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. Also for home applications such as HEPA filter mask, HEPA vacuum, etc., a HEPA filter is in use.
Advantages of HEPA Filter
It is useful in the filtration of the following particles.
- Virus, etc.
Types of HEPA Filter
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 this criterion 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.
Particles below 0.3 microns undergo diffusion while particles above 0.3 microns undergo inertial impaction or interception. However, particles having 0.3 microns are really difficult to capture. Thus this size of 0.3 microns is known as the Most Penetrating Size (MPS).
Some researches have shown that the effectiveness of the HEPA filter was insignificant by reducing the porosity of the filter from 0.3 microns. So, a filter with a porosity of 0.3 microns is highly preferred.
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%
When the contaminated air passes through the true HEPA filter, it can undergo three different processes.
- 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.
- 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.
- 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, they will be easily trapped by the filter. However, you can not fully consider it to be the best option for virus filtration.
HEPA Filter for Covid
The true HEPA filter is effective against the covid virus to some extent. However, you can not totally rely on it.
Covid is a type of virus. Generally, the size of the virus ranges from 0.03 to 0.39 micron which is really small in comparison to the filter. So, this virus can undergo diffusion and be trapped inside the filter.
Similarly, when a covid-19 patient coughs or sneezes, the virus will be released in the form of droplets. So, these droplets having a bigger diameter will be trapped by the filter. But still, you cannot fully trust this filter for virus filtration.
1. HEPA Filter Mask
It is a simple kind of mask with a layer of HEPA filter inside of it. The details of these kinds of masks are given in the video below.
2. HEPA Vacuum
HEPA Vacuum is a type of vacuum cleaner with a HEPA filter in it. It is mostly useful for people who are likely to suffer from allergies. It is also useful for patients who are suffering from asthma.
It is useful for the filtration of the following things.
- Mold and Germs
- Microorganisms such as bacteria and viruses.
Maintenance of True 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 true 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.