Once the treatment system is installed, validate it with a basic compressed air test. Work with a qualified partner using methods in accordance with the ES 8573 series and ensure that the sampling points reflect the actual conditions of use (after the filters, at the actual point of use). The laboratory report should indicate the class achieved for each dimension at each sampling point.

Monitor in daily operation:

• Dew point at appropriate locations to verify dryer performance.
  Differential pressure across filters to detect strain and possible breakthroughs.
  Signs of condensate in pipework or Header Tanks.

Set inspection intervals that suit your scheme (often at least once a year for certification schemes and more frequently for internal quality assurance). Keep all test reports, trend logs and maintenance records so that they can be quickly retrieved during audits.

Step 4 - Continuous optimization of TCO and ROI

Compressed air systems and production requirements evolve over time. New production lines, product changes or seasonal fluctuations can change both the risks and the consumption structures. Check regularly:

• Whether the current classes are still suitable for the respective use.
• Whether filters and dryers are still optimally dimensioned.
• Whether the service life and pressure drop curves of the filters suggest alternative media or stages.

Our filtration specialists at Hengst can help you analyze your test data and operating history to suggest improvements - such as converting to lower Δp Filter Elements, implementing dew point dependent dryer control or making specific recommendations to optimize your filtration process. Our recommendations will help you to ensure that both compliance and efficiency are in line with the current conditions in the plant.

A common misconception is that oil-free compressors alone guarantee food-grade air. Oil-free technology significantly reduces the risk of contamination from compressor oil, but does not help to remove moisture, particles from the ambient air or hydrocarbons and microorganisms. Dryers and filters are still required to meet ISO 8573-1 classes and food safety requirements.

Another misconception is that a clean system outlet means that point-of-use filters are optional. In reality, piping and downstream equipment can cause particulates, moisture and microbial growth. Sterile point-of-use filters serve precisely to provide a final barrier at the most critical points. For direct contact applications, many guidelines and schemes require such filters to be in place and validated.
A third misconception is that more filters always mean better quality, regardless of their impact on pressure drop. Excessive filtration or the use of multiple stages without considering pressure drop can significantly increase energy consumption. The goal is not to blindly add filters, but to design an optimized treatment system that achieves the required purity with the lowest possible pressure drop and maintenance.

Compressed air quality can be perceived as a compliance burden, but it is also an opportunity. By clearly defining the ISO 8573-1 classes, designing the filter and dryer combinations accordingly and systematically monitoring performance, you can reduce the risk of contamination, improve product integrity and reduce energy costs at the same time.

Our filtration experts can help you translate regulations and customer expectations into a concrete compressed air quality concept for your site. This includes assigning classes to applications, selecting and sizing filters and dryers, and assisting with documentation and testing guidance for audits.

If your operation relies on compressed air at critical steps - and most dairy, beverage and food operations do - the logical next step is to assess whether your current filters and dryers are delivering the air quality you expect. An assessment that focuses on both ISO 8573-1 compliance and total cost of ownership can show you where you stand and what you stand to gain in terms of safety and efficiency.