ISO 8573-1 is the international standard that defines compressed air purity. It splits contaminants into three groups: solid particles, water and oil. A compressed air specification is written as a three-part code such as ISO 8573-1:2010 [2:4:2], with each number describing one contaminant group.
Reading the three-part code
- First digit — solid particle size and concentration
- Second digit — pressure dew point and liquid water
- Third digit — oil concentration in mg/m³
A lower number means cleaner air. Class 0, for oil, is stricter than Class 1 and is defined by agreement between user and supplier, usually meaning 100% oil-free air below detectable limits.
Common target classes by industry
- General workshop air — 7:4:4
- Food and beverage contact air — 2:2:1 or better
- Pharmaceutical and medical — 1:2:1
- Semiconductor and electronics — 1:1:1 with Class 0 oil
How to reach the required class
Start with the right compressor technology, then add treatment in order: aftercooler, water separator, coalescing filters, adsorption dryer and, where needed, activated-carbon filtration. Each stage removes a specific contaminant, and skipping a stage makes the final air quality unpredictable. Always specify the class at the point of use, not just at the compressor outlet.