What is a HEPA Filter

Andishegaran Jame Sanat Iranian Company is a designer and manufacturer of all kinds of clean room equipment with the best quality. A clean room is used in environments or production lines that are highly sensitive and should not contain dust, aerobic microbes, particulate matter and chemical vapors.

HEPA filters may seem complicated, but HEPA filters are not as complex. HEPA filters were invented in the 1940s when scientists were making the atomic bomb, and they are just a more randomly made mat of fibers made of glass or synthetic materials.

The synthetic materials used in the HEPA air filter are similar to those used in fast-drying T-shirts.

What is a HEPA Filter?

Fiberglass filters, on the other hand, are made of glass - this means materials such as silica, alumina, calcium oxide, boron oxide, magnesium oxide, sodium oxide.
What is important about HEPA air filters is that they absorb almost any amount of particles.

They can absorb viruses, bacteria, pollen, PM2.5, allergens and so on. HEPA air filters are the most important integral part of any air purifier.

hepa filter

To see what the randomly aligned mat of fibers look like, here’s a closeup of the HEPA filter Smart Air makes for The Sqair air purifier, and then alongside it a view at the nano-level with the help of a microscope.

Closeup of Smart Air HEPA filter

Closeup of Smart Air HEPA filter

Microscopic view of Smart Air HEPA filter

Microscopic view of Smart Air HEPA filter


What Makes a Filter a HEPA Filter?

OK, so if HEPA filters were invented in the 1940s, and they’re nothing fancy, then what makes any old filter a HEPA filter? Turns out using the term “HEPA” has a strict set of requirements. In Europe, HEPA filters must remove 99.95% (ISO) of particles. In the US, they must remove 99.97% of particles.

Standard                                                           Filtration Rate of MPPS

ISO / European (ISO29463 / EN 1822) ≥ 99.95%

US Standard (MIL-STD-282)                   ≥ 99.97%

When following the ISO or European rules, filters that capture ≥85% of particles but less than 99.95% are called ‘EPA filters’ or ‘efficient particulate air filter’. These air filters do not meet the filtration requirement to be considered a ‘HEPA air filter’.
On the other hand, filters that exceed the requirements of a ‘HEPA air filter’ and capture more than 99.999% of particles are called ‘ULPA filters’ or ‘ultra low penetration air filter’.

Designation                                          Filtration Rate

EPA (efficient particulate air filter) 85% – 99.95%

HEPA (high efficiency particulate air filter) 99.95% – 99.999%

ULPA (ultra low penetration air filter) ≥99.999%

OK, but what does “particles” mean? All particles? A particular size of particles? Turns out HEPAs are tested against the “most penetrating particle size” (MPPS)–more on that in a bit.


How Do HEPA Filters Work?

The answer to this question is the most fascinating thing about HEPA filters. Most of us might start out thinking HEPA filters work like a net, like this.

How Do HEPA Filters Work?

If a particle is smaller than the holes in the net, it gets through. Makes sense!

HEPA Filter Method 1: Large Particles

That intuition is true for big particles. By “big,” we’re talking typically larger than 1 micron. For comparison, a human hair is about 50 microns wide. So 1 micron is actually quite small.

 HEPA Filter Method 1: Large Particles

But these “large” particles fly into a HEPA filter, they’re too big to get through, so they get stuck. Scientists have a name for that. When particles get stuck between two fibers, they call it “straining.”



HEPA Filter Method 2: Smaller Particles

What happens for particles smaller than 1 micron? Let’s look at the next size range down: 0.3 – 1 microns. We’re talking about the size of a bacteria.

 HEPA Filter Method 2: Smaller Particles

Particles this size can fit between the gaps in the filter. But they have a problem. They’ll try to follow the air around a HEPA filter fiber, but they are a bit heavy. So some of them don’t move fast enough and thus end up getting stuck. Scientists call this “interception.”



HEPA Filter Method 3: Really Small Particles

OK, so do the particles below that size get through? For the really small particles (less than 0.3 microns), the science gets weirder. These particles that small have so little mass that they actually get bounced around like a pinball when they hit gas molecules (that’s called Brownian Motion). So they move in random zigzag patterns.

 brownian movement

These particles are so small they could easily fit through HEPA filters. But sadly (for their freedom) and happily (for our lungs), they don’t fly in straight lines. Because they fly in zigzag patterns, they end up hitting the fibers and getting stuck. Scientists call that diffusion.

Here’s how all three capture mechanics work:

And here’s how the three different mechanics work for different particles sizes. Straining and impact capture large particles; interception captures medium particles; and diffusion captures the smallest particles. 

particle diameter


What’s The Most Penetrating Particle Size For a HEPA Air Filter

So the larger the particle, the better a HEPA filter filters out the particle? Not so fast! Did you notice the dip in the last graph? That happens because diffusion works really well under about 0.3 microns. Straining and other mechanics that are more intuitive work really well above 0.3 microns.

Where those two mechanics intersect is the hardest particle size to capture. That’s because it’s not quite so small for diffusion to work its full strength, and it’s not quite large enough for straining to work its full strength. Call it the “weak spot” of HEPA filters. This dip in the graph is called the most penetrating particle size.

What’s The Most Penetrating Particle Size For a HEPA Air Filter

The dip in the graph most commonly occurs around the 0.3 microns mark, which is why people mention 0.3 microns all the time.


HEPA Filters Can Capture Nanoparticles

See how the line goes up to the left of the dip in the graph.

HEPA Filters Can Capture Nanoparticles

That’s Brownian motion and diffusion in action. Diffusion is incredibly effective at capturing nanoparticles. That means HEPA filters are also incredible effective at capturing nanoparticles too.

Read More: Can HEPA Filters Capture the Coronavirus?

Can HEPA filters also capture gases and VOCs?

Since HEPA filters are so great at capturing nanoparticles, it’s reasonable to think they might capture VOCs and gases too. Unfortunately this is not the case. Since gases are not particles, they move and behave differently in the air. To capture VOCs and gases you’ll need a carbon filter for that.

Can I clean a HEPA filter?

Experts of Andishegaran Jame Sanat Iranian Company have tested the washing of HEPA filters in the laboratory. It is not recommended to clean HEPA filters with water or vacuum or stir them, as they may damage the fibers of HEPA filters.

Construction and supply of clean room supplies and equipment For a clean room free from pollution and equipped, the quality of materials and equipment used in the clean room and also the up-to-date facilities of this equipment is very important.

Accreditation and GMP Specialization Validation and GMP Design of equipment for human and animal pharmaceutical projects and factories, medical equipment and food Press with GMP and GMP principles Design and construction of human and animal pharmaceutical projects and factories, medical equipment, cosmetics and Health and Press In accordance with the principles of GMP based on the European Union (PICS), FDA and WHO, the experts of Andishgaran company act exclusively and therefore can be used to ensure proper operation and testing of HEPA filters.

The most important issue in carrying out any special project in extraordinary projects is the standard monitoring and validation of them to meet the requirements.