Understanding ISO 8573-1 and What ‘Class 0’ Means

Compressed air is a fundamental part of industry, and its purity affects the quality, safety and continuity of your operations. When air carries contaminants, it can impact product integrity and equipment reliability. For instance, in pharmaceuticals and food and beverage, a single trace of oil vapour can compromise products, while excess moisture in data centre cooling can threaten uptime.

That’s why global industries rely on ISO 8573, and specifically ISO 8573-1, the internationally recognised standard for defining compressed air purity. This framework sets clear, measurable limits for three primary contaminant groups – particles, water and oil – allowing businesses to specify, validate and maintain the level of air quality their processes demand.

This guide explains ISO 8573-1 Class 0, including what it means, how it differs from standard purity classes and what organisations should look for when they see ‘Class 0’ on compressors, filtration systems or air treatment equipment.

ISO 8573 is a comprehensive, multi-part standard developed to bring clarity and consistency to compressed air quality across industries. Rather than treating air purity as a vague concept, the standard breaks it into measurable parameters and defines how each should be tested. Each part of ISO 8573 focuses on a different aspect of air quality, from measurement methods to test equipment, giving operators a complete framework for specifying, evaluating and verifying the performance of their compressed air systems.

At the heart of the series is ISO 8573-1:2010, the section most frequently referenced by engineers, OEMs and quality managers. ISO 8573-1 defines the purity classes used worldwide to classify compressed air. These numerical classes set allowable limits for the three major contaminant groups, enabling organisations to clearly specify what level of cleanliness their processes require.

The standard focuses on three primary categories of contaminants:

1. Solid particles: such as dust, rust or scale resulting from corrosion or wear within the compressed air system. These particles may block valves, damage tools or compromise product quality in sensitive manufacturing environments.
2. Water: present as liquid water, moisture or vapour, and typically assessed through pressure dew point. Excess water promotes corrosion, microbial growth and freezing in outdoor lines, making moisture control essential for reliability and compliance.
3. Oil: including liquid oil, oil aerosols and oil vapours. Trace amounts of oil contamination can damage downstream equipment or jeopardise safety in food, pharmaceutical or breathable-air applications.

Together, these contaminant groups form the backbone of the ISO 8573-1 classification system.

Choosing the correct compressed air purity level is an operational decision that affects production quality, system reliability and long-term cost control. Whether your facility requires Class 0 air or a well-defined standard class, the consequences of getting it wrong can be significant.