Compressed Air Cleanliness Standards: ISO 8573 Explained
Compressed air is not clean just because the compressor is new. Ambient air carries water vapor, dust and oil vapor, and the compression process can add oil and wear particles into the stream.
ISO 8573 gives industrial buyers a common language for air purity. This guide explains the main contaminants, how the standard classifies particles, water and oil, and how to select treatment equipment.
The main contaminants in compressed air
- Water: Condenses from atmospheric humidity and causes corrosion, freezing and product spoilage.
- Oil: Comes from lubricated compressors or intake air and can contaminate product-contact processes.
- Solid particles: Include dust, rust, pipe scale and compressor wear debris.
- Microorganisms: Can grow in wet systems and matter in food, beverage and pharmaceutical air.
How ISO 8573-1 classifies air quality
ISO 8573-1 groups compressed air quality into classes for solid particles, water and oil. A complete specification is written as three values, for example ISO 8573-1:2010 [1:2:1], which states particle class 1, water class 2 and oil class 1.
Lower class numbers mean cleaner air. Class 1 oil limits total oil to no more than 0.01 mg/m³. Class 2 allows up to 0.1 mg/m³, Class 3 up to 1 mg/m³, and Class 4 up to 5 mg/m³.
Class 0 is not simply cleaner than Class 1. It means the user and equipment supplier define a purity target that is stricter than Class 1 for the specific contaminant and application.
Match air treatment to the required class
- General plant air: A refrigerated dryer plus a coalescing filter and particulate filter is usually the starting point.
- Instrument air: Use desiccant drying and fine filtration to reach a low dew point and low particle class.
- Food and pharmaceutical air: Specify oil-free air or very low oil carryover plus sterile filtration where product contact is possible.
- Electronics and semiconductor air: Tight particle, water and oil limits usually require multiple treatment stages.
Test, do not assume
Air quality changes with compressor condition, filter life, dryer performance and ambient conditions. A periodic test of dew point, oil carryover and particle count confirms that the system still meets the target class after months of operation.
Frequently asked questions
What does ISO 8573-1:2010 [1:2:1] mean?
It means particle class 1, water class 2 and oil class 1. Each number applies to a different contaminant group.
Does oil-free compressor air always meet Class 1 oil?
Not automatically. Ambient air can contain oil vapor, so an oil-free compressor still needs filtration and testing to verify the final oil class.
When is Class 0 required?
Class 0 is used when an application or customer specification requires a contaminant limit stricter than Class 1. The exact limit must be defined by the user and supplier.
Next step
Define the application, product-contact risk and required dew point first. Then write the target ISO 8573-1 class and select filtration and drying in the correct order.
Need help specifying air treatment? Contact Panrui with your process and required air quality class.
Related guide: How to Choose a Compressed Air Dryer