Lesson 4: Air Quality and ISO 8573-1
“Clean dry air” means different things to a tire shop and a pharmaceutical plant. ISO 8573-1 gives everyone the same language. Learn to read it and you can quote air treatment with confidence.
The three contaminants
- Particulates. Dust from the room, rust and scale from old pipe, desiccant dust, wear particles.
- Water. Vapor that condenses into liquid as air cools. It rusts pipe, washes out tool lube, ruins paint, and freezes in outdoor lines.
- Oil. Aerosol, liquid, and vapor. It comes from lubricated compressors and from the intake air itself.
How ISO 8573-1 works
The standard (2010 edition) gives a class number for each contaminant, written in this order: particles : water : oil. Lower numbers mean cleaner air. Class 0 means a limit tighter than Class 1, set by the user or maker.
Example: ISO 8573-1:2010 [1:4:2] means Class 1 particles, Class 4 water, Class 2 oil.
Water classes (pressure dew point)
| Class | Pressure dew point |
|---|---|
| 1 | -94°F (-70°C) or lower |
| 2 | -40°F (-40°C) or lower |
| 3 | -4°F (-20°C) or lower |
| 4 | 37°F (+3°C) or lower |
| 5 | 45°F (+7°C) or lower |
| 6 | 50°F (+10°C) or lower |
Classes 7 to 9 cover liquid water content and apply to untreated air.
Oil classes (total oil: aerosol, liquid, vapor)
| Class | Maximum total oil |
|---|---|
| 1 | 0.01 mg/m³ |
| 2 | 0.1 mg/m³ |
| 3 | 1 mg/m³ |
| 4 | 5 mg/m³ |
Particle classes
Classes 1 to 5 limit particle counts per cubic meter by size range. Class 1 is the tightest. Classes 6 and 7 use mass instead (up to 5 mg/m³ and up to 10 mg/m³). The full count table is in the standard. You rarely need it at the counter, but you do need to know a lower class is cleaner.
Matching equipment to classes
- A refrigerated dryer at roughly 35 to 39°F pressure dew point lands around water Class 4 or 5. Check the dryer’s stated rating.
- A desiccant dryer at -40°F reaches water Class 2.
- Coalescing filters and activated carbon filters set the oil class. Use the maker’s rated class, at their rated conditions.
What to ask
- What is the air used for? Tools, paint, food contact, instruments, breathing?
- Do any lines run outdoors or through cold areas?
- Does the customer or their customer specify an ISO 8573-1 class?
Breathing air is its own category with separate rules. Do not quote it off this lesson. Send it to someone qualified.
Sources
- ISO 8573-1:2010, Compressed air: Part 1: Contaminants and purity classes (class order, water pressure dew point classes 1 to 6, oil classes 1 to 4, particle mass classes 6 and 7, Class 0 definition). Values reproduced from the standard’s class tables; check the current edition before publishing in a spec.
- DOE/Compressed Air Challenge, Improving Compressed Air System Performance, 3rd ed. (refrigerated dryer 35 to 39°F and desiccant dryer -40°F pressure dew points).
- Fahrenheit values are conversions of the standard’s Celsius limits, rounded to the nearest degree.