Compressed Air Oil Content: Understand ISO 8573-1 Standard and Oil-Free Cleanliness Level

What is the oil content of compressed air?

Compressed air oil content refers to the total oil content in the form of aerosol (oil mist), liquid oil and oil vapor in compressed air, usually in mg/ m³. It is one of the key indicators to measure the quality of compressed air, directly affecting industries with strict cleanliness requirements such as precision manufacturing, food packaging, pharmaceutical production, etc.

ISO 8571-1: internationally recognized cleanliness classification standard

ISO 8571-1 divides compressed air quality into three levels of pollutants: solid particles, water and oil. Among them, the oil content level ranges from 0 (the most strict) to 5 (the highest allowable value),level 0 represents ‘technically accessible oil-free’, not absolute zero oil, but the verified oil content ≤ 0.01 mg/ m³, and there is no oil vapor and oil mist residue.

How to achieve low oil/oil-free compressed air?

• SOURCE control: use oil-free air compressor (such as scroll and screw oil-free model);
• end purification: equipped with high-efficiency oil mist filter (such as condensed or activated carbon composite), the oil content can be reduced to less than 0.003 mg/m³;
• periodic Verification: conduct third-party oil content testing according to ISO 8573-1 to ensure continuous compliance with the target cleanliness level.

Cleanliness level selection needs to match application scenarios

for example, Class 1 is often required for electronic assembly (oil ≤ 0.01 mg/ m³), and general pneumatic tools may be applicable to Class 4 (oil ≤ 5 mg/ m³). Incorrect selection not only increases energy consumption and maintenance costs, but also may lead to product pollution or equipment failure.

Class 0

Class 1

Class 3
oil content grade (ISO 8573-1)
→ increasing oil content and decreasing cleanliness