Challenge: Filtering air

Air quality can be improved by actively filtering the air.

Various types of filters ensure that the ambient air can be improved to reach clean room quality.

History of fibre filters

Air filters are used in ventilation systems to clean the air in residential buildings, schools, offices, hospitals, isolation stations and nuclear power plants. There are various air filtration solutions available. The most known are cyclones, electrical precipitators, scrubbers or the most conventional mechanical filters made of fibre material. Fibre filters were first developed more than two thousand years ago in ancient times, when desert dwellers recognised that sand dust could be filtered by using simple cloths.

In the 18th century, cotton filters were used for various purposes e.g. microbiological research and in the gold processing industry to filter mercury vapours. At the latest in the 1940s, during the Manhattan project, the previously unknown radioactive particles were filtered by means of HEPA filters; then they were gradually classified and are now used in all safety-relevant facilities such as in clean rooms, shelters, operating theatres or isolation stations. They are so effective that the best filters only allow 10 particles of the size 0.1 micrometre (=100 nanometre) per cubic meter of air.

The various filter classes

The filter classes serve classification based on efficiency and filter particle size.

To simplify filter selection, they are assigned into 17 classes. Classification into classes G1 to F9 for coarse and particulate matter filter is based on the norm DIN EN 779:2012.

Coarse dust filter G1-G4 with a mean filtering level of between 50 - 90% of test dust. Application scope: pre-filter for fibres, ash, sand, insects, dust, pollen, spores.

Particulate matter filters M5-M6 with a mean efficiency level of between 50-80% of particles 0.4µm Application scope: pre-filter for fibres, ash, sand, insects, dust, pollen, spores.

Particulate matter filter F7-F9 with a mean efficiency level of between 80-90% of particles 0.4µm Application scope: main filter for smoke, mist, ash, bacteria and germs, oil vapour, soot, tobacco smoke, dye dust, carbon dust, asbestos, fibres. Classification into classes E10 to U17 (for EPA, HEPA and ULPA filters) is based on the norm EN 1822-1:2009. These HEPA filters are also used in operating theatres, intensive care units or clean rooms and nuclear plants. There are a wide range of filters available for non-industrial applications (e.g. for vacuum cleaners) that bear the name HEPA but do not guarantee the specifications of the EN 1822.

The designation HEPA filter is also used outside the scope of the EN norms; however, here too, non-comparable test conditions are used for this designation.

The clean room - the grey room

A clean room is a room in which the concentration of airborne particles is kept as low as necessary. Clean rooms are installed for special production procedures, especially in the semiconductor industry, for optical and laser technology applications, in the aerospace engineering sector and in facilities focusing on the research and treatment of food, pharmaceuticals and nanotechnology. These clean rooms are built using special materials so that no dust can adhere to surfaces; a clean room is also kept permanently at over-pressure and the air is usually fed in through a particulate matter filter, HEPA and ULPA filters.

Usually, humans represent the largest source of particles and other dirt which is why special workwear, work equipment and tools, as well as appropriate work methods help to ensure that the respective clean room class can be maintained. Also, to operate a clean room, continuous particle measurements must be taken after its construction and also during operation.

These measurements are used to classify the purity of the room based on a norm. For example, for class ISO 5, there may be max. 29 particles in max. 5.0 µm per cubic meter. (See: EN ISO 14644-1 Clean room). There are 9 clean room classes (ISO1-9); the strictest class is ISO1. Here, there are actually no more particles in the air!

A grey room is a term used to state the technical cleanliness that represents adequate protection against contamination of cleanliness-sensitive or technical parts with harmful particles.

The environment in which cleaning takes place is defined as the cleanliness area in the VDA 19 Part 2. Cleanliness areas are also classified into cleanliness levels.

  • Non-regulated areas (SaS0)
  • Clean zone (SaS1)
  • Grey room (SaS2)
  • Clean room (SaS3) (see also EN ISO 14644-1)

Put another way, anyone who creates clean room-like conditions automatically has a clean room!

Benefits of grey rooms

The effect of clean rooms is so good that more and more production-sensitive systems and companies want to work with rooms with at least clean room-like conditions.

In this case we speak of a grey room and this is possible by means of permanent air filtration.

The advantages are:

- Longer maintenance intervals for computers, charging stations, control cabinets and systems

- Improved measuring results for laser diodes for weighing scales, conveyor belts or  foil technology

- Higher quality for machines and moulds with 0% tolerance

- Material savings thanks to more precise production

- Lower cleaning costs

- Better work conditions and fewer illness-related absenteeism

- General improvement of quality management

- Sustainable dust reduction and therefore avoidance of explosive atmospheres (ATEX)

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