The International Organization for Standardization (ISO) is the world’s largest developer of voluntary International Standards. It is a network of national standards bodies. These national standards bodies make up the ISO membership. It is an independent, non-governmental organization made up of members from 164 countries.

The ISO 8573-1 specification is used by a variety of industries requiring clean, dry, and contaminant free compressed air. Industries that use this compressed air testing specification include Food, Pharmaceutical, Medical Device, Power Generation, Plastics, Automotive, Electronics, and more. Any process that uses compressed air and needs clean compressed air having no contaminants flawing the final product often use ISO 8573 in its entirety or adopt sections of it, creating a custom specification.

ISO 8573 is a series of nine documents under the general title Compressed Air. They include information on contaminants, purity classifications, sampling techniques, and analytical methods. Part 1 identifies Particles, Water and Oil as the three major contaminants in compressed air. Part 1 was revised in 2010 to align the particle classes with standard equipment found in practice.

Although 8573-1 lists gaseous and microbiological contaminants; it does not provide purity classes. Test methods for gaseous contaminants are addressed in ISO 8573-6.

ISO 8573-1 provides Purity Classes for each contaminant. The user can select a combination of Purity Classes based on their specific requirements. ISO does not provide guidance on which classes are appropriate for any particular application. This is left to the quality assurance team and their organization to determine. To date ISO 8573 has not been officially adopted by any governing agency in the United States although it is widely used and referred to for guidance in the US and throughout the world.

Parts 2-9 are the test methods for all of the referenced contaminants.

ISO 8573 also sites Class 0 which means the limits are more stringent than Class 1 however the limits must be specified, otherwise Class 0 holds no true meaning. Class 1 & 2 of particles includes 3 ranges on particle size. Class 3 includes 2 size ranges and 4 & 5 only include one range. Classes 6 & 7 measure particles by mass. And Class X is used to report levels that are outside of the other 9 Classes.

Water is measured by Vapor or Liquid while Oil is measured by Aerosol and Vapor. The measurement of Oil Vapor is optional in Classes 3, 4 & X.

Industrial Air / ISO 8573-1 Compressed Air & Gas Testing Specifications

Trace Analytics, LLC can test to a wide variety of specifications. Some example specs commonly used in Industrial Air / ISO 8573-1 are shown below:

ISO 8573-1:2010 Compressed Air Contaminants and Purity Classes
By Particle Size
(maximum number of particles per m3) See Note 2
By Mass Vapor Pressure Dewpoint Liquid Liquid, Aerosol, & Vapor
See Note 1
0.1 µm < d ≤ 0.5 µm 0.5 µ m< d ≤ 1.0 µm 1.0 µm < d ≤ 5.0 µm mg/m3 °C °F g/m3 mg/m3
0 As specified by the equipment user or supplier and more stringent than class 1
1 ≤ 20,000 ≤ 400 ≤ 10 - ≤ -70 ≤ -94 - ≤ 0.01
2 ≤ 400,000 ≤ 6,000 ≤ 100 - ≤ -40 ≤ -40 - ≤ 0.1
3 - ≤ 90,000 ≤ 1,000 - ≤ -20 ≤ - 4 - ≤ 1
4 - - ≤ 10,000 - ≤ +3 ≤ +37 - ≤ 5
5 - - ≤ 100,000 - ≤ +7 ≤ +45 - -
6 - - - 0 – ≤ 5 ≤ +10 ≤ +50 - -
7 - - - 5 – ≤ 10 - - ≤ 0.5 -
8 - - - - - - ≤ 5 -
9 - - - - - - ≤ 10 -
X - - - > 10 - - > 10 > 5
No purity classes are identified No purity classes are identified
Gases mentioned are: CO, CO2, SO2, NOX, Hydrocarbons in the range of C1 to C5
Note 1: ISO 8573 Oil includes aerosol, vapor in the range of C6+, and liquid oil. Liquid oil is typically sampled when wall flow is present, contamination is suspected, or results are greater than 5 mg/m3. Trace can provide a separate kit for liquid oil testing.
Note 2: For Particle Class 0, 1, & 2 (0.1 - 0.5 µ range only), a laser particle counter with a high-pressure diffuser is required. Rental of this equipment is available on a reservation basis. Contact us for details. To qualify for Particle Classes 0 through 5, there can be no particles greater than 5µ present.
In some cases, Trace uses alternative sampling techniques or analytical methods to those specified in ISO 8573, for details see Smith White Paper, 2012.
Air & Gas Specifications referenced above may be viewed and/or purchased from: ANSI - American National Standards Institute

Other uses for compressed air testing per ISO 8573 include:

  1. Determining if filtration, dryers, etc. are functioning properly
  2. Detecting a problem before it reaches a catastrophic level
  3. Determining if maintenance and/or corrective actions are indeed working

Designating Purity Classes is done in this format:
ISO 8573-1:2010 [A:B:C]
A = Particles
B = Water
C = Oil

For Example: ISO 8573-1:2010 [2:2:1]

  • Class 2 for Particles
  • Class 2 for Water
  • Class 1 for Oil

BCAS the (British Compressed Air Society) Food Grade Compressed Air – A Code of Practice states that Classes [2:2:1] should be used for compressed air that comes in direct contact with the product and [2:4:2] for indirect contact.

BCAS Food and Beverage Grade Compressed Air
Best Practice Guideline 102
ISO 8573-1:2010
By Particle Size
(maximum number of particles per m3)
Vapor Pressure Dewpoint Aerosol & Vapor
0.1 µm < d ≤ 0.5 µm 0.5 µm < d ≤ 1.0 µm 1.0 µm < d ≤ 5.0 µm °C °F mg/m3
Direct Contact
400,000 6,000 100 ≤ -40 ≤ -40 ≤ 0.01
Indirect Contact
400,000 6,000 100 ≤ +3 ≤ +37 ≤ 0.1
Microbial Contaminants Hazard analysis shall establish the risk of contamination by microbiological contaminants from compressed air. The level of control identified as being required over microbiological contaminants in the compressed air shall be detected using the test method specified in ISO 8573-7.
Footnotes (P) Particle classes 1-5 may not be employed if particles >5 micron are present according to ISO 8573-1.
Air & Gas Specifications referenced above may be viewed and/or purchased from: BCAS - British Compressed Air Society

We offer Baseline testing, which allows the user to determine what classes their system is currently performing at without predetermining what classes the compressed air is required to meet. Baseline testing is extremely useful when trying to determine SOPs. Using higher purity classes than needed can be more expensive and can produce an unnecessary failed report if those more stringent classes are not met.

Surprisingly enough, Breathing Air specifications are not suitable or stringent enough for most critical application manufacturers including food, pharmaceutical and medical device manufacturers, among others.

Maintenance on the compressor, storage receivers and piping can loosen and distribute rust, pipe scale, etc. and release it into the system. Adding new piping can also have this same effect, contaminating new piping that is installed. Learn more about Sources of Compressed Air and Gas Contamination.

Microbial contaminants will not grow at -40°F. However, this does not mean that -40°F will kill any microbial activity it just won’t allow it to grow. If there is microbial activity it could remain dormant until the microbes are released into a temperature above the -40°F. For example if you have microbes in your system and then they are transferred to your product they can begin to grow again once they are introduced into an ambient environment. It is important to include 0.1 micron size particle filters at the point of use to eliminate microbes from contaminating your final product.

To ensure the quality of your compressed air at the point where it comes into contact with your product, a Best Practice will include routine, periodic compressed air quality testing from a sufficient number of outlets. A single test once a year does not provide enough data to assure that your compressed air is not a hazardous risk to your product. Compressor systems and the quality of the air they produce are not static. Air quality is affected by the ever changing quality of intake air which can introduce micro-organisms, particles, water, and gaseous contaminants into the compressor system. The distribution piping can also contribute to contamination through buildup. See Sources of Compressed Air and Gas Contamination.

Compressed air quality monitoring and testing provides you with valuable data to identify trends and prevent problems which can result in lost production time, recalls, and much more.