General

HEPA Filter: types, application, working mechanism and handling

HEPA filter

HEPA filter stands for a High-Efficiency Particulate Air filter. It is mostly used in hospitals, (e.g oxygen concentration), pharmaceuticals, the food industry, etc. It is available in various shapes (rectangular, cylindrical) and sizes.

Applications of HEPA filter

It is useful in the filtration of the following particles.

  • Dust
  • Smoke
  • Bacteria
  • Spores
  • Pollen
  • Virus, etc.

Types

According to the HEPA standards, there is only one type of HEPA filter which is known as a true HEPA filter. It should filter out 99.97% of particles as small as 0.3 microns. Any filter which fails to maintain these criteria is known as a failed HEPA filter. They can filter out particles with sizes of 2 microns or more. Besides, they are also cheaper in comparison to true HEPA filters. They are found in the market with different names such as HEPA-like, HEPA type, etc.

Classes of HEPA filter

Based on the European Union (EN 1822) different types of HEPA filters are as follows

Class of HEPA filter The efficiency of HEPA Filter at MPS
H10 At least 85%
H11 At least 95%
H12 At least 99.5%
H13 At least 99.95%
H14 At least 99.995%

Working mechanism

When the contaminated air passes through the HEPA filter, it can undergo three different processes

  1. Interception:- Larger particles such as dust and dirt, etc. whose size is more than 0.3 microns will come in contact with the glass fibers and then get trapped.
  2. Inertial Impaction:- When air goes through the filter it can easily divert its direction based on the path of flow. On the other hand, particles tend to move in the same path due to the phenomena known as the inertia of motion. So, due to this glass fibers will trap the particles.
  3. Diffusion:- Particles whose size is less than or equal to 0.1 microns (e.g. viruses) follow the Brownian motion. In other words, there are molecules in the air. When the size and mass of the particles are very small, the collision of particles with air molecules will cause the particles to move in a random direction. Since the particles of a size less than 0.1 microns move in a zigzag direction, it will be easily trapped by the filter. However, you can not fully consider it to be the best option for virus filtration.

Maintenance of HEPA filter

  • Do not expose it to direct air. It is better to use an air filter to get rid of dust particles first.
  • If the efficiency of the filter decreases, it is best to replace it with a new one.
  • It is generally not washable. You might clean it with a clean cloth.
  • A HEPA filter can last from six months to about 10 years based on the handling process. But, it is best to remove it once every two or three years.

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