ISO 8573 Compressed Air Purity Classes Explained (With a Quick Reference Table)

Compressed air touches your product more often than most quality teams realise — drying a vial, driving a filling nozzle, purging a line, blowing a pack open before it is sealed. Yet it is one of the least-tested utilities in a typical Bangladeshi plant. ISO 8573 is the standard that turns “the air seems fine” into a number an auditor can check.

ISO 8573 is a family, not a single test

Each part measures a different contaminant, and your air receives a class for each one:

How to read a class number

A result reads as something like Class 1.4.1. Those are three separate figures on three separate scales, and lower is cleaner: the first is the particle class, the second the pressure dew point class, the third the oil class. There is no universal pass mark. Air driving a pneumatic cylinder can be far dirtier than air blown across an open tablet or into a sterile filling zone — the correct class depends entirely on what the air touches.

Where testing goes wrong

• Sampling at the compressor instead of the point of use. Fifty metres of old pipework can add moisture and particulate that the compressor room sample will never show. The point of use is where the product is, so that is where the sample belongs.
• Assuming new equipment equals compliance. A new dryer or a fresh filter element is a purchase order, not a measurement. Auditors ask for data.
• Skipping ISO 8573-7 on sterile-area air. Microbial testing is the part most often left out, and the one that matters most in an aseptic filling area.
• Testing once and filing it. Filters load, dryers drift, pipework corrodes. A single certificate from two years ago describes a plant that no longer exists.

What a usable report contains

At minimum: the class achieved at each tested point, the method used for each parameter, the date and conditions of sampling, a tagged location map so the next test repeats the same points, and a clear pass or fail against your specification rather than a bare table of numbers. Where a point fails, the report should name the likely cause and the fix — a moisture trap, a filter change, a line re-route — not simply advise better air quality.

Auditors do not expect perfect air. They expect you to know what class you have, at the point that matters, and to have measured it there.

How often

Annual testing is the common baseline for product-contact and sterile-area air, and after any major maintenance on the compressor, dryer or distribution system. Plants running continuous production or supplying export-audited customers often move to a six-month cycle for critical points, keeping the annual cycle for utility air.

ION Engineering tests compressed air, pure steam and process gases to ISO 8573 at the actual point of use, alongside ISO 14644 cleanroom validation for the room that air flows into. If your last audit raised a compressed air finding, tell us which areas are involved and we will scope a testing visit.