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What is a HEPA Filter? How does HEPA Filter work?

Have you ever come across the term HEPA Filter? Have you ever wondered what does that mean? Well if you don’t know and was curious about what does that term means.

Then congratulations you have landed in the right place.

HEPA stands for High-Efficiency Particulate Air and also known as high-efficiency particulate absorbing and high-efficiency particulate arrestance. HEPA is used as an efficiency standard of an air purifier.

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How efficient are HEPA Filters?

A HEPA air filter is designed to trap 99.97 percent of particles of size greater than or equal to 0.3 microns when air passes through it.

The 0.3-micron size is referred to as the MPPS by scientists. MPPS stands for the most penetrating particle size. As per different studies conducted on pollutant size, it has been found that particles of this size evade air filters more than the larger or smaller particles.

Now, as we have an idea about this dimension, let’s have a look at various airborne particles and their sizes.

  ParticlesSizes 
Bacteria0.3 to 60 microns
Car emission1 to 150 microns
Spores
3 to 40 microns
Mould3 to 12 microns
Antiperspirant6 – 10 microns
Fly Ash1 – 1000 microns
Household dust0.05 – 100 microns
Oil Smoke0.03 – 1 microns
How HEPA Filter works?

hepa filter working

HEPA filters consist of different fibers in the structure of a maze. Randomly twisted and turned fibers arranged together to form a mat. Usually, they are made of fiberglass of diameters between 0.5 to 2 micrometers.

As airflow through this web of fibers, particles get captured within the web. HEPA filters are designed in such a way so that they can capture even the smallest particle. HEPA works on the following mechanism:

Direct Impaction: Large particles, such as dust, mold, and pollen, travel in a straight path. As they are unable to pass through the curving space present in-between the filter, they got captured between the spaces.

Sieving: In this case, the size of the particle is larger than the size of the gap between the fibers. So, when the air stream passes through the filter, the mesh ensnares those particles.

Interception: Small particles that flow along with the air stream, hit the sides of fibers and stick to it.

Diffusion: At low air velocity, the ultra fine pollutants collide with the gas molecules & got arrested either by interception or impaction process.

With the help of all the above mechanisms, HEPA filters can trap particles of up to 0.3-micron size.

What are the uses of HEPA Filter?

Originally the HEPA filters were designed to use in the nuclear industry to filter out the dangerous radioactive particles.

Later on, HEPA filters came into commercial use. Now we use them in Air purifiers, hospitals, cars, Air Conditioners & vacuum cleaners.

Where do HEPA filters fail?

HEPA filters do remove 99.97% of particulate pollutants from the air but, some harmful contaminants can’t be filtered.

Many pollutants like allergens, bacteria & other chemicals that are much smaller than the 0.3-micron escape through the HEPA filters very easily.

The other main reason for their failure is microorganisms. As the HEPA filter trap different types of spores & mold in their active state, they get collected in the filters & then multiply on HEPA filters itself.

This affects the filter performance & also they get released back into the air.

Should you buy a HEPA Air Purifier for your home?

Before buying a HEPA filter for your home, you have to understand your needs. Like if you are more concerned about the larger particles like dust, pollen & animal dander – HEPA filters will be the right choice for you.

But, if your concern is more on indoor air pollution, such as Volatile Organic Compounds (VOCs), microorganisms, HEPA might not be a good option.

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