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What is a HEPA filter?
An HEPA filter is a "high efficiency particulate air filter. An HEPA according to theory can remove 99.97% of the dust, pollen and bacteria etc from the air. The HEPA filter has randomly arranged fibres in it. The basic difference in the types of filters arises from the fibre density and diameter and filter thickness. HEPA filters are meant for the purpose of trapping those pollutants which are much smaller than the usual particles and often stick to a fibre.
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A HEPA filter works to trap the pollutants using three methods like
- Interception- Here the fibres travelling in the airstream come close to the fibres of the filter and get stuck to it.
- Impaction- Here the large particles are unable to keep away from the fibres of the filter and owing to the airstream get diverted towards them. However with the increase of the air flow this activity gets reduced.
- Diffusion- Here the gas molecules and the smallest particles of the pollutants collide and in this fashion the filter impends and delays the path of the polltuants.
It is important to note that in a HEPA filter when the particle size of the pollutant is 0.1 µm in diameter then diffusion predominates the working of the filter. Whereas Impaction and interception predominate above 0.4 µm. In between, near the 0.3 µm MPPS, diffusion and interception predominate.
The 1940s saw the making of the original HEPA filter where it was used to prevent the contamination of the air from radioactive contaminants. This type of filter got commercialized in the 1950s and after that has been increasingly used. The biggest demand for HEPA filters is in industries like aerospace, pharmaceutical processing, hospitals, healthcare, nuclear fuels, nuclear power, and electronic microcircuitry (computer chips).
The NIOSH N100 rating judges whether a filter can be qualified as a HEPA filter based on its filter efficiency performance standards.
Note: This article is currently under review by our editors.