AES Environmental established its first NATA test facility as Vokes Australia, at Rockdale NSW in the late 1960’s for liquid/air filtration. AES Environmental became a founding member of the first Australian Standard AS1132 1973, for methods of test with specifications for test apparatus for determining properties of air filters. This standard is today referred to as AS1324.

AES Environmental offers Air Filter Testing Services within its purpose-built rig to validate those products that are offered to the market. Validating the performance of any filter product is essential to ensure that the product does what it is supposed to and that it doesn’t contribute negatively to indoor air quality (IAQ) in the process.

Our engineering team is constantly testing and validating the products we produce; this is the data that is published on our literature on this very site. We also routinely complete testing and validation services for large multi-national organisations that wish to verify compliance to AS 1324.


AS 1324 sets out specific requirements for the performance and construction of air filters for
use in general ventilation and air conditioning systems. The Standard classifies air filters on the basis of
design, construction, performance and application, and establishes minimum criteria for
acceptance of an air filter into a particular category.

Filter Categories

A filter’s efficiency rating is its defined category. This rating describes the relationship between particles retained or trapped by the filter to the number of particles entering the filter.

The category that a filter is placed in to is defined by a number of tests, those tests use different types of dusts.

Test Dust 4 is used to determine the filters Gravimetric Efficiency, or Arrestance against a course test dust. The dust is fed at a specific rate over the course of a period of time to determine the average arrestance and total dust holding capacity

Test Dust 1 is used to determine the efficiency of the filter against a fine test dust. As with the gravimetric tests, the dust is fed over a period of time that aims to simulate the air filters total life cycle.

Filter Rating Guide as per AS 1324


Test Dust 1 is a Methylene Blue Powder includes particles in the range 0.2 μm to 3 μm diameter and has a mass median diameter of 0.6 μm

Test Dust 4 is a composite dust consisting of 72% by mass of Standardized air cleaner test dust fine, 23% by mass of ‘Molocco black’, 5% by mass of No. 7 cotton linters.

The various components of Test Dust No. 4

  1. (a) Cotton linters 5%.
  2. (b) Molocco black 23% with average particle size of 0.8 μm.
  3. (c) Standardized air cleaner fine 72%
    • 39% 0 to 5 μm.
    • 18% 5 to 10 μm.
    • 16% 10 to 20 μm.
    • 18% 20 to 40 μm.
    • and 9% 40 to 80 μm.



The three performance characteristics of greatest interest to users and manufacturers of air cleaning equipment are the ability of the equipment to remove particulates from the air stream, the resistance to airflow, and the dust holding capacity before cleaning or replacement is required. – AS 1324.2

In order to select the right filter for any application it’s crucial to have some understanding of the expected performance of that product. That is to understand what the filtration efficiency will be vs the resistance to air flow vs expected life. An Air Filter might seem as though it’s a relatively inexpensive product, but in operation an air filter can become very expensive if incorrect selection has occurred. Furthermore, we want to be able to specify filters suitable for their applications, for instance we need to have good quality air in commercial buildings, but we don’t need those areas to meet the same exacting standards as an operating theatre. By understanding how our filters perform and the particles that we are targeting then we can determine the correct filter for the application.


Particles are generated or become airborne with everyday human, commercial and industrial activity. In the post-pandemic environment, this has become a significant issue to protect individuals and keep everyone safe when at home, work or in the greater community.
Airborne particles are generally measured in microns (millionths of a meter) and vary in size depending on the source. A strand of human hair, which is considered between 50 and 150 microns, is a good reference point when considering the relative size of large and small airborne particles.

micron scale is 1000:1 (1mm equals 1000 microns)

Why be concerned about the size of the above particles?

Common ParticlesSize
Human Hair50-150 microns
Household dust and lint0.01-100 microns
Pollen10-110 microns
Mould1-50 microns
Pet dander0.1-10 microns
Tobacco Smoke or Soot0.01-1 micron
Viruses and Bacteria0.001-10 microns


Our AS 1324 Standards are comparable to overseas standards, EN779, ASHRAE and ISO 16890. Test methods vary as do definitions, classification and terminology however the outcome is largely similar. The Australian Standards AS 1324 do define some stringent criteria associated with the construction of the filter and other performance requirements; AS 1324 specifies that no filter can contain hazardous materials and it also requires filters to meet fire classification standards, this is above the requirements of other standards.

The Filter Efficiency Table helps to demonstrate the cross reference of 1324, EU and Merv ratings


The Australian Standards defines efficiency of the filter through loading the filter with a salt-based “test-dust” called Methylene Blue. This test-dust travels through the filter and stains papers downstream, the staining is assessed by photometers to determine the efficiency of the filter. In ISO 16890 the salt-based “test-dust”, KCI, is fed through the filter and particle counters are used to assess the mass concentration of particles that made it through, effectively determining the filtration efficiency.

ISO16890 allows filters to be classified against known PM (Fine Particulate Matter). The classification of filters to a known PM will help industry to effectively evaluate indoor air conditions in the future.

AS1324 identifies additional test methods for carry-over, or the shedding of particles and oils from the filter prior to testing.



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