What the heck is a HEPA filter? How airplane air stays clean

If you're traveling these days, airlines want you to know they're doing everything in their power to keep you healthy.

American, Delta, United and Southwest have all emphasized their in-depth cleaning procedures in e-mails to customers during the past week. All four airlines have also made a point to specifically note that many of their aircraft are equipped with high-efficiency particulate air (HEPA) filters.

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It's a piece of equipment you may have never heard of before this week, but now that it's become so high-profile, we figured you'd want to know everything you can about it. So, TPG reached out to R. Eric Jones, an associate professor and chair of the Aviation Maintenance Sciences Department at Embry-Riddle Aeronautical University. The conversation has been edited for length and clarity, and some contextual information from other sources is included in brackets.

What are HEPA filters?

HEPA filters are a very high-intensity system of fibers that you essentially run air through to filter out an incredible amount of contaminants — not just dust, not just bacteria, but moisture, any sort of contamination that could potentially harm or create an atmosphere in the cabin or the cockpit that could harm the passengers or the crews. The material in them is much closer together compared to cheaper air filters, and that makes it very difficult for biological elements to penetrate them.

How common are HEPA filters?

I don't know of an airline that's operating right now that does not have HEPA-level filters on them, but that does not mean that one does not exist. There's a certain amount of air quality that you have to maintain in your commercial airplane. If you're flying commercial passengers or corporate passengers, you're going to have a HEPA filter or better air filtration system.

Related: The most up-to-date information about airlines' coronavirus waivers and schedule changes.

Just to be clear, these HEPA filters are also on high-end vacuums and other commercial air filtration systems. They're not exclusive to the airlines or the airline experience, they're used in lots of areas of your everyday life.

[Commercial airlines in the U.S. need to maintain minimum cabin air quality standards set by the Federal Aviation Administration. HEPA filters are the most common way to meet those guidelines, but some aircraft use other approved methods.]

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How effective are HEPA filters?

The airlines are trying to do everything they can to mitigate the spread of these viruses.

[According to the Centers for Disease Control and Prevention, HEPA filters capture 99.9% of particles (bacteria, fungi, and larger viruses or virus clumps) 0.1–0.3 micrometers in diameter, and cabin air generally passes through the filters 20-30 times per hour.]

Related: Everything you need to know about traveling during the coronavirus outbreak.

The airlines started to put in HEPA filters because they are effective, but they will only protect you from airborne viruses or bacteria. If you touch a tray table, a HEPA filter is not going to help you. There is a misperception that the public feels that "I got sick on an airplane because I breathed air that is filled with a virus," but normally, it's from touching hard surfaces that haven't been cleaned properly.

How are HEPA filters maintained?

They do need to be changed, but it's a very simple job. You just go into a panel, pull out the old filter and put in a new one. Every airline has what's called an operations specifications manual, and that dictates how that airline runs, including how often components are changed. There's some variation in how often they're changed, but it's been my experience that those HEPA filters are changed more frequently than what the manufacturers require.

HEPA filters are also made by a number of manufacturers, and each may have its own maintenance guidelines.