High Quality Compressed Air

from Generation to Application

A Guide to ISO 8573.1:2001
Air Quality Classes

www.domnickhunter.com
1 An Introduction to ISO 8573.1 Air Quality Classes

domnick hunter is an international group of companies specialising in the high quality filtration, separation and
purification of compressed air, gases and liquids.
domnick hunter has over 40 years of experience in the purification industry and has been instrumental in the
development of both the international standards for compressed air and the standards for filter testing. domnick
hunter continues to work closely on new standards with such governing bodies as British Compressed Air Society
(BCAS) the International Standards Organisation (ISO), PNEUROP and the Compressed Air and Gas Institute (CAGI).
This document provides an introduction to ISO 8573.1 the international standard for compressed air quality,
purification equipment required to achieve the standards and how to apply the standard to typical applications.

ISO 8573 – The compressed air quality standard Solid Particulate

ISO8573 is the group of international standards relating to the The changes introduced to ISO 8573.1 in 2001 were
quality of compressed air. The standard is made up of nine specific to particulate contamination, however the
separate parts, part 1 specifying the quality requirements significant improvements in particulate cleanliness are
of the compressed air and parts 2 – 9 specifying the methods not always apparent when comparing the tables from
of testing for a range of contaminants. the 1991 and 2001 editions.

In 2001, the ISO 8573.1 air quality standard was amended in Extract from ISO 8573 : 1991 Part 1 for particulate (previous standard)
an effort to provide a more stringent air quality specifications
for critical applications and the latest revision is expressed DIRT
QUALITY Concentration
as ISO8573.1 : 2001. Particle size
mg/m3
CLASS
in micron
Within ISO8573.1 : 2001, a number of quality classes are 1 0.1 0.1
shown in tabular form, each specifying the maximum amount 2 1 1
of solid particulate, water and oil allowable per cubic metre
3 5 5
of compressed air.
4 15 NOT SPECIFIED

Solid Particulate Extract from ISO 8573 : 2001 Part 1 for particulate (latest standard)
Maximum number of particles per m3
Water Oil
Class Pressure (incl. vapour)
0.1-0.5micron 0.5-1 micron 1.0-5micron Dewpoint °C mg/m3 Solid Particle
Maximum number of particles per m3
Class
1 100 1 0 -70 0.01 0.1-0.5micron 0.5-1 micron 1.0-5micron
2 100,000 1,000 10 -40 0.1
1 100 1 0
3 - 10,000 500 -20 1
4 - - 1,000 3 5
2 100,000 1,000 10
5 - - 20,000 7 - 3 - 10,000 500
6 - - - 10 - 4 - - 1,000
5 - - 20,000
6 - - -
Using the classes, a maximum level can be specified for
each contaminant which is expressed as
As can be seen above, the two editions of the standard
ISO 8573.1 : 2001 Class Solid Particulate - Water - Oil do not present particle contamination requirements in
For example the same way.

ISO 8573.1 : 2001 Class 1.2.1 The table from the 1991 edition shows a maximum size
rating for the solid particulate and a concentration
Which equates to whilst the 2001 edition shows both a size rating for the
100 Solid Particles 0.1-0.5 micron/m3 particulate and the maximum number of particles
allowed per cubic metre. To show the differences
1 Solid Particle 0.5 - 1 micron/m3 between the two tables and highlight the improved air
0 Solid Particles 1 - 5 micron/m3 quality requirements, the concentration levels shown in
the 1991 edition must be converted into a quantity of
Water Vapour Pressure Dewpoint -40°C particles.
Oil aerosol and vapour 0.01 mg/m3
 2

Using this method, shows that class 1 from the 1991

edition permitted a maximum of 191 billion particles per
cubic metre, whereas the 2001 edition only allows 101.
The table below highlights exactly how much cleaner the
2001 edition is.
QUALITY ISO 9001:2000 ISO 14001
2001 EDITION X TIMES CLEANER THAN 1991 EDITION
CLASS

1 1.9 billion times cleaner than 1991 Class 1

2 19 thousand times cleaner than 1991 Class 2
3 7 thousand times cleaner than 1991 Class 3
4 -
When specifying purification equipment, consideration should
be given to the requirements of the user. It should not be Q 05240
assumed that an application that previously required particulate
removal to class 1 still requires this level today.
Wet particulates are removed using a coalescing type filter which
provide the additional function of removing oil / water aerosols.
Dry particulate filters are also available and are typically used
after adsorption dryers or at the point of use. The test methods
for measuring solid particles are covered in ISO 8573.4 International Standards
Organisation
Water
The values for water refer to water vapour and are expressed
as pressure dewpoints in degree’s Celsius. Water vapour is INTERNATIONAL
removed using a dryer, of which there are various types APPROVALS
available. Of the six dewpoint levels shown in the quality
classes, the first three are typical of dewpoints achieved by
adsorption dryers and the last three are those achieved by
refrigeration dryers. The test methods for the measurement
of pressure dewpoint are covered in ISO 8573.3
Oil
The ISO8573.1:2001 table shows the recommended maximum
levels for oil including vapour. Oil aerosols can be removed by
using a coalescing type filter, whilst oil vapour must be
removed using an adsorption type filter. Removal of aerosol &
CRN
vapour will require the use of both filter types. The total value
for oil in a system is a combination of test results from both
ISO8573.2 & ISO8573.5.
AS1210
Micro-organisms
Many applications within the food and pharmaceutical ASME VIII National Board
industries require air which is free from micro-organisms such
as bacteria, viruses, yeast and fungi. ISO8573.1 considers these
as solid contaminants and is limited to identifying systems as
either sterile or non-sterile. The test methods for measuring
micro-organisms are covered in ISO 8573.7

Air quality & energy efficiency

Choosing purification equipment for today’s modern
production facilities that can deliver the right balance of air
quality and low cost of ownership can be a daunting task.
At domnick hunter, uncompromising performance and energy
efficiency are paramount and in these energy conscious days,
selecting domnick hunter purification equipment not only
means that you get air quality to international standards but
also ensures operating costs are kept to a minimum.
3 Filtration, Separation and Drying Technologies

BULK LIQUID REMOVAL HIGH FLOW BIO-X

Sterile Air / Particulate Free
GRADE WS Full retention of bacteria, viruses and particulate.
High Efficiency Water Separators Based on depth filter technology. Retention correlated
to an aerosol bacterial and viral challenge.
WS water separators employ centrifugal and impingement
separation techniques for the removal of up to 99% of bulk
liquid contamination. MEMBRANE FILTRATION
DEPTH FILTRATION (COALESCING Microporous membrane filters remove contaminants by a
combination of mechanisms. Larger particles and micro-
& DRY PARTICULATE FILTER) organisms are retained by size exclusion / sieve captured
Depth filters generally constitute a fibrous material on the membrane surface. Smaller bacteria and viruses
made into flat sheets of randomly distributed formed (as small as 0.02 micron) are fully retained within the
nanofibres. Depth filters rely on the density and depth of the membrane, and significant retention takes
thickness of the fibre layers to trap the particulate. place at even smaller sizes. Membranes used for air
Removal of the particulate occurs both on the surface filtration do not have such a defined pore structure as
and within the depth of the media. The size of the those associated with liquid applications. They have a
particle that can be captured has finite limits dictated by structure that is similar to that of a depth media apart
the diameter of the fibres used in the media construction from the pores being significantly smaller in size.
and the degree of free space between the fibres. By
using this method of filtration, large quantities of
particulate can be captured before blockage occurs.

Air Membrane Liquid Membrane

Nanofibre filter media

HIGH FLOW TETPOR MEMBRANE FILTERS

GRADE AO Sterile Air / Particulate Free
Full retention of bacteria, viruses and particulate.
High Efficiency General Purpose Protection Based on membrane technology. Retention correlated
Particle removal down to 1 micron, including water to a liquid bacterial challenge (ASTM 838-38) as well
and oil aerosols. as bacterial and viral aerosol challenge. Used for the
Maximum remaining oil aerosol content : 0.6 mg/m3 most critical of applications including medical,
at 21°C / 0.5 ppm(w) at 70°F. pharmaceutical / aseptic packaging and electronics.

GRADE AA
High Efficiency Oil Removal Filtration
(Precede with Grade AO filter)
Particle removal down to 0.01 micron, including water
and oil aerosols.
Maximum remaining oil aerosol content : 0.01 mg/m3
at 21°C / 0.01 ppm(w) at 70°F.

GRADE AR
General Purpose Dust Filtration
Dry particle removal down to 1 micron

GRADE AAR
High Efficiency Dust Filtration
Dry particle removal down to 0.01 micron.

OIL-X EVOLUTION Depth filters High Flow BIO-X Depth Filters

High Flow TETPOR Membrane Filters
 4

ADSORPTION FILTRATION ADSORPTION DRYING

Adsorption filter elements are made up of various materials An adsorption dryer extracts water vapour from the
in granular form arranged in a deep bed. This filtration compressed air by attraction and adhesion of molecules
technique relies on contact or dwell time between the air and in a gaseous or liquid phase to the surface of an
the adsorption media. It is during this time that vapour adsorbent material. The adsorbent can often be
molecules are attracted to and held on the surface area of regenerated by removing the adsorbed water. Although
the media. Activated carbon is employed for oil vapour the principle of water removal is common, various
removal using this technique with its high affinity for oil methods of regenerating the adsorption bed are available
vapour and its extremely high surface area, created by its and include heatless regeneration (Pressure Swing
porous structure. A handfull of activated carbon has a Adsorption), heat regenerative (Thermal Swing
surface area larger than a football field. Adsorption elements Adsorption), vacuum regeneration and blower
have a limited life, which is affected by many factors, regeneration.
principally temperature and relative humidity.

Activated carbon

GRADE ACS, AC & OVR

Adsorbent Desiccant Bead
Oil Vapour & Odour Removal
(Precede Grade ACS, AC and OVR with Grade AA filter)
Maximum remaining oil vapour content : 0.003 mg/m3 High Efficiency Adsorption Dryers
at 21°C / 0.003 ppm(w) at 70°F. Delivering Pressure Dewpoints of -70°C (-100°F) /
-40°C (-40°F) / -20°C (-4°F)
REFRIGERATION DRYING
A full range of PSA, TSA, Vacuum & Blower
A refrigeration dryer extracts water vapour by the regeneration adsorption dryers are available from
application of cooling and subsequent condensation. domnick hunter for compressor room and point of use
Condensation of water vapour occurs on internal cooling applications.
surfaces and is then separated and drained. Refrigeration
dryers are designed to deliver pressure dewpoints above 0°C Adsorption dryers are selected to match not only air
to prevent freezing on the internal cooling surfaces. Air is quality requirements, but also capital and operational
reheated before it re-enters the system to prevent piping cost targets of the user. Dryer types include:
from ‘sweating’ in humid conditions.
PNEUDRI - Modular PSA / TSA Regeneration
Refrigeration Dryers Classic - Twin Tower PSA / TSA & Blower Regeneration
CRD Refrigeration Dryers Delivering Pressure Dewpoints DTV - Vacuum Regeneration
of 3°C (37°F) & 10°C (50°F).

OVR 6000 hour Oil Vapour Removal CRD Refrigeration Dryers PNEUDRI Modular Adsorption Dryers DTV and Classic
Twin Tower Adsorption Dryers
5 High Quality Compressed Air from Generation to Application

High quality compressed air from Product Selection

generation to application
Solid Particulate
Maximum number of particles per m3
Water Oil
The quality of air required throughout a typical compressed Class Pressure (incl. vapour)
0.1-0.5micron 0.5-1 micron 1.0-5micron Dewpoint °C mg/m3
air system can vary. The extensive range of purification
equipment available from domnick hunter is ideal for both
1 100 1 0 -70 0.01
centralised and decentralised compressed air systems. This
2 100,000 1,000 10 -40 0.1
allows the user to tailor the quality of air for each specific
3 - 10,000 500 -20 1
application, from general purpose ring main protection,
4 - - 1,000 3 5
through to critical clean dry air (CDA) point of use systems.
5 - - 20,000 7 -
domnick hunter can tailor its range of purification 6 - - - 10 -
equipment to exactly match system requirements, ensuring
both capital and operational costs are kept to a minimum. Solid Particulate
To achieve the levels of cleanliness specified by ISO 8573.1 CLASS FILTRATION GRADES
2001 a careful approach to system design, commissioning Class 1 High Flow BIO-X / High Flow TETPOR
and operation must be employed. (Requires pre-filtration)
It is highly recommended that the compressed air is treated Class 2 AO + AA (AR+AAR for dry particulate)
prior to entry into the distribution system as well as at each Class 3 AO (AR for dry particulate)
usage point or application.
This approach to system design provides the most cost
effective solution to system purification as it not only removes Water
the contamination already in the distribution system, it CLASS DRYER
ensures that only the most critical area’s receive air treated Class 1 PNEUDRI / Classic / DTV Sized for –70°C PDP
to the highest level.
Class 2 PNEUDRI / Classic / DTV Sized for –40°C PDP
The typical system layout drawings included in this document
show installations with purification equipment in the Class 3 PNEUDRI / Classic / DTV Sized for –20°C PDP
compressor room to protect the distribution system and also Class 4 CRD Refrigeration Dryer Sized for +3°C PDP
at the point of application. Class 5 CRD Refrigeration Dryer Sized for +3°C PDP
In many instances the compressed air system will be Class 6 CRD Refrigeration Dryer Sized for +10°C PDP
supplying air to more than one application and although the
purification equipment specified in the compressor room
would remain unchanged, the point of use protection will vary Oil
depending upon the air quality requirements of each CLASS FILTRATION GRADES
application.
Class 1 AO + AA
For example, air used for the pneumatic conveying of food + OVR, AC or ACS if the maximum inlet oil vapour
stuffs or ingredients will require the highest level of concentration exceeds 0.005mg/m3
purification, whilst the air used to operate the pneumatics on
Class 2 AO + AA
the production machinery may only require general purpose
protection. Class 3 AO
Class 4 AO
 6

CRITICAL APPLICATIONS - Air Quality to ISO 8573.1: 2001 Class 1.1.1, Class 1.2.1, Class 1.3.1 at application
Bulk contamination is removed to an adequate level prior to the air entering the distribution system.
Point of use oil vapour removal and sterile air filtration (membrane or depth) installed for critical application at point of use.

Only air for the critical application should be treated to the highest level. For non-critical applications fed by the same distribution
system, high efficiency point of use filtration should be installed.

ISO 8573.1 Class 3.1.2 -70°C (-100°F) PDP

ISO 8573.1 Class 3.2.2 -40°C (-40°F) PDP
ISO 8573.1 Class 3.3.2 -20°C (-4°F) PDP

AAR

GENERAL USE

PNEUDRI
MODULAR TYPE ISO 8573.1 Class 2.1.2
ILLUSTRATED ISO 8573.1 Class 2.2.2
ISO 8573.1 Class 2.3.2
Typical layout for a system requiring AAR
critical and general use compressed air.

Typical Applications
Pharmaceutical products Hard disk manufacturing
Silicon wafer manufacturing Foodstuffs
TFT / LCD Screen manufacturing Dairies
Memory device manufacturing Breweries
Optical storage devices (CD, CDRW, DVD, DVDRW) CDA systems for electronics manufacturing
Optical disk manufacturing (CD’s/DVD’s):
7 High Quality Compressed Air from Generation to Application

HIGH QUALITY OIL FREE AIR - Air Quality to ISO 8573.1: 2001 : Class 2.1.1, Class 2.2.1, Class 2.3.1 at application
Bulk contamination is removed to an adequate level prior to the air entering the distribution system.
Point of use particulate filter(s) are used for removal of contamination within the distribution system.
*For Class 1 oil, if the maximum inlet oil vapour concentration exceeds 0.005mg/m3, an additional oil vapour removal filter will be required.

Typical layout for a system

requiring high quality oil-free air.

Typical Applications
Blow Moulding of Plastics e.g. P.E.T. Bottles Dental air Blanketing
Film processing Lasers and optics Modified atmosphere packaging
Critical instrumentation Robotics Pre-treatment for on-site
Advanced pneumatics gas generation
Spray Painting
Air blast circuit breakers Air bearings
Decompression chambers Pipeline purging
Cosmetic production Measuring equipment
Medical air
 8

GENERAL PURPOSE OIL FREE AIR - Air Quality to ISO 8573.1: 2001 Class 2.4.2. at application
Bulk contamination is removed to an adequate level prior to the distribution system.
Point of use particulate filter(s) are used for removal of contamination within the distribution system.
Point of use adsorption dryer installed where lower dewpoints are required.
*For Class 1 oil, if the maximum inlet oil vapour concentration exceeds 0.005mg/m3, an additional oil vapour removal filter will be required.

ISO 8573.1 Class 2.4.2

GENERAL PURPOSE
OIL-FREE AIR

ISO 8573.1 Class 2.4.2

AAR

CRITICAL
REFRIGERATION DRYER INSTRUMENTATION
+3°C (37°F) PDP
ISO 8573.1 Class 2.1.1 -70°C (-100°F) PDP
AC*
ISO 8573.1 Class 2.2.1 -40°C (-40°F) PDP
Typical layout for a system requiring
general purpose oil-free air.

Typical Applications
General ring main protection Air motors

Pre-filtration to point of use adsorption air dryers Temperature control systems

Plant automation Blow guns

Air Logistics Gauging Equipment

Pneumatic tools Raw material mixing

General instrumentation Sand / bead blasting

Air conveying
9 High Quality Compressed Air from Generation to Application

GENERAL PURPOSE OIL-FREE AIR - Air Quality to ISO 8573.1: 2001 Class 3.-.2, Class 2.-.1.
(water vapour removal not specified)
Bulk contamination is removed to an adequate level prior to the distribution system.
*For Class 1 oil, if the maximum inlet oil vapour concentration exceeds 0.005mg/m3, an additional oil vapour removal stage
will be required.
The requirements for breathable quality air are not covered in ISO 8573.1:2001. Refer to breathing air standards for the
country of installation.

Typical Applications (Water Vapour Removal Not Specified)

General ring main protection
Metal stamping
Forging
General industrial assembly (no external pipework)
Pre-filtration to point of use breathing air systems
Workshop
Garage
 10

System Recommendations The piping used downstream of membrane filters should be electro-
polished stainless steel and be crevice free at all joints. Clean down time
To achieve the levels of cleanliness specified by ISO 8573.1:2001 a
for a newly commissioned system will depend upon the surface area of
careful approach to system design, commissioning and operation must
the system, the system flow rate and the initial cleanliness of the piping
be employed.
and fittings. Clean down can be achieved by high flow clean air purging
It is recommended that the compressed air is treated prior to entry into for extended periods of time during which all air should be purged to
the distribution system and also at critical usage points / applications. atmosphere.
This ensures that contamination already in the distribution system is
removed. Installation of compressed air dryers to a previously wet Sterile Air
system could result in additional dirt loading for point of use filters for If running an aseptic process (i.e. free from microbiological
a period whilst the distribution system dries out. Filter elements may contamination) it is essential that a sterile filter is installed at the point
need to be changed more frequently during this period. of use. This may either be based on glass nanofibre depth media or
membrane.
For installations where oil-free compressors are used, both general
purpose Grade AO and high efficiency Grade AA should be used. The Sterility can only be guaranteed and maintained if the filter and
general purpose filter must be installed to protect the high efficiency associated downstream process equipment are sterilised and
filter from bulk water aerosols and solid particulate. maintained in accordance with manufacturers instructions. This is
Install purification equipment at the lowest temperature above freezing normally achieved using steam sterilisation but chemical sterilisation
point downstream of aftercoolers and air receivers. This allows a greater techniques such as vapour hydrogen peroxide can also be used.
amount of oil and or water vapour to condense out for removal by water It is recommended that sterile filters are tested for efficiency
separators & coalescing filters prior to a dryer. on a regular basis.
Point of use purification equipment should be installed as close to the
application as possible. This ensures that the maximum amount of rust Maintaining System Efficiency
and pipe scale is removed prior to the application.
Regular service is essential to maintaining system performance.
Purification equipment should not be installed downstream of quick To maintain your guaranteed compressed air quality, purification
opening valves and should be protected from possible reverse flow or equipment must be maintained annually with genuine domnick hunter
other shock conditions. parts. Failure to maintain your purification equipment will invalidate
Purge all piping leading to the purification equipment before installation performance guarantees and could result in reduced production
and all piping after the purification equipment is installed and before performance, degrading air quality and increased running costs.
connection to the final application. Preventative maintenance provides you with the following benefits:

If by-pass lines are fitted around purification equipment, ensure • Lowest running costs
adequate filtration is fitted to the by-pass line to prevent contamination
• Guaranteed compressed air quality
of the system downstream.
• Continued protection of downstream equipment and processes
Provide a facility to drain away collected liquids from the purification
equipment. Collected liquids should be treated and disposed of in a • Peace of mind
responsible manner.
In critical applications, membrane filters should be used at point of use After sales care package
to ensure no particulate is carried over to the application.
For peace of mind, domnick hunter can manage your compressed air
The lifetime of oil vapour removal filter elements is affected by the inlet quality and guarantee future performance with a world-wide aftersales
oil concentration, relative humidity and temperature of the compressed care package. Further details can be found on www.servicereminder.com
air. For critical applications or systems where frequent element changes
are not possible, domnick hunter OVR oil vapour removal systems
should be installed.
 dh, domnick hunter, OIL-X, PNEUDRI, BIO-X and TETPOR are
registered trademarks of domnick hunter limited.

domnick hunter limited

domnick hunter limited has a continuous policy of product
Dukesway, Team Valley Trading Estate,
development and although the Company reserves the right to Gateshead, Tyne and Wear,
change specifications, it attempts to keep customers informed of
any alterations. This publication is for general information only and
England NE11 0PZ
customers are requested to contact our Industrial Division Sales Tel: +44 (0)191 402 9000
Department for detailed information and advice on a products Telefax: +44 (0)191 482 1722
suitability for specific applications. All products are sold subject to ISO 14001
the Company’s standard conditions of sale. http://www.domnickhunter.com

For further information visit: www.domnickhunter.com

Copyright domnick hunter limited 2005
a member of the domnick hunter group plc Publication Reference: 765 02/05 Rev. 001
Stock No. 17 400 4765