ISO 8573-1 Compressed-Air Purity Classes
“Oil-free” is not a complete compressed-air quality specification.
Use the full class notation
ISO 8573-1 classifies compressed-air purity with respect to particles, water and oil and also identifies gaseous and microbiological contaminants. A procurement document should state the class for each category in the correct order and identify the measurement point and operating condition.
Class 0 is not a universal zero-contaminant value. It is a user/manufacturer-defined class more stringent than Class 1 for the stated contaminant, so the limit and test evidence must be written. The supplied catalogue presents a Class 0 claim; this website does not convert that marketing statement into a project certificate.
Sampling and evidence
Ask for the test method, instrument, calibration, stabilization period, inlet conditions and uncertainty. Decide whether testing is at the package outlet, after treatment or at the point of use. A compressor can be oil-free while ambient hydrocarbon vapor, downstream contamination or maintenance practices still affect measured oil.
Standards status
ISO 8573-1:2010 remains the published edition and is marked “to be revised.” ISO lists an edition 4 approved work item under development. Purchase documents should name the edition and avoid assuming a draft has already replaced the published standard.