HEPA is a term quite commonly heard by buyers of air purifiers, HVAC systems, or vacuum cleaners. People see it on the packages of things among other vaguely scientific-sounding terms and usually proceed to be confused by it. Big time.
Here is that All-in-One guide for you to understand everything you need to know about HEPA Filter. In this trip, we take you down the rabbit hole of HEPA, and you shall know the answers to:
- What is a HEPA Filter?
- How many types of HEPA filters are there?
- How do HEPA filters work?
- How often should HEPA filters be changed?
- What's the difference between a HEPA filter and a carbon filter?
- Fun facts about HEPA filters.
What is a HEPA filter?
HEPA stands for High-Efficiency particulate air/ arrestance (filter). Instead of a type of filter made with a certain technique or material, HEPA is a term used to describe a standard applied to all air filters. The term indicates that a certain filter has the ability to filter particles larger than 0.3 micrometers in diameter. A group of American scientists established the standard to deal with nuclear dust, which has approximately said diameter, after the second world war. It remains a critical standard until nowadays since 0.3 micrometer is coincidentally also the size of many types of harmful practicals such as smoke particles, pet dander, dust, bacteria, airborne fungi, pollen, virus, and human hair.
Why 0.3 Micrometers? What is a micrometer?
Many of you reading this article probably wonder why is 0.3 micrometers so significant? 0.3-micrometer size is the most penetrating particle size.
Micrometer refers to practices ranging from ultra-microscopic to entirely detectable to the human eyes. A meter equal to 1 million micrometers, 1 inch equals 25,400 micrometers. To give you a better idea of micrometers:
- Spores: 3 – 40 micrometers
- Mold: 3 – 12 micrometers
- Bacteria: 0.3 – 60 micrometers
- Car emissions: 1 – 150 micrometers
- Pure oxygen: 0.0005 micrometers
Most of the HEPA filter screen is shown below, in order to increase its dust capacity and fold out dozens of folds, the texture feels a bit like a thick paper.
How many types of HEPA filters are there?
Technically, there are no ‘different’ types of HEPA filters – since filters either meet or fail the HEPA standard – some HEPA filters outperform others. So, the better question would be: how do different HEPA filters differ? True HEPA generally ranges from H10-H14. This is the “grade” of HEPA or the level of efficiency. The higher the grade, the better the filter. HEPA H13-H14 is within the highest tier of HEPA and is considered medical-grade quality. Whereas H10-H12 filters only trap 85-99.5% of all particles that are 0.1 micrometers in diameter, HEPA H13 and H14 trap 99.95% and 99.995% of such particles, respectively. Overall, a typically desirable grade for appliances used in a home would be H12-13.
There are plenty of reasons why manufacturing companies like Afloia rarely equip their items with filters graded higher than H13. The first consideration is cost. Evidently, not every household’s air quality needs to match that of an operation room. The second, which is arguably more important, is efficiency. The higher-grade a HEPA filter is, the slower it typically takes for it to filter a certain amount of air. At one point, it might be hard for these high-grade filters to catch up with the particularly complicated environment (compared to an operating room or a chip manufacturing plant, that is) of the household.
Afloia HEPA filter: H13 grade
How do HEPA filters work?
There are a few ways how a HEPA could filter out the pesky micro-particles in the air of everybody’s bedrooms and living rooms:
- Some larger, mainly 5-10 micrometer particles, simply hit the materials of the filter and get intercepted. Plain and simple, like how a barbeque mesh stops your steak from falling into the charcoal pile.
- Gravitational condensation
- Particles with low relative volume and high density, typically bacteria, will slow down when they go through the filter, condensing on the latter like sand in a river sinking to the riverbed.
- Turbulence adhesion
- The complex microstructure of the filter will cause the air going through to form many streams of turbulent flow- a physics term for a fluid (yes, the air is a fluid) flowing through its path to unpredictably form small swirls – that could cause the particles to adhere (stick to) the filter material.
- Van-der-Waals attractive interaction
- In the 1870s, a Dutchman called Johannes Diderik van der Waals discovered the therefore named Van der Waal force (after some intense fiddling with his fancy electron clouds of course). It is a force that is constantly exerted among small particles in general. Smaller particles, especially those smaller than 0.3 micrometers, will interact intensely with the filter’s material, and be attracted, finishing the filtering process. (this will also come in later!)
How often should HEPA filters be changed?
HEPA filters are generally made of polypropylene or other composite materials, most of which are not washable. A small part of the HEPA filter made of PET material can be washed, but the filtering effect of this kind of filter is low.
The filters should be retired when the resistance that the air flowing through the filter experiences exceeds a certain value. This is measured, typically, when it is twice as high as it was when a filter leaves the factory.
Sometimes people like to ‘eye it’. This is not the best idea since sometimes a filter could appear clean but in fact, filled with filthy germs and dust. Other times, it could appear grayish and gross but actually is still functional.
Long story short, change it when your Afloia machine shows you a glowing red light. Hold the power button for 7 seconds, and just put a new one in. By the way, DO NOT wash your old filters. It messes the whole thing up and completely invalidates what the filter does by messing with its structure.
What’s the difference between HEPA filter and carbon filter?
HEPA filters were originally used in World War II to eliminate the radioactive particles in the air that were affecting soldiers’ respiratory systems. Unlike carbon filters, HEPA filters are not designed to remove odors, smoke, fumes, or chemicals. HEPA filters also trap microorganisms, which is why it is recommended to use both HEPA filters and carbon filters.
Carbon Filters：Carbon or charcoal filters were designed to filter out doors, smoke, fumes, and other chemicals. Therefore, carbon filters are suitable for commercial buildings where chemicals are common. Carbon filters come in many different forms, including foam, powder, cloth, and solid carbon. In short: charcoal is treated with oxygen, which opens up the pores between the carbon atoms. As contaminants pass through the filter, the tiny pores chemically react and neutralize. Once all of the pores have been filled with contaminants, the filter needs to be replaced so that it can remain at optimal performance. Keep in mind that carbon filters can also purify liquids, which is why these filters are also used in coffee machines and when distilling whisky.
And more (fun facts!)
- HEPA filters were originally developed secretly by the military for chemical, biological, and radiation defense purposes. "After World War II, the U.S. Atomic Energy Commission (AEC) chose to use military AEC filters as the primary particulate removal equipment for all waste gas systems at nuclear facilities." HEPA filters were first used by the Manhattan Project to prevent the spread of radioactive contaminants in the air and were commercialized in the 1950s.
- HEPA filter when it is brand new is actually not so much as good as when it has been used for a while. This is because the adhered particles in the fibers could act as another mesh on the original mesh structure.
- Contrary to common belief, HEPA, at least on a scale of 0.1-0.3 micrometers, does not work exactly the same as a mesh. People sometimes think since 0.3-micrometer particles are a struggle for HEPA to clear completely, surely it would be near- impossible to deal with particles sized around 0.1 micrometers, right? Actually, no. HEPA relies a lot on our old pal Van der Waals’s force to filter out those particles. And since the force is mostly constant, it works even better on the relatively smaller particles around 0.1 micrometers. While a typical HEPA filters 99.97% of 0.3 particles, it could do a phenomenal job at 99.99% for the 0.1 ones.
- Someone says HEPA filters help eliminate viruses in the air, that is Not true! HEPA filters only help eliminate mucus, a vector of viruses.