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For many years two basic tests have been applied to grade air filters for use in heating, ventilation, air conditioning, clean rooms, hospitals and food process air supply systems.
The test for primary and secondary filters, mainly panel and pocket/rigid media type filters, is based on the US ASHRAE 52 standard which was adopted in Britain as BS 6540 and in other European countries as Eurovent 4/5. In 1993 the EC adopted the standard as EN779 and in Britain this became BS EN779. The test is based on the use of a known size of coarse synthetic dust to measure arrestance (dust holding capacity) on primary filters, and a combination of synthetic and atmospheric dust test measurements to establish efficiency on secondary filters. The efficiency test is known as the "atmospheric dust spot efficiency test" because it measures the level of discolouration caused by the small staining particulate in the air. The BS EN779 test does not grade filters by particle size, and the results give a range of efficiency levels (F5 – F9) from a new to a loaded filter condition.
Higher
efficiency filters, better known as HEPA (High Efficiency Particulate Air)
and ULPA (Ultra Low Penetration Air) filters, have always been tested for
efficiency using a challenge of known particle size. These filters are installed
where critical high quality air filtration is required. Test results should
be expressed as a percentage penetration, but we usually discuss efficiency
when designing a system. The test used in UK until some years ago was BS3928
(Eurovent 4/4), now replaced with BS EN1822.
The design and construction of air filters for food industry use forms part of the overall air system performance, to ensure that at all times the air quality at point of use is guaranteed.
The following chart illustrates current test grading and the BS EN1822 standard based on measuring the most penetrating particle size (MPPS) to establish the performance for high efficiency filters. Air quality at point of introduction into the food process space is the result of air filter efficiency, filter framework integrity and location of the air filtration within the supply air system.
Air Filter Test Reference Chart
General Filter Type |
Filter Test Reference and Classification |
Filter Test Type
and Application for the Food Industry |
|
Previous |
Current |
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Primary filters
to collect coarse dust |
BS6540 Arrestance % |
BS EN779 Arrestance % |
Average value for collection
of large particles using synthetic test dust. Filters used to prevent
mechanical system fouling and as pre-filters to secondary and semi-HEPA
range. |
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|
|
Secondary filters
to collect and retain small particle dust |
BS6540 Efficiency % |
BS EN779 Efficiency % |
Average percentage value
test using atmospheric air. Filters installed to keep general food processing
areas clean and free from airborne pollution. Some high care use with
risk assessment. |
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|
|
Small particulate
air filters of the semi-HEPA and HEPA type for specific particulate
control |
Eurovent 4/4 Initial efficiency % |
BS EN1822 Minimum MPPS % |
Filters installed for high
care/high risk food process applications.
Was Eurovent 4/4 Sodium chloride test Now BS EN1822 aerosol MPPS |
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|
|
Highly efficient
air filters ULPA type |
BS EN1822 Minimum MPPS % |
Filters used for Laboratory
work, in cabinets and some mini environments.
BS EN1822 aerosol MPPS |
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|
MPPS - Most penetrating particle size
HEPA - High Efficiency Particulate Air (filters)
ULPA - Ultra Low Penetration Air (filters)
BS6540 / BS EN779 arrestance and efficiency test references are based on average percentage values. Primary and secondary filters are at their lowest efficiency when they are new, and at their most efficient at the end of their useful life. BS EN1822 tested filters offer a guarantee of minimum performance when newly installed.
Design, installation and management of air quality control systems
Air filtration products, Air conditioning, Mini-environments,
Isolation containment, Air process hardware, Consultancy,
Re-commissioning