ISO 8573 Standard: A Complete Compressed Air Quality Guide

Compressed air is often called the "fourth utility" in a plant, after electricity, water, and gas, because almost every production line depends on it, from driving pneumatic tools to becoming a direct part of the production process itself. But not all compressed air is of the same quality. Contamination in the form of particles, water, and oil carried through the system can damage equipment, contaminate products, and cause expensive downtime.

This is exactly why the ISO 8573 compressed air quality standard exists, serving as an international reference used almost worldwide to determine the level of air purity required for a given application.

What Is ISO 8573?

ISO 8573 is a series of international standards that govern the classification of compressed air purity. The standard was first published in 1991 and revised in 2010 into ISO 8573-1:2010, which remains the most commonly used reference in industry today. The full ISO 8573 series consists of nine parts: ISO 8573-1 defines the air purity classes, while the other parts cover test methods for particles, water, oil, gases, and microorganisms.

With this standard in place, manufacturers, contractors, and end users share a common technical language for specifying and verifying the level of compressed air cleanliness a process requires.

Why Compressed Air Quality Matters to Industry

Compressed air quality requirements differ from one sector to another. The food and pharmaceutical industries need genuinely clean air because it comes into direct contact with the product, while the automotive and construction industries focus more on reliability and the service life of pneumatic equipment. There are two main reasons why understanding the ISO 8573 classification is important:

Regulatory compliance. A number of industries are legally bound to meet certain air quality standards, and non-compliance can result in penalties or a production shutdown.

Cost efficiency. The higher the purity level targeted, the greater the investment and energy consumption required. Specifying the right class, neither excessive nor insufficient, helps balance compliance, process reliability, and cost efficiency.

The Three Contaminant Categories in ISO 8573-1

ISO 8573-1 groups compressed air purity according to three types of contaminant, where the lower the class number, the cleaner the air.

Particle Class (P)

This class measures the quantity and size of solid particles such as dust, rust, or pipe debris in every cubic metre of compressed air.

• Class 1: maximum particle size of ≤0.1 micron with a very low particle count, used in highly critical environments such as semiconductor manufacturing, pharmaceuticals, and medical applications.
• Classes 2–3: particle sizes up to 1 micron (class 2) or 5 microns (class 3), commonly used in the food and beverage, chemical, and precision engineering industries.
• Classes 4–6: minimal filtration through to no filtration at all, with progressively larger tolerated particle sizes, and generally not recommended for pneumatic tools or other sensitive equipment.

Water Content Class (W)

This class is determined by the pressure dew point (PDP), the temperature at which water vapour begins to condense at a given pressure. The lower the PDP value, the drier the air.

• Class 1: PDP ≤ -70°C, for ultra-critical environments such as semiconductors, pharmaceuticals, and high-precision electronics.
• Classes 2–3: PDP between -40°C and -20°C, common in the food and beverage, chemical, and medical application sectors.
• Classes 4–5: PDP between +3°C and +7°C, sufficient for general industrial needs such as automotive, metal fabrication, and packaging.

Oil Content Class (O)

This class covers oil content in both aerosol and vapour form, which may originate from an oil-lubricated compressor or from the surrounding environment.

• Class 0: the highest level of purity, defined specifically by the user or the equipment manufacturer because it is stricter than class 1, and generally achieved using an oil-free compressor.
• Class 1: a maximum of 0.01 mg/m³, required by the food, beverage, and healthcare industries.
• Classes 2–3: up to 0.1 mg/m³, commonly used across general industrial processes.
• Classes 4–5: up to 1 mg/m³ and 5 mg/m³ respectively, sufficient for pneumatic applications with less stringent requirements.

How to Read the ISO 8573-1 Class Notation

Under ISO 8573-1, compressed air quality is written as three numbers separated by colons, following the order [Particles : Water : Oil]. For example, the notation ISO 8573-1:2010 [1:2:1] means:

• Class 1 for particles
• Class 2 for water content (PDP of approximately -40°C)
• Class 1 for oil content (≤0.01 mg/m³)

This format prevents misunderstandings between suppliers, operators, and auditors, because air quality requirements can be stated concisely yet precisely.

The ISO 8573 Standard Across Industrial Sectors

Each industrial sector generally has a different target ISO 8573 class, matched to how sensitive the process is to contamination:

Bear in mind that the figures above are general guidance; actual requirements still depend on the specific process, climatic conditions, and the type of compressor in use.

How to Achieve the ISO 8573 Standard in Your Compressed Air System

Once you know which ISO 8573 class you need, the next step is choosing the right combination of filters and dryers:

• Particulate filters screen out dust and solid contaminants to meet the particle class (P).
• Coalescing filters capture oil and water aerosols as well as particles, helping to meet both the oil (O) and particle classes at once.
• Activated carbon filters remove oil vapour and odours, and are needed when the air must be extremely pure, for instance in the food or pharmaceutical industries.
• Air dryers reduce humidity to meet the water class (W). Refrigerant dryers suit general industrial needs, while desiccant dryers produce far drier air for critical applications or low-temperature environments.

The right combination of compressor, filter, and dryer, such as the compressed air treatment line from Ingersoll Rand, ensures your compressed air system consistently meets the targeted ISO 8573 class without placing an excessive burden on energy costs.

Conclusion

The ISO 8573 compressed air quality standard provides clear, measurable guidance for determining the level of air purity a process requires, while helping companies avoid filtration investments that are either excessive or inadequate. Understanding its three contaminant categories, particles, water, and oil, is the first step before specifying the right compressor, filters, and dryers.

As the official Ingersoll Rand distributor in Indonesia, FMM is ready to help you audit your compressed air quality requirements and recommend a compressor, filter, and dryer configuration that matches the ISO 8573 class your industry demands.