Air quality standards (ISO 8573-1)

In the world of compressed air systems, the quality of air plays a crucial role. This blog post delves into the heart of ISO 8573-1, a key standard that defines air quality and sets the benchmark for compressed air systems globally. Understanding this standard is essential for industries relying on compressed air for their operations.


What is ISO 8573-1?

ISO 8573-1 is a critical standard within the field of compressed air quality, providing a comprehensive framework for the classification of air purity. Developed and maintained by the International Organization for Standardization, this standard is pivotal in defining the levels of various contaminants in compressed air systems. It sets out specific requirements for three primary types of contaminants: particulates, water, and oil, each of which can significantly impact the performance and safety of compressed air applications.

The standard is structured into several parts, with ISO 8573-1 being the primary document that outlines the main categories of air contaminants and their permissible limits. It provides a detailed classification system for each contaminant type, specifying the maximum allowable concentration levels in compressed air. These levels are defined in a series of purity classes, which vary depending on the sensitivity of the application and the potential impact of contamination.

For solid particles, the standard specifies the maximum number of particles allowed per cubic meter of air and categorizes them based on their size, measured in microns. For water, ISO 8573-1 defines limits based on the form of moisture present (vapor, liquid, or aerosol) and uses the concept of pressure dew point to quantify moisture content. For oil, the standard includes both liquid and vapor forms of oil, with limits expressed in terms of concentration (mg/m³).

ISO 8573-1 is not just a static document; it evolves to reflect advancements in technology and changes in industrial practices. It is widely used across various industries, including pharmaceuticals, food and beverage, and manufacturing, where the quality of compressed air is critical. Compliance with ISO 8573-1 is essential for ensuring the reliability, safety, and efficiency of compressed air systems, and it serves as a benchmark for quality assurance and regulatory compliance in many sectors.

The three key components of ISO 8573-1

ISO 8573-1 categorizes air purity into three critical components: solid particles, water, and oil. Each category has specific classes that define the concentration levels of these contaminants, providing a clear framework for maintaining air quality in compressed air systems.

1. Solid Particles
This category addresses the concentration of solid particles in the air, which can range from microscopically small dust particles to more significant debris. The standard defines several classes of particle size and concentration, measured in microns and the number of particles per cubic meter of air. For instance, Class 1 specifies a particle size of 0.1 to 0.5 microns with a concentration limit, whereas Class 5 allows larger particles with a higher concentration. Adherence to these classes is crucial in applications where even the smallest particle can cause significant product contamination or damage to precision equipment.

2. Water
Water in compressed air can exist in various forms: vapor, liquid, or aerosol. ISO 8573-1 classifies water content based on the dew point, which is the temperature at which air becomes saturated and water vapor begins to condense into liquid. The classes range from a lower dew point, indicating drier air, to a higher dew point, signifying more moisture. For example, Class 1 requires a pressure dew point of -70°C or lower, suitable for environments where moisture can severely impact product quality or cause freezing in pneumatic controls.

3. Oil
The oil content in compressed air includes both liquid and vapor forms of oil. This category is critical because oil contamination can degrade product quality, damage equipment, and pose health risks. The standard specifies classes based on the concentration of oil (including oil aerosol, vapor, and liquid) measured in milligrams per cubic meter. For instance, Class 0 represents the highest purity level with the least oil content, essential for industries like pharmaceuticals and food processing, where even trace amounts of oil can be unacceptable.

By adhering to these detailed specifications in each category, industries can ensure that their compressed air systems meet the highest standards of purity and efficiency, as outlined in ISO 8573-1. This adherence is not just about compliance; it's a commitment to quality, safety, and operational excellence.

Purity class

Solid particles


Total oil

Number of particles per m3

Pressure dewpoint


0.1 < d ≤ 0.5 μm**

0.5 < d ≤ 1.0 μm**

1.0 < d ≤ 5.0 μm**





As specified by the equipment user or supplier and more stringent than Class 1.


≤ 20000

≤ 400

≤ 10

≤ -70

≤ -94

≤ 0.01


≤ 400000

≤ 6000

≤ 100

≤ -40

≤ -40

≤ 0.1



≤ 90000

≤ 1000

≤ -20

≤ -4

≤ 1




≤ 10000

≤ 3

≤ 37.4

≤ 5




≤ 100000

≤ 7

≤ 44.6



≤ 5 mg/m3

≤ 10

≤ 50


Compliance with ISO 8573-1

Compliance with ISO 8573-1 is not just a regulatory obligation; it's a fundamental aspect of operational excellence in industries using compressed air. By adhering to this standard, operators ensure that their compressed air is free from contaminants like solid particles, water, and oil, which are critical for maintaining system efficiency, product quality, and safety. This compliance is essential for preventing costly downtimes, ensuring the longevity of equipment, and upholding the highest standards of production and environmental safety. In essence, ISO 8573-1 is not just a guideline but a cornerstone of quality assurance in compressed air applications.